Renewable Energy for Rural Schools

8/4/2019 Renewable Energy for Rural Schools

1/64

Renewable Energy for Rural Schools


2/64


Cover Photos:Upp er Right: Children at a school pow ered by renewable energy sources in Neu qun, Argentina.

Tom Lawand , Solargetics/ PIX008261

Left: Two 1.0 kW wind tur bines sup ply electricity to the dorm atory of the Villa Tehuelche Rural School, a remoteboarding school located in southern Chile.

Arturo Kuntsmann, CERES/ UMAG/ PIX08262

Lower Right: Small boys p lay in the school yard of the new ly electrified Ip olokeng School in South Africa.Bob McConnell, NREL/ PIX02890


3/64



Antonio C. JimenezNational Renewable Energy Laboratory

Tom LawandBrace Research Institute

November 2000

Published by theNational Renewable Energy Laboratory

1617 Cole BoulevardGolden, Colorado 80401-3393United States of America


4/64

ii Renewable Energy for Rural Schools

FOREWORDA few years ago, during my tenure as the United States ambassador to the small African nations of Rwanda

and Lesotho, I was responsible for adm inistering the Ambassad or's Self-Help Fun ds Program . This discretionarygrants p rogram , supp orted by th e United States Agency for Interna tional Development (USAID) fun ds, allowedthe am bassador to selectively supp ort small initiatives generated by local comm un ities to make their schoolsmore efficient, increase economic produ ctivity, and raise health stan dard s. These fund s were u sed to p urchaseequipm ent and m aterials, and th e comm unities provided th e labor necessary for construction. During this time,I was rem inded of my earlier training in a one-room school in ru ral Bellair, Florida, in th e United States. Theschool, which was w ithout heat and hot water and depend ent solely on kerosene lamps for lighting, made mewond er how much m ore I might have learned had todays advanced renewable energy technologies for ru ralschools been available to my generation. Following this d iplomatic tour, I was asked to serve as chair p erson forRenewable Energy for African Develop ment (REFAD)a non profit organization d edicated to the ap plication of renewa ble energy technologies in the r ura l villages of Africa.

In South Africa, with sup port from t he Na tional Renew able Energy Laboratory (NREL) and the U.S. Depart-men t of Energy (DOE), more than on e hund red college teachers and rep resentatives from non governm ental

organizations (NGOs) have par ticipated in renewable energy capacity building p rogram s. As a result, severalinstitutions initiated research projects. In Port Elizabeth, the technikon n ow offers a bachelor's degree in renew-able energy stud ies. In South Africa, the governm ent collaborated with ind ustry and a ward ed concessionairefund s to implem ent a countr y-wide ru ral electrification progr am. In several South African countries, the UnitedNat ions Educational, Scientific, and Cu ltural Organ ization (UNESCO) provid ed 2-year funding t o establishun iversity chairs in renew able energy. In Botswan a, REFAD condu cted a careful evaluation of the govern ment 's40-home p hotovoltaic (PV) pilot project. The evaluat ion show ed th at the introd uction of solar technology to thisrur al village had a decided p ositive impa ct on microeconomic developm ent, health improvem ents, and schoolperform anceeach of wh ich plays an importa nt role in ensuring continued sustainability in rural villages.

Perhap s one of the m ost satisfying achievemen ts of REFAD's work was th e establishment of a "LivingRenewable Energy Demonstr ation Center" in the KwaZulu / Nata l region near Dur ban, South Africa. The major

universities and technikons in Durban w orked together to establish a KwaZulu/ Natal/ Renewable EnergyDevelopment Group (KZN/ REDG) among the N GOs. This group p ooled its limited resources to provide renew-able energy inpu t to a single comm un ity. As a result of the group 's action, three schools are being transform edinto solar schools. Myeka High School now op erates a 1.4kWp hy brid PV/ gas system, which pow ers 20 compu t-ers, a television, a video cassette recorder (VCR), the lights in three classrooms and the head master s persona lcompu ter and printer. Systems are also being installed at Chief Divine Element ary School and Kamangw a HighSchool.

When you t alk with the beneficiaries of these solar projects, you cannot h elp but be imp ressed by how m uchthese initiatives are needed by th ose of us who labor at th e grass-roots level in developing countr ies. When onefamily return ed from Gabarone to Botswana's Man yana Village following th e installation of the 40-home PVpilot project, they were asked wh y they had return ed. The fathers reply was qu ite a revelation: "BecauseManyan a is now a mod ern city." The defining param eter for determining city status for his family wa selectrification.

"Renewa ble Energy in Rural Schools" is an inexpensive, yet comp rehensive reference source for all localNGO s and schools that are seeking technical guidan ce for the integration of renew ables as a part of the ph ysicaland instructional aspects of their schools. This practical one-stop, hand s-on Guide will be welcomed by in-country p ractitioners, Peace Corps volunteers, and by U.S. colleges and universities engaged in t he prep arationof stud ents for services in developing countr ies. I comm end th e authors for prepar ing this much-neededdocum ent, and I hope that NRELw ill continue to provide the necessary supp ort for these kinds of initiatives.

Leonard H .O. Spearman , Ph.D,Chair, Renewable Energy for African D evelopmen tDistinguished Professor, Coppin State College


5/64

PREFACEEducation of rural commu nities is an imp ortant n ational and international pr iority. In m any

count ries, how ever, the ava ilability of electricity to supp ort ru ral edu cational activities is less than

adequ ate. In recent years the d evelopm ent of reasonably p riced an d reliable renewable energysystems has m ade it p ossible to provide electricity and thermal energy for lighting, compu ters,telecommu nications/ distance learning, and on-site living accomm odations in rem ote areas.A nu mber of international, national, and local institutions, nongovernmental organizations,found ations, and private comp anies are sup porting the d eployment of renewable energy systemsin rural comm un ities in the developing w orld w here rural edu cation is a national priority.

Because renewable energy is regionally diverse, choosing the app ropr iate renew able energysystem w ill be regionally and site depend ent. Although ph otovoltaic (PV) lighting systems havepaved the way and are being deployed in many remote commu nities around th e world, other smallrenew able sources of electricity shou ld be considered. One of the objectives of this guidebook is toexpand the remote electricity opp ortun ity beyond PV to areas of good wind or hyd ro resources.Also, in the near futu re we expect to see micro-biomass gasification and d irect combustion, as wellas concentrated solar therm al-electric techn ologies, become comm ercial rural options.

The three impor tant factors driving th e selection of the app ropr iate technology are the localnatu ral resource, the size and timing of the electrical loads, and the cost of the various components,includ ing fossil fuel alternatives. This guidebook reviews th e considerations an d dem onstrates thecomp arisons in the selection of alternat ive renewab le and hybrid system s for health clinics.

The National Renewable Energy Laboratory s (NRELs) Village Pow er Program h as comm is-sioned this guidebook to help commu nicate the app ropriate role of renewables in p roviding ruraledu cational electricity services. The tw o prim ary au thor s, Tony Jimen ez and Tom Law and , combinethe technical analysis and practical design, deployment, and training experience that have mad ethem such an effective team. This guidebook shou ld p rove useful to those stakeholders consideringrenew ables as a serious op tion for electrifying ru ral edu cational facilities (and , in m any cases, associ-ated ru ral clinics). It may be useful as well to those renew able energy practitioners seeking to definethe param eters for d esigning and dep loying their prod ucts for the needs of rural schools.

This is the second in a series of rura l app lications gu idebooks that NRELs Village Pow erProgram h as commissioned to coup le comm ercial renewable systems w ith rur al app lications, suchas w ater, health clinics, and microenterp rise. The gu idebooks are comp lemented by N RELs VillagePow er Program s app lication developm ent activities, international pilot projects, and visitingpro fessionals prog ram . For more information on th is program , please contact our Web site,http:/ / www.rsvp.nrel.gov/ rsvp/ .

Larry FlowersTeam Leader, Village Pow erNational Renewable Energy Laboratory

Renewable Energy for Rural Schools i


6/64

CONTENTSHow to UseThis Gu ide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1

Int rod uction : Definition of N eed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2

Chap ter 1: School Energy Ap plication s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4

Chap ter 2: Solar Therm al Applications and Com ponents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9

Case Study: Solar Stills for Water Supply for Rura l Schools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12

Case Stu dy: Solar Hot-Water H eating in Nepal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14

Chap ter 3: Electr ical System Com ponents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16

System Ov erview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16

Photovoltaics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16

Wind-Turb ine Generator s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18Micro-hyd ro . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19

Diesel Generators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21

Batteries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22

Inverters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23

Con trollers/ Meters/ Balance of Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24

Chap ter 4: System Selection and Economics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25

Chap ter 5: Institu tion al Considera tion s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30

Chap ter 6: Case Stud ies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36

#1A School Electrification Program in N euqu n, Argent ina . . . . . . . . . . . . . . . . . . . . . . . . . . .36

#1B School Electr ification in Neuqu n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38

#2 The Concessions Program in Salta, Argentin a . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .39

#3 Wind Turbin e Use at a Rural School in Chile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .42

#4 School Ligh ting in Honduras . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .42

#5 Biogas Plant in a Ru ral School in Bangladesh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43

#6 A Renew able Trainin g Center in Lesotho . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .46

Chap ter 7: Lessons Learn ed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .49

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51

Bibliog raphy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51

Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .53

Abou t the Au th ors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .56

Acknowled gem ents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .57

iv Renewable Energy for Rural Schools


7/64

HOW TO USE THISGUIDE

Who is this guide for?This guide is d esigned for decision-makers

in develop ing areas respon sible for schools, par-ticularly those w ho are charged w ith selecting,installing, and maintaining energy systems.Schools are run by m any d ifferent types of orga-nizations, includ ing govern ment agencies,religious institutions, and many private organi-zations. This guid e is designed to help decision-makers in all these types of agencies to better

un derstand the available options in providingenergy to schools.

