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 1058 kWh per year on a south-facing roof. We value self-used electricity at 26.8p 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: £885, Upfront: £10,173, 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 | 2116 kWh | 846 kWh | 1269 kWh | £227 | £127 | £354 | £4,069 | 11.5 yrs | £3,009 |
| 3 kW | 3174 kWh | 1269 kWh | 1904 kWh | £340 | £190 | £531 | £6,104 | 11.5 yrs | £4,514 |
| 4 kW | 4231 kWh | 1693 kWh | 2539 kWh | £454 | £254 | £708 | £8,138 | 11.5 yrs | £6,019 |
| 5 kW | 5289 kWh | 2116 kWh | 3174 kWh | £567 | £317 | £885 | £10,173 | 11.5 yrs | £7,523 |
| 6 kW | 6347 kWh | 2539 kWh | 3808 kWh | £681 | £381 | £1,062 | £12,207 | 11.5 yrs | £9,028 |
| 7 kW | 7405 kWh | 2962 kWh | 4443 kWh | £794 | £444 | £1,239 | £14,242 | 11.5 yrs | £10,532 |
| 8 kW | 8463 kWh | 3385 kWh | 5078 kWh | £908 | £508 | £1,416 | £16,276 | 11.5 yrs | £12,037 |
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: £1,063, Upfront: £12,273, 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 | 2116 kWh | 1269 kWh | 846 kWh | £340 | £85 | £425 | £6,169 | 14.5 yrs | £2,333 |
| 3 kW | 3174 kWh | 1904 kWh | 1269 kWh | £511 | £127 | £638 | £8,204 | 12.9 yrs | £4,549 |
| 4 kW | 4231 kWh | 2539 kWh | 1693 kWh | £681 | £169 | £850 | £10,238 | 12.0 yrs | £6,765 |
| 5 kW | 5289 kWh | 3174 kWh | 2116 kWh | £851 | £212 | £1,063 | £12,273 | 11.5 yrs | £8,982 |
| 6 kW | 6347 kWh | 3808 kWh | 2539 kWh | £1,021 | £254 | £1,275 | £14,307 | 11.2 yrs | £11,198 |
| 7 kW | 7405 kWh | 4443 kWh | 2962 kWh | £1,192 | £296 | £1,488 | £16,342 | 11.0 yrs | £13,414 |
| 8 kW | 8463 kWh | 5078 kWh | 3385 kWh | £1,362 | £339 | £1,700 | £18,376 | 10.8 yrs | £15,631 |
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: £1,152, Upfront: £13,673, Break-even: 11.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2116 kWh | 1481 kWh | 635 kWh | £397 | £63 | £461 | £7,569 | 16.4 yrs | £1,644 |
| 3 kW | 3174 kWh | 2221 kWh | 952 kWh | £596 | £95 | £691 | £9,604 | 13.9 yrs | £4,217 |
| 4 kW | 4231 kWh | 2962 kWh | 1269 kWh | £794 | £127 | £921 | £11,638 | 12.6 yrs | £6,789 |
| 5 kW | 5289 kWh | 3702 kWh | 1587 kWh | £993 | £159 | £1,152 | £13,673 | 11.9 yrs | £9,361 |
| 6 kW | 6347 kWh | 4443 kWh | 1904 kWh | £1,192 | £190 | £1,382 | £15,707 | 11.4 yrs | £11,933 |
| 7 kW | 7405 kWh | 5183 kWh | 2221 kWh | £1,390 | £222 | £1,612 | £17,742 | 11.0 yrs | £14,506 |
| 8 kW | 8463 kWh | 5924 kWh | 2539 kWh | £1,589 | £254 | £1,843 | £19,776 | 10.7 yrs | £17,078 |
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: £1,178, Upfront: £15,423, 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 | 2116 kWh | 1544 kWh | 571 kWh | £414 | £57 | £471 | £9,319 | 19.8 yrs | £108 |
| 3 kW | 3174 kWh | 2317 kWh | 857 kWh | £621 | £86 | £707 | £11,354 | 16.1 yrs | £2,787 |
| 4 kW | 4231 kWh | 3089 kWh | 1142 kWh | £828 | £114 | £943 | £13,388 | 14.2 yrs | £5,466 |
| 5 kW | 5289 kWh | 3861 kWh | 1428 kWh | £1,036 | £143 | £1,178 | £15,423 | 13.1 yrs | £8,145 |
| 6 kW | 6347 kWh | 4633 kWh | 1714 kWh | £1,243 | £171 | £1,414 | £17,457 | 12.3 yrs | £10,824 |
| 7 kW | 7405 kWh | 5406 kWh | 1999 kWh | £1,450 | £200 | £1,650 | £19,492 | 11.8 yrs | £13,503 |
| 8 kW | 8463 kWh | 6178 kWh | 2285 kWh | £1,657 | £228 | £1,885 | £21,526 | 11.4 yrs | £16,182 |
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: £1,196, Upfront: £17,173, Break-even: 14.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2116 kWh | 1587 kWh | 529 kWh | £426 | £53 | £478 | £11,069 | 23.1 yrs | £-1,500 |
| 3 kW | 3174 kWh | 2380 kWh | 793 kWh | £638 | £79 | £718 | £13,104 | 18.3 yrs | £1,250 |
| 4 kW | 4231 kWh | 3174 kWh | 1058 kWh | £851 | £106 | £957 | £15,138 | 15.8 yrs | £4,001 |
| 5 kW | 5289 kWh | 3967 kWh | 1322 kWh | £1,064 | £132 | £1,196 | £17,173 | 14.4 yrs | £6,751 |
| 6 kW | 6347 kWh | 4760 kWh | 1587 kWh | £1,277 | £159 | £1,435 | £19,207 | 13.4 yrs | £9,501 |
| 7 kW | 7405 kWh | 5554 kWh | 1851 kWh | £1,490 | £185 | £1,675 | £21,242 | 12.7 yrs | £12,251 |
| 8 kW | 8463 kWh | 6347 kWh | 2116 kWh | £1,702 | £212 | £1,914 | £23,276 | 12.2 yrs | £15,001 |
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: £1,214, Upfront: £19,623, Break-even: 16.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2116 kWh | 1629 kWh | 487 kWh | £437 | £49 | £486 | £13,519 | 27.8 yrs | £-3,807 |
| 3 kW | 3174 kWh | 2444 kWh | 730 kWh | £655 | £73 | £728 | £15,554 | 21.4 yrs | £-986 |
| 4 kW | 4231 kWh | 3258 kWh | 973 kWh | £874 | £97 | £971 | £17,588 | 18.1 yrs | £1,835 |
| 5 kW | 5289 kWh | 4073 kWh | 1217 kWh | £1,092 | £122 | £1,214 | £19,623 | 16.2 yrs | £4,657 |
| 6 kW | 6347 kWh | 4887 kWh | 1460 kWh | £1,311 | £146 | £1,457 | £21,657 | 14.9 yrs | £7,478 |
| 7 kW | 7405 kWh | 5702 kWh | 1703 kWh | £1,529 | £170 | £1,700 | £23,692 | 13.9 yrs | £10,299 |
| 8 kW | 8463 kWh | 6516 kWh | 1946 kWh | £1,748 | £195 | £1,942 | £25,726 | 13.2 yrs | £13,121 |
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.