Side-by-side comparison
Worked example: 480 kWp office solar in Manchester. Annual consumption 1.4 GWh. Day rate 30p/kWh.
| Factor | Solar only | Solar + 215 kWh battery |
|---|---|---|
| System size | 480 kWp PV | 480 kWp PV + 215 kWh battery |
| Capex | £408,000 | £556,000 (battery adds £148,000) |
| Annual generation | 442,000 kWh | 442,000 kWh |
| Self-consumption % | 78% | 91% |
| Annual cost avoided (28p) | £103,500 | £120,600 |
| Annual SEG revenue (10p) | £9,700 | £4,000 |
| DUoS red-band shifting | £0 | £8,500/year |
| Capacity market revenue | £0 | £8,000/year |
| Total annual benefit | £113,200 | £141,100 |
| Simple payback | 3.6 years | 3.9 years (+0.3) |
| 25-year cumulative benefit | £2.83m | £3.53m |
| NPV uplift from battery | — | +£127,000 at 7% discount |
The decision
Pick on the basis of your specific situation:
Solar only
Best for: Office solar above 200 kWp, annual electricity consumption above 800 MWh, day-rate tariff above 25p/kWh. Three revenue streams stack to flip NPV positive.
Solar + 215 kWh battery
Best for: Office solar below 200 kWp, lower-consumption building, or day-rate below 22p/kWh. Battery economics don't justify the additional capex over 10-15 year battery lifespan.
How we model it for you
For every office solar proposal, we model the relevant comparison options side-by-side. Send us your half-hourly meter data and roof plan via the quote form, and we'll return a fixed-price proposal within 7 working days with all relevant routes compared in your specific situation.