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Renewable Energyfor Rural Schools
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Renewable Energy for Rural Schools
Cover Photos:
Upp er Right: Children at a school powered 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 remot
boarding school located in southern Chile.
Arturo Kuntsmann, CERES/ UMAG/ PIX08262
Lower Right: Small boys p lay in the school yard of the newly electrified Ip olokeng School in South Africa.
Bob McConnell, NREL/ PIX02890
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Renewable Energy for Rural Schools
Renewable Energyfor Rural Schools
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
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ii Renewable Energy for Rural Schools
FOREWORD
A 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 discretionar
grants p rogram, supp orted by th e United States Agency for Interna tional Development (USAID) fun ds, allowe
the ambassador to selectively supp ort small initiatives generated by local comm un ities to make their schools
more efficient, increase economic produ ctivity, and raise health stan dard s. These fund s were u sed to p urchase
equipm 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. The
school, which was w ithout heat and hot water and depend ent solely on kerosene lamps for lighting, made me
wond er how much m ore I might have learned had todays advanced renewable energy technologies for ru ral
schools been available to my generation. Following this d iplomatic tour, I was asked to serve as chair p erson for
Renewable Energy for African Develop ment (REFAD)a non profit organization d edicated to the ap plication o
renewa ble energy technologies in the r ura l villages of Africa.
In South Africa, with sup port from the Na tional Renewable Energy Laboratory (NREL) and the U.S. Depar
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 rograms. 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 government collaborated with ind ustry and a ward ed concessionaire
fund s to implement a countr y-wide ru ral electrification progr am. In several South African countries, the United
Nat ions Educational, Scientific, and Cu ltural Organ ization (UNESCO) provid ed 2-year funding t o establish
un iversity chairs in renew able energy. In Botswan a, REFAD condu cted a careful evaluation of the govern ment '
40-home p hotovoltaic (PV) pilot project. The evaluat ion show ed th at the introd uction of solar technology to thi
rur al village had a decided p ositive impa ct on microeconomic developm ent, health improvem ents, and school
performanceeach of wh ich plays an importa nt role in ensuring continued sustainability in rural villages.
Perhap s one of the most satisfying achievemen ts of REFAD's work was th e establishment of a "Living
Renewable 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 transformed
into solar schools. Myeka High School now op erates a 1.4kWp hy brid PV/ gas system, which pow ers 20 compu
ers, a television, a video cassette recorder (VCR), the lights in three classrooms and the head master s persona l
compu ter and printer. Systems are also being installed at Chief Divine Elementary School and Kamangw a High
School.
When you t alk with the beneficiaries of these solar projects, you cannot h elp but be imp ressed by how m uc
these initiatives are needed by th ose of us who labor at th e grass-roots level in developing countr ies. When one
family return ed from Gabarone to Botswana's Man yana Village following th e installation of the 40-home PV
pilot project, they were asked wh y they had return ed. The fathers reply was qu ite a revelation: "Because
Manyan a is now a mod ern city." The defining param eter for determining city status for his family wa s
electrification.
"Renewa ble Energy in Rural Schools" is an inexpensive, yet comp rehensive reference source for all local
NGOs and schools that are seeking technical guidan ce for the integration of renew ables as a part of the ph ysical
and 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 aration
of stud ents for services in developing countr ies. I comm end th e authors for prepar ing this much-needed
docum 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 Developmen t
Distinguished Professor, Coppin State College
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PREFACE
Education 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 systems
in 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 th e app ropr iate renewable energy
system w ill be regionally and site depend ent. Although ph otovoltaic (PV) lighting systems have
paved the way and are being deployed in many remote commu nities around th e world, other smal
renew able sources of electricity shou ld be considered. One of the objectives of this guidebook is to
expand the remote electricity opp ortun ity beyond PV to areas of good wind or hyd ro resources.
Also, in the near fu ture we expect to see micro-biomass gasification and d irect combustion, as well
as 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 local
natu 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 the considerations an d dem onstrates the
comp arisons in the selection of alternat ive renewable and hybrid system s for health clinics.
The National Renewable Energy Laborator ys (NRELs) Village Pow er Program has commis-
sioned this guidebook to help commu nicate the app ropriate role of renewables in p roviding rural
edu cational electricity services. The tw o prim ary au thors, Tony Jimen ez and Tom Lawand , combin
the technical analysis and practical design, deployment, and training experience that have mad e
them such an effective team. This guidebook shou ld p rove useful to those stakeholders considering
renew ables as a serious op tion for electrifying ru ral edu cational facilities (and , in m any cases, assoc
ated ru ral clinics). It may be useful as well to those renew able energy practitioners seeking to defin
the 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 er
Program has comm issioned to couple comm ercial renewable systems w ith ru ral app lications, such
as w ater, health clinics, and microenterp rise. The gu idebooks are comp lemented by N RELs Village
Power Program s app lication developm ent activities, international pilot projects, and visiting
professionals program . For more information on th is program , please contact our Web site,
http:/ / www.rsvp.nrel.gov/ rsvp/.
Larry Flowers
Team Leader, Village Pow er
National Renew able Energy Laboratory
Renewable Energy for Rural Schools
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CONTENTS
How to UseThis Guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
Int rod uction : Definit ion of N eed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2
Chap ter 1: School Energy Ap plication s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
Chapter 2: Solar Therm al App lications and Com ponents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9
Case Study: Solar Stills for Water Supply for Rural Schools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12
Case Stu dy: Solar Hot-Water H eating in Nepal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14
Chap ter 3: Electrical System Com ponents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16
System Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16
Photovoltaics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16
Wind-Turb ine Generators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18Micro-hyd ro . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19
Diesel Gen erators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21
Batteries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22
Inverters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23
Controllers/ Meters/ Balance of Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24
Chap ter 4: System Selection and Economics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25
Chap ter 5: Institution al Considera tion s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30
Chap ter 6: Case Stud ies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36
#1A School Electrification Program in N euqu n, Argen tina . . . . . . . . . . . . . . . . . . . . . . . . . . .36
#1B School Electr ification in Neuqu n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38
#2 The Concessions Program in Salta, Argen tina . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .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 Renewable Trainin g Center in Lesotho . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .46
Chap ter 7: Lessons Learn ed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .49
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51
Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51
Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .53
Abou t the Au th ors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .56
Ackn ow led gem ents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .57
iv Renewable Energy for Rural Schools
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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 for
energy in schools, primarily those schools that
are not conn ected to the electric grid . This gu ide
will app ly mostly to primary an d secondary
schools located in n on-electrified areas. In areas
wh ere grid p ower is expensive and un reliable,this guide can be used to examine other energy
options to conventional pow er. The au thors
goal is to help the reader to accurately assess a
schools energy n eeds, evaluate app ropriate and
cost effective technologies to meet those needs,
and to imp lement an effective infrastructure to
install and m aintain 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 asis
is on electrification, the u se of solar therm al
technologies to m eet various h eating app lica-
tions is also presented . Chap ter 1 d iscusses
typ ical school electrical and heating app lica-
tions, such as lighting, commu nications, water
pu rification, and water heating. Information on
typical pow er requirements and du ty cycles for
electrical equ ipm ent is given. Chap ter 2 is an
overview of solar thermal ap plications and
hard ware. Chapter 3 discusses the components
of stand -alone electrical pow er systems. For
each comp onen t, there is a description of how
it works, its cost, lifetime, prop er operation and
maintenance, and limitations. Chapter 4 includan overview of life-cycle cost analysis, and a
discussion of the var ious factors that influence
the d esign of stand -alone RE systems for a p ar-
ticular location. Chap ter 5 ad dresses the variou
social and institutional issues that are required t
have a successful school electrification p rogram
Although there is an emph asis on large-scale
projects sup ported by governm ents or large,
pr ivate agencies, mu ch of the content relating
to m aintenance, user training, and project
susta inability will be of interest to a w ideraud ience. Chap ter 6 describes six school case
stud ies. Chapter 7 sum marizes general lessons
learned that can be ap plied to futu re projects.
