Water Pumping - The Solar Alternative

8/9/2019 Water Pumping - The Solar Alternative

1/67


2/67

Issued by Sandia National Laboratories, operated for the United StatesDepartment of Energy by Sandia Corporation.NOTICE: This report was prepared as an account of work sponsored by anagency of the United States Government. Neither the United States Govern-ment nor any agency thereof, nor any of their employees, nor any of theircontractors, subcontractors, or their employees, makes any warranty, expressor implied, or assumes any legal liability or responsibility for the accuracy,completeness, or usefulness of any information, apparatus, product, orprocess disclosed, or represents that its use would not infringe privatelyowned rights. Reference herein to any specific commercial product, process, orservice by trade name, trademark, manufacturer, or otherwise, does notnecessarily constitute or imply its endorsement, recommendation, or favoringby the United States Government, any agency thereof or any of theircontractors or subcontractors. The views and opinions expressed herein donot necessarily state or reflect those of the United States Government, anyagency thereof or any of their contractors.

Printed in the United States of America. This report has been reproduceddirectly from the best available copy.

Available to DOE and DOE contractors fromOffice of Scientific and Technical InformationPO BOX 62Oak Ridge, TN 37831Prices available from (615) 576-8401, FTS 626-8401

Available to the public fromNational Technical Information ServiceUS Department of Commerce5285 Port Royal RdSpringfield, VA 22161NTIS price codesPrinted copy: A06Microfiche copy: AO1

Cover design: Gene Clardy, Sandie National LaboratoriesCover photo: Anne V. Poore, Sandla National Laboratories


3/67

DistributionCategory UC-276

SAND87-0804Unlimited Release

WATERPUMPING:THESOLARALTERNATIVE

Michael G. ThomasPhotovoltaic Systems Design Assistance Cen ter

Sandia National LaboratoriesAlbuquerque, NM 87185-0753

ABSTRACTThis report was prepared to provide an introduction into understand-

ing the characteristics, including economics, of photovoltaically poweredwater pumping systems. Although thousands of these systems existworldwide, many potential users do not know how to decide whether ornot photovoltaic pumping systems are an attractive option for them. Thisreport provides current information on design options, feasibility assess-ment, and system procurement so that the reader can make an informeddecision about water pumping systems, especially those powered withphotovoltaics.


4/67

Major contributions to this docum ent were mad e by SolavoltInternational, Chronar Trisolar Corp., and I. T. Power. Indu stry govern-ment, and privat e organizations reviewed this information to eliminatequestions and to check its accuracy. The final docum ent, edited by thePhotovoltaic Systems Design Assistance Center staff, is based on the orig-inal inputs and the comments of the reviewers.

iv


5/67

Chapter1 INTRODUCTION

BackgroundSuitability of System to Moderate Pum ping Needs

2 DESIGN CON SIDERATION S FOR PV-POWEREDWATER SYSTEMSPV System Power Produ ctionTypes of Water PumpsTypes of MotorsEnergy Storage: BatteriesEnergy Storage: Water TanksControls: What is Need edDetermining Water NeedsDaily Insolation LevelsOrientation and Location of Photov oltaic ArraysTilt of Photovoltaic ArraysDetermining Peak Water FlowWater ProductionStatic and Dynamic Head s

3 SYSTEM SELECTIONSizing Systems and Selecting Equipm entThe Effect of Varying Solar Rad iation on Ou tpu tEquipment Type vs. Pum ping RequirementSpecifying System Performance

4 COST AN D ECONOMICS OF PUMPING SYSTEMSDeterm ining the Cost-Effectiveness of a Pum ping SystemMeasu ring Cost-Effectiveness of a Pum ping SystemMeasu ring Life-Cycle Costs of a Pum ping System

PAGE111

44557777999111112

1515182122

23232323


6/67

CONTENTS(Continued)

ChapterCost App raisal of a PV-Powered Pum ping System

Capital and Installation CostsPump CostsPump Replacement Costs

Evaluating the Costs of a Diesel Pum ping SystemSpecial ConsiderationsComp aring Costs of a Diesel System

Comparative Costs of Other Pumping Systems

5 PREPARING A REQUEST FOR PROPOSALPrepar ing a Technical Specification

Scope of WorkQualified BiddersWarranty and Spare PartsPrice and Delivery

Evaluating Responses (Optional Recommendations)Detailed Assessment

BIBLIOGRAPHYLIST OF MAN UFACTURERSAppendix

A Insolation AvailabilityB Samp le Calculations of System Sizing, EquipmentSelection and Cost Evaluat ion

FIGURESFigure

1 Regions of App licability for Various Pum ping Op tions2 PV de-Electric Gener ator3 Block Diagram of PV-Powered Water Pum ping System4 Types of Water Pum ps

Page2424252629292931

33333434343434353637

A-1B-1

vi


7/67

FIGURES(Continued)

Figure56789

1011121314

Table12345678

Winter Insolation ContoursTotal Dynamic Head (TDH) FactorsHydraulic Energy NomographArray Power NomographTypical Daily Variations in Solar Rad iationRelation between Peak Daily Insulation andPerformance of Centrifugal Pum psRelative Energy Ou tpu t at Various Tilt AnglesCentrifugal Pum p and Volum etric Pump Outpu tPum pset Type vs. Pum ping RegimeProcedu res for Cost App raisal of a Water Pumping System

TABLES

Comparison of Pum ping OptionsTypical Daily Water Usage for Farm AnimalsMaximum Daily Pum ped Water Requirements for Crop IrrigationFriction Losses in Head (ft) per 100 ft of 1.5-inch Pip eCost, Discoun t and NPV Examp lesLCCS for the Hypoth etical PV Pum ping SystemLCCS for a Hypot hetical Diesel Pump ing SystemCost Data for Wind-Powered , Anima l-Pow eredand Hand Pumps

Page10131617192020212228

2881424273132

vii


8/67


9/67

WATER PUMPING: THE SOLAR ALTERNATI VE1.0 NTRODUCTION

BackgroundThe availability of water h as never b eenmore important than today. The UnitedNat ions, wh ile naming the 1980s as the

Decade for Water, estimates that it wou ldtake more than $90 billion to meet thewor lds curren t deficits for clean wa teralone. As we app roach the 1990s, it is clearthat even with vast sum s of money, thewa ter needs of tens of millions of peop le w illnot be met by the end of the decade.

Although methods for water deliveryhave been known for thousand s of years,prob lems still rema in. The simp lest andmost economical way is to divert rain orriver water by a gravity flow system to thedesired location. This meth od is not avail-able in mu ch of the world, at least not on aregular or demand basis. Where this is notpossible, manu al pu mp ing has been themost common method for many years.Although these pu mp s require regularmaintenance and mu st be attended, their useis critical to wa ter su pp ly, esp ecially forhuman consumption, throughout the world.This method , in fact, has been chosen by theUnited N ations as the primary method intheir program s to alleviate the water supp lyproblems in the world.

Moving large volumes of water and/ orpum ping from deep w ells cannot be doneeffectively with hand pum ps, bu t requiresthe use of mechanical pu mp s p owered byengines or electric motor s. Engine-pow eredsystems are providing water to larger com-mu nities throughou t the world. The infras-tructure of the large comm unities can pro-vide the fuel and maintenance required bythe engines.

There are also many thousand s of solar-powered systems in the world today, pow -ered by wind generators or photovoltaic(PV) arrays. The PV-pow ered systems havedemonstrated higher reliability and lowercosts than the alternative methods in a large

class of app lications. This repor t describesthe characteristics of PV-pow ered pu mp ingsystems includ ing their ease of procurementand installation, and small maintenancerequirements, which account for their grow-ing popularity.

No single pu mp ing technique is suitablefor the entire ran ge of existing app lications.Each type of pump has its own set of appro-priate applications. Solar pum ps are particu-larity useful for intermediate app licationslike small villages (100-1,000 inh abitan ts)and moderate agricultural needs. This reportprovides a methodology for selecting thebest system design for a particular app lica-tion. Often a combination of techniques (e.g.,manu al and solar) can dram atically reducecosts and im prove the reliability of a pu mp -ing netw ork, or pr ovide the design flexibilityto cover a wide range of app lications.

Sui tab i l i ty o f System to Modera tePumping NeedsSome circumstances have made PV pow er

the preferred choice, especially wh ere thereis adequate solar resource and mod eratewater demand . Characteristics of the threepum ping options available for water deliv-ery (manu al, solar, and diesel) ar e listed inTable 1.

These advantages/ disadvantages havebeen analyzed many times. Generally theseanalyses identify three distinct r anges ofapp licability (Figure 1). Ranges of pu mp ingrequirements are expressed in meters to thefourth p ower p er day calculated by mu lti-plying the head (the distance the waterneeds to be lifted, m easured in meters) andthe flow volume (measured in cubic metersper day). Simply stated, hand p um ps arewell suited to needs for small volumes atlow-tomodera te head (50 m4). For large vol-um es and h igh head (> 2,000 m4), enginesare required.

1


10/67

For years, the large region between the load, but it mu st operate inefficiently at par-two cur ves in Figur e 1 has been met less tial power. Multiple hand p ump s require athan optimally by either oversized diesel- well for each pu mp and the costs of diggingpow ered systems or by a nu mber of hand the wells can exceed the cost of the rest ofpu mp s. An oversized diesel can meet the the pu mp ing system. Because PV systems

Table 1

Comparison of Pumping Options

Pump Type Principal Advantages Disadvantages

Hand Low cost Regular maintenance(manual) Simple technology Low flowEasy maintenance Absorbs time and energyClean that might be used moreNo fuel requirement productively elsewhereApplicable to Uneconomic use ofhand-dug wells expensive borehole

Solar Low maintenance Relatively high(PV-powered) Clean capital cost

No fuel needed Lower output inEasy to install cloudy weatherReliable Long lifeUnattended operationLow recurrent costsSystem is modular

and can be matchedclosely to need

Diesel (or Moderate capital cost Maintenance oftengas) -powered Can be portable inadequate, reducing life

Extensive experience Fuel often expensive andEasy to install supply intermittentNoise, dirt and fume

problems

2


11/67

500

200 - Head--flow product = 2000

100 -50 -

Es: 20c...- 10 - }icad--flow product = 50~..

