A typical roof here lands around 6.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 1041 kWh per year on a south-facing roof. We value self-used electricity at 26.5p and exported surplus at a baseline 10p via SEG. Use the calculator above for your exact tariff.
Browse the scenarios below. Each battery size has its own expand — open the one that matches your plan (or just explore). For each system size (2–8 kW) we show annual output, how much you use directly, what gets exported, annual benefit, upfront cost, break-even, and a 20-year net. Negative numbers are possible — that’s the honest trade-off when adding more battery than your usage profile justifies.
No battery 5 kW example → Annual benefit: £865, Upfront: £10,173, Break-even: 11.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2083 kWh | 833 kWh | 1250 kWh | £221 | £125 | £346 | £4,069 | 11.8 yrs | £2,850 |
| 3 kW | 3124 kWh | 1250 kWh | 1874 kWh | £332 | £187 | £519 | £6,104 | 11.8 yrs | £4,276 |
| 4 kW | 4165 kWh | 1666 kWh | 2499 kWh | £442 | £250 | £692 | £8,138 | 11.8 yrs | £5,701 |
| 5 kW | 5207 kWh | 2083 kWh | 3124 kWh | £553 | £312 | £865 | £10,173 | 11.8 yrs | £7,126 |
| 6 kW | 6248 kWh | 2499 kWh | 3749 kWh | £663 | £375 | £1,038 | £12,207 | 11.8 yrs | £8,551 |
| 7 kW | 7289 kWh | 2916 kWh | 4374 kWh | £774 | £437 | £1,211 | £14,242 | 11.8 yrs | £9,976 |
| 8 kW | 8331 kWh | 3332 kWh | 4998 kWh | £884 | £500 | £1,384 | £16,276 | 11.8 yrs | £11,402 |
Assumptions: south-facing, sensible tilt; self-use shares from site rules; export at 10p baseline. Costs: panels £/kW = 2,035, battery £/kWh = 700.
3 kWh battery 5 kW example → Annual benefit: £1,037, Upfront: £12,273, Break-even: 11.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2083 kWh | 1250 kWh | 833 kWh | £332 | £83 | £415 | £6,169 | 14.9 yrs | £2,127 |
| 3 kW | 3124 kWh | 1874 kWh | 1250 kWh | £497 | £125 | £622 | £8,204 | 13.2 yrs | £4,241 |
| 4 kW | 4165 kWh | 2499 kWh | 1666 kWh | £663 | £167 | £830 | £10,238 | 12.3 yrs | £6,355 |
| 5 kW | 5207 kWh | 3124 kWh | 2083 kWh | £829 | £208 | £1,037 | £12,273 | 11.8 yrs | £8,469 |
| 6 kW | 6248 kWh | 3749 kWh | 2499 kWh | £995 | £250 | £1,244 | £14,307 | 11.5 yrs | £10,582 |
| 7 kW | 7289 kWh | 4374 kWh | 2916 kWh | £1,160 | £292 | £1,452 | £16,342 | 11.3 yrs | £12,696 |
| 8 kW | 8331 kWh | 4998 kWh | 3332 kWh | £1,326 | £333 | £1,659 | £18,376 | 11.1 yrs | £14,810 |
Assumptions: south-facing, sensible tilt; self-use shares from site rules; export at 10p baseline. Costs: panels £/kW = 2,035, battery £/kWh = 700.
5 kWh battery 5 kW example → Annual benefit: £1,123, Upfront: £13,673, Break-even: 12.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2083 kWh | 1458 kWh | 625 kWh | £387 | £62 | £449 | £7,569 | 16.8 yrs | £1,416 |
| 3 kW | 3124 kWh | 2187 kWh | 937 kWh | £580 | £94 | £674 | £9,604 | 14.3 yrs | £3,874 |
| 4 kW | 4165 kWh | 2916 kWh | 1250 kWh | £774 | £125 | £899 | £11,638 | 13.0 yrs | £6,332 |
| 5 kW | 5207 kWh | 3645 kWh | 1562 kWh | £967 | £156 | £1,123 | £13,673 | 12.2 yrs | £8,790 |
| 6 kW | 6248 kWh | 4374 kWh | 1874 kWh | £1,160 | £187 | £1,348 | £15,707 | 11.7 yrs | £11,248 |
| 7 kW | 7289 kWh | 5103 kWh | 2187 kWh | £1,354 | £219 | £1,572 | £17,742 | 11.3 yrs | £13,706 |
| 8 kW | 8331 kWh | 5831 kWh | 2499 kWh | £1,547 | £250 | £1,797 | £19,776 | 11.0 yrs | £16,164 |
Assumptions: south-facing, sensible tilt; self-use shares from site rules; export at 10p baseline. Costs: panels £/kW = 2,035, battery £/kWh = 700.
