4kW Solar System Savings UK
A 4kW solar PV system is a common planning size for UK homes. The annual saving is not fixed: it changes with generation, import tariff, export tariff and how much solar you use in the home.
In the middle example below, a 4kW system produces 3,600kWh a year and gives an estimated annual benefit of £680. That is a planning example, not a guarantee. Your roof, tariff, export rate and quote can all move the answer.
Quick answer
A sensible 4kW UK planning range is about 3,200 to 4,000kWh of annual generation. With the current default assumptions on this site, the middle 3,600kWh case gives about £680a year in combined bill savings and export income.
Example scenarios
| Scenario | Annual benefit | Payback | 20-year net |
|---|---|---|---|
| Careful | £430 | 16.3 years | £1,595 |
| Middle | £680 | 10.3 years | £6,597 |
| With battery | £780 | 16.7 years | £2,595 |
Why your result may differ
- A shaded or awkward roof can produce much less than a clean south-facing roof.
- High daytime usage improves bill savings because more solar is self-consumed.
- A strong export tariff can make exported kWh more valuable.
- A battery can improve self-use, but it adds cost and may lengthen payback.
How to run your own 4kW case
- Set system size to 4kW.
- Enter a realistic annual generation estimate, such as 3,200 to 4,000kWh.
- Use your own import unit rate and export tariff.
- Compare no battery first, then add battery cost and a modest self-use uplift.
Start here: solar savings calculator · generation by system size · solar savings guide · battery vs no battery