These are followed by a list of references, a
bibliograph y, and a glossary of terms used
throughout this guide
Renewable Energy for Rural Schools
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INTRODUCTION:DEFINITION OF NEED
Current State of Rural SchoolsA large proportion of schools in the develop-
ing world d o not have access to basic services,
includ ing run ning w ater, toilets, lighting, and in
some cases, even th e pencils and books so neces-
sary to the process of edu cation. Schools in rural
commu nities are generally worse off than those
located in urban areas, and those schools located
in 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 they
are on th e periph ery. Commu nications with
these schools are difficult, and they rarely have
the infrastructure required to keep things ru n-
ning sm oothly. Despite their being last in line
for resources, schools in remote areas often fill a
larger local role than do schools in ur ban areas.
The school may be the only institut ion in a given
rural area, and serves not only for education, but
also for other commu nity activities.
-There is an increasing n eed for ru ral pop ula-
tions to imp rove education so that they may
increase produ ctivity and improve th eir
standard of living. It is importan t to bridge this
gap so that th e rural areas can become more
economically susta inable and reverse the trendof migration from the rur al to the urban areas
with all the latter's problems.
Renewable energies hav e a role to play in
rural schools. Remote commu nities are often
ideal sites for many RETs (renewable energy
technologies) for tw o reasons: (1) the higher
costs of providing conventional energy in these
areas, and (2) reduced d epend ence on fuel and
generator m aintenan ce. RETs offer lower opera
ing costs and red uced environm ental pollution
This provid es long-term benefits, wh ich, if fullyevaluated by decision-makers, could impact the
choice of technology in favor of RE (renew able
energy) systems. However, since RE systems ar
relative newcomers on th e energy-supp ly side,
they are not often given p roper consideration fo
remote school ap plications. Part of the fault lies
in the lack of wid ely available informat ion abou
the capabilities and app lications of RETs. Part o
the problem is du e to the reluctance of planners
and policy m akers to change from accepted
practices. They are m ore comfortable withproven, w ell-accepted systems, notwithstand in
the existing p roblems and costs of conventional
energy systems.
Problems Associatedwith Existing EnergyDelivery Systems
Often, electricity for rem ote schools is sup -
plied by standard -diesel or gasoline-powered
electric generators. In m any cases, the schooland adjacent bu ildings form a m ini-grid d irectl
connected to the gen erator. The latter is operate
periodically during the day and evening when
pow er is required. In som e instances, the gen-
erator can be operated continuously, bu t this is
costly, and only hap pen s in rare circum stances.
A large problem with standard energy delivery
systems is that school personn el require trainin
in the use, operation, and m aintenance of the
2 Renewable Energy for Rural Schools
Figure I.1. Children of the Miaozu people in front
of their school on Hainan Island.
SimonTsuo,NREL/PIX01914
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system. Most of the p eople associated with
edu 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. This
lesson shou ld be retained w hen considering the
imp lementa tion of RE systems. The use of RE
systems w ill not eliminate the training requ ire-
men t. While simp le RE systems requ ire less
training than conventional systems, the training
requ irements increase with increasing system
comp lexity. Thus simp le, rugged d esigns arevital for systems that are destined for u se in
remote areas.
Problems with conventional systems include:
Fuel provision
Fuel cost
Fuel-delivery system reliability
Generator sp are par ts: availability, cost, and
delivery
Generator rep air: the availability of a qualified
mechan ic or techn ician
Maintenance and rep air costs.
Conventional generators are a m ature tech-
nology, and w hen used u nd er the prop er cond i-
tions, with a prop er service infrastru cture in
place, they can prov ide years of satisfactory
service. Unfortu nately, in a significant nu mber
of remote rural schools, the generators are often
in a state of disrepa ir, lead ing to serious conse-
quences that ad versely imp act the functioning o
the school. The lack of electricity exacerbates th
already high teacher-turn over rate, which has a
negative impact on the quality of education.
The Role of Energy andWater in the Appropriate
Functioning of SchoolsThe app lications of energy in remote school
are discussed in Chap ter 1. In order for schools
to function p roper ly, clean wa ter is necessary
for drink ing, sanitary cooking, kitchen require-
ments, and gardening. It is also essential that th
stud ents (frequently coming from p oor back-
ground s, living in houses often d evoid of fresh
water), learn the u se and man agement of clean-
water sources as par t of their education. Water
and energy are vital comp onents of lifethe
opp ortunity to learn about these fun dam entals
in school should not be m issed. For studen ts
attending ru ral schools, it m ay constitute th e
only occasion when they can learn about th ese
essential compon ents of modern society. This is
a vital opp ortun ity to train the stu dents in basic
life skills before send ing them back to the often
grim reality of rural poverty and dep rivation.
Renewable Energy for Rural Schools
Figure I.2. PV system, including panels, batteries, and regulator box at a school
in Collipilli Abajo, Argentina.
TomLawand,Solargetics/PIX08290
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CHAPTER 1:SCHOOL ENERGY
APPLICATIONS
Chapter OverviewThe overall needs of ru ral schools differ
from the needs of u rban schools. In many remote
rural schools, the teacher, often accomp anied by
his/ her family, lives in residence, either d irectly
in the school building or in an attached bu ilding.
This Chapter d escribes the most comm on
school 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 school
electrical 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 ich
gas or kerosene cannot comp are. Kerosene
lighting is most comm on in non -electrified com
mu nities. Kerosene is a kn own safety hazard an
contributes to poor indoor air qu ality. Electric
light greatly improves the teacher s ability to
4 Renewable Energy for Rural Schools
02622201m
Windturbine
Solar hotwater heater Audio visual
equipmentPV modules
Ventilationfans
Flourescentlights
Computer
Radio-transmitter
Water purifier
Sand filter
Figure 1.2. PV powered lights in a rural school inNeuqun, Argentina.
Figure 1.1. School showing potential applications.
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presen t a variety of subjects in a more app ealing
way. It also perm its the more efficient hand ling
of adm inistrative tasks, and other n on-teaching
functions. Outd oor light makes the rural school
more accessible at night. In n on-electrified com-
mu nities, a school with light becomes a strong
commu nity focus. The building can be used at
night for training pu rposes, adult ed ucation, cul-
tural events, comm un ity meetings, and the like.
When u sing a RE
system, energy efficiency
is key to affordability.
