28-11-2012, 04:17 PM
Solar-Powered Livestock Watering Systems
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Introduction
Many livestock producers allow their animals free access to the rivers, streams and creeks that run through
rural Tennessee. Along these surface water sources are areas commonly referred to as riparian zones. A wellvegetated
riparian zone establishes a buffer between agricultural land and surface water sources. These buffer
strips filter and purify water as it moves across the riparian zone, reduce sediment loads and support soil stability
while providing additional benefits such as improved wildlife and
fisheries habitat. Over time, allowing livestock access to these buffer
areas can lead to poorly vegetated riparian zones with unstable,
erosion-prone stream banks.
Livestock producers are hearing more these days about the need
to protect water quality through riparian zone management. Allowing
the riparian zone to revegetate by removing or limiting livestock
access to these buffer areas is one method of protecting water quality.
However, the major problem most livestock producers face when
considering limiting cattle access to riparian zones is that these rivers,
streams and creeks are the only water source for their livestock.
Fencing livestock out of these streams dictates the need for an
alternative watering system. In areas where AC electric power is
readily available, an AC-powered pump is by far the best
choice for pumping water from the stream. More often than not, AC
power is not available. Since the stream is generally lower in elevation
than the fields bordering the riparian zone, gravity systems are usually not an option. Several alternative
pumping systems are available, including ram, sling and solar-powered pumps. While ram and sling pumps
require specific conditions to operate (i.e., adequate elevation head or stream velocity), solar pumps can be
operated at any sunny location within reasonable elevation limits between the watering tank and water supply.
For more information about alternative livestock watering options, see PB 1641, Selection of Alternative Livestock
Watering Systems.
How Does a Solar Water Pumping System Work?
Photovoltaic Panels
A solar-powered water pumping system is made up of two basic components. The first component is the
power supply consisting of photovoltaic (PV) panels (Figure 1). The smallest element of a PV panel is the solar cell.
Each solar cell has two or more specially prepared layers of semiconductor material that produce direct current (DC)
electricity when exposed to light. This DC current is collected by the wiring in the panel. It is then supplied either to a
DC pump, which in turn pumps water whenever the sun shines, or stored in batteries for later use by the pump.
Manufacturers normally rate voltage (volts) and current (amps) output from PV panels under peak power
conditions. Peak power (watts=volts x amps) is the maximum power available from the PV panel at 1000 W/m2 solar
irradiance (amount of sunshine) and a specified temperature, usually 25C (77 F). Typical output from a 60-watt PV
panel is shown in Table 1. The amount of DC current produced by a PV panel is much more sensitive to light intensity
striking the panel than is voltage generated. Roughly speaking, if you halve the light intensity, you halve the DC
current output, but the voltage output is reduced only slightly.
Solar (DC) Water Pumps
The other major component of these systems is the pump. Solar water pumps are specially designed to
use solar power efficiently. Conventional pumps require steady AC current that utility lines or generators
supply. Solar pumps use DC current from batteries and/or PV panels. Also, they are designed to work effectively
during low-light conditions, at reduced voltage, without stalling or overheating.
Although a wide range of sizes are available, most pumps used in livestock-watering applications are
low volume, yielding two to four gallons of water per minute. Low-volume pumping keeps the cost of the
system down by using a minimum number of solar panels and using the entire daylight period to pump water
or charge batteries. Some solar pumps are fully submersible, while others are not. The use of submersible
pumps eliminates potential priming and freezing problems. Most solar water pumps are designed to use solar
power most efficiently and operate on 12 to 36 volts DC.
Many solar pumping systems use positive displacement pumps that seal water in cavities inside the
pump and force it upward. Their design enables them to maintain their lift capacity all through the solar day at
the slow, varying speeds that result from varying light conditions. Positive displacement pumps include piston
and jack pumps, diaphragm, vane and screw pumps.
Centrifugal-type pumps that impart energy to the water using a rotating impeller are typically used for
low-lift or high-volume systems. Centrifugal pumps start gradually and their flow output increases with the
amount of current. For this reason, they can be tied directly to the PV array without including a battery or
controls. However, because their output drops off at reduced speeds, a good match between the pump and PV
array is necessary to achieve efficient operation.
Solar-Powered Water Pumping System Configurations
There are two basic types of solar-powered water pumping systems, battery-coupled and direct-coupled.
