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Economic Impact of Solar Lighting
A Randomised Field Experiment in Rural Kenya
Adina Rom1, Isabel Günther1 & Kat Harrison2
1NADEL Center for Development and Cooperation, ETH Zürich
2Acumen
Study Report. Version v1.
December 2016.
Working Paper ‐ Please do not quote or cite without permission of the authors.
Please direct any questions and correspondence to: [email protected]
Most recent version: http://www.dec.ethz.ch/research/solar‐lighting.html
Page 2 of 54
Contents
Executive Summary ................................................................................................................................. 4
Acknowledgments ................................................................................................................................... 7
List of Acronyms ...................................................................................................................................... 8
List of Figures & Tables ............................................................................................................................ 9
1 Introduction ................................................................................................................................... 10
1.1 Background ............................................................................................................................ 10
1.2 Research Questions ............................................................................................................... 11
2 Methodology ................................................................................................................................. 13
2.1 Research Design .................................................................................................................... 13
2.2 Sample Selection ................................................................................................................... 15
2.3 Balance Test across Treatments at Baseline ......................................................................... 16
2.4 Intervention ........................................................................................................................... 17
2.5 Data ....................................................................................................................................... 18
2.5.1 Qualitative Data and Piloting......................................................................................... 18
2.5.2 Survey Data.................................................................................................................... 18
2.5.3 Sensor Data ................................................................................................................... 19
2.6 Estimation Approach ............................................................................................................. 19
2.6.1 Summary Statistics and Sample Description ................................................................. 19
2.6.2 Analysis of Take‐up ........................................................................................................ 20
2.6.3 Analysis of Impact .......................................................................................................... 20
2.7 Limitations of the Research Design ....................................................................................... 23
3 Results ........................................................................................................................................... 24
3.1 Description of Households .................................................................................................... 24
3.2 Take‐Up of Solar Lights .......................................................................................................... 29
3.2.1 Availability of Solar Lights .............................................................................................. 29
3.2.2 Impact of Prices on Take‐Up ......................................................................................... 31
3.2.3 School Differences in Take‐Up ...................................................................................... 32
3.3 Use of Solar Lights ................................................................................................................. 33
3.4 Impact of Solar Lights on Kerosene Use ................................................................................ 38
3.5 Financial Impact of Solar Lights ............................................................................................. 42
3.6 Time Impact of Solar Lights ................................................................................................... 46
3.6.1 Adult’s Time Use ............................................................................................................ 46
3.6.2 Children’s Time Use ....................................................................................................... 48
Page 3 of 54
4 Bibliography ................................................................................................................................... 52
Page 4 of 54
ExecutiveSummary
Universal access to electricity has become a policy goal in many countries in sub‐Saharan Africa, where
most of the population remains unelectrified. Electrification has been linked to a range of development
improvements such as higher income, increased female employment, and better health and
educational outcomes. On the one hand, researchers, policy‐makers, energy providers and financiers
debate whether electrification should be achieved through large‐scale infrastructure or through
decentralized solutions (such as mini grids or home systems), or a combination of the two (Lee, Miguel
& Wolfram, 2016a). On the other hand, concerns about climate change combined with the continued
decline in solar photovoltaic (PV) and battery prices makes solar‐powered electricity more and more
attractive to donors, NGOs, and policy makers. At the intersection of these two debates are small‐scale
solar lights, which have attracted increasing attention from practitioners. The hope is that solar lights
have large social and economic benefits for consumers such as allowing poor households to save
money on kerosene and spending more time on productive activities as well as improving indoor air
quality and health outcomes, and to helping children to study more and improving their learning.
Despite growing interest, there is still little rigorous evidence regarding the demand for modern energy
products and services by the poor, and the impact of solar lights on households’ well‐being. We hope
this randomised controlled trial (RCT) can contribute to this debate by revealing more about the
demand for small‐scale solar products and how these products are used, as well as how usage impacts
households’ energy expenditure and household members’ time use. To get a detailed and objective
measure of the use of solar lights, we used novel sensor technology in addition to conventional survey
data. Moreover, we analyze both the impact of solar lights sold at market price as well as the impact
of highly subsidized solar lights.
The International NGO SolarAid has done primary research in this space and commissioned this study
to gather independent, rigorous evidence – Google funded the research, which is now managed at
Acumen.
This RCT was conducted with 1,401 households in the rural areas surrounding the town of Busia in
Western Kenya, where less than 5% of the population is connected to the national electricity grid.
These households have very limited access to energy: they rely on kerosene‐based products for
lighting, firewood for cooking, and local shops to charge mobile phones. For an average household, 3‐
5% of overall monthly cash expenditure goes to energy, and the poorest 20% of households spend up
to 10% of their cash budget on energy needs. Lighting expenditure alone accounts for around 60% of
energy expenditure.
To understand price sensitivity of demand, we randomized prices at the household level. Respondents
received an offer to buy a solar light at either a high discount, a low discount, or the market price. The
take‐up rate for people who were offered a solar light at the market price of US $9 was 29%, the rate
for those who received an offer to buy for US $7 was 37%, and the rate among those with an offer
valued at US $4 was 69%. Every household adopted the solar light when it was provided at no cost. In
our study, almost all households (98%) who received a free light or purchased one kept the solar light
until the end of the study, but around 10% of households who received a free light reported that their
solar light was no longer functional when the 7 months study was over.
Page 5 of 54
Both sensor data and survey data reveal that most households that receive or purchase a solar light
use it almost every day for about 4 hours per day on average, and mostly in the evening hours.
A solar light replaced one of the 2.2 kerosene‐based tin lamps that the average household used before
the study. As a result, access to a standard solar light reduces households’ energy expenditure by about
US $0.5 to US $1.5 per month, corresponding to about 1% to 2.5% of household total cash expenditure
and about 25% to 60% of household energy expenditure. Based on these financial savings, the
amortization time of solar lanterns is between 6 and 22 months at current kerosene prices. These
calculations may change as the price of solar lighting drops further and/or the price for kerosene
increases.
Men and women with access to a solar light do not use more lighting during the day, but boys and girls
increase daily lighting use by 12 minutes, corresponding to a 6% increase in light use. Boys and girls
who receive access to a solar light spend less time sleeping (between 20‐30 minutes per day) and boys
tend to spend 17 minutes more studying, corresponding to an 11% increase in study time. The question
is whether this slight increase in study time (in addition to improved lighting quality) leads to better
schooling outcomes. While most other studies did not find any effects of solar lighting on test scores
(Furukawa 2013a; Grimm et al., 2016; Smith, 2014; Kudo, Shonchoy & Takahashi, 2015) and nothing in
our preliminary analysis of test scores points in that direction, further work on our data is needed
before such impacts can be excluded. SolarAid/Acumen, in partnership with Stanford University, are
conducting research looking specifically at the effects of (solar) lighting on educational outcomes in
Zambia. We do not see any difference in how women use their time once they have access to solar
lighting. We see, however, that men with access to solar lighting tend to have more time for recreation.
Neither men nor women increase the hours they engage in productive activities.
In summary, we see that most households who purchase or receive a solar light use it daily for several
hours and often tend to treat the solar light as a substitute for a kerosene light. This allows households
to reduce monthly kerosene costs and to save between 1% and 2.5% of their total cash expenditures.
However, about a tenth of the lights are broken after 7 months, indicating that quality improvements
to the solar lights are still necessary. Demand for solar lights is 29% at market price and increases
sharply to almost 70% when offered at a discounted price of US $4. We detect almost no difference in
usage between lamps provided free and lamps sold to households, which means that full subsidies
would increase solar light adoption without altering solar light usage. There is some evidence that
access to solar lights increases children’s light use and slightly increases the time boys spend studying,
but we find no gains in study time for girls or shifts to more productive time use for adults.
These results suggest that the effects of solar lights are welfare improving for most households;
however, unsurprisingly, they do not seem to be transformational in the sense that they do not lift
people out of poverty. Nevertheless, governments, NGOs and other organizations may still consider
accelerating the adoption of solar lights through tax cuts, subsidies, creating more favourable business
environments, or other means for the following reasons:
First, as has been shown in this study, solar lights reduce kerosene lighting use of households by about
half. Burning kerosene emits fine particulate matter (Jacobson et al., 2013; Lam et al., 2012; Lam et al.
2016), which may causes adverse health and environmental effects (often referred to as externalities).
Moreover, these are adverse effects that are not immediately visible to the consumer but manifest
themselves in the long run, while the costs have to be covered immediately. We know that consumers
Page 6 of 54
tend to invest less in products with positive externalities and such “lagged benefits” than would be
socially optimal, and this could provide a role for public organizations to step into. In future work we
will quantify the extent of kerosene reduction using sensor data and the associated reduction in fine
particular matter, as well as their related health outcomes. In addition, SolarAid, in partnership with
UC Berkeley, are conducting research on the impact of kerosene and solar lighting on indoor air
pollution and health effects; this will provide additional insight on this subject.
Second, if the policy goal is to provide all citizens with a minimum level of access to modern forms of
energy, solar lanterns are probably the least expensive way to do so. However, one needs to bear in
mind that solar lanterns only provide minimal access to energy that does not go beyond lighting and,
in some cases, mobile phone charging capability.
In resource‐constrained settings like Kenya, the cost‐effectiveness of any policy intervention should be
compared to the cost‐effectiveness of policy alternatives to achieve the same (combination of) policy
goals. For example, if the goal is to reduce households’ kerosene consumption, policy makers in Kenya
should also consider abolishing kerosene subsidies. If the focus is on providing some access to modern
energy, our findings should be compared with studies looking at the impacts of access to other forms
of modern energy access. An extensive analysis of various policy options lies beyond the scope of this
report. However, we hope that the results we outline here as well as the work on education, health
and environmental impacts we plan to undertake in the future contribute to the body of evidence that
is necessary for policy makers to make informed decisions about the allocation of scarce resources in
the energy space.
Page 7 of 54
Acknowledgments
We would like to thank Kat Harrison (SolarAid/Acumen Fund) for initiating this study and supporting it
from beginning to end, and Google for funding the study. We are also grateful for support from the
SolarAid and the SunnyMoney field team, as well as Innovations for Poverty Action (IPA) and VYXER
Research Management, for implementing the research so thoroughly. A special thanks to Carol Nekesa,
Charles Amuku, Seline Obwora, Erick Bwire, Yael Borofsky, and Nikita Trokhin for outstanding
management and research support as well as Prof Edward Miguel, Prof Jamie McCasland and the Chair
of Development Economics at ETH Zurich for their intellectual input. We are also very grateful to the
entire field staff for carefully collecting the data, as well as the teachers and head teachers of the
selected schools in Nambale and Teso South, for participating in our study. Finally, we would like to
thank each and every respondent who generously contributed their time to help us learn. Asanteni
Sana! We hope that this report contributes to a better understanding of lighting needs, solar energy,
and poverty reduction.
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ListofAcronyms
GoK Government of Kenya
IEA International Energy Agency
ITT Intention to Treat Effect
IPA Innovations for Poverty Action
KCPE Kenya Certificate of Primary Education
LPG Liquefied Petroleum Gas
NGO Non‐governmental Organization
PPP Purchasing Power Parity
ToT Treatment Effect on the Treated
RCT Randomised Control Trial
SHS Solar Home System
SK Sun King (Solar Light Brand produced by Greenlight Planet)
US $ United States Dollar
WB World Bank
WTP Willingness to Pay
%‐points Percentage points = unit for the difference of two percentages (e.g., going from 40%
to 47% is a 7%‐point increase)
Page 9 of 54
ListofFigures&Tables
Figure 2.1: Research Design .................................................................................................................. 13
Figure 2.2: Sun King Eco Light Figure 2.3: Sun King Mobile Light ... 18
Figure 2.4: Solar Light Ownership at Endline ........................................................................................ 21
Figure 3.1: Household’s Main Income Source ...................................................................................... 25
Figure 3.2: Tin Lantern Figure 3.3: Kerosene Lantern .................................................................. 26
Figure 3.4: Average Monthly Cash Expenditure by Households ........................................................... 28
Figure 3.5: Average Monthly Cash Expenditure by Poor Households ................................................... 28
Figure 3.6: Location of First Encounter with Solar Light ....................................................................... 30
Figure 3.7: Location of First Encounter with Solar Light Sales .............................................................. 30
Figure 3.8: Take‐up Ratio at Different Prices ........................................................................................ 31
Figure 3.9: Take‐Up Ratio by School and Subcounty ............................................................................. 32
Figure 3.10: Primary Activity Aided by Solar Light, Previous Evening ................................................... 34
Figure 3.11: Daily “On‐Switches” of Solar Lights ................................................................................... 35
Figure 3.13: Duration of Solar Light Use ............................................................................................... 37
Figure 3.14: Daily Solar Light Use .......................................................................................................... 37
Figure 3.15: Daily Solar Light Use Across Months ................................................................................. 38
Figure 3.16: Lighting Sources used Previous Evening ........................................................................... 39
Figure 3.18: Number of Hours of Lighting Use ...................................................................................... 41
Figure 3.19: Household’s Monthly Energy and Lighting Expenditure ................................................... 43
Figure 3.20: Men’s and Women’s Time Use ......................................................................................... 46
Figure 3.21: Daily Routine by Gender ................................................................................................... 47
Figure 3.22: Impact on Men’s and Women’s Time Use ........................................................................ 47
Figure 3.23: Boys’ and Girls’ Time Use .................................................................................................. 49
Figure 3.24: Impact on Girls’ and Boys’ Daily Routine .......................................................................... 49
Figure 3.25: Impact on Boy’s and Girls’ Time Use ................................................................................. 50
Table 2.1: Intervention Arms ................................................................................................................. 14
Table 2.2: Busia County compared with the rest of Kenya ................................................................... 15
Table 2.3: Balance Test between Control Group and Free Solar Light Group ...................................... 16
Table 3.2: Impact on Expenditure Categories ....................................................................................... 44
Table 3.3: Upper Bound Savings Effects on Expenditure ...................................................................... 45
Table 3.4: Impact on Men’s and Women’s Time Use in Minutes ......................................................... 48
Table 3.5: Impact on Boys’ and Girls’ Time Use in Minutes .................................................................. 50
Page 10 of 54
1 Introduction
1.1 Background
Access to electricity is a critical part of modern life and is considered both an outcome and a driver of
development. A number of studies show that electrification is linked to a range of development
improvements, such as higher income, employment, and better health and educational outcomes
(Dinkelman, 2011; Lipscomb, Mobarak & Barham, 2013; Chakravorty, Emerick & Ravago 2016; Baron
& Torero, 2015). However, extending the grid to poor and remote rural areas and providing access to
unelectrified households is expensive and poses a number of political, administrative, and technical
challenges (World Bank, 2010). Hence, 68% of all households and 83% of rural households in sub‐
Saharan Africa remain without access to electricity (IEA, 2015). In rural Kenya, around 95% of the
population does not have access to electricity (Kenya Population and Housing Census, 2009).