5

2 -

1 -

o~o 25 75 100hi]y f]OW, )]) /day

Figure 1. Regions of Applicability for Various Pumping Options

are mod ular, sizing to meet the specific PV-pow ered systems require only thatrequiremen ts in this area is easily and eco- there be adequate sunsh ine and a source ofnom ically accomplished. A detailed treat- water. The number of PV-pow ered systemsment of these op tions is in A Comp arative in the world is probably limited only by theAssessment of Photovo ltaics, Han d Pum ps, fact that PV-pow er is a new technology, andand Diesels for Rural Water Sup ply, many poten tial u sers are simply unfamiliarSAND87-7015, Sandia Na tional Laborat - with it.ories, Albuquerque, May 1988.

3


12/67

2.0 DESIGN CONSIDERATIONS FORPV-POWERED WATER SYSTEMSPV System Power Product ion

PV power is produ ced directly by sun-light sh ining on an array of PV mod ules,requires no moving par ts, and is extremelysimp le and reliable. Many materials respondto visible light; the most common is silicon, aconstituent of ordinary sand . A thin, siliconcell, 10 cm across, can prod uce more than 1watt (W) of dc electrical pow er und er clear-sky conditions.Generally, man y individu al cells are com-bined into mod ules sealed between layers of

glass or transparent polymer to protect theelectric circuit from the environm ent (Figure2). These m odu les are capable of prod ucing

tens of watts of pow er. Several mod ules arethen connected in an array to provideenough power to run a motor-pump set in apu mp ing system. This array is usu allymounted on a simple, inexpensive structureoriented toward the sun at an inclinationangle close to the latitud e of the site. Thisensures that ample energy from the sun willshine on the array du ring all seasons of theyear.

A PV-pow ered water system is basicallysimilar to any other water system (Figure 3).All PVpowered pum ping systems have, as aminimum , a PV array, a motor, and a pum p.The array can be coupled directly to a dcmotor or, through an inverter, to an ac

Figure 2. PV de-Electric Generator

4


13/67

--- -------%--=..---- --.\ \POWER %%GENERATOR MOTOR -.

PUMP

I WELL 1Figure 3. Block Diagram of PV-Powered Water Pumping System

motor. For both ac and dc systems a batterybank can be used to store energy or thewater can be stored. The motor is connectedto any one of a variety of variable-speedpumps.Types of Water PumpsPum ps of many different varieties aresuitable for inclusion in a PV-pow eredpu mp ing system. They do, how ever, fallbroad ly into two categories, centrifuga l(rotodynam ic) and volum etric (positive dis-placement), wh ich have inherently differentcharacteristics. Figure 4 shows thr ee com-mon typ es of pu mp s.Centrifugal pu mp s are ideally suited forconditions of mod erateto-high flow in tubewells, cisterns, or other reserv oirs. Thesepu mps are designed for a fixed head andtheir water ou tpu t increases w ith rotationalspeed. Their efficiency decreases at head sand flows away from their design point.Centrifugal pu mps have been installed withcapacities as high as 1,200 cubic meters/ dayand can be used for flow rates as low as 10-15 cubic meters/ day. However, these pum psare not recommend ed for suction lifts higherthan 5-6 meters.

Volum etric pu mps have a water outpu tthat is almost independent of head butdirectly prop ortional to volum e. There aremany different types of volum etric pu mp s.The most interesting for inclusion in PV-powered pu mp ing systems are the counter-balanced piston pum ps (usually called jackor donkey pu mps) and the progressive cavi-ty pu mp s (sometimes called screw pump s).The efficiency of these pum ps increases asthe head increases. Volum etric pu mp s areideally suited for conditions of low flowrates and / or high lifts. Pump s of this typehave been installed with flow rates as low as0.3 cubic meters/ day and as high as 40 cubicmeters / day , and with lifts from as little as 10meters to as great as 500 meters.

Types o f MotorsThe choice of the motor for a PV-pow ered

system is dep endent on the size require-ment, need for the motor to be subm ersibleor not, and availability of dr iving electron-ics. Three basic types are perm anent magn etdc motors (brushed or brush less type),wou nd -field dc motors, and ac motors.The choice of a dc motor is attractivebecause PV arrays supp ly dc power.

5


14/67


15/67

How ever, ac motors in conjun ction with dc-ac inverters can be used for high-powerapplications.The criteria for choosing a motor are: effi-ciency, pr ice, reliability and availability.

Generally, the wa ttage d etermines the choiceof the motor: perm anent magnet dc motorsund er 2,250 watts (3 horsepower), woun d-field dc motor s for 2,250-7,500 wa tts (3-10horsep ower ), and ac moto rs abov e 7,500watts (10 horsepower).

Generally, ac moto rs are limited to high-pow er app lications in PV-pow ered pu mp ingsystems because they require inverters,thereby introducing add itional costs andsome energy loss. Although ac systems areusu ally less efficient than d c mo tors, specialimproved -efficiency mod els are now avail-able for PV systems.

Energy Storage: Bat ter iesA pum p powered by a PV array supp lieswater du ring su nlight hours only, un less

storage batteries are includ ed. Should batter-ies be included ? Introducing batteries intothe ph otovoltaic-powered pu mp ing systemmay decrease its reliability and increase itsmaintenance requirements. The inclusion ofbatteries is justified wh en the maximumyield of the well du ring sunlight hours isinsufficient to meet the da ily wa ter requ ire-ment; alternatively, a new w ell could be dug.

Energy Storage: Water TanksWater storage is an important considera-tion, regard less of the intend ed use for thewater. Pumps without batteries will not pro-duce any water when the sun does not

shine. Th is is least troublesom e in thoseplaces w here the wa ter is for irrigation. Theevapotran spiration of plants is prop ortionalto the solar intensity: plan ts n eed less wa terduring those periods when the pum p p ro-du ces less wa ter. Also, two to three d ays ofwater storage is usu ally available at the rootzone of plan ts. Water need s for livestock andhum ans also vary in relation to solar intensi-ty. How ever, several days wa ter storage in atank or reservoir is recomm ended . Threedays is a typ ical storage size, but local

weather conditions and water use shoulddetermine the optimum size to meet theneeds.

Controls : What is NeededFor efficient operation, it is necessary thatthe voltage/ current characteristics of the

pu mp set match those of the array. There arethree basic ways in wh ich a pu mp set can beconnected to a PV array . The simplest is todirectly couple th e pu mp set and array.Another method is to interpose a battery.The third is to use an electronic controller.

The oper ation characteristics of centrifu-gal pu mp s are reasonably well matched tothe outp ut of PV arrays. Therefore, the twoare most often directly coup led. This directcoupling requires that gear ratios, motorspeed, and voltage and pump stage charac-teristics be carefully chosen for pr oper oper -ation. Array m atching to pu mp characteris-tics is comp licated by the limited nu mber ofpump sizes.

Electronic controls can enhance perfor-mance of a well-matched array-pum p sys-tem by 10-15%. These controls are frequentlyused in locations with fluctuating water lev-els or weath er characteristics.

The oper ating characteristics of volum et-ric pu mp s are badly matched to the outp utof PV arrays. Batteries can imp rove thismatch and a llow the motor to be started atlow sun levels. How ever, batteries havedraw backs, as outlined above.

Maximu m pow er controllers (MPCS) areusu ally used with volumetric pu mp s. Theyemp loy intelligent electronic devices totransform the array outp ut to matchpu mp set power requirements. These con-trols allow operation over a wide ran ge ofirrad iance levels, wa ter levels, and flowrates. In addition, they solve the volumetr icpu mp starting problem. Electronic controlstyp ically consum e 4-7% of the array s p oweroutput .

Determin ing Water NeedsThe designer of a water system needs toknow the volume of water required per dayand how far the water is to be transported


16/67

Table 2Typical Daily Water Usage for Farm Animals

Animal Water Usage (liters/animal)Horses 50Dairy cattle 40Steers 20Pigs 20Sheep 5Goats 5Chickens 0.1

and , for PV-pow ered systems, the amou nt of and lifestyle. For planning the introd uctionenergy available from the sun. The designer of mechanical pu mp ing systems into a vil-can then design several a lternate systems lage currently using hand pu mp s, a dailyand d etermine the cost of each. usage of 40 liters/ person/ day is suggested.

Three different needs should be consid- For a larger town , wh ere ind oor toilets andered to determine the quan tity of water to be showers are more common, a consump tionmm ~ed bv a water svstem: figure of 100 liters/ person/ day is often1 , .

q Water for drinking and cooking. Water for livestockq Water for crop irrigation.Hum an and animal water needs can beestimated by mu ltiplying the daily usage by

the pop ulation. Typical daily requirementsfor farm an imals are shown in Table 2.Determining water needs for hu mans is

somewhat more complicated because waterusage va ries based on village size, location,

used.It is mor e comp lex to estimate the waterrequirements for an irrigation app lication,

and this is beyond the scope of this report.Crop type, meteo rological factors (tempera -ture, hum idity, wind speed, and cloudcover), method of irrigation, and season ofthe year are the pr incipal factors to be con-sidered . Trickle or low-loss chann el irriga -tion techniques are more suitable for usewith PV-pow ered pu mp s than flood or

Table 3Maximum Daily Pumped Water Requirements for Crop Irrigation

Crop Water Usage

Rural village farms 60ms/haRice 100ms/haCereals 45ms/haSugar Cane 66ms/haCotton 55ms/ha

(ha = hectacre)

8


17/67

sprink ler techniques. Water requ irements forseveral common crops are presented in Table3. How ever, local pra ctice and local experi-ence are probably the best guide to waterrequ irements for a specific application.

