This document discusses solar powered water pumping systems for agricultural use. It describes the basic components, which include photovoltaic panels that convert sunlight to electricity, and pumps that use this electricity to pump water from wells or other sources. There are two main types of systems - battery-coupled systems, which store electricity in batteries to power pumps day or night, and direct-coupled systems that only pump during daylight hours and rely on water storage tanks to provide water after dark. The document provides details on components like pumps, mounting structures, controllers and water storage options to help farmers understand how solar powered pumping can provide an alternative to diesel generators for powering agricultural water needs.

1. Trakia Journal of Sciences, Vol. 3, No. 7, pp 7-11, 2005
Copyright © 2005 Trakia University
Available online at:
http://www.uni-sz.bg
ISSN 1312-1723
Feature Article
B. Eker*
Trakya University, Tekirdağ Agriculture Faculty, Agricultural MachineryDepartment,Tekirdağ,Turkey
ABSTRACT
Agricultural technologyis changingrapidly. Farmmachinery, farmbuildingandproductionfacilities are constantlybeing
improved. Agriculturalapplications suitable for photovoltaic (PV) solutions are numerous. These applications are a mix of
individualinstallations andsystems installedbyutilitycompanies when theyhave foundthat a PV solutionis the best solution
for remote agricultural needsuch as water pumping for crops or livestock. A solar powered water pumpingsystemis made up
of two basic components. These are PV panels andpumps. The smallest element of a PV panel is the solar cell. Eachsolar cell
has twoor more speciallypreparedlayers of semiconductor material that produce direct current (DC) electricitywhenexposed
to light. This DCcurrent is collectedbythe wiring in the panel. It is then supplied either to a DCpump, which inturn pumps
water whenever the sunshines,or storedin batteries for later use bythe pump. The aimof this article is to explainhow solar
powered water pumping system works andwhat the differences withthe other energysources are.
Key words:Agriculture, water, solar cell, pump
INTRODUCTION
It is commonto use diesel to power generators inagricultural operations. While these systems canprovide power where
needed1 there are some significant drawbacks, including:
• Fuel has to be transported to the generator’s location, whichmaybe quite a distance over some challenging roads and
landscape.
• Their noise and fumes candisturb livestock.
• Fuel costs addup, andspills can contaminate the land.
• Generators require a significant amount of maintenance and, like all mechanical systems, theybreak downandneed
replacement parts that are not always available.
There are alsomajor disadvantages inusing propane or bottledgas to heat water for pen cleaning or incropprocessing
applications, or

2. Figure 1. A range and solar system are side by side [1]
In general, there are two types of solar systems – those that convert solar energyto D.C. power andthose that convert solar
energyto heat. Bothtypes have manyapplications in agricultural settings, making life easier andhelping to increase the
The solar cellsina PV module are made from semiconductor materials. When light energystrikesthe cell, electrons are
knockedloose fromthe material’s atoms. Electricalconductors attached to the positive andnegative sides ofthe material allow
the electrons to be capturedinthe formof a D.C. current. This electricitycan thenbe usedto power a load, such as a water
pump, or it canbe storedina battery[2]

3. It’s a simple fact that PV modules produce electricityonlywhen the sun is shining, sosome form ofenergystorage is necessary
to operate systems at night. Youcan store the energyas water bypumping it intoa
Figure 2. A typical assemblyof solar cells [3]
Photovoltaic is a well-established, proventechnologywitha substantial international industrynetwork. And PV is increasingly
more cost-effective comparedwith either extending the electrical grid or usinggenerators in remote locations. The cost per
peakwatt oftoday’s PV power is about $7. Local supplyconditions, including shippingcosts andimport duties, varyandmay
add to the cost.
PV systems are veryeconomical in providingelectricityat remote locations onfarms, ranches, orchards and other agricultural
operations. A “remote” locationcanbe as little as 15 meters from an existing power source. PV systems can be much cheaper
than installing power lines andstep-downtransformers inapplications such as electric
fencing, area or buildinglighting, andwater
pumping– either for livestock watering or
crop irrigation.
WATER PUMPING
Water pumping is one of the simplest and
most appropriate uses for photovoltaic. From
crop irrigationto stock watering to domestic
uses, photovoltaic-poweredpumping systems
meet a broad range of water needs. Most of
these systems have the addedadvantage of
storing water for use when the sun is not
shining, eliminating the needfor batteries,

