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 894 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: £730, Upfront: £10,173, Break-even: 13.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1787 kWh | 715 kWh | 1072 kWh | £185 | £107 | £292 | £4,069 | 13.9 yrs | £1,770 |
| 3 kW | 2681 kWh | 1072 kWh | 1609 kWh | £277 | £161 | £438 | £6,104 | 13.9 yrs | £2,656 |
| 4 kW | 3575 kWh | 1430 kWh | 2145 kWh | £369 | £214 | £584 | £8,138 | 13.9 yrs | £3,541 |
| 5 kW | 4468 kWh | 1787 kWh | 2681 kWh | £462 | £268 | £730 | £10,173 | 13.9 yrs | £4,426 |
| 6 kW | 5362 kWh | 2145 kWh | 3217 kWh | £554 | £322 | £876 | £12,207 | 13.9 yrs | £5,311 |
| 7 kW | 6255 kWh | 2502 kWh | 3753 kWh | £647 | £375 | £1,022 | £14,242 | 13.9 yrs | £6,196 |
| 8 kW | 7149 kWh | 2860 kWh | 4289 kWh | £739 | £429 | £1,168 | £16,276 | 13.9 yrs | £7,082 |
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: £871, Upfront: £12,273, 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 | 1787 kWh | 1072 kWh | 715 kWh | £277 | £71 | £349 | £6,169 | 17.7 yrs | £803 |
| 3 kW | 2681 kWh | 1609 kWh | 1072 kWh | £416 | £107 | £523 | £8,204 | 15.7 yrs | £2,254 |
| 4 kW | 3575 kWh | 2145 kWh | 1430 kWh | £554 | £143 | £697 | £10,238 | 14.7 yrs | £3,706 |
| 5 kW | 4468 kWh | 2681 kWh | 1787 kWh | £693 | £179 | £871 | £12,273 | 14.1 yrs | £5,157 |
| 6 kW | 5362 kWh | 3217 kWh | 2145 kWh | £831 | £214 | £1,046 | £14,307 | 13.7 yrs | £6,608 |
| 7 kW | 6255 kWh | 3753 kWh | 2502 kWh | £970 | £250 | £1,220 | £16,342 | 13.4 yrs | £8,060 |
| 8 kW | 7149 kWh | 4289 kWh | 2860 kWh | £1,108 | £286 | £1,394 | £18,376 | 13.2 yrs | £9,511 |
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: £942, Upfront: £13,673, Break-even: 14.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1787 kWh | 1251 kWh | 536 kWh | £323 | £54 | £377 | £7,569 | 20.1 yrs | £-31 |
| 3 kW | 2681 kWh | 1877 kWh | 804 kWh | £485 | £80 | £565 | £9,604 | 17.0 yrs | £1,704 |
| 4 kW | 3575 kWh | 2502 kWh | 1072 kWh | £647 | £107 | £754 | £11,638 | 15.4 yrs | £3,438 |
| 5 kW | 4468 kWh | 3128 kWh | 1340 kWh | £808 | £134 | £942 | £13,673 | 14.5 yrs | £5,173 |
| 6 kW | 5362 kWh | 3753 kWh | 1609 kWh | £970 | £161 | £1,131 | £15,707 | 13.9 yrs | £6,907 |
| 7 kW | 6255 kWh | 4379 kWh | 1877 kWh | £1,131 | £188 | £1,319 | £17,742 | 13.4 yrs | £8,642 |
| 8 kW | 7149 kWh | 5004 kWh | 2145 kWh | £1,293 | £214 | £1,508 | £19,776 | 13.1 yrs | £10,376 |
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: £963, Upfront: £15,423, Break-even: 16.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1787 kWh | 1305 kWh | 483 kWh | £337 | £48 | £385 | £9,319 | 24.2 yrs | £-1,611 |
| 3 kW | 2681 kWh | 1957 kWh | 724 kWh | £506 | £72 | £578 | £11,354 | 19.6 yrs | £208 |
| 4 kW | 3575 kWh | 2609 kWh | 965 kWh | £674 | £97 | £771 | £13,388 | 17.4 yrs | £2,028 |
| 5 kW | 4468 kWh | 3262 kWh | 1206 kWh | £843 | £121 | £963 | £15,423 | 16.0 yrs | £3,847 |
| 6 kW | 5362 kWh | 3914 kWh | 1448 kWh | £1,011 | £145 | £1,156 | £17,457 | 15.1 yrs | £5,667 |
| 7 kW | 6255 kWh | 4567 kWh | 1689 kWh | £1,180 | £169 | £1,349 | £19,492 | 14.5 yrs | £7,486 |
| 8 kW | 7149 kWh | 5219 kWh | 1930 kWh | £1,349 | £193 | £1,542 | £21,526 | 14.0 yrs | £9,306 |
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: £978, Upfront: £17,173, Break-even: 17.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1787 kWh | 1340 kWh | 447 kWh | £346 | £45 | £391 | £11,069 | 28.3 yrs | £-3,248 |
| 3 kW | 2681 kWh | 2011 kWh | 670 kWh | £520 | £67 | £587 | £13,104 | 22.3 yrs | £-1,372 |
| 4 kW | 3575 kWh | 2681 kWh | 894 kWh | £693 | £89 | £782 | £15,138 | 19.4 yrs | £504 |
| 5 kW | 4468 kWh | 3351 kWh | 1117 kWh | £866 | £112 | £978 | £17,173 | 17.6 yrs | £2,380 |
| 6 kW | 5362 kWh | 4021 kWh | 1340 kWh | £1,039 | £134 | £1,173 | £19,207 | 16.4 yrs | £4,256 |
| 7 kW | 6255 kWh | 4692 kWh | 1564 kWh | £1,212 | £156 | £1,369 | £21,242 | 15.5 yrs | £6,132 |
| 8 kW | 7149 kWh | 5362 kWh | 1787 kWh | £1,385 | £179 | £1,564 | £23,276 | 14.9 yrs | £8,008 |
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: £992, Upfront: £19,623, Break-even: 19.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1787 kWh | 1376 kWh | 411 kWh | £356 | £41 | £397 | £13,519 | 34.1 yrs | £-5,585 |
| 3 kW | 2681 kWh | 2064 kWh | 617 kWh | £533 | £62 | £595 | £15,554 | 26.1 yrs | £-3,652 |
| 4 kW | 3575 kWh | 2752 kWh | 822 kWh | £711 | £82 | £793 | £17,588 | 22.2 yrs | £-1,719 |
| 5 kW | 4468 kWh | 3441 kWh | 1028 kWh | £889 | £103 | £992 | £19,623 | 19.8 yrs | £213 |
| 6 kW | 5362 kWh | 4129 kWh | 1233 kWh | £1,067 | £123 | £1,190 | £21,657 | 18.2 yrs | £2,146 |
| 7 kW | 6255 kWh | 4817 kWh | 1439 kWh | £1,245 | £144 | £1,389 | £23,692 | 17.1 yrs | £4,079 |
| 8 kW | 7149 kWh | 5505 kWh | 1644 kWh | £1,422 | £164 | £1,587 | £25,726 | 16.2 yrs | £6,011 |
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.