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 781 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: £657, Upfront: £10,173, 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 | 1563 kWh | 625 kWh | 938 kWh | £169 | £94 | £263 | £4,069 | 15.5 yrs | £1,190 |
| 3 kW | 2344 kWh | 938 kWh | 1407 kWh | £254 | £141 | £394 | £6,104 | 15.5 yrs | £1,785 |
| 4 kW | 3126 kWh | 1250 kWh | 1875 kWh | £338 | £188 | £526 | £8,138 | 15.5 yrs | £2,380 |
| 5 kW | 3907 kWh | 1563 kWh | 2344 kWh | £423 | £234 | £657 | £10,173 | 15.5 yrs | £2,974 |
| 6 kW | 4689 kWh | 1875 kWh | 2813 kWh | £507 | £281 | £789 | £12,207 | 15.5 yrs | £3,569 |
| 7 kW | 5470 kWh | 2188 kWh | 3282 kWh | £592 | £328 | £920 | £14,242 | 15.5 yrs | £4,164 |
| 8 kW | 6252 kWh | 2501 kWh | 3751 kWh | £677 | £375 | £1,052 | £16,276 | 15.5 yrs | £4,759 |
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: £791, Upfront: £12,273, 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 | 1563 kWh | 938 kWh | 625 kWh | £254 | £63 | £316 | £6,169 | 19.5 yrs | £156 |
| 3 kW | 2344 kWh | 1407 kWh | 938 kWh | £381 | £94 | £474 | £8,204 | 17.3 yrs | £1,284 |
| 4 kW | 3126 kWh | 1875 kWh | 1250 kWh | £507 | £125 | £633 | £10,238 | 16.2 yrs | £2,413 |
| 5 kW | 3907 kWh | 2344 kWh | 1563 kWh | £634 | £156 | £791 | £12,273 | 15.5 yrs | £3,541 |
| 6 kW | 4689 kWh | 2813 kWh | 1875 kWh | £761 | £188 | £949 | £14,307 | 15.1 yrs | £4,669 |
| 7 kW | 5470 kWh | 3282 kWh | 2188 kWh | £888 | £219 | £1,107 | £16,342 | 14.8 yrs | £5,797 |
| 8 kW | 6252 kWh | 3751 kWh | 2501 kWh | £1,015 | £250 | £1,265 | £18,376 | 14.5 yrs | £6,925 |
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: £857, Upfront: £13,673, Break-even: 15.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1563 kWh | 1094 kWh | 469 kWh | £296 | £47 | £343 | £7,569 | 22.1 yrs | £-710 |
| 3 kW | 2344 kWh | 1641 kWh | 703 kWh | £444 | £70 | £514 | £9,604 | 18.7 yrs | £684 |
| 4 kW | 3126 kWh | 2188 kWh | 938 kWh | £592 | £94 | £686 | £11,638 | 17.0 yrs | £2,079 |
| 5 kW | 3907 kWh | 2735 kWh | 1172 kWh | £740 | £117 | £857 | £13,673 | 15.9 yrs | £3,474 |
| 6 kW | 4689 kWh | 3282 kWh | 1407 kWh | £888 | £141 | £1,029 | £15,707 | 15.3 yrs | £4,869 |
| 7 kW | 5470 kWh | 3829 kWh | 1641 kWh | £1,036 | £164 | £1,200 | £17,742 | 14.8 yrs | £6,263 |
| 8 kW | 6252 kWh | 4376 kWh | 1875 kWh | £1,184 | £188 | £1,372 | £19,776 | 14.4 yrs | £7,658 |
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: £877, Upfront: £15,423, Break-even: 17.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1563 kWh | 1141 kWh | 422 kWh | £309 | £42 | £351 | £9,319 | 26.6 yrs | £-2,301 |
| 3 kW | 2344 kWh | 1711 kWh | 633 kWh | £463 | £63 | £526 | £11,354 | 21.6 yrs | £-826 |
| 4 kW | 3126 kWh | 2282 kWh | 844 kWh | £617 | £84 | £702 | £13,388 | 19.1 yrs | £649 |
| 5 kW | 3907 kWh | 2852 kWh | 1055 kWh | £772 | £105 | £877 | £15,423 | 17.6 yrs | £2,124 |
| 6 kW | 4689 kWh | 3423 kWh | 1266 kWh | £926 | £127 | £1,053 | £17,457 | 16.6 yrs | £3,598 |
| 7 kW | 5470 kWh | 3993 kWh | 1477 kWh | £1,081 | £148 | £1,228 | £19,492 | 15.9 yrs | £5,073 |
| 8 kW | 6252 kWh | 4564 kWh | 1688 kWh | £1,235 | £169 | £1,404 | £21,526 | 15.3 yrs | £6,548 |
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: £891, Upfront: £17,173, Break-even: 19.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1563 kWh | 1172 kWh | 391 kWh | £317 | £39 | £356 | £11,069 | 31.1 yrs | £-3,944 |
| 3 kW | 2344 kWh | 1758 kWh | 586 kWh | £476 | £59 | £534 | £13,104 | 24.5 yrs | £-2,416 |
| 4 kW | 3126 kWh | 2344 kWh | 781 kWh | £634 | £78 | £713 | £15,138 | 21.2 yrs | £-888 |
| 5 kW | 3907 kWh | 2930 kWh | 977 kWh | £793 | £98 | £891 | £17,173 | 19.3 yrs | £640 |
| 6 kW | 4689 kWh | 3516 kWh | 1172 kWh | £952 | £117 | £1,069 | £19,207 | 18.0 yrs | £2,168 |
| 7 kW | 5470 kWh | 4103 kWh | 1368 kWh | £1,110 | £137 | £1,247 | £21,242 | 17.0 yrs | £3,697 |
| 8 kW | 6252 kWh | 4689 kWh | 1563 kWh | £1,269 | £156 | £1,425 | £23,276 | 16.3 yrs | £5,225 |
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: £904, Upfront: £19,623, Break-even: 21.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1563 kWh | 1203 kWh | 359 kWh | £326 | £36 | £362 | £13,519 | 37.4 yrs | £-6,287 |
| 3 kW | 2344 kWh | 1805 kWh | 539 kWh | £488 | £54 | £542 | £15,554 | 28.7 yrs | £-4,706 |
| 4 kW | 3126 kWh | 2407 kWh | 719 kWh | £651 | £72 | £723 | £17,588 | 24.3 yrs | £-3,124 |
| 5 kW | 3907 kWh | 3009 kWh | 899 kWh | £814 | £90 | £904 | £19,623 | 21.7 yrs | £-1,543 |
| 6 kW | 4689 kWh | 3610 kWh | 1078 kWh | £977 | £108 | £1,085 | £21,657 | 20.0 yrs | £38 |
| 7 kW | 5470 kWh | 4212 kWh | 1258 kWh | £1,140 | £126 | £1,266 | £23,692 | 18.7 yrs | £1,620 |
| 8 kW | 6252 kWh | 4814 kWh | 1438 kWh | £1,303 | £144 | £1,446 | £25,726 | 17.8 yrs | £3,201 |
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.