Does a solar irrigation pump in the field need a battery?

An irrigation pump can run on an off-grid system with solar panels, with or without a battery. For drip lines, filling a basin or watering livestock, the pump can run directly on the panels during the day. For night irrigation, a fixed pressure or a large pump, a battery and an inverter take over. The inverter is the box that turns battery power into normal 230 V or 400 V. A generator covers the rare long grey spell.

Maybe your field lies a kilometre from the yard, with a well or a pond at the edge. Every dry spell, you drag the diesel pump or the tractor out, and someone checks on it day and night. You asked about a cable to the field, and the answer was a trench across other people's land. On forums, growers ask the same question: can the sun not do this? One grower in the Canaries was told that reinforcing the rural grid "is not a priority". Another saw his inverter beep in overload "when it's kicking about 10 kW for a second to start the pump".

That start is what most solar pump kits leave out. A kit sized on the running power of the pump fails at the first start, and a battery sized on a sunny day runs empty on the first grey one. Meanwhile, the diesel pump keeps costing fuel and hours. A Dutch study quoted by the water research body STOWA puts the running cost of irrigation at about 0.21 euro per cubic metre of water, for energy and labour alone.

We solved the pump problem once already, with the grid still in place. A plant nursery in Jabbeke had a 3 x 400 V 32 A connection, and a new irrigation pump needed a heavier one. The grid operator proposed medium voltage at a high price. With a semi-off-grid system of 45 kVA and 92.4 kWh, the nursery kept its street connection and uses it only as a charger. In the field, without any connection, the same logic applies: the battery and the panels deliver the power the cable cannot.

Can an irrigation pump run directly on solar panels without a battery?

Yes. Most solar pumps run directly on the panels, without a battery: the pump turns faster when the sun is strong and slower when it is not. A pump controller (a frequency drive that adapts the pump speed to the power available) does that work. The water you pump goes into a tank, a basin or straight onto the crop.

The French solar pump supplier Solaris-Store explains it plainly to the farm software company Isagri: most of its pumps run "au fil du soleil", following the sun. A battery is expensive, so it is only used when you need water at night. The flow of the pump is proportional to the sunshine, and today's controllers can limit the power so a slow well does not run dry.

Direct solar pumping fits well when:

• you fill a tank or basin on higher ground and irrigate by gravity, at a pressure set by the height of the tank;
• a drip line or low-pressure sprinklers can take a flow that changes during the day;
• you water livestock in the pasture: a float valve in the trough stops the pump when the trough is full;
• the irrigation can wait a day when the weather turns grey.

Irrigating in the daytime is not the waste many growers fear. According to STOWA, spraying in the daytime loses about 3 to 6% of the water to evaporation, against 2 to 3% at night. Wind matters more than the sun: STOWA advises not to irrigate above 3 m/s of wind.

When does a solar irrigation pump need a battery?

A solar irrigation pump needs a battery when the water has to flow at a time, a pressure or a power the panels cannot give on their own. In practice, that comes down to four situations.

For a night now and then, a small generator is sometimes cheaper than a big battery. Isagri's source describes exactly that hybrid for large irrigation sites: solar in the daytime and a generator for the night. Our article on a generator with a battery off-grid explains how the two work together with automatic start.

How much power does an irrigation pump need?

The power of an irrigation pump follows from two numbers: the flow (cubic metres per hour) and the total head (the height plus the pressure the pump works against, in metres). One bar of pressure is about 10 metres of head. The hydraulic power in kW is flow times head divided by 367.

The pump itself loses part of the energy, so the motor needs more than the hydraulic power. Check the efficiency on the pump curve of your own pump. The examples below assume an efficiency between 50% for a small pump and 60% for a large one:

The examples are calculations with the formula from the Engineering ToolBox, not measured pumps. They show the order of size. A reel irrigator asks about ten times more power than a drip line, because it pushes more water at a far higher pressure. In the Netherlands, STOWA estimates that 95 to 98% of arable irrigation runs on a reel irrigator, a high-pressure system.

Write down the rating plate of the pump, the depth of the well or the height to the field, and the pressure your sprinklers or drippers need. That short list sizes the system better than any kit description. A 3-phase pump on a frequency drive is often the best choice: it starts gently and can adapt its speed. At Jabbeke we fitted frequency drives on the heaviest pumps to keep them running smoothly. How a frequency drive helps a pump on a connection that is too small is explained in our article on more power for a new pump or machine.

How many solar panels do you need for an irrigation pump in Belgium?

Count about 4 kWh a day for every kWp of panels in the irrigation season in Belgium, and divide the daily energy of your pump by that. A 1.6 kW drip pump that runs six hours uses about 10 kWh a day, so about 2.5 kWp of panels plus a margin for lighter days.