What is the purposeof this guide?

This publication add resses the n eed forenergy in schools, primarily those schools thatare not conn ected to the electric grid . This gu idewill app ly mostly to primary an d secondaryschools located in n on-electrified areas. In areas

wh ere grid p ower is expensive and u nreliable,this guide can be used to examine other energyoptions to conventional pow er. The au thorsgoal is to help the reader to accurat ely assess aschools energy n eeds, evaluate app ropriate andcost effective technologies to meet those needs,and to imp lement an effective infrastructure toinstall and maintain the hardw are.

What is in this guide?This Guide provides an overview of school

electrification with an emp hasis on th e use of renewable energy (RE). Although the em ph asisis on electrification, the u se of solar therm altechnologies to m eet various h eating app lica-tions is also presented . Chap ter 1 d iscussestyp ical school electrical and heating app lica-tions, such as lighting, commu nications, wa terpu rification, and water heating. Information ontypical pow er requirements and du ty cycles forelectrical equ ipm ent is given. Chap ter 2 is an

overview of solar thermal ap plications andhard ware. Chapter 3 discusses the componentsof stand -alone electrical pow er systems. Foreach comp onen t, there is a description of howit works, its cost, lifetime, prop er operation and

maintenance, and limitations. Chapter 4 includesan overview of life-cycle cost analysis, and adiscussion of the var ious factors that influencethe d esign of stand -alone RE systems for a p ar-ticular location. Chap ter 5 ad dresses the variou ssocial and institutional issues that are required tohave a successful school electrification p rogram .Although there is an emp hasis on large-scaleprojects sup ported by governm ents or large,pr ivate agencies, mu ch of the content relatingto m aintenance, user training, and project

susta inability will be of interest to a wid eraud ience. Chap ter 6 describes six school casestud ies. Chapter 7 sum marizes general lessonslearned that can be ap plied to futu re projects.These are followed by a list of references, abibliograph y, and a glossary of terms usedthroughout this guide



8/64

INTRODUCTION:DEFINITION OF NEED

Current State of Rural SchoolsA large proportion of schools in the develop-

ing w orld d o not have access to basic services,includ ing run ning w ater, toilets, lighting, and insome cases, even th e pencils and books so neces-sary to the process of edu cation. Schools in ruralcommu nities are generally worse off than thoselocated in urban areas, and those schools locatedin remote rural areas are least favored of all.They sit at the far end of the table, are often the

last to be served from the edu cation bu dget, andwh at they do g et tends to cost more because theyare on the p eriphery. Commu nications withthese schools are difficult, and they rar ely havethe infrastructure required to keep things ru n-ning sm oothly. Despite their being last in linefor resou rces, schools in remote areas often fill alarger local role than do schools in ur ban areas.The school may be the only institut ion in a givenrural area, and serves not only for education, butalso for other commu nity activities.

-There is an increasing n eed for ru ral pop ula-tions to imp rove education so that they mayincrease produ ctivity and improve th eirstandard of living. It is importan t to bridge thisgap so that th e rural areas can become more

economically susta inable and reverse the trendof migration from the rur al to the urban areaswith all the latter's problems.

Renewab le energies have a role to play inru ral schools. Remote commu nities are oftenideal sites for man y RETs (renewable energytechnologies) for tw o reasons: (1) the highercosts of providing conventional energy in theseareas, and (2) reduced d epend ence on fuel andgenerator maintenan ce. RETs offer lower op erat-ing costs and red uced environm ental pollution.

This provid es long-term benefits, which, if fullyevaluated by decision-makers, could impact thechoice of technology in favor of RE (renew ableenergy) systems. How ever, since RE systems arerelative newcomers on the energy-supp ly side,they are not often given p roper consideration forremote school ap plications. Part of the fault liesin the lack of w idely available inform ation abou tthe capabilities and app lications of RETs. Part of the problem is du e to the reluctance of plannersand policy m akers to change from accepted

practices. They are m ore comfortable withproven, w ell-accepted systems, notwithstand ingthe existing p roblems and costs of conventionalenergy systems.

Problems Associatedwith Existing Energy Delivery Systems

Often, electricity for rem ote schools is sup -plied by standard -diesel or gasoline-poweredelectric generators. In m any cases, the schooland adjacent bu ildings form a m ini-grid d irectlyconnected to the gen erator. The latter is operatedperiodically during the day and evening whenpow er is required. In som e instances, the gen-erator can be operated continuously, bu t this iscostly, and only hap pen s in rare circum stances.A large problem with standard en ergy deliverysystems is that school personn el require trainingin the use, operation, and m aintenance of the

2 Renewable Energy for Rural Schools

Figure I.1. Children of the Miaozu people in frontof their school on Hainan Island.

S i m o n

T s u o , N

R E L / P I X 0 1 9 1 4


9/64

system. Most of the people associated w ithedu cation in ru ral schoolsteachers and custo-diansdon't h ave the training, or the experi-ence, to opera te equipmen t of this type. Thislesson shou ld be retained w hen considering theimp lementa tion of RE systems. The use of REsystems w ill not eliminate the training requ ire-men t. While simp le RE systems requ ire lesstraining than conventional systems, the trainingrequ irements increase with increasing system

comp lexity. Thus simp le, rugged d esigns arevital for systems that are destined for u se inremote areas.

Problems with conventional systems include:

Fuel provision

Fuel cost

Fuel-delivery system reliability

Generator spare parts: availability, cost, anddelivery

Generator repair: the availability of a qualifiedmechan ic or techn ician

Maintenance and rep air costs.

Conventional generators are a m ature tech-nology, and w hen u sed un der the p roper condi-tions, with a prop er service infrastru cture inplace, they can prov ide years of satisfactoryservice. Unfortu nately, in a significant n um ber

of remote rural schools, the generator s are oftenin a state of disrepa ir, lead ing to serious conse-quences that ad versely imp act the functioning of the school. The lack of electricity exacerbates thealready high teacher-turn over rate, which has anegative impact on the quality of education.

The Role of Energy andWater in the Appropriate

Functioning of SchoolsThe app lications of energy in remote schoolsare discussed in Chap ter 1. In order for schoolsto function p roper ly, clean water is necessaryfor drink ing, sanitary cooking, kitchen require-ments, and gardening. It is also essential that thestud ents (frequently coming from p oor back-ground s, living in houses often d evoid of freshwater), learn the u se and man agement of clean-water sou rces as par t of their education. Waterand energy are vital comp onen ts of lifetheopp ortunity to learn about these fun dam entalsin school should not be m issed. For studen tsattending ru ral schools, it m ay constitute th eonly occasion wh en they can learn about theseessential compon ents of modern society. This isa vital opp ortun ity to train the stu dents in basiclife skills before send ing them back to the oftengrim reality of rural poverty and dep rivation.


Figure I.2. PV system, including panels, batteries, and regulator box at a schoolin Collipilli Abajo, Argentina.

T o m

L a w a n

d , S

o l a r g e

t i c s

/ P I X 0 8 2 9 0


10/64

CHAPTER 1:SCHOOL ENERGY APPLICATIONS

Chapter OverviewThe overall needs of ru ral schools differ

from the needs of u rban schools. In many remoteru ral schools, the teacher, often accomp anied byhis/ her family, lives in residence, either d irectlyin the school building or in an attached bu ilding.

This Chapter d escribes the most comm onschool app lications, wh ich are listed below.

The Tables in this Chap ter give typ ical pow errequirements and du ty cycles for rur al schoolelectrical ap plications.

Lighting, water pum ping and treatment,refrigeration, television, VCR

Space heating and cooling

Cooking

Water heating

Water pu rification

Radio communications equipment.

Lighting (Indoor/Outdoorand Emergency Lights)

Electricity offers a qu ality of light to wh ichgas or kerosene cannot comp are. Kerosenelighting is most comm on in non -electrified com-mu nities. Kerosene is a know n safety hazard an dcontributes to poor indoor air qu ality. Electriclight greatly improves the teacher s ability to


0 2 6 2 2 2 0 1 m

Windturbine

Solar hotwater heater Audio visual

equipmentPV modules

Ventilationfans

Flourescentlights

Computer

Radio-transmitter

Water purifierSand filter

Figure 1.2. PV powered lights in a rural school inNeuqun, Argentina.

Figure 1.1.School showing potential applications.


11/64

presen t a variety of subjects in a more app ealingway. It also perm its the more efficient hand lingof adm inistrative tasks, and other n on-teachingfunctions. Outd oor light makes the ru ral schoolmore accessible at night. In n on-electrified com-mu nities, a school w ith light becomes a strongcommu nity focus. The building can be used atnight for training pu rposes, adult ed ucation, cul-tural events, comm un ity meetings, and the like.

