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 of SQFlex sizing in Grundfos’ sizing programme – Grundfos Product Center. 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 have the following data:

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 on which 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.
Select the type of application and installation you wish to utilise.

From there, you need to select a host of important parameters.

We’ll start by changing our location to Seville, Spain.

Now you have to select your pump type.

As we’re basing this sizing on a submersible pump, select the ‘Borehole’ option as your pump type.

Next up, we’re going to enter the daily water volume. Choose to size by Water Volume. In this case, we’ve determined that the daily water demand is 10m3 or 2650 gallons. In case you don’t know the daily water demand, a general rule is to multiply the hourly fixed flow rate by 6.

If needed, you can also use the Calculate tool, to help find the proper water volume.

You also have the option of sizing by Number of solar modules.
Enter the number of solar modules you want to use.
You can also enter the number of solar modules in a series you want to use.

In this case we’ll stick to sizing by Water Volume.

Then you have to enter the static lift above ground and the dynamic water level. Typically, a well-driller will provide you with this information. In this example, we have already determined both values, so we’ll simply enter this information.

You 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.

Setting your month of sizing is important in order to meet your duty point. For instance, for an irrigation system, it should be set to the month in which growth peaks. For drinking water, you should select the month in which the solar irradiation is at its weakest. A general rule is that if you’re in the northern hemisphere, it should be set to July, and if you’re in the southern hemisphere, January. As we’re in Seville, we’ll set it to July.

Next, you need to select your solar module type. You can also 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.

When all input points are selected, it’s time to see the sizing results. Click ‘Start sizing’.

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

Note that the results labeled  “Lower” are solutions that use fewer solar panels and deliver less water than required, and the results labeled “Higher” are solutions that use more panels and bigger pumps and delivers more water than requested.

Click on your preferred solution. It will give you a detailed performance curve, while you can also scroll through the specifications, system parts and more details of your sizing result.

You also have the option to see a graph of the daily water production, as well as the monthly water production during an entire year.

Finally, you can generate a PDF report by clicking ‘Print’.

From here, you can add the content you like – ensuring that the report has the exact information that you want to display. We recommend that you choose ‘Sizing result’ and ‘Accessories’ as a minimum. Now click Generate PDF to see the report.

That just about covers it. In short, all the information you need to size a solar pump system in Grundfos Product Center is the project’s location, the flow per day, the static lift and the dynamic water level. It’s that simple. Now, it’s your turn!

Course overview

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