7.5 kWh battery 5 kW example → Annual benefit: £1,149, Upfront: £15,423, Break-even: 13.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2083 kWh | 1520 kWh | 562 kWh | £403 | £56 | £460 | £9,319 | 20.3 yrs | £-127 |
| 3 kW | 3124 kWh | 2281 kWh | 843 kWh | £605 | £84 | £689 | £11,354 | 16.5 yrs | £2,434 |
| 4 kW | 4165 kWh | 3041 kWh | 1125 kWh | £807 | £112 | £919 | £13,388 | 14.6 yrs | £4,995 |
| 5 kW | 5207 kWh | 3801 kWh | 1406 kWh | £1,008 | £141 | £1,149 | £15,423 | 13.4 yrs | £7,556 |
| 6 kW | 6248 kWh | 4561 kWh | 1687 kWh | £1,210 | £169 | £1,379 | £17,457 | 12.7 yrs | £10,118 |
| 7 kW | 7289 kWh | 5321 kWh | 1968 kWh | £1,412 | £197 | £1,609 | £19,492 | 12.1 yrs | £12,679 |
| 8 kW | 8331 kWh | 6081 kWh | 2249 kWh | £1,613 | £225 | £1,838 | £21,526 | 11.7 yrs | £15,240 |
Assumptions: south-facing, sensible tilt; self-use shares from site rules; export at 10p baseline. Costs: panels £/kW = 2,035, battery £/kWh = 700.
10 kWh battery 5 kW example → Annual benefit: £1,166, Upfront: £17,173, Break-even: 14.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2083 kWh | 1562 kWh | 521 kWh | £414 | £52 | £466 | £11,069 | 23.7 yrs | £-1,740 |
| 3 kW | 3124 kWh | 2343 kWh | 781 kWh | £622 | £78 | £700 | £13,104 | 18.7 yrs | £890 |
| 4 kW | 4165 kWh | 3124 kWh | 1041 kWh | £829 | £104 | £933 | £15,138 | 16.2 yrs | £3,521 |
| 5 kW | 5207 kWh | 3905 kWh | 1302 kWh | £1,036 | £130 | £1,166 | £17,173 | 14.7 yrs | £6,151 |
| 6 kW | 6248 kWh | 4686 kWh | 1562 kWh | £1,243 | £156 | £1,399 | £19,207 | 13.7 yrs | £8,781 |
| 7 kW | 7289 kWh | 5467 kWh | 1822 kWh | £1,450 | £182 | £1,633 | £21,242 | 13.0 yrs | £11,411 |
| 8 kW | 8331 kWh | 6248 kWh | 2083 kWh | £1,658 | £208 | £1,866 | £23,276 | 12.5 yrs | £14,041 |
Assumptions: south-facing, sensible tilt; self-use shares from site rules; export at 10p baseline. Costs: panels £/kW = 2,035, battery £/kWh = 700.
13.5 kWh battery 5 kW example → Annual benefit: £1,183, Upfront: £19,623, Break-even: 16.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2083 kWh | 1604 kWh | 479 kWh | £425 | £48 | £473 | £13,519 | 28.6 yrs | £-4,052 |
| 3 kW | 3124 kWh | 2405 kWh | 719 kWh | £638 | £72 | £710 | £15,554 | 21.9 yrs | £-1,353 |
| 4 kW | 4165 kWh | 3207 kWh | 958 kWh | £851 | £96 | £947 | £17,588 | 18.6 yrs | £1,346 |
| 5 kW | 5207 kWh | 4009 kWh | 1198 kWh | £1,064 | £120 | £1,183 | £19,623 | 16.6 yrs | £4,045 |
| 6 kW | 6248 kWh | 4811 kWh | 1437 kWh | £1,276 | £144 | £1,420 | £21,657 | 15.3 yrs | £6,744 |
| 7 kW | 7289 kWh | 5613 kWh | 1677 kWh | £1,489 | £168 | £1,657 | £23,692 | 14.3 yrs | £9,443 |
| 8 kW | 8331 kWh | 6415 kWh | 1916 kWh | £1,702 | £192 | £1,893 | £25,726 | 13.6 yrs | £12,142 |
Assumptions: south-facing, sensible tilt; self-use shares from site rules; export at 10p baseline. Costs: panels £/kW = 2,035, battery £/kWh = 700.
Figures are illustrative and use the same method as the calculator above. For exact results, adjust your roof direction, tariff, and usage in the calculator.