When u sing a REsystem, energy efficiencyis key to affordability.Investm ents in efficientsystems generally result incapital and operating costsavings . Table 1.1 showsthe light prod uced bycand les, kerosene lamps,

and various typ es of elec-tric lights. The Table alsoshow s the electrical con-sum ption of the variouselectric light s. What isnot sh own in th e Table isthe large qu alitative supe-riority of electric lightingover kerosene and cand les.

The Table makes clear great efficiency of compact- fluorescent (CF) lights comp ared toother electric lighting technologies. Comparedto incand escent lights, CF lights g ive four toseven times the light per w att-hour consumed .

With an expected service life of up to 10,000hour s, CF lights last up to ten times longer thanincand escent bulbs.

CommunicationsRadio-Telephone, Email,Fax, and Short-Wave Radio

Radio and radio-telephone commu nicationsgreatly increase the efficiency of school opera-tions in remote locations. Commun ication is

essential for routine operation and man agementfunctions, including procurement of sup pliesand visits by other teachers. Reliable commu ni-cations facilitate emergen cy med ical treatmen tand evacuation w hen a stud ent or staff memberbecomes su dd enly ill.

School commu nications requ ire very littleelectrical energy. Stand -by pow er consum ptionmay be as little as 2 watts (W). Power consum p-tion for transm itting and receiving are high er, onthe o rder of 30-100 W, but this is gen erally forvery short periods of time. For examp le, many


Lamp Type Rated Light Efficiency LifetimePower Output (lumens/watt) (hours)(watts) (lumens)

Candle 1-16

Kerosene lamp 10-100

Incandescent 15 135 9 850bulb 25 225 9 850

100 900 9 850

Halogen 10 140 14 2,000bulb 20 350 18 2,000

Fluorescent 8 400 40 5,000tube 13 715 40 5,000

20 1,250 40 7,500

Compact 15 940 72 10,000

fluorescent 18 1,100 66 10,00027 1,800 66 10,000

Table 1.1. Power Consumption for Lighting

0 2 6 2 2 2 0 7 m

Figure 1.3. PV panels mounted on the ground and on a radio-transmittertower.


12/64

ru ral schools and health clinics have reliable,two-way regional comm un ication by means of very h igh frequen cy (VHF) radio w ith electricityprovided by a single 30-W PV modu le.

ComputersThe use of compu ters, which requ ire small

amou nts of reliable pow er, for information tran s-mittal pu rposes is burgeoning around the w orld.There are photo-cell powered telephon es thatuse satellites for telephon e transmission, permit-ting access to em ail services. The availability of acompu ter system can expose the stud ents to thistyp e of techn ology. In m ost ru ral schools, it maybe impossible to envisage the use of this equip-ment. How ever, the world situation is changing

rapid ly and th e use of RE-pow er generating sys-tems offers a w ealth of opp ortun ities that w erenot imaginable some decades ago.

Teaching AidsVCRs,Televisions, Radios, FilmProjectors, and Slide Projectors

Aud io-visual equipment can m ake a signi-ficant contribution to th e improvem ent of

edu cation in rur al areas and the use of theseteaching aids is increasing. The energy requ iredto operate sma ll television sets or v ideo-cassetterecord ers is not excessive (see Table 1.2). Theseloads can easily be p rovided by sma ll RE systems.

Water Delivery and TreatmentWater is used for drinking, w ashing, cooking,

toilets, show ers, and possibly, garden ing. Watermay hav e to be pu mp ed from a well or surfacesource or it may flow by gravity from a spring.Depend ing up on the local situation, it may benecessary to pum p w ater to an overhead tank inorder to make water ava ilable to the school facili-ties. Rainwater migh t also be collected from theschool roof and stored in a rainwater cistern.

Cooking and dr inking water may have to betreated if the w ater is dirty or contaminated w ithfecal coliforms. In th e latter case, solar wa ter d is-infection can be used. The prov ision of someclean, potable water is essential for the operationof any school.

Food PreparationIn many ru ral schools, snacks and a m id-day

meal are often p rovided. Cooking energy is


Figure 1.4. The interior of a classroom at the Ipolokeng School in South Africa, showing one of the computers powered by the PV unit on the roof.

B o b

M c C o n n e

l l , N R E L / P I X 0 2 8 8 4


13/64

generally best m et by biomass sources (wood,charcoal, biogas, etc.) or by conventional sou rceskerosene, bottled gas, etc. In som e cases, solarcookers can also be u sed. The selection of themost ap prop riate mix of cooking fuels willdepend up on the nu mber of stud ents and staff tobe fed, the available bud gets, the reliability of

conventional energy sources, and the m anage-men t capabilities of the school st aff. Even if aschool has a generator or a PV or wind pow eredbattery storage system, this energy should not beused for cooking pu rposes. Cooking requ ires

considerab le energy and the u se of electricity forthis pu rpose is very inefficient.

RefrigerationIn som e schools, refrigeration is necessary for

preserving food and med ical supp lies. A refrig-erator must often be provided to ensure that thefamily of the teacher enjoys a certain level of comfort. Maintenance of this equipment mu st beaddressed.

There are two m ain classes of refrigerators,compression an d absorption. Compressionrefrigeration offers great convenience and goodtemp eratu re control. Vaccine refrigerators areavailable that use on ly a small amou nt of elec-tricity. These refrigerator s are very sm all andvery expen sive. Larger compression refrigera-tors tend to hav e large energy consum ption.Planners should pu rchase energy efficient mod -els if comp ression refrigerators are envisioned .Manual d efrost refrigerator/ freezers use signifi-

cantly less energy than d o mod els with au to-mat ic defrost.

Absorption refrigerators use prop ane orkerosene to d rive an absorp tion cycle that keepsthe comp artm ent cold. Due to difficulties inmaintaining stable temp eratures, particularlywith the kerosene m odels, absorption refrigera-tors hav e lost favor for use in storing vaccines.However, tight temp eratu re control is lessimportant for food storage. Unless fuel sup ply isa p roblem, absorption refrigerators shou ld beconsidered for use in o ff-grid schools. This willredu ce the size of the electrical pow er systemand can result in significant cap ital-cost savings.

Space Heating and CoolingThere is no q uestion that th e renewable-

energy system m ight provid e space heating, inpar ticular, if the school is located in an area w itha cold w inter. Generally, this load is handled by


Figure 1.5.This young girl in Cardeiros, Brazilcan fill her jug from the school water tank thanksto a PV powered pumping system installed 1992. Additional PV systems with batteries powerlights, a refrigerator, and a television set for theschool.

R o g e r

T a y l o r ,

N R E L / P I X 0 1 5 3 8

Figure 1.6. A PV system at the Laguna MirandaSchool in Argentina powers lights, a water pumpand a radio.

T o m

L a w a n

d , S

o l a r g e

t i c s

/ P I X 0 8 2 7 0


14/64

using heaters powered by petroleum p rodu ctssuch as heating oil and kerosene, or wood orcoal. However in some instan ces, the space-heating furnace might require a small amou ntof electricity to pow er the bu rner or operate fans.

In addition, some simp le electric fans could beuseful, both in w inter and in su mm er, to imp rovethe comfort level w ithin th e school. If the schoolis located in a very w arm area, the renewable-energy system probably w ill not be designed tohand le an air-cond itioner because the load canbe excessive. If some air-cond itioning is p ro-vided, it should be used sparingly. In ad dition,maintenance for this equipm ent mu st be pro-vided. In dry climates, evaporative cooling m ayprovide a less energy-intensive option.

In most cases, load redu ction should be theinitial strategy. Ensur ing tha t the bu ilding is wellinsulated and sealed can redu ce heating loads.

Shad ing and natur al ventilation can redu ce cool-ing loads.

Water Heating for Kitchenand Bathing Facilities

Like space heating, cooling, and cooking, theenergy use for w ater heating norm ally exceedsthe potential for pow er generated by sm all,electricity-prod ucing RE systems. Hot w ater isneeded for the kitchen and bathroom facilities of the teachers and their families (especially incolder regions). Normally this load can be m etwith simple solar water h eaters or fossil fuel/ biomass-combustion w ater heaters. The amoun tof hot water requ ired for the teacher and kitchen

is usu ally small, unless the school has facilitiesfor all stud ents to take regular h ot show ers, inwhich case the load can be significant.

Washing MachineAs a labor and timesaving d evice a washing

machine contributes to th e quality of life of theteacher and his/ her family. If the washing of add itional school articles is min imized, then theelectric load will not be excessive, especially if energy efficient m odels are selected. Front-load-ing wash ers tend to be more efficient than thetop-load ing variety.

Kitchen AppliancesApp liances shou ld be selected and used so as

to avoid overloading the RE generating system.Such ap pliances could include items such asmixers and juicers, bu t shou ld not includ e elec-tric toasters, irons or electric kettles, as these con-sum e too much electricity.

WorkshopGiven the remoteness of the school, and the

necessity to u nd ertake minimal repairs, it m aybe useful to prov ide electricity to run som e sim-ple pow er tools, such as electric d rills, sander s,and p ortable saws.