Unelectrified households typically rely on kerosene lanterns for lighting, which have high operational
costs, give off low‐quality light, and could lead to adverse health and environmental effects.
Prices for solar lights have fallen by around 80% in the past 6 years and are expected to drop even
further (Bloomberg 2016). Therefore, solar lights may provide a clean and cost‐effective solution to
provide poor households with access to lighting. Although there are a wide variety of off‐grid solar
products, ranging from large installations powering entire villages to small portable lights (see Figures
2.2 and 2.3), small, portable solar lights have become increasingly widespread in low‐ and middle‐
income countries, like Kenya, as a low‐cost means of providing very basic lighting services. They are
particularly popular because they are easy to deploy, do not require a large up‐front investment, and
only need limited maintenance. Once fully charged, small solar lights provide light for 3‐45 hours
depending on the brand, size, and quality of the light. On the other hand, these solar lights only provide
minimal access to energy and cannot satisfy energy needs beyond simple lighting (and in some cases
mobile phone charging). While there are high hopes for solar‐powered lights, there is little empirical
evidence concerning their cost‐effectiveness, impact on household welfare, or potential effect on the
environment. Even less is known about what drives the adoption of this technology or what impact
further price reductions might have on demand.
With this randomized field experiment we intend to help close this knowledge gap by studying current
demand for solar lights and the constraints which might limit their adoption, as well as the impact of
owning a light on the lives of rural households.
SolarAid, and its social enterprise SunnyMoney, is one example of an organization that has seen
promise in solar lights and developed a business model to distribute these lights to rural households.
SolarAid has also been very committed to research, conducting its own on the ground, and
commissioning this study to better understand their impact on poverty reduction. Its social enterprise,
SunnyMoney, is one of the largest distributors of solar lighting products in East Africa. SolarAid has
sold over 1.87 million solar units to date, and more than 513,000 in Kenya alone (SolarAid 2016). The
study was funded by Google, alongside a pilot study conducted by researchers at UC Berkeley to look
at the impact of lighting on indoor air pollution and health. The study has been managed by impact
investor Acumen since January 2016, when the SolarAid Research and Impact department moved
under its auspices.
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This report begins with a summary of the research questions and related literature, followed by an
explanation of the research design, the data, and the estimation approach. The report concludes with
a presentation of the main results.
1.2 ResearchQuestions
The first part of the study focuses on the take‐up of solar lights. In particular, we will study the
following questions:
Price elasticity of demand: To what extent does demand for solar lights change if the market price
decreases?
The second part looks at the use of solar lights. In particular, we will pose the following questions:
Main Users: Who uses the solar lights within a household and for what purposes?
Light consumption: Does access to a solar light change households’ light consumption?
The third part discusses the economic impact of solar lights. We will first look at the financial returns
to these investments, i.e., does average household spending on kerosene, candles, or batteries change
with access to solar lights, and by how much? We will then assess the impact of solar lights on time
use. In particular, we will focus on the following questions:
Energy Expenditure: To what extent does a household’s expenditure on energy change with access
to a solar light? How long does it take to amortize a solar light investment?
Time Use: Do children and adults change their time use habits once they have access to a solar
light? Do people have more hours engaged in productive activities in a given day?
In this report, we analyze both the use and impact of solar lights when they are distributed free and
compare that to usage and impact on households that purchased a light to test if there is any significant
difference between the two groups. The broader study also investigated educational, health and
environmental outcomes; however, this report focuses on the demand and economic impact of solar
lights, with subsequent analysis and work being conducted on educational, health, and environmental
outcomes. Literature Review and Research Gaps
While there is an extensive literature on technology adoption in general, few studies look at the
adoption of solar lights in particular. In a working paper by Yoon et al. (2014), the authors use a game
to elicit willingness to pay under different payment conditions for solar lights in India. They find little
evidence for the constraints they test for (uncertain quality of the product, liquidity constraints, and
present bias1), however, take‐up was very low overall and it is hard to know if, in a context where
overall interest in the product is higher, the constraints they identify would be binding. In a study from
Bangladesh, the authors show that people who had a chance to test and use a solar product for some
time were more likely to buy it at the end of the study (Kudo, Shonchoy & Takahashi, 2015). Along
similar lines, a study conducted by SolarAid in Senegal identified lack of trust and lack of awareness as
constraints to adoption (SolarAid 2014c).
Due to the novelty of affordable solar lighting technology there is still little empirical evidence on the
impact of solar lights. To our knowledge, there are only four working papers (Furukawa, 2013b; Smith,
1 Present bias is the tendency to over‐value immediate costs (and benefits) relative to future costs (and benefits).
Page 12 of 54
2014; Hassan & Lucchino, 2016; Kudo, Shonchoy & Takahashi, 2015) and two published papers from
Rwanda and Uganda (Grimm et al., 2016, Furukawa, 2013a) on the issue. Research from Rwanda has
found that access to solar lighting leads to a reduction in overall household expenditure of around 3%
(Grimm et al., 2016). An RCT conducted in Bangladesh found a 2% reduction of overall expenditure –
corresponding to 50% of total kerosene expenditure – when one solar light was provided. Savings
increased to 7% of overall expenditure and 75% of kerosene expenditure when three solar products
were handed out (Kudo, Shonchoy & Takahashi, 2015). In Solar Aid’s own data collection consumers
also reported energy expenditures savings as an important reason to purchase a solar light.
There is no conclusive evidence on whether and how solar lanterns influence time use among different
household members and very few studies have even looked at this outcome (Grimm et al. 2016). With
regard to educational outcomes, an RCT in Uganda finds that while study time increased, surprisingly,
average test scores decreased slightly (Furukawa 2013a). Other studies find that test scores remained
unchanged (Grimm et al., 2016; Smith, 2014; Kudo, Shonchoy & Takahashi, 2015) or that they
increased after taking spillovers between households who received a free solar light and the control
group into consideration (Hassan & Lucchino, 2016).
When looking at children’s health outcomes related to coughing, difficulty breathing, chest pain, sore
throat, eye irritation, fever, and headache, Furukawa (2013b) reports a slight improvement in self‐
reported health for those who received a solar light during exam time, but is not able to measure any
effect when using spirometers to measure breath volume. The author of the study specifically sampled
children who experienced these health problems (coughing, chest pain, or difficulty with breathing)
before the research started. The study in Bangladesh found no effect on self‐reported health, but they
did find a slight decrease in eye irritations when a doctor examined the children (Kudo, Shonchoy &
Takahashi, 2015).
The existing evidence on the impact of solar lights on household light use, expenditure, wellbeing, and
productivity is not conclusive. Moreover, only a few studies have been conducted on these effects;
most have small sample sizes (155‐341 households) and, at times, conflicting results. In addition, most
previous studies distributed free lights, which does not allow for reliable estimation of willingness to
pay or assessment of whether effects are different for people who purchase a solar light and people
who receive a free one. Finally, previous work has solely relied on self‐reported data to estimate solar
and kerosene light usage, a method which can be both imprecise and biased. The current study
complements existing research in the following ways:
The RCT offered solar lights at different prices (including SunnyMoney’s market price) to
understand people’s price elasticity of demand for solar lights.
The RCT had a large sample size of around 1,400 households, which makes it possible to detect
smaller effect sizes than studies with smaller samples.
The RCT used sensor data in addition to survey data to obtain more accurate and objective data
on light use.
The RCT collected detailed time use data for both schoolchildren and one of their guardians.
The RCT provided solar lights for free to a randomly selected sub‐sample and solar lights at a
positive price to another sub‐sample, in order to study whether the use and impact of solar lights
is dependent on whether people had to pay for this new technology or not.
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2 Methodology
The following section describes the methods used in this study, as well as the sample selection process
and how data was collected.
2.1 ResearchDesign
We conducted an RCT between July 2015 and March 2016 in 20 schools. Students (and their respective
households) were randomly assigned to one of the following groups:
a group with no intervention (control group),
a group that received a free solar light (free solar light group),
a group that had the opportunity to buy a solar light (voucher group or offer to buy group).
Those households which were given the opportunity to buy a solar light (voucher group) were
randomly assigned a price of US $4, US $7 (subsidized prices), or US $9 (the market price at the time
of the study).
The random assignment ensures that, on average, there is no difference between individuals assigned
to these different groups, apart from exposure to the intervention, (receiving a free light; the
opportunity to purchase a solar light; no intervention). Any observed differences between the three
groups at the end of the study can be attributed to the intervention, and is not the result of other
systematic differences between the groups (Duflo, Glennerster, and Kremer, 2007).
Randomization was conducted at the household level, meaning that within each of the 20 participating
schools each eligible student (and his/her respective household) was randomly assigned to one of the
experimental groups.
Figure 2.1: Research Design
The RCT was conducted in Busia County in Western Kenya. Within this region we selected 20 public
primary schools for the study out of a total of 97 eligible schools (see Section 2.2 for more details).
1: Control Group
400 Households
2: Free Light
400 Households
20 schools in Nambale and Teso South
3: Vouchers
601 Households
209 @ 400 KES/$4
195 @ 700 KES/$7
197 @ 900 KES/$9
All public primary schools in Teso South and Nambale of Busia County, Kenya
97 eligible schools
Randomly selected
Page 14 of 54
From each of the 20 primary schools, about 70 households with at least one child in standards (or class)
five, six, or seven were randomly selected and received one of the aforementioned interventions (see
also: Table 2.1 and Figure 2.1):
(1) Control group: 20 households per school, 400 households total.
(2) Free solar lights group: 20 households per school, 400 households total, received a free solar light,
of which 200 received a solar light that also had a port to charge a mobile phone (see also: Section
2.4).
(3) Voucher group: About 30 households per school,2 601 households in total, received a voucher to
purchase a solar light. In each school, 10 households were offered a solar light for 400 KES (US $4), 10
households were offered a solar light for 700 KES (US $7), and 10 households were offered a solar light
at the (summer 2015) market price of 900 KES (US $9).
Table 2.1: Intervention Arms
This research design allows us to estimate:
Price elasticity of demand for solar lights
Impact of receiving a free solar light on household light use, energy expenditure, and time use
Impact of receiving an offer to buy a solar light (at different price levels) on household light use,
energy expenditure, and time use
Any differences in impact between receiving a solar light for free and purchasing a solar light
2 Two of the schools did not have enough households that corresponded to the selection criteria. In these two schools, we reduced the number of vouchers distributed to 0 (Sango) and to 10 (Aburi) and increased the sampled students in larger schools instead. 3 Product specification sheet here: https://www.lightingglobal.org/products/glp‐sunkingeco/ 4 Product specification sheet here: https://www.lightingglobal.org/products/glp‐sunkingmobile/
Treatment Number of Households
(1) Control 400
(2) Free Solar Lights 400
Free light "Eco" (light only)3 200
Free light "Mobile" (light and phone charging)4 200
(3) Voucher 601
Voucher to buy for 400 KES 209
Voucher to buy for 700 KES 195
Voucher to buy for 900 KES (market price) 197
Total 1401
Page 15 of 54
2.2 SampleSelection
We selected Busia County in Western Kenya because SunnyMoney was operating in this part of the
country at the time of the study (July 2015‐March 2016). Busia is one of the more densely populated
and poorer counties of Kenya’s 47 counties: it is below the national average when it comes to urban
population, literacy, and share of population with a secondary education. Moreover, fewer people are
electrified and fewer paved roads exist in Busia than the Kenyan national average. These differences
may be related to the fact that Busia is more rural than the average county (Table 2.2).
