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Advantages of MicroHydropower SystemsTyler Smallwood
HSA 107 The Economics of Oil and EnergyMarch 3, 2014
I. Introduction
Hydropower produces more energy than every other renewable combined , but it is important1
to consider the difference between renewable energy and environmentally friendly energy. Today
hydroelectric plants have a tarnished reputation due to the severe environmental damage caused by
largescale dams. In this paper we will examine the cost, power output, and environmental effects of
implementing smallscale micro hydropower systems for residential use.
II. Basics of Hydropower
A. Types of Plants
There are many different types of hydropower plants, but the majority of plants utilize power
from running rivers. These plants can be divided into two distinct types: reservoirbased facilities, and
runoftheriver plants.
Reservoir plants, also called impoundment facilities, strictly control water flow by using a dam to
hold water in a reservoir or lake above the turbines. Headwater is funneled through intake ports along
the dam, fed into a penstock, or pipeline, and finally through turbine blades, which spins a large
generator. The generator acts similarly to an electric motor with the exception that the turbine’s circular
motion is converted into electricity rather than vice versa. Water is then fed out of the hydroelectric
facility into the afterbay, where it continues flowing down the river.
Runoftheriver plants divert a portion of the upstream river’s water flow through a separate
pipeline or creek. Water then flows directly into the generation building and spins hydraulic turbines,
which in turn spins the electric generator.2
1 http://www2.hmc.edu/~evans/AEOearly2014.pdf pg 172 http://energy.gov/eere/water/types-hydropower-plants
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Figure 1 | Reservoir Hydroelectric Plant 3 Figure 2 | RunoftheRiver Plant 3
Reservoir plants have the advantage of maintaining precise control of water flow, which means
that the plant can produce more or less electricity depending on demand. For example, in colder
climates residences use more power at night heating their homes, so a hydroelectric dam would provide
peak power output at night when demand is higher. Runoftheriver plants depend almost entirely on
natural river flow, which can be very unpredictable and cannot be mapped to consumer demand.
Hydroelectric dams can also be built at a much larger scale than runoftheriver plants, because the
creation of a large reservoir significantly increases the power capacity of the plant. 3
The major disadvantage to a reservoir plant is the adverse environmental effects created by
altering water flow. Most dams create an artificial reservoir that can flood nearby habitats and destroy
vegetation. In addition, dams decrease downstream water flow, which can cause rivers to dry up
entirely. Runoftheriver systems have a negligible effect on river flow because they only divert water
through a penstock for a short distance before releasing the water back into the river.
Other radically different forms of hydropower include utilizing wave and tidal energy. Wave
generators are almost nonexistent on a largescale, but many companies such as Pelamis are
conceptualizing increasingly efficient systems that use offshore wave farms to produce energy on the
order of 1050 MW. Most of these systems work by using the power of buoyancy to slide magnetic4
shafts through an electric coil, which produces electricity. Tidal energy also does not make up a5
3 http://srren.ipcc-wg3.de/report/IPCC_SRREN_Ch05.pdf pg 4514 http://www.pelamiswave.com/our-projects5 http://www.alternative-energy-news.info/technology/hydro/wave-power/
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significant fraction of world energy generation, although countries such as the United Kingdom have
plans to generate over 120MW in new tidal energy farms over the next decade. Tidal energy functions6
similarly to riverbased hydropower, where running water spins underwater turbines, which spins an
electric generator. Tidal energy systems can be very simple, where turbines are placed on offshore
markers, or complex systems can be built to increase water flow through the turbines.
Figure 3 | Simple vertical turbine system Figure 4 | Complex tidal barrage design 7 8
B. Global Production
Hydropower generation has seen consistent growth over the last century. Global production has
more than tripled over the last fifty years, with the majority of this growth attributed to new plants in
Eastern Asia and South America. Hydropower currently supplies about 1/5th of the world’s electricity,
or 850900 GW.9
[1745]
6 http://www.renewableuk.com/en/renewable-energy/wave-and-tidal/7 http://www.renewableuk.com/en/renewable-energy/wave-and-tidal/how-it-works.cfm8 http://www.darvill.clara.net/altenerg/tidal.htm9 http://spectrum.ieee.org/energy/renewables/future-of-hydropower
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Figure 5 | Global hydropower generation from 19652009 (in TWh)10
In 2012, the US produced 3.11 quadrillion BTUs in the form of hydroelectricity, while all other
renewables combined only produced 1.70 quadrillion BTUs of energy. Thus, hydroelectric power is a11
significant player in the energy industry, and it still has potential to be more prevalent on the global scale.
Although the United States utilizes approximately 70% of its hydropower capacity, underdeveloped
regions such as Africa have only tapped into 7% of its economic potential for hydropower.12
Hydroelectricity has come along way over the last few decades, but there is still a long way to go to
reduce the world’s reliance on fossil fuels and invest in clean energy.
Unfortunately, in order to invest in hydropower plants it is essential to minimize the
environmental effects resulting from controlling water flow. Hydroelectric dams can be extremely
detrimental to the surrounding landscape, because the reduction in water flow can flood huge areas of
land above the dam. For example, the Balbina hydroelectric plant in Brazil flooded 2,360 square
kilometers to generate 250 MW of electricity. Although hydropower has zero CO2 emissions and13
does not rely on fossil fuels, they can easily cause adverse environmental impacts by altering natural
water flow. In order to make hydropower a more inviting prospect for future energy generation, it is
essential to mitigate serious effects to the environment. One option is to employ smallscale hydropower
systems for residences and small businesses.