Table 1.2. Power and Energy Consumptionfor Various Appliances

0 2 6 2 2 2 0 8 m Appliances Power On-time Energy/day

(watts) (hours/day) (watt-hrs)

Lights (compact flourescent) 530 212 10360

Lights (tube flourescent) 2040 212 40480Communication VHF Radio

Stand-by 2 12 24Transmitting 30 1 30

Overhead Fan 40 412 160480

Water Pump (1500 liters/day 100 6 600from 40 meters)

TV 12" B&W 15 1.04.0 156019" Color 60 1.04.0 6024025" Color 15 130 1.04.0 130520

VCR 30 1.04.0 30120 AM/FM Stereo 15 1.012 15180

Refrigerator/Freezer variable 1,1003,000

Vaccine Refrigerator variable 5001,100

Freezer variable 7003,000

Washing Machine 1 100400 1.03.0 6001,000/load(Energy Efficient Models)

Hand Power Tools 1.03.0 1008001 Energy usage figures do not reflect energy needed to heat the water used in the washer.


15/64

CHAPTER 2:SOLAR THERMAL APPLICATIONS ANDCOMPONENTS

Chapter IntroductionSolar therm al technologies are used for ap pli-

cations in w hich heat is more app ropriate thanelectricity. This chap ter gives an overview of sev-eral solar therm al app lications and generaldescriptions of the hard ware involved. Solarthermal energy is used to heat air or w ater using

solar collectors. Collectors a re shallow insu latedboxes covered by a rigid transp arent cover mad eof glass or certain t ypes of plastic. Solar energy istrapp ed in the exposed sp ace and converted intolow grad e heat that is extracted by blowing air orcirculating water throu gh the collector. A varietyof temp eratures can be achieved d epend ing

up on the construction of the solar collector andthe rate of flow of the water or air.

Solar Water HeatingFor most hot water app lications, 45 to 50C

is sufficient for showering and kitchen use.

A typical solar water h eating system consistsof a solar collector connected to a hot w aterreservoir. Active systems u se pu mp s and con-trollers to circulate a fluid between th e collectorand the storage tank. Due to their complexityand expense, active systems are generally notwell suited for use in remote developing areas.This chapter w ill focus on cheaper and simplerpassive system s. Passive systems are easiest to

design in use in w arm climates wh ere there areno hard freezes (i.e., temp eratu res don t typ icallygo below 10C). These system s can be u sed incolder clima tes as w ell, but in these cases, provi-sion mu st be mad e for freeze protection.

Passive systems can be furth er subd ividedinto thermosyphon systems and batch systems.

In solar thermosyp hon systems, asolar collector (located a t least tw o-thirds of a meter below th e bottom of the hot-w ater reservoir) is connectedby mean s of plumbing to create aclosed loop w ith the hot-water tank.Typ ically, water is heated in p ipes inthe collector, which consists o f ametal absorber plate to which areattached w ater tubes spaced rou ghlyevery 15 cm in an insu lated box fittedwith a tran sparent glazing. Water isheated in the collector and r ises to thetop of the hot-water tank, replaced bycolder w ater from the bottom of thereservoir. During th e day, this ther-mosyp hon process continues. It ispossible to extract hot water from thetank as n eeded w hile the p rocess con-tinues. The ad vantage of the ther-mosyp hon system is that the heatedwater can be stored in an insulatedcontainer, possibly located ind oors.This means the water loses less heatovernight compared to a batch system.


Figure 2.1. The simplest solar water heaters consist simply of ablack tank placed in the sun. Collector efficiency can beincreased by placing the tank inside inside an insulated glazedbox, as shown above.

0 2 6 2 2 2 1 4 m

Batch Solar Collector

Tank

Glazing

Drain valvesInsulated plumbing lines

Insulated collectionbox

Pump flow


16/64

The hot water reservoir must be prop erly insu-lated to conserve the heat in the hot w ater.

A batch type of solar water heater is the sim-plest design an d can be easily constructed. Thiscan consist of a metallic wa ter tank p laced h ori-zontally on an insulated base and covered w ith atran sparen t cover. Reflectors can be u sed toincrease the rad iation incident on the tank. Thesun h eats the reservoir during the d ay, and hotwater can be extracted for evening show ers andkitchen u se at the end of the day. In areas w herethere are clear, cool nights w ith low, relativehu mid ity, these systems w ill lose quite a bit of heat, and limited hot w ater may be available in

the early morning hou rs.The costs of solar water h eating systems var y

wid ely, depend ing up on w hether they are site-constructed w ith free labor/ materials, or aremanu factured components / systems pu rchasedfrom a su pp lier. Prices might ran ge from $0 (allused/ donated materials constructed on site withdonated labor) to $200 (manufactured collec-tors/ tanks/ systems) per square meter.

To estimate the energy d elivered per d ay,

mu ltiply the system collector area times the aver-age system efficiency times the av erage insola-tion (typically 3 kWh/ m 2 to 7 kWh/ m 2 per d ay,)incident on th e collector. Use Table 2-1 to esti-mate syst em efficiency.

Solar Space HeatingBefore consid ering solar space heating, it is

essential that the bu ilding be prop erly insulatedand sealed. Otherw ise, using solar air heaters

could be w asteful. After that, to the extent possi-ble, passive solar/ daylighting strategies shouldbe used . (For pre-existing stru ctures, the oppor-tunities for imp lementing passive strategies m aybe limited .) Finally, after insu lation, sealing an d

passive strategies have been examined, simplesolar air h eaters can furth er redu ce the require-ment for fuel oil or w ood, w hich are common lyused for space heating p urp oses. Solar airheaters are best suited for use in schools thathave reasonably good solar radiation regimes inwinter. There are several typ es of solar airheaters, but th e simplest and most effective con-sists of an external transparent glazing coveringa shallow collector insu lated at the base, andgenerally containing a d ark grill or mesh located

in the air space.For space heating app lications, an exit-air

temp eratu re from the solar air heater of 30 to50C is ad equa te to contr ibute to increasing theambient temperatu res within the school build-ing. The size of the solar air heaters d epends onthe indoor temp erature that the school wouldlike to m aintain. A small PV panel to operate asimp le fan is very useful in increasing the effi-ciency of heat extraction from th e collector. Thesolar collectors can be mou nted on the w alls of the bu ilding facing th e Equator. In th is way, theycan be used for either n atural convection heatingand for summer ven tilation. These relativelysimple systems have few m aintenance problems,provided they are fitted with simple filters, espe-cially in d usty ar eas.

The estimated cost for a simp le solar airheater system ran ges up to $35.00 per squaremeter, depend ing as in the w ater case, howmuch d onated labor/ materials are used.

Solar PasteurizationSolar flat-plate collectors can be u sed to pas-

teur ize water. These collectors consist of a black absorber plate in an insulated box covered by asheet of tempered glass. Water is circulatedthrough the collector for heating and thenpum ped to a storage tank.


Table 2.1. Solar Water Heater Efficiencies

0 2 6 2 2 2 0 9 mSystem Type System Efficiency

Active System1 50%

Thermosyphon System 1 45%Batch System 1 30%

Batch System 50%(day/evening loads only)1Standard draw, equal weight to morning and evening draws.


17/64

Water or milk may be p asteurized by h eatingit to 65C for 30 minu tes. Pasteurization d isin-fects microbiologically contam inated water bykilling viruses, bacteria, and pro tozoa. How ever,it will not eliminate chemical pollutant s or salts.

Solar pasteurization m ay also beachieved by placing w ater or m ilk contain-ers in a solar cookeran insu lated box cov-ered w ith glass. Reflectors increase theamou nt of sun light d irected into the box. In

d irect sun light, tempera tures su fficient forpasteur ization are easily achieved in th ismanner.

Solar Water DisinfectionAs an alternative to pasteu rization,

solar water d isinfection can be used toeliminate bacteriological contaminationfrom d rinking w ater sup plies. (Note: Thistechniqu e only works against bacteriologi-cal contam inants, it will not eliminatechemical pollutan ts or salts.) Clear, bu tbacteriologically contam inated , water intransparent plastic bags is exposed tod irect sun light for fou r to six hou rs. Thewater can also be placed in thin, plastictransparent bottles, but care should betaken N OT to use bottles man ufacturedfrom plastics mad e with th e add ition of an

Renewable Energy for Rural Schools 1

Figure 2.2. Solar wall collector (SWC) operating modes. A solar wall collector may be used for both heating and ventilation as illustrated above.

Air evacuation opening closed Exhaust port open Air intake opening closed Return port open

Heating

Air from the space to be heated, orfrom the HVAC system, is circulatedthrough the SWC and back to theheated space.

Air evacuation opening closed

Exhaust port open Air intake open Return port closed

Ventilation Air Preheating

Fresh air from outside is drawn throughthe SWC and into the heated space orto the HVAC system. No air from theheated space is recirculated backthrough the SWC.

Air evacuation opening open Exhaust port closed Air intake partially open Return port partially open

Thermosyphon Venting

The natural force of the thermosyphon,created by the flow of outside air throughthe SWC, will also draw air from thebuilding through the SWC to the outside.This air must be replaced by air enteringthe building elsewhere (preferably fromthe north side).

02622213m

Figure 2.3. Solar water disinfection in theCaribbean.


18/64

ultra -violet (UV) wavelength inhibitor (used toensu re a longer life for the bottle wh en exposedto solar radiation.) These bottles may not p roveto be suitable for the solar w ater d isinfectionprocess. The UV rays in su nlight inactivate path -

ogenic bacteria su ch as fecal coliform s. There is asynergetic effect with w ater tempera ture. Betterresults are achieved w hen the p lastic bags areplaced ou tside on smooth, dark su rfaces thatperm it an increase in the temp erature level of thewater. Decontamination takes longer in hu mid,cloud ier regions than in d ry and sunn y climates.The required m aterials consist of suitable plasticbags and a thin, dark sheet, preferably of metalresting on a straw m at (to provide some insula-tion). This techn ique could be used in isolated

schools to prod uce potable drinking w ater forthe staff and stu dents.

