An 8 kW solar system: cost and output
Eight kilowatts generates more than a typical household uses in a year, all of it in daylight. At this size the system is an export business with a domestic roof, unless storage or a large electrified load is part of the plan.
| Roughly how many panels | 19 at 430 W |
|---|---|
| Published size band | 4-10 kW |
| Installed cost, median | £12,367 (£1,546/kW) |
| Installed cost, mean | £12,974 (£1,622/kW) |
| Generation, south-facing at 35° | 6,848 kWh a year for a median location; 5,536 to 8,336 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% | 959 kWh | 5,889 kWh | £957 | £492 |
| 19% | 1,301 kWh | 5,547 kWh | £1,005 | £567 |
| 23% | 1,575 kWh | 5,273 kWh | £1,044 | £627 |
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
- large detached properties with substantial roof area
- homes with a heat pump and an electric vehicle, ideally both
- properties running a home business or workshop with real daytime load
Roughly 19 panels at 430 W, needing about 38 m² of roof. Higher-rated modules need fewer panels for the same capacity, which matters on a tight roof.
This is a G99 system
At 8 kWp the inverter will be well above the 3.68 kW single-phase threshold, so you are in the G99 process: the network operator assesses the application before anything is installed.
Two consequences worth planning for:
Timetable. Application, assessment, then installation. This is not a two-week job.
Conditions. The operator may grant the connection subject to export limitation, which caps what you can sell without affecting what you can use. If your case depends on export income, that condition matters to the arithmetic. What happens if the answer is no is covered in when your DNO refuses.
A three-phase supply, if you have one, changes the picture — G98’s limit is 16 A per phase, which the ENA converts to 11.04 kW across three phases.
The economics are export economics
An 8 kWp array on a median location generates roughly 6,800 kWh a year. Very few households consume that much during daylight hours.
So the value depends on:
- the export rate you can get, which is the single biggest lever
- storage, and how much of the evening it can cover
- electrified loads — heat pump, EV, hot water — and whether they can be shifted into daylight
If none of those applies, the honest advice is that a smaller array may return more per pound, because the marginal kilowatt-hour is being sold at a low rate rather than saving you a high one.
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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