Water usage is the first requiremen t to bedetermined. If water u sage varies over theyear, the mean d aily water requ irements foreach month mu st be calculated. For drinkingand livestock watering, water needs will beabout the same every month , but waterneeds for crop irrigation vary over the grow-ing season. The critical mon th from adesign viewpoint is the one with the mini-mu m ratio of sunlight available to theamoun t of water required. The month w iththe least sunlight is the month in wh ich theleast pow er is prod uced by the PV system.

**W+*

The hyp othetical village has 115 peop lewho are presently limited to water from ahand -dug well. Water for crop irrigation andlivestock wa tering is available from anoth ersource. The village is grow ing and is expect-ed to dou ble in pop ulation in a few years.Therefore, using the 40-liters/ person/ dayfigu re for wa ter consu mp tion, the villagewill soon need a minim um of 40 liters x 230people = 9,200 liters (9.2 m3) per day , year -round. *

******

Dai ly Insolat ion LevelsThe pow er prod uced by a PV systemdepend s on the insolation (amount of sun-light) available. This insolation varies for

each site and month-to-month, du e to sea-sonal and climat ic variations. Insolation isusually measured in sun-hours (1 sun hour 1 kWh/ m2, about equal in intensity to

*In this repo rt, pa ragrap hs or calculationsset off from the rest of the text by rows ofasterisks are por tions of a typ ical w orkedexample of a water-pump ing system d esign.

sunshine on a clear su mmer day at solarnoon).If water needs stay the same year-round ,solar design calculations shou ld be based onthe mon th w ith the lowest insolation levelsto ensure adequ ate water throughou t the

year. If water is to be used for crop irriga-tion, the mon ths with th e lowest insolationoften correspond to those in which cropdem and for water is lowest; thu s, calcula-tions do not need to be as conservative asthose for drink ing water only. If wa ter con-sump tion varies throughou t the year, thesystem design should be based on the ratioof water requ ired to insolation available. Themon th in wh ich this ratio is largest willdeterm ine the PV array size. When d eter-mining irrad iation for a specific location,data should be obtained from the nearestavailable meteor ological station andallowan ce mad e for any known local climatedifferences.

Or ientat ion and Locat ion o fPhotovo l ta ic Ar raysOrientation refers to the position of a sur-face relative to true south . Although ph oto-voltaic arrays that face within 15 of truesouth receive alm ost full sunshine, anyun obstructed , generally south -facing surfaceis a poten tial array location. In man y a reas, a

slightly w esterly orienta tion is preferable todu e south to avoid morning haze or fog. Anarray should not be shaded by obstructionslike buildings or trees. Obstructions thatcause no interference in sum mer may castlong shadows when the winter sun is low inthe sky.

Ti l t of Photovo l ta ic Ar raysModule surfaces tilted at a right angle tothe sun s rays catch the most sun shine perunit area. An angle equal to the local latitudeis the closest app roximation to that tilt orslope on a year-round basis. This means thatthe ideal pitch of an array for year-round

operation is about the same as the num ber ofdegrees of local latitude. If the water needsare not the same throu ghout the year, a high-er or lower array -tilt angle m ay be advan ta-

9


18/67

IJ

5

L-4

Yo

Fge5WneInaoCos

1


19/67

geous and lead to better system perfor-man ce. For example, if the summ er monthshave the highest water needs, an array tilt of15 less than the latitud e ang le is recom-mended . Similarly, if the winter mon thshave the highest w ater needs, increasing thetilt by 15 shou ld be considered .

The da ily total insolation incident on asouth -facing surface tilted at an angle equalto the local latitude du ring the winter seasonis show n in Figure 5. A set of insolationava ilability maps for all seasons of the yearand for three tilt angles is contained inApp endix A. This seasonal value will beadequ ate for preliminary design and costingpu rposes. Note that the num ber of sun-hou rs at a site is different from the totalnu mber of hou rs the sun is shining. Theworldw ide yearly avera e insolation is 5

Psun-hours (or 5 kWh/ m / day). Base yourdesign on the site closest in both d istanceand climate conditions to your own .

* * *X-* *

The hyp othetical village receives 5 sun -hours/ day during the winter. Based onFigu re 5 the village could be located in cen-tral Africa, north-central South America, etc.******

Determin ing Peak Water F lowAs mentioned above, insolation is mea-

sured in sun -hours. If, for examp le, 5 sun -hours/ day are available at a site, this doesnot mean that the sun p rodu ces 1 full sun-hour for 5 hours. In actuality, the sun pro-du ces less than 1 full sun for a periodlonger than 5 hours. The maximum requiredwater flow in liters/ h will be app roximatelythe systems requirement divided by thenum ber of sun-hours. Dividing this figureby 3,600 seconds/ hour gives the maximumexpected water flow in liters/ s.

******

Since the villages pro jected grow threqu ires that 9,200 liters be pu mp ed eachday, and 5 sun-hours per day of insolation isava ilable, the peak flow rate from the systemw ill be 9,200 liters/ 5 sun -hours = 1,840liters/ h = 0.5 liters/ s.

******

The next step is to determine wh ether thevillage well is capab le of pr oducing thatflow.

Water Product ionThe amou nt of water prod uced by thewell, like the amou nt of water needed by a

village, is one of the most importan t factorsin the design of a pu mp ing system. A cor-rectly operating pu mp ing system should notexceed the wells prod uction. For examp le, ifa well can prod uce only 0.5 liter/ s, a pu mp -ing system capable of pu mp ing twice thatamou nt will only pu mp the well dry. Forthat reason, and for future planning, it isimportant to know how mu ch water a wellcan produ ce. (In the illustr ative examp le, theprod uctivity of the well is presum ed to beknown . If new wells are required, thehyd rology of the site mu st be assessed.)

There are techniques commonly used todetermine the amou nt of water a well canprod uce. The method presented here willwork with both shallow, hand -dug wellsand deep-tube wells. To perform this test, aportable pu mp is needed that is capable ofpu mp ing at a rate at least as high as thepeak required rate. A means is needed formeasuring the water level in the well, eithera measuring rule or a line with knots tiedevery half-meter, for examp le.

First, measure the dep th-to-water in thewell (the static wa ter level). Install thepum p, and let it pum p water until the waterlevel stabilizes. Now , with the pu mp stilloperating, measure the dep th-to-wateragain. To ensu re that the level has stabilized,check it at several time interva ls. Now , mea-sure the water flow rate by filling a contain-er of known volume and measuring the timerequ ired to do so. For accuracy, perform this

11


20/67


21/67


22/67


23/67

In the previousnum ber of options

3.0 Systemchapter we looked at afor a PV water-tmm~irwsystem. We ~lso discussed the eval~ati~n o~

water requirements and the capacities ofexisting wells. In this chapter we will com-bine this information to choose the systemconfiguration and its compon ents. Thechoice of compon ents is dep enden t on theconfiguration. Several possible designs mayemerge. If the availability of compon ents isrestricted, then th e choice of configur ationsis limited to those that u se the availablecompon ents. Otherw ise, the choice can bemad e by several techniques in current use.

The basic design of a PV wa ter system isstraightforward . After the water need hasbeen determined the water source is testedfor its capacity, If the capacity is equal to orgreater than the need, selection of compo-nents begins.

Sizing Syst ems and Select ingEquipmentAs used in this guide, the term sizingmean s estimating the required size or capac-ity of all major ph otovoltaic system elements

so that the system will be able to satisfactori-ly serve the intended load.Potential users of PV-pow ered water-pu mping systems will want to estimate sys-tem size, perform ance, and cost in ord er togauge usefulness for a par ticular app lica-tion. Most methods to do this are complexand require computer programs to obtainpr ecise answ ers. This section outlines a sim-ple method intended to assist potential buy-ers in makin g rough estimates. These esti-mates should be with in 2070 of the truevalue for systems with some sor t of voltageregu lation. (Without voltage control, as isthe case for a direct-coupled system, arrayefficiency can be decreased by as mu ch as50%.)

This chapter contains two nomograph y(Figures 7 and 8) to assist the potentialbuyer, freeing this person from making theabove detailed calculations. These nomo-

graphy can be used to determine the size ofthe PV array requ ired to meet the hydrau licload du ring the critical d esign p eriod. Inadd ition, they generate the informationneeded to select m otor and pu mp size.. Ifafter read ing this section, you have ques-tions on this procedu re, there is a completeexample provided in Append ix B. Thenomography replace the following basicsteps in system sizing:

1. Calculate the hyd rau lic load Theaverage daily energy load in kilowatthours is calculated for the peak m onthin each season. The hyd rau lic load isdirectly prop ortional to the daily watervolume-head product.2. Estimate system losses Thisincludes mismatch effects and losses inthe wires, electron ic controls, pu mp ,and m otor. The losses in the pum p (40-6070) and motor (10-20%) dominate.3. Determine local insolation Theappr opriate amount of input solar radi-ation (insolation) to the ph otovoltaicsystem at the app lication site may beobtained from Append ix A for varioustilt angles. Average daily values forspring, summer, au tum n, and winterare included in the charts.4. Determin e the critical d esign p eri-od The available solar insolationvaries a s the seasons change, as may thewater r equirements or water level in thewell. For this reason, the wor st combi-nation of load and insolation mu st beidentified. It is this combination thatdeterm ines the size of the system.

This wor st combination can be identifiedby constructing a table of average seasonalinsolation and load values, and then deter-mining the season with the lowest ratio ofinsolation to load.This value is then u sed in the next step:

5. Calculate the array pow er Aftersteps 1-4 have been completed , thearray p ower is calculated . PV arrays a reusually rated by specifying their outpu tin watts under standard conditions of

15


24/67

1II

I

III

r

1

A

1

1

t

I

:P

/

/

Do................................+......

~.+

+

~

&@~o

/1

1

i

11

111

I

1

1

I

I1

11

1E15

2

1

1

DyHacEg

w~

Fge7HacEgNma

1


25/67

15

/I

1I

1

III

I

(.

.