Simp le solar therm al techn ologies, such aspasteurization and solar water disinfection, areeffective for tr eating sm all quantities of biologi-cally contaminated w ater. These are good alter-natives to boiling w ater for 15 to 20 minu tes tokill bacteria. Often, boiling is not considered

because of the inconvenience and the require-men t for fuel.

Solar Water DistillationDistillation is the best single-method for

pu rifying wa ter. It removes bacteria, salts, andpollutants of all types. Distillation is often u sedto pu rify brackish water. The simp lest stills con-sist of a sloping tran spa rent cover (usually glass)over a shallow basin filled w ith 8 to 10 cm of clean saline wa ter. Solar rad iation heats up th esaline water, causing evap oration. Water vap orcondenses on the und erside of the transparentcover, where it is collected an d stored in conta in-ers. This condensed w ater vapor d oes not con-tain dissolved sa lts or bacterial and viralcontaminants, making it drinkable. Depend ingup on sun light and temperatu re, solar distillerscan prod uce 3-6 liters of potable water p er d ayper square meter of collector area. Sizes rangefrom family-sized u nits of two squ are meters tocommu nity scale un its of several thousandsquare meters. The costs of a solar d istiller sys-tem vary from $30 to $300 per squ are meter. In a


CASE STUDYSolar Stills for Water Supply for Rural SchoolsCountry: ArgentinaLocation: Chaco Salteo

Latitude: Trop ic of Cap ricorn

Altitud e (average): 350 m above sea level

Climatic conditions : Average insolation: 6 kWh/ m 2 / da y; Average yearly ambient temp erature: 21C

Period o f ope ration during the year: Continuous

Schools provided w ith solar stills: Los Blancos and Cap itan de Fragata Pag

RE sys tem: Site-assembled solar stills for the p rodu ction of fresh drinkin g w ater

Installation: June 1995

Capacity: 6 greenhouse-type un its, each 2.2 m 2 in area produ cing approximately 50 liters distillate per day

Materials used: Fiberglass basins, glass covers, aluminu m frames, Stainless-steel gutters, PVC p iping

Feed water: Saline ground water up to 7 g/ l salinity

Back-up sys tems: Rainfall catchmen t; delivery by tank er tru ck

Less ons Learned : The maintena nce of the stills did n ot app ear to be a major problem. Several of theconstruction ma terials selected for the stills could not w ithstand the h igh-levels of U.V. radiation a ndthe effects of hot saline br ine


19/64

remotely located school, this techniqu e could beused to p rodu ce water that can be used fordr inking, cooking and med icinal purp oses.

Solar CookingSolar cookers can be used un der favorable

solar rad iation cond itions to reduce the fossilfuel or biomass energy load n ormally used for

prep aring m eals. The majority of the energy isused for cooking the mid-day meal. Smalleramou nts of energy are used for preparing break-fast and d inner for the staff and h ot beverages

du ring the d ay. Some of the energy dem andcould be m et using simple box cookers. Theseconsist of insu lated boxes with a slop ing glazedcover and a rear h inged reflector. The cooker ismou nted facing the Equator and is generally

tur ned 3 to 5 times a d ay to face the sun d irectly,thus, improving its p erforman ce. Other types of cookers includ e concentra ting cookers usingpar abolic reflectors, or steam cookers u sing a flatplate collector to prod uce the steam conn ectedto an insulated d ouble boiler. Under reasonablesolar cond itions, i.e., above 700 Watts/ m 2, it ispossible to cook a va riety of meals. If the schoolhas a large pop ulation of stud ents to feed, thensolar cooking is not the p referred op tion. Solarcooking should only be used to red uce the

energy dem and from conventional sources.

Biomass CookersIn recent years, improved wood and charcoal

stoves have been developed with increasedefficiency of biomass use. As wood and charcoalare generally the fuels most read ily available inremote d eveloping areas, it is possible to makeuse of more efficient commun ity-sized stoves forthis pu rpose. It is easily possible to cook m ealswith a mean -specific fuel consu mp tion of 8 to

10 kilograms of food cooked p er kilogram of dry wood.


Figure 2.4. Solar Stills at a school in the Chaco, Argentina.

T o m

L a w a n

d , S o l a r g e t

i c s /

P I X 0 8 2 7 1

B e t

h e l C e n

t e r /

P I X 0 8 2 7 2

Figure 2.5. Solar ovenshousehold model on right.


20/64


CASE STUDYSolar Water Heating in NepalDetails of School Location

Bud hanilkantha SchoolP.O. Box 1018Bud H anilkanthaKathmand u, Nepal

This school uses solar w ater heaters to p ro-vide hot w ater for bathrooms.

Specific Conditions of the School The school consists of 24 bu ildings. The ori-entations of the bu ildings vary and in general,

the roofs are pitched. The num ber of stud ents at the school is 850,with 70 teachers and 150 custod ians.

The school operates for 9 months of the year.The norm al occup ancy time is from 08:30 to16:30 hours. It is a full board ing school w ith allstud ents residing on the Campu s. In add ition,55 staff mem bers reside at th e school, andthere are residents at the school through out theyear, even in holiday p eriods. The school is not

used in the evening for comm un ity educationpurposes.

Energy End Use in the Schoo Water H eatingThis consistsmainly of solar w ater heating forthe stud ent hostels and electricwater h eaters for the staff quarters.

Due to its urban location, theschool gets its electricity from thegrid . The electrical energy con-sum ption (includ ing lighting):Rs 80,000 ($U.S. 1,176) per month.The peak expend iture is Rs 150,000($U.S. 2,205) for a month du ringwinter. Note the exchan ge rate forNep ali rupees at the time of thiswriting (Ap ril 99) is $U.S. 1 =NRs 68.

Figure 2.6. Demonstration of improved woodcookstoves at the Renewable Energy Training Center, Nuequen, Argentina.

T o m

L a w a n

d , S o l a r g e t

i c s /

P I X 0 8 2 7 3

Figure 2.7. This solar water heater has providedhot water to this school in Nepal since 1978.

T o m

L a w a n

d , S

o l a r g e

t i c s

/ P I X 0 8 2 7 4


21/64


Space heating (winter only)liquid prop ane gas (LPG)

and electricity Cookingcommu nal an d familialelectricity andLPG

Educational aidestelevision sets 60VCRs 30Computers 30Printers 10

Type of Renewable Energy

System in OperationSolar Water Heaters: Nu mber of solar collectors40 units.

Collector typesMost of the installed w ater heatersuse an integrated design, wh ere the collector and storageare in one p iece. The more recent installations are th er-mosiphon types.

Locationthe collectors are fixed on th e wa lls, or onthe terrace, and som e are ground mou nted.

Equipment man ufactured by the following compa-niesBalaju Yan tra Shala; Sun Works ; Laxmi Mechan icalSolar Works.

All solar equipm ent manu factured in Nep al.

Years of installationmajor installation d one from 1977to 1979 and some in the 1990s.

Present cond ition of SWH systems75% of the p anelsare performing w ell, includ ing the SWH systemsinsta lled in 19771979.

The school paid for the equipm ent and its installation.The school also hand led the financial arrangemen tsof capital investment an d p ays the operation and mainte-nan ce expen ses. (Most O & M consists of changing bro-ken glass and repainting).

Cost of equipmen ta 300-liter SWH system costs $500to $600, including installationthere w ere extra chargesfor the plumbing for the supp ly of the hot water in thebuildings.

Micro-Hydro Turbine:

A dem onstration 300-watt cross-flow, micro-hydroturbine provides electricity for lighting.

Operation and Maintenanceof the Energy System The School Maintenance Departm ent hand les the REsystems at th e school. Technicians are tr ained in-house bythe Maintenance Departm ent.

Despite a slight d rop in system efficiencies over theyears and some leakage, school author ities are satisfied

with the p erformance of the un its.

Education and SocioculturalConsiderations Stud ents are familiarized w ith the RE systems suchsolar water h eaters, PV cells, and the micro-hydro tur -bine. They stu dy these systems as p art of their courses.

Due to the introduction of the solar water heating sys-tems, there are many SWH in the local commu nity partic-ularly in th e dom estic sector. The p rincipal barrier to thespread of this technology has been the affordability andthe developm ent of an economic design. There is also alack of aw areness of the techn ology.

Although a complete survey has not been und ertaken,there are a num ber of boarding schools in N epal thathave installed SWH systems. A fund ing and familiariza-tion program w ould p rovide local imp etus to the installa-tion of more systems in N epal.

On th e regional and national scale, it should be notedthat m any sm all comp anies man ufacture SWH. Typ ically,the man ufacturers d o the system maintenance as well.

Acknowledgment:The information was p rovided by:

Gyani R. Shaky aChief Technology DivisionRoyal Nep al Academy of Science and TechnologyP.O. Box 3323Kathmand u, NEPAL


22/64

CHAPTER 3:ELECTRICAL SYSTEMCOMPONENTS

Chapter IntroductionThis chap ter gives an overview of the m ain

comp onen ts typically used in RE systems. Dieseland gasoline engine generators are also d is-cussed . For each item, the discussion includeshow the component w orks, prop er use, cost,lifetime, and limitations.

