By Jeffrey R. Yago, P.E., CEM

In the last issue, there was anexcellent article by DorothyAinsworth on water pumpingusing mechanical windmills. Inthis issue I will address another formof free water pumping. There aremany remote applications where asolar-powered water pump is morecost effective than installing a con-ventional grid-connected AC pump.

I recently designed a solar-poweredpumping system for a local farmerwanting to pump water from a lakeup to a watering trough for cattle in adistant fenced field. We have alsodesigned larger systems to pumpdirectly from drilled wells up to ele-vated storage tanks, which providegravity-fed water back down toremote ranch buildings.

BBaassiicc ssyysstteemm ddeessccrriippttiioonnThese solar applications made eco-

nomic sense because the location wastoo remote to run a long power line.A solar-powered water system is oneof the easiest solar power systems toinstall, since you will not need a bat-tery or battery charging equipment.When the sun is shining, the systemis pumping, when the sun is not shin-ing, the system is offsimple.

By adding a storage tank andincreasing the size of the pumpingsystem, excess pumped water can bestored, which can continue to supplywater during the night or when itscloudy and the pump is off.

Low voltage DC pumps designed tooperate on solar power are notdesigned like 220-volt AC waterpumps. A DC water pump is designedto pump using the absolute minimum

of electrical power. Unfortunately,this also usually means a very lowflow rate, so having a storage tank oropen trough is essential.

Although the flow rate can be lessthan one gallon per minute (GPM) forthe smaller pump sizes, this smallflow will be fairly constant through-out the solar day (9 AM to 3 PM formost locations). This low flow ratecan still provide over 350 gallons ofwater per day from all but the deepestwell applications.

A solar module can be mountedalmost anywhere, but should face in asoutherly direction (for NorthAmerica). Most farm and ranch appli-cations should have the modules andpump controller mounted on a raisedpole to stay above snow drifts andpotential damage from animals.

A pole mount also allows easieradjustment of module tilt and east-

west orientation during initial setupto achieve the best overall year-roundperformance. For most applicationsthe tilt will be equal to your latitude.

PPuummpp ccoonnttrroolllleerrYour solar powered pumping sys-

tem should include a pump controllersuch as the one in the photo on page37. Although it is possible to connectthe pump leads directly to the outputterminals of the solar module, a con-troller provides much better pumpperformance and start/stop control. Itwill also avoid trying to operate thepump in a stalled condition whensolar output is too low.

Each residential-size solar modulewill produce a fairly constant 17-voltsoutput at almost any level of sunlight.However, the current output (amps)will be directly proportional to sunintensity. The pump will have a mini-

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Build your own solar-poweredwater pumping station

Local residents enjoying the solar water supplyat the open top drinking tank.

mum current draw when stalled andno pumping is taking place. As thevoltage is increased, pump rotationand water pumping is increased aslong as enough current is available.During less than ideal solar periods,the current output of the solar mod-ule(s) can be below the amp drawrequired for the pump to begin pump-ing. A solar pump controller will con-vert any excess voltage of the solararray to more output current.

The resulting lower voltage will notprovide the normal flow output fromthe slower turning pump, but it willallow reduced flow during thosehours the pump will normally bestalled. In addition to matching thevoltage and current load of the pumpwith the charging current and voltageoutput of the solar module, a solar-pump controller also includes wiring

terminals for normally open (n.o.)and normally closed (n.c.) switchcontacts. This makes it easy to add ahigh and low level float switch to thestorage tank, or a low-limit floatswitch for the well or pond providingthe water source.

The following information is takenfrom my book titled, AchievingEnergy IndependenceOne Step at aTime. You might find this book help-ful if you are considering installingyour own solar power system, and itgoes into much more detail thanspace allows here.

Table 1 will get you started by esti-mating how much water you willneed per day. Since your pump willnot work during cloudy weather, besure to have a tank or trough that canhold several days usage.