*

Amear

temuum

2

1

1

A

PwRreWp

1I12

Fge8AaPwNma

1


26/67

100 mW/ cm2 insolation with the celltemp eratu re at 25C. This outp ut is,how ever, ad versely affected by temp er-atur e, falling app roximately 0.570 perdegree centigrade above this standard.Since norm al cell temp eratur e isapp roximately 30 C above ambient airtemp eratur e (which, in turn , is oftenwell above 25C), actual array outputmay be significantly less than ratedpower.

The starting point is Point A on theHyd raulic Energy Nomograp h. This waterrequirement mu st be specified by the user.Moving next to Point B, (the pu mp ing headat the well site) leads to point C (thehyd rau lic energy) Point D (an estimate ofsystem efficiency) leads to Point E (wh ichgives the daily required motor energy).Now, move to the Array PowerNomograph.

Starting at Point E (daily required motorenergy, as determined on the previousnomograph y), move to Point F (the insolationlevel). The value for insolation level can beobtained from local sources or App end ix A.Point F leads to Point G (the array pow errequirem ent). The motor rating shouldexceed the array pow er by 2570 to prot ectagainst m otor overload ing. Last, Point H(the ambient air temperature obtained fromlocal weather data) leads to the rated arraypower, WP, Point I.

*****

Followin g this proced ure, we obtain anarray size of 160 Wp for the hypoth eticalsystem.

*X-***

Centrifugal pum ps achieve maximumefficiency only wh en operating at designcapacity; when pum ping at less than designcapacity the efficiency is less. Since thepower outpu t of a PV system is constantlychanging, the long-term average efficiencyof a centrifugal pum p is hard to predict, butwill be less than its rated efficiency at

design capacity. In contrast, the efficiency ofa volumetric pum p is constant throughoutits operat ing range. The followin g sectiondescribes some of the interactions amon ginsolation, PV array output, and pum pingefficiency. The nomograph y accoun t forthese phenomena over the long-term aver-age.

The Effec t Of Varying SolarRadiat ion On Output

A major factor in sizing systems is thenatu re of solar rad iationit changesthroughout the day is affected by the weath-er, and chan ges from season to season.

This variation in input power does notgreatly affect systems that are able to deliverwater in prop ortion to the ambient solarintensity: they produce less water w hen thesolar level is low and p roduce more w henthe solar level is high. This evens out overtime.

This variation does affect pu mp ing sys-tems where w ater output is nonlinear withsolar intensity, e.g., the wa ter outp ut doesnot vary d irectly with the speed at whichthe pum p operates. The implications foroutpu t are complex. In add ition, they high-light the imp ortance of pr operly definingthe desired average daily water delivery inthe pu rchase sp ecifications, and requiring awell-defined acceptance test.Daily Variations The most important

characteristic of insolation is its diu rnal pat-tern. The expected pow er available to afixed flat-plate array ov er a 24-hour periodun der clear skies is represented by a hill-shaped curve that increases from sunrise tonoon and decreases thereafter until sunset.In general, volumetric pum ps are linear, andwhen coupled to a smart electronic con-troller, can fully utilize the available solarradiation. Centrifugal pum ps are nonlin-earefficiency and , hence, water prod uc-tion decrease when these pump s are operat-ed away from an optimum design condi-tion. Manu facturers should take theseeffects into account wh en quoting averageda ily flow rates. Figure 9 illustrates thesevariations. The preceding sizing nomo-grap hy (Figures 7 and 8) allow for this.

18


27/67

Weather Variations Cloudy w eatherconsiderably redu ces the amou nt of insola-tion, and thus the output of photovoltaicsystems. Solar insolation tables includeadjustments for weath er variations becausethese variations are norm ally present a saverage daily levels over a full month .Therefore, weather variations do not, on theaverage, affect the water delivery of linearsystems, e.g., volum etric pu mp s. How ever,centrifugal pu mp s are considerably affected.The accomp anying curve (Figure 10) showsthe drop in water outpu t with the drop insolar rad iation. When sizing ph otovoltaic-powered centrifugal pum ps in areas thatexperience weather conditions of generallydecreased or overcast insolation (fog, haze,du st, dispersed cloud s, or smog), u se a max-imum value of 80 mW / cm2 instead of 100mW/ cm2 for the daily solar profile. Thislower peak value at noon, coupled with theaverage daily insolation level (kWh/m2/ day) in the solar tables, should accountfor those weather variations.

gy striking a fixed array will vary seasonally.Note that these effects are du e only to annu -al changes in sun an gle and ar e distinct fromtypical seasonal changes in insolation du e tochanging weather patterns.

Figure 11 illustr ates the effect for array tiltangles equal to the latitude and equ al to lati-tud e plu s or minu s 15. In this figure, arrayoutputs are normalized and appear as frac-tions of the output from an array at latitudetilt.

The outpu t of a volumetric pum pdepends on the the amount of total dailysolar insolation striking the array. By con-trast, the output of a centrifugal pum p isaffected by the peak value of the solar inso-lation as well as by the amou nt. For a fixed-tilt-angle array, peak power w ill vary sea-sonally as the sun s angle with r espect to thearray changes. Figure 12 illustrates thiseffect.Purchase specification should requireman ufacturers to accoun t for this effect andth~ Other effects described in this sectionSeasonal Variat ions Since there are when presenting expected water outpu t. Theseasonal differences in the daily p ath of the techniques presented earlier did account forsun across the sky, the amount of solar ener- these effects.

100

75

50

25

0

\ OVERCAST DAY

SUNRISE NOON SUNSETFigure 9. Typical Daily Variations in Solar Radiation

19


28/67

100

75

50

25

0 0

TYPICAL PUMP NO. 1TYPICAL PUMP NO. 2

.

.

I25 50 75 100

PEAK INSOLATION DURING DAY (mW/cm2)

Figure 10. Relation between Peak Daily Insolation and Performance of Centrifugal Pumps1.2 I 1 I I I I I I I 1

1.1+>n1- 1.030$ 0.9aU$ 0.8w>Fy 0.7wK

0.610.5 1 I I 1 I 1 I I 1

JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DECTIME OF YEAR

Figure 11. Relative Energy at Various Tilt Angles

20


29/67

1.25

1.00

0.75

0.50

0.25

I I I I I I I I I I Ip/L 4OLUMETRIC PUMP(NORMALIZED YEARLYOUTPUT = 1.00)\ / \/ -~ \i \CENTRIFU&AL PUMP

(NORMALIZED YEARLYOUTPUT = 0.89) 1

I I I 1 I I I 1 I 1 I

Figure 12, Centrifugal Pump and Volumetric Pump Output(Array at Fixed Tilt Angle Equal to Latitude Angle)

Equipment Type vs. PumpingRequirementThe best type of equipment for a particu-lar pu mp ing app lication depend s on dailywater requirement, pum ping h ead, suctionlift, and w ater source (e.g., tube well or openwell). Generally, positive d isplacement

pum ps are best for low flows (under 15

m3/ day) and high heads (30-500 m).Submersible centrifugal pu mp s are best forhigh flow rates (25-100 m3/ day) and medi-um head s (10-30 m). Self-pr iming pu mp sshould be investigated for high flow ratesand low head s (und er 5 m). Figur e 13presents the most suitable pum p typ es forthe different ranges of head and flow w henusing photovoltaic pow er.

21


30/67

LlVolumetric pump200 /100 Al \ /w - ric or ac submersible IL

p- ~d~ self-priming,Hand pump size surface-mounted Io I 1 Io ;5 50 75 100

Daily f l o w, m3 / d a y

Figure 13. Pumpset Types vs. Pumping Regime

Speci fy ing System Per formance Next, Chapter4 allows the buyer toesti-mate the economic worth of the system. InUtilizing the information in this chapter in man y cases, this determ ination leads to theconjunction with the nomography and other prep aration of pu rchase specifications andcomp utational aids should allow a potential to the acquisition of one or more ph oto-buver voltaic-powered pum ping units.J . to determ ine the technical viability ofusing photovoltaic-powered pum pingsystems, and

q to estimate the size of the system.22


31/67

4.0 Cost and Ec onomic s o f Pumping System sDetermin ing the Cost-Effect ivenessof a Pumping System

To be cost-effective, the PV option mu st beless expensive (over the systems life) thanfeasible mechanical pu mp ing alternatives,such as diesel, wind , or other electric sys-tems. In many remote areas, hand pu mpswill be the norm for village water sup ply,and the costs of hand pum p use will be thebaseline against which other mechanical sys-tems are compared.

In order for PV-powered pum ping sys-tems to come into wid espread use, theymu st be attractive to users and investors, aswell as to policy makers. For examp le,although a policy maker may p lace a highprem ium on foreign exchange savings, th eindivid ual farmer w ill be more concernedwith the mon ey saved on fuel (based ondelivered local fuel prices) and by suchissues as reliability and availability of pow eror fuel. This is par ticularly imp ortant inmore remote ar eas, wh ere logistical con-cerns, i.e., delivery costs for fuel, systemdown time caused by missing spare parts orlack of trained repair personn el, etc., canoften result in a pum ping system beingabandoned.Measur ing Cost-Effect iveness of aPumping System

Although there are several acceptablemeasur es of econom ic cost-effectiveness, themost objective and wid ely used by largeorganiza tions is the life-cycle cost (LCC)analysis. We will also keep tra ck of initialcapital, because this measu re is also impor -tant. In practice, w hen the pu mp ing systemis to supp ly drinking water, it is most im por-tant to establish the compa rative life-cyclecost of PV versus other p um ping systems,because the economic benefits of sup plyingdr inking water are difficult to quan tify. Forexample, if both a diesel and a PV pu mp canreliably furn ish the same quan tity of water,it is safe to assume that they p rovide equal

benefits. In this case, the lower cost option ispreferred.In LCC analysis, the net present value(NPV) of all the capital and recurr ing costsfor the test project (in this case, PV-pow ered

pu mp s) is compar ed to the NPV of all thecosts of comp etitive pr ojects. If the NPV ofcosts of PV-pow ered pu mp ing is less thanthe costs of the alternatives, PV should befirst choice for the power source.