10 http://srren.ipcc-wg3.de/report/IPCC_SRREN_Ch05.pdf11 http://www2.hmc.edu/~evans/AEOearly2014.pdf pg 1712 http://spectrum.ieee.org/energy/renewables/future-of-hydropower13 http://www.ucsusa.org/.../renewable-energy/environmental-impacts-hydroelectric-power.html
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III. MicroHydropower Systems
Microhydropower systems are runoftheriver plants that generate less than 100 kW.14
Because they are runoftheriver, they have little to no effect on river flow rate, so the environmental
impact due to flooding and largescale construction is almost nonexistent. The systems we will be
looking into are small 110 kW projects that can be set up for a few thousand dollars.
Microhydropower relies on two properties: head and flow rate. The head refers to the height
that the water falls (which adds pressure to spin the turbines), while flow rate is the volume of water
flowing through the turbines per unit of time. To calculate the power generated by a hydropower system
we can use the following equation:
ρqghP = μ 15
represents the efficiency of the system (most hydropower systems run at 7595% efficiency.μ
is the density of water, which we can define simply as . q is the flow rate measure inρ 000 kg/m1 3
. g is the acceleration due to gravity, and h is the head in meters. As an example, if we have/sm3
constructed a micro hydropower system running at 90% efficiency with a 10m head, and a flow rate of
, we can generate 8.82 kW of power..1m /s0 3
.90 0m , 20W 8.82kWP = 0 * m3 1000kg
* s0.1m3
* s 2 9.8m * 1 = 8 8 =
This power output can only be matched if the system if equipped with a generator that produces
peak output with these parameters. In addition to a generator, a microhydropower system needs many
physical and electrical components to convert water flow into electricity.
At the water source there must be a filtered intake box that diverts clean stream water into the
system. The intake connects water flow to the penstock, which is the primary pipeline that feeds water
into the generator. Penstocks are usually made of PVC in homescale systems, or steel in larger
systems. The penstock transports the water directly into the turbine. There are two major turbine16
shapes that are implemented in modern systems. In a Pelton turbine system water is fed through a nozzle
which shoots highpressure water at rotating “buckets”. Pelton turbines are generally used with high
heads and low flow rates, and they can achieve approximately 90% efficiency on small micro
hydroelectric systems. Turgo turbines generate motion by directing water at the top of each bucket,
14 http://www.energyalternatives.ca/PDF/Micro-Hydropower%20Systems...Buyer%27s%20Guide.pdf15 http://www.engineeringtoolbox.com/hydropower-d_1359.html16 http://www.microhydropower.com/Articles/MicroHydroSystems.pdf
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which forces the water to exit the bottom of each bucket. Turgo systems can be used with much higher
flow rates, but their efficiency is capped at 85%. Turbines are connected directly to a either a17
permanent magnet DC alternator or an induction AC generator.
Figure 6 | Turgo turbine Figure 7 | Pelton turbine18 19
In any smallscale energy system, there are two main options for power delivery. Power can be
stored in expensive battery banks before sending power to a house or business, or power can be fed
directly into the system. ACdirect systems have the advantage of being much simpler and less
expensive to set up, but they also must meet the peak power requirement of the residence. Battery
banks allow much smaller hydropower systems to be installed, and instead of powering a house
batteries can feed power to a smaller portion of appliances or lighting. In a batterybased system
electricity is fed through a charge controller into a set of deepcycle batteries. From the batteries DC
power is converted into AC via an inverter, and then the electricity can be fed into the residence.
ACdirect systems feed power directly into the residence from the generator or alternator, and extra
electricity is distributed into a dump load to prevent damage to the system.20
A 3.5 kW hydropower system costs around $11,000, and the addition of a battery bank and
inverter will set you back an additional $6,000$8,000 20 (let’s assume the higher figure the purpose of
this paper). Installation will probably cost another $2,000. If we add up these components we get an
upfront cost of for a substantial 3.5 KW hydroelectric11, 00 8, 00 2, 00 21, 00$ 0 + $ 0 + $ 0 = $ 0
17 http://en.wikipedia.org/wiki/Turgo_turbine18 http://hydrover.co.uk/19 http://www.southerncross.pentair.com/Hydro_Turbines_and_Controls/pelton-hydro-turbines20 http://www.microhydropower.com/Articles/MicroHydroSystems.pdf
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system. If we assume this system runs continuously overnight at 90% efficiency then it will produce
approximately . For reference, an Energy Star Refrigerator uses.5kW .90 4 hr3 * 0 * 2 ≈ day 76 kWh
approximately
mo132 kWh * 1 mo
30 days = day
4.4 kWh
A lighting system including 30 60W incandescent bulbs left on for 12 hours per day will consume
0 lights light0.06 kW * 5 * day
12 hr = day36 kWh 21
Therefore this 3.5 kW micro hydropower system will comfortably power kitchen appliances as well as
residential lighting.
Finally, a huge benefit of smallscale hydropower is the reduced effects to the surrounding
environment. Micro hydroelectric plants provide truly clean energy because they don’t emit greenhouse
gases and they have little impact on water flow and flooding. It is impractical to design massive
hydropower plants with runoftheriver designs, but micro systems can easily be made efficient while
avoiding the creation of costly reservoirs and dams.
21 http://siliconvalleypower.com/index.aspx?page=1922
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