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 1086 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: £911, Upfront: £10,173, 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 | 2173 kWh | 869 kWh | 1304 kWh | £234 | £130 | £364 | £4,069 | 11.2 yrs | £3,217 |
| 3 kW | 3259 kWh | 1304 kWh | 1955 kWh | £351 | £196 | £546 | £6,104 | 11.2 yrs | £4,826 |
| 4 kW | 4345 kWh | 1738 kWh | 2607 kWh | £468 | £261 | £729 | £8,138 | 11.2 yrs | £6,435 |
| 5 kW | 5432 kWh | 2173 kWh | 3259 kWh | £585 | £326 | £911 | £10,173 | 11.2 yrs | £8,043 |
| 6 kW | 6518 kWh | 2607 kWh | 3911 kWh | £702 | £391 | £1,093 | £12,207 | 11.2 yrs | £9,652 |
| 7 kW | 7604 kWh | 3042 kWh | 4563 kWh | £819 | £456 | £1,275 | £14,242 | 11.2 yrs | £11,261 |
| 8 kW | 8691 kWh | 3476 kWh | 5214 kWh | £936 | £521 | £1,457 | £16,276 | 11.2 yrs | £12,869 |
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: £1,095, Upfront: £12,273, 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 | 2173 kWh | 1304 kWh | 869 kWh | £351 | £87 | £438 | £6,169 | 14.1 yrs | £2,588 |
| 3 kW | 3259 kWh | 1955 kWh | 1304 kWh | £526 | £130 | £657 | £8,204 | 12.5 yrs | £4,932 |
| 4 kW | 4345 kWh | 2607 kWh | 1738 kWh | £702 | £174 | £876 | £10,238 | 11.7 yrs | £7,276 |
| 5 kW | 5432 kWh | 3259 kWh | 2173 kWh | £877 | £217 | £1,095 | £12,273 | 11.2 yrs | £9,620 |
| 6 kW | 6518 kWh | 3911 kWh | 2607 kWh | £1,053 | £261 | £1,314 | £14,307 | 10.9 yrs | £11,963 |
| 7 kW | 7604 kWh | 4563 kWh | 3042 kWh | £1,228 | £304 | £1,532 | £16,342 | 10.7 yrs | £14,307 |
| 8 kW | 8691 kWh | 5214 kWh | 3476 kWh | £1,404 | £348 | £1,751 | £18,376 | 10.5 yrs | £16,651 |
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: £1,187, Upfront: £13,673, Break-even: 11.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2173 kWh | 1521 kWh | 652 kWh | £409 | £65 | £475 | £7,569 | 15.9 yrs | £1,923 |
| 3 kW | 3259 kWh | 2281 kWh | 978 kWh | £614 | £98 | £712 | £9,604 | 13.5 yrs | £4,635 |
| 4 kW | 4345 kWh | 3042 kWh | 1304 kWh | £819 | £130 | £949 | £11,638 | 12.3 yrs | £7,346 |
| 5 kW | 5432 kWh | 3802 kWh | 1630 kWh | £1,024 | £163 | £1,187 | £13,673 | 11.5 yrs | £10,058 |
| 6 kW | 6518 kWh | 4563 kWh | 1955 kWh | £1,228 | £196 | £1,424 | £15,707 | 11.0 yrs | £12,769 |
| 7 kW | 7604 kWh | 5323 kWh | 2281 kWh | £1,433 | £228 | £1,661 | £17,742 | 10.7 yrs | £15,481 |
| 8 kW | 8691 kWh | 6084 kWh | 2607 kWh | £1,638 | £261 | £1,898 | £19,776 | 10.4 yrs | £18,192 |
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: £1,214, Upfront: £15,423, Break-even: 12.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2173 kWh | 1586 kWh | 587 kWh | £427 | £59 | £486 | £9,319 | 19.2 yrs | £394 |
| 3 kW | 3259 kWh | 2379 kWh | 880 kWh | £640 | £88 | £728 | £11,354 | 15.6 yrs | £3,215 |
| 4 kW | 4345 kWh | 3172 kWh | 1173 kWh | £854 | £117 | £971 | £13,388 | 13.8 yrs | £6,037 |
| 5 kW | 5432 kWh | 3965 kWh | 1467 kWh | £1,067 | £147 | £1,214 | £15,423 | 12.7 yrs | £8,859 |
| 6 kW | 6518 kWh | 4758 kWh | 1760 kWh | £1,281 | £176 | £1,457 | £17,457 | 12.0 yrs | £11,681 |
| 7 kW | 7604 kWh | 5551 kWh | 2053 kWh | £1,494 | £205 | £1,700 | £19,492 | 11.5 yrs | £14,503 |
| 8 kW | 8691 kWh | 6344 kWh | 2347 kWh | £1,708 | £235 | £1,943 | £21,526 | 11.1 yrs | £17,325 |
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: £1,232, Upfront: £17,173, 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 | 2173 kWh | 1630 kWh | 543 kWh | £439 | £54 | £493 | £11,069 | 22.5 yrs | £-1,209 |
| 3 kW | 3259 kWh | 2444 kWh | 815 kWh | £658 | £81 | £739 | £13,104 | 17.7 yrs | £1,686 |
| 4 kW | 4345 kWh | 3259 kWh | 1086 kWh | £877 | £109 | £986 | £15,138 | 15.4 yrs | £4,581 |
| 5 kW | 5432 kWh | 4074 kWh | 1358 kWh | £1,097 | £136 | £1,232 | £17,173 | 13.9 yrs | £7,477 |
| 6 kW | 6518 kWh | 4889 kWh | 1630 kWh | £1,316 | £163 | £1,479 | £19,207 | 13.0 yrs | £10,372 |
| 7 kW | 7604 kWh | 5703 kWh | 1901 kWh | £1,535 | £190 | £1,725 | £21,242 | 12.3 yrs | £13,267 |
| 8 kW | 8691 kWh | 6518 kWh | 2173 kWh | £1,755 | £217 | £1,972 | £23,276 | 11.8 yrs | £16,163 |
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: £1,251, Upfront: £19,623, 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 | 2173 kWh | 1673 kWh | 500 kWh | £450 | £50 | £500 | £13,519 | 27.0 yrs | £-3,512 |
| 3 kW | 3259 kWh | 2509 kWh | 750 kWh | £676 | £75 | £751 | £15,554 | 20.7 yrs | £-543 |
| 4 kW | 4345 kWh | 3346 kWh | 999 kWh | £901 | £100 | £1,001 | £17,588 | 17.6 yrs | £2,425 |
| 5 kW | 5432 kWh | 4182 kWh | 1249 kWh | £1,126 | £125 | £1,251 | £19,623 | 15.7 yrs | £5,394 |
| 6 kW | 6518 kWh | 5019 kWh | 1499 kWh | £1,351 | £150 | £1,501 | £21,657 | 14.4 yrs | £8,363 |
| 7 kW | 7604 kWh | 5855 kWh | 1749 kWh | £1,576 | £175 | £1,751 | £23,692 | 13.5 yrs | £11,332 |
| 8 kW | 8691 kWh | 6692 kWh | 1999 kWh | £1,801 | £200 | £2,001 | £25,726 | 12.9 yrs | £14,301 |
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.