Last edited: August 2018
All solar water pumping systems make use of solar panels which transfer the energy of photons (sunlight) into electrons (electricity). For a further description of the specifications, the brands and quality indicators visit the components page of a solar power system.
There is little to no difference between the solar panels which are used in a solar water pumping system compared to the solar panels used in a regular solar power system. The only aspect to pay particular attention to is the output voltage of the (array of) solar panels. This has to match the input voltage of the controller. The design software of the solar water pumping companies can inform which solar panels are most optimal to use.
Solar Water Pump Controllers
The pump controller is the most important part of the system. Some manufacturers integrate a large part of the controller into the pump itself, however, most have a separate box which houses the pump controller.
The function of the solar water pump controller is, amongst others, to:
- Modify the power from the solar array into power suitable for the pump
- Protect the pump from running dry (without water)
- Ensuring the right amount of power delivery from the solar panels to the pump
- Ensure the pump stops or starts at a certain thresholds in pressure / water level
- Collect data for remote monitoring
Which solar water pump controller you should use very much depends on the overall system design. Normally there is a recommendation for the purchase of the solar water pump and the controller from the same manufacturer.
Solar Water Pumping Controller Specifications
- DC or AC – Whether to use a DC or AC pump (and associated controller) depends on your application. Generally speaking, the smaller pumps are using DC (brushless) engines whereas the larger pumps are using engines that run on AC power. This means that the controller also converts the DC power from the solar panels to AC power.
- Voltage – The controller can only use voltage up to a certain level. To prevent damage, the solar modules need to be connected in parallel, series or a combination of both to get the right voltage.
- Output power – Most pumps have a controller which has a corresponding power output. For example, it is most cost-effective to use a 1500W controller for a 1500W pump.
- Other settings / function: In order for the controller to be capable of the above mentioned functions it needs to have the right input/outputs for meters and sensors as well as the right motor controllers and protections.
Solar Water Pumping Controller Brands & Quality
Getting a good quality solar water pumping controller starts with knowing your requirements for the system and having a good system design. Since the system design is such an integral part of the performance of the system, the manafacturer often provides a design tool.
That said, there are two companies which have the best reputation when it comes to solar water pumping systems. Lorentz has its headquarters located in northern Germany and has an exclusive focus on solar water pumps. Grundfos is located in Denmark and has a product portfolio which also includes more regular AC pumps. The solar water pumping systems from these companies have been distributed all over Tanzania which means spare parts and service is more readily available.
There are many manufacturers of controllers from China and India which have brought similar products onto the Zambian market, however, as of yet these suppliers do not seem to have gained the same reputation as above mentioned companies (even though it must be noted that the Lorentz and Grundfos pumps are often manufactured in China).
The Solar Water Pump
There are thousands of different solar water pumps on the market, even one manufacturer might have a hundred pump (configurations) or more. This is due to the many factors which determine whether a particular pump suits your needs (or not).
DC Solar Water Pump vs. AC Solar Water Pump
The first difference is whether the pump runs on DC or AC power. Generally speaking, the DC pumps are more efficient than AC pumps, which means that they will pump more water with the same amount of sunlight. Due to the low costs of solar panels, however, this difference is less important nowadays. There are also some pumps which can run both on DC and AC power.
Helical Rotor vs. Centrifugal Solar Water Pumps
Regularly, a solar water pump consists of two parts, the pump head, which houses the engine, and the pump end, which houses the pump mechanics. For very deep wells/boreholes helical rotor pumps are most often used, due to the high pressure they can deliver. Centrifugal pumps are the preferred choice when a high volume of water needs to be pumped.
- Lift – Lift is the total amount of meters which the water needs to be pumped up. The higher the lift, the higher the amount of energy required to pump the water and hence the more powerful pump you will need. Each pump will be able to support a lift within a certain range (for example between 20 and 60m).
- Flow – How much water do you need? Aside from the lift, a pump will also have a certain flow (in liters or cubic meters per hour). The lift and the flow are closely connected and a lift vs. flow graph can determine which pump would suit your needs best.
- Temperature – Since water temperature has an effect on the expansion of materials inside a pump, they sometimes have a specific temperature class. Using a pump with a temperature rating for cold waters in Norway in a pond in Zambia (or vice versa) will probably damage the pump.
Solar Water Pumps – Brands & Quality
As described above, Lorentz and Grundfos are the two market leaders within solar water pumping systems and have a good reputation in Tanzania. Lorentz is particularly strong with regards to DC-brushless pumps whereas Grundfos has had a focus on AC-powered pumps.
Balance of System
The “balance of system” is used as the term for all additional components which ensure the system works and get proper protection. It is normally possible to buy these components from the same manufacturer as the supplier of the pump system. However, they can also be bought from third parties.
The solar mounting system, the cables, conduit, breakers, grounding and lightning protections
All above mentioned components are also used in regular solar power systems, read more about them here.
Unless you are pumping to a reservoir or directly into a irrigation system, a water storage tank is mandatory. The water storage tank acts as a “battery” in the solar water pumping system. When it is not sunny for a couple of days, water from the storage tanks can be used. Due to this reason, a storage tank which is the size of 4 days of water consumption is the normal recommendation (unless a backup source of electricity is available).
Pipes and distribution
The pipes used in a solar water pumping system are normally an output from the design process. The wider the diameter of the pipes, the easier it is to pump water through them. This means you might be able to use a less powerful pump. Similarly, rusty old pipes create more friction with the water running through, which means you need a more powerful pump. In order to pump water from deep wells or boreholes, the pump needs to be capable of creating a high pressure. This also means that the material and thickness of the pipes are able to withstand this pressure.
Normally a solar water pumping system includes several valves with various functions. For example a one-way (or non-return) valve can ensure that water in a pipe does not flow back through the pump during the night. Service valves ensure it is possible to easily service the pump or other components of a solar water pumping system.
Sensors / Switches / Meters
The sensors, switches and meters ensure that the system performs according to your expectations. You can for example thing about:
- Float switch, which switches off the pump when a storage tank is full.
- Liquid level sensor, which switches off the pump when the water level is low.
- Pressure sensor, which can ensure the pump delivers a specific pressure as input to your irrigation systems.
- Sunsensor, which ensures the pump does not constantly switch on/off in poor sun conditions (increasing the lifetime of the pump).
- Water meters, especially for large systems it is smart to include a water meter (at several places) to be able to register leakages or theft of water.
- And many more, due to the wide variety of applications there are many different types of sensors, switches and meters which interact with the solar water pumping system.
Remote monitoring (and control)
Since solar water pumps are regularly fitted in remote locations and provide water for critical purpose (drinking water for people or cattle, or water for irrigation) it is important that the pump works every day (and is repaired quickly in case of failure).
A remote monitoring system is either integrated in the controller or can be connected to the controller. Aside from being able to see the status of the pump, it provides information about upcoming maintenance. With advanced systems it is also possible to remotely turn the pump (or a connected generator) on/off and change the settings according to which the pump operates.
Generator / Hybrid Controller
Integrating a generator into a system design would be only be necessary in the following cases:
- The water demand exceeds the average amount of water pumped with solar during a day. In this case, the generator ensures it is possible to pump from the borehole/well for a longer time.
- There is no possibility to store water. However, there is a need for water during times that the sun does not shine.
- The water supply is so critical that any failure would put people’s/animals’ lives at risk. A standby generator can provide backup power in extreme weather conditions or failure of the solar array.
The generator needs to be integrated into the system. This generally requires an additional module to switch between or blend solar power with generator (or grid) power.