Investm ents in efficient
systems generally result in
capital and operating cost
savings. Table 1.1 shows
the light prod uced by
candles, kerosene lamps,
and various typ es of elec-tric lights. The Table also
show s the electrical con-
sum ption of the various
electric light s. What is
not sh own in the Table is
the large qu alitative supe-
riority of electric lighting
over kerosene and cand les.
The Table makes clear great efficiency of
compact- fluorescent (CF) lights comp ared to
other electric lighting technologies. Compared
to incand escent lights, CF lights g ive four to
seven 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 than
incand escent bulbs.
CommunicationsRadio-Telephone, Email,Fax, and Short-Wave Radio
Radio and radio-telephone commu nication
greatly increase the efficiency of school opera-
tions in remote locations. Commun ication is
essential for routine operation and man agemenfunctions, including procurement of sup plies
and visits by other teachers. Reliable commu ni-
cations facilitate emergen cy medical treatmen t
and evacuation wh en a stud ent or staff member
becomes su dd enly ill.
School commu nications requ ire very little
electrical energy. Stand -by pow er consum ption
may be as little as 2 wa tts (W). Power consum p-
tion for transm itting and receiving are high er, o
the o rder of 30-100 W, but this is gen erally for
very short periods of time. For examp le, many
Renewable Energy for Rural Schools
Lamp Type Rated Light Efficiency Lifetime Power 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 10,000 27 1,800 66 10,000
Table 1.1. Power Consumption for Lighting
02622207m
Figure 1.3. PV panels mounted on the ground and on a radio-transmitter
tower.
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ru ral schools and health clinics have reliable,
two-way regional comm un ication by means of
very h igh frequen cy (VHF) rad io with electricity
provided by a single 30-W PV mod ule.
ComputersThe use of compu ters, which requ ire small
amou nts of reliable p ower, for information trans-
mittal pu rposes is burgeoning around the world .
There are photo-cell powered telephon es that
use satellites for telephon e transmission, permit-
ting access to em ail services. The availability of a
compu ter system can expose the stud ents to this
typ e of techn ology. In m ost ru ral schools, it may
be impossible to envisage the use of this equip-
ment. How ever, the world situation is changing
rapid ly and the u se of RE-pow er generating sys-tems offers a w ealth of op portu nities that w ere
not 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 these
teaching aids is increasing. The energy requ ired
to operate sma ll television sets or v ideo-cassett
record ers is not excessive (see Table 1.2). These
loads can easily be p rovided by small RE system
Water Delivery and TreatmentWater is used for drinking, w ashing, cookin
toilets, show ers, and possibly, garden ing. Water
may hav e to be pu mp ed from a well or surface
source or it may flow by gravity from a spring.
Depend ing up on the local situation, it may be
necessary to pum p w ater to an overhead tank in
order to make wa ter available to the school faci
ties. Rainwater m ight also be collected from the
school roof and stored in a rainwater cistern.
Cooking and dr inking water may have to betreated if the water is d irty or contaminated w it
fecal coliforms. In th e latter case, solar water dis
infection can be used. The prov ision of some
clean, potable water is essential for the opera tio
of any school.
Food PreparationIn many ru ral schools, snacks and a m id-day
meal are often p rovided. Cooking energy is
6 Renewable Energy for Rural Schools
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.
BobMcConnell,NREL/PIX02884
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generally best m et by biomass sources (wood,charcoal, biogas, etc.) or by conventional sources
kerosene, bottled gas, etc. In som e cases, solar
cookers can also be u sed. The selection of the
most ap prop riate mix of cooking fuels will
depend up on the nu mber of stud ents and staff to
be 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 a
school has a generator or a PV or wind p owered
battery storage system, this energy should not b
used for cooking pu rposes. Cooking requ ires
considerab le energy and the u se of electricity fothis pu rpose is very inefficient.
RefrigerationIn som e schools, refrigeration is necessary fo
preserving food and med ical supp lies. A refrig-
erator must often be provided to ensure that the
family of the teacher enjoys a certain level of
comfort. Maintenance of this equipment mu st b
addressed.
There are two m ain classes of refrigerators,compression an d absorption. Compression
refrigeration offers great convenience and good
temp eratu re control. Vaccine refrigerators are
available that use on ly a small amou nt of elec-
tricity. These refrigerators are very sm all and
very 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 signif
cantly less energy than d o mod els with au to-mat ic defrost.
Absorption refrigerators use prop ane or
kerosene to d rive an absorp tion cycle that keep
the comp artm ent cold. Due to d ifficulties in
maintaining stable temp eratures, particularly
with th e kerosene mod els, absorption refrigera-
tors hav e lost favor for use in storing vaccines.
How ever, tight temp eratu re control is less
important for food storage. Unless fuel sup ply i
a p roblem, absorption refrigerators shou ld be
considered for use in o ff-grid schools. This will
redu ce the size of the electrical pow er system
and 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, in
par ticular, if the school is located in an area w ith
a cold winter. Generally, this load is handled by
Renewable Energy for Rural Schools
Figure 1.5. This young girl in Cardeiros, Brazil
can fill her jug from the school water tank thanks
to a PV powered pumping system installed 1992.
Additional PV systems with batteries power
lights, a refrigerator, and a television set for the
school.
RogerTaylor,NREL/PIX01538
Figure 1.6.A PV system at the Laguna Miranda
School in Argentina powers lights, a water pump
and a radio.
TomLawand,Solargetics/PIX08270
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using heaters powered by petroleum p rodu cts
such as heating oil and kerosene, or wood or
coal. How ever in some instan ces, the space-
heating furnace might require a small amou nt
of electricity to pow er the bu rner or operate fans.
In addition, some simp le electric fans could beuseful, both in winter and in sum mer, to improve
the comfort level w ithin th e school. If the school
is located in a very w arm area, the renewable-
energy system probably w ill not be designed to
hand le an air-cond itioner because the load can
be 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 ay
provide a less energy-intensive option.
In most cases, load redu ction should be the
initial strategy. Ensur ing tha t the bu ilding is well
insulated and sealed can redu ce heating loads.
Shad ing and natur al ventilation can redu ce coo
ing loads.
Water Heating for Kitchenand Bathing Facilities
Like space heating, cooling, and cooking, th
energy use for w ater heating norm ally exceeds
the potential for pow er generated by sm all,
electricity-prod ucing RE systems. Hot w ater is
needed for the kitchen and bathroom facilities o
the teachers and their families (especially in
colder regions). Nor mally this load can be met
with sim ple solar water h eaters or fossil fuel/
biomass-combustion w ater heaters. The am oun
of hot water required for the teacher and kitche
is usu ally small, unless the school has facilitiesfor all stud ents to take regular h ot show ers, in
wh ich case the load can be significant.
Washing MachineAs a labor and timesaving device a w ashing
machine contributes to th e quality of life of the
teacher and his/ her family. If the washing of
add itional school articles is min imized, then the
electric load will not be excessive, especially if
energy efficient m odels are selected. Front-load
ing wash ers tend to be more efficient than th e
top-load ing variety.
Kitchen AppliancesApp liances shou ld be selected and used so a
to avoid overloading the RE generating system
Such ap pliances could include items such as
mixers 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 ay
be useful to prov ide electricity to run som e sim-
ple power tools, such as electric d rills, sanders,
and p ortable saws.
