How do Solar Pumps work and what do I need?

How do Solar Pumps work and what do I need?


What is a solar pump.

A solar pump is a water pump that is powered directly by the sun. This allows you to have an electric pump to transfer water that can easily be installed in a remote area away from mains power and can also reliably operate to give you a constant water supply all year around.  The pump generally consists of 3 parts:

  1. The solar panels. These panels are mounted on a post or frame and provide the electricity for the pump to run.
  2. The controller and switches. The power is fed into a control unit. This unit ensures that a constant amount of the correct voltage of power is being fed into the motor to operate the pump. The switching part of the unit also turns the pump on and off if the pressure switch or float switch that is attached tells the pump if water is required or not.
  3. The pump. The pump consists of generally a floating submersible bore pump or a multistage pump on a float platform. Both pumps are designed to pump from the water they are floating in and supply the pipework that is attached.

The pump system is generally a fixed installation next to a dam, river or bore and the pump is either suspended in or floating on the water surface. This allows for a pump working at maximum efficiency to do the work required to deliver the maximum amount of water possible.

What can you use a solar pump for.

As technology has increased over the past couple of years, then there is a growing list of applications that solar pumps can be used for. As they are suited to providing a fairly constant supply of water without needing to connect mains power, then the main application for solar pumps is for stock and drinking/ house water in remote areas.


In these situations, the most common way to set the pump up is to have it pump from the water source into a tank on the highest point of the property. As it can fill the water tank during the day, then once there is a volume in the tank, gravity can take over and the water can be distributed to houses and water points with zero power required. This means that all that is required at the tank is a float valve and a poly or PVC pipe up to the tank to fill it and another pipe out to distribute the water via gravity. This system relies on the pipe from the pump up to the tank being sealed and the float valve working. When the tank fills the float valve shuts off and the pipe pressure increases. There is a pressure switch installed on the line up to the tank and when the line pressure increases as there is no water required, then the pump shuts down and waits for a signal that water is required. If the tank is really close to the solar pump, then you can utilise a float switch to turn the pump on and off, this works more effectively than a pressure switch but has it limits as you need to run a cable from the switch to the pump to make it work.

Another use that is becoming more common for solar pumps is working direct on line with a system to provide either irrigation or pressure direct to troughs or outlets. This has come from modern  pump systems that can produce much higher flows and pressures (up to 250L/min if needed) . This type of system though is always going to be a compromise and you will never get it to work effectively. The reason behind this is that water is only going to be available during daylight hours and can vary if there is cloud cover or if it’s during summer or winter. Having said that, if the system is used for irrigation or for stock water, then the highest demand for this is during the sunny and long days of summer and this is when the pump will produce its maximum volume of water and pressure. You might not achieve 100% of the irrigation effectiveness you are after but if mains power is either not available or very expensive to install (the majority of rural power installations) then this can work quite well. Especially if the pump is set up with a pressure switch and low flow protection, then there is going to be minimal damage done to the system if water is not required.

The other really useful application for solar pump systems is as a swimming pool pump. These rather smart little pumps made by Lorentz are designed to pump when there is sunlight and then not work when the sun goes down. They are there to circulate and filter the pool water in a domestic sized swimming pool and not cost anything to run. Considering that the average electric pool pump can use $700-$1000 worth of power a year, then a solar pool pump can quickly pay itself off. The only compromise here is that pool pumps also work in conjunction with the chlorinator unit on salt water pools to make chlorine. As the pump only works during the day and the volume of water being pumped can very a fair bit, then the water flow needs to be managed with a controller so that problems with chlorination don’t happen.  But like stock water and irrigation, the highest demand for a pool circulator pump is when the weather is hottest and sunniest, then this also coincides with the peak performance time for a solar pump so it will be a very effective solution.

How does a solar pump work?

A solar pump works by having the panels connected to the controller unit and this is connected to the pump. Most modern solar panels are 40V 200W and produce DC power at generally 40V per panel. If there is more than once panel in a string, then you will increase your voltage (40V +40V etc.) which will determine your potential pressure. Depending on the model and brand of pump and control unit, then there is a maximum amount of panels that can be connected in series as the excess voltage will damage the internals of the controller and the motor. In a Franklin Solar Sub Drive this is 350V, other units can be 100V to 350V. Once the raw DC power is fed into the control unit, it is either switched, regulated or fed into the motor via the motor lead and can power the pump. The input electricity into a solar pump is generally DC and can vary in voltage and current depending on brand, model and requirement.  The control of the pump is either cutting the power supply to the pump directly or more commonly allowing the controller unit (either a VFD or switch) to slow or stop supply to the pump and therefore slow down and stop the pump running. As we discussed before the control of the pump is generally from a pressure switch or a flow switch which are installed on the supply pipe or in a storage tank.

