How to size and select a solar water pumping system

Get a comprehensive step-by-step guide as we take you through the sizing and selection process of an SQflex in Grundfos Product Center.

When sizing Grundfos solar water solutions, it’s important that the pump is sized according to the application and the specific requirements that it’s intended for. In this module, we’re going to take a closer look at the sizing process of an SQFlex.

Based on a hypothetical example consisting of a realistic data profile, we will take you through a step-by-step guide to SQFlex sizing at But before we start, let’s go over an important consideration worth making before you begin the sizing process.

First of all, compared to traditional pumping systems, it’s not as straightforward to select a pump based on data sheets when you’re operating with solar water pumping systems.

This is because the day profile is based on the sun – and as we all know, there are more hours of sun during the summer than during the winter. Therefore, it’s crucial that the reference month for sizing is set to the month in which the water requirement is at its most critical.

So, let’s imagine that we’re using a submersible solar pump at a ranch and our intention is to provide water for livestock.

There are a few important parameters worth considering in order to complete the sizing process properly. This includes the installation’s location, the desired daily water production and the total dynamic head, which is the sum of the static lift above ground and the dynamic water level. In this example, we will size a system for watering livestock, but Grundfos Solar Pumping Systems can be used to provide water for potable water consumption and irrigation.

The location of our project is Seville, Spain.

The desired flow per day is 10m3 (2650 US gallons)

The total dynamic head is 110m (360ft)

The static lift is 10m

The dynamic water level is 100m  

And the type of pump is submersible

The system is able to determine whether it should be an SQflex or RSI system with an SP pump. There is no need to pre-determine this.

Based on this data, we have everything we need to size and select a system. So, let’s go to Grundfos Product Center and get started.

Once you’re on the main screen, you have the option to create your own free account by clicking the sign-in option at the top left… …and then selecting “create an account”. By doing so, you can store your own solar panels, allowing quick access to all your entered information. Creating an account is recommended but it is voluntary, and you can continue without doing so.

Click the dotted icon to open the quick links, … … and select “Grundfos Product Center”. Now we’re ready to begin. We’ll do this sizing by “Application”… …and then select “Solar water & pumping solutions” as the application area… Next, choose “Livestock watering with solar solutions” as the application, and automatically, “Livestock watering with solar solutions installation” appears as the installation type. Proceed by clicking the arrow to the right.

Let’s start with the location… As we start typing, we immediately get suggestions for locations… And we choose “Seville, Spain”. We’ll leave the power supply as “Solar only”, the pump type as “Borehole”, and the “size by”-option as “Water volume”.

Next is the water volume in cubic meters per day. In case you don’t know the daily water demand, a general rule is to multiply the hourly fixed flow rate by 6.

In this case, we leave it as 10, as this was what we decided earlier on. Now we need to fill out the static lift… …which we set to 10 meters, and the dynamic water level… ...which we set to 100 meters. Typically, a well-driller will provide you with information for static lift and dynamic water level.

We can also calculate any potential pipe system friction losses. This is particularly relevant if your static lift above ground is high or if you have to pump the water far, but in this example, we’ll leave it blank.

Now we must set the ”Month for sizing”, which is very important in order to meet our duty point. For instance, for an irrigation system, it should be set to the month in which growth peaks. For drinking water, we should select the month in which the solar irradiation is at its weakest, i.e. size the system for the worst conditions of irradiation. For example: for the Northern Hemisphere, this will be December - February. And for the Southern Hemisphere, this will be June - August.

In this example, we will leave the month as July.

Next, we need to select our module type. You are able to select two if you wish to compare two different types.

We’ll leave it at the standard model in this example – the GF270."

Now that all the main settings are in place, we are ready to see the sizing results. However, if you want to customise your sizing project even further, check out the available settings in the various drop-down menus – all of which can be customised according to your project.

Now, let’s head to the top and see the results by clicking the green “Start sizing” button.

Here, we’ll be given a list of sizing results. You can toggle through them to see various parameters.

Note that the results with the labels “Lower” are solutions that use fewer solar panels and deliver less water than required. The results with the labels “Higher” are solutions that use more panels and bigger pumps and deliver more water than requested. Let’s click on one of the results. "

Now we see all the different components of our watering system. We can also see pump curves and get options to see a graph of the daily water production, as well as the monthly water production during an entire year. Further down, the most important system parameters are listed. Finally, we can generate a PDF report by clicking the "Print PDF" button. From here, you can add the content you like – ensuring that the report has the exact information that you want to display.

We recommend you choose ‘Sizing result’ and ‘Accessories’ as a minimum. Now click Generate PDF to see the report.

The generated PDF is a great way to share your selection with colleagues or clients. That just about covers it.

In short, all the information we need to size a solar pump system at is the project’s location, the flow per day, the static lift and the dynamic water level. It’s that simple and easy.

Course overview

Modules: 3
Completion time
Completion time: 25 minutes
Difficulty level
Difficulty level: Intermediate