For irrigation systems, the benefitspotential increases in agriculturaloutp utare quan tifiable, that is, an add i-tional volum e of water translates into a larg-er herd of livestock or add itional hectares ofcrops und er cultivationitems that have ameasurable market value. How ever,attemp ting to measu re these benefits isbeyond the scope of this docum ent, sincebenefits to crop and livestock prod uctionvary wid ely with local circum stances. Inthese circumstan ces, it mu st be shown boththat the pu mp ing system selected is the leastcost option and that the value of increasedyields (benefits) more than offsets th e add edcost of the pu mp ing system. The value ofthese ben efits over th e life of the project iscalculated in the same m anner as the costs,i.e., the NPV of all the annu al benefits is cal-culated and compared to the NPV of thecosts. In this chapter, step-by-step instru c-tions are prov ided for evaluating costs. InApp end ix B, a worked example of systemcost evaluation is provided via a nomo-graph , eliminating the separate step s.

Measur ing L i fe-Cycle Costs of aWmping System

A pum ping system will last a certain timebefore it needs replacement. In a PV system,for example, the pan els sh ould last 20-30years, wh ereas the pum p may have to berep laced every 5-10 years . The life of thesystem is the life of the componen t with thelongest replacement interval (the mod ules inthis examp le). The LCCS are the initia l costof the complete, installed system in year O,

23


32/67

Table 5Cost, Discount, and NPV Examples

Year cost ($) Discount Factor NPV ($)o 100 1/1 1 0/1 = 1001 110 1/1.1 110/1.1 =1002 121 1/(1.1)2 121/(1.1)2=100

plus a replacement pu mp (with installation)in year 10, plu s annua l operation, repa ir andmaintenance expenses.For an irrigation examp le, the life-cycle

benefits can be measu red in terms ofincreased agricultural prod uction in each yearof the pum ping systems life (for this examp lethe minimu m life is assumed to be 20 years).

Benefits and costs are likely to occur at dif-ferent points in time. The economic methodfor mak ing future costs of benefits directlycomparable to those that occur tod ay is toapp ly a discount rate to all future costs andbenefits. For example, with a 10% discoun trate, this means that a $100 cost today may beconsidered equivalent to a $110 cost incurred1 yr from today, or a $121 cost incurred 2years from today etc. This is because the cap i-tal, when otherw ise invested, w ould p rovidethe investor with add itional funds over futuretime. Alternatively, each of the costs has anNPV of $100.

Mathem atically, NPV = C/ (l+d)Y wh ereNPV = net pr esent value, C cost at year y, d= discount rate, and y = year in which the costoccurs. For the above example, the NPV ofyear 2 cost is NPV = 121/ (1.1)2 = 121/ 1.21 =100. The relationship amon g cost, discountfactor, and NPV is shown in Table 5.Note that the discount factor (10% / yr in the

present examp le) is based on a chosen rate ofreturn (after inflation) of mon ies that couldhave been invested in an alternative finan cialend eavor. If this analysis were performedbased on an economy with an annual inflationrate of 10%, the discount factor wou ld be 20%to keep the net discount factor at 10Yo. A dis-coun t factor of 1070 (after inflation ) is com-

mon ly used for LCC ana lvsis. How ever, ahighe~ or lower value may be chosen, basedon the specific investors finan cial require-ments.This discussion assum es that the costs asso-ciated with the project follow the overall infla-tion rate. If certain costs are expected tochange at a different rate (fuel costs, for exam-

ple), it maybe advisable to app ly a differentialinflation rate to these items.

Cost Appraisal of a PV- Powere dPumping SystemThe following information is needed for thecost appraisal of a water-pu mp ing system:

Econom ic: Period of analysis

Technical:costs:

(usually ecpni to the lifetime of thelongest lived component)Discount rateDifferen tial inflation rates for cer-tain items (if any)Lifetime of each main comp onentin yearsCapital cost for complete systemCapital cost for replacement com-ponentsAnnual maintenance and repaircostInstallation costs

Capital and Installation Costs There arefour m ajor elements in the capital costs of aPV-powered water system:1. PV array mod ules2. Balance-of-system (BOS) comp onen ts(structures, wiring, control devices, etc.)

24


33/67

3. Water pump and motor4. Water storage and distribution networkNOTE: All costs given in this section aregeneral estimates to be used for project feasi-bility analysis only.

Since the storage an d distribu tion systemwou ld be the same for all pow er sources forthe water-pum ping projects, we will disre-gard it for the purposes of this analysis.Note, how ever, that a larger capital expendi-ture for the storage system may be requiredwith a PV system than for other types ofwater-pum ping systems. This is because ofthe recommend ed 3 sunless days waterstorage for PV systems.

PV mod ules: Curren t (1987) costs from thefactory are about $8.75/ W for 50 or fewermod ules and about $7.50/ % for quantitiesff 100 to 250 mod ules. Even ower costs (aslow as $6.00/ WP) are available for largerprocurements but would usually requirethat the mod ules be bought in large singlepu rchase-order lots. Significant red uction inmod ule costs is anticipated in the future.(See your local supp lier for specific costs.)

The array BOS compon ents are those ele-men ts directly associated with the PV array.Experience indicates t hat these compon entsrepr esent abou t 159o of the PV mod ule costs,or $1.13 to $1.31 / WP.

Water pump s: Costs for pu mp s varydepend ing on the type required for theapp lication. The various types of pu mp s an dtheir respective selection criteria werediscussed pr eviously. The following esti-mates include all electrical and mechanicalhardw are required but omit pipework andother costs associated with the distribu tionsystem.

. Subm ersible centrifugal pu mp s: Use abase cost of $2,000.

. Surface centrifugal pu mp s: Use a basecost of $500 plu s $1 / WP. (Examp le: A200-WP system wou ld cost app roxi-mately $500 + $200 for a total pu mpprice of $700.)

q Lineshaft tur bine an d jack pu mp s: Usea base cost of $2,500 = $1 / WP.(Examp le: A 5-kWP system wou ld costap pr oxima tely $2,500 + $5,000 for atotal pump cost of $7,500.)

Costs of PV equipm ent are expected tostabilize over the next few years, w ith a pos-sible decline in pr ices thereafter as new tech-nologies become available. The BOS compo-nent costs w ill remain about the same.Future w ater pum p costs should go dow n asthe demand for PV-powered pum ping goesup worldwide.

Installation costs for PV systems, du e totheir requirement for array found ations,add itional shipp ing cost, labor to assemblethe stru ctures, etc., are higher than costs fordiesel systems and roughly equal to thosecosts for a wind-pow er system. As a guide-line, a figure of $0.50 WP of PV array can beused. For pu mp installation, the followingestimates can be used :

. Submersible centr ifuga l - $200 +o.50/ wp

q Surface-centrifu gal -$100 + 0.50/ Wpq Lineshaft tur bin~ or jack pu mp -$500 +

o.50/ wp******

For the hypothetical water pum ping sys-tem, capital bud getary costs wou ld be exti-mated as shown below.1.

2.3.4.

160-WP array@ $8.75/WP (delivered) $1,400Balance-of-systemcompon ents (1570 ofarray costs) 210Submersible centri-fugal pump 2,000Insta llation ($200 forpu mp + $0.50/ WP) 280TOTAL: $3,890This example is marginal between a sur-

face centrifugal pum p and a submersiblepu mp . The cost for the more expensive sys-tem is shown.

******

Note that for these analyses, installationcosts are based on local technical person nelperform ing installation tasks. Turnkey

25


34/67

installations, for wh ich the PV equipm entsup plier performs p re-installation site visits,actual installation/ checkout, and detaileddocum entation, will cause the installedcosts to rise. Note also that site work (welldrilling, clearing and leveling the land,trenching for pip es, etc.) is not included inthese installation cost estimates.

Opera tions and Maintenance (O&M)Costs The operat ing costs of a PV pu mpare nil. The cost of maint aining the pu mp isdifficult to estimate because of variations inlocal repa ir capabilities, but a figure of $20plus $0.02/ WP per year can be used as ageneral guid eline, dep ending on the systemsize and pump type used. Repair costs canvary greatly from year to year, depend ingon the nature of the repair and whether itcan be handled within the country con-cerned.

**%***

For the hyp othetical 160-W pu mp ingsystem, the O&M costs would Be app roxi-mately $20 = (0.02 o160) = $23.20 per year.

******

Pum p Replacement Costs Experiencehas shown that the pump and motor subsys-tem is likely to need r eplacement after about10 years, p erhap s earlier in a difficult ru ralenvironment. For pum p replacement costs,use the information for initial capital andinstallation costs given earlier.

******

For the hypothetical pum p system,rep lacement costs are $2,000 (capita l) + $200(installat ion) = $2,200.

***X-**

Table 6 lists these costs over a 20-year pro-jected system life, using the LCC methoddescribed earlier. The examp le used is thehypothetical village water pumping system.Table 6 uses a 10% discount rate an d, forsimp licity, assumes zero differential infla-tion. The discount factor is obtained by d =1 / (1 .l)Y, wh ere y = year. For examp le, thediscou nt factor in year 9 is 1/ (1.1)9 = 0.424.NPV is found by taking the sum of capital,replacement, and O&M costs mu ltiplied by

the discount factor for the same year.The overall step-by-step procedu re issum marized in Figure 14.

