Energias Alternativas Para Escuelas Rurales

7/29/2019 Energias Alternativas Para Escuelas Rurales

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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 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



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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



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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.


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


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


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


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


13/64

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


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.



14/64

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.


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.


15/64

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


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


16/64

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.


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.


17/64

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


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.


18/64

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


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


19/64

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.


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

Argentina.


BethelCenter/PIX08272

Figure 2.5. Solar ovenshousehold model on right.


20/64


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.


Figure 2.7. This solar water heater has provided

hot water to this school in Nepal since 1978.



21/64


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


22/64

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


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


23/64

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,


Figure 3.2. Ground-mounted PV panels at a rural

school in Neuqun province, Argentina.



24/64

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


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 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


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


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


27/64

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


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.


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 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


Figure 3.9. Batteries allow an RE system to provid

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


29/64

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

Energias Alternativas Para Escuelas Rurales

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