Solar + battery vs solar only
What could a 15 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£472 estimated annual value
£7,000 extra battery cost · 2,500 kWh solar shifted · 1,000 kWh tariff shifted
Scenario comparison
| Scenario | Extra cost | Solar shifted | Tariff shifted | Import/export | Cheap rate | Annual value | Simple payback |
|---|---|---|---|---|---|---|---|
| Cautious | £8,050 | 1,750 kWh | 700 kWh | 24/15p | 10p | £225/yr | 35.8 yrs |
| Base | £7,000 | 2,500 kWh | 1,000 kWh | 28/15p | 8p | £472/yr | 14.8 yrs |
| High-use | £6,300 | 3,000 kWh | 1,150 kWh | 32/10p | 7p | £872/yr | 7.2 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.