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 883 kWh per year on a south-facing roof. We value self-used electricity at 25.8p 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: £721, Upfront: £10,173, Break-even: 14.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1767 kWh | 707 kWh | 1060 kWh | £183 | £106 | £289 | £4,069 | 14.1 yrs | £1,703 |
| 3 kW | 2650 kWh | 1060 kWh | 1590 kWh | £274 | £159 | £433 | £6,104 | 14.1 yrs | £2,554 |
| 4 kW | 3533 kWh | 1413 kWh | 2120 kWh | £365 | £212 | £577 | £8,138 | 14.1 yrs | £3,405 |
| 5 kW | 4416 kWh | 1767 kWh | 2650 kWh | £456 | £265 | £721 | £10,173 | 14.1 yrs | £4,257 |
| 6 kW | 5300 kWh | 2120 kWh | 3180 kWh | £548 | £318 | £866 | £12,207 | 14.1 yrs | £5,108 |
| 7 kW | 6183 kWh | 2473 kWh | 3710 kWh | £639 | £371 | £1,010 | £14,242 | 14.1 yrs | £5,959 |
| 8 kW | 7066 kWh | 2826 kWh | 4240 kWh | £730 | £424 | £1,154 | £16,276 | 14.1 yrs | £6,810 |
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: £861, Upfront: £12,273, Break-even: 14.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1767 kWh | 1060 kWh | 707 kWh | £274 | £71 | £345 | £6,169 | 17.9 yrs | £722 |
| 3 kW | 2650 kWh | 1590 kWh | 1060 kWh | £411 | £106 | £517 | £8,204 | 15.9 yrs | £2,133 |
| 4 kW | 3533 kWh | 2120 kWh | 1413 kWh | £548 | £141 | £689 | £10,238 | 14.9 yrs | £3,544 |
| 5 kW | 4416 kWh | 2650 kWh | 1767 kWh | £685 | £177 | £861 | £12,273 | 14.2 yrs | £4,955 |
| 6 kW | 5300 kWh | 3180 kWh | 2120 kWh | £822 | £212 | £1,034 | £14,307 | 13.8 yrs | £6,366 |
| 7 kW | 6183 kWh | 3710 kWh | 2473 kWh | £959 | £247 | £1,206 | £16,342 | 13.6 yrs | £7,777 |
| 8 kW | 7066 kWh | 4240 kWh | 2826 kWh | £1,096 | £283 | £1,378 | £18,376 | 13.3 yrs | £9,188 |
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: £931, Upfront: £13,673, 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 | 1767 kWh | 1237 kWh | 530 kWh | £320 | £53 | £373 | £7,569 | 20.3 yrs | £-118 |
| 3 kW | 2650 kWh | 1855 kWh | 795 kWh | £479 | £79 | £559 | £9,604 | 17.2 yrs | £1,572 |
| 4 kW | 3533 kWh | 2473 kWh | 1060 kWh | £639 | £106 | £745 | £11,638 | 15.6 yrs | £3,263 |
| 5 kW | 4416 kWh | 3091 kWh | 1325 kWh | £799 | £132 | £931 | £13,673 | 14.7 yrs | £4,954 |
| 6 kW | 5300 kWh | 3710 kWh | 1590 kWh | £959 | £159 | £1,118 | £15,707 | 14.1 yrs | £6,645 |
| 7 kW | 6183 kWh | 4328 kWh | 1855 kWh | £1,118 | £185 | £1,304 | £17,742 | 13.6 yrs | £8,335 |
| 8 kW | 7066 kWh | 4946 kWh | 2120 kWh | £1,278 | £212 | £1,490 | £19,776 | 13.3 yrs | £10,026 |
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: £952, Upfront: £15,423, Break-even: 16.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1767 kWh | 1290 kWh | 477 kWh | £333 | £48 | £381 | £9,319 | 24.5 yrs | £-1,701 |
| 3 kW | 2650 kWh | 1934 kWh | 715 kWh | £500 | £72 | £571 | £11,354 | 19.9 yrs | £74 |
| 4 kW | 3533 kWh | 2579 kWh | 954 kWh | £666 | £95 | £762 | £13,388 | 17.6 yrs | £1,849 |
| 5 kW | 4416 kWh | 3224 kWh | 1192 kWh | £833 | £119 | £952 | £15,423 | 16.2 yrs | £3,624 |
| 6 kW | 5300 kWh | 3869 kWh | 1431 kWh | £1,000 | £143 | £1,143 | £17,457 | 15.3 yrs | £5,398 |
| 7 kW | 6183 kWh | 4514 kWh | 1669 kWh | £1,166 | £167 | £1,333 | £19,492 | 14.6 yrs | £7,173 |
| 8 kW | 7066 kWh | 5158 kWh | 1908 kWh | £1,333 | £191 | £1,524 | £21,526 | 14.1 yrs | £8,948 |
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: £966, Upfront: £17,173, Break-even: 17.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1767 kWh | 1325 kWh | 442 kWh | £342 | £44 | £387 | £11,069 | 28.6 yrs | £-3,339 |
| 3 kW | 2650 kWh | 1987 kWh | 662 kWh | £514 | £66 | £580 | £13,104 | 22.6 yrs | £-1,508 |
| 4 kW | 3533 kWh | 2650 kWh | 883 kWh | £685 | £88 | £773 | £15,138 | 19.6 yrs | £323 |
| 5 kW | 4416 kWh | 3312 kWh | 1104 kWh | £856 | £110 | £966 | £17,173 | 17.8 yrs | £2,153 |
| 6 kW | 5300 kWh | 3975 kWh | 1325 kWh | £1,027 | £132 | £1,160 | £19,207 | 16.6 yrs | £3,984 |
| 7 kW | 6183 kWh | 4637 kWh | 1546 kWh | £1,198 | £155 | £1,353 | £21,242 | 15.7 yrs | £5,815 |
| 8 kW | 7066 kWh | 5300 kWh | 1767 kWh | £1,369 | £177 | £1,546 | £23,276 | 15.1 yrs | £7,645 |
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: £980, Upfront: £19,623, Break-even: 20.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1767 kWh | 1360 kWh | 406 kWh | £351 | £41 | £392 | £13,519 | 34.5 yrs | £-5,677 |
| 3 kW | 2650 kWh | 2040 kWh | 609 kWh | £527 | £61 | £588 | £15,554 | 26.4 yrs | £-3,790 |
| 4 kW | 3533 kWh | 2720 kWh | 813 kWh | £703 | £81 | £784 | £17,588 | 22.4 yrs | £-1,903 |
| 5 kW | 4416 kWh | 3401 kWh | 1016 kWh | £879 | £102 | £980 | £19,623 | 20.0 yrs | £-17 |
| 6 kW | 5300 kWh | 4081 kWh | 1219 kWh | £1,054 | £122 | £1,176 | £21,657 | 18.4 yrs | £1,870 |
| 7 kW | 6183 kWh | 4761 kWh | 1422 kWh | £1,230 | £142 | £1,372 | £23,692 | 17.3 yrs | £3,757 |
| 8 kW | 7066 kWh | 5441 kWh | 1625 kWh | £1,406 | £163 | £1,568 | £25,726 | 16.4 yrs | £5,643 |
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.