A 5 kW solar system: cost and output
Five kilowatts is where the cost per kW starts falling — you move into the larger published band — and where the inverter decision stops being routine, because 5 kW of panels is more than the simpler network process allows an inverter to register.
| Roughly how many panels | 12 at 430 W |
|---|---|
| Published size band | 4-10 kW |
| Installed cost, median | £7,729 (£1,546/kW) |
| Installed cost, mean | £8,109 (£1,622/kW) |
| Generation, south-facing at 35° | 4,280 kWh a year for a median location; 3,460 to 5,210 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% | 599 kWh | 3,681 kWh | £598 | £307 |
| 19% | 813 kWh | 3,467 kWh | £628 | £354 |
| 23% | 984 kWh | 3,296 kWh | £652 | £392 |
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
- larger semi-detached and detached houses with a full roof plane
- households with an electric vehicle, a heat pump, or a battery in mind
- anyone whose roof takes twelve or more panels
Roughly 12 panels at 430 W, needing about 24 m² of roof. Higher-rated modules need fewer panels for the same capacity, which matters on a tight roof.
Two things change at this size
The published cost per kW falls. Five kilowatts sits in the 4–10 kW band, where the median cost per kW is lower than in the 0–4 kW band. The fixed costs are spread further.
The inverter needs a decision. G98 covers registered capacity up to 3.68 kW single-phase. A 5 kWp array can still sit behind a 3.68 kW inverter and stay inside G98 — clipping some summer peak — or go to a larger inverter and into the G99 process.
Neither is wrong. What matters is that you know which you are being sold, because it affects the timetable, the paperwork and what you can add later.
Self-consumption becomes the binding constraint
At around 4,300 kWh a year on a median location, a 5 kWp array produces more than many households can absorb during daylight. On MGD 003’s figures, self-consumption at this level of generation is lower in percentage terms than for a smaller array.
That is not an argument against 5 kWp. It is an argument for knowing what the surplus is worth to you:
- with a good export tariff, surplus is genuinely valuable — the gap between the best and median rates in our SEG table is stark
- with a battery, MGD 003’s own figures show self-consumption rising substantially
- with an EV charged at home during the day, the surplus has somewhere useful to go
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.
Sorry to hear that. What was the problem?