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 773 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: £650, Upfront: £10,173, Break-even: 15.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1546 kWh | 618 kWh | 927 kWh | £167 | £93 | £260 | £4,069 | 15.6 yrs | £1,132 |
| 3 kW | 2318 kWh | 927 kWh | 1391 kWh | £251 | £139 | £390 | £6,104 | 15.6 yrs | £1,697 |
| 4 kW | 3091 kWh | 1236 kWh | 1855 kWh | £335 | £185 | £520 | £8,138 | 15.6 yrs | £2,263 |
| 5 kW | 3864 kWh | 1546 kWh | 2318 kWh | £418 | £232 | £650 | £10,173 | 15.6 yrs | £2,829 |
| 6 kW | 4637 kWh | 1855 kWh | 2782 kWh | £502 | £278 | £780 | £12,207 | 15.6 yrs | £3,395 |
| 7 kW | 5410 kWh | 2164 kWh | 3246 kWh | £586 | £325 | £910 | £14,242 | 15.6 yrs | £3,960 |
| 8 kW | 6182 kWh | 2473 kWh | 3709 kWh | £669 | £371 | £1,040 | £16,276 | 15.6 yrs | £4,526 |
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: £782, Upfront: £12,273, 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 | 1546 kWh | 927 kWh | 618 kWh | £251 | £62 | £313 | £6,169 | 19.7 yrs | £86 |
| 3 kW | 2318 kWh | 1391 kWh | 927 kWh | £376 | £93 | £469 | £8,204 | 17.5 yrs | £1,179 |
| 4 kW | 3091 kWh | 1855 kWh | 1236 kWh | £502 | £124 | £626 | £10,238 | 16.4 yrs | £2,273 |
| 5 kW | 3864 kWh | 2318 kWh | 1546 kWh | £627 | £155 | £782 | £12,273 | 15.7 yrs | £3,366 |
| 6 kW | 4637 kWh | 2782 kWh | 1855 kWh | £753 | £185 | £938 | £14,307 | 15.2 yrs | £4,459 |
| 7 kW | 5410 kWh | 3246 kWh | 2164 kWh | £878 | £216 | £1,095 | £16,342 | 14.9 yrs | £5,552 |
| 8 kW | 6182 kWh | 3709 kWh | 2473 kWh | £1,004 | £247 | £1,251 | £18,376 | 14.7 yrs | £6,645 |
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: £848, Upfront: £13,673, Break-even: 16.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1546 kWh | 1082 kWh | 464 kWh | £293 | £46 | £339 | £7,569 | 22.3 yrs | £-786 |
| 3 kW | 2318 kWh | 1623 kWh | 696 kWh | £439 | £70 | £509 | £9,604 | 18.9 yrs | £570 |
| 4 kW | 3091 kWh | 2164 kWh | 927 kWh | £586 | £93 | £678 | £11,638 | 17.2 yrs | £1,927 |
| 5 kW | 3864 kWh | 2705 kWh | 1159 kWh | £732 | £116 | £848 | £13,673 | 16.1 yrs | £3,284 |
| 6 kW | 4637 kWh | 3246 kWh | 1391 kWh | £878 | £139 | £1,017 | £15,707 | 15.4 yrs | £4,641 |
| 7 kW | 5410 kWh | 3787 kWh | 1623 kWh | £1,025 | £162 | £1,187 | £17,742 | 14.9 yrs | £5,998 |
| 8 kW | 6182 kWh | 4328 kWh | 1855 kWh | £1,171 | £185 | £1,357 | £19,776 | 14.6 yrs | £7,354 |
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: £868, Upfront: £15,423, Break-even: 17.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1546 kWh | 1128 kWh | 417 kWh | £305 | £42 | £347 | £9,319 | 26.9 yrs | £-2,378 |
| 3 kW | 2318 kWh | 1692 kWh | 626 kWh | £458 | £63 | £521 | £11,354 | 21.8 yrs | £-942 |
| 4 kW | 3091 kWh | 2257 kWh | 835 kWh | £611 | £83 | £694 | £13,388 | 19.3 yrs | £494 |
| 5 kW | 3864 kWh | 2821 kWh | 1043 kWh | £763 | £104 | £868 | £15,423 | 17.8 yrs | £1,930 |
| 6 kW | 4637 kWh | 3385 kWh | 1252 kWh | £916 | £125 | £1,041 | £17,457 | 16.8 yrs | £3,365 |
| 7 kW | 5410 kWh | 3949 kWh | 1461 kWh | £1,069 | £146 | £1,215 | £19,492 | 16.0 yrs | £4,801 |
| 8 kW | 6182 kWh | 4513 kWh | 1669 kWh | £1,221 | £167 | £1,388 | £21,526 | 15.5 yrs | £6,237 |
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: £881, Upfront: £17,173, Break-even: 19.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1546 kWh | 1159 kWh | 386 kWh | £314 | £39 | £352 | £11,069 | 31.4 yrs | £-4,023 |
| 3 kW | 2318 kWh | 1739 kWh | 580 kWh | £471 | £58 | £528 | £13,104 | 24.8 yrs | £-2,534 |
| 4 kW | 3091 kWh | 2318 kWh | 773 kWh | £627 | £77 | £705 | £15,138 | 21.5 yrs | £-1,045 |
| 5 kW | 3864 kWh | 2898 kWh | 966 kWh | £784 | £97 | £881 | £17,173 | 19.5 yrs | £443 |
| 6 kW | 4637 kWh | 3478 kWh | 1159 kWh | £941 | £116 | £1,057 | £19,207 | 18.2 yrs | £1,932 |
| 7 kW | 5410 kWh | 4057 kWh | 1352 kWh | £1,098 | £135 | £1,233 | £21,242 | 17.2 yrs | £3,420 |
| 8 kW | 6182 kWh | 4637 kWh | 1546 kWh | £1,255 | £155 | £1,409 | £23,276 | 16.5 yrs | £4,909 |
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: £894, Upfront: £19,623, Break-even: 21.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1546 kWh | 1190 kWh | 355 kWh | £322 | £36 | £358 | £13,519 | 37.8 yrs | £-6,367 |
| 3 kW | 2318 kWh | 1785 kWh | 533 kWh | £483 | £53 | £536 | £15,554 | 29.0 yrs | £-4,826 |
| 4 kW | 3091 kWh | 2380 kWh | 711 kWh | £644 | £71 | £715 | £17,588 | 24.6 yrs | £-3,285 |
| 5 kW | 3864 kWh | 2975 kWh | 889 kWh | £805 | £89 | £894 | £19,623 | 21.9 yrs | £-1,743 |
| 6 kW | 4637 kWh | 3570 kWh | 1066 kWh | £966 | £107 | £1,073 | £21,657 | 20.2 yrs | £-202 |
| 7 kW | 5410 kWh | 4165 kWh | 1244 kWh | £1,127 | £124 | £1,252 | £23,692 | 18.9 yrs | £1,340 |
| 8 kW | 6182 kWh | 4760 kWh | 1422 kWh | £1,288 | £142 | £1,430 | £25,726 | 18.0 yrs | £2,881 |
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.