Solar water pumping system is a stand-alone system operating on power generated by Solar Photovoltaic panels.
The power generated by solar panels is used for operating DC surface centrifugal mono-block pump set for lifting water from open well or water reservoir for minor irrigation and drinking water purpose. The system requires a shadow-free area for installation of the Solar Panels.
This opportunity lies in two areas:
Stock and domestic pumping; and Bulk water pumping for irrigation.
Whether your pumping task is large or small, it is important that you approach solar from an informed position. Typically, diesel-powered pumps are used in areas where connecting to the electricity grid is difficult. Solar photovoltaic (PV) systems can be an attractive complementary energy source deployed alongside diesel pumps in areas with plenty of sunshine and where the cost to run power lines is high.
Photovoltaic systems have the benefit of being scalable, with capacity ranging from a few watts for applications such as automated farm gates or timers to hundreds of kilowatts for the homestead and farm sheds. Rather than having one large centralized system, a number of distributed PV systems can be deployed at pump sites.
Solar pumping systems are best suited for transfer operations (to pump water out of bore, for instance, or transfer it from dam to storage tank) in which pumps run continuously for most of the day.
Applications that require water to be pumped at night are not as well suited to solar-powered pumps, as storage solutions such as batteries and storage tanks can add significantly to the cost of the system. Although these energy storage solutions can be expensive, they allow for greater utilization of the PV system. Depending on the application, stocked water can be fed by gravity when there is insufficient sunlight to power the solar pumps, thus reducing diesel consumption further.
Due to the high capital costs that are still associated with solar systems, simple paybacks of seven to eight years are generally achievable only where pumping currently occurs for more than half the year. These costs are expected to reduce over the coming years as price reductions occur within the solar PV and commercial battery storage industries.
How does it work?
A typical solar-powered pumping system consists of solar panels connected to an electric motor that runs a bore or surface electric pump. A solar pumping solution available from your irrigation supplier will typically supply a DC (mains-powered) pump that is connected directly to the solar panel and does not require a DC/AC inverter. DC brushless motors also offer very high efficiency levels (over 90 percent). In cases where an AC (battery-powered) pump is already in place, an inverter is required between the PV panel and the motor to convert from the direct current generated by the solar panel to the alternate current required by the electric pump motor.
In the case of a solar-diesel hybrid system, a solar pumping system (PV panel plus pump) is installed to complement the existing diesel pump operation. The solar pump can either pump directly into the system to offset diesel pump operation during daytime, or pump water to a storage tank or reservoir (which is part of the solar pumping solution) so that water is also available on cloudy days and at night. This is illustrated in the figure below.
Key steps in sizing a solar pumping system
Determine the total dynamic head (TDH) of the system using flow-rate requirements (L/min), pipe length and diameter, and height between suction and discharge points. TDH = static head + dynamic head (line friction).
Determine the daily flow (m3/day) requirement and the expected number of weeks per year of pumping.
Depending on the water source, choose a surface or submersible (bore) pump.
Using manufacturer pump curves, select a pump of adequate size to meet head and flow requirements.
Knowing the power requirement and running time for the selected pump, determine the electrical load profile of the pumping operation to then size the solar PV system.
Refer to supplementary paper, solar photovoltaics.
Ascertain the capacity of the storage dam or tank by determining the flow rate the process requires and the storage time, which equals the amount of time outside daylight hours for which the pump normally runs. Consider using battery storage or combinations.