Table 2.2: Busia County compared with the rest of Kenya
Source: GoK, CRE County Fact Sheets 2013. Note that two of the sub‐counties included here (Nairobi and
Mombasa) are almost entirely urban and Busia moves closer to the average if these are excluded.
Within Busia, two sub‐counties, Nambale and Teso‐South, were selected for the study because they
had sufficiently large rural populations and no other large ongoing research projects at the time. We
selected 10 schools in each of these sub‐counties using the following procedure: the local
administration provided a list of every public school (50 in Nambale; 77 in Teso South). Schools with
fewer than 100 pupils, schools with only girls or only boys, boarding schools, schools located in urban
areas or too far from the research office to be easily reached, and schools whose head teacher was
not present at the head teacher meeting5 were excluded. Of the remaining 97 schools we randomly
picked 10 in each sub‐county, i.e., 20 schools in total.
Within each of these 20 schools, a random sample of pupils was drawn from standards five, six, and
seven. Standard eight was not included since these pupils would have left school by the time the
endline survey was conducted. Students in lower classes (1‐4) were not included, as it would have been
harder for them to answer questions about homework, time use, light use, etc. On average, each
school had 578 pupils and 168 households with at least one student in the fifth, sixth, or seventh
standard. In each of the selected schools, we randomly selected 20 students as a control group, 20
students who received a free light, and around 30 students who received a voucher to purchase a solar
light (10 at each price). However, two of the selected schools did not have enough pupils; we did not
hand out any vouchers in these schools. Visits to schools were announced in advance and children
5 Once per school term all head teachers from a sub‐county are invited for a meeting to receive information from the local administration.
Busia Kenya
Busia’s Rank out of all
Counties (1=highest
47=lowest)
Total Population (2009) 743,946 38,610,097 25
Pop. per sq. km 439 66 10
Share urban pop. 16% 29.9% 28
HIV prevalence 7.1% 6.2% 38
Literacy rate 56.7% 66.4% 35
Pop. with secondary education 9.9% 12.7% 34
Electricity 6% 22.7% 32
Paved roads 0.5% 9.4% 31
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were encouraged to come to school; however, if a selected pupil was absent that day s/he was
replaced with another pupil who was drawn at random.
Out of 3,360 eligible households (with at least one child in standard 5‐7 in the 20 schools in our sample)
a total of 1,410 households were selected. All 1,410 pupils were surveyed for the first time in July and
August 2015 (baseline) and seven months thereafter (endline). From the 1,410 pupils interviewed at
baseline, we were able to interview 1,285 (91%) at endline: 9.6% of pupils moved to different schools
and we were not able to track all the pupils down in their new schools.
One of the pupils’ guardians, in most cases the mother (50.2%) or the father (28.7%), was interviewed
at both baseline and endline. At baseline, we surveyed all but nine of the sampled guardians. Those
nine guardians preferred not to participate in the study, meaning that we remained with 1,401
households that were willing to participate in the study. Seven months later (at endline) we were able
to track 1,326 respondents, corresponding to 94% of the original sample. However, of these
respondents, 13 did not agree to an interview, leaving a sample of 1,313 (93.1%) at endline.
2.3 BalanceTestacrossTreatmentsatBaseline
We tested the balance across the different treatment groups and the control group using key
household characteristics and questions relevant to energy and light use at baseline. The table below
displays the averages of these in the control group, the offer to buy group and the free solar light
group, and if any of these differences are statistically significant.6 We found no statistically significant
differences between the groups except that the offer to buy group had a lower percentage of business
owners.
Table 2.3: Balance Test
Control
Offer to
Buy p Value Free Light
p
Value Prob > F
Household Head Female 31% 28% 0.36 33% 0.61 1.15
Iron Roof 66% 62% 0.14 67% 0.92 0.18
Household Size 6.81 6.70 0.42 6.61 0.18 0.40
Chickens Owned 6.22 5.71 0.27 6.06 0.73 0.63
Main Income from Agriculture 69% 70% 0.67 65% 0.27 0.26
Household Head Years of Education 6.61 6.29 0.21 6.35 0.38 0.45
Owns Business 33% 25%*** 0.01 31% 0.58 0.02***
Owns Radio 55% 57% 0.70 52% 0.37 0.67
Electricity through Grid 1% 2% 0.47 1% 0.74 0.53
Number of Mobile Phones 1.43 1.40 0.63 1.39 0.50 0.79
Monthly Spending on Kerosene (US$) 2.09 0.43 0.14 1.99 0.39 0.34
Owns Any Solar Light 6% 7% 0.30 7% 0.46 0.58
Nr of Tin Lights Owned 2.10 2.03 0.31 2.17 0.28 0.11
Total Expenditure (US$) 71.74 69.94 0.64
Notes: * Statistically significant difference at the 10% level ** 5% level *** 1% level
6 We regressed the various household characteristics on treatment status (control, offer to buy, free light). The p‐values show whether the treatment groups are statistically different from the control group. The F‐test shows whether the treatment statuses have joint explanatory power for the household characteristics.
Page 17 of 54
2.4 Intervention
While there are a number of different types of solar products on the market, we analyze the impact of
low‐cost solar lights — small portable lighting units, which are the focus of SunnyMoney’s business.
These products provide 30‐100 lumens of light for 4‐36 hours on each charge, depending on the model
and the brightness setting used. For comparison, a simple tin lamp (see Figure 3.2 in Section 3.1)
provides around 7.8 lumens and a kerosene lantern (see Figure 3.3) provides 45 lumens (Mills, 2003). As opposed to grid connection and larger off‐grid solutions, these portable solar lights cannot be used
to power larger appliances such as TVs, fans, or refrigerators. These products are, however, less
expensive than larger home systems and typically require no installation and little maintenance. They
currently cost between US $7.5–US $35, depending on the size and functionality of the unit. The price
for a solar light is low compared to the cost of around US $400 for a household grid connection (wiring
the house or usage costs are not included in that figure) in Busia, Kenya (Lee, Miguel & Wolfram,
2016b).7 That said, a solar light is still a non‐negligible cost burden, given that 58.9% of the rural
population in Kenya lives on less than US PPP $3.10 per capita per day (World Bank, 2005).
Two different types of lights were used in this study: the Sun King Eco and the Sun King Mobile, both
manufactured by Greenlight Planet and quality assured by Lighting Global, a joint initiative of the
World Bank and the International Finance Cooperation.
In 2015, SunnyMoney was selling the Sun King Eco light (Figure 2.2) for US $9 in Kenya. According to
the producer, that model provides light for 4‐30 hours of lighting, depending on which brightness mode
is used.8 During the same time period, SunnyMoney was selling the Sun King Mobile light (Figure 2.3)
for US $24. According to the manufacturer, the model can charge a mobile phone and provide light for
3‐18 hours, depending on which brightness mode is used.9 Half of the 400 households who received a
solar light free got a Sun King Eco light (200 households) and half received a Sun King Mobile light (200
households). The discount vouchers (distributed to 600 households) were for the Sun King Eco model.
7 While there has been an announcement by the GoK to reduce connection costs, this has not been implemented yet in the study area: http://www.businessdailyafrica.com/Kenya‐Power‐connections‐lowered‐to‐Sh15‐000/539546‐2731146‐mddaukz/index.html 8 A specification sheet provided by Lighting Global can be found here: https://www.lightingglobal.org/products/glp‐sunkingeco/ and by the producer here: http://arti‐africa.org/wp‐content/uploads/2013/06/Product‐Overview‐Sun‐King‐Eco.pdf 9A specification sheet provided by Lighting Global can be found here: https://www.lightingglobal.org/products/glp‐sunkingmobile/ and by the producer here: http://arti‐africa.org/wp‐content/uploads/2014/06/SK‐Pro‐2_Product‐Sheet_2yr_040913_Lowres.pdf
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Figure 2.2: Sun King Eco Light Figure 2.3: Sun King Mobile Light
2.5 Data
2.5.1 QualitativeDataandPiloting
Prior to commencing the full study, we conducted a number of in‐depth interviews with solar light
users and non‐users, as well as with teachers. We also held five focus group discussions with users and
non‐users of solar lights before conducting the surveys. The information from the in‐depth interviews
and focus groups was used to design the survey instruments. In addition, we tested the random
distribution of free lights, as well as the survey questions and the acceptability of the sensor technology
(see Section 2.5.3). Moreover, we interviewed SunnyMoney’s senior management team and field
workers and shadowed them during their marketing and sales work. This allowed us to learn about
SunnyMoney’s operations and get a sense of how the solar lights are marketed and used.
2.5.2 SurveyData
We surveyed the randomly selected pupils (see Section 2.2) as well as their primary guardian, which in
most cases (78.8%) was the mother or the father of the child. Data was collected at baseline
(July/August 2015) before the intervention and around seven months after baseline (February/March
2016). Due to budget constraints, during baseline a shorter survey was administered for those
households which received a voucher.
We created survey instruments based on previous studies conducted by leading researchers in the
field, including Grimm et al. (2016), Cattaneo et al. (2009), Furukawa (2013, 2014), and Lee, Miguel &
Wolfram (2016a), as well as standardized scales (World Value Survey, European Community
Respiratory Health Survey II, the Standard Dry Eyes Disease Questionnaire and CES‐D) and SolarAid’s
internal research tools.
The advantage of building the questionnaire on other researchers’ work is that we can learn from
previous experience and compare our results to previous work. Surveys and rapid observations were
collected electronically on tablets or smart phones using Survey CTO software, and data was analyzed
using STATA.
Page 19 of 54
Besides surveying pupils and guardians, we also conducted a short survey with the head teacher from
each school to learn about their role in the SunnyMoney program delivered through the research and
to obtain information about the infrastructure and the performance of the school.
2.5.3 SensorData
In addition to survey data, which, in most cases, is self‐reported by respondents, we used sensors to
measure light use.
A sub‐sample (300) of the solar lamps that were distributed free or purchased were equipped with
Bluetooth enabled sensors developed by Bonsai Systems.10 At endline, 187 sensors (62.2%) were still
operating, while the remaining 37.8% were experiencing some form of technical malfunction; from
these, no data could be retrieved.11 Sensors tracked when the solar lights were used and for how long.
The solar light sensor determines when the lamp is in use by measuring the change in voltage across
the device’s light emitting diode (LED). The solar light sensor was installed by soldering three wires
from the sensor to the board inside the light (voltage, ground, side of the LED). The sensor draws a
very small amount of power from the lamp battery12. Hence, the solar sensor remains functional as
long as the lamp battery is charged (and assuming it does not break for another reason). The sensor
records an “ON” event when one presses a button to turn the light on and records an “OFF” event
when one turns the light off.
The solar sensor data includes the simple unique identifier, the device identifier, the date and time
(day, month, year, hour, minute) a lamp turned on or off, a dummy variable to indicate whether the
event was an “ON” or “OFF” event, the voltage across the light, and the voltage of the battery inside
the light.
Using smartphones enabled with Bluetooth and an iPhone application called “Lamplogger” (which was
specially developed for this project), field officers visited households at endline and wirelessly
uploaded data directly from the sensor to the phone. Field staff explained how the sensor worked and
what data it recorded to study participants and asked them for permission before downloading any
data. No data was downloaded if the participant had any objections. The app sent data from the iPhone
to a secure server once field officers returned to the home office and were in range of a Wi‐Fi
connection. The data can be reviewed and downloaded from the server in comma‐separated values
(CSV) format.
2.6 EstimationApproach
2.6.1 SummaryStatisticsandSampleDescription
For the summary statistics and sample description we used the baseline data from July/August 2015.
Because of budget constraints, some questions were only asked to those in the free solar light group
and the control group (N=800) and not to those who received a voucher (N=601). Whenever this is the
case, it is indicated either in the text or with a footnote.
10 http://www.bonsai‐systems.com 11 This number is as of 15.11.2016. We are still in the process of retrieving data and hope to increase the number of sensors from which we can retrieve data. 12 The use of power was so small that it would not change the charging time needed and use of the solar light.
Page 20 of 54
2.6.2 AnalysisofTake‐up
When looking at take‐up rates, the sample is restricted to the 601 households who received a voucher
to purchase a solar light. We use the following equation to estimate price elasticity of demand:
′
designates whether a household j in school i purchased a solar light.
α indicates the take‐up price at the references price of 900 KES (market price).
α shows the effect of a discounted price (400 KES or 700 KES) in relation to the market price of 900
KES on the take‐up of solar lanterns
is a set of dummies for the price level at which a household received a voucher to purchase a
solar light (400 KES or 700 KES). The reference price is 900 KES.
X ′refers to other independent variables associated with the individual, such as levels of education,
wealth, etc.
λ refers to school fixed effects.