8 Renewable Energy for Rural Schools
Table 1.2. Power and Energy Consumptionfor Various Appliances
02622208mAppliances 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 Machine1 100400 1.03.0 6001,000/load(Energy Efficient Models)
Hand Power Tools 1.03.0 100800
1Energy usage figures do not reflect energy needed to heat the water used in the washer.
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CHAPTER 2:SOLAR THERMAL
APPLICATIONS AND
COMPONENTS
Chapter IntroductionSolar therm al technologies are used for ap pli-
cations in w hich heat is more app ropriate than
electricity. This chap ter gives an overview of sev-
eral solar therm al app lications and general
descriptions of the hard ware invo lved. Solar
thermal energy is used to heat air or water u sing
solar collectors. Collectors a re shallow insu latedboxes covered by a rigid transp arent cover mad e
of glass or certain types of plastic. Solar energy is
trapp ed in the exposed sp ace and converted into
low grad e heat that is extracted by blowing air or
circulating wa ter throu gh the collector. A variety
of temp eratures can be achieved d epend ing
up on the construction of the solar collector and
the rate of flow of the water or air.
Solar Water HeatingFor most hot w ater applications, 45 to 50C
is sufficient for showering an d kitchen u se.
A typical solar water h eating system consist
of a solar collector connected to a hot w ater
reservoir. Active systems u se pu mp s and con-
trollers to circulate a fluid between the collector
and the storage tank. Due to their complexity
and expense, active systems are generally not
well suited for use in rem ote developing areas.
This chapter w ill focus on cheaper and simpler
passive system s. Passive systems are easiest to
design in u se in warm climates where there areno hard freezes (i.e., temp eratu res don t typ ical
go below 10C). These system s can be u sed in
colder clima tes as well, but in these cases, provi
sion mu st be mad e for freeze protection.
Passive systems can be furth er subd ivided
into thermosyphon systems and batch systems
In solar thermosyp hon systems, a
solar collector (located a t least two-
thirds of a meter below the bottom o
the hot-w ater reservoir) is connected
by mean s of plumbing to create a
closed loop w ith the hot-water tank
Typically, water is heated in p ipes in
the collector, which consists of a
metal absorber plate to w hich are
attached w ater tubes spaced rou ghl
every 15 cm in an insu lated box fitte
with a transparent glazing. Water is
heated in the collector and r ises to th
top of the h ot-water tank, replaced b
colder w ater from the bottom of the
reservoir. Dur ing the d ay, this ther-
mosyp hon process continues. It is
possible to extract hot water from th
tank as n eeded w hile the p rocess co
tinues. The ad vantage of the ther-
mosyp hon system is that the heated
water can be stored in an insulated
container, possibly located ind oors.
This means the water loses less heat
overnight compared to a batch system
Renewable Energy for Rural Schools
Figure 2.1. The simplest solar water heaters consist simply of a
black tank placed in the sun. Collector efficiency can be
increased by placing the tank inside inside an insulated glazed
box, as shown above.
02622214m
Batch Solar Collector
Tank
Glazing
Drain valves
Insulated plumbing lines
Insulated collectionbox
Pump flow
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The hot water reservoir mu st be properly 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. This
can consist of a metallic water tank p laced h ori-
zontally on an insulated base and covered w ith a
tran sparen t cover. Reflectors can be u sed to
increase the rad iation incident on the tank. The
sun h eats the reservoir during the d ay, and hot
water can be extracted for evening show ers and
kitchen u se at the end of the day. In areas wh ere
there a re clear, cool nights w ith low, relative
hu 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 heating systems var y
widely, depend ing up on w hether they are site-
constructed w ith free labor/ materials, or are
manu factured components / systems pu rchased
from a su pp lier. Prices might ran ge from $0 (all
used/ donated materials constructed on site with
donated 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/ m2 to 7 kWh/ m2 per d ay,)
incident on th e collector. Use Table 2-1 to esti-
mate system efficiency.
Solar Space HeatingBefore consid ering solar space heating, it is
essential that the bu ilding be prop erly insulated
and sealed. Otherwise, using solar air heaters
could be w asteful. After that, to the extent possi
ble, passive solar/ daylighting strategies should
be used . (For pre-existing stru ctures, the oppor-
tunities for imp lementing passive strategies m a
be 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 wood , which are comm only
used for space heating p urp oses. Solar air
heaters are best suited for use in schools that
have reasonably good solar radiation regimes in
winter. There are several typ es of solar air
heaters, but th e simplest and most effective con
sists of an external transparent glazing covering
a shallow collector insulated a t the base, and
generally containing a d ark grill or mesh locate
in the air space.
For space heating app lications, an exit-air
temp eratu re from the solar air heater of 30 to
50C is ad equa te to contr ibute to increasing the
ambient temperatu res within the school build-
ing. The size of the solar air heaters d epends on
the indoor temp erature that the school would
like to m aintain. A small PV panel to operate a
simp le fan is very useful in increasing the effi-
ciency of heat extraction from th e collector. The
solar collectors can be mou nted on the w alls of
the bu ilding facing th e Equator. In th is way, the
can be used for either n atural convection heatin
and for summer ven tilation. These relatively
simple systems have few maintenan ce problem
provided they are fitted with simple filters, esp
cially in d usty areas.
The estimated cost for a simp le solar air
heater system ran ges up to $35.00 per square
meter, depend ing as in the w ater case, how
much d onated labor/ materials are used.
Solar PasteurizationSolar flat-plate collectors can be u sed to pas
teur ize wa ter. These collectors consist of a b lack
absorber plate in an insulated box covered by a
sheet of tempered glass. Water is circulated
through the collector for heating and then
pum ped to a storage tank.
10 Renewable Energy for Rural Schools
Table 2.1. Solar Water Heater Efficiencies
02622209mSystem Type System Efficiency
Active System1 50%
Thermosyphon System1 45%Batch System1 30%
Batch System 50%(day/evening loads only)
1 Standard draw, equal weight to morning and evening draws.
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Water or milk may be p asteurized by h eating
it to 65C for 30 minu tes. Pasteurization d isin-
fects microbiologically contam inated wa ter by
killing viruses, bacteria, and pro tozoa. However,
it will not eliminate chemical pollutant s or salts.
Solar pasteurization m ay also be
achieved by placing w ater or m ilk contain
ers in a solar cookeran insu lated box co
ered with glass. Reflectors increase the
amou nt of sun light d irected into the box.
d irect sun light, tempera tures su fficient fopasteur ization are easily achieved in th is
manner.
Solar Water DisinfectionAs an alternative to pasteu rization,
solar water d isinfection can be used to
eliminate bacteriological contamination
from d rinking w ater sup plies. (Note: This
techniqu e only works against bacteriolog
cal contam inants, it will not elimina te
chemical pollutan ts or salts.) Clear, bu t
bacteriologically contam inated , water in
transparent plastic bags is exposed to
d irect sun light for four to six hou rs. The
water can also be placed in th in, plastic
transparent bottles, but care should be
taken NOT to u se bottles manu factured
from plastics mad e with the ad dition of an
Renewable Energy for Rural Schools
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 the
Caribbean.