System OverviewIntroduction

A hybrid system comp rises comp onents thatprod uce, store, and deliver electricity to the

app lication. Figu re 3.1 show s a schema tic of ahybrid system. The compon ents of a hybrid sys-tem fall into one of four categories describedbelow.

Energy GenerationWind turbines and engines use generators to

convert mechan ical motion in to electricity. PVpan els convert su nlight d irectly into electricity.

Energy StorageThese devices store energy and release it

wh en it is needed. Energy storage oftenimproves both the p erforman ce and economicsof the system. The m ost common energy storagedevice used in hybrid systems is the battery.

Energy ConversionIn hybrid system s, energy conversion refers

to converting AC electricity to DC o r vice versa.A variety of equipm ent can be used to do this.

Inverters convert DC to AC. Rectifiers convertAC to DC. Bi-d irectional inverters combine thefunctions of both inverter s and rectifiers.

Balance of System (BOS)BOS items includ e monitoring equip men t, a

du mp load (a device that shed s excess energyprod uced by the system), and the wiring andhard ware needed to comp lete the system. Notethat the term "BOS" is not str ictly defined . Inother contexts, energy conversion equ ipmentand batteries may be considered BOS items.

PhotovoltaicsIntroduction

PV mod ules convert sun light d irectly intoDC electricity. The m odules themselves, havingno m oving p arts, are highly reliable, long lived,and requ ire little main tenan ce. In add ition, PVpan els are mod ular. It is easy to assemble PV


Figure 3.1. Hybrid System Configuration:Generalized hybrid system configuration showing

energy generation components (photovoltaic,wind turbine, and generator), energy storagecomponents (batteries), energy conversioncomponents (inverter), and balance of systemcomponents (direct current source center andcharge controller). Courtesy of Bergey WindCompany

BatteriesDC loads AC loads

Inverter

Generator

PV array

Wind turbine

0 2 6 2 2 2 1 0 m

Wind/PV/Diesel Hybrid System

DC sourcecenter


23/64

pan els into an array of arbitrary size. The maind isadvantage of PV is its high cap ital cost.Despite th is, especially for small systems, PVis often a cost-effective option , with or w ithou tanother p ower sou rce, as the savings of usepays back the initial cost.

PV Module ConstructionPV mod ules consist of ind ividu al cells that

are wired together in series and in parallel toprod uce the desired voltage and current. Thecells are u sually encapsu lated in a tran sparentprotective material and typically housed in analuminum frame.

PV cells fall into th ree types, monocrys-talline, polycrystalline, and th in film (am or-ph ous). Amorph ous cells are gen erally lessefficient, and may be less-long lasting, bu t areless expensive and easier to m anu facture.

Performance CharacterizationPV modu les are rated in terms of peak w atts

(W p ). This rating is a function of both p anel sizeand efficiency. This rating schem e also makes it

easy to compare mod ules from d ifferent sourcesbased up on cost per W p . The rating is theamou nt of pow er that the modu le will prod uceun der stand ard reference cond itions (1kW/ m 2;25C [77F] panel tem peratu re.) This is rou ghly

the intensity of sunlight at noon on a clear sum-mer d ay. Thu s, a modu le rated at 50 W p will produ ce 50 W wh en the insolation on th e mod ule is1 kW/ m 2. Because pow er outp ut is roughly p ro-portional to insolation, this same mod ule couldbe expected to prod uce 25 W when the insolationis 500 W/ m 2 (when operating at 25C).

PV array energy p rodu ction can be estimatedby mu ltiplying the arrays rated pow er by thesites insolation on the pan els su rface (typically14002500 kWh/ m2 per year; 47 kWh/ m2/ day). The resulting p rodu ct is then d erated byapp roximately 10%20% to accoun t for lossescaused by such things as temperatu re effects(panels produ ce less energy at higher tempera-tures) and wire losses.

Module OperationMost PV panels are designed to charge 12-V

battery ban ks. Larger, off-grid system s may h aveDC bus bar voltages of 24, 48, 120 or 240 V. Con-necting the ap prop riate num ber of PV pan els inseries enables them to charge batteries at thesevoltages. For non-battery charging ap plications,such as w hen th e pan el is directly connected to awater pu mp, a maximum -point p ower tracker(MPPT) may be necessary. A MPPT will matchthe electrical characteristics of the load to thoseof the mod ule so that t he arr ay can efficientlypower the load.

Module Mounting and Tilt Angles

In order to m aximize energy prod uction, PVmod ules need to be moun ted so as to be orientedtoward s the sun. To do th is, the mod ules aremou nted on either fixed or tracking mou nts.Because of t heir low cost and simp licity, fixedmou nts are most commonly u sed. These type of mou nts can be made of wood or m etal, and canbe pu rchased or fabricated almost an ywh ere.

Tracking moun ts (either single or d ua l axis)increase the energy produ ction of the mod ules,


Figure 3.2. Ground-mounted PV panels at a ruralschool in Neuqun province, Argentina.

T o m

L a w a n

d , S

o l a r g e

t i c s

/ P I X 0 0 8 2 7 5


24/64

particularly at low latitud es, but at the p rice of ad ditional cost and complexity. The relative costeffectiveness of tracking mou nts v ersus ad di-tional mod ules w ill vary from p roject to project.

Capital and Operating CostsPV mod ules are available in a variety of rat-ings u p to 300 W p . Ind ividu al PV panels can beconnected to form arrays of any size. Modulesmay be connected in series to increase the arrayvoltage, and can be conn ected in parallel toincrease the array current. This mod ularitymakes it easy to start out w ith a small array andadd add itional mod ules later.

The costs of a PV array are d riven by the costof the modules. Despite declining p rices in thelast two d ecades, PV modu les remain expensive.Retail prices for mod ules bottom ou t at abou t$5.50 per W p . For bu lk pu rchases, prices can gobelow $4.00 per W p . Warrantees typically are for10 to 25 years. Cur rent m odules can be expectedto last in excess of 20 years. The remaining PVarray costs consist of mou nts, wiring, and instal-lation . These are t yp ically $0.50$1.50 per W p .

PV panels (not necessarily the remaind er of the system ) are almost main tenan ce free. Mostly,

they just need to be kept clean, and the electricalconnections need p eriodic insp ection for looseconnections and corrosion.

Wind-Turbine GeneratorsIntroduction

Wind turbines convert the energy of movingair into u seful mechan ical or electrical energy.Wind turbines need m ore maintenance than a PVarray, but w ith mod erate wind s, > 4.5 meters persecond (m/ s), will often p rodu ce more energythan a similarly priced array o f PV pan els. LikePV panels, mu ltiple wind turbines can be usedtogether to p rodu ce more energy. Because w ind-turbine energy prod uction tends to be highlyvariable, wind turbines are often best combinedwith PV panels or a generator to ensure energyprod uction during times of low wind sp eeds.This section will focus on small w ind tu rbineswith ratings of 10 kW or less.

Wind-Turbine ComponentsThe components common to most wind tu r-

bines are shown in Figure 3.3 below. The blad escapture the energy from the w ind, transferring itvia the shaft to the generator. In sm all wind tu r-

bines, the shaft usu ally d rives the generatordirectly. Most small wind turbines u se a p erma-nent m agnet alternator for a generator. Theseprod uce variable frequency (wild) AC that thepow er electronics convert into DC curren t. Theyaw bearing allows a w ind tu rbine to rotate toaccomm odate changing wind direction. Thetower sup ports the wind turbine and p laces itabove any obstructions.

Wind-Turbine PerformanceCharacteristics

A wind -turbines performan ce is character-ized by its power curve, wh ich relates wind -tur-bine pow er outpu t to the hu b-height w indspeed. Pow er curves for selected m achines areshown in Figure 3.4. Turbines n eed a minimu mwind sp eed, the "cut-in" speed , before they startprod ucing pow er. For sm all turbines, the cut-inspeed typ ically ranges from 3 to 4 m/ s. Aftercut-in, wind-turbine p ower increases rapidly

with increasing w ind speed un til it starts level-ing off as it app roaches peak p ow er. The energy


Figure 3.3. Typical wind-turbine components

Blades

Generator

Tail

Tower

Yawbearing


25/64

density in m oving air is proportional to the cube

of the velocity. Thus, wind tu rbines prod ucemu ch m ore power at higher wind sp eeds than atlower wind speeds, until the wind speed reachesthe "cut-out" speed. Most small turbines p rodu cepeak p ower at about 1215 m/ s. The turbine willprodu ce at peak pow er until the wind speedreaches the tur bines "cut-out" speed. Cut-ou t,usu ally occurr ing at 14 to 18 m/ s, protects theturbine from overspinning in high wind s. Mostsma ll tur bines cut-out by passively tilting (furl-ing) the nacelle and rotor out of the wind . After

cut-out, wind-turbine power outp ut usu allydoes n ot d ecrease to zero, but remains at30%70% of rated p ow er.

Wind turbines are rated by th eir power out-pu t at a specified w ind sp eed, e.g., 10 kW at12 m/ s. The wind speed at w hich a turbine israted, though u sually chosen somewh at arbitrar-ily by the manufacturer, is typically near thewind speed at wh ich the turbine produ ces themost pow er.

