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 912 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: £745, Upfront: £10,173, Break-even: 13.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1823 kWh | 729 kWh | 1094 kWh | £188 | £109 | £298 | £4,069 | 13.7 yrs | £1,888 |
| 3 kW | 2735 kWh | 1094 kWh | 1641 kWh | £283 | £164 | £447 | £6,104 | 13.7 yrs | £2,832 |
| 4 kW | 3647 kWh | 1459 kWh | 2188 kWh | £377 | £219 | £596 | £8,138 | 13.7 yrs | £3,776 |
| 5 kW | 4558 kWh | 1823 kWh | 2735 kWh | £471 | £273 | £745 | £10,173 | 13.7 yrs | £4,720 |
| 6 kW | 5470 kWh | 2188 kWh | 3282 kWh | £565 | £328 | £894 | £12,207 | 13.7 yrs | £5,664 |
| 7 kW | 6382 kWh | 2553 kWh | 3829 kWh | £660 | £383 | £1,042 | £14,242 | 13.7 yrs | £6,608 |
| 8 kW | 7293 kWh | 2917 kWh | 4376 kWh | £754 | £438 | £1,191 | £16,276 | 13.7 yrs | £7,552 |
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: £889, Upfront: £12,273, Break-even: 13.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1823 kWh | 1094 kWh | 729 kWh | £283 | £73 | £356 | £6,169 | 17.3 yrs | £943 |
| 3 kW | 2735 kWh | 1641 kWh | 1094 kWh | £424 | £109 | £533 | £8,204 | 15.4 yrs | £2,465 |
| 4 kW | 3647 kWh | 2188 kWh | 1459 kWh | £565 | £146 | £711 | £10,238 | 14.4 yrs | £3,987 |
| 5 kW | 4558 kWh | 2735 kWh | 1823 kWh | £707 | £182 | £889 | £12,273 | 13.8 yrs | £5,508 |
| 6 kW | 5470 kWh | 3282 kWh | 2188 kWh | £848 | £219 | £1,067 | £14,307 | 13.4 yrs | £7,030 |
| 7 kW | 6382 kWh | 3829 kWh | 2553 kWh | £989 | £255 | £1,245 | £16,342 | 13.1 yrs | £8,552 |
| 8 kW | 7293 kWh | 4376 kWh | 2917 kWh | £1,131 | £292 | £1,422 | £18,376 | 12.9 yrs | £10,073 |
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: £961, Upfront: £13,673, 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 | 1823 kWh | 1276 kWh | 547 kWh | £330 | £55 | £384 | £7,569 | 19.7 yrs | £121 |
| 3 kW | 2735 kWh | 1914 kWh | 820 kWh | £495 | £82 | £577 | £9,604 | 16.7 yrs | £1,931 |
| 4 kW | 3647 kWh | 2553 kWh | 1094 kWh | £660 | £109 | £769 | £11,638 | 15.1 yrs | £3,742 |
| 5 kW | 4558 kWh | 3191 kWh | 1367 kWh | £824 | £137 | £961 | £13,673 | 14.2 yrs | £5,552 |
| 6 kW | 5470 kWh | 3829 kWh | 1641 kWh | £989 | £164 | £1,153 | £15,707 | 13.6 yrs | £7,363 |
| 7 kW | 6382 kWh | 4467 kWh | 1914 kWh | £1,154 | £191 | £1,346 | £17,742 | 13.2 yrs | £9,173 |
| 8 kW | 7293 kWh | 5105 kWh | 2188 kWh | £1,319 | £219 | £1,538 | £19,776 | 12.9 yrs | £10,984 |
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: £983, Upfront: £15,423, Break-even: 15.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1823 kWh | 1331 kWh | 492 kWh | £344 | £49 | £393 | £9,319 | 23.7 yrs | £-1,456 |
| 3 kW | 2735 kWh | 1997 kWh | 738 kWh | £516 | £74 | £590 | £11,354 | 19.3 yrs | £441 |
| 4 kW | 3647 kWh | 2662 kWh | 985 kWh | £688 | £98 | £786 | £13,388 | 17.0 yrs | £2,338 |
| 5 kW | 4558 kWh | 3328 kWh | 1231 kWh | £860 | £123 | £983 | £15,423 | 15.7 yrs | £4,236 |
| 6 kW | 5470 kWh | 3993 kWh | 1477 kWh | £1,032 | £148 | £1,179 | £17,457 | 14.8 yrs | £6,133 |
| 7 kW | 6382 kWh | 4659 kWh | 1723 kWh | £1,204 | £172 | £1,376 | £19,492 | 14.2 yrs | £8,030 |
| 8 kW | 7293 kWh | 5324 kWh | 1969 kWh | £1,376 | £197 | £1,573 | £21,526 | 13.7 yrs | £9,927 |
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: £997, Upfront: £17,173, Break-even: 17.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1823 kWh | 1367 kWh | 456 kWh | £353 | £46 | £399 | £11,069 | 27.7 yrs | £-3,090 |
| 3 kW | 2735 kWh | 2051 kWh | 684 kWh | £530 | £68 | £598 | £13,104 | 21.9 yrs | £-1,135 |
| 4 kW | 3647 kWh | 2735 kWh | 912 kWh | £707 | £91 | £798 | £15,138 | 19.0 yrs | £819 |
| 5 kW | 4558 kWh | 3419 kWh | 1140 kWh | £883 | £114 | £997 | £17,173 | 17.2 yrs | £2,774 |
| 6 kW | 5470 kWh | 4102 kWh | 1367 kWh | £1,060 | £137 | £1,197 | £19,207 | 16.0 yrs | £4,729 |
| 7 kW | 6382 kWh | 4786 kWh | 1595 kWh | £1,237 | £160 | £1,396 | £21,242 | 15.2 yrs | £6,684 |
| 8 kW | 7293 kWh | 5470 kWh | 1823 kWh | £1,413 | £182 | £1,596 | £23,276 | 14.6 yrs | £8,639 |
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: £1,012, Upfront: £19,623, Break-even: 19.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1823 kWh | 1404 kWh | 419 kWh | £363 | £42 | £405 | £13,519 | 33.4 yrs | £-5,425 |
| 3 kW | 2735 kWh | 2106 kWh | 629 kWh | £544 | £63 | £607 | £15,554 | 25.6 yrs | £-3,412 |
| 4 kW | 3647 kWh | 2808 kWh | 839 kWh | £726 | £84 | £809 | £17,588 | 21.7 yrs | £-1,399 |
| 5 kW | 4558 kWh | 3510 kWh | 1048 kWh | £907 | £105 | £1,012 | £19,623 | 19.4 yrs | £613 |
| 6 kW | 5470 kWh | 4212 kWh | 1258 kWh | £1,088 | £126 | £1,214 | £21,657 | 17.8 yrs | £2,626 |
| 7 kW | 6382 kWh | 4914 kWh | 1468 kWh | £1,270 | £147 | £1,416 | £23,692 | 16.7 yrs | £4,638 |
| 8 kW | 7293 kWh | 5616 kWh | 1677 kWh | £1,451 | £168 | £1,619 | £25,726 | 15.9 yrs | £6,651 |
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.