A typical roof here lands around 5.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 817 kWh per year on a south-facing roof. We value self-used electricity at 27.1p 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: £688, Upfront: £10,173, Break-even: 14.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1635 kWh | 654 kWh | 981 kWh | £177 | £98 | £275 | £4,069 | 14.8 yrs | £1,432 |
| 3 kW | 2452 kWh | 981 kWh | 1471 kWh | £265 | £147 | £413 | £6,104 | 14.8 yrs | £2,148 |
| 4 kW | 3270 kWh | 1308 kWh | 1962 kWh | £354 | £196 | £550 | £8,138 | 14.8 yrs | £2,864 |
| 5 kW | 4087 kWh | 1635 kWh | 2452 kWh | £442 | £245 | £688 | £10,173 | 14.8 yrs | £3,580 |
| 6 kW | 4905 kWh | 1962 kWh | 2943 kWh | £531 | £294 | £825 | £12,207 | 14.8 yrs | £4,296 |
| 7 kW | 5722 kWh | 2289 kWh | 3433 kWh | £619 | £343 | £963 | £14,242 | 14.8 yrs | £5,012 |
| 8 kW | 6540 kWh | 2616 kWh | 3924 kWh | £708 | £392 | £1,100 | £16,276 | 14.8 yrs | £5,728 |
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: £827, Upfront: £12,273, Break-even: 14.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1635 kWh | 981 kWh | 654 kWh | £265 | £65 | £331 | £6,169 | 18.6 yrs | £448 |
| 3 kW | 2452 kWh | 1471 kWh | 981 kWh | £398 | £98 | £496 | £8,204 | 16.5 yrs | £1,721 |
| 4 kW | 3270 kWh | 1962 kWh | 1308 kWh | £531 | £131 | £662 | £10,238 | 15.5 yrs | £2,995 |
| 5 kW | 4087 kWh | 2452 kWh | 1635 kWh | £664 | £163 | £827 | £12,273 | 14.8 yrs | £4,269 |
| 6 kW | 4905 kWh | 2943 kWh | 1962 kWh | £796 | £196 | £993 | £14,307 | 14.4 yrs | £5,543 |
| 7 kW | 5722 kWh | 3433 kWh | 2289 kWh | £929 | £229 | £1,158 | £16,342 | 14.1 yrs | £6,817 |
| 8 kW | 6540 kWh | 3924 kWh | 2616 kWh | £1,062 | £262 | £1,323 | £18,376 | 13.9 yrs | £8,091 |
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: £897, Upfront: £13,673, Break-even: 15.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1635 kWh | 1144 kWh | 490 kWh | £310 | £49 | £359 | £7,569 | 21.1 yrs | £-395 |
| 3 kW | 2452 kWh | 1717 kWh | 736 kWh | £465 | £74 | £538 | £9,604 | 17.8 yrs | £1,158 |
| 4 kW | 3270 kWh | 2289 kWh | 981 kWh | £619 | £98 | £717 | £11,638 | 16.2 yrs | £2,711 |
| 5 kW | 4087 kWh | 2861 kWh | 1226 kWh | £774 | £123 | £897 | £13,673 | 15.2 yrs | £4,264 |
| 6 kW | 4905 kWh | 3433 kWh | 1471 kWh | £929 | £147 | £1,076 | £15,707 | 14.6 yrs | £5,816 |
| 7 kW | 5722 kWh | 4005 kWh | 1717 kWh | £1,084 | £172 | £1,256 | £17,742 | 14.1 yrs | £7,369 |
| 8 kW | 6540 kWh | 4578 kWh | 1962 kWh | £1,239 | £196 | £1,435 | £19,776 | 13.8 yrs | £8,922 |
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: £918, Upfront: £15,423, Break-even: 16.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1635 kWh | 1193 kWh | 441 kWh | £323 | £44 | £367 | £9,319 | 25.4 yrs | £-1,977 |
| 3 kW | 2452 kWh | 1790 kWh | 662 kWh | £484 | £66 | £551 | £11,354 | 20.6 yrs | £-341 |
| 4 kW | 3270 kWh | 2387 kWh | 883 kWh | £646 | £88 | £734 | £13,388 | 18.2 yrs | £1,296 |
| 5 kW | 4087 kWh | 2984 kWh | 1104 kWh | £807 | £110 | £918 | £15,423 | 16.8 yrs | £2,932 |
| 6 kW | 4905 kWh | 3580 kWh | 1324 kWh | £969 | £132 | £1,101 | £17,457 | 15.9 yrs | £4,569 |
| 7 kW | 5722 kWh | 4177 kWh | 1545 kWh | £1,130 | £154 | £1,285 | £19,492 | 15.2 yrs | £6,205 |
| 8 kW | 6540 kWh | 4774 kWh | 1766 kWh | £1,292 | £177 | £1,468 | £21,526 | 14.7 yrs | £7,841 |
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: £932, Upfront: £17,173, Break-even: 18.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1635 kWh | 1226 kWh | 409 kWh | £332 | £41 | £373 | £11,069 | 29.7 yrs | £-3,616 |
| 3 kW | 2452 kWh | 1839 kWh | 613 kWh | £498 | £61 | £559 | £13,104 | 23.4 yrs | £-1,923 |
| 4 kW | 3270 kWh | 2452 kWh | 817 kWh | £664 | £82 | £745 | £15,138 | 20.3 yrs | £-231 |
| 5 kW | 4087 kWh | 3065 kWh | 1022 kWh | £829 | £102 | £932 | £17,173 | 18.4 yrs | £1,461 |
| 6 kW | 4905 kWh | 3678 kWh | 1226 kWh | £995 | £123 | £1,118 | £19,207 | 17.2 yrs | £3,153 |
| 7 kW | 5722 kWh | 4292 kWh | 1431 kWh | £1,161 | £143 | £1,304 | £21,242 | 16.3 yrs | £4,845 |
| 8 kW | 6540 kWh | 4905 kWh | 1635 kWh | £1,327 | £163 | £1,491 | £23,276 | 15.6 yrs | £6,538 |
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: £946, Upfront: £19,623, Break-even: 20.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1635 kWh | 1259 kWh | 376 kWh | £341 | £38 | £378 | £13,519 | 35.7 yrs | £-5,954 |
| 3 kW | 2452 kWh | 1888 kWh | 564 kWh | £511 | £56 | £567 | £15,554 | 27.4 yrs | £-4,206 |
| 4 kW | 3270 kWh | 2518 kWh | 752 kWh | £681 | £75 | £756 | £17,588 | 23.2 yrs | £-2,458 |
| 5 kW | 4087 kWh | 3147 kWh | 940 kWh | £852 | £94 | £946 | £19,623 | 20.8 yrs | £-710 |
| 6 kW | 4905 kWh | 3777 kWh | 1128 kWh | £1,022 | £113 | £1,135 | £21,657 | 19.1 yrs | £1,038 |
| 7 kW | 5722 kWh | 4406 kWh | 1316 kWh | £1,192 | £132 | £1,324 | £23,692 | 17.9 yrs | £2,786 |
| 8 kW | 6540 kWh | 5035 kWh | 1504 kWh | £1,363 | £150 | £1,513 | £25,726 | 17.0 yrs | £4,534 |
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.