A typical system consists of four major components that together make up a solar water pumping unit capable of providing large capacities of water during summer and winter times. The major components are the PV panels, the solar pump, the controller, and the storage volume. Some systems use batteries as a storage volume while others use water tanks.
There are other minor components that are also used such as the mounting structure, wiring, piping, float switch and others.
The photovoltaic panel is the energy collector that receives solar radiations and converts them to electrical energy. This conversion process loses as much as 80% of the energy thus leaving us with an efficiency of 20% at best cases.
PV panels are considered the most important and effective items in the PV system, making up almost 80% of the overall system cost (assuming no battery storage needed). How many modules and how much collection area is a topic that will be studied under the system sizing section.
PV panels produce DC electricity, they are interconnected together in series and parallel to achieve the desired voltage and current.
The choice of pump type, size, and capacity depends on the application and its requirements. In principle, submersible pumps are used in wells deeper than 7 meters and surface are used for shallow wells.
Regardless of that, DC motors are widely applied in small applications with capacity not exceeding 3 kW, mainly applicable for small water demand such as gardening, landscaping, small volume livestock watering, etc. DC pumps are more efficient and more practical as they do not require an additional component to convert current to Ac for instance. This reduces costs and avoids additional efficiency drops.
Ac pumps are used for larger applications with capacities exceeding 3 kW, requiring an inverter to change the current that the solar panels produce (DC) to a current that is suitable for the pump (AC).
Latest 3-phase pumps use a variable frequency AC motor and a three-phase AC pump controller that enables them to be powered directly by DC power produced by the solar modules.
The controller plays a vital role in the system performance due to its ability to regulate the power production to match that produced by the panels with that required by the pump. It also plays a critical role in protecting the system by turning it off when the voltage is at inappropriate level, meaning too low or too high compared to the operating voltage range of the pump. This voltage protection role helps extend the lifetime of the pump and reduce maintenance requirements.
The sun is not always there, and even when it is there the flow rate doesn’t always meet the daily water demand. This requires the use of a storage volume that can benefit from the solar energy available all day long and store it either in electrical energy form in batteries or as potential energy form in storage tanks.
Batteries are only used when there is no possibility to have a water storage volume or when the volume is not sufficient. They increase the set up invoice by almost double and require frequent maintenance and replacement at least every 4 years. This makes water storage a more practical and efficient solution.
The storage volume and capacity requirements depends on the application and the pattern of water demand, but in principle the tank is sized with a capacity that is 3 times the daily demand on average . In some applications storage volume can go to a capacity of 10 times the daily water demand.