A 12 kW solar system: cost and output
Twelve kilowatts crosses into the 10–50 kW published band, where installed cost per kW is markedly lower. It also crosses out of ordinary domestic territory: planning, structure and network capacity all need checking rather than assuming.
| Roughly how many panels | 28 at 430 W |
|---|---|
| Published size band | 10-50 kW |
| Installed cost, median | £14,446 (£1,204/kW) |
| Installed cost, mean | £15,202 (£1,267/kW) |
| Generation, south-facing at 35° | 10,272 kWh a year for a median location; 8,304 to 12,504 kWh across our 25 reference locations |
Cost: Solar photovoltaic (PV) cost data, Department for Energy Security and Net Zero, 2025/26, Total Installed Capacity basis, OGL v3.0. Generation: our own PVGIS modelling at 20% system losses — see generation by region. Panel count is illustrative and depends on the modules quoted.
| Self-consumption | Used at home | Exported | At 12.0p export | At 4.1p export |
|---|---|---|---|---|
| 14% | 1,438 kWh | 8,834 kWh | £1,436 | £738 |
| 19% | 1,952 kWh | 8,320 kWh | £1,508 | £851 |
| 23% | 2,363 kWh | 7,909 kWh | £1,566 | £941 |
Self-consumption rates are MCS guidance note MGD 003's figures for a household using 2,500–2,999 kWh a year — 14% out all day, 19% in half the day, 23% home all day. They are averages for similar households, not a prediction for yours, and self-consumption falls as the array gets larger. Import is the price cap unit rate for 1 July to 30 September 2026. The two export columns are the best and the median open untied rate in our SEG table — the gap between them is what choosing an export tariff is worth, and it is larger than most people expect.
Who this size suits
- farms, smallholdings and properties with outbuilding roofs
- large houses with three-phase supply
- small commercial premises with a domestic-style roof
Roughly 28 panels at 430 W, needing about 56 m² of roof. Higher-rated modules need fewer panels for the same capacity, which matters on a tight roof.
The cheapest kilowatts on the table
The 10–50 kW band’s published median cost per kW is well below the domestic bands. Same scaffolding logic, spread over three times the panels.
That is the strongest argument for filling available roof area where you have it — provided the output has somewhere to go.
What changes above 10 kW
Planning. Domestic roof-mounted solar is usually permitted development within the conditions, but the array’s size, the building type and whether it is a dwelling at all all matter. Ground-mounted arrays have their own rules — see ground-mounted solar.
Structure. A larger array on an agricultural or outbuilding roof needs proper assessment. Older farm buildings are exactly the case where assumptions are dangerous.
Network. A G99 application at this size may attract conditions, including export limitation, depending on local capacity.
Export income. Domestic-style SEG tariffs may not be the right route at this scale, and the terms available to larger generators differ. Establish the export arrangement before you commit to the capacity — the economics turn on it.
Check the quote, not the brochure
Divide the quoted price by the array’s kWp and compare it with the published benchmark. Then check what the quote includes, and what it does not — the costs outside the headline are where budgets break.
Sources
- Solar photovoltaic (PV) cost data Release 2025-26, published 28 May 2026, Total Installed Capacity basis. Derived by the department from the MCS Installation Database.
- MGD 003: Solar PV Self-Consumption, issue 2.0 (1 April 2022) Read locally. MCS restricts reproduction, so we cite clauses and quote sparingly.
- Energy price cap unit rates and standing charges
Contains public sector information licensed under the Open Government Licence v3.0.
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