How to choose a solar pump with the right flowrate

Choosing the right solar pump for your farm can feel difficult as there are several things you should consider, and you must relate these to your specific farm.

Unfortunately, some farmers end up disappointed when their solar pump doesn’t pump water as quickly as they expected or needed. But, this shouldn’t be the case – a correctly sized solar pump should provide you with all the water you need.

This blog is designed to help you decipher what the flowrate you see on your pump box refers to, what factors on your farm will influence how much water you require and how you can use your water pump most efficiently.

Pump manufacturers flowrate

First things first, the flowrate referred to by pump manufacturers will usually be the maximum flowrate for that pump.

Often this means it will have been measured in optimal conditions – a low pumping head and in the strongest sunlight. It is important to bear this in mind as we consider the factors which will influence the flowrate and the amount of water you need.

What flow rates mean for irrigation on you farm:

What affects flowrate?

1. Total lift/slope of land

The greater the vertical distance that the pump needs to lift water, the harder it will be working. That means more energy goes to lifting the water up and your pump won’t be able to lift as much water to that height.

2. Sunshine levels (climate)

The brighter the sun shines, the more energy is available to be captured by the solar panel and turned into pumping energy. So, if you are trying to irrigate in the morning or evening or on a cloudy day when the sun’s rays do not have so much energy, you won’t be able to pump as much water.

3. Pipe sizes (backpressure)

Much like lifting water up higher, backpressure also reduces the amount of water you see coming out of the end of the hose. Backpressure is usually caused by pumping water through a constricted space, this uses more energy as the pump has to force the water through a small hole. Excessive backpressure can be caused by using a hosepipe which is too small or having kinks or blockages in the hosepipe.

In the Futurepump user manual we include recommended pipe sizes for maximum efficiency for your situation – take some time to familiarise yourself with this to get the most from your pump.

4. Pump efficiency

Different pump designs come with different efficiencies. A low-efficiency pump will use more energy per litre of water pumped as energy is lost through the system. Pump efficiency isn’t usually clearly displayed in pump marketing materials, but it is something worth asking your pump dealer as it relates to the amount of solar PV the system requires…

5. Amount of solar PV

Increasing the amount of solar PV with your pump will increase the flowrate as more energy is available for pumping water.

However, do not always assume that a pump with more solar PV will have a higher flowrate, a lot of low-efficiency solar pumps pile on the PV to make up for the energy losses in the system, in this situation you end up paying more without a benefit.

6. Don’t be fooled by HP

Much like the amount of solar PV, rated horsepower (HP) of pumps can be misleading. For a solar pump, if HP is stated, this usually refers to the maximum solar panel which can be used with the system. If the pump is inefficient and simply using more energy, it doesn’t always mean you’ll get more flow. Always check both HP and stated flowrates.

What flowrate do you need?

The six factors above affect what the pump can deliver to your farm…. But how do you work out how much water you need to get to your farm in the first place?

1. Land size (area you want to irrigate)

The larger the area you want to irrigate, the more water you will need.

2. The soil on your farm

Clay soils hold water close to the surface, it can become waterlogged easily requires less frequent water application than sandy soils which drain quickly and freely. You can explore more about getting the most from the soil on your farm in our blog.

3. The crops you want to grow

Different crops have different water needs, it is a good idea to have made a plan and know which crops you want to be growing before investing in irrigation.

Examples of water intense crops:

  • Rice
  • Cotton
  • Sugar cane
  • Soya
  • Wheat

Example of crops with low water requirements:

  • Sorghum
  • Cassava
  • Sweet potato
  • Cowpea
  • Groundnut

If you are unsure about the water requirements for a crop you want to grow, it is a good idea to get advice from an agronomist.

4. Your irrigation application method

You can use a solar pump to apply the water to your crops in several different ways. You can use furrow irrigation, hose pipe irrigation, sprinklers or drip.

If you want to use furrow irrigation, you will need a higher flowrate as this method floods the land quickly, on the other end of the spectrum is drip irrigation which uses a slow drip of water to irrigate over a longer time period. Drip irrigation needs a lower flowrate than furrow. See more about the pros and cons of different irrigation options here.

How to estimate your water requirements:

As these things will change over the years you have your farm, the best way to size your irrigation pump is by doing a simple calculation for the peak water you would need during the growing season.

Area of land needing irrigating multiplied by crop water requirement = volume of water required

If you have not decided which crops you want to grow yet, a good estimate for average crop water requirement is 5mm.

If you consider these factors when choosing your solar pump you will be able to find the correct solution and enjoy the benefits of free solar energy on your farm.

Futurepump solar pump range - SF2 and SE1

Futurepump manufactures surface solar pumps suitable for up to two acres of land across a range of pumping heads. To see our full range and find out how to purchase directly from our factory, visit our webshop.