Dairy farm solar calculator: size, saving and payback

Enter your herd size, the array size you are considering and your tariff to see what a dairy farm's solar array generates, how much of it the farm might use, and the simple payback. The starting values are examples with their sources named below, not a typical dairy; change them to yours. Indicative only, not a quote.

Cows in milk Electricity use per cow per year (kWh) AHDB and NFU Energy (2021) gave 400 to 600 kWh; use your own bills if you have them. Your electricity unit price (p/kWh) Example value: the DESNZ average non-domestic price for Q1 2026, including CCL. Use the rate on your bill. Array size (kWp) Location (annual yield per kWp) PVGIS v5.3 estimates, south-facing 35 degree roof, 14% system losses. Share of the output you use on site: 60% Set it from your meter data; there is no typical figure here. The table below the results shows what a lower share does. Installed cost (£ per kWp) Example value: the DESNZ 2025/26 mean for 10 to 50 kW systems in Wales, which includes domestic installs. Replace it with your quote. Export rate (p/kWh) In October 2026 small suppliers paid 3 to 6p and the best open fixed rates were around 12 to 13p.

Indicative estimate

Annual electricity use: 100,000 kWh
Annual generation: 48,400 kWh
Used on site: 29,040 kWh
Exported: 19,360 kWh
Annual saving: £7,978
Installed cost: £62,850
Simple payback: 7.9 years

Get a precise figure

What if the farm uses less of the output?

Same inputs, different share of the output used on site. Payback moves a lot, which is why the share matters more than the headline array size.

Share used on site	Used on site	Annual saving	Simple payback
40%	19,360 kWh	£6,126	10.3 years
60%	29,040 kWh	£7,978	7.9 years
80%	38,720 kWh	£9,831	6.4 years
100%	48,400 kWh	£11,684	5.4 years

Assumptions: electricity use is cows multiplied by kWh per cow (AHDB and NFU Energy, 2021, range 400 to 600; example 500). Yield is the PVGIS v5.3 estimate for a south-facing 35 degree roof with 14% system losses. The unit price example is the DESNZ Quarterly Energy Prices average non-domestic price for Q1 2026 including CCL (24.14p). The cost example is the DESNZ 2025/26 mean for 10 to 50 kW systems in Wales (£1,257 per kW, which includes domestic installs and excludes batteries). Export rates in October 2026: small suppliers 3 to 6p, best open fixed rates 12 to 13p. The model values the share of output you use at your unit price and the rest at your export rate, caps use at the farm's annual consumption, and ignores degradation, finance and VAT. This tool does not store any data you enter.

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Calculator FAQs

How accurate is this calculator?

It is a simple model with inputs you can change. It multiplies array size by a regional PVGIS yield, applies the share of output you say the farm uses, and values what is used at your unit price and what is exported at your export rate. The starting values are examples with sources named on this page; replace them with your own. A precise figure needs half-hourly meter data, the roof and the grid connection.

What is self-consumption and why does it matter?

Self-consumption is the share of solar output you use on site rather than export. On-site use saves the price you pay for imported electricity, while exported units earn only the Smart Export Guarantee rate, so a higher share used on site shortens the payback. The slider sets that share, and the table below the results shows how the saving changes if the farm uses less.

Does the estimate include tax relief?

Not as a figure. Solar PV is plant and machinery, and the £1 million Annual Investment Allowance usually means 100% relief in year one for a business under the limit, but the tax you save depends on your tax rate and profits, so the calculator does not put a number on it. Ask your accountant.

Is this a quote?

No. It is an indicative estimate to help you scope the opportunity. A real proposal needs meter data, a roof assessment and a grid check from an installer you choose; this site does not provide one.