PPuummppiinngg bbaassiiccssAny well or pressure pump is

designed to provide a given flow ofwater (GPM) for a given pressure orlift (head). Pumping head is meas-ured in feet, and represents the totallift the pump can raise water from alow point to a high point. Whenmeasuring the distance a submergedpump must raise water, you do notstart with how far down the pump isin the well. You start by measuringfrom the above ground surface downto the lowest level the well water willbe during pumping.

For example, lets say we want tofill an open water tank (no pressure)that is on the top of a small hill. Weestimate that thewater level in thistank will be 3 feethigh above groundlevel, but the hill topis 50-feet higherthan where the wellis going to bedrilled. The well willbe 100 feet deep andthe pump will bepositioned 80 feetdown. We notice the

water level is only 30 feet below thesurface, but will probably drop con-siderably when the pumping startsunless it is a very fast refilling well.

If your well driller cannot providethis information, you will need toestimate how much draw-down thewell will have during pumping. For afairly fast recharging well, lets addanother 20 feet for this estimateddraw-down. For our example, the

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Table 1: Water usage *

Per Person (incl. washing) 75 gallons per dayBath 30 gallons per dayToilet 3 gallons per flushShower 3 gallons per minuteHorse or Cow (drinking) 12 gallons per day

Water Weight 8.33 pounds per gallonConvert Head (ft) to PSI Divide by 2.31

* From Achieving Energy IndependenceOne Step at a Time

A 24-volt DC SolarJack pump for a 4-inch well casing

Pole-mounted solar array during initial setup

pump would need to have a minimumlift of (30 feet + 20 feet to lowestwater level) + 50 feet elevation of thetank + 3 feet tank water depth = 103feet total pumping head. If you wantto convert feet head to pounds persquare inch (PSI) pressure, divide by2.31 which equals 45 PSI (103/2.31).If your tank will be closed and pres-surized, you will need to add thedesired tank water pressure to thispumps head pressure.

Instead of a deep well, you mayneed to pump from a lake or pond ata lower level up to a storage tank. Thepump lift estimating procedures weused in the above deep well examplealso applies. However, you measurefrom the lakes surface level, regard-less of how deep the pump will bebelow the surface.

When using a large body of wateras a water source, you will want tosuspend the pump off the bottomusing an underwater support or sur-

face floats to avoid plugging thepump intake with mud from the bot-tom.

Another common mistake to avoid,is do not oversize the piping. Formost applications, you will be pump-ing less than two GPM, and at thislow flow rate, these low flow solarpumps will not provide enough watervelocity through a large pipe to keep

suspended solidsfrom settling outonto the bottom ofthe piping. A typi-cal residential size-HP deep wellpump can pumpover six GPM,which produces amuch higher veloc-ity. For these largerflow AC pumps,larger pipe sizing isused to keep flowresistance low onlong piping runs.However, for alow-flow solarpump for applications requiring lessthan 100 feet of piping, a -inchPVC pipe size will probably workjust fine. For runs over 100 feet, Isuggest using -inch PVC piping. Ifyou need to pump water over 300feet, a 1-inch pipe size will lower the

high pressuredrop of thesmaller pipe, butyou may haveproblems withsediment set-tling in the bot-tom of the pipedue to the lowflow ratesinvolved.

R e m e m b e r ,the purpose ofthe storage tankor drinkingtrough is toallow a veryslow water flow

constantly pumping throughout theday, to build up a large volume ofwater to supply brief periods of highwater usage.

SSoollaarr mmoodduullee ssiizziinnggYou may want to consult the DC

pump distributor to determine the sizeof solar array that will be required foryour specific application. For high

pumping heads (feet of lift) or highflow rates, you may want to considerbuying a higher voltage DC pumpinstead of a smaller 12-volt DCpump. This will require using two ormore nominal 12-volt solar modulesto provide the higher voltage.

To get you started with solar arraysizing, it is rare that any solar-pump-ing application can get by with lessthan a 75-watt solar module, and larg-er applications will require two mod-ules for acceptable pump perform-ance. A 48-volt DC pump will requirea minimum of four nominal 12-voltsolar modules (4x12).