ϵ is an error term.
2.6.3 AnalysisofImpact
For the analysis of impact we apply two measures: the intention to treat (ITT) effect and the treatment
effect on the treated (ToT).
Imperfect Compliance
Of those who received a free solar light in the treatment, 87.9% still had a functional light at endline.
Technical problems were more common for solar lights with sensors than the other lights. Only 85%
of the households who received a free solar light with a sensor still had a functioning light at endline,
versus 90% of the households who got a conventional solar light. In the control group, around 17.4%
had a functional light even though they did not receive a light through the study (see Figure 2.4). In
the group that received a voucher to buy a light, not everyone (45.6%) decided to purchase a solar
light and not everyone who bought a light still had a functioning light at endline.
Under “perfect compliance”, 100% of households in the free solar light group would have functioning
lights and 0% of households in the control group would have functioning solar lights (or any lights at
all). This is not the case in our study and we therefore have “imperfect compliance”. It is important to
note, however, that most studies and, in fact, most development policies and interventions have
imperfect compliance. In this study, we report both the intention to treat (ITT) effect, which ignores
noncompliance, and the treatment effect on the treated (ToT), which accounts for imperfect
compliance (see next sections for a detailed description).
Page 21 of 54
Figure 2.4: Solar Light Ownership at Endline
Notes: Statistically significant difference at the 10% level ** 5% level *** 1% level.
Intention to Treat (ITT)
The intention to treat (ITT) effect describes the average effect of the treatment (in our case, two
treatments: obtaining a solar light free or receiving an offer to buy one) on the outcome of interest,
independent of whether households actually had a functioning solar light at the end of the study.
Hence, it is a simple comparison of means between the treatment group (everyone who received a
free solar light or an offer to buy one) and the control group (everyone who neither received a free
solar light nor an offer to buy one). As mentioned above, some households in the control group decided
to purchase a solar light independent of this study and these people are still part of the control group.
The effect of having received a free solar light (or the offer to buy one) can be estimated using the
following equation:
′
designates the outcome of interest of household j in school i at endline.
is a dummy variable indicating the treatment assignment of the respective household. In the
first estimation, will be equal to 1 if the household was assigned to receive a free solar light and
it will be equal to 0 if the household was assigned to the control group. In a second estimation,
will be equal to 1 if the household had the option to purchase a solar light at a subsidized price and
will be equal to 0 if the household was assigned to the control group.
captures the effect of having received a solar light for free (estimation 1) or having received an offer
to buy one (estimation 2) on the outcomes of interest.
refers to a set of control variables at the individual level.
refers to school fixed effects.
is an error term.
87,9%
50,5%
17,4%
10,3%
4,2%
1,6%
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Free Solar Lantern Offer to Buy Comparison Group
Non‐functional Solar Lantern
Functional Solar Lantern
***
Page 22 of 54
Whenever possible, regressions were run with and without controlling for baseline (outcome) levels
as well as other control variables to check for the robustness of the estimated effects. It was not always
possible to control for baseline levels, as we do not have baseline data for all measures. In discussing
the results, we always indicate whether control variables were included. In general, the direction and
significance levels of the results did not change when baseline controls were included.
Treatment effect on the treated (ToT)
The treatment effect on the treated (ToT) is the effect of having a functioning solar light (either having
received a free one or having bought one from the “offer to buy” intervention). In this estimation, we
correct for the fact that fewer than 100% of households in the treatment group had a functioning light
and that some households in the control group purchased a solar light independently of the study.
Thus, broadly speaking, the ITT measures the effect of a “free lamp” policy (or a policy, which creates
a market for solar lights, possibly at reduced prices), while the ToT measures the effect of owning a
functioning solar light compared to not having a solar light at all.
We use an instrumental variable (IV) approach to calculate the ToT. This approach is relevant for two
reasons. First, not all households who received the voucher to buy a lamp decided to redeem it.
Second, even amongst those that received a free light (and the control group), we did not have “perfect
compliance”; some households in the control group purchased a solar light independent of the study
and some households in the treatment group no longer had access to a functioning solar light at the
end of the study (see figure 2.4).
The validity of the instrumental variable approach depends mainly on two assumptions.13 The first
assumption is that the instrument (being assigned to a free solar light or a voucher) indeed increases
the chances that the household owns a solar light at endline.14 The second assumption is that being
assigned to receive a free solar light (or receiving an offer to buy one) only affects the outcome of
interest (for example, spending on energy) through solar light ownership, and not through any other
channel.15 The first assumption can be tested with our data and we find that it is fulfilled in our case.
The second assumption cannot be formally tested, but is highly plausible, given that households were
randomly assigned to one group or the other.
An important issue to keep in mind is that ToT estimates the impact of a solar light for people who
“comply” with the research design. For the voucher group, this is the effect of owning a solar light if a
household decides to purchase one. It is possible that the impact of a solar light is different for buyers
and non‐buyers. Hence, the ToT is only used to analyze the impact of having a solar light on those in
compliance with the intervention (those who purchase a solar light if offered one).
For the case of imperfect compliance (as in our study), the ITT effect is smaller than the ToT effect.
Intuitively, the effect of the intervention is watered down by those in the control group who purchased
a light independently and those in the treatment group who no longer have a functioning light (and
potentially on those receiving an offer to buy who did not buy). In this study, we had an overall
compliance of around 70% for the free distribution (that is deducting the 17.4% who had a functioning
13 The formal econometric assumptions are not discussed here. See Imbens & Angrist (1994) for more details. 14 This is known as the “first stage” association. 15 This is known as exclusion restriction.
Page 23 of 54
light in the control group from the 87.9% who had one in the treatment group) and an overall
compliance of around 33% for the offer to buy group. General differences between the treatment and
control group as estimated with ITT effects can be multiplied by around 1.4 for free solar light and by
around 3.0 for the offer‐to‐buy group to get the treatment effect on the treated (that is, if no control
variables are used). See Imbens & Angrist (1994) for more details. The analyses that follow refer to ITT,
unless otherwise specified. ITT effects are the standard in public policy literature as they provide
estimates of the impact of the policy being studied (which also includes non‐compliers). Moreover,
ITT effects require less assumptions ToT effects to infer from the statistical estimates about the true
effects
2.7 LimitationsoftheResearchDesign
The design of the study allows us to make unbiased estimates of take‐up rates and impacts; it is,
however, also subject to a number of limitations.
First, the study was conducted in two sub‐counties in Western Kenya and results are thus not
necessarily generalizable to other contexts without making further assumptions. Results on energy
expenditure savings, for example, depend on the local cost of kerosene as well as the income level of
the sampled households.
Second, while our sample size of 1,401 households is larger than most previous studies, it is still not
large enough to detect very small effects. Some of the insignificant results could be driven by a lack of
statistical power rather than the absence of an effect. In addition, the study only lasted about seven
months, so we do not know how usage patterns and impacts might evolve a year or two after having
purchased or received a solar light.
Third, as is common in most experimental studies, some of the respondents we interviewed at baseline
did not participate in endline, either because they moved far away, chose not to participate, passed
away, or were not available for other reasons. Specifically, 9% of the children and 6% of the adults
originally surveyed at baseline could not be interviewed at endline. Attrition was similar in the control
and the treatment groups. There was a 50% split between the free solar light group and the control
group at baseline. At endline, 50.9% of households were in the treatment group and 49.1% in the
control group (the difference is not statistically significant). Still, we cannot rule out that those who
dropped out of the study are systematically different from those who remained, and hence cannot
exclude the possibility that attrition biases our results. The bias could go in either direction (under‐ or
overestimation of effects).16
Fourth, spillover effects may occur if household members from the control group start to visit
household members who received or purchased a light in order to enjoy their better lighting. Spillover
effects could lead to an underestimation of the overall effects.17
Fifth, as with all survey‐based studies, we face some risk of social desirability bias. Social desirability
bias can lead to biased results if respondents who received access to a solar light feel for some reason
more obliged to answer in a certain way (to say, for example, that they spend a lot of time on
homework) than those who did not receive access to a solar light. To minimize this bias, respondents
16 More investigation of attrition will be done in further analysis. 17 More investigation of spillover effects will be done in further analysis
Page 24 of 54
were reminded that the research was independent and that their answers were treated confidentially.
In addition, sensor data allows us to check the accuracy of survey responses about solar light usage.
Sixth, the current version of the working paper does not include adjustments for multiple hypothesis
testing. This means that some of the results, that are only significant at the 10 percent level, may not
be statistically significant once we control of multiple hypothesis testing.
3 Results
This chapter summarises findings about solar light adoption and usage, as well as the effect of solar
light access on economic welfare. The chapter starts with a description of the sampled households,
continues with a summary of adoption and usage patterns and concludes with the impact of solar
lighting on household energy expenditure and time use (education and health outcomes will be
analyzed in future work as they were not the core focus of this particular study).
3.1 DescriptionofHouseholds
Household Characteristics
The average household in our sample has 6.7 members, with an average of 4.3 children under the age
of 18. Most houses have earth floors (85.5%) and iron sheet roofs (77%) on their main building.18 A
typical household has four separate rooms. The average household head attended school for 6.3 years.
Women head 30.3% of households. At baseline, the average household spent around US $70 in cash
per month (US $10 per capita per month, or US $0.30 per capita per day).19 However, expenditure is
very seasonal and the average household expenditure was much higher (US $85) during endline, which
was conducted shortly after school fees were due. In addition, endline data collection took place
mostly after harvest, while most of the baseline data was collected shortly before harvest. The average
household owns 1.9 acres of land, 0.8 cows, and 6.1 chickens.20 In terms of asset ownership, 53.7% of
households own at least one radio, 53.8% own a bicycle, and 7.8% own a motorbike. The most common
drinking water sources are protected springs (36.9%), bore holes (25.4%), and rivers, streams, or ponds
(18.9%).
Almost all households (98.8%) conduct agricultural activities and around a third own at least one
business, most of them selling fish or other food items. Most of these businesses (85.2%) have no
employees. Only 20.1% of households have at least one member who was employed in the previous
year (formally or informally). As shown in Figure 3.1, the self‐reported main income source for the
largest share of households is agriculture (68.2%), followed by casual (informal) labour contracts
(14.7%), own business income (11.1%), formal employment (3.7%), and remittances and transfers
(1.7%).
18 People in the study area tend to live in compounds containing one or more small houses. 19 All US $ amounts are in current exchange rate (US $1 = 100 KES on 01‐07‐2016) and not PPP adjusted. Also, note that the cash expenditure does not include own agricultural production and consumption. 20 This information was collected for the free‐solar‐light group and the control group only.
Page 25 of 54
Figure 3.1: Household’s Main Income Source (baseline; N= 1,397)
Around 91% of households own at least one mobile phone, and 41% have more than one mobile
phone. Meanwhile, 72.6% of respondents are registered with MPESA or another mobile money
provider and 47.3% participate in one or more savings groups. Of those participating in savings groups,
the average contribution is US $11.20 in the month previous to the survey (median US $6).21
Using the Progress Out of Poverty Index22 developed for Kenya in 2016 to estimate the likelihood a
household lives in poverty, we calculate an average score of 42.6 for the households included in our
study. According to Schreiner (2016a), this score is associated with a 42.2% likelihood of living below
the national poverty line, a 30.6% likelihood of living with less than US $1.90 per day and a 66.3%
likelihood of living with less than US $3.10 (PPP adjusted).
Household Energy and Light Use
In our study, access to modern energy sources are limited and only 8.7% of households have access to
some form of electricity. To break this number down: 2.8% of households are connected to the grid,
3.3% have access to a solar home system, 2.3% have access to a car battery (which provided energy
for the house), and 0.3% have access to a generator. The vast majority of the sampled households use
an open fire (98.4%) or charcoal stoves (1.0%) for cooking. Kerosene, LPG, and other stoves are much
less common (0.6% combined).
When asked at baseline to list all the lighting sources used within the household during the past month
(multiple answers possible), most households indicated that they used tin lamps (99.1% ‐ see Figure
3.2) and cell phone lights (47.6%), followed by kerosene lanterns (17.6% ‐ see Figure 3.3), battery‐
powered torches (17.3%), solar lights (5.9%), candles (4%), other rechargeable lights (2.7%), and
21 This information was only collected for the free‐solar‐light group and the control group. 22 More information can be found at: http://www.progressoutofpoverty.org/country/kenya
Agriculture68%
Casual Labour15%
Business11%
Formal Wage4%
Remittances & Transfers
2%
Page 26 of 54
electricity (2.0%).23 Tin lanterns are small lights, typically made locally out of recycled tins. They
produce an open flame that provides a weak light (around 7.8 lumens according to Mills, 2003) and
can be bought for US $0.25‐US $0.50, depending on the size and quality of the lamp. Kerosene lanterns,
on the other hand, are larger and provide a much stronger light (around 45 lumens according to Mills,
2003). Kerosene lanterns cost between US $3‐US $6, depending on the size and quality. They also use
more kerosene per unit of time and, for that reason, are more expensive to operate (Mills, 2003).