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ultra -violet (UV) wavelength inhibitor (used to
ensu re a longer life for the bottle wh en exposed
to solar radiation.) These bottles may not p rove
to be suitable for the solar w ater d isinfection
process. 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. Better
results are achieved w hen the p lastic bags are
placed ou tside on smooth, dark su rfaces that
perm it an increase in the temp erature level of the
water. Decontamination takes longer in h um id,
cloud ier regions than in d ry and sunn y climates.
The required m aterials consist of suitable plastic
bags and a thin, dark sheet, preferably of metal
resting 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 as
pasteurization and solar water d isinfection, are
effective 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 to
kill 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 water. It removes bacteria, salts, and
pollutants of all types. Distillation is often u sed
to pu rify brackish water. The simp lest stills con
sist of a sloping tran spa rent cover (usually glas
over a shallow basin filled w ith 8 to 10 cm of
clean saline water. Solar rad iation heats up th e
saline water, causing evap oration. Water vap or
condenses on the und erside of the transparent
cover, 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 viral
contaminants, making it dr inkable. Depending
up on sun light and temperatu re, solar distillers
can prod uce 3-6 liters of potable water per day
per square meter of collector area. Sizes range
from family-sized u nits of two squ are meters to
commu nity scale un its of several thousand
square meters. The costs of a solar d istiller sys-
tem vary from $30 to $300 per squ are meter. In a
12 Renewable Energy for Rural Schools
CASE STUDYSolar Stills for Water Supply for Rural SchoolsCountry: ArgentinaLocation: Chaco Salteo
Latitude: Trop ic of Cap ricorn
Altitude (average): 350 m above sea level
Climatic conditions : Average insolation: 6 kWh/ m2/ day; Average yea rly ambient t em perature: 21C
Period o f operation during the year: Continuous
Schools provided w ith solar stills: Los Blancos and Cap itan de Fragata Pag
RE system: Site-assembled solar stills for the p rodu ction of fresh drinking water
Installation: June 1995
Capacity: 6 greenhouse-type un its, each 2.2 m2 in area producing 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 tanker tru ck
Lessons Learned: The maintenance of the stills did n ot app ear to be a major problem. Several of the
construction ma terials selected for the stills could not w ithstand the h igh-levels of U.V. radiation and
the effects of hot saline br ine
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remotely located school, this techniqu e could be
used to p rodu ce water that can be used for
dr inking, cooking and med icinal purp oses.
Solar Cooking
Solar cookers can be used un der favorable
solar rad iation cond itions to reduce the fossil
fuel or biomass energy load n ormally used for
prep aring m eals. The majority of the energy isused for cooking the mid-day meal. Smaller
amou 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 and
could be m et using simple box cookers. These
consist of insu lated boxes with a slop ing glazed
cover and a rear h inged reflector. The cooker is
mou nted facing the Equator and is generally
tur ned 3 to 5 times a d ay to face the sun d irectlythus, improving its p erforman ce. Other types o
cookers includ e concentra ting cookers using
par abolic reflectors, or steam cookers u sing a fla
plate collector to prod uce the steam conn ected
to an insulated d ouble boiler. Under reasonable
solar cond itions, i.e., above 700 Watts/ m2, it is
possible to cook a va riety of meals. If the school
has a large pop ulation of stud ents to feed, then
solar cooking is not the p referred op tion. Solar
cooking should only be used to red uce the
energy dem and from conventional sources.
Biomass Cookers
In recent years, improved wood and charco
stoves have been d eveloped with increased
efficiency of biomass use. As wood and charcoa
are generally the fuels most read ily available in
remote d eveloping areas, it is possible to make
use of more efficient commun ity-sized stoves fo
this pu rpose. It is easily possible to cook m eals
with a m ean-specific fuel consum ption of 8 to
10 kilograms of food cooked p er kilogram ofdry wood.
Renewable Energy for Rural Schools
Figure 2.4. Solar Stills at a school in the Chaco,
Argentina.
TomLawand,Solargetics/PIX08271
BethelCenter/PIX08272
Figure 2.5. Solar ovenshousehold model on right.
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14 Renewable Energy for Rural Schools
CASE STUDYSolar Water Heating in Nepal
Details of School Location
Bud hanilkantha SchoolP.O. Box 1018
Bud H anilkantha
Kathmand u, Nepal
This school uses solar water h eaters to pr
vide hot water for bathrooms.
Specific Conditions of the School
The school consists of 24 bu ildings. The ori
entations of the bu ildings vary and in genera
the roofs are pitched. The num ber of stud ents at the school is 850
with 70 teachers an d 150 custod ians.
The school operates for 9 months of the yea
The norm al occup ancy time is from 08:30 to
16:30 hours. It is a full board ing school w ith a
stud ents residing on the Campu s. In add ition
55 staff mem bers reside at th e school, and
there are residents at the school through out t
year, even in holiday p eriods. The school is n
used in the evening for comm un ity educationpurposes.
Energy End Use in the Scho
Water HeatingThis consists
mainly of solar water heating for
the stud ent hostels and electric
water h eaters for the staff quarter
Due to its urban location, the
school gets its electricity from the
grid . The electrical energy con-
sum ption (includ ing lighting):
Rs 80,000 ($U.S. 1,176) per month
The peak expend iture is Rs 150,00
($U.S. 2,205) for a m onth du ring
winter. Note th e exchan ge rate fo
Nepali rup ees at the time of this
writing (April 99) is $U.S. 1 =
NRs 68.
Figure 2.6. Demonstration of improved wood
cookstoves at the Renewable Energy Training
Center, Nuequen, Argentina.
TomLawand,Solargetics/PIX08273
Figure 2.7. This solar water heater has provided
hot water to this school in Nepal since 1978.
TomLawand,Solargetics/PIX08274
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Renewable Energy for Rural Schools
Space heating (winter only)liquid prop ane gas (LPG)
and electricity Cookingcommu nal an d familialelectricity and
LPG
Educational aides
television sets 60
VCRs 30
Computers 30
Printers 10
Type of Renewable Energy
System in OperationSolar Water Heaters:
Nu mber of solar collectors40 units.
Collector typesMost of the installed w ater heaters
use an integrated d esign, wh ere the collector and storage
are in one p iece. The more recent installations are th er-
mosiphon types.
Locationthe collectors are fixed on th e walls, or on
the terrace, and som e are ground mou nted.
Equipment man ufactured by the following compa-niesBalaju Yantra Shala; Sun Works; Laxmi Mechan ical
Solar Works.
All solar equipm ent manu factured in Nepal.
Years of installationmajor installation d one from 1977
to 1979 and some in the 1990s.
Present condition of SWH system s75% of the panels
are performing well, including the SWH systems
insta lled in 19771979.
The school paid for the equipm ent and its installation.
The school also hand led the financial arrangemen ts
of 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 $500
to $600, including installationthere were extra charges
for the plumbing for the sup ply of the hot water in the
buildings.
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 han dles the RE
systems at th e school. Technicians are tr ained in-house by
the Maintenance Departm ent.
Despite a slight d rop in system efficiencies over the
years 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 such
solar water h eaters, PV cells, and the micro-hyd ro tur -
bine. They stu dy these systems as p art of their courses.