4. enhancingsimplicityandreducing overall
systemcosts. Manypeople considering
installing a solar water pumping system are
put off bythe expense. Viewingthe expense
over a periodof 10 years, however, gives a
better idea of the actual cost. Bycomparing
installationcosts (includinglabour), fuel
costs, andmaintenance costs over 10 years,
you mayfindthat solar is aneconomical
choice. A solar-poweredpumping system is
generallyin the same price range as a new
windmill but tends to be more reliable and
require less maintenance. A solar-powered
pumpingsystemgenerallycosts more initially
than a gas, diesel, or propane-powered
generator but again requires far less
maintenance andlabour [4]. The cost of solar
pumped water per cow ranged from$0.03 to
$0.15 per day. The cost per gallonof water
pumped ranged from$0.002 to $0.007 per
gallon.
Solar-Powered Water Pumping System
Configurations
There are two basic types of solar-powered
water pumpingsystems, battery-coupledand
direct-coupled. A varietyof factors must be
consideredin determiningthe optimum
systemfor a particular application[1].
Figure 3.Battery-coupled solar water pumping

5. system [5]
Battery-coupled water pumping systems consist of photovoltaic (PV) panels, charge control regulator, batteries, pump
controller, pressure switchandtankand DCwater pump(Figure 3). The electric current producedbyPV panels during daylight
hours charges the batteries, and the batteries inturnsupplypower to the pumpanytime water is needed. The use of batteries
spreads the pumping over a longer periodof time byprovidinga steadyoperating voltage to the DCmotor of the pump. Thus,
during the night andlow light periods, the systemcanstill deliver a constant source of water for livestock.
The use ofbatteries has its drawbacks. First, batteriescanreduce the efficiencyof the overall system because the operating
voltage

6. Figure 4.Direct coupled solar pumping system [5]
In direct-coupledpumping systems, electricityfrom the PV modules is sent directlyto the pump, which inturn pumps water
through a pipe to where it is needed (Figure 4). This system is designed to pumpwater onlyduring the day. The amount of
water pumpedis totallydependent on the amount of sunlight hittingthe PV panels and the type of pump. Because the intensity
of the sunandthe angle at which it strikes the PV panel changes throughout the day, the amount of water pumped bythis
systemalso changes throughout the day. For instance, duringoptimum sunlight periods (late morning to late afternoonon
bright sunnydays) the pump operates at or near 100 percent efficiencywith maximumwater flow. However, duringearly
morning andlate afternoon, pumpefficiency
maydrop byas muchas 25 percent or more
under these low-light conditions. During
cloudydays, pumpefficiencywilldropoff
even more. To compensate for these variable
flow rates, a goodmatchbetween the pump
and PV module(s) is necessaryto achieve
efficient operationof the system.
Direct-coupledpumping systems are
sizedto store extra water on sunnydays soit
is available on cloudydays and at night.
Water canbe stored ina larger-than-needed

7. wateringtankor ina separate storage tank and
then gravity-fedto smaller watering tanks.
Water-storage capacityis important in this
pumpingsystem. Two to five days’ storage
maybe required, depending onclimate and
pattern ofwater usage. Storing water intanks
has its drawbacks. Considerable evaporation
losses canoccur if the water is storedinopen
tanks, while closedtanks big enoughto store
several days water supplycanbe expensive.
Also, water in the storage tankmayfreeze
during cold weather.
Main solar powered stock watering system
components
A typical solar-powered stock watering
systemincludesa solar array, pump, storage
tank and controller [6], (Figure 5).
Figure 5. A typical solar-powered stock watering
system [1]
Solar Modules
Solar electric systems are sometimes called
photovoltaic systems. The word
“photovoltaic” is often abbreviatedPV. Most
solar panels, or modules, generate direct
current (DC) electricity. A group ofmodules
is called an array.
Mounting Structures
There are two ways to mount solar modules:
either on a fixed structure or on a tracking

