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 887 kWh per year on a south-facing roof. We value self-used electricity at 27.1p 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: £747, Upfront: £10,173, 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 | 1773 kWh | 709 kWh | 1064 kWh | £192 | £106 | £299 | £4,069 | 13.6 yrs | £1,904 |
| 3 kW | 2660 kWh | 1064 kWh | 1596 kWh | £288 | £160 | £448 | £6,104 | 13.6 yrs | £2,857 |
| 4 kW | 3546 kWh | 1419 kWh | 2128 kWh | £385 | £213 | £597 | £8,138 | 13.6 yrs | £3,809 |
| 5 kW | 4433 kWh | 1773 kWh | 2660 kWh | £481 | £266 | £747 | £10,173 | 13.6 yrs | £4,761 |
| 6 kW | 5319 kWh | 2128 kWh | 3192 kWh | £577 | £319 | £896 | £12,207 | 13.6 yrs | £5,713 |
| 7 kW | 6206 kWh | 2482 kWh | 3724 kWh | £673 | £372 | £1,045 | £14,242 | 13.6 yrs | £6,665 |
| 8 kW | 7093 kWh | 2837 kWh | 4256 kWh | £769 | £426 | £1,195 | £16,276 | 13.6 yrs | £7,617 |
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: £898, Upfront: £12,273, 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 | 1773 kWh | 1064 kWh | 709 kWh | £288 | £71 | £359 | £6,169 | 17.2 yrs | £1,018 |
| 3 kW | 2660 kWh | 1596 kWh | 1064 kWh | £433 | £106 | £539 | £8,204 | 15.2 yrs | £2,577 |
| 4 kW | 3546 kWh | 2128 kWh | 1419 kWh | £577 | £142 | £719 | £10,238 | 14.2 yrs | £4,136 |
| 5 kW | 4433 kWh | 2660 kWh | 1773 kWh | £721 | £177 | £898 | £12,273 | 13.7 yrs | £5,695 |
| 6 kW | 5319 kWh | 3192 kWh | 2128 kWh | £865 | £213 | £1,078 | £14,307 | 13.3 yrs | £7,254 |
| 7 kW | 6206 kWh | 3724 kWh | 2482 kWh | £1,009 | £248 | £1,258 | £16,342 | 13.0 yrs | £8,813 |
| 8 kW | 7093 kWh | 4256 kWh | 2837 kWh | £1,154 | £284 | £1,437 | £18,376 | 12.8 yrs | £10,371 |
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: £974, Upfront: £13,673, Break-even: 14.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1773 kWh | 1241 kWh | 532 kWh | £336 | £53 | £390 | £7,569 | 19.4 yrs | £225 |
| 3 kW | 2660 kWh | 1862 kWh | 798 kWh | £505 | £80 | £585 | £9,604 | 16.4 yrs | £2,087 |
| 4 kW | 3546 kWh | 2482 kWh | 1064 kWh | £673 | £106 | £779 | £11,638 | 14.9 yrs | £3,949 |
| 5 kW | 4433 kWh | 3103 kWh | 1330 kWh | £841 | £133 | £974 | £13,673 | 14.0 yrs | £5,812 |
| 6 kW | 5319 kWh | 3724 kWh | 1596 kWh | £1,009 | £160 | £1,169 | £15,707 | 13.4 yrs | £7,674 |
| 7 kW | 6206 kWh | 4344 kWh | 1862 kWh | £1,178 | £186 | £1,364 | £17,742 | 13.0 yrs | £9,536 |
| 8 kW | 7093 kWh | 4965 kWh | 2128 kWh | £1,346 | £213 | £1,559 | £19,776 | 12.7 yrs | £11,399 |
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: £997, Upfront: £15,423, 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 | 1773 kWh | 1294 kWh | 479 kWh | £351 | £48 | £399 | £9,319 | 23.4 yrs | £-1,343 |
| 3 kW | 2660 kWh | 1942 kWh | 718 kWh | £526 | £72 | £598 | £11,354 | 19.0 yrs | £610 |
| 4 kW | 3546 kWh | 2589 kWh | 957 kWh | £702 | £96 | £798 | £13,388 | 16.8 yrs | £2,563 |
| 5 kW | 4433 kWh | 3236 kWh | 1197 kWh | £877 | £120 | £997 | £15,423 | 15.5 yrs | £4,517 |
| 6 kW | 5319 kWh | 3883 kWh | 1436 kWh | £1,053 | £144 | £1,196 | £17,457 | 14.6 yrs | £6,470 |
| 7 kW | 6206 kWh | 4530 kWh | 1676 kWh | £1,228 | £168 | £1,396 | £19,492 | 14.0 yrs | £8,423 |
| 8 kW | 7093 kWh | 5178 kWh | 1915 kWh | £1,404 | £191 | £1,595 | £21,526 | 13.5 yrs | £10,377 |
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: £1,012, Upfront: £17,173, Break-even: 17.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1773 kWh | 1330 kWh | 443 kWh | £361 | £44 | £405 | £11,069 | 27.3 yrs | £-2,972 |
| 3 kW | 2660 kWh | 1995 kWh | 665 kWh | £541 | £66 | £607 | £13,104 | 21.6 yrs | £-958 |
| 4 kW | 3546 kWh | 2660 kWh | 887 kWh | £721 | £89 | £810 | £15,138 | 18.7 yrs | £1,056 |
| 5 kW | 4433 kWh | 3325 kWh | 1108 kWh | £901 | £111 | £1,012 | £17,173 | 17.0 yrs | £3,070 |
| 6 kW | 5319 kWh | 3990 kWh | 1330 kWh | £1,082 | £133 | £1,215 | £19,207 | 15.8 yrs | £5,084 |
| 7 kW | 6206 kWh | 4654 kWh | 1551 kWh | £1,262 | £155 | £1,417 | £21,242 | 15.0 yrs | £7,098 |
| 8 kW | 7093 kWh | 5319 kWh | 1773 kWh | £1,442 | £177 | £1,619 | £23,276 | 14.4 yrs | £9,112 |
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: £1,027, Upfront: £19,623, Break-even: 19.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1773 kWh | 1365 kWh | 408 kWh | £370 | £41 | £411 | £13,519 | 32.9 yrs | £-5,301 |
| 3 kW | 2660 kWh | 2048 kWh | 612 kWh | £555 | £61 | £616 | £15,554 | 25.2 yrs | £-3,226 |
| 4 kW | 3546 kWh | 2731 kWh | 816 kWh | £740 | £82 | £822 | £17,588 | 21.4 yrs | £-1,151 |
| 5 kW | 4433 kWh | 3413 kWh | 1020 kWh | £925 | £102 | £1,027 | £19,623 | 19.1 yrs | £923 |
| 6 kW | 5319 kWh | 4096 kWh | 1223 kWh | £1,110 | £122 | £1,233 | £21,657 | 17.6 yrs | £2,998 |
| 7 kW | 6206 kWh | 4779 kWh | 1427 kWh | £1,295 | £143 | £1,438 | £23,692 | 16.5 yrs | £5,073 |
| 8 kW | 7093 kWh | 5461 kWh | 1631 kWh | £1,481 | £163 | £1,644 | £25,726 | 15.7 yrs | £7,148 |
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.