A typical roof here lands around 4.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 903 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: £760, Upfront: £10,173, Break-even: 13.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1806 kWh | 722 kWh | 1083 kWh | £196 | £108 | £304 | £4,069 | 13.4 yrs | £2,014 |
| 3 kW | 2708 kWh | 1083 kWh | 1625 kWh | £294 | £163 | £456 | £6,104 | 13.4 yrs | £3,021 |
| 4 kW | 3611 kWh | 1444 kWh | 2167 kWh | £392 | £217 | £608 | £8,138 | 13.4 yrs | £4,028 |
| 5 kW | 4514 kWh | 1806 kWh | 2708 kWh | £490 | £271 | £760 | £10,173 | 13.4 yrs | £5,034 |
| 6 kW | 5417 kWh | 2167 kWh | 3250 kWh | £587 | £325 | £912 | £12,207 | 13.4 yrs | £6,041 |
| 7 kW | 6320 kWh | 2528 kWh | 3792 kWh | £685 | £379 | £1,064 | £14,242 | 13.4 yrs | £7,048 |
| 8 kW | 7222 kWh | 2889 kWh | 4333 kWh | £783 | £433 | £1,217 | £16,276 | 13.4 yrs | £8,055 |
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: £915, Upfront: £12,273, Break-even: 13.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1806 kWh | 1083 kWh | 722 kWh | £294 | £72 | £366 | £6,169 | 16.9 yrs | £1,150 |
| 3 kW | 2708 kWh | 1625 kWh | 1083 kWh | £441 | £108 | £549 | £8,204 | 14.9 yrs | £2,774 |
| 4 kW | 3611 kWh | 2167 kWh | 1444 kWh | £587 | £144 | £732 | £10,238 | 14.0 yrs | £4,399 |
| 5 kW | 4514 kWh | 2708 kWh | 1806 kWh | £734 | £181 | £915 | £12,273 | 13.4 yrs | £6,024 |
| 6 kW | 5417 kWh | 3250 kWh | 2167 kWh | £881 | £217 | £1,098 | £14,307 | 13.0 yrs | £7,649 |
| 7 kW | 6320 kWh | 3792 kWh | 2528 kWh | £1,028 | £253 | £1,281 | £16,342 | 12.8 yrs | £9,273 |
| 8 kW | 7222 kWh | 4333 kWh | 2889 kWh | £1,175 | £289 | £1,464 | £18,376 | 12.6 yrs | £10,898 |
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: £992, Upfront: £13,673, Break-even: 13.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1806 kWh | 1264 kWh | 542 kWh | £343 | £54 | £397 | £7,569 | 19.1 yrs | £367 |
| 3 kW | 2708 kWh | 1896 kWh | 813 kWh | £514 | £81 | £595 | £9,604 | 16.1 yrs | £2,301 |
| 4 kW | 3611 kWh | 2528 kWh | 1083 kWh | £685 | £108 | £794 | £11,638 | 14.7 yrs | £4,235 |
| 5 kW | 4514 kWh | 3160 kWh | 1354 kWh | £857 | £135 | £992 | £13,673 | 13.8 yrs | £6,169 |
| 6 kW | 5417 kWh | 3792 kWh | 1625 kWh | £1,028 | £163 | £1,190 | £15,707 | 13.2 yrs | £8,102 |
| 7 kW | 6320 kWh | 4424 kWh | 1896 kWh | £1,199 | £190 | £1,389 | £17,742 | 12.8 yrs | £10,036 |
| 8 kW | 7222 kWh | 5056 kWh | 2167 kWh | £1,371 | £217 | £1,587 | £19,776 | 12.5 yrs | £11,970 |
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: £1,015, Upfront: £15,423, Break-even: 15.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1806 kWh | 1318 kWh | 488 kWh | £357 | £49 | £406 | £9,319 | 22.9 yrs | £-1,197 |
| 3 kW | 2708 kWh | 1977 kWh | 731 kWh | £536 | £73 | £609 | £11,354 | 18.6 yrs | £829 |
| 4 kW | 3611 kWh | 2636 kWh | 975 kWh | £715 | £98 | £812 | £13,388 | 16.5 yrs | £2,856 |
| 5 kW | 4514 kWh | 3295 kWh | 1219 kWh | £893 | £122 | £1,015 | £15,423 | 15.2 yrs | £4,882 |
| 6 kW | 5417 kWh | 3954 kWh | 1463 kWh | £1,072 | £146 | £1,218 | £17,457 | 14.3 yrs | £6,908 |
| 7 kW | 6320 kWh | 4613 kWh | 1706 kWh | £1,251 | £171 | £1,421 | £19,492 | 13.7 yrs | £8,935 |
| 8 kW | 7222 kWh | 5272 kWh | 1950 kWh | £1,429 | £195 | £1,624 | £21,526 | 13.3 yrs | £10,961 |
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: £1,031, Upfront: £17,173, Break-even: 16.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1806 kWh | 1354 kWh | 451 kWh | £367 | £45 | £412 | £11,069 | 26.8 yrs | £-2,824 |
| 3 kW | 2708 kWh | 2031 kWh | 677 kWh | £551 | £68 | £618 | £13,104 | 21.2 yrs | £-735 |
| 4 kW | 3611 kWh | 2708 kWh | 903 kWh | £734 | £90 | £825 | £15,138 | 18.4 yrs | £1,353 |
| 5 kW | 4514 kWh | 3386 kWh | 1129 kWh | £918 | £113 | £1,031 | £17,173 | 16.7 yrs | £3,441 |
| 6 kW | 5417 kWh | 4063 kWh | 1354 kWh | £1,101 | £135 | £1,237 | £19,207 | 15.5 yrs | £5,529 |
| 7 kW | 6320 kWh | 4740 kWh | 1580 kWh | £1,285 | £158 | £1,443 | £21,242 | 14.7 yrs | £7,617 |
| 8 kW | 7222 kWh | 5417 kWh | 1806 kWh | £1,469 | £181 | £1,649 | £23,276 | 14.1 yrs | £9,705 |
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: £1,046, Upfront: £19,623, Break-even: 18.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1806 kWh | 1390 kWh | 415 kWh | £377 | £42 | £418 | £13,519 | 32.3 yrs | £-5,150 |
| 3 kW | 2708 kWh | 2085 kWh | 623 kWh | £565 | £62 | £628 | £15,554 | 24.8 yrs | £-3,000 |
| 4 kW | 3611 kWh | 2781 kWh | 831 kWh | £754 | £83 | £837 | £17,588 | 21.0 yrs | £-850 |
| 5 kW | 4514 kWh | 3476 kWh | 1038 kWh | £942 | £104 | £1,046 | £19,623 | 18.8 yrs | £1,300 |
| 6 kW | 5417 kWh | 4171 kWh | 1246 kWh | £1,131 | £125 | £1,255 | £21,657 | 17.3 yrs | £3,450 |
| 7 kW | 6320 kWh | 4866 kWh | 1454 kWh | £1,319 | £145 | £1,465 | £23,692 | 16.2 yrs | £5,600 |
| 8 kW | 7222 kWh | 5561 kWh | 1661 kWh | £1,508 | £166 | £1,674 | £25,726 | 15.4 yrs | £7,750 |
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.