When asked what lighting source respondents predominantly relied upon (only one answer possible)
during the past month, the most frequent answers were: 88.4% tin lamps, 5.3% larger kerosene
lanterns, 3.7% solar lights and only 1.1% electricity powered lighting. On average, a household owns
2.2 tin lamps.
Importantly, though, 76.4% of the sample uses more than one type of lighting source in their home. If
households only use one light source (23.6%), they reported only using tin lamps. Every household
which uses grid electricity also uses at least one other source of lighting — possibly a reaction to the
frequent blackouts in the study region, and/or possibly the desire for portability of lighting outside the
home. The most frequent combinations of household light sources was tin lamps plus cell phone light
(14.9%), tin lamps, cell phone light, and firewood (11.2%), and tin lamps and firewood (10.2%).
Figure 3.2: Tin Lantern24 Figure 3.3: Kerosene Lantern
Household Expenditure on Energy and Lighting25
An average household spends around US $3.66 (KES 366) per month on energy,26 corresponding to
5.1% of the households’ total cash expenditure — US $70.75 per household per month (current US $).
Note that expenditures captured here only include cash spending and do not include items that
households consume from their own farms, which are likely to constitute a large fraction of overall
consumption for many rural households. If we were to include own consumption as well, the fraction
23 This information was only collected for the free‐solar‐light group and the control group. 24 Source: https://islandenergysystems.wordpress.com 25 Since expenditure measures are very sensitive to outliers, for this section the highest 0.5% of expenditures of each expenditure type was replaced with the value at 95.5%. 26 Not PPP adjusted.
Page 27 of 54
spent on energy would likely be considerably lower. The seasonality of expenditure, as mentioned
earlier, also influences these estimates.
For lighting alone, households spend US $2.19 (KES 219) per month, which corresponds to 59.7% of
the total energy expenditure and 3.1% of total cash expenditure. Kerosene accounts for 94.5% of the
US $2.19 per month used on lighting (Figure 3.4). Energy expenditures unrelated to light use include
expenditure on mobile phone charging (US $0.42), charcoal (US $0.24), batteries not used for lighting
(US $0.30), firewood (US $0.21), and electricity bills (US $0.18).
The total spending on lighting measured in this survey is similar to national representative surveys of
Kenya. For example, according to the 2005/2006 Kenya Integrated Household Budget Survey (KIHBS),
a median household spends 2.0% of its annual expenditure (including own consumption) on kerosene
and the poorest quartile of the population spends 2.9% of its annual expenditure on kerosene (Lighting
Global, 2012).27
In the study conducted by Kudo, Shonchoy & Takahashi (2015) in Bangladesh, expenditure on kerosene
was around 2% of total expenditure.28 In a study in Rwanda, Grimm et al. (2016) found that households
in rural Rwanda spend around 5% of their total cash expenditure on lighting.29 This finding is a slightly
higher fraction compared to what we found, on average, and might be partially explained by the fact
that kerosene prices in Rwanda were at around US $2 per litre at the time — more than twice the cost
of kerosene at the time of data collection in our study.30
To provide a reference for comparison, European households spend on average around 4% of their
total expenditure on electricity, gas, and other fuels used by the household, 31 however, those
households use around five times more energy even when compared with the small fraction of
households in sub‐Saharan Africa who are connected to the grid (IEA, 2014b). Hence, households in
our sample pay a slightly higher fraction of their cash expenditure on energy (5.1%) than households
in Europe, but consume much less energy of poorer quality.
27 We don’t know the current subsidy level for kerosene in Kenya which is an important part of the story on spending. 28 Authors calculations based on information provided by Kudo, Shonchoy & Takahashi, 2015. 29 This is the households’ spending on kerosene, candles, and dry‐cell batteries. 30 Information according to email exchange with authors. 31 Based on Eurostat numbers from 2011 found here: http://ec.europa.eu/eurostat/statistics‐explained/index.php/Archive:Household_consumption_expenditure_‐_national_accounts
Page 28 of 54
Figure 3.4: Average Monthly Cash Expenditure by Households (free lighting and control group combined at baseline; N= 795)
Figure 3.5: Average Monthly Cash Expenditure by Poor Households (free lighting and control group combined at baseline, poorest quintile only; N=157)
Food; 45,5%
Education; 18,5%
Health ; 6,5%Funerals/Weddings/Church; 6,1%
Farm inputs; 5,3%
Kerosene ; 2,9%
Lighting other than Kerosene; 0,2%
Energy Other; 2,1%
Other; 3,3%
Travel ; 3,2%
Cloths/Hair; 2,5%Communication;
2,1%
House repairs; 1,8%
Food; 57,6%
Education; 10,4%
Health ; 5,6%
Funerals/Weddings/Church; 5,1%
Farm inputs; 1,6%
Kerosene ; 7,5%
Lighting other than Kerosene; 0,1%
Energy Other; 2,3%Other; 5,5%
Travel ; 1,2% Cloths/Hair; 0,9% Communication; 1,9%
House repairs; 0,2%
Page 29 of 54
Household Expenditure on Energy and Lighting among the Poorest Quintile
An average household in the poorest quintile32 spends around US $2.05 (KES 205) per month on energy
(in comparison to US $3.66 (KES 366) for the average household) corresponding to 9.8% of its total
cash expenditure (US $20.59). This amount is almost double the share of cash expenditure paid by the
average household in our sample, which spends 5.1% of total cash expenditure on energy. For lighting
alone, the poorest 20% of households spend US $1.60 (in comparison to US $2.16 for the average
household), which corresponds to 77% of the total energy expenditure and 7.5% of total cash
expenditure (in comparison with 3.1% for the average household ‐ see Figure 3.5).
Even if the absolute spending on energy and lighting is somewhat lower for poorer households, it is a
much larger fraction of their overall spending, which amounts to only US $20.70 per household per
month (compared to US $70 per household per month of the average household). This disparity
suggests that poor households view energy (as well as food expenditures) as a necessity: households
with lower income reduce spending on other goods more than their spending on energy (and food). In
other words, demand for energy is less income elastic than it is for other goods.
3.2 Take‐UpofSolarLights
3.2.1 AvailabilityofSolarLights
Lack of information about, exposure to, and availability of high‐quality and low‐cost solar products has
been mentioned in previous studies as a potential constraint to the adoption of solar lanterns (Kudo,
Shonchoy & Takahashi, 2015; SolarAid, 2014c). We collected information about the availability and
cost of solar lights to test this hypothesis.
The majority of adults in our survey (88.9%) mentioned that they had seen a solar light before; most
commonly they reported encountering a solar light for the first time at a relative’s or neighbor’s house
(see Figure 3.6).33
32 This consists of the 20% of households in the free solar light group and the control group who have the lowest total expenditures at baseline. 33 This information was only collected for the free‐solar‐light group and the control group.
Page 30 of 54
Figure 3.6: Location of First Encounter with Solar Light
(pre‐intervention, free solar light group and control group; N= 796)
Slightly more than half of all adults in our sample have seen a solar light for sale before (see Figure
3.7). We asked those 52.6% where they saw the product for sale before (multiple responses possible).
Most (33.5%) saw them being sold at the closest market center (a place where people typically go once
a week to buy items that cannot be found in their own village), about 13.3% saw them for sale in a
nearby town (typically referring to Busia, Bungoma, or Kakamega), and 5.3% saw them sold in their
own village. Fewer than 1% saw them being sold in a large city (Nairobi, Kisumu, or Mombasa), because
rural households rarely travel to larger cities.
Figure 3.7: Location of First Encounter with Solar Light Sales
(pre‐intervention, free solar light group and control group; N=796)
61,9%
11,6% 11,1%7,3%
3,0% 2,6% 1,8% 0,8%0%
10%
20%
30%
40%
50%
60%
70%Neighbour's/Relative's
House
Market Cen
tre
Never saw
before
NGO Cam
paign
Own house
Town
Other
School
47,4%
5,3%
33,5%
13,2%
0,5%0%
5%
10%
15%
20%
25%
30%
35%
40%
45%
50%
Never Saw a SolarLight being sold
Own Village Closest MarketCentre
Town City (Kisumu,Nairobi, Mombasa)
Page 31 of 54
The prices of solar lights sold by vendors other than SunnyMoney tended to be above the price of
SunnyMoney’s cheapest light (US $9). Of the respondents who already owned a solar light at baseline
(5.2% of the sample), 90% paid US $10 (1,000 KES) or more for it. The average price paid was around
US $33. Of those households who did not own a solar light at baseline, 93.5% said that the reason they
had not purchased one was that they could not afford one. Only 1.3% said the reason was that the
product was not available for purchase.
These results indicate that most respondents had seen solar lights before (88.9%), many knew people
who owned a solar light already (85.6%), and 52.6% had seen one for sale. One could conclude from
this information that a lack of exposure might not be the most important constraint to adoption. We
do not, however, have information about the quality of the products that people encountered.
According to Bloomberg (2016), there are a large number of very low‐quality products on the market,
and it is not always easy for consumers to assess the quality of a product. Hence, the exposure to low‐
quality products could actually lower the chances of adopting any solar light (of low or high quality). In
addition, easy access to solar lights might still be an issue: while most of the respondents were exposed
to solar lights before (i.e. they saw them before), only 38.8% of respondents said they could be
purchased from a nearby store (own village and closest market center).
3.2.2 ImpactofPricesonTake‐Up
The experimental design of the study allows us to determine take‐up rates at different price levels and
hence, to measure the price sensitivity of households in our sample. Households responded strongly
to price differences. Specifically, 28.9% of the households who received the offer to buy a solar light
at the market price of 900 KES (US $9) chose to purchase one, 37.4% of the households who were
offered a reduced price of 700 (US $7) made a purchase, and 68.8% of those who were offered a solar
light for 400 KES (US $4) bought one (see Figure 3.8).34
Figure 3.8: Take‐up Ratio at Different Prices (N=601)
Notes: Statistically significant difference from the market price at the *10% level, ** 5% level, *** 1% level. No control variables used.
34 Note that because of the limited time offer of the vouchers, take‐up rates might be different than take‐up rates if prices would permanently change, but that should not affect the price elasticity of demand estimated.
100%
69%
37%29%
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Free 400 KES 700 KES 900 KES (Market Price)
Page 32 of 54
3.2.3 SchoolDifferencesinTake‐Up
All of the 20 sampled schools are rural, public, and non‐boarding schools that educate both boys and
girls (see Section 2.2 for more detail). Schools had an average total enrolment of 578 students, and
193 students were enrolled in standards six, seven, and eight at endline (corresponding to standards
five, six, and seven at the beginning of the study). The smallest school had 284 students and the largest
one had 862 students. Out of the 20 schools, 13 had access to electricity. For the 17 schools which had
students taking the 2015 Kenya Certificate of Primary Education (KCPE) national exam the pass rate
was 54.2%.35 This rate is very close to the reported national average of 50%.36
Take‐up of solar lights offered at 400, 700 or 900 KES varied a lot between the 19 schools where
vouchers to purchase a solar light were offered.37 In the school with the lowest adoption rate, only
14.7% of households who were offered a voucher to buy a solar light decided to purchase one, whereas
in the school with the highest level of adoption, 75.8% of households who received a voucher bought
a light (see Figure 3.9).
Figure 3.9: Take‐Up Ratio by School and Subcounty (N=601)
Notes: No control variables used.
There are at least two possible explanations for the high variation in take‐up rates across different
schools.
35 KCPE test is only taken in the end of eight grade. The remaining three schools opened recently and did not have a class eight in 2015. 36 Source: http://www.capitalfm.co.ke/news/2014/12/more‐than‐half‐kcpe‐candidates‐score‐above‐250/ 37 In one of the 20 schools, no solar lights were offered for sale, as there were too few students in classes five, six, and seven.
71%
57%
50%45% 44%
38% 37%31%
20%
76%
60%54%
52% 51%49%
40%37%
30%
15%
0%
10%
20%
30%
40%
50%
60%
70%
80%
Schools in Nambale Subcounty Schools in Teso‐South Subcounty
Page 33 of 54
One possible explanation is that SunnyMoney sells solar lights through the head teacher of each school
and head teachers do not execute their solar light distribution responsibilities uniformly.38 Following
SunnyMoney’s usual business practice, during our experiment, households who wanted to purchase a
solar light had to place an order with the head teacher and make a 100% cash payment to the head
teacher in advance39. On a designated distribution day, the head teachers travelled to a SunnyMoney
distribution point to purchase the solar lights on behalf of the households. Alternatively, households
could also come to the distribution point independently, but would then have to bear the travel cost
themselves. The challenge with this distribution model (both for the study and for SunnyMoney’s
business model, in general) is that solar light take‐up depends on a trusting relationship between
households and the head teacher at the pupil’s school. It also places a lot of the responsibility for
distribution on the head teacher, who is a public servant and not an employee of SunnyMoney.
According to the interviews we conducted with SunnyMoney staff, head teachers, and households,
some head teachers were more active in promoting the solar lights to pupils and their households than
others, and some households mentioned that they did not want to pay the head teacher in advance
because they did not trust him/her.