Due to the introdu ction of the solar water h eating sys-
tems, there are many SWH in the local commu nity partic-
ularly in th e dom estic sector. The p rincipal barrier to the
spread of this technology has been the affordability and
the developm ent of an economic design. There is also a
lack of awareness of the technology.
Although a complete survey has not been und ertaken,
there are a num ber of boarding schools in Nep al that
have 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 the regional and n ational scale, it should be noted
that m any sm all comp anies man ufacture SWH. Typically,
the man ufacturers d o the system maintenance as well.
Acknowledgment:
The information was provid ed by:
Gyani R. Shaky a
Chief Technology Division
Royal Nep al Academy of Science and Technology
P.O. Box 3323
Kathm and u, N EPAL
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CHAPTER 3:ELECTRICAL SYSTEMCOMPONENTS
Chapter IntroductionThis chap ter gives an overview of the m ain
comp onents typically used in RE systems. Diesel
and gasoline engine generators are also d is-
cussed . For each item, the discussion includes
how th e comp onent works, prop er use, cost,
lifetime, and limitations.
System Overview
Introduction
A hybrid system comp rises comp onents tha
prod uce, store, and deliver electricity to the
app lication. Figure 3.1 shows a schematic of ahybrid system. The compon ents of a hybrid sys
tem fall into one of four categories described
below.
Energy Generation
Wind turbines and engines use generators t
convert mechan ical motion in to electricity. PV
pan els convert su nlight d irectly into electricity.
Energy Storage
These devices store energy and release it
wh en it is needed. Energy storage often
improves both the p erforman ce and economics
of the system. The m ost common energy storag
device used in hybrid systems is the battery.
Energy Conversion
In hybrid system s, energy conversion refers
to converting AC electricity to DC or vice versa
A variety of equipm ent can be used to do this.
Inverters convert DC to AC. Rectifiers conver tAC to DC. Bi-directional inverters combine the
functions 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 energy
prod uced by the system), and the wiring and
hard ware needed to comp lete the system. Note
that the term "BOS" is not strictly d efined . In
other contexts, energy conversion equ ipment
and batteries may be consid ered BOS items.
Photovoltaics
Introduction
PV modu les convert su nlight d irectly into
DC electricity. The m odules th emselves, hav ing
no m oving p arts, are highly reliable, long lived
and requ ire little main tenan ce. In add ition, PV
pan els are mod ular. It is easy to assemble PV
16 Renewable Energy for Rural Schools
Figure 3.1. Hybrid System Configuration:
Generalized hybrid system configuration showing
energy generation components (photovoltaic,wind turbine, and generator), energy storage
components (batteries), energy conversion
components (inverter), and balance of system
components (direct current source center and
charge controller). Courtesy of Bergey Wind
Company
Batteries
DC loads AC loads
Inverter
Generator
PV array
Wind turbine
02622210m
Wind/PV/Diesel Hybrid System
DC sourcecenter
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pan els into an array of arbitrary size. The main
d isadvantage of PV is its high cap ital cost.
Despite th is, especially for small system s, PV
is often a cost-effective op tion, with o r w ithou t
another p ower sou rce, as the savings of use
pays back the initial cost.
PV Module Construction
PV modules consist of ind ividu al cells that
are wired together in series and in parallel to
prod uce the desired voltage and current. The
cells are u sually encapsu lated in a tran sparent
protective material and typically housed in an
aluminum frame.
PV cells fall into three ty pes, monocrys-talline, polycrystalline, and th in film (am or-
ph ous). Amor ph ous cells are generally less
efficient, and may be less-long lasting, bu t are
less expensive and easier to m anu facture.
Performance Characterization
PV modu les are rated in terms of peak watts
(Wp). This rating is a function of both p anel size
and efficiency. This rating schem e also makes it
easy to compare mod ules from d ifferent source
based up on cost per Wp . The rating is the
amou nt of pow er that the modu le will prod uce
un der stand ard reference cond itions (1kW/ m2;
25C [77F] panel tem perature.) 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 Wp will pro
du ce 50 W wh en the insolation on th e mod ule i
1 kW/ m2. Because pow er outp ut is roughly p ro
portional to insolation, this same mod ule could
be expected to prod uce 25 W when the insolatio
is 500 W/ m2 (when operating at 25C).
PV array energy prod uction can be estimate
by mu ltiplying the arrays rated p ower by the
sites insolation on the pan els su rface (typically
14002500 kWh/ m2 per year; 47 kWh/ m2/
day). The resulting p rodu ct is then d erated by
app roximately 10%20% to accoun t for losses
caused by such things as temperatu re effects
(panels produ ce less energy at higher tempera-
tures) and w ire losses.
Module Operation
Most PV panels are d esigned to charge 12-V
battery ban ks. Larger, off-grid system s may h av
DC bu s bar voltages of 24, 48, 120 or 240 V. Con-
necting the ap prop riate num ber of PV pan els in
series enables them to charge batteries at these
voltages. For non-battery charging ap plications
such as w hen th e pan el is directly connected to
water pu mp, a maximum -point p ower tracker
(MPPT) may be necessary. A MPPT will match
the electrical characteristics of the load to those
of the mod ule so that the array can efficiently
power 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 oriente
toward s the sun . To do this, the mod ules are
mou nted on either fixed or tracking mou nts.
Because of their low cost and simp licity, fixed
mou nts are most commonly u sed. These type o
mou nts can be made of wood or m etal, and can
be 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,
Renewable Energy for Rural Schools
Figure 3.2. Ground-mounted PV panels at a rural
school in Neuqun province, Argentina.
TomLawand,Solargetics/PIX008275
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particularly at low latitud es, but at the p rice of
ad ditional cost and complexity. The relative cost
effectiveness of tracking mou nts v ersus ad di-
tional mod ules w ill vary from pro ject to project.
Capital and Operating CostsPV modules are available in a variety of rat-
ings u p to 300 Wp . Ind ividu al PV panels can be
connected to form arrays of any size. Modules
may be connected in series to increase the array
voltage, and can be conn ected in parallel to
increase the array current. This mod ularity
makes it easy to start out w ith a small array and
add add itional mod ules later.
The costs of a PV array are d riven by the cost
of the mod ules. Despite declining p rices in the
last two d ecades, PV modu les remain expensive.
Retail prices for mod ules bottom ou t at abou t
$5.50 per Wp. For bu lk pu rchases, prices can go
below $4.00 per Wp. Warrantees typically are for
10 to 25 years. Cur rent m odules can be expected
to last in excess of 20 years. The remaining PV
array costs consist of mou nts, wiring, and instal-
lation . These are typ ically $0.50$1.50 per Wp.
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 loose
connections and corrosion.
Wind-Turbine Generators
Introduction
Wind turbines convert the energy of moving
air into u seful mechan ical or electrical energy.
Wind turbines need m ore maintenance than a PV
array, but w ith mod erate wind s, > 4.5 meters per
second (m/ s), will often p rodu ce more energy
than a similarly priced ar ray of PV panels. Like
PV panels, mu ltiple wind turbines can be used
together to p rodu ce more energy. Because w ind-
turbine energy prod uction tends to be highly
variable, wind turbines are often best combined
with PV panels or a generator to ensu re energy
prod uction during times of low wind speed s.
