Solar + battery vs solar only
What could a 5 kWh battery add to a solar system?
This example separates extra solar electricity kept for later use from optional cheap-rate tariff shifting.
Base worked example£168 estimated annual value
£3,500 extra battery cost · 900 kWh solar shifted · 350 kWh tariff shifted
Scenario comparison
| Scenario | Extra cost | Solar shifted | Tariff shifted | Import/export | Cheap rate | Annual value | Simple payback |
|---|---|---|---|---|---|---|---|
| Cautious | £4,025 | 630 kWh | 245 kWh | 24/15p | 10p | £80/yr | 50.3 yrs |
| Base | £3,500 | 900 kWh | 350 kWh | 28/15p | 8p | £168/yr | 20.8 yrs |
| High-use | £3,150 | 1,080 kWh | 402 kWh | 32/10p | 7p | £311/yr | 10.1 yrs |
Why export value is deducted
An extra self-consumed solar kWh is not worth the full import rate if it would otherwise have earned export income. The model values extra solar self-use at the import/export difference, then separately values tariff shifting.
These are illustrative scenarios, not a battery-size recommendation. Usable capacity, power limits, degradation, export arrangements, tariff rules and half-hourly demand determine real value.