26


35/67

Yearo123456789

1011121314151617181920

Table 6LCCS for the Hypothetical PV Pumping System

ReplacementCapital Cost for Discountcosts ($) Subsytem O&M ($) Factor3,890 23.2023.2023.2023.2023.2023.2023.2023.2023.2023.20

2,200 23.2023.2023.2023.2023.2023.2023.2023.2023.2023.2023.20Total NPV

1.0.909.826.751.683.621.564.513.467.424.386.350.319.290.263.239.218.198.180.164.149

NPV($)3,913.2021.0919.1717.4315.8514.4113.1011.9110.829.84

858.148.137.396.726.115.555.054.594.173.793.454,959.91

27


36/67

STEP 1DETERMINE THE ARRAY PEAK WATTS ANDPUMP TYPE REQUIRED FOR THE SYSTEM

STEP 2DETERMINE THE INSTALLED CAPITAL COST

OF THE COMPLETE SYSTEM

STEP 3DETERMINE RECURRENT COSTS SUBDIVIDED INTO

O & M COSTS AND REPLACEMENT COSTS/

I

STEP 4DETERMINE NPV OF ALL CAPITAL

AND RECURRING COSTS

Figure 14. Procedures for Cost Appraisal of a Water Pumping System

28


37/67

Evaluat ing the Costs o f a Diese lPumping System

When comparing PV with diesel as anoption for a pu mp ing system, an NPV calcu-lation of intital replacemen t, and O&M costsshould be mad e for both systems to deter-mine wh ich is the most cost-effective overthe projected system life. This section dis-cusses the factors in costing d iesel pum pingsystems. Detailed design of diesel pu mp ingsystems is beyond the scope of this docu -ment.

Special Considerations 1. Minimu m Diesel Engine Sizing. D ue

to efficiencies of scale, d iesel engines su it-able for pu mp ing systems are usu ally 2.5kW (3.35 HP) or larger. This means that forpu mp ing systems requiring lower pow er,almost an y procured diesel engine will beun der utilized. As a result, diesel cap italcosts are higher than needed based onpow er requirements; how ever, this is partial-ly offset by lower fuel and m aintenancecosts, since the diesel engine will be able topu mp the required water in a shorter periodof time. Care must be taken in an NPV calcu-lation to ensure that the pu mp ing rate of thisrelatively large diesel pu mp does not exceedthe wells recharge rate. It may thu s beimp ractical to use a diesel en gine in somesmall-system app lications, and no economicana lysis is requ ired in this case.

2. Logistics of Fuel and Parts Sup ply.Compa risons between diesel and other sys-tems m ay take into accoun t costs for d ieselfuel and p arts based on both being readilyaccessible. However, remote pumping sitesare often removed from the nearest locationwhere p arts, fuel, and repair p ersons areavailable. Thus, fuel costs are escalatedbecause of logistics and transporta tionrequirements. More important, though, isthe d ifficulty in getting a qu alified repa ir-man to the scene of a disabled system.Importing a service technician from anoth erarea can substan tially raise the costs of a ser-vice trip. If the repairman requires an add i-tional p art, repair is often delayed for sever-al days, placing the villages wa ter sup ply injeopa rdy. The remote system is often inop er-able for days or weeks wh ile aw aiting fuel,

pa rts, or services. The costs associated withthese periods are difficult to quantify butshould be factored into any remote systemcosting ana lysis. This is also a pr oblem forPV systems, bu t the anticipated frequency ofmaintenance is mu ch less.

Based on these consideration s, we notethat the pro jected costs of a remote dieselsystem are increased by 100% over the samesystem located near a major urban area.

Comp aring Costs of a Diesel System A rigorous procedu re to estimate therequired size of the diesel pu mp is beyondthe scope of this docum ent, but for many sit-uations, the simplified procedu re givenbelow will be adequate.

On the assump tion that, for practical rea-sons, it wou ld not be acceptable to run adiesel pum p for more than 8 h/ day, thehyd raulic pow er rating of the diesel pump isobtained by dividing the peak month d ailyhyd raulic energy requirement, Eh, by 8,where

Eh = [9.8 q TDH (m) Daily WaterRequiremen ts (m3)] / 3,600.Assuming an average p um p efficiency of

50%, the required pow er rating of the dieselengine, pd, k giVen by Eh/ 4. Since the mini-mu m size of a diesel engine suitable for usewith pu mp ing systems is about 2.5 kW ifEh/ 4


38/67

operating conditions typical for rural instal-lations is 5 to 10 years, dep ending on operat-ing hou rs and th e quality of maintenance.For present pu rposes, an average life of 7years is assumed, after which time the com-plete system mu st be replaced at the originalcapital cost.

Assuming that the owner of the dieselpu mp m akes no charge for operating thesystem, oper ating costs (exclud ing fuel) arenil. Maintenance costs for a diesel pu mp ingsystem vary widely. Sometimes this can beestimated on the basis of run ning hou rs oras a prop ortion of capital cost. How ever,maintenance costs are largely independ entof size up to about 10 kW engine rating,since they are mainly determined by the fre-quency of servicing visits and the chargesmad e for each service. For diesel pum ps inthis size rang e, typical maintenance costs are$200o $900 per year.

To calculate the ann ua l fuel cost, AFC~,the total num ber of run ning hou rs isrequired, as given app roximately by:Td = 2 Eh, ~O~/ p&

wh ere Eh, ~Ot s the total annu al hyd raulicenergy requ iremen t in kilowatt-hou rs (i.e.,the sum of the daily hyd raulic energyrequirements). pd is the diesel engine rating,as determined above. This relationshipassum es an average efficiency of 509Z0 or theratio of hyd raulic pow er to engine-ratedpower.

The average fuel consump tion und er typi-cal operating conditions dep ends principallyon engine size, but other factors include thequality of maintenance, the ambient temper-ature, and the actual h ydra ulic load. If thecost of d iesel fuel delivered to the site isCf/ liter, and the average fuel consump tion isfd liters/ kW of engine rating p er hou r, theannual fuel cost is

AFCd=TdfdpdC~.Based on field observa tions, typ ical aver-age consump tion figures for engine sizes upto 10 kW are rating per h our of operation,

about 0.5 liter/ kWh of engine rating p erhou r of operation. Delivered fuel costs rangefrom $0.20 to $1.50 per liter. We take$0.30/ liter as the base assump tion for anear-urban area. The estimated average cost

of fuel over the period of analysis should beused for the calculation, taking into accountany expected real price inflation of fuel (i.e.,the inflation of fuel pr ices relative to genera linflation).

******

For our hyp othetical system,Eh 9.8 10 9.2 -0.25 kw h ,

3,600an d

pd = Eh/ 4 = 0.063,so a minim um -sized d iesel of 2.5 kW isrequ ired and the capital cost is 2.50$1,600 =$4,000. Now, total ann ua l hou rs of oper ationareTd = 20 Eh, ~O~/ pd 2 0.25 kWh

365/ 2.5= -75 h .No te that this relatively large d iesel

engine mu st operate for only 75 h/ yr to pro-vide the required water. It therefore wou ldpu mp water at a far higher rate than the PV-powered pu mp, possibly overpump ing thewell. It also represents a case wh ere diesel isnot a reasonable technical choice.Nonetheless, we shall look at the costs forcomparison purposes.

The annu al fuel cost isAFCd = 75 q 0.5 2.5

0.5= -$50.Since our example system will operate ata very low duty cycle, low maintenancecosts will be incurred . For the near-u rbancase, we will assum e $200/ year O&M costs.Table 7 is an LCC cost ana lysis for this sys-tem.NOTE: Discoun t and inflation assump -

tions as in PV case (Table 7). NPV is the sumof capital, rep lacement, O&M, and fuel costsmu ltiplied by the discount factor. Note thatthis analysis was don e for a near-urban site.For a remote location, the costs of dieseloperation wou ld be even higher.

For the same amount of pum ped water asin the PV case, the NPV for the diesel systemcase can be directly compared to that for an

30


39/67

equivalent PV-powered pu mp ing system.Thus, for this app lication, a PV-pow ered sys-tem wou ld be significantly more econom ical.The results of the comparison between PVand diesel pum ping systems will be influ-enced by changes in any of the key assump-tions used. Increases in fuel price sharp ly

increase the cost of pu mp ing with d iesel, rel-ative to PV. The use of a higher discoun t rateimproves the relative cost of the diesel,because most of the cost of the PV systemoccurs in the first year and is not sensitive tothe discoun t factor.

Comparat ive Costs of Othe rPumping SystemsThe proced ures outlined above for calcu-lating the cost for a solar or a diesel pu mpsystem may be app lied to other typ es ofpu mps, such as wind-powered pu mp s, ani-

mal-powered pu mp s, and hand pu mp s. It isparticularly important to make the compari-son for identical hyd rau lic du ties, i.e., thevolume of water supp lied per day to a com-mon point, for the same degree of reliability.When wa ter costs are calculated for differ-For the same reason (that recurren t costs ent pu mping systems and for the conditionsof PV are low), PV-powered systems are lit- relating to pa rticular app lications at speci-tle affected by rising futu re p rices, wh ereas fied sites, the results will be strongly dep en-the cost of diesel pu mp ing may be strongly den t on certain assum ptions. For examp le,affected. PV-powered pu mp s w ill, in general, provide

cheaper water for low-head and low-water-

Table 7LCCS for a Hypothetical Diesel Pumping System

Capital &Replacement Fuel DiscountYear costs ($) O&M ($) cost ($) Factor NPV($)o 4,000 200 50 1.000 4,250.001 200 50 .909 227.252 200 50 .826 206.503 200 50 .751 187.754 200 50 .683 170.755 200 50 .621 155.256 200 50 .564 141.007 4,000 200 50 .513 2,180.258 200 50 .467 116.259 200 50 .424 106.0010 200 50 .386 96.5011 200 50 .350 87.5012 200 50 .319 79.7513 200 50 .290 72.5014 4,000 200 50 .263 1,117.7515 200 50 .239 59.75

16 200 50 .218 54.5017 200 50 .198 49.5018 200 50 .180 45.0019 200 50 .164 41.0020 200 50 .149 37.25Total NPV 9,482.50

31


40/67

volume situations, provided the water tors plus the cost assumed for labor neededdeman d is reasonably well matched to the to operate them. An important point con-solar energy availability. cerning both animal-pow ered and handpu mp s is that their input pow ers are limited,

**X-*** and as the lift increases, the flow r atedecreases and the pu mp and borehole needto be re~licated. This is ua rticularlv im~or-Wind-powered pum ps may produce

cheaper water at sites where the averagewind speeds du ring th e period of maximumwater demand are higher than about 3 m/ s(10.8 km/ h).The costs of animal-pow ered pu mp s are

strongly depend ent on the assump tionsmad e regard ing capitaI costs, Iifetime,pow er input, and feeding costs. Handpu mp s are similarly depend ent on these fac-

tant if tke boreho le is e~pensive. Bore~olecosts for deep wells m ay exceed all othercosts.The final choice of a pu mp ing system

shou ld not be based solely on costs. Otherfactors, su ch as reliability and ease of main -tenance are also important; in these respects,PV-pow ered pu mp s offer significant advan -tages over diesel and hand pumps. Table 8overviews various costs for wind -powered,animal-powered, and hand pum ps.