Another possible explanation is that variation in take‐up across schools is caused by systematic
differences in household characteristics of enrolled children across schools. Hence, differences in take‐
up rates between schools might be explained by differences in households being more (or less) likely
to purchase a solar light. For example, households of one school might be on average richer, better
educated, have had more exposure to solar lights, or different in some other way that might lead to
higher take‐up rates in comparison to others.
We will analyze the relevance of school effects versus household effects to explain variations in take‐
up in a future analysis.
3.3 UseofSolarLights
Establishing the extent to which solar lights are used and how they are used is an important first step
to understanding the impact of solar lights on household welfare. In the following section, we analyze
whether households who have solar lights use them, who uses them, and for what purposes.
In addition to self‐reported data, we have data from 187 sensors, which measure the use of solar lights
(see Section 2.5.3 for more information). In the analysis of the sensor data, we did not differentiate
between sensors in households who received a free light from sensors in households that purchased
a light. We will use the sensor data to study how frequently the solar lights are being used, for how
long they are typically being used, and at what time of the day. Unless otherwise specified, the
following section relies on sensor data.
38 Head teachers are in charge of managing the school. SunnyMoney’s distribution model works together with head teachers to sell solar lights to parents of pupils and other community members who are interested in the product. 39 Anecdotal evidence suggest that head teachers in some cases advanced some of the buyers part of the up‐front cost.
Page 34 of 54
Solar Lights Users and Usage
When we asked respondents in the free solar light group which household members had used the solar
light the previous evening (multiple responses possible), 79.5% said children, 54.0% said adults, and
18.4% of households reported that no one had used it (this includes the 12.1% of households which
no longer had a functioning light). In 51.8% of the households, both adults and children used the solar
lights, whereas in 27.6% only children and in 2.1% only adults used it. Answers from respondents who
purchased a solar light were not statistically different from households who had received a solar light
for free.
We also asked both children and adults in the survey to indicate the main purpose for which the
different household members had used the solar light the previous evening (one answer only). If they
had used the solar light for more than one activity, they were asked to choose the one that had taken
the most time. Children reported having used the solar light primarily for homework. Only 4%
mentioned other activities, such as talking (2%), cooking (1%), and reading (1%). Adults reported
having used the light for a much more diverse set of main activities. The most frequently reported
activities were eating (28%), talking (24%), and cooking (19%), as shown in Figure 3.10 below.
Figure 3.10: Primary Activity Aided by Solar Light, Previous Evening
(post‐intervention, free solar light; N = 296 for children, N = 205 for adults)40
Note: Responses refer to activities on the evening prior to the day of the survey.
40 Note the question asked about the respondent, his/her spouse, and other adults in the household. Here, we summarized activities done by one or more adults in a household.
95,6%
4,4%
28,6%24,8%
19,7%
6,7% 6,3% 5,5% 4,6% 1,7% 0,8% 0,8% 0,4%0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Homew
ork (Pupils)
Other (Pupils)
Eat (Adults)
Talk (Adults)
Cook (Adults)
Rest (Adults)
Listen
to Radio
(Adults)
Read (Adults)
Household Chores
(Adults)
Help with Homew
ork
(Adults)
Work (Adults)
Pray (Adults)
Travel (Adults)
Page 35 of 54
Frequency of Use
We first look at the amount of time that respondents reported using solar lights in the survey.
Respondents who received a free light or purchased one reported that, on average, they used the solar
light 5.8 days out of the last week; however, this group includes people who did not have a functioning
solar light at endline. When the sample is restricted to those who received a free light (or purchased
one) and still had a functioning light seven months later, the average was 6.7 out of 7 days.
Households with a functioning light at endline (February/March 2016) reported that they used the
solar light 3.33 hours the previous day.41 This figure is the same whether we look at households who
received a free solar light or households who purchased a solar light using a voucher.
According to the sensor data, most households use the solar lights nearly every day: more than a third
of the households (38%) use the solar light every single day and an additional 45% of households use
them 9 out of 10 days. The remaining 17% use them 6 out of 10 days or less. Overall, average use
according to the sensor data is 6.16 out of 7 days. Households used the solar lights more frequently
(6.3/7 days) in the first month after receiving the solar light and less towards the end of the study
(6.0/7 days). Note that the results of the sensor data are very similar to the results of the survey data.
Figure 3.11 shows the distribution of daily “on‐switches”, and we see that most people use the lights
between 2 and 4 times per day and, on average, 4.27 times per day.42 This number increases to 4.78 if
we consider only those days on which the solar light was switched on at least once.
Figure 3.11: Daily “On‐Switches” of Solar Lights (N = 40,732: days*solar lights)
41 This information is based on the following question, “Yesterday, for how many hours did you use a solar lantern?” We will also use the information from the time use data (see Section 3.6) in future analyses to analyze the number of hours households used the solar lights. 42 This figure only includes “on switches” if the lamp was on for more than one minute.
10,7%
9,3%
13,3%14,0%
12,8%
10,4%
8,1%
6,0%
4,5%
3,0%2,3%
1,6%1,1%
0,7% 0,5% 0,3% 0,2% 0,1% 0,1% 0,1% 0,0%0%
2%
4%
6%
8%
10%
12%
14%
16%
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
% of all Solar Lights
Total On‐Switches per Day
Page 36 of 54
The next figure show at what point during the day people tend to switch the solar lights on (and off).
We see that solar lights are switched on most often in the evening hours between 18:00 and 19:00,
followed by the morning hours between 5:00 and 6:00. In the early mornings, solar lights are typically
switched off at around 6:00, while in the evening solar lights are typically switched off between 19:00
and 22:00. Solar lights are also used throughout the night and during the day; however, this happens
much less frequently (see Figure 3.12).
Figure 3.12: “On‐Switches” and “Off‐Switches” by Time of Day (N=254,754)
Note: This graph contains all events in the sensor data set.
Duration of Use
Again using the senor data, each time someone turns a solar light on, it is used for about 50 minutes,
on average.43 Often when the light is turned on, though, it is for a rather short time: in 50% of cases
solar lights are only used for 10 minutes or less. The reason is unclear as these short incidences did not
show up in the survey data, but some anecdotal evidence suggests that people use the solar lights to
quickly look for something in the dark or that people want to test if the solar light is charged.
Moreover, households do not use the solar light for the same amount of time throughout the day.
Depending on the time of day it is used, the solar light tends to be turned on for a shorter or a longer
period. Figure 3.13 illustrates the typical duration of light use for each hour of the day. If the lights are
used during the day, it is for a short period of time: around 10 minutes on average. If they are used in
the early evening (between 19:00 and 20:00), people keep the lights on for about 1.5 hours.
Interestingly, people still use the lights for around 30 minutes when they turn them on in the middle
of the night (after midnight and before 6:00).
43 Events which lasted less than one minute are excluded from the analysis.
0%
2%
4%
6%
8%
10%
12%
14%
16%
18%
20%
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
% of Lights Switched
‐On/O
ff
Hour of the Day
On‐Switches Off‐Switches
Page 37 of 54
Figure 3.13: Average Duration of Solar Light Use by Time of Day
(N = 146,633)
Note: This graph contains all events > 1min and <720min in the sensor data set.
Households use the solar light for an average of 212.3 minutes (3.5 hours) per day. The average rises
to 238.1 minutes (4.0 hours) per day if only days with any solar light use at all are considered. Looking
at the distribution in Figure 3.14, we see that on 12% of days solar lights are not used at all.
Figure 3.14: Daily Solar Light Use (N = 40,732: days*solar lights)
The sensor data can also help us understand how usage evolves over time. It could be the case, for
example, that excitement over the novelty of the product induces people to use solar lights in the early
stages of the study; at the same time, it is plausible that usage increases over time as household
members become comfortable using the product. Looking at the number of hours per day that solar
lights are used across different months (Figure 3.15), there is a very slight decrease in use over time.
During the last month of the study the solar lights were still being used for 3.46 hours per day on
average, only 0.2 hours (12 minutes) less than in the first month. Note that this analysis does not
include households that were no longer using their light at the end of the study (around 10%).
30 27 27 2834
25
1510 11 9 10 11 9 9 10 10 12
22
89 86
56
47
36 36
0
10
20
30
40
50
60
70
80
90
100
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Minutes of Solar LIght Use
Hour of the Day
0%
2%
4%
6%
8%
10%
12%
14%
0 30 60 90 120 150 180 210 240 270 300 330 360 390 420 450 480 510 540 570 600
% of all Solar LIghts
Average Minutes Used per Day
Page 38 of 54
Figure 3.15: Daily Solar Light Use Across Months (N = 40,732: days*solar lights)
3.4 ImpactofSolarLightsonKeroseneUse
To establish possible environmental and health impacts of solar lights it is essential to understand
whether solar lights complement or replace existing light sources, which are typically kerosene‐based
products. In other words, it is necessary to determine whether solar lights are used in addition to or
instead of existing lighting sources. In this section we will look at this question from two different
perspectives: first, we look at the impact of receiving (or buying) a solar light on the type and number
of non‐solar lighting sources used, and second, we analyze the impact of access to solar lighting on the
total number of lighting hours per day for adults and children.
Types of lighting sources used
Households were asked what type of lighting source anyone in their household used the previous
evening (multiple answers possible). Figure 3.16 shows the different types of lights used in the control
group (orange) in comparison with the light sources used by respondents in the two intervention
groups. Notably, 100% of control group respondents used kerosene‐based products the previous
evening. The share of people who used kerosene‐based lighting products drops to 86% for the voucher
recipients (including both households who bought and who did not buy a solar light), to 75% for those
voucher recipients who actually bought a solar light, and to 72% for the free solar light recipient
households. These findings indicate that while access to solar lighting reduces the use of kerosene
lighting, the majority of households did not completely replace kerosene‐powered lighting products,
since for most households one solar light does not provide all household lighting needs.
The “other” category predominantly consists of lanterns powered by battery or by electricity, and also
includes candles and cell phone lights. Access to solar lighting does not have an impact on the use of
other forms of lighting.
3,66 3,59 3,683,54 3,43 3,41 3,49 3,46
0,00
0,50
1,00
1,50
2,00
2,50
3,00
3,50
4,00
August September October November December January February March
Average
Hours per Day
Page 39 of 54
Figure 3.16: Lighting Sources used Previous Evening (ITT; N = 1,313)
Notes: Statistically significant difference from control group at the *10% level ** 5% level *** 1% level. No control variables used. ****The difference between the buyers group and the control group cannot be interpreted as causal due to possible selection bias.
Number of lighting sources used
Figure 3.17 shows that an average household in the control group uses two tin lamps.44 This number
drops to 1.7 for the households which received an offer to buy a lamp and to 1.4 for those, which
bought a lamp or received one for free. Larger kerosene lanterns are less frequently used and the
reduction is from 0.23 in the control group to 0.16 in the free solar light group.In addition to leading
to lower usage of kerosene based products, solar light adoption also (marginally) reduced use of
cellphone lights, both among households which bought a light and those which received one free.
There is no significant difference between the different experimental groups with regard to the use of
battery powered/other rechargeable lights.
When we analyze the ToT (treatment effect on the treated), the average number of tin lamps among
the control group is 2.2 tin lamps per household. Households who received a free solar light use 0.9
fewer tin lamps, and those who bought a light use 0.8 fewer tin lamps. Hence, we see a replacement
rate of 1:0.9 and 1:0.8 respectively (one solar light replaces 0.9/0.8 tin lamps).45 The effect size of the
free group is not statistically different from the effect size of the buyers,46 meaning that buyers of solar
lights and households who received a free light exhibit approximately the same replacement ratio.
44 The survey question was: “How many of the following lighting sources did you use in the past month?” 45 This estimation is not statistically different from a 1:1 replacement. 46 The estimated effect of a free solar light is ‐.88 fewer tin lamps and ‐.82 fewer tin lamps for a bought solar light.
83%72%
4%
22%
81%75%
7%
29%
47%
86%
5%
29%13%
100%
7%
26%
0%
20%
40%
60%
80%
100%
120%
Solar Lantern Kerosene Based Lighting Solar Home & Electricity Other
Free Solar Light Buyers**** Offer to Buy Control
Page 40 of 54
Figure 3.17: Number of Lighting Sources Used in the Past Month, by Type
(ITT, post‐intervention; N = 1,313)
Notes: Statistically significant difference from the control group at the *10% level ** 5% level *** 1% level. No control variables used. ****The difference between the buyers group and the control group cannot be interpreted as causal due to possible selection bias.
Lighting Hours for Pupils and Adults
To calculate the number of hours that adults and children use solar and other lighting each day we
included a detailed set of survey questions about light use. For every hour of the day we asked
respondents to report the primary activity, they had engaged in.47 For every hour without sunlight
(18:00 to 7:00),48 we also asked respondents whether they used any lighting source. If they did use a
lighting source, we asked them which one. From that information, we calculated the total number of
hours per day that adults and children reported using any lighting source (i.e., total hours of lighting
regardless of source used). Lighting hours mostly occur in the evenings (i.e., after 18:00) and not in the
morning (i.e., before 7:00). Among children, around 80% of lighting hours occur in the evenings, and
among adults, around 90% of lighting hours occur in the evenings.