This section will focus on sm all wind tu rbines
with ratings of 10 kW or less.
Wind-Turbine Components
The components common to most wind tur-
bines are shown in Figure 3.3 below. The blad es
capture the energy from the w ind, transferring
via the shaft to the generator. In sm all wind tu r-
bines, the shaft usu ally d rives the generatordirectly. Most small wind tu rbines use a p erma-
nent m agnet alternator for a generator. These
prod uce variable frequency (wild) AC that the
pow er electronics convert into DC current. The
yaw bearing allows a wind turbine to rotate to
accomm odate changing wind direction. The
tower sup ports the wind tu rbine and p laces it
above any obstructions.
Wind-Turbine Performance
CharacteristicsA wind -turbines p erformance is character-
ized by its power curv e, which relates wind-tur
bine pow er outpu t to the hub-height wind
speed. Power curves for selected machines are
shown in Figure 3.4. Turbines n eed a minimu m
wind speed , the "cut-in" speed , before they start
prod ucing power. For small tur bines, the cut-in
speed typ ically ranges from 3 to 4 m/ s. After
cut-in, wind-turbine pow er increases rapidly
with increasing w ind speed un til it starts level-ing off as it approaches peak p ower. The energy
18 Renewable Energy for Rural Schools
Figure 3.3. Typical wind-turbine components
Blades
Generator
Tail
Tower
Yawbearing
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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 speeds than at
lower wind speeds, until the wind speed reaches
the "cut-out" speed. Most small turbines p rodu ce
peak p ower at about 1215 m/ s. The turbine w ill
prod uce at peak pow er until the wind speed
reaches the tur bines "cut-out" speed. Cut-ou t,
usu ally occurr ing at 14 to 18 m/ s, protects the
turbine from overspinning in high w inds. Most
small 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 at
30%70% of rated p ower.
Wind turbines are rated by th eir power out-
pu t at a specified w ind speed , e.g., 10 kW at
12 m/ s. The wind speed at which a turbine is
rated, though u sually chosen somewh at arbitrar-
ily by the manufacturer, is typically near the
wind speed at w hich the tu rbine produ ces the
most pow er.
The non-linear n ature of
the wind-turbine power curv
makes 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, requires the wind
speed d istribution rather than
just the average wind speed .
Long-term performance can
then be foun d by integrating
the wind-turbine power curv
over the wind sp eed distribu-
tion. Wind -turbine perfor-
mance may also depend u pon
the ap plication for which it is
used.
Wind-Turbine Costs
Wind -turbine prices vary
more than PV mod ule prices.
Similar sized tu rbines can d if
fer significantly in p rice. This
caused by w ide pricing varia-
tions among different turbine
man 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. Unlike the case for PV, win
tur bines offer econom ies of scale, with larger
wind turbines costing less per kW th an sm aller
wind turbines.
Maintenance costs for w ind turbines are
variable. Most small wind tu rbines require som
preventive maintenance, mostly in th e form of
period ic inspections. Most maintenan ce costs
will probably be due to un scheduled repairs
(e.g., lightning strikes an d corrosion). Gipe1
claims a consen sus figure of 2% of the total sys-
tem cost ann ually.
Micro-hydro
Introduction
Micro-hyd ro installations convert the kineti
energy of m oving or falling w ater into electricit
These installations may requ ire more extensive
Renewable Energy for Rural Schools
3.5
3.0
2.5
2.0
1.5
1.0
0.50
00 5 10 15 20 25
Wind speed (m/s)
02622206m
Power(kW)
Wind Turbine Power Curves
World Power Whspr 3000
Bergey 1500
SW Air 303
World Power Whspr 600
Bergey 850
Source: Manufacturer's data
Figure 3.4. Selected wind-turbine power curves
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civil works than other technologies, but at
app ropriate sites, micro-hydro can be, on a life
cycle basis, a very low cost op tion. The water
resource of a micro-hyd ro installation may be
sub ject to seasonal weather extremes su ch as
drou ght or freezing, but u nlike PV or wind tu r-bines, a micro-hyd ro installation can prod uce
pow er continuou sly on a day-to-day basis.
Because of this continu ous p ower p rodu ction,
even a small installation will produ ce large
amoun ts of energy.
Components
The comp onents of a micro-hydro installa-
tion are shown in Figure 3.6. The civil works,
consisting of a water channel, d iverts water from
the stream or river to the p enstock. The p enstocconveys the water u nd er pressure to the turbine
The piping used in the penstock mu st be large
enou gh to avoid excessive friction losses. Differ
ent types of tu rbines are available, dep ending o
the head and flow rate available at the site.
Impu lse turbines, such as th e Pelton or Turgo
turbine have on e or more jets of water impingin
on the tu rbine, which sp ins in the air. These
types of turbines are most used in medium and
high h ead sites. Reaction turbines, such as the
Francis, Kaplan, and axial tu rbines are fullyimmersed in water. They are used m ore in low
head sites. The tu rbine is connected to a genera-
tor that p roduces electricity. Both AC an d DC
generators are available. Governors an d contro
equipm ent are used to ensu re frequency contro
on AC systems and du mp excess electricity pro
du ced by the w ind turbine.
Performance and Cost
The power ou tpu t of a micro-hydro system
a function of the p rodu ct of the pressure (head)
and flow rate of the water going throu gh the tur
bine. Figure 3.7, shows th e expected generator
outp ut un der various site cond itions. The selec-
tion of a site is usu ally a comp romise between
the available head & flow rate and the cost of th
water channel & pen stock. Because micro-hydr
systems produ ce continuou s pow er, even a sma
system will produ ce a large amou nt of energy.
For examp le, a 125-wa tt system w ill prod uce
20 Renewable Energy for Rural Schools
Figure 3.5. Small wind turbines, solar oven, and
radio tower at the Las Cortaderas Primary School
250 km west of Neuqun, Argentina.
BergeyWindpowerC
o.,Inc./PIX02103
Figure 3.6. Components of a micro-hydro
installation. Fraenkel, Peter (1991) Micro-hydro
Power: A Guide for Development Workers. IT
Publications in association with the Stockholm
Environment Institute, London.
Weir andintakeCanal
Forebay
Spillway
Penstock
Powerhouse
Tail race
02622212m
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3 kWh a d ay. The water resource of a micro-hydro
installation may be su bject to seasonal variations
du e to winter freezing, spring runoff, and drought.
In cases where peak pow er deman d is greater
than wh at the installation can sup ply, a battery
bank can be used to store energy du ring low
demand periods for use in high demand periods.
Due to varying requirements 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 loosely
estimated to be aroun d 3% of the capital cost per
year. 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 ma in-tained systems lasting in excess of 50 years.
Unlike PV and w ind systems, micro-hyd ro
installations are not mod ular. The available
wa ter resource and size of the civil wor ks and
penstock place an ultimate limit on th e pow er
outp ut of a given micro-hyd ro system. Increas-
ing the capacity of the civil wor ks is expensive.
Thus, micro-hyd ro installations requ ire that
long-term load dem and be carefully considered.