The installation shown in this arti-cle supplies water to a cattle drinkingtrough located 75 feet higher than anearby lake, which is 300 feet away.We used a 24-volt DC Solar Jack TMpump, two Kyocera 60-watt solarmodules, and 320 feet of -inch PVCpipe. The photos were taken in lateOctober after 6 p.m. and the panelswere no longer facing the setting sun,yet there was still almost -gallonper minute flow of fresh water up tothe trough.

PPiippiinngg hheeaadd lloossssIn addition to the elevation head

(feet) your pump must lift the waterfrom a low pond or drilled well up toa storage tank, it also must overcome

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Float switch in the tank to turn off the pump when tank is filled

Kyocera solar pump controller (cover removed)

the resistance to flow of the pipe. As Istated earlier, for small-flow DCpumping applications, if you oversizethe piping to reduce friction loss, youcould increase sediment problems atthese low flow data rates. Table 2

provides piping resistanceto flow in terms of head(feet). This makes it easy tocalculate total pump size,by adding this pipe frictionhead loss to the lift head weestimated earlier.

As an example, lets sayyou need to calculate thepiping pressure loss for a 2-gallon per minute flowthrough 250 feet of pipe. Ifwe use -inch PVC pipe,the loss would be 8.9 feethead (3.56 x 250/100). Ifwe increased the pipe sizeto -inch PVC, the losswould be 2.3 feet head(0.90 x 250/100). At thislow flow rate either pipe

size will work, unless your pumpcannot handle the additional pressureloss of the smaller pipe. As flow ratesincrease, a larger pipe may beunavoidable on longer pipe runs.

PPuummpp sseelleeccttiioonnTable 3 provides a size comparison

of several popular models of smallerDC pumps, and the relationship ofpump flow (GPM) to pump head(feet). Notice how the same pumpwill have a substantially reduced flowrate as this head pressure is increased.Since this is only a very limited list of

pump models and brands available,please consult the dealer for morespecific sizing information.

The manufacturers listed in Table 3offer many other pump models hav-ing many different combinations ofDC voltage, flow rate, and head orlift. Selecting the right pump for yourspecific application can reduce thesize and cost of the solar array thatwill be required to provide the power.Buying a low cost pump with poorefficiency will require a much moreexpensive solar array.

Jeff Yago is a licensed professional engi-neer and certified energy manager with over25-years experience in the energy conserva-tion field. He is also certified by the NorthAmerican Board of Certified EnergyPractitioners as a licensed solar installer. Hehas extensive solar thermal and solar photo-voltaic system design experience and hasauthored numerous articles and texts. Mr.Yagos most recent book; titled AchievingEnergy IndependenceOne Step At A Time,includes many solar system wiring examplesand is available from the Backwoods HomeBookstore or by calling 804-457-9566.

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TABLE 2: PVC piping head loss (feet) for each 100 feet of pipe

FLOW GPM -INCH -INCH 1-INCH0.5 0.27 X X1.0 0.99 X X1.5 2.09 X X2.0 3.56 0.90 X2.5 5.38 1.37 X3.0 X 1.92 X4.0 X 3.26 1.015.0 X 4.93 1.526.0 X X 2.138.0 X X 3.64

Note: X not recommended due to low velocity or highpressure drop.

TABLE 3: DC pump flow vs. head

PUMP MODEL DC Volts 25 ft. head 100 ft. head 200 ft. head

ShurFlo #9300 12 0.98 GPM 0.86 GPM X24 1.9 GPM 1.72 GPM X

SolarJack SCS 30 6.5 GPM X X60 X 5.1 GPM X75 X X 3.0 GPM

Dankoff #5218 48 2.7 GPM 2.1 GPM 1.8 GPM

Dankoff #5226 48 3.6 GPM 3.2 GPM 2.7 GPM

Note: Some DC pumps are designed to operate at several different voltages, producing higher flowas you add more solar modules.

Solar pump suppliers

Dankoff Solar Pumpswww.dankoffsolar.com

Backwoods Solarwww.backwoodssolar.com

Real Goodswww.realgoods.com