How Much Can a 4kW Solar System Save in the 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 £662. Your quote can be higher or lower, so use this as a starting point, not a guarantee.
Example scenarios
| Scenario | Annual benefit | Payback | 20-year net |
|---|---|---|---|
| Careful | £416 | 16.8 years | £1,326 |
| Middle | £662 | 10.6 years | £6,244 |
| With battery | £750 | 17.3 years | £1,990 |
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 · battery vs no battery