The non-linear n ature of the wind-turbine power curvemakes long-term en ergy per-formance pred iction m ore d if-ficult than for a PV system.

Long-term p erforman ce pre-diction, requ ires the windspeed d istribution rather than

just the average w ind sp eed.Long-term performance canthen be foun d by integratingthe wind-turbine power curveover the wind speed distribu-tion. Wind -turbine perfor-mance may also depend u ponthe ap plication for w hich it is

used.

Wind-Turbine CostsWind -turbine prices vary

more than PV mod ule prices.Similar sized tu rbines can d if-fer significantly in p rice. This iscaused by w ide pricing varia-tions among different turbineman ufacturers and by wid ely

varying tower costs based on d esign and height.

Installed costs gen erally vary from $2,000 to$6,000 per ra ted kW. Un like the case for PV, windtur bines offer economies of scale, with largerwind turbines costing less per kW th an sm allerwind turbines.

Maintenance costs for w ind turbines arevariable. Most small wind tu rbines require somepreventive maintenance, mostly in th e form of period ic inspections. Most maintenan ce costswill probably be due to un scheduled repairs

(e.g., lightning strikes an d corrosion). Gipe1

claims a consen sus figu re of 2% of the total sys-tem cost ann ually.

Micro-hydroIntroduction

Micro-hyd ro installations convert the kineticenergy of m oving o r falling w ater into electricity.These installations may requ ire more extensive


3.5

3.0

2.5

2.0

1.5

1.0

0.50

00 5 10 15 20 25

Wind speed (m/s)

0 2 6 2 2 2 0 6 m

P o w e r

( k W )

Wind Turbine Power Curves

World Power Whspr 3000

Bergey 1500

SW Air 303

World Power Whspr 600Bergey 850

Source: Manufacturer's data

Figure 3.4. Selected wind-turbine power curves


26/64

civil works than other technologies, bu t atapp rop riate sites, micro-hydro can be, on a lifecycle basis, a very low cost op tion. The waterresource of a micro-hyd ro installation may besub ject to seasonal weath er extremes such as

drou ght or freezing, but u nlike PV or wind tur-bines, a micro-hyd ro installation can prod ucepow er continuou sly on a day-to-day basis.Because of this continu ous p ower prod uction,even a small installation w ill produ ce largeamoun ts of energy.

ComponentsThe comp onen ts of a micro-hydro installa-

tion are shown in Figu re 3.6. The civil work s,consisting of a water channel, diverts water from

the stream or river to the p enstock. The p enstock conveys the water u nd er pressure to the turbine.The piping used in the penstock mu st be largeenou gh to avoid excessive friction losses. Differ-ent types of tu rbines are available, dep ending onthe head and flow rate available at the site.Impu lse turbines, such as th e Pelton or Turgoturbine have on e or more jets of water impingingon the turbine, wh ich sp ins in the air. Thesetypes of turbines are most used in medium andhigh h ead sites. Reaction turbines, such as the

Francis, Kaplan, and axial tu rbines are fullyimmersed in water. They are used m ore in lowhead sites. The tu rbine is connected to a genera-tor that p roduces electricity. Both AC an d DCgenerators are available. Governors an d controlequipm ent are used to ensu re frequency controlon AC systems an d du mp excess electricity pro-du ced by the w ind turbine.

Performance and CostThe power ou tpu t of a micro-hydro system is

a function of the p rodu ct of the pressure (head)and flow rate of the water going through the tu r-bine. Figure 3.7, shows the expected gen eratoroutp ut un der various site cond itions. The selec-tion of a site is usu ally a comp romise betweenthe available head & flow r ate and the cost of thewa ter chann el & pen stock. Because micro-hydrosystems produ ce continuou s pow er, even a smallsystem w ill prod uce a large amou nt of energy.For examp le, a 125-watt system w ill prod uce


Figure 3.5. Small wind turbines, solar oven, andradio tower at the Las Cortaderas Primary School250 km west of Neuqun, Argentina.

B e r g e y

W i n d p o w e r C o . , I

n c . /

P I X 0 2 1 0 3

Figure 3.6. Components of a micro-hydroinstallation. Fraenkel, Peter (1991) Micro-hydroPower: A Guide for Development Workers. ITPublications in association with the StockholmEnvironment Institute, London.

Weir andintakeCanal

Forebay

Spillway

Penstock

Powerhouse

Tail race

02622212m


27/64

3 kWh a d ay. The water resource of a micro-hyd roinstallation may be su bject to seasonal variationsdu e to winter freezing, spring runoff, and d rought.In cases where peak pow er deman d is greaterthan wh at the installation can sup ply, a batterybank can be used to store energy du ring lowdemand periods for use in high demand periods.

Due to varying requ irements for water chan-nels and p enstock, the cost of micro-hydro sys-tems w ill vary w idely from location to location.In general, the cost for most system s is $1,000 to$4,000 per kW. Maintenance costs are looselyestimated to be aroun d 3% of the capital cost peryear. Much of the m aintenance consists of regu-lar inspections of the water channel and pen-stock to keep them free of debris. Micro-hyd ro

installations can be very long lived, with main-tained systems lasting in excess of 50 years.

Unlike PV and wind systems, micro-hydroinstallations are not mod ular. The availablewater resource and size of the civil works an dpenstock place an ultimate limit on th e pow eroutp ut of a given micro-hyd ro system. Increas-ing the capacity of the civil works is expensive.Thus, micro-hyd ro installations requ ire thatlong-term load dem and be carefully considered.

Diesel GeneratorsIntroduction

Generators consist of an engine d riving anelectric generator. Generato rs run on a va riety of

fuels, includ ing d iesel, gasoline, prop ane, andbiofuel. Generators have the ad vantage of pro-viding p ower on d emand, without the need forbatteries. Comp ared to wind turbines and PVpan els, generators have low capital costs buthigh op erating costs.

Cost and PerformanceDiesel generators are the m ost comm on typ e.

They are available in sizes ranging from un der2.5 kW to over 1 megawa tt (MW). Comp ared togasoline generators, diesel genera tors are moreexpensive, longer lived , cheaper to maintain,and consum e less fuel. Typ ical costs for sm alld iesel generator s (up to 10 kW) are $800 to $1,000per kW. Larger d iesels show economies of scale,costing rou gh ly $7,000$9,000 plus ~$150 perkW. Typ ical d iesel lifetimes are on the o rder of 25,000 operating h ours 2. Larger d iesels are usu -ally overhau led rather th an rep laced. Overallmain tenan ce costs can be estimated to be 100%

to 150% of the cap ital cost over this 25,000-hourlifetime. An op erator mu st provide d ay to daymaintenance and the generator mu st be periodi-cally overhau led by a qualified m echanic. Dieselgenerator fuel efficiency is generally 2.53.0 kWh/ liter when run at a high load ing. Efficiency drop s


Figure 3.7. Estimated hydropower generator outputas a function of head and flow rate.

60

50

40

30

20

10

00 10 20 30 40 50 60

Flow rate (liters/second) 02622211m

H e a d ( m )

Hydropower Electrical Output

PowerOutput(kW)0.1250.250.51.01.52.04.010.0

Figure 3.8. Typical generator at an isolatedmountain school. Teachers and custodiansgenerally have no training in the maintenance andoperation of these units.


28/64

off sharply at low loads. This poor low -load effi-ciency is the bane of many gen erator-only sys-tems. The generator m ust be sized to cover thepeak load, but then often runs at low load mu chof the time.

Less common than d iesels, gasoline genera-tors cost less and a re available in very sma ll sizes(as low as a few h un dred watts). Otherw ise,gasoline generator s are inferior in most resp ectsto their d iesel counterpa rts. For sizes larger thanabou t 1 kW, prices range from $400 to $600 perkW. The minim um pr ice is rough ly $400 regard -less of size. Lifetimes are short , typically only1,000 to 2,000 operat ing h ours. Fuel efficiency ispoor, peaking at rough ly 2.0 kWh/ liter. Part-load fu el efficiency is worse th an for d iesel gen-erators. Gasoline generators are best u sed w henthe loads are very sm all or the an ticipated ru nhou rs total no m ore than roughly 400600 hou rsper year.

Given the p revious d iscussion, several pointsregarding the optimu m u se of generatorsemerge. For maximum fuel econom y, the genera-tor shou ld be ru n at a high load (> 60%). Con-versely, low-load operation shou ld be avoided.Not on ly does this d ecrease the fuel efficiency,

there is evidence that low-load op eration resultsin greater maintenance costs.

BatteriesIntroduction

Batteries are electrochemical d evices th atstore energy in chemical form. They store excessenergy for later use in ord er to improve systemava ilability and efficiency. By far the m ost com-mon type of battery is the lead-acid type. A dis-tant second is the nickel-cadm ium type. Theremainder of this section d iscusses the lead-acidbattery.

Battery Selection Considerations

D eep-Cycle versus Shallow-CycleAlthough batteries are sized according to

how mu ch energy they can store, in most casesa lead-acid battery cannot be d ischarged all the

way to a zero state of charge without sufferingdam age in the process. For remote p ower ap pli-cations, deep-cycle batteries are generally recom-mend ed. Depending u pon th e specific mod el,they m ay be d ischarged dow n to a 20%50%state of charge. Shallow-cycle batteries, such ascar batteries, are generally n ot recommend ed,though they are often u sed in sm all PV systems

because of the lack of any altern atives. They canbe pru dently discharged only to an 80%90%state of charge and will often be d estroyed byonly a han dful of deeper d ischarges.

