A typical roof here lands around 3.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 1113 kWh per year on a south-facing roof. We value self-used electricity at 26.9p 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: £933, Upfront: £10,173, Break-even: 10.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2226 kWh | 890 kWh | 1335 kWh | £240 | £134 | £373 | £4,069 | 10.9 yrs | £3,395 |
| 3 kW | 3338 kWh | 1335 kWh | 2003 kWh | £359 | £200 | £560 | £6,104 | 10.9 yrs | £5,092 |
| 4 kW | 4451 kWh | 1780 kWh | 2671 kWh | £479 | £267 | £746 | £8,138 | 10.9 yrs | £6,790 |
| 5 kW | 5564 kWh | 2226 kWh | 3338 kWh | £599 | £334 | £933 | £10,173 | 10.9 yrs | £8,487 |
| 6 kW | 6677 kWh | 2671 kWh | 4006 kWh | £719 | £401 | £1,120 | £12,207 | 10.9 yrs | £10,184 |
| 7 kW | 7790 kWh | 3116 kWh | 4674 kWh | £839 | £467 | £1,306 | £14,242 | 10.9 yrs | £11,882 |
| 8 kW | 8902 kWh | 3561 kWh | 5341 kWh | £959 | £534 | £1,493 | £16,276 | 10.9 yrs | £13,579 |
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: £1,121, Upfront: £12,273, Break-even: 10.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2226 kWh | 1335 kWh | 890 kWh | £359 | £89 | £449 | £6,169 | 13.8 yrs | £2,801 |
| 3 kW | 3338 kWh | 2003 kWh | 1335 kWh | £539 | £134 | £673 | £8,204 | 12.2 yrs | £5,252 |
| 4 kW | 4451 kWh | 2671 kWh | 1780 kWh | £719 | £178 | £897 | £10,238 | 11.4 yrs | £7,702 |
| 5 kW | 5564 kWh | 3338 kWh | 2226 kWh | £899 | £223 | £1,121 | £12,273 | 10.9 yrs | £10,153 |
| 6 kW | 6677 kWh | 4006 kWh | 2671 kWh | £1,078 | £267 | £1,346 | £14,307 | 10.6 yrs | £12,603 |
| 7 kW | 7790 kWh | 4674 kWh | 3116 kWh | £1,258 | £312 | £1,570 | £16,342 | 10.4 yrs | £15,054 |
| 8 kW | 8902 kWh | 5341 kWh | 3561 kWh | £1,438 | £356 | £1,794 | £18,376 | 10.2 yrs | £17,504 |
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: £1,215, Upfront: £13,673, Break-even: 11.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2226 kWh | 1558 kWh | 668 kWh | £419 | £67 | £486 | £7,569 | 15.6 yrs | £2,154 |
| 3 kW | 3338 kWh | 2337 kWh | 1002 kWh | £629 | £100 | £729 | £9,604 | 13.2 yrs | £4,981 |
| 4 kW | 4451 kWh | 3116 kWh | 1335 kWh | £839 | £134 | £972 | £11,638 | 12.0 yrs | £7,809 |
| 5 kW | 5564 kWh | 3895 kWh | 1669 kWh | £1,048 | £167 | £1,215 | £13,673 | 11.2 yrs | £10,636 |
| 6 kW | 6677 kWh | 4674 kWh | 2003 kWh | £1,258 | £200 | £1,458 | £15,707 | 10.8 yrs | £13,463 |
| 7 kW | 7790 kWh | 5453 kWh | 2337 kWh | £1,468 | £234 | £1,702 | £17,742 | 10.4 yrs | £16,290 |
| 8 kW | 8902 kWh | 6232 kWh | 2671 kWh | £1,678 | £267 | £1,945 | £19,776 | 10.2 yrs | £19,117 |
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: £1,244, Upfront: £15,423, Break-even: 12.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2226 kWh | 1625 kWh | 601 kWh | £437 | £60 | £497 | £9,319 | 18.7 yrs | £630 |
| 3 kW | 3338 kWh | 2437 kWh | 901 kWh | £656 | £90 | £746 | £11,354 | 15.2 yrs | £3,570 |
| 4 kW | 4451 kWh | 3249 kWh | 1202 kWh | £875 | £120 | £995 | £13,388 | 13.5 yrs | £6,510 |
| 5 kW | 5564 kWh | 4062 kWh | 1502 kWh | £1,093 | £150 | £1,244 | £15,423 | 12.4 yrs | £9,451 |
| 6 kW | 6677 kWh | 4874 kWh | 1803 kWh | £1,312 | £180 | £1,492 | £17,457 | 11.7 yrs | £12,391 |
| 7 kW | 7790 kWh | 5686 kWh | 2103 kWh | £1,531 | £210 | £1,741 | £19,492 | 11.2 yrs | £15,331 |
| 8 kW | 8902 kWh | 6499 kWh | 2404 kWh | £1,749 | £240 | £1,990 | £21,526 | 10.8 yrs | £18,271 |
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: £1,262, Upfront: £17,173, 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 | 2226 kWh | 1669 kWh | 556 kWh | £449 | £56 | £505 | £11,069 | 21.9 yrs | £-969 |
| 3 kW | 3338 kWh | 2504 kWh | 835 kWh | £674 | £83 | £757 | £13,104 | 17.3 yrs | £2,046 |
| 4 kW | 4451 kWh | 3338 kWh | 1113 kWh | £899 | £111 | £1,010 | £15,138 | 15.0 yrs | £5,062 |
| 5 kW | 5564 kWh | 4173 kWh | 1391 kWh | £1,123 | £139 | £1,262 | £17,173 | 13.6 yrs | £8,077 |
| 6 kW | 6677 kWh | 5008 kWh | 1669 kWh | £1,348 | £167 | £1,515 | £19,207 | 12.7 yrs | £11,093 |
| 7 kW | 7790 kWh | 5842 kWh | 1947 kWh | £1,573 | £195 | £1,767 | £21,242 | 12.0 yrs | £14,108 |
| 8 kW | 8902 kWh | 6677 kWh | 2226 kWh | £1,797 | £223 | £2,020 | £23,276 | 11.5 yrs | £17,123 |
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: £1,281, Upfront: £19,623, Break-even: 15.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2226 kWh | 1714 kWh | 512 kWh | £461 | £51 | £513 | £13,519 | 26.4 yrs | £-3,269 |
| 3 kW | 3338 kWh | 2571 kWh | 768 kWh | £692 | £77 | £769 | £15,554 | 20.2 yrs | £-178 |
| 4 kW | 4451 kWh | 3427 kWh | 1024 kWh | £923 | £102 | £1,025 | £17,588 | 17.2 yrs | £2,913 |
| 5 kW | 5564 kWh | 4284 kWh | 1280 kWh | £1,153 | £128 | £1,281 | £19,623 | 15.3 yrs | £6,004 |
| 6 kW | 6677 kWh | 5141 kWh | 1536 kWh | £1,384 | £154 | £1,538 | £21,657 | 14.1 yrs | £9,094 |
| 7 kW | 7790 kWh | 5998 kWh | 1792 kWh | £1,615 | £179 | £1,794 | £23,692 | 13.2 yrs | £12,185 |
| 8 kW | 8902 kWh | 6855 kWh | 2048 kWh | £1,845 | £205 | £2,050 | £25,726 | 12.5 yrs | £15,276 |
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.