Students who received a free solar light used lighting sources for 3.55 hours per day (ITT effect), those
who received a voucher to buy a solar light used a lighting source for 3.47 hours per day (ITT effect),
and those in the control group used it for 3.32 hours per day. The difference between the free solar
light group and the control group is statistically significant at the 5% level, and the difference between
those who received a voucher to purchase a solar light and the control group is significant at the 10%
level. Hence, in households that received a free solar light, children increased lighting use by 0.23 hours
(13.6 minutes) corresponding to a 6.8% increase and children whose household received a voucher to
purchase a solar light increased usage by 0.15 hours, or 8.8 minutes, corresponding to a 4.4 % increase
(see Figure 3.18).
47 Half hour slots were used for the evenings between 19:00 and 22:00 for more detailed and accurate information. Time slots were longer between 23:00 and 3:00, when we expect most people to be asleep. 48 Since Kenya is at the equator, sunrise and sunset remains the same throughout the year.
1,071,38
0,16 0,17
0,751,08
1,42
0,18 0,22
0,710,63
1,73
0,17 0,22
0,69
0,19
2,00
0,23 0,20
0,79
0,0
0,5
1,0
1,5
2,0
2,5
Solar light
Tin Lam
p
Kerosene lantern
Battery
powered
/rechargeable light
Cell phone light
Free Solar Light Buyers**** Offer to Buy Control
Page 41 of 54
When looking at the ToT for students, the difference between the control group and the free solar
light group is 0.37 hours, or 22 minutes. The ToT difference between the voucher recipient group and
the control group is 0.45 hours, or 27 minutes. Hence, having access to a solar light increases lighting
hours among students by about 10‐15% per day, or by about 80‐100 hours per year.
Figure 3.18: Number of Hours of Lighting Use (ITT; N = 1280 for pupils and N = 1313 for adults)
Notes: Statistically significant difference from control group at the *10% level ** 5% level *** 1% level. No control variables used. The difference between the buyers group and the control group cannot be interpreted as causal due to possible selection bias.
For adults, on the other hand, there is neither a statistically significant difference between those who
received a free light and the control group nor between the buyers and the control group. We see a
decrease in number of lighting hours for the full voucher recipient group (including those who chose
not to buy), and this reduction is driven by the non‐buyers (since the number of hours that buyers use
a lighting source did not change). The reduction of 0.18 hours (10.8 minutes) is, however, only
significant at the 10% level. At this point we do not know what drives this reduction, and we plan to
investigate this result further.
In summary, we find that solar lights are a substitute for rather than a complement to kerosene‐based
lighting for adults, as their lighting hours do not increase with access to a solar light. For children, solar
lights seem to mostly substitute for kerosene lighting, but they also act as a complement to some
extent, given that students reported a slight increase in light usage (about 20‐30 minutes from a
baseline of 3 hours and 20 minutes). Light use changes for households which purchase a solar light and
those which receive one for free are very similar.
Interruptions in Light Consumption
During qualitative interviews prior to the start of the baseline survey, we learned that kerosene is
sometimes perceived as an inconvenient lighting source. For one thing, it is necessary to rely on
material for wick in order to burn it, which must be replaced when it runs out. In addition, a household
must constantly be (thinking about) purchasing and transporting kerosene. As a result, people who fail
to anticipate their wick or kerosene needs sometimes have to sit in the dark or need to rely on another
3,323,47 3,55 3,56
3,213,03 3,07 3,21
0,0
0,5
1,0
1,5
2,0
2,5
3,0
3,5
Control(Pupils)
Offer to BuySolar Light(Pupils)
Free SolarLight
(Pupils)
Buyers(Pupils)
Control(Adults)
Offer to Buy(Adults)
Free SolarLight
(Adults)
Buyers(Adults)
*
Page 42 of 54
lighting source. We therefore analyzed whether access to solar lights reduces such lighting
interruptions.
Amongst households in the control group, 44.5% reported that they had to sit in the dark at least once
during the previous month, while among the free light recipients only 17.1% experienced such a
situation; among households who received an offer to buy a solar light 28.3% had that experience. Still,
we learned that such instances are not frequent, even for those in the control group: on average, the
treatment group was stranded without light 0.3 times during the past month, while the control group
was stranded 1.1 times.
Similarly, we find that 40% of households in the control group had to resort to a secondary lighting
source in the past month, compared to 27.8% of households who received a voucher and only 18% of
free treatment households. The most frequently used alternative was a cell phone light. Resorting to
a secondary lighting source is also a relatively rare occurrence: treatment households experienced this
an average of 0.4 times during the past month, voucher recipient households experienced it an average
of 0.7 times, and control households used a secondary light source about 0.8 times, on average.
3.5 FinancialImpactofSolarLights
Impact on Monthly Energy Expenditures
During our endline data collection in February/March 2016, an average household in the control group
spent US $2.86 (KES 286) per month on energy, corresponding to 3.34% of total expenditure. Energy
spending at endline was lower than in the beginning of the study due to lower kerosene prices; total
expenditure at endline was higher than at baseline due to school fees, which are due early in the year.
Lighting alone accounts for US $1.61 (KES 161), or 56.5% of energy expenditure – and almost all of this
(90.7%) is spent on kerosene.49
Households who received a voucher to buy a solar light spent US $0.53 (KES 53) less per month on
energy, out of a total of US $2.32 (KES 232) per month spent on energy, of which US $1.38 (KES 138)
was spent on lighting. In the free solar light group, the average spending on energy per month was
lower by US $0.93 (KES 93), with a total of US $1.93 (KES 193) per month on energy, of which US $1.05
(KES 105) is spent on lighting (see Figure 3.19).50
Half of the group receiving a free light was given a Sun King Eco (SK Eco) and the other half a Sun King
Mobile (SK Mobile) solar light. The difference between the two lights is that the SK Mobile has a larger
and stronger light than SK Eco, with the ability to charge a mobile phone (for more information see
Section 2.4). Those households which received a SK Mobile incur lower mobile phone charging costs
(US $0.08 or KES 8) per month compared to those which received an SK Eco light (US $0.29 or KES 29).
This difference is significant at the 1% level. The overall energy expenditure is thus lower for people
who received a SK Mobile (see Figure 3.19). However, given the much higher price for SK Mobile lights
(US $24 instead of US $9 for the Sun King Eco) these additional savings do not translate into shorter
amortization periods (see Table 3.1).
49 These numbers are slightly different from what is described in Section 3.1, probably due to lower kerosene prices during endline data collection. 50 These are simple differences between the groups, with no control variables used.
Page 43 of 54
Figure 3.19: Household’s Monthly Energy and Lighting Expenditure by Treatment
(ITT, post‐intervention, all groups; N=1,313)
Notes: Statistically significant difference at the *10% level ** 5% level *** 1% level. No control variables used.
Savings prove to be a large share of energy expenditure (ITT around 20%‐40% and ToT around
40%60%), which is expected given that lighting is a large fraction of energy expenditure (see Section
3.1 and Table 3.1). They are, however, a rather small percentage (ITT around 1% and ToT around 2%)
of total cash expenditure. This finding is in line with the fact that energy accounts for only 3.3%‐ 5.1%
of total cash expenditure.51
When we focus on the ToT estimates, which assess the impact of having a functioning solar light, we
see that households who purchased a solar light save around 1.9% of their total cash expenditure while
households who received one free only save 1.3%. This difference could be caused either by a selection
effect, whereby people who use more kerosene are more likely to buy a solar lantern, or by a sunk cost
effect, whereby the act of purchasing could lead people to use the solar light more often, or by a
combination of both effects.
Overall, these estimates are in line with existing literature. Grimm et al. (2016) discovered expenditure
reduction of US $0.92 as a result of providing solar lights free, corresponding to 1.7% of total
expenditure of the control group in their study in Rwanda52 and an amortization period of purchasing
a solar light of around 18 months. Kudo et al. (2016), in their study in Bangladesh, calculate expenditure
51 During baseline it was at 5.1% and during endline 3.3%, due to lower kerosene prices and higher overall expenditure (because of schooling fees) at endline. 52 Calculations made by authors based on numbers provided by Grimm et al. (2016).
$1.05 $1.00 $1.10$1.38
$1.61
$0.89$0.76
$1.00
$0.95
$1.24
$0,00
$0,50
$1,00
$1,50
$2,00
$2,50
$3,00
$3,50
Free
Solar
Lantern
Free
Solar
Lantern
(Mobile)
Free
Solar
Lantern (Eco)
Offer to Buy
Control G
roup
$1.93
$2.32
Expenditiureon Energy Except Lighting
Expenditure on Lighting
$2.86
$1.76
$2.10
Page 44 of 54
savings of 1.6% of total expenditure, which is not significant at the 10% level,53 and a pay‐back period
of 21 months.54
Table 3.1: Monthly Expenditure Savings
(ITT & ToT, post‐intervention, all groups; N=1,313)
Effect Type of Light
Savings in USD
% energy exp1
% tot exp endline2
% tot exp baseline3
Payback Period in months4
Free Solar Light (ITT) SK Eco 0.76** 26.6% 0.9% 1.1% 11.9
Free Solar Light (ToT) SK Eco 1.14** 39.8% 1.3% 1.6% 7.9
Free Solar Light (ITT) SK Mobile 1.10*** 38.4% 1.3% 1.6% 21.9
Free Solar Light (ToT) SK Mobile 1.51*** 53.0% 1.8% 2.2% 15.9
Offer to Buy (ITT) SK Eco 0.53** 18.6% 0.6% 0.8% 16.9
Offer to Buy (ToT) SK Eco 1.61** 56.5% 1.9% 2.3% 5.6 Notes: Statistically significant difference from control group at the * 10% level ** 5% level *** 1% level. No control variables used. If we control for baseline, we find similar effects overall. 1 Energy expenditure of control group at endline. 2 Total expenditure of control group at endline. 3Total expenditure of free group and control at baseline. We added this information to account for the fact that right
before the endline survey took place yearly school fees were due, which substantially increased overall expenditure.55 4Assuming a price of US $9 for a Sun King Eco and US $24 for a Sun King Mobile solar light and a 0% interest rate.
Impact on Expenditure Pattern
The next question is how households spend the savings on kerosene of around US $0.80‐$1.60 (KES
89‐160) per month: in other words, how does the expenditure pattern (as shown in Section 3.1) change
once households have access to a solar light? Since the savings as a percentage of total expenditure
per month are just 1%‐2%, we do not find any significant changes in expenditures for any of the
categories, except an increase in food expenditure of US$ 2.75 in households that received a voucher.
This change is only significant at the 10% level (see Table 3.2).
Table 3.2: Impact on Monthly Expenditure Categories (ITT, post‐intervention, all groups; N=1,313)
ITT ToT
Expenditure Type Control (US $)
Control vs. Free (US $)
Control vs. Voucher (US $)
Control vs. Free (US $)
Control vs. Voucher (US $)
Food 30.14 0.44 2.75* 0.64 8.33*
Education & Health 38.52 2.04 1.84 2.92 5.59
Other Expenditure 16.29 1.04 0.98 1.5 3
Energy 2.86 ‐0.93*** ‐0.53** ‐1.34*** ‐1.61***
Notes: Statistically significant difference from control group at the * 10% level ** 5% level *** 1% level. No control variables used. Results do not change significantly when controlling for baseline expenditure (only possible for the free solar light group).
53 It is significant at the 10% and higher (3.2%) when they do not control for baseline. 54 Author’s calculation based on information in the paper that products costs 37 USD and average yearly savings are around 21 USD. 55 In future analyses we will use monthly expenditure data from the region of Busia available from another study to model expenditure fluctuations and kerosene savings across seasons.
Page 45 of 54
Kerosene Price Fluctuations
When we conducted the endline survey beginning in February 2016, kerosene prices were at a historic
low due to falling global oil prices.56 According to the Kenyan Energy Regulatory Commission, pump
prices for kerosene were 42.83 KES (US $0.43) per litre, while at baseline they were 64.92 KES (US
$0.65) per litre.57 This baseline price (July/August 2015) is similar to the average kerosene price in the
year before our study took place (July 2014‐July 2015).58 This reduction in kerosene prices is only
reflected in our survey to the extent that respondents who buy kerosene by the litre (N=580) reported
that they paid 80 KES (US $0.80) per litre at baseline and 70 KES (US $0.70) at endline.59 In Kenya, as in
other countries in sub‐Saharan Africa, kerosene prices in rural and remote areas are much higher than
at the pump stations in the city center due to high transportation costs and lower quantities being sold
(Lighting Africa, 2012).60
When calculating the effect of access to solar lighting above, we compared the free solar light group
(or the voucher recipient group) to the control group at endline. Since kerosene prices were very low
at that time, the savings estimates are likely to be lower than they would be if prices were higher.