The European PVGIS tool calculates what 1 kWp of south-facing panels at 35 degrees produces near Ghent, after 14% losses. The irrigation season falls exactly in the strong months:

From May to July, 1 kWp gives about 125 kWh a month, or about 4 kWh a day on average. A pump that only runs in summer is the easiest load there is for solar panels. The same panels give about 1 kWh a day in December, which matters only if the system also has winter work to do.

The reel irrigator in the table is a different story. At about 15 kW for eight hours, it needs about 120 kWh a day, or about 30 kWp of panels, before any night irrigation. That is possible on a large farm, but it is a serious installation for a machine that may only run a few weeks a year.

How big must the battery be for a field irrigation pump?

Size the battery on the energy the pump uses outside sun hours, plus a reserve, and check that the inverter can deliver the start of the motor. The pump power times the hours it runs without sun gives the kWh the battery must deliver.

Add a reserve on top of these figures, because a battery should not be emptied to zero every night and the grey days still come. The Jabbeke nursery, which runs several heavy pumps, has 92.4 kWh of battery. For night irrigation with a reel, the battery quickly becomes the largest item of the whole system. That is why a tank, a basin or a generator for the night is often the smarter choice.

Storing surplus energy in water is not a new idea for us. At a semi-off-grid project in Wingene, a full battery sends its surplus to a boiler through a resistor, so water becomes the battery. That kind of smart control can also switch pumps on a farm when there is overproduction. Let the pump work when the sun produces most, and keep the battery for what cannot wait.

Solar pump, battery, generator or a grid cable to the field: what fits your farm?

Direct solar pumping fits small and medium pumps that can work in the daytime. A battery fits when water is needed at night or at a steady pressure. For a big reel irrigator a few weeks a year, a generator or a grid connection stays the better choice.

Electric irrigation pays. STOWA quotes a study by Wageningen University on switching from diesel to electric irrigation. It found savings of about 1,300 to 3,600 euro a year per farm, depending on the region, and a little more with own solar power. The same study names the main obstacle: electricity has to be available at the field, and a connection has to be built and kept. That is exactly the gap an off-grid system fills.

When the pump stands close to the yard and the existing connection is simply too weak, a semi-off-grid system like the one in Jabbeke is usually the better road. And if you are weighing a cable to the field against a battery, our article on grid extension costs versus a battery shows how to compare them.

Can a solar irrigation system do more than water the crop?

Yes, and that is usually what makes it pay off: an irrigation pump runs a few months a year, the panels produce all year. Outside the irrigation season, the same system can power a shed, lighting, a cold store, livestock water or chargers for tools.

Take the farm in St-Georges-sur-Meuse, in the province of Liège. The street had no electricity connection, and the farm ran entirely on a generator, day and night. After solar panels and a battery were installed, the generator only serves as a back-up. The farm is fully off-grid and never needed a street connection.

Our off-grid systems are built for private, industrial and agricultural use, and they stay expandable: more panels, more battery or another source later, such as a small wind turbine. The system can still be connected to a generator or to the grid later. More about energy on farms is in our articles on solar panels and a battery for a farm and on a battery in a greenhouse or nursery.

Which rules apply when you pump water for irrigation in Belgium?

The rules are about the water more than about the solar panels: pumping groundwater in Flanders needs a permit, and taking water from a watercourse is regulated by the water manager. Check this before you size the pump.

• Groundwater (Flanders): according to the Flemish Environment Agency (VMM), you need a permit to pump groundwater. Agriculture held 21% of the permitted groundwater volume at the end of 2024.
• Watercourses: in the province of Antwerp, for example, you must file a notification before you take water from a watercourse to irrigate crops. In a severe drought, a ban on taking water can apply, and for some vulnerable watercourses the ban is permanent.
• Wallonia and Brussels: the rules for taking groundwater or surface water differ; ask your municipality or the regional administration before you drill or pump.
• The electrical installation: the Belgian electrical safety code (AREI) applies with or without a grid connection, and a new installation is inspected by an approved body before use.

A drought ban is also a reason to think about water storage. A basin that you fill when water may be taken keeps your crop going when it may not.

How do we design a solar irrigation system?

We start from your pump, your water source and your season, not from a standard kit. The steps are the same for a vegetable field, an orchard or a pasture.

1. Step 1: You send us the pump details (rating plate, flow, pressure), the depth of the well or the height to the field, the hours you irrigate and the other loads on the site.
2. Step 2: We calculate the panels (type, number and orientation for your location), the inverters, the battery and, where needed, a generator.
3. Step 3: We check where the water can be stored instead of the electricity, and whether a frequency drive makes the pump start more gently.
4. Step 4: We install and commission the system, and have it inspected before it is put into use.
5. Step 5: You follow production, battery and use in real time with our monitoring software. The system stays expandable when you add a pump or a building.

Want to see how the parts fit together first? Read our overview of the components of an off-grid system, or see how our off-grid solutions for farms and businesses are built.