One of the main functions that a solar pump has to be able to handle well is low flow situations. This is because there is a wide range of requirements on the system during a normal day.

  1. Morning start up. When the sun rises in the morning and solar energy starts hitting the panels, then they start to produce voltage. The controllers on all pump systems will only start the pump flowing at a certain minimum voltage.
  2. Once the minimum voltage has been reached, the pump will then start working. At this stage, the pump is only running slowly as it is only producing minimum voltage. This means that the pump cannot produce much pressure and if it needs to pump up a high hill to a tank, then it will not be pumping any water. At this stage a low flow cut out (flow switch) may come into action to prevent damage to the pump. On a Mono or Grundfos pump, the low flow function is built into the pump electric itself and simply reads motor current draw and motor temperature to determine if it needs to shut down.
  3. Once sufficient sunlight is hitting the panels, then the pump can produce enough pressure to pump all the way up to a storage tank or do the pumping function that it needs to (ie watering trees or crops). Unless a pressure cut out or float switch turns the pump off, then the pump will continue to keep working through the day producing flow and pressure.
  4. In the afternoon, the opposite effect to the morning occurs and the pump gradually looses the ability to produce pressure and then finally insufficient voltage is created to operated the pump and the controller unit shuts the system down for the day.
  5. The low flow and low voltage cut out can also occur during the day if there is a large amount of cloud cover. In this case, the pump system shuts down until the sunny conditions return and then starts working.

A Grundfos CU200 Solar Pump Controller










A solar pump generally is a submersible or floating multistage or helical rotor pump. These types of pumps are used because they are very efficient and can produce a large amount of pressure for a very small amount of power usage. If a pump is submerged in the water, it has the added benefit of not losing any performance from having to suck water into it before pumping it. The pump is attached to a pipe which can then distribute the water from the dam or river up to the storage or water point.

What are the different types of pumps available.

There are two main brands of solar pump that we recommend and install for our customers, Grundfos and Franklin Electric.

Grundfos SQ Flex Cut away


The main pump in the Grundfos solar range is the SQ-Flex. This pump is the solar version of the popular and versatile SQ 3 inch pump. It is also a 3 inch submersible bore pump but it is also widely used in dams and rivers by floating it just under the surface. The SQ-Flex is a remarkable piece of engineering. Its motor is variable speed (as it speeds up and slows down depending on the power supply fed to it from the solar panels). It is also variable voltage and can operate on both AC and DC power. Yes if you want to you can simply plug the pump into the mains or a generator and it will work but it will also operate of the DC power produced form the panels. The IO101 isolator unit that comes with the kit, has a switch over device and an input lead to attach a generator to the system to operate it.

The beauty of a Grundfos SQ-Flex is that it is simple and the majority of the electronics are sealed inside the pump motor. In addition all that is required to control the pump is a float switch or reverse acting pressure switch. The CU200 control unit controls power supply to the pump and the internal pump motor control works out if there is sufficient voltage and operates the pump.


Depending on available sunlight, the SQ Flex range can deliver 25L/min up to 185L/min and very high pressures of up to 250m (2465kpa). They are designed as simple to install, simple to operate and on the off chance that something goes wrong they are easy to fix. If you want reliability and longevity then this is the option for you. Having said that they are not cheap, with a system costing anywhere from $8000 up to nearly $15,000 installed.


The other option we often utilise for our customers if the Franklin Subdrive Solar. The Subdrive Solar is a fairly recent entrant into the marketplace for Solar pumps. It is the DC/solar version of the very reliable and popular Subdrive VFD submersible pump system. While the systems are bulkier and have more complicated components to the Grundfos, their main claim is the large volumes and pressures available.  The Subdrive Solar has pumps that can run from 25L/min up to a whopping 400L/min.  There are also options that can produce up 340m head, that 3,350kpa ! These multi  panel high voltage systems can take input voltages up to 330V  and 3.5kw of solar power. With 2 options for motors, a 1.1kw and 2.2kw there are many different applications that can be matched to the Franklin solar Subdrive. They are also not a super cheap option but you get amazing value for money as you can move an incredible amount of water a long way simply with the power of the sun. So the system may cost from $7500 -$18,000 for the largest options there is the added bonus that the system costs absolutely nothing to operate and provide you with a reliable and constant source of water for your animals and crops.

As we have discussed, there are some amazing options available today for solar powered pump systems. If you would like us to assist you with selecting and installing a system on your property please give the shop a call on (08) 9721 3577 or send our staff an email.

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