A variety of factors must be considered in determining the optimum system for a particular application.
Battery-Coupled Solar Pumping Systems
Battery-coupled water pumping systems consist of photovoltaic (PV) panels, charge control regulator,
batteries, pump controller, pressure switch and tank and DC water pump (Figure 2 ). The electric current
produced by PV panels during daylight hours charges the batteries, and the batteries in turn supply power to
the pump anytime water is needed. The use of batteries spreads the pumping over a longer period of time by
providing a steady operating voltage to the DC motor of the pump. Thus, during the night and low light
periods, the system can still deliver a constant source of water for livestock.
System Components
Pump Controller: The primary function of a pump controller in a battery-coupled pumping system is to boost
the voltage of the battery bank to match the desired input voltage of the pump. Without a pump controller, the
PV panels’ operating voltage is dictated by the battery bank and is reduced from levels which are achieved by
operating the pump directly off the solar panels. For example, under load, two PV panels wired in series
produce between 30 to 34 volts, while two fully charged batteries wired in series produce just over 26 volts. A
pump with an optimum operating voltage of 30 volts would pump more water tied directly to the PV panels
than if connected to the batteries. In the case of this particular pump, a pump controller with a 24-volt input
would step the voltage up to 30 volts, which would increase the amount of water pumped by the system.
Charge Control Regulators: Solar panels that are wired directly to a set of batteries can produce voltage
levels sufficient enough to overcharge the batteries. A charge control regulator should be installed between the
PV panels and the batteries to prevent excessive charging. Charge controllers allow the full current produced
by the PV panels to flow into the batteries until they are nearly fully charged. The charge controller then
lowers the current, which trickle charges the battery until fully charged. The regulator installed should be
rated at the appropriate system voltage (i.e., 12-volt, 24-volt, etc.) and the maximum number of amperes the
solar panels can produce. The regulator should be installed near the batteries, in accordance with the
manufacturer’s instructions. This usually requires only four connections: the PV panel “POS” and “NEG”
terminals and the battery “POS” and “NEG” terminals.
Direct-Coupled Solar Pumping System
In direct-coupled pumping systems, electricity from the PV modules is sent directly to the pump, which
in turn pumps water through a pipe to where it is needed (Figure 3). This system is designed to pump water
only during the day. The amount of water pumped is totally dependent on the amount of sunlight hitting the
PV panels and the type of pump. Because the intensity of the sun and the angle at which it strikes the PV
panel changes throughout the day, the amount of water pumped by this system also changes throughout the
day. For instance, during optimum sunlight periods (late morning to late afternoon on bright sunny days) the
pump operates at or near 100 percent efficiency with maximum water flow. However, during early morning
and late afternoon, pump efficiency may drop by as much as 25 percent or more under these low-light conditions.
During cloudy days, pump efficiency will drop off even more. To compensate for these variable flow
rates, a good match between the pump and PV module(s) is necessary to achieve efficient operation of the
system.
Selecting a Solar-Powered Water Pumping System
Cost
Cost is a factor that must be considered when selecting a solar pumping system. Total cost depends on
many factors, such as the type of system (direct-coupled or battery-coupled), daily water requirements,
pressure the pump must work against to supply the required water flow, complexity of the water delivery
system, etc. For example, low-volume solar pumping systems keep costs down, when compared to higheroutput
solar pumping systems, by using a minimum number of solar panels and by using the entire daylight
period to charge batteries or pump water. Producers who participate in cost-sharing programs offered by the
USDA Natural Resources Conservation Service and the Tennessee Department of Agriculture can greatly
reduce their portion of the system cost.
Livestock Water Requirements
The daily livestock water requirement is one of the key factors in the design of the solar water pumping
system. Size of the herd, pregnancy, lactation, animal weight, type of feed, physical activity and time of year
all have to be considered when determining the minimum volume of water the solar pumping system must
supply each day. The daily water intake by various types of beef cattle for each month of the year, shown in
Table 3, gives a good estimate of the daily water needs that must be met by the solar pumping system. For
example, an average cow/calf operation in Tennessee may need to water 30 cows and one bull year round. If
the cows have nursing calves from February through June and the calves are sold in October for finishing, the
pumping system must be designed to supply a maximum of roughly 740 gallons per day during July, the
hottest month of the year (Table 3.)