8. structure. Fixedmounts are less expensive and
tolerate higher wind loading but have to be carefullyorientedso theyface true south(not magnetic south).
An arraycan easilybe mountedon a trailer to make it portable. A tracking arrayfollows the sun across the sky. A tracker will
add at least $400 to $800 to the cost of a system, but canincrease water volume by25 percent or more inthe summertime,
compared to a fixed array.
Pumps
DC water pumps in general use one-thirdto one-half the energyof conventional AC(alternating current)pumps. DCpumps are
classedas either displacement or centrifugal, andcanbe either submersible or surface types. Displacement pumps use
diaphragms, vanes or pistons to seal water ina chamber and force it througha discharge outlet. Centrifugalpumps use a
spinning impeller that adds energyto the water andpushesintothe system, similar to a water wheel. Submersible pumps,
placed downa well or sump, are highlyreliable because theyare not exposedto freezing temperatures, donot need special
protectionfrom the elements, anddonot require priming. Surface pumps, locatedat or near the water surface, are used
primarilyfor movingwater througha pipeline. Some surface pumps candevelophigh heads andare suitable for moving water
long distancesor to highelevations.
Storage
Batteries are usuallynot recommendedfor solar-powered livestock watering systems because theyreduce the overall
efficiencyof the system and add to the maintenance andcost. Insteadof storingelectricityinbatteries, it is generallysimpler
and more economical to install 3 to 10 days’ worthof water storage.
Controller or Inverter
The pumpcontroller protects the pump from high-or low-voltage conditions andmaximizes the amount of water pumped in
less thanideallight conditions. An ACpump requires aninverter, an electronic component that converts DCelectricityfrom the
solar panelsintoACelectricityto operate the pump.
Other equipment
A float switchturns a pumpon and off whenfillingthe stock tank. It’s similar to the float in a toilet tank but is wiredto the
pump controller. Low water cut-off electrodes
protect the pumpfrom low water conditions in
the well.
Designing and Installing Systems
Every pumping andstock-watering situation
is unique. The average consumer is likelyto
be intimidated bythe prospect ofsizing and
designinga solar pumpingsystem, andmost
people needthe assistance of a qualifiedsolar
dealer. Ingeneraldealers are eager to help.
Manywill provide a no-cost proposalbased

9. on a few simple questions that can be asked
over the phone. Ifthe price seems toohigh,
you can easilyget bids from other dealers.
In order to size anddesigna system correctly,
the dealer will want to know:
• how much water you need;
• when you needthe water;
• whether your water source is a stream,
pond, spring, or well;
• water available ingallons per minute
(gpm);
• well depth;
• how far the water needs to be pumped,
and with what elevationgain;
• water qualityproblems (e.g., silt or high
mineralcontent) that maydamage the
pump;
• how much volume is available in storage
tanks andhowthe tanks are arranged.
Installing a solar pumpis a complex task,
combining elements of electrical work,
plumbing, andheavyconstruction (often
includingearthmoving, pouring concrete, and

10. welding). Written instructions are not always
as complete as theyshouldbe. A backhoe or
tractor with a front-endloader is almost a
necessityfor some larger projects.
CONCLUSION
Since the increase inprice per increaseinunit
power output of a photovoltaic system is
greater thanthat for a diesel, gasoline, or
electric system, photovoltaic power is more
cost competitive whenthe irrigationsystem
with whichit operates hasa lowtotal dynamic
head. For this reason, photovoltaic power is
more cost-competitive when used to power a
micro irrigationsystemas comparedto an
overheadsprinkler system. Photovoltaic
power for irrigation is cost-competitive with
traditional energysources for small, remote
applications, if the total system designand
utilisationtimingis carefullyconsidered and
organisedto use the solar energyas efficiently
as possible. Inthe future, whenthe prices of fossil fuelsrise and the economic advantagesof massproductionreduce the peak
watt cost of the photovoltaic cell, photovoltaic power will become more cost-competitive and more common.
REFERENCES
1. Anonymous, Uni-solar, Solar energyproducescatalogandbrochures, USA, 2001. 2. Anonymous, Solar Cells EİE Department
of Researchon electricityapplications, Ankara, Turkey, 1992. 3. Anonymous, www.sandia.gov4. Eker, B and A.Akdogan,
Protectionmethods of corrosion onsolar systems, TMMOB MachineryEngineeringSociety, Mersin, Turkey, 2005. 5.
Anonymous, Solar Powered LivestockWateringSystems, http://www.utextension.utk.edu6. Helikson,H.J andOthers, Pumping
water for irrigationusingsolar energy, Universityof Florida, USA, 1995.