Diesel Generators
Introduction
Generators consist of an engine driving an
electric generator. Generators run on a var iety o
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 for
batteries. Comp ared to wind turbines and PV
pan els, generators have low capital costs but
high op erating costs.
Cost and Performance
Diesel generators are the m ost common type
They are available in sizes ranging from un der
2.5 kW to over 1 megawat t (MW). Compared to
gasoline generators, diesel genera tors are more
expensive, longer lived , cheaper to maintain,
and consum e less fuel. Typical costs for sm all
diesel generators (up to 10 kW) are $800 to $1,00
per kW. Larger d iesels show economies of scale
costing rou ghly $7,000$9,000 plus ~$150 per
kW. Typical d iesel lifetimes are on the o rder of
25,000 operating h ours2. Larger d iesels are usu -
ally overhau led rather th an rep laced. Overall
main 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 day
maintenance and the generator mu st be periodi
cally overhau led by a qualified m echanic. Diese
generator fuel efficiency is generally 2.53.0 kWh
liter when ru n at a high load ing. Efficiency drop
Renewable Energy for Rural Schools
Figure 3.7. Estimated hydropower generator output
as 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
Head(m)
Hydropower Electrical Output
PowerOutput(kW)
0.125
0.25
0.5
1.0
1.5
2.0
4.0
10.0
Figure 3.8. Typical generator at an isolated
mountain school. Teachers and custodians
generally have no training in the maintenance and
operation of these units.
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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 the
peak load, but then often runs at low load mu ch
of 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 hu nd red w atts). Otherwise,
gasoline generator s are inferior in most resp ects
to their d iesel counterpa rts. For sizes larger than
abou t 1 kW, prices range from $400 to $600 per
kW. The minim um pr ice is roughly $400 regard -
less of size. Lifetimes are short , typically only
1,000 to 2,000 operat ing h ours. Fuel efficiency is
poor, 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 hen
the loads are very sm all or the an ticipated ru n
hou rs total no m ore than roughly 400600 hou rs
per year.
Given the p revious d iscussion, several points
regarding the optimu m u se of generators
emerge. For maximum fuel econom y, the genera-
tor shou ld be ru n at a high load (> 60%). Con-
versely, low-load op eration should be avoided .
Not only d oes this d ecrease the fuel efficiency,
there is evidence that low-load op eration resultsin greater maintenance costs.
Batteries
Introduction
Batteries are electrochemical d evices th at
store energy in chemical form. They store excess
energy for later use in ord er to improve system
ava 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. The
remainder of this section d iscusses the lead-acid
battery.
Battery Selection Considerations
Deep-Cycle versus Shallow-Cycle
Although batteries are sized according to
how mu ch energy they can store, in most cases
a lead-acid battery cannot be d ischarged all the
way to a zero state of charge withou t suffering
dam 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 as
car 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 by
only a han dful of deeper d ischarges.
Flooded versus Valve Regulated
Flooded batteries have their plates immerse
in a liquid electrolyte and n eed p eriodic rewate
ing. In contrast, in valve regulated batteries, the
electrolyte is in th e form of a paste or contained
with in a glass mat. Valve regulated batteries do
not n eed rew atering. Flooded batteries generallhave lower cap ital costs than valve regulated
batteries and w ith proper m aintenance, tend to
last longer. On the oth er hand , where mainte-
nan ce is difficult, valve regulated batteries may
be the better choice.
Lifetime
Battery lifetime is measured both in terms o
cumu lative energy flow throug h th e battery (fu
cycles) and by float life. A battery is dead wh en
22 Renewable Energy for Rural Schools
Figure 3.9. Batteries allow an RE system to provid
24 hour power. Photovoltaic panels or a windgenerator can recharge the batteries.
7/29/2019 Energias Alternativas Para Escuelas Rurales
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reaches either limit. For example, discharging a
battery twice to 50% is one full cycle. For m any
batteries, as long as the battery state of charge is
kept within the man ufacturer s recomm ended
limits, the lifetime cumu lative energy flow is
roughly indep enden t of how d eeply the batteryis cycled. Depend ing upon the brand an d m odel,
battery lifetimes va ry w idely, ranging from less
than 100 full cycles to more than 1500 full cycles.
Float life refers to how long a battery that is con-
nected to a system will last, even if it is never or
only lightly u sed. Typical float lives for good
qu ality lead-acid batteries range betw een 3 and
10 years at 20C (68F). Note tha t high ambient
temp eratu res will severely shorten a batterys
float 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.
Size
The 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 batterys
nom inal voltage (usually 2, 6, or 12 V), this gives
the storage capacity of the battery in w att-hours.
(Dividing this nu mber by 1000 gives the battery
storage capacity in kWh ) This storage capacity is
not a fixed qu antity, but rath er varies somewhatdep ending on the rate at which the battery is dis-
charged. A battery will provide m ore energy if it
is discharged slow ly than if it is discharged
rap idly. In ord er to facilitate un iform compari-
son, most battery man ufacturers give the storage
for a given d ischarge t ime, usu ally 20 or 100
hou rs. Ind ividu al batteries used in RE and
hybrid system s are available in capacities rang-
ing from 50 amp hou rs at 12 V to thou sands of
amp h ours at 2 V (0.5 kWh to several kWh).
Cost
The var iations in cycle and float life,
described earlier, make comparison of the cost-
effectiveness of d ifferent batteries somewh at
problematical. As a genera l starting p oint, costs
are on the ord er of $70$100 per kWh of storage
for batteries w ith lifetimes o f 250 to 500 cycles
and float lives in the range of 5 to 8 years. There
will be add itional one-time costs for a shed,
racks, and connection w iring.
Inverters
Introduction
Inver ters conver t DC to AC electricity. This
capability is needed because PV mod ules and
most sm all wind turbines p rodu ce DC electricitwh ich can be used by DC app liances or stored i
batteries for later use. Most comm on electrical
app lications an d dev ices requ ire AC electricity,
wh ich cannot be easily stored.
Inverter Selection Considerations
Output wave form: Inverter output wave
forms fall into on e of three classes, square wave
mod ified sine wave, and sine wave. Square-
wav e inverters are the least expensive, but their
outp ut, a squ are wave, is suitable only for resis-
tive load s such as resistance heaters or incand es
cent lights. Modified sine-wave inverters
prod uce a staircase square wave that m ore
closely app roximates a sine wave. This type of
inverter is the most common . Most AC electron
devices and motors w ill run on mod ified sine
wav e AC. Some sen sitive electronics may no t
work w ith mod ified sine wave AC and requ ire
sine-wave inverter s. Sine-wave inverter s pro-
du ce utility grade p ower, but of course cost morthan th e other types of inverters.
Conversion efficiency: Inver ter efficiency
varies w ith th e load on th e inverter. Efficiencies
are poor at low pow er levels and generally very
good (>90%) at high pow er levels. Mid ran ge
efficiency varies wid ely between inv erters and
may be an impor tant selection criterion. Other
items to consider are the inver ter s no-load
pow er draw and the presence of a "sleep m ode"
Sleep m ode redu ces the inverter pow er draw to
few w atts when there is no load on th e inverter.
Sw itched versus parallel:A parallel inverte