[attachment=41529]
Introduction
Many livestock producers allow their animals free access to the rivers, streams and creeks that run through
rural Tennessee. Along these surface water sources are areas commonly referred to as riparian zones. A wellvegetated
riparian zone establishes a buffer between agricultural land and surface water sources. These buffer
strips filter and purify water as it moves across the riparian zone, reduce sediment loads and support soil stability
while providing additional benefits such as improved wildlife and
fisheries habitat. Over time, allowing livestock access to these buffer
areas can lead to poorly vegetated riparian zones with unstable,
erosion-prone stream banks.
Livestock producers are hearing more these days about the need
to protect water quality through riparian zone management. Allowing
the riparian zone to revegetate by removing or limiting livestock
access to these buffer areas is one method of protecting water quality.
However, the major problem most livestock producers face when
considering limiting cattle access to riparian zones is that these rivers,
streams and creeks are the only water source for their livestock.
Fencing livestock out of these streams dictates the need for an
alternative watering system. In areas where AC electric power is
readily available, an AC-powered pump is by far the best
choice for pumping water from the stream. More often than not, AC
power is not available. Since the stream is generally lower in elevation
than the fields bordering the riparian zone, gravity systems are usually not an option. Several alternative
pumping systems are available, including ram, sling and solar-powered pumps. While ram and sling pumps
require specific conditions to operate (i.e., adequate elevation head or stream velocity), solar pumps can be
operated at any sunny location within reasonable elevation limits between the watering tank and water supply.
For more information about alternative livestock watering options, see PB 1641, Selection of Alternative Livestock
Watering Systems.
How Does a Solar Water Pumping System Work?
Photovoltaic Panels
A solar-powered water pumping system is made up of two basic components. The first component is the
power supply consisting of photovoltaic (PV) panels (Figure 1). The smallest element of a PV panel is the solar cell.
Each solar cell has two or more specially prepared layers of semiconductor material that produce direct current (DC)
electricity when exposed to light. This DC current is collected by the wiring in the panel. It is then supplied either to a
DC pump, which in turn pumps water whenever the sun shines, or stored in batteries for later use by the pump.
Manufacturers normally rate voltage (volts) and current (amps) output from PV panels under peak power
conditions. Peak power (watts=volts x amps) is the maximum power available from the PV panel at 1000 W/m2 solar
irradiance (amount of sunshine) and a specified temperature, usually 25C (77 F). Typical output from a 60-watt PV
panel is shown in Table 1. The amount of DC current produced by a PV panel is much more sensitive to light intensity
striking the panel than is voltage generated. Roughly speaking, if you halve the light intensity, you halve the DC
current output, but the voltage output is reduced only slightly.
Solar (DC) Water Pumps
The other major component of these systems is the pump. Solar water pumps are specially designed to
use solar power efficiently. Conventional pumps require steady AC current that utility lines or generators
supply. Solar pumps use DC current from batteries and/or PV panels. Also, they are designed to work effectively
during low-light conditions, at reduced voltage, without stalling or overheating.
Although a wide range of sizes are available, most pumps used in livestock-watering applications are
low volume, yielding two to four gallons of water per minute. Low-volume pumping keeps the cost of the
system down by using a minimum number of solar panels and using the entire daylight period to pump water
or charge batteries. Some solar pumps are fully submersible, while others are not. The use of submersible
pumps eliminates potential priming and freezing problems. Most solar water pumps are designed to use solar
power most efficiently and operate on 12 to 36 volts DC.
Many solar pumping systems use positive displacement pumps that seal water in cavities inside the
pump and force it upward. Their design enables them to maintain their lift capacity all through the solar day at
the slow, varying speeds that result from varying light conditions. Positive displacement pumps include piston
and jack pumps, diaphragm, vane and screw pumps.
Centrifugal-type pumps that impart energy to the water using a rotating impeller are typically used for
low-lift or high-volume systems. Centrifugal pumps start gradually and their flow output increases with the
amount of current. For this reason, they can be tied directly to the PV array without including a battery or
controls. However, because their output drops off at reduced speeds, a good match between the pump and PV
array is necessary to achieve efficient operation.
Solar-Powered Water Pumping System Configurations
There are two basic types of solar-powered water pumping systems, battery-coupled and direct-coupled.
