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 958 kWh per year on a south-facing roof. We value self-used electricity at 25.6p 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: £779, Upfront: £10,173, Break-even: 13.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1916 kWh | 766 kWh | 1150 kWh | £197 | £115 | £311 | £4,069 | 13.1 yrs | £2,161 |
| 3 kW | 2874 kWh | 1150 kWh | 1725 kWh | £295 | £172 | £467 | £6,104 | 13.1 yrs | £3,241 |
| 4 kW | 3832 kWh | 1533 kWh | 2299 kWh | £393 | £230 | £623 | £8,138 | 13.1 yrs | £4,321 |
| 5 kW | 4790 kWh | 1916 kWh | 2874 kWh | £491 | £287 | £779 | £10,173 | 13.1 yrs | £5,402 |
| 6 kW | 5748 kWh | 2299 kWh | 3449 kWh | £590 | £345 | £934 | £12,207 | 13.1 yrs | £6,482 |
| 7 kW | 6706 kWh | 2683 kWh | 4024 kWh | £688 | £402 | £1,090 | £14,242 | 13.1 yrs | £7,563 |
| 8 kW | 7665 kWh | 3066 kWh | 4599 kWh | £786 | £460 | £1,246 | £16,276 | 13.1 yrs | £8,643 |
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: £929, Upfront: £12,273, Break-even: 13.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1916 kWh | 1150 kWh | 766 kWh | £295 | £77 | £371 | £6,169 | 16.6 yrs | £1,259 |
| 3 kW | 2874 kWh | 1725 kWh | 1150 kWh | £442 | £115 | £557 | £8,204 | 14.7 yrs | £2,939 |
| 4 kW | 3832 kWh | 2299 kWh | 1533 kWh | £590 | £153 | £743 | £10,238 | 13.8 yrs | £4,619 |
| 5 kW | 4790 kWh | 2874 kWh | 1916 kWh | £737 | £192 | £929 | £12,273 | 13.2 yrs | £6,299 |
| 6 kW | 5748 kWh | 3449 kWh | 2299 kWh | £884 | £230 | £1,114 | £14,307 | 12.8 yrs | £7,978 |
| 7 kW | 6706 kWh | 4024 kWh | 2683 kWh | £1,032 | £268 | £1,300 | £16,342 | 12.6 yrs | £9,658 |
| 8 kW | 7665 kWh | 4599 kWh | 3066 kWh | £1,179 | £307 | £1,486 | £18,376 | 12.4 yrs | £11,338 |
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: £1,003, Upfront: £13,673, Break-even: 13.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1916 kWh | 1341 kWh | 575 kWh | £344 | £57 | £401 | £7,569 | 18.9 yrs | £459 |
| 3 kW | 2874 kWh | 2012 kWh | 862 kWh | £516 | £86 | £602 | £9,604 | 16.0 yrs | £2,438 |
| 4 kW | 3832 kWh | 2683 kWh | 1150 kWh | £688 | £115 | £803 | £11,638 | 14.5 yrs | £4,418 |
| 5 kW | 4790 kWh | 3353 kWh | 1437 kWh | £860 | £144 | £1,003 | £13,673 | 13.6 yrs | £6,397 |
| 6 kW | 5748 kWh | 4024 kWh | 1725 kWh | £1,032 | £172 | £1,204 | £15,707 | 13.0 yrs | £8,377 |
| 7 kW | 6706 kWh | 4695 kWh | 2012 kWh | £1,204 | £201 | £1,405 | £17,742 | 12.6 yrs | £10,356 |
| 8 kW | 7665 kWh | 5365 kWh | 2299 kWh | £1,376 | £230 | £1,606 | £19,776 | 12.3 yrs | £12,335 |
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: £1,026, Upfront: £15,423, Break-even: 15.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1916 kWh | 1399 kWh | 517 kWh | £359 | £52 | £410 | £9,319 | 22.7 yrs | £-1,111 |
| 3 kW | 2874 kWh | 2098 kWh | 776 kWh | £538 | £78 | £616 | £11,354 | 18.4 yrs | £958 |
| 4 kW | 3832 kWh | 2798 kWh | 1035 kWh | £717 | £103 | £821 | £13,388 | 16.3 yrs | £3,027 |
| 5 kW | 4790 kWh | 3497 kWh | 1293 kWh | £897 | £129 | £1,026 | £15,423 | 15.0 yrs | £5,097 |
| 6 kW | 5748 kWh | 4196 kWh | 1552 kWh | £1,076 | £155 | £1,231 | £17,457 | 14.2 yrs | £7,166 |
| 7 kW | 6706 kWh | 4896 kWh | 1811 kWh | £1,255 | £181 | £1,436 | £19,492 | 13.6 yrs | £9,235 |
| 8 kW | 7665 kWh | 5595 kWh | 2069 kWh | £1,435 | £207 | £1,642 | £21,526 | 13.1 yrs | £11,305 |
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: £1,041, Upfront: £17,173, Break-even: 16.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1916 kWh | 1437 kWh | 479 kWh | £368 | £48 | £416 | £11,069 | 26.6 yrs | £-2,741 |
| 3 kW | 2874 kWh | 2156 kWh | 719 kWh | £553 | £72 | £625 | £13,104 | 21.0 yrs | £-612 |
| 4 kW | 3832 kWh | 2874 kWh | 958 kWh | £737 | £96 | £833 | £15,138 | 18.2 yrs | £1,517 |
| 5 kW | 4790 kWh | 3593 kWh | 1198 kWh | £921 | £120 | £1,041 | £17,173 | 16.5 yrs | £3,646 |
| 6 kW | 5748 kWh | 4311 kWh | 1437 kWh | £1,105 | £144 | £1,249 | £19,207 | 15.4 yrs | £5,776 |
| 7 kW | 6706 kWh | 5030 kWh | 1677 kWh | £1,290 | £168 | £1,457 | £21,242 | 14.6 yrs | £7,905 |
| 8 kW | 7665 kWh | 5748 kWh | 1916 kWh | £1,474 | £192 | £1,666 | £23,276 | 14.0 yrs | £10,034 |
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: £1,056, Upfront: £19,623, Break-even: 18.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1916 kWh | 1475 kWh | 441 kWh | £378 | £44 | £422 | £13,519 | 32.0 yrs | £-5,072 |
| 3 kW | 2874 kWh | 2213 kWh | 661 kWh | £567 | £66 | £634 | £15,554 | 24.5 yrs | £-2,882 |
| 4 kW | 3832 kWh | 2951 kWh | 881 kWh | £757 | £88 | £845 | £17,588 | 20.8 yrs | £-693 |
| 5 kW | 4790 kWh | 3689 kWh | 1102 kWh | £946 | £110 | £1,056 | £19,623 | 18.6 yrs | £1,496 |
| 6 kW | 5748 kWh | 4426 kWh | 1322 kWh | £1,135 | £132 | £1,267 | £21,657 | 17.1 yrs | £3,685 |
| 7 kW | 6706 kWh | 5164 kWh | 1542 kWh | £1,324 | £154 | £1,478 | £23,692 | 16.0 yrs | £5,874 |
| 8 kW | 7665 kWh | 5902 kWh | 1763 kWh | £1,513 | £176 | £1,689 | £25,726 | 15.2 yrs | £8,064 |
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.