Table 8Cost Data for Wind-Powered, Animal-Powered, and Hand Pumps

Pump TypeWind Animal Hand

Hydraulic output Depends on 21OW 36 Wrating of one wind regimepumpCapital cost 330/m2 of 300/animal = 240 to 320 perof pump rotor area 6.2fW of hy- pump unit =(1 m < dia draulic power 6.50 to 9/W of


41/67

5.0 Prepar ing a Request forThe proposed water-pump ing site hasnow been evaluated, and both water needsand the pow er required to prod uce that

water h ave been determined. How to esti-mate th e costs of a PV-pow ered water-pu mp ing installation and how to makeeconomic comparisons between PV-pow -ered and competing systems have been dis-cussed. If a PV-pow ered system is best foryour app lication, the next step is to beginthe procurement process.

Buying the components from individualvendors and assembling them on-site toyour own design specifications can be aprob lem. The difficulties of proper d esign,installation, and checkout, coup led withthe difficulty of securing a system war ran-ty, may make p urchasing a system on acomponent level inadvisable except for themost knowledgeable and experiencedusers.

The choices are two: (1) pu rchase a totalsystem designed by a qualified vendor andhave it installed and checked out for you or(2) perform the installation and test of avendor-designed and supp lied systemyou rself. The first of these choices, theturnkey system, is recommend ed for agen-cies with limited experience in PV pu mp -ing applications. Although capital costs fora turnkey system can be higher than for acustomer-installed system, these additionalcosts can be more than offset by the guar-antee of a prop erly installed and opera-tional system . If the turn key option is cho-sen, a training session is a good option tobe included as a prop osal requirement, sothat your agency can acquire the expertiseto install this type of system in the futu re.

In either case a perform ance specifica-tion mu st be prepared that requires designcalculations and performance guarantees.This techn ical specification is a criticalcomponent in procuring the system. Werecommend using the local standard pro-curemen t practices along with the technicalspecifications for the PV-pow ered pu mp ingsystem.

Prepar ing a

ProposalTechnica l Spec i f ica t ion

The technical specification, combinedwith standard procurement requirementsand terms, must be stated. Since the biddersdesigns are based on this specification, youshould incorporate, at a minimum , the fol-lowing information:

q Daily water needs (on a mon thly basis)and use of the waterq Type and qu ality of water sourceq Static water levelq Draw dow n (water level in the well) as afunction of flow ra teq Height (or pressu re) of the storage tanks

and the type of tanks usedq Type, length, and diam eter of requiredpipeworkc Average mon thly insolation da ta (over al-year period ) for the siteq Average monthly temperature data

(over a l-year period ) for the siteq Soil conditions (used to determ ine theoptimum array and tank foundations)If any of these d ata are un available to you,it shou ld be specifically stated, along withinstructions to bidders regarding the

assump tions they are to make regarding themissing data. Also, include any other datayou might have for the site. Occasionally, anapp arently unrelated item of informationmay provide the bidders with the means tooffer a more cost-effective system. As mu chinformation as possible regarding environ -men tal conditions shou ld be listed, includ -ing average and extreme values of ambientair temperature, relative hum idity, windspeed, water temperature, and water quality(physical and chemical). The possibility ofsand storms, hurricane winds, and otherenvironmental extremes should be men-tioned.

Remember, thou gh, not to include designchoices or equipmen t selections in the speci-fication. Doing so will comprom ise thebuyers position shou ld the un it fail to pro -du ce the required water outp ut. Instead, th e

33


42/67

technical specification shou ld specifyrequired performance only.Scope of Work The specification

shou ld includ e details of any special require-ments for packing for shipm ent, documen ta-tion, and insu rance un til the system is deliv-ered to the purchaser.

A list should be given of the work andservices to be carried out by others, forexample, clearance through customs, trans-por t to the site, construction of found ations,erection and s ystern startup , opera tion, androutine maintenance.Bidders shou ld be required to specificallystate any assumptions and deviations fromthe specification in their design an alysis.Acceptance Test The best protectionfor the buyer is to include an acceptancetest in the specifications so that the bidd er

knows final p ayment will not be madeun less the equipm ent passes the test.The acceptance test is of utm ost impor-tance and should be designed with carebecause the outpu t of a PV-powered pu mp-ing system is heavily d ependent up on many

variables, including weather conditions,ambient temperature, and time of year.Further, the outp ut of most PV-pow eredpu mp ing systems is nonlinear: a drop in thelevel of solar rad iation leads to a disp ropor -tionately greater drop in the amoun t ofwater being pum ped . For these reasons, theacceptance test should consist of a series ofmeasurements of pum p water outpu t as afunction of irradiance level and temperatu reto determine system performance und er thevariou s cond itions that will be encoun tered.

Qua lified Bidd ers After including theacceptance test in the technical specification,the next greatest protection is to buy th e un itfrom a bidd er wh o is active in the field.These manu facturers supp ly systems thatwor k. It is unwise to buy a system from aman ufacturer of limited experiencesuchmanu facturers do not yet und erstand whatlevel of experience is needed to make theproper choices in designing a PV-pow eredpu mp ing system. Includ ing criteria to quali-fy bidd ers will gua rd against inexperiencedbidd ers. Buyers sh ould follow the old adage,Ask the person who owns one.Bidders shou ld be requ ired to complete a

questionnaire to dem onstrate their experi-ence and resources to meet the requirementsof the project. The questionnaire shou ldcover such matters as experience in PV-pu mp ing technology and recommend edmaintenance requirements.

Warranty and Spare Parts The buyershou ld require a full-coverage war ranty fora period of time sufficient to assess thepumping systems acceptable performance.Typically, th is period is 1 year, but the periodcan be negotiated. Warran ties up to 5 yearsare common.

Buyers shou ld also request separate costinformation for an extended warranty peri-od of an ad ditional 2 to 5 years, at least. Thiswill allow the buyer to evaluate the cost ofthe warranty separately.

The supp lier should be asked to include alist of requ ired tools and spare par ts for theextended warranty period, plus extra num -bers of small items that may be lost duringinstallation or maintenance (e.g., nu ts, bolts,cable clamps, etc.).

The supp lier should also be asked todetail in his prop osal the warranty periodand technical sup port after installation,including manuals. Especially important towar ranty service is the availability of servicewithin the region, or at least in a timely fash-ion.Price and Delivery The bidd er should

complete a schedu le of prices covering themain items, including the design, m anu fac-ture, and testing of the complete system;transp ortation of materials from the factoryt o the point of delivery; spare parts andtools; prep aration of documen tation, trans-porta tion, and labor for turnkey installa-tions; and any other items. The currency andterms of payment may be specified or leftopen for the sup plier to complete. The sup -plier should also state the delivery period.

Evaluating Responses (Optional Recom-mendations) Each pr oposal receivedshould be checked to ensure that the systemoffered is complete, that it can be deliveredwithin the maximum delivery period, andthat an acceptable warranty can be provid-ed .Detailed Assessmen t The proposals thatsatisfy the preliminary evalua tion shou ld then

34


43/67

be assessed in detail und er the following fourheadings, w ith app roximately equal impor-tance being a ttached to each:1. Comp liance with the Specification. Theperformance of the proposed system shouldbe carefully assessed to ensure that it meetsthe requ irements of the specification.Justification for any deviations shou ld be care-fully evaluated.2. System Design. The suitability of thesystem for the intended use should beassessed, taking into account such matters asease of opera tion and mainten ance, generalcomplexity, reliability, safety features, lifetimeof individual components and parts subject towear and tear, etc. The adequacy of the sup-porting d ocumentation should also be consid-

ered. Emp hasis shou ld be placed on the fieldreliability of the system design being p ro-posed , since this can significantly impact thelong-term success of the water p um ping pro-ject.3. Capital and Life Cycle Costs. Besidescompa ring systems on the basis of initial capi-tal cost, a comparison should be mad e u singlife cycle costing, based on maintenance andrepa ir costs incurred du ring the life of the sys-tem.4. Overall Credibility of Supp lier. Theexperience and resou rces of the sup plier rele-vant to PV-powered pu mp ing technology indeveloping countries shou ld be assessed,together with the proposals for war ranty, after-sales service, training, and documentation.

35


44/67

Bibl iography1.

2.

3.

4.

5.

6.

7.

Small-Scale Solar-Pow ered 8. IrrigationPum ping Systems: Phase I ProjectReport, Sir William Ha lcrow & Partn ersin association with IntermediateTechnology Development Group Ltd.,World Bank, July 1981.Small-Scale Solar-Powered IrrigationPumping Systems: Technical andEconom ic Review, Sir William Ha lcrow& Partners in association withIntermediate Technology DevelopmentGroup Ltd., World Bank, September1981.

Small-Scale Solar-Powered PumpingSystems: The Technology, Its Economicsand Adva ncement (Report prepa red forWorld Bank under UNDP ProjectGLO/ 80/ 003). Halcrow/ I. T. Power,World Bank, June 1983.Solar Water Pump ing - A Han dbook, J.P. Kenna and W. B. Gillett, I. T.Publications, London, 1985.Village W ater Supp ly, W orldBank,Washing ton, DC, 1976.Small Commu nity Water Sup plies:Technology of Small Water Sup plySystems in 15. Develop ing Coun tries, I.R. C., The Hagu e, Aug ust 1981.Wind Technology Assessment Stud y(for UNDP/ World Bank ProjectGLO/ 80/ 003). I. T. Pow er Ltd., Februar y1983.