Flooded versus Valve Regu latedFlooded batteries have their plates immersed

in a liquid electrolyte and n eed p eriodic rewater-ing. In contrast, in valve regulated batteries, theelectrolyte is in th e form of a paste or containedwithin a glass mat. Valve regulated batteries do

not n eed rew atering. Flooded batteries generallyhave lower capital costs than valve regulatedbatteries and w ith proper m aintenance, tend tolast longer. On th e other han d, w here mainte-nan ce is difficult, valve regulated batteries maybe the better choice.

LifetimeBattery lifetime is measu red both in terms of

cumu lative energy flow throu gh th e battery (fullcycles) and by float life. A battery is dead wh en it


Figure 3.9. Batteries allow an RE system to provide

24 hour power. Photovoltaic panels or a windgenerator can recharge the batteries.


29/64

reaches either limit. For example, discharging abattery tw ice to 50% is one full cycle. For m anybatteries, as long as the battery state of charge iskept w ithin the manu facturer s recomm endedlimits, the lifetime cumu lative energy flow is

roughly indep enden t of how deeply the batteryis cycled. Depend ing upon the brand an d m odel,battery lifetimes va ry w idely, ranging from lessthan 100 full cycles to more than 1500 fu ll cycles.Float life refers to how long a battery that is con-nected to a system w ill last, even if it is never oronly lightly u sed. Typ ical float lives for goodqu ality lead-acid batteries range between 3 and10 years at 20C (68F). Note that h igh am bienttemp eratu res will severely shorten a batterysfloat life. A ru le of thu mb is that every 10C

(18F) increase in average ambient temp eratu rewill halve th e battery float life.

SizeThe storage capacity of a battery is com-

mon ly given in amp hou rs at a given rate of dis-charge. When mu ltiplied by the batterysnom inal voltage (u sually 2, 6, or 12 V), this givesthe storage capacity of the battery in w att-hours.(Dividing this nu mber by 1000 gives the batterystorage capacity in kWh ) This storage capacity is

not a fixed qu antity, but rather var ies somew hatdep ending on th e rate at which the battery is dis-charged. A battery will provide m ore energy if itis discharged slow ly than if it is dischargedrap idly. In ord er to facilitate un iform compari-son, most battery man ufacturers give the storagefor a given d ischarge t ime, usu ally 20 or 100hou rs. Ind ividu al batteries used in RE andhybrid system s are available in capacities rang-ing from 50 amp hou rs at 12 V to thousand s of amp h ours at 2 V (0.5 kWh to several kWh ).

CostThe var iations in cycle and float life,

described earlier, make comparison of the cost-effectiveness of d ifferent batteries somewh atproblematical. As a general starting p oint, costsare on the ord er of $70$100 per kWh of storagefor ba tteries w ith lifetimes o f 250 to 500 cyclesand float lives in the r ange of 5 to 8 years. Therewill be add itional one-time costs for a shed,racks, and connection w iring.

InvertersIntroduction

Inverters convert DC to AC electricity. Thiscapability is needed because PV mod ules and

most sm all wind turbines p rodu ce DC electricitywh ich can be used by DC app liances or stored inbatteries for later use. Most comm on electricalapp lications an d dev ices requ ire AC electricity,which cann ot be easily stored .

Inverter Selection ConsiderationsOutput wave f orm: Inverter output w ave

forms fall into on e of three classes, square wave,mod ified sine wave, and sine wave. Square-wave inverters are the least expen sive, bu t theiroutp ut, a squ are wav e, is suitable only for resis-tive load s such as resistance heaters or incand es-cent lights. Mod ified sine-wav e invertersprod uce a staircase square wav e that moreclosely app roximates a sine wav e. This type of inverter is the most common . Most AC electronicdevices and motors w ill run on mod ified sinewave AC. Some sen sitive electronics may no twork w ith mod ified sine wave AC and requiresine-wave inverter s. Sine-wave inverter s pro-

du ce utility grade p ower, but of course cost morethan th e other types of inverters.

Conversion efficiency: Inver ter efficiencyvaries w ith th e load on th e inverter. Efficienciesare poor at low p ower levels and generally verygood (>90%) at high pow er levels. Mid ran geefficiency varies widely between inverters andmay be an impor tant selection criterion. Otheritems to consider are the inver ter s no-loadpow er draw and the presence of a "sleep m ode".Sleep m ode redu ces the inverter pow er draw to afew w atts when there is no load on the inverter.

Sw itched versus parallel: A parallel invertercan supp ly power to a load simu ltaneously witha d iesel generator. With a sw itched inver ter,either the inverter or the generator, but not bothat the same time, sup plies pow er to the load.

Stand-alone capability: A line-comm utatedinverter uses the 50Hz/ 60Hz signal from thegrid to regu late the frequency of its outp ut. Such



30/64

un its are not for u se in stand-alone systemsun less it is planned to keep a d iesel on continu -ously. A self-commu tated inverter d oesnt n eedthe grid for frequ ency regulation. Related con-siderations are how tightly the inverter can regu-

late frequency and v oltage and its ability tosup ply reactive pow er.

One-phase or three-phase: Whether to get aone phase or three ph ase inverter depend s uponthe loads to be served and the type of distribu-tion system to be used . Three phase inverters aremore costly th an on e-ph ase inverters becauseeach ph ase requires a separate inverter stage. Aconsideration w hen selecting a three-ph aseinverter is its ability to serve unbalanced loads.

Sizing: Inverters are u sually sized accordingto their maximum continuous pow er output.Most inverters, how ever, are capable of han dlingsignificantly more p ower than their rated sizefor short p eriods of time. This surge capability isusefu l for meeting the occasional oversized loadsuch as starting a m otor.

Costs: Inver ter costs are rou gh ly $600$1,000per kW for good qu ality mod ified sine- wav einverters. The technology for inverters largerthan 5 kW is not as mature as for smaller invert-ers and costs may be somew hat higher.

Controllers/Meters/Balance of SystemsIntroduction

Controllers and meters act as the brains andnervou s system of a RE or hybrid system. Con-trollers route the en ergy through the systemcomponents to th e load. Metering allows th e

user to assess system health and performance. Inman y cases, the various controlling and meter-ing functions of a system w ill be spread ou t overseveral different comp onen ts. The comp lexity of the controls depend s up on the size and complex-ity of the system and the p references of the user.Controllers have had problems w ith reliabilityand lightning strikes, making careful controllerdesign and lightning p rotection important con-siderations.

Purposes and Functions Battery h igh/low voltage dis connect: Ahigh-voltage disconnect protects the battery againstovercharging. A low-voltage d isconnect p rotectsthe battery against over discharging. These are

critical functions that shou ld be includ ed in allsystems w ith batteries.

System protection: A controller can includefuses or breakers to p rotect against short circuitsand current surges.

Battery charging: A controller with a prop erbattery charge algorithm (with tem peratu recompensation) will do m uch to increase batterylifetime.

AC and D C bus current and vo ltage mon itor-ing: Monitoring the current an d v oltage on theDC and AC buses lets the user check that thecomponents and system are prop erly operating.

Turn components on or off: The controller canbe programmed to turn comp onents on and off as needed w ithout user intervention.

D ivert energy to a dump load: The purp ose ofa d um p load is to shed excess energy. Dumploads may be need ed if the system contains windturbines, micro-hydro, or generators. A du mpload is essentially one or m ore big resistors tha tdissipa te electricity by conver ting it to heat.Available du mp loads are either water- or air-cooled. Dump loads are sometimes used to con-trol the frequency of the AC ou tpu t of a system.

Balance of system (BOS): The BOS includesthe ad ditional items such as w iring, cond uit, andfuses that are needed to complete a system.

D C source center use : Several manufacturersnow offer DC sou rce centers. These combinemu ch of the system w iring, fusing, and con-trollers into one tidy, easier to install package.The use of sou rce centers w ill increase systemcosts somewhat, but offer easier system installa-tion, less comp lex wiring, and easier systemmon itoring and control. The use of a source cen-ter shou ld be considered , especially for systemsin remote sites that lack easy access to techn icalassistance.



31/64

CHAPTER 4:SYSTEM SELECTION AND ECONOMICS

IntroductionThe first section of th is chapter describes life-

cycle cost analysis and explains how and wh y itshould be used w hen analyzing the economics of various op tions. The second p art of this chapterd iscusses the var ious factors influencing systemdesign: load, available resource, comp onen tcosts, and desired level of service. Includ ed arecharts that show how typical system costs varyas a fun ction of load an d resource.

Life-Cycle Cost AnalysisWhy Use Life Cycle Cost Analysis?

A common error w hen performing simpleeconomic analysis is basing the analysis up oninitial cost and sh ort time periods. Because thetotal cost of a p roject is the sum total of its initialcost and its fu tu re costs, life-cycle cost (LCC)

analysis is more app ropr iate. Initial costs areincurred at the beginn ing of the project; thesetypically include expenditures for equipm entpu rchase and installation. Future costs areincurred later in the life of the project, includ ingoperation and maintenance costs such as person-nel, fuel, and replacement equ ipment.

Documents

Renewable Energy for Rural Schools