A serious solar proposal starts with your half-hourly meter data, a structural survey, and a DNO capacity check. But you can get a useful order-of-magnitude sizing with three numbers: roof area, annual electricity spend, and farm type.
Quick sizing rules
- 📐 Roof area to kWp: 6 sqm per kWp installed (modern 410W panels).
- 🔆 Annual generation: 950 kWh per kWp installed (UK average, south-facing 30° pitch).
- 📊 Self-consumption: the share of output the farm uses itself. Read it from your half-hourly meter data: it is higher where loads run in daylight, and a battery raises it further if the farm has an evening or early-morning load.
- 💰 Cost: about £1,262 per kW, the DESNZ 2025/26 median for a 10–50 kW system (Great Britain; including VAT where charged; excluding batteries). There is no official series above 50 kW, so larger arrays are priced from itemised quotes.
- 📈 Tariff offset: the unit rate on your own electricity bill for each kWh the farm uses, plus whatever your Smart Export Guarantee supplier pays for exported kWh (Great Britain only; each licensed supplier sets its own rate; systems up to 50 kW need MCS certification or equivalent).
- ⏱️ Payback: simple payback = cost ÷ annual saving, using your own quote, meter data and tariff. No farm solar grant is open (England's IFP grant has closed, and the FETF item lists did not include solar panels to power a farm), but most farm businesses can deduct the whole cost in year one through the £1 million Annual Investment Allowance.
Worked examples by farm type
| Farm | Roof m² | System | kWh/yr |
|---|---|---|---|
| 200-head dairy | 450 | 75kW | 71,000 |
| Arable 800ac | 800 | 130kW | 123,000 |
| Free-range poultry (16k bird) | 500 | 80kW | 76,000 |
| Mixed 500ac | 350 | 55kW | 52,000 |
| Soft fruit + packhouse | 1,200 | 200kW | 190,000 |
System size uses 6 sqm of roof per kWp and generation uses 950 kWh per kWp, as above. Savings, cost and payback are left out because they depend on your own tariff, meter data and quote: every example here is above 50 kW, where there is no official price series, and no farm solar grant is open. For each, simple payback = cost ÷ (kWh used on the farm × your import unit rate + kWh exported × your export rate).