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 991 kWh per year on a south-facing roof. We value self-used electricity at 26.5p 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: £823, Upfront: £10,173, 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 | 1982 kWh | 793 kWh | 1189 kWh | £210 | £119 | £329 | £4,069 | 12.4 yrs | £2,517 |
| 3 kW | 2974 kWh | 1189 kWh | 1784 kWh | £316 | £178 | £494 | £6,104 | 12.4 yrs | £3,776 |
| 4 kW | 3965 kWh | 1586 kWh | 2379 kWh | £421 | £238 | £659 | £8,138 | 12.4 yrs | £5,034 |
| 5 kW | 4956 kWh | 1982 kWh | 2974 kWh | £526 | £297 | £823 | £10,173 | 12.4 yrs | £6,293 |
| 6 kW | 5947 kWh | 2379 kWh | 3568 kWh | £631 | £357 | £988 | £12,207 | 12.4 yrs | £7,552 |
| 7 kW | 6938 kWh | 2775 kWh | 4163 kWh | £736 | £416 | £1,153 | £14,242 | 12.4 yrs | £8,810 |
| 8 kW | 7930 kWh | 3172 kWh | 4758 kWh | £841 | £476 | £1,317 | £16,276 | 12.4 yrs | £10,069 |
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: £987, Upfront: £12,273, 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 | 1982 kWh | 1189 kWh | 793 kWh | £316 | £79 | £395 | £6,169 | 15.6 yrs | £1,728 |
| 3 kW | 2974 kWh | 1784 kWh | 1189 kWh | £473 | £119 | £592 | £8,204 | 13.9 yrs | £3,642 |
| 4 kW | 3965 kWh | 2379 kWh | 1586 kWh | £631 | £159 | £790 | £10,238 | 13.0 yrs | £5,556 |
| 5 kW | 4956 kWh | 2974 kWh | 1982 kWh | £789 | £198 | £987 | £12,273 | 12.4 yrs | £7,470 |
| 6 kW | 5947 kWh | 3568 kWh | 2379 kWh | £947 | £238 | £1,185 | £14,307 | 12.1 yrs | £9,384 |
| 7 kW | 6938 kWh | 4163 kWh | 2775 kWh | £1,104 | £278 | £1,382 | £16,342 | 11.8 yrs | £11,298 |
| 8 kW | 7930 kWh | 4758 kWh | 3172 kWh | £1,262 | £317 | £1,579 | £18,376 | 11.6 yrs | £13,212 |
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: £1,069, Upfront: £13,673, Break-even: 12.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1982 kWh | 1388 kWh | 595 kWh | £368 | £59 | £428 | £7,569 | 17.7 yrs | £983 |
| 3 kW | 2974 kWh | 2081 kWh | 892 kWh | £552 | £89 | £641 | £9,604 | 15.0 yrs | £3,225 |
| 4 kW | 3965 kWh | 2775 kWh | 1189 kWh | £736 | £119 | £855 | £11,638 | 13.6 yrs | £5,467 |
| 5 kW | 4956 kWh | 3469 kWh | 1487 kWh | £920 | £149 | £1,069 | £13,673 | 12.8 yrs | £7,708 |
| 6 kW | 5947 kWh | 4163 kWh | 1784 kWh | £1,104 | £178 | £1,283 | £15,707 | 12.2 yrs | £9,950 |
| 7 kW | 6938 kWh | 4857 kWh | 2081 kWh | £1,289 | £208 | £1,497 | £17,742 | 11.9 yrs | £12,192 |
| 8 kW | 7930 kWh | 5551 kWh | 2379 kWh | £1,473 | £238 | £1,710 | £19,776 | 11.6 yrs | £14,433 |
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: £1,094, Upfront: £15,423, 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 | 1982 kWh | 1447 kWh | 535 kWh | £384 | £54 | £437 | £9,319 | 21.3 yrs | £-570 |
| 3 kW | 2974 kWh | 2171 kWh | 803 kWh | £576 | £80 | £656 | £11,354 | 17.3 yrs | £1,770 |
| 4 kW | 3965 kWh | 2894 kWh | 1070 kWh | £768 | £107 | £875 | £13,388 | 15.3 yrs | £4,110 |
| 5 kW | 4956 kWh | 3618 kWh | 1338 kWh | £960 | £134 | £1,094 | £15,423 | 14.1 yrs | £6,450 |
| 6 kW | 5947 kWh | 4341 kWh | 1606 kWh | £1,152 | £161 | £1,312 | £17,457 | 13.3 yrs | £8,790 |
| 7 kW | 6938 kWh | 5065 kWh | 1873 kWh | £1,344 | £187 | £1,531 | £19,492 | 12.7 yrs | £11,130 |
| 8 kW | 7930 kWh | 5789 kWh | 2141 kWh | £1,536 | £214 | £1,750 | £21,526 | 12.3 yrs | £13,470 |
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: £1,110, Upfront: £17,173, Break-even: 15.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1982 kWh | 1487 kWh | 496 kWh | £394 | £50 | £444 | £11,069 | 24.9 yrs | £-2,189 |
| 3 kW | 2974 kWh | 2230 kWh | 743 kWh | £592 | £74 | £666 | £13,104 | 19.7 yrs | £217 |
| 4 kW | 3965 kWh | 2974 kWh | 991 kWh | £789 | £99 | £888 | £15,138 | 17.0 yrs | £2,622 |
| 5 kW | 4956 kWh | 3717 kWh | 1239 kWh | £986 | £124 | £1,110 | £17,173 | 15.5 yrs | £5,028 |
| 6 kW | 5947 kWh | 4460 kWh | 1487 kWh | £1,183 | £149 | £1,332 | £19,207 | 14.4 yrs | £7,433 |
| 7 kW | 6938 kWh | 5204 kWh | 1735 kWh | £1,381 | £173 | £1,554 | £21,242 | 13.7 yrs | £9,839 |
| 8 kW | 7930 kWh | 5947 kWh | 1982 kWh | £1,578 | £198 | £1,776 | £23,276 | 13.1 yrs | £12,244 |
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: £1,126, Upfront: £19,623, Break-even: 17.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1982 kWh | 1526 kWh | 456 kWh | £405 | £46 | £451 | £13,519 | 30.0 yrs | £-4,508 |
| 3 kW | 2974 kWh | 2290 kWh | 684 kWh | £607 | £68 | £676 | £15,554 | 23.0 yrs | £-2,037 |
| 4 kW | 3965 kWh | 3053 kWh | 912 kWh | £810 | £91 | £901 | £17,588 | 19.5 yrs | £434 |
| 5 kW | 4956 kWh | 3816 kWh | 1140 kWh | £1,012 | £114 | £1,126 | £19,623 | 17.4 yrs | £2,905 |
| 6 kW | 5947 kWh | 4579 kWh | 1368 kWh | £1,215 | £137 | £1,352 | £21,657 | 16.0 yrs | £5,376 |
| 7 kW | 6938 kWh | 5343 kWh | 1596 kWh | £1,417 | £160 | £1,577 | £23,692 | 15.0 yrs | £7,847 |
| 8 kW | 7930 kWh | 6106 kWh | 1824 kWh | £1,620 | £182 | £1,802 | £25,726 | 14.3 yrs | £10,319 |
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.