8. Crop Water Requirem ents, J.Dooren bos and W. O. Praitt, FAO, Rome,1977.9. Comm unity Water Sup ply and SewageDisposal in Developing Countries, Wor ld H ealth Statistics, Vol. 26, No. 11,1973.10. Small Scale Irrigation , P. H. Stern, I. T.Publications, 1980.11. Evalua ting the Technical an d EconomicPerformance of Photovoltaic Pum ping

Systems: A Method ology (Prepared forUSAID, Africa Bur eau ), I. T. Pow er,Washing ton, DC, 1985.

12. Field Performan ce of Diesel Pum ps an dTheir Relative Econom ics withWindpu mp s, I. T. Pow er, Reading, UK,1985.

13. A Gu ide to the Phot ovoltaicRevolution, P. D. Maycock and E. N.Shirewalt, Rodale Press, Emm aus, PA,1985.14. Meridian Report on Evaluation ofInterna tional Phot ovoltaic Projects, 1986,SAND85-7018, Sept. 1986.15. Solar Pum ping Upd ate, 1986, WorldBank and I. T. Pow er, Inc.

36


45/67

Lis t o f ManufacturersFor the most recent and comprehensive Copies of these docum ents are availablelist of U.S. man ufacturers, distribu ters, and from Linda Ladas, Solar Energy Industriessuppliers, see: Association, 1732 North Lynn Street, Suite

The Solar Source Book 610, Arling ton, VA 22209, U.S.A. Teleph oneSolar Electricity: A Director y of the (703) 524-6100.U.S. Photov oltaic Indu stry

37


46/67


47/67

Appendix AInso la t ion Ava i lab i l i t yThe following charts are included for usewh en information regard ing local insolation

is not available. It is suggested that prior tousing these charts, in-country meteorologi-cal stations, un iversities, governm ent min-istries or other information dep ositories becontacted to determ ine if they have morecomplete or accurate data.

The seasons men tioned in the titles foreach chart (spring, summ er, autu mn and

winter) are those for the northern hemi-spher e. In the souther n hemisphere, the sea-sons will be reversed . Also, the tilt angle,defined as the angle a t wh ich a PV array israised from the horizontal in order to cap-ture the suns rays, is measured with thearray pointing south in the northern hemi-sphere an d with the array pointing north inthe southern hemisphere.

A-1


48/67

nGKz

a o 20 40 60 24 loo 120 MO 160 180 160 1$o 120 100 60 60I

40_- 1 J/J+-l

55

u5055

-.E.5 -

20 ~ 70

70- . . _ _

40

6020 0 20 40 60 60 100 120 140 160 160 160 MO I I120 1(24JWINTER lilt Angle equals the IatItude mgle +15 20 60 40

Dady total solar radmtmn mcldent cm a t!ltec surface m kWH/rn2/day


49/67

c

0

c

R

*)

FgeA2naoAay(Lu+1TSm

A3


50/67

>A

20 0 20 40 60 so 100 120 140 160 180 160 140 m 100 so 60 w

Gcapw

~mc-.0s=Q1=-.

n-.* okm+. ,ul~ -7?4 45=@ 40M ~.

# - ,s

%0

3m~60

20 0 20 40 60 so 100 120 140 mo lea 160 la 120 100 m en .A .SUMMER Till AWk equals tb Iatit@e ang~ +150 -. . .Dady total solar radmt,on mcndent m a treed surf... I. kWH/m2/day


51/67

+

20 0 m 40 60 60 100 120 140 160 180 160 l-to 120 100 80 60 40

80 e a

7

40

M

60 LLL20 0

.

L 1 l\ x 1 I \ I t I I I I ! j I I Iw x. w-1~ v5.5- \ \ 80-60. 65 o

( < : 60 &o55 ,.0>. SD/ _ _ _ _ 5.-w

%0-5 -- - --

20 40 60 80 I100 120 140 160 180 160 140 120 100 80 60 40 AUTUMN -T,lt Angle equals the Mtude angle +15Da41y total solar rad!atm lmc,dent M a ttlted surface t. kWH/rn2 /day


52/67

l-md

t

.

I

FgeA5naoAay(LuTWne

A6


53/67

w(L

t

I

I

FgeA6naoAay(LuTSn

A7


54/67

. . --- . . ..- - IEI

!/ 1 I I I I I I &o.5-50

, In

I I I I I i I I ! r I I I ,

5

*

-H--k!&I I%!7. I I I

l,, l-, ,,ti, 2!315,

m- Fm. 4 0 I I I I I I I I60 1 1 I 1 1 1 , , 1 1 , , ,20 0 20 40 m 80 m 120 140 Im 1s0 160 140 120 100 &z 60 40

SUMMER -Tilt Arxje equals the lat#tude angleDa,ly total SOla, rad,at,.n ,nc,dent rx a t,lted surface ,. kWH/!n21day


55/67

>&l

20 0 20 40 60 80 100 120 w 160 180 160 140 120 100 80 60 40

60 a n

%9!p ) . *55 b.,60/ 1/[ /A / ,,,fl , , , , I A 1 I 1 I I I I I w& , , 1 1 1 1 1 I I I I ..,.I 1 n ,

, . 1 , 1 1 I 1 I I 1 1 ,.bT

r6.0f hY&O I I 1 1 1 1 / 8 D7M] ~ 7 / r T Kd5040 55- - / 5.5-5,0 5. 5.0-, 5 45

6020 0 20 40 60 80 100 120 I140 160 180 160 140 120 100 60 60 m AUTUMN - T,lt angle equals the Iat,tude angle .

Dady total SOlar rad,at,.n ,nc,de.t w a t,l!ed surface 4. kWH/rn2/day


56/67

0sMR0R

lJRQ

FgeA9naoAay(Lu-1TWne

A1O


57/67

I-+-Hw

-A

FgeA1OnaoAay(Lu-1TSn

A11


58/67

-nGc7

nra-.FQm

Y 1/ A 1 (-JQ-j~0 ,555

20

40

I I I I I I II I I I I I II ,ANl I

%04540

,I I I I I I IW31\ k IIfiv , , I I I I I I 2

1 t , , ,60 I I I I I I I I 1 I I 1 I I I 1 1 1 I 1 1 1 I 1 I I 1 I I I20 0 20 40 60 so too 120 140 mo 1S42 leo MO 120 100 so 60 40 SUMMER -Tilt Angle equals the IatttuJe angle -15

Daalv t.tal solar radat,cm mc,de.t cm a t,lted surface t kWHfm21daY


59/67

m o 20 40 m m


60/67


61/67

Appendix BSim ple Calculat ions of System Sizing, EquipmentSelec t ion, and Cost Evaluat ionA typical case is shown for the sample calculations. The following assump tions were mad e:1. Flow& Head :

Required total AverageDaily Flow Dynamic Ambient

Season (mS/day) Head (m) Temperature (C)Spring 11 12 24Summer 22 15 36Autumn 18 15 30Winter 15 12 14

2. Location: Phoenix, Arizona3. Array tilt ang le: latitud e -154. Discount rate: 7.5% per annum

Step 1: Determine wh ether pu mp is centrifugal or volumetr ic from Figure 13, p. 24. From thefigu re it is seen tha t the pum p will be of the centrifugal type.

2C0

100

50Em- 20!02 ,0MG.+!2!5Ed

2

1L H a n d p u mp s i z e L d c ~ e] f . p , j mj n g ,s u r f a c e - mo u n t e d

o I i 10 25 50 75 100

Daily flow, m31day

Pumpset Type vs. Pumping Regime

B-1


62/67


63/67

Step 3: Determine insolation from Append ix A charts. Tilt angle equals latitud e -15 deg. Thisshows the following:

InsolationSeason kW/m2/daySpring 7.5Summer 7.5Autumn 6.5Winter 4.6

140 120 100 80 60 40 20

SPRING SUMMER

AUTUMN WINTERB-3


64/67

Step 4: Determine array p ower at standar d conditions from Figure 8, p. 18. This showsthe following:Array Power

at Standard Conditions*Season (WATTS-PEAK)Spring 150Summer 390Autumn 360Winter 310

* Stand ard conditions are insolation equal to 100 mW/ cm2 and cell temp erature equal to 25 C.

1 I I I 11

78

Insolat[orkkWh/m2-day

2 0 100 1000Array Power Required, W (peak)

Array Power Nomograph

B-4


65/67

Step 5: Determine app roximately system cost and annualized system cost from the figur e below.The system cost exclusive of installation is app roximately $13/ watt. This yields an esti-mated system cost of $5,070 (exclusive of shipp ing and installation) and an annu alizedsystem cost of $500/ year at 7.5% discount rate.

2 0 0 0

$& 1 5 0 0(h1 -1 -< 5 0 0a%

oQu )1 - 5 0 0: 1 0 0 00: 1 5 0 01 -U)> 2 0 0 0conW 2 5 0 0Ni< 3 0 0 02~ 350( 3

//Y//// WWPISYSTEMUNIT PRICES15 2 0 2 5

I I Iw SYSTEM COST ($K)

\

~ .7.5%

10%DISCOUNT RATE-

Annualized System Costs for Specified Array Size System Prices and Selection DiscountRates (N =20 Years)

Sum mary: Thus, a centrifugal-type pu mp with an array of 390 watts rated at standar d condi-tions (100 mW/ cm2 insolation with cell temp erature equal to 25C) will meet theflow and head requ irements in all seasons. The systems estimated cost, less installa-tion and shipp ing, will be $5,070 with an annu alized cost of $500/ year at a 7.5% dis-count rate.

.* U.S. GOVERNMENT PRINTING OFFICE, 1995774125-02333B-5/6


66/67


67/67

Printing HistoryPrinted April 1987Second Printing, September 1987Third Printing, December 1988Fourth Printing, November 1989Fifth Printing, May 1990Sixth Printing, March 1991Seventh Printing, January 1992Eighth Printing, October 1992Ninth Printing, October 1993Tenth Printing, August 1994Eleventh Printing, January 1996

Water Pumping - The Solar Alternative

Documents

Transcript of Water Pumping - The Solar Alternative