If the demand for kerosene were perfectly non‐responsive (i.e., inelastic) to kerosene price changes,
the savings in kerosene per household would increase in proportion to the increase in price (since
consumers would use the same amount of kerosene no matter the price). This assumption is very likely
to lead to an overestimation of the savings potential, since households are likely to reduce the use of
kerosene to some extent as prices go up (i.e., demand is not perfectly inelastic).
Table 3.3: Upper Bound Monthly Expenditure Savings
(ITT & ToT, post‐intervention, all groups; N=1,313)
*Based on assumption that kerosene prices are 1.14 times higher than measured and demand is perfectly inelastic. ** Assuming a price of US $9 for a Sun King Eco and US $24 for a Sun King Mobile and assuming a 0% interest rate.
56 http://www.nation.co.ke/news/Fuel‐Prices‐Energy‐Regulatory‐Authority/‐/1056/2624228/‐/vdfd6e/‐/index.html 57 http://www.erc.go.ke/index.php?option=com_content&view=article&id=162&Itemid=666 However, pump prices differ a lot from the prices people face in remote areas (see Lighting Africa (2012)). 58 ERC (2015) provides information on three price points (July 14, Feb 15, and Jun 15). The average of these three points is 66.09 KES (Nairobi) and 69.54 KES if adjusted for Busia. 59 We focus here on the 39.4% who purchase kerosene by the liter, since others purchase it using “tins” as a measure – an unspecified amount that costs 10 KES or 20 KES. 60 We do not know why the price drop is only partially reflected in local prices. This might be a sign of market failures such as information asymmetries between kerosene sellers and consumers and may partially be a result of a monopolistic market structure.
Effect Type of Light
(SK) Upper bound energy savings
US $ per month* Amortization in months (5%)**
Free Solar Light (ITT) Eco 0.87 10.4
Free Solar Light (ToT) Eco 1.30 6.9
Free Solar Light (ITT) Mobile 1.25 19.2
Free Solar Light (ToT) Mobile 1.73 13.9
Offer to Buy (ITT) Eco 0.61 14.8
Offer to Buy (ToT) Eco 1.84 4.9
Page 46 of 54
To give us an upper bound estimate for the savings at the household level we assume that consumption levels are the same as they are at endline, but prices are at the reported baseline level (80 KES per litre instead of 70 KES per litre). Under these assumptions, the amount saved should increase by a factor of 1.14 and the amortization time is reduced accordingly. Table 3.3 shows the corresponding figures.
3.6 TimeImpactofSolarLights
When higher quantity or higher quality lighting becomes available, households may increase the
number of hours they are awake as their time becomes more productive or enjoyable. Moreover,
households might shift some of the activities they used to do during the day to the evening, and/or
change the number of hours they devote to different types of activities. We collected detailed time
use data for adults and children in our sample. Specifically, we asked about their activity for every one
hour slot for the previous day and for every 30 minute slot for the previous evening.61 Moreover, for
the early morning and evening slots we asked which lighting source (if any) they used for the activity.
This information was collected at baseline for the free solar light group and the control group and at
endline for the entire sample.
3.6.1 Adult’sTimeUse
We find considerable differences in time use between male and female adults. Men tend to be more
engaged in productive activities (agriculture and off‐farm work) than women, but women work much
more in total (i.e largely involving household chores). Total working hours are 9.2 hours for women
and 7.5 hours for men. Men enjoy double the amount of recreational time of women (see Figure 3.20).
Due to these large gender differences in time use we conduct the impact analysis separately for men
and women.
Figure 3.20: Men’s and Women’s Time Use (post‐intervention, control group; N = 367)
Notes: Statistically significant difference between male and female respondents at the * 10% level ** 5% level *** 1% level. No control variables used.
61 More detailed information was collected on evening hours since information from the pilot suggested that solar lights are used more in the evening.
4,1
5,1
1,1
6,8
0,5
1,1
5,8
1,72,2
6,9
0,5
1,4
0,00
1,00
2,00
3,00
4,00
5,00
6,00
7,00
8,00
Working Hours HH Chores Recreation Sleep/Rest Travel Religous &Volunteer
Women
Men
Page 47 of 54
Figure 3.21: Daily Routine by Gender (ITT, post‐intervention, all groups; N=1,313)
Notes: Statistically significant difference at *10% level ** 5% level *** 1% level. No control variables used.
First, we do not observe any significant impact of solar lights on the time women (or men) get up in
the morning or go to sleep in the evening (see Figure 3.21). Second, we compare how women and men
in each of the groups use the 24 hours of the day. Figure 3.22 shows a full day for an average person
for each of the groups, not controlling for any variables. We do not observe any obvious changes in
working hours (or other activities) for women. Men in both the offer‐to‐buy and the free solar light
group tend to increase their recreational time slightly and marginally decrease their working time
(including household chores). These differences are small and therefore not easy to distinguish in
Figure 3.22.
Figure 3.22: Impact on Men’s and Women’s Time Use
(ITT, post‐intervention, all groups; N=1,313)
Notes: No control variables used.
To have a closer look at time use effects, we look at the impact of receiving access to a free solar light,
or getting the opportunity to buy one on men’s and women’s time use when controlling for a set of
control variables (ITT in table 3.4) as well as the effect of having a functioning solar light on time use
9,2
5,4
9,3
5,4
9,2
5,3
9,3
5,2
9,2
5,3
9,3
5,2
0,0
2,0
4,0
6,0
8,0
10,0
Go to Bed Wake Up Go to Bed Wake Up
Women Men
Control Offer to buy Free Solar Light
0,00
5,00
10,00
15,00
20,00
Control Offer to Buy Free SolarLight
Control Offer to Buy Free SolarLight
Women Men
Other
Religous &VolunteerTravel
Sleep/Rest
Recreation
HH Chores
Working Hours
Page 48 of 54
(ToT in table 3.4). We do not observe any statistically significant differences in the number of hours
that women spend on different activities between the control group and the treatment groups. Men,
on the other hand, seem to experience an increase in recreational time of around half an hour when
given access to a solar light, and decrease their working time (and time spent on household chores) by
about one hour (see Table 3.4). Since all hours of the day must add up to 24 hours by construction,
analysing the impact of solar lights on time use using OLS regression is not ideal. We will follow up on
this issue in a future analyses.
Table 3.4: Impact on Men’s and Women’s Time Use in Minutes per Day
(ITT & ToT, post‐intervention, all groups; N=1,313)
ITT ToT
Free Offer to Buy Free Offer to Buy
Women Men Women Men Women Men Women Men
Working ‐2.7 ‐53.7** 5.9 29.9 ‐3.9 ‐76.1** 19.1 78.3
HH Chores ‐0.6 2.1 20 ‐55.3*** ‐0.9 3 64.9 ‐144.5***
Recreation 2.2 28.3* ‐3.7 32.6** 3.2 40.3* ‐12.1 85.3**
Sleep/Rest ‐15 16.3 ‐8.1 0.3 ‐21.6 23.3 ‐26.3 0.7
Travel 2.1 5.3 ‐2.5 7.6 3 7.6 ‐8.2 19.9
Rel. & Volunt. 15.1 10.7 6.4 ‐16.3 21.8 15.2 20.9 ‐42.7
Notes: Statistically significant difference at *10% level ** 5% level *** 1% level. Controlled for years of education and baseline levels of the respective variable when comparing the free solar light group with the control group. It was not possible to control for baseline levels in the offer‐to‐buy group as this data was not collected.
3.6.2 Children’sTimeUse
In contrast to adults, where women seem to spend their time differently than men, we only find small
differences in the daily activities of boys and girls. Boys and girls are both in class for around 4‐5 hours
and do homework and personal studies for around 2.5 hours per day. Girls, however, get slightly less
sleep than boys (0.6 hours) and they spend one hour more on household chores. Figure 3.23 illustrates
the differences in time use between girls and boys.
Page 49 of 54
Figure 3.23: Boys’ and Girls’ Time Use (post‐intervention, control group; N=366)
Notes: Statistically significant difference at *10% level ** 5% level *** 1% level. No control variables used.
We first calculated the average time of the day children get up in the morning and go to sleep in the
evening, and similar to the results for adults, we do not observe any differences between the control
group and the treatment groups (see Figure 3.24).
Figure 3.24: Impact on Girls’ and Boys’ Daily Routine
(ITT, post‐intervention, all groups; N=1,280)
Notes: Statistically significant at the *10% level ** 5% level *** 1% level. No control variables included.
Second, we calculated the impact of solar lights on the amount of time spent on different activities by
girls and boys separately. Figure 3.25 represents a day for an average boy and an average girl in the
control and treatment groups without using any control variables. Controlling for a set of control
variables (see Table 3.5), we find that boys and girls living in households which received access to a
free solar light tend to sleep about half an hour less than children in the control group. Moreover, boys
tend to study about 16.9 minutes more than boys in the control group (ITT), corresponding to a ToT
4,7
0,91,5
7,8
1,72,5
1,3
3,4
4,2
0,91,6
8,4
1,8 1,5 1,3
4,4
0,0
1,0
2,0
3,0
4,0
5,0
6,0
7,0
8,0
9,0
Hours inSchool
Studyduring Day
Study atNight
Sleep Time Recreation HH Chores Travel Other
Girls Boys
21,3
5,7
21,3
5,9
21,5
5,7
21,4
5,8
21,4
5,7
21,4
5,8
0
5
10
15
20
25
Go to Bed Wake Up Go to Bed Wake Up
Girls Boys
Control
Offer to buy
Free Solar Light
Page 50 of 54
increase of 31.3 minutes if they received a free solar light. No statistically significant effect can be
found for girls. Similar to our results for adults, where we only observe changes in men’s time
allocation, it seems that access to a solar light has a bigger impact on boys’ time use than on girls’ time
use. The most significant effect is a reduction in sleeping hours for both boys and girls — an unintended
consequence of the solar light (see Table 3.5).
Figure 3.25: Impact on Boy’s and Girls’ Time Use
(ITT, post‐intervention, all groups; N= 1,280)
Notes: No control variables used.
Table 3.5: Impact on Boys’ and Girls’ Time Use in Minutes per Day
(post‐intervention, all groups; N = 1,280)
ITT ToT
Free Offer to Buy Free Offer to Buy
Girls Boys Girls Boys Girls Boys Girls Boys
Study Total 8.1 16.9* 4.0 1.7 10.1 31.3* 5.5 6.5
Study at Night 3.6 10.2 6.2 4.9 4.2 17.82* 16.4 12.1
Hours in School 12.9 12.1 7.5 8.4 20.0 20.6 32.3 17.9
HH Chores ‐1.2 ‐9.6 ‐9.1 ‐7.9 ‐4.9 ‐17.2 ‐31.2 ‐24.2
Recreation 1.9 ‐3.7 8.2 ‐1.8 1.7 ‐6.7 17.8 ‐21.5
Sleep & Rest ‐19.68** ‐29.3** ‐9.5 ‐14.8 ‐27.12* ‐55.6*** ‐18.8 ‐61.5*
Travel ‐3.7 ‐21.0 ‐1.4 ‐13.7** ‐3.2 ‐32.0*** ‐2.8 ‐38.28**
Notes: Statistically significant at *10% level, ** 5% level, and *** 1% level. Controlled for school fixed effects, pupil class, whether yesterday was a school day, number of days that pupil was given homework past week.
0,00
5,00
10,00
15,00
20,00
Control Offer to Buy Free SolarLight
Control Offer to Buy Free SolarLight
Girls Boys
Other
Travel
HH Chores
Recreation
Sleep
Study
Hours in School
Page 51 of 54
We also asked children specifically about homework completion. Pupils in both the control and the
treatment groups reported that they had received homework on 2.6 days out of the past week, on
average.
In general, children complete their homework after sunset (80% of the time). In the control group,
76.9% of homework assignments that pupils received the previous week were completed after dark.
In households which received a free solar light the pupil is 5.1%‐points more likely to complete
homework after dark (significant at the 5% level) and pupils in households which received an offer to
buy a solar light are 4%‐points more likely to finish after dark (significant at the 10% level). These
overall differences are mostly driven by boys who tend to shift homework time to the evening hours
(again see Table 3.5).
On average, 30.8% of the children in the control group who had received homework in the past week
reported that they had not been able to complete it one or more times. Children who accessed a free
solar light were 9.9%‐points more likely to have completed all the homework in the past week (this
difference is significant at the 1% level) and children who live in households who received a voucher
were 5.3%‐points more likely to complete homework, on average. However this difference is not
statistically significant at the 10% level. 62 Looking at the ToT estimates we find that children in
households which received a free light are 14.4%‐points more likely to complete homework after dark
(significant at the 1% level). While the ToT estimate for the offer‐to‐buy group is 15.5%‐points, the
effect is not statistically different from zero.63
However, homework completion is purely based on self‐reported data and it is possible that
respondents are inclined to tell us what they think we would like to hear (social desirability bias). It is
possible that children who received a solar light over‐reported homework completion and it is
important to check these results against more objective schooling measures such as test scores, which
we will do in future analyses.
62 Controlling for school fixed effects, class, pupil, gender. 63 Controlling for school fixed effects, class, pupil, gender.
Page 52 of 54
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