The Design of a Typical Solar Water Pump

Solar water pumping system has become the preferred solution for the water use due to its ease of installation, no labor guard, low cost, zero carbon emissions and so on, and with the development of solar power technology and people's comprehensive requirements for water consumption, water quality, and water supply system reliability and environmental protection.

Main constitutions of solar water pump system

Essentially, the solar water pump system consists of solar panels, solar pumps, inverters, water pumps, pipelines, and water tanks. Due to the direct driving of the water pump, the storage battery is omitted, creating an extremely reliable system and reducing costs.

1. Solar cell module

Solar cell modules create direct current electrical energy directly from solar energy. Solar cells in a series-parallel array are made up of several panels. By using solar energy to create electricity, it provides the power necessary for pumping water throughout the entire system.

A solar cell module can be composed for individual use (for power and voltage) or several solar cell modules can be employed in parallel and in series for power and voltage requirements, thus producing a power supply array.

The solar cells increase their generating capacity proportionally to the intensity of sunlight. With increasing component surface temperature, the height of the components decreases slightly. Solar cells will also change according to the temperature, so when designing a solar panel in series, the negative temperature coefficient of the voltage must be taken into account.

2. Solar pump inverter

Direct output of solar cells typically varies from 12V or 24V to 48V. Solar power systems generate direct current energy which can be converted into AC power by using DC-AC inverters. In order to supply AC energy to appliances and devices, direct current energy is converted into AC power. In some cases, a DC-DC inverter is needed to convert power from one voltage to another, such as when converting power from 24V DC to 5V DC (note that it is not simply a simple buck). Such an inverter is needed in solar pump applications.

In a photovoltaic water pumping system, the solar pump inverter is crucial and what keeps the system running smoothly. PV pumps are regulated and controlled by inverters. The inverters convert DC power generated by solar cell arrays into AC power, drive the pumps, and adjust the output frequency based on the intensity of the sun in real time, maximizing the solar energy utilization.

3. Water pump, pipeline and reservoir

Pumps, pipelines and reservoirs are used for pumping, delivering and storing water.

A three-phase AC motor drives the water pump, which pumps water from a deep well, from rivers or lakes, injects it into the pool or reservoir, or directly accesses irrigation systems and fountains, and so on. Basically, there are two types of pumps, centrifugal pumps and volumetric pumps, based on their working principles. Gear pumps, screw pumps, and piston pumps all fall into the volumetric pump category. Centrifugal pumps are made up of an impeller and a volute structure that work by centrifugal force. A volumetric pump generates pressure due to the movement of its enclosure. From the entry port, the unit loads liquid, then moves between the entrance and the outlet to discharge liquids. In cycles, the unit discharges liquid in the same manner. There are many varieties of volumetric pumps, including vane pumps, gear pumps, screw pumps, plunger pumps, and more.

When connecting photovoltaic water pumps to grids, the pump choice directly affects the system's economics and stability. The most common type of solar water pump in a PV water pumping system is a submersible pump, which has a wide application range and a wide speed range, allowing for greater water output and daily working time.

Typical design of solar water pump system

Various regions and customers require different designs, so it is necessary to create different designs for each requirement. To ensure that the customer gets the most optimal solution that meets the user's needs, the design is designed around fully understanding the customer's needs.

1. Model selection procedure

• Make sure water pumps are performing correctly Water consumption is equal to the pump's flow times the vertical distance from the inlet to the outlet.
• Make sure it has sufficient power. Several factors are involved, including head, flow, outlet diameter, etc.
• Be sure to confirm that the inverter is functioning properly. The inverter is around one and one-third and a half times as powerful as the water pump motor.
• Be certain the panels are of sufficient power. Solar panels have a power of 1.3-1.5 times that of an inverter.
• How to select cables for the inverter and the water pump depends on their connection distance.

2. Obtain user demand - Daily water demand, head and diameter of the well

In order to offer the most effective solutions for the customer, detailed information about them must be acquired prior to configuring the solar water pump system.

The client information, for instance, should be understood beforehand as follows:

• Approximately 55m deep, 48m head height, and 200mm diameter, the well is situated in the basement of a residential neighborhood.
• A 5-hectare irrigated field will be constructed. In total, 27000 m3 of water are used during the irrigation period, which continues for six months.
• In terms of average daily hours of sunshine, there are about 5 hours each day.

About the head of water pump, the following is a bried introduction about it.

The head refers to the height at which the pump can lift water, usually expressed in H, and the unit is m.

Pump head = static head + horizontal delivery distance + loss head

An altitude difference between the pump's suction point and the high control point is defined as the static head. A static head refers, for example, to the altitude difference between a deep well and a high water tank that is being pumped up from that well to supply the high water tank. Figure H2 shows the horizontal delivery distance, as well as the static and moving heads in the figure. It is generally accepted that the head is counted as 1 meter for every 10 meters horizontally.head. There are usually six to nine percent loss heads, such as elbows, waterheads, etc, which are generally one and two meters above the ground.

Now see the specific selection of the solar water pump system configuration

1. Solar water pump

According to the known head and flow, a suitable water pump can be referred in a reversed manner: for examp, 1000 m3 water is pumped in 300 days, the local sunshine is 3.5 hours, and the system efficiency is 0.8.

Head: 110m Flow: 1000/（300*0.8*3.5）= 1.19 m3/h Pump selection: pump motor power 1.5kW, flow 1.2m3/H, head 115m.

2. Solar pump inverter

The inverter specification should generally be larger than the pump size. The 1.5KW water pump is equipped with 2.2KW solar pump inverter at least.

3. Solar panels

A solar panel's power to be chosen will generally be about one third to one half the water pump's power. So 1.5 x 1.4 equals 2.1 kW. Solar pump inverters work with a voltage range of 200V to 360V. A total of 2.24 kW can be obtained from eight of the 280W solar panels connected in series.