7.5 kW solar borehole pump in Wolwehoek, Free State

The challenge: a new Eskom connection or a diesel generator?

The farm needed a reliable supply of water from a borehole to keep two 30 000-litre dams filled. There were two obvious ways to power the pump, and neither was attractive.

Running it on a diesel generator would have cost roughly R6 000 to R9 000 a month in fuel, plus generator wear, refuelling and servicing. A new Eskom connection would have meant a monthly electricity bill of around R15 000 for the pump. Because pumping is a daytime job anyway, solar was the natural fit.

The system we installed

Instead of a generator or a grid connection, we built a solar-direct pumping system. A 10 kWp array of LONGi panels feeds an INVT 16 kW solar variable speed drive (VSD), which runs the 7.5 kW borehole pump straight from the panels.

There are no batteries. Rather than storing electricity, the system stores water in the dams, which is far cheaper. The VSD constantly matches the pump's speed to the sunlight available: in bright sun it runs at full speed, and when a cloud passes it slows down smoothly instead of stopping, so water keeps flowing.

The array is about 1.3 times the pump's rating, which allows for cloud, heat and system losses and gets the pump up to speed earlier in the morning. The controller sits in a weatherproof enclosure under the panels, which keeps cable runs short and the installation neat.

The results

• No fuel cost during daylight hours: the pump runs on sunlight alone.
• No monthly Eskom bill for the pump.
• About 12 m³ of water an hour into two 30 000-litre dams.
• Runs on its own, with no one needed to start a generator, refuel or watch the pump.
• Indicative payback of 18 to 24 months on diesel savings alone.

Could this work on your farm?

If your pump runs mostly in daylight and you are paying for diesel or a large Eskom pumping bill, a solar borehole pump is usually worth a look. Our farmer's guide to solar borehole pumps explains how these systems work and how they are sized, and our farm solar page covers irrigation, cold rooms and other farm loads.