A variety of factors must be considered in determining the optimum system for a particular application.
Battery-Coupled Solar Pumping Systems
Battery-coupled water pumping systems consist of photovoltaic (PV) panels, charge control regulator,
batteries, pump controller, pressure switch and tank and DC water pump (Figure 2 ). The electric current
produced by PV panels during daylight hours charges the batteries, and the batteries in turn supply power to
the pump anytime water is needed. The use of batteries spreads the pumping over a longer period of time by
providing a steady operating voltage to the DC motor of the pump. Thus, during the night and low light
periods, the system can still deliver a constant source of water for livestock.
System Components
Pump Controller: The primary function of a pump controller in a battery-coupled pumping system is to boost
the voltage of the battery bank to match the desired input voltage of the pump. Without a pump controller, the
PV panels’ operating voltage is dictated by the battery bank and is reduced from levels which are achieved by
operating the pump directly off the solar panels. For example, under load, two PV panels wired in series
produce between 30 to 34 volts, while two fully charged batteries wired in series produce just over 26 volts. A
pump with an optimum operating voltage of 30 volts would pump more water tied directly to the PV panels
than if connected to the batteries. In the case of this particular pump, a pump controller with a 24-volt input
would step the voltage up to 30 volts, which would increase the amount of water pumped by the system.
Charge Control Regulators: Solar panels that are wired directly to a set of batteries can produce voltage
levels sufficient enough to overcharge the batteries. A charge control regulator should be installed between the
PV panels and the batteries to prevent excessive charging. Charge controllers allow the full current produced
by the PV panels to flow into the batteries until they are nearly fully charged. The charge controller then
lowers the current, which trickle charges the battery until fully charged. The regulator installed should be
rated at the appropriate system voltage (i.e., 12-volt, 24-volt, etc.) and the maximum number of amperes the
solar panels can produce. The regulator should be installed near the batteries, in accordance with the
manufacturer’s instructions. This usually requires only four connections: the PV panel “POS” and “NEG”
terminals and the battery “POS” and “NEG” terminals.
Direct-Coupled Solar Pumping System
In direct-coupled pumping systems, electricity from the PV modules is sent directly to the pump, which
in turn pumps water through a pipe to where it is needed (Figure 3). This system is designed to pump water
only during the day. The amount of water pumped is totally dependent on the amount of sunlight hitting the
PV panels and the type of pump. Because the intensity of the sun and the angle at which it strikes the PV
panel changes throughout the day, the amount of water pumped by this system also changes throughout the
day. For instance, during optimum sunlight periods (late morning to late afternoon on bright sunny days) the
pump operates at or near 100 percent efficiency with maximum water flow. However, during early morning
and late afternoon, pump efficiency may drop by as much as 25 percent or more under these low-light conditions.
During cloudy days, pump efficiency will drop off even more. To compensate for these variable flow
rates, a good match between the pump and PV module(s) is necessary to achieve efficient operation of the
system.
Selecting a Solar-Powered Water Pumping System
Cost
Cost is a factor that must be considered when selecting a solar pumping system. Total cost depends on
many factors, such as the type of system (direct-coupled or battery-coupled), daily water requirements,
pressure the pump must work against to supply the required water flow, complexity of the water delivery
system, etc. For example, low-volume solar pumping systems keep costs down, when compared to higheroutput
solar pumping systems, by using a minimum number of solar panels and by using the entire daylight
period to charge batteries or pump water. Producers who participate in cost-sharing programs offered by the
USDA Natural Resources Conservation Service and the Tennessee Department of Agriculture can greatly
reduce their portion of the system cost.
Livestock Water Requirements
The daily livestock water requirement is one of the key factors in the design of the solar water pumping
system. Size of the herd, pregnancy, lactation, animal weight, type of feed, physical activity and time of year
all have to be considered when determining the minimum volume of water the solar pumping system must
supply each day. The daily water intake by various types of beef cattle for each month of the year, shown in
Table 3, gives a good estimate of the daily water needs that must be met by the solar pumping system. For
example, an average cow/calf operation in Tennessee may need to water 30 cows and one bull year round. If
the cows have nursing calves from February through June and the calves are sold in October for finishing, the
pumping system must be designed to supply a maximum of roughly 740 gallons per day during July, the
hottest month of the year (Table 3.)