A 20 kW solar system: cost and output
Twenty kilowatts is commercial-scale generation on a small site. The cost per kW is the lowest in the published series, the connection process is a real project, and the household benchmarks on the rest of this site stop being the right comparison.
| Roughly how many panels | 47 at 430 W |
|---|---|
| Published size band | 10-50 kW |
| Installed cost, median | £24,077 (£1,204/kW) |
| Installed cost, mean | £25,337 (£1,267/kW) |
| Generation, south-facing at 35° | 17,120 kWh a year for a median location; 13,840 to 20,840 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% | 2,397 kWh | 14,723 kWh | £2,393 | £1,229 |
| 19% | 3,253 kWh | 13,867 kWh | £2,513 | £1,418 |
| 23% | 3,938 kWh | 13,182 kWh | £2,610 | £1,569 |
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
- commercial and agricultural sites with substantial daytime demand
- community buildings — halls, schools, places of worship
- large multi-building rural properties
Roughly 47 panels at 430 W, needing about 94 m² of roof. Higher-rated modules need fewer panels for the same capacity, which matters on a tight roof.
Why the domestic figures stop applying
Everything else in this section is built on domestic assumptions: a household’s consumption profile, MCS’s self-consumption archetypes, a domestic export tariff, the price cap unit rate.
None of those is the right frame at 20 kWp. A commercial site has a different consumption profile, buys electricity on a contract rather than under the cap, and may have entirely different export arrangements available.
We publish the cost figure here because the official series covers this band, and because the cost per kW is genuinely informative: it is the lowest in the series, and it shows how far fixed-cost spreading goes.
What a project at this size involves
A G99 application with a real assessment — see how to apply and what happens if the operator refuses.
Structural engineering, not a structural assessment form.
A planning check. Larger arrays, and any ground-mounted element, need the planning position established properly rather than assumed.
A commercial export arrangement, negotiated rather than selected from a table.
Business rates, VAT and capital allowances, which are outside what this site covers and are questions for an accountant.
What we can tell you honestly
The cost per kW, from the official statistics. The generation, from our own modelling. Both are on this page.
What we cannot tell you is whether the investment works for your site, because that depends on your daytime load and your electricity contract — neither of which we can see. Anyone who quotes you a payback figure without asking about both is not calculating, they are selling.
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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