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 927 kWh per year on a south-facing roof. We value self-used electricity at 25.6p 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: £754, Upfront: £10,173, Break-even: 13.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1854 kWh | 742 kWh | 1113 kWh | £190 | £111 | £301 | £4,069 | 13.5 yrs | £1,960 |
| 3 kW | 2782 kWh | 1113 kWh | 1669 kWh | £285 | £167 | £452 | £6,104 | 13.5 yrs | £2,940 |
| 4 kW | 3709 kWh | 1484 kWh | 2225 kWh | £380 | £223 | £603 | £8,138 | 13.5 yrs | £3,920 |
| 5 kW | 4636 kWh | 1854 kWh | 2782 kWh | £475 | £278 | £754 | £10,173 | 13.5 yrs | £4,900 |
| 6 kW | 5563 kWh | 2225 kWh | 3338 kWh | £571 | £334 | £904 | £12,207 | 13.5 yrs | £5,880 |
| 7 kW | 6491 kWh | 2596 kWh | 3894 kWh | £666 | £389 | £1,055 | £14,242 | 13.5 yrs | £6,860 |
| 8 kW | 7418 kWh | 2967 kWh | 4451 kWh | £761 | £445 | £1,206 | £16,276 | 13.5 yrs | £7,841 |
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: £899, 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 | 1854 kWh | 1113 kWh | 742 kWh | £285 | £74 | £359 | £6,169 | 17.2 yrs | £1,020 |
| 3 kW | 2782 kWh | 1669 kWh | 1113 kWh | £428 | £111 | £539 | £8,204 | 15.2 yrs | £2,580 |
| 4 kW | 3709 kWh | 2225 kWh | 1484 kWh | £571 | £148 | £719 | £10,238 | 14.2 yrs | £4,141 |
| 5 kW | 4636 kWh | 2782 kWh | 1854 kWh | £713 | £185 | £899 | £12,273 | 13.7 yrs | £5,701 |
| 6 kW | 5563 kWh | 3338 kWh | 2225 kWh | £856 | £223 | £1,078 | £14,307 | 13.3 yrs | £7,261 |
| 7 kW | 6491 kWh | 3894 kWh | 2596 kWh | £999 | £260 | £1,258 | £16,342 | 13.0 yrs | £8,821 |
| 8 kW | 7418 kWh | 4451 kWh | 2967 kWh | £1,141 | £297 | £1,438 | £18,376 | 12.8 yrs | £10,381 |
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: £971, Upfront: £13,673, Break-even: 14.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1854 kWh | 1298 kWh | 556 kWh | £333 | £56 | £388 | £7,569 | 19.5 yrs | £200 |
| 3 kW | 2782 kWh | 1947 kWh | 834 kWh | £499 | £83 | £583 | £9,604 | 16.5 yrs | £2,051 |
| 4 kW | 3709 kWh | 2596 kWh | 1113 kWh | £666 | £111 | £777 | £11,638 | 15.0 yrs | £3,901 |
| 5 kW | 4636 kWh | 3245 kWh | 1391 kWh | £832 | £139 | £971 | £13,673 | 14.1 yrs | £5,751 |
| 6 kW | 5563 kWh | 3894 kWh | 1669 kWh | £999 | £167 | £1,165 | £15,707 | 13.5 yrs | £7,601 |
| 7 kW | 6491 kWh | 4543 kWh | 1947 kWh | £1,165 | £195 | £1,360 | £17,742 | 13.0 yrs | £9,451 |
| 8 kW | 7418 kWh | 5192 kWh | 2225 kWh | £1,331 | £223 | £1,554 | £19,776 | 12.7 yrs | £11,301 |
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: £993, 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 | 1854 kWh | 1354 kWh | 501 kWh | £347 | £50 | £397 | £9,319 | 23.5 yrs | £-1,376 |
| 3 kW | 2782 kWh | 2031 kWh | 751 kWh | £521 | £75 | £596 | £11,354 | 19.1 yrs | £562 |
| 4 kW | 3709 kWh | 2707 kWh | 1001 kWh | £694 | £100 | £794 | £13,388 | 16.9 yrs | £2,499 |
| 5 kW | 4636 kWh | 3384 kWh | 1252 kWh | £868 | £125 | £993 | £15,423 | 15.5 yrs | £4,436 |
| 6 kW | 5563 kWh | 4061 kWh | 1502 kWh | £1,041 | £150 | £1,192 | £17,457 | 14.7 yrs | £6,373 |
| 7 kW | 6491 kWh | 4738 kWh | 1752 kWh | £1,215 | £175 | £1,390 | £19,492 | 14.0 yrs | £8,310 |
| 8 kW | 7418 kWh | 5415 kWh | 2003 kWh | £1,388 | £200 | £1,589 | £21,526 | 13.5 yrs | £10,247 |
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: £1,007, 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 | 1854 kWh | 1391 kWh | 464 kWh | £357 | £46 | £403 | £11,069 | 27.5 yrs | £-3,010 |
| 3 kW | 2782 kWh | 2086 kWh | 695 kWh | £535 | £70 | £604 | £13,104 | 21.7 yrs | £-1,014 |
| 4 kW | 3709 kWh | 2782 kWh | 927 kWh | £713 | £93 | £806 | £15,138 | 18.8 yrs | £981 |
| 5 kW | 4636 kWh | 3477 kWh | 1159 kWh | £892 | £116 | £1,007 | £17,173 | 17.0 yrs | £2,976 |
| 6 kW | 5563 kWh | 4172 kWh | 1391 kWh | £1,070 | £139 | £1,209 | £19,207 | 15.9 yrs | £4,971 |
| 7 kW | 6491 kWh | 4868 kWh | 1623 kWh | £1,248 | £162 | £1,410 | £21,242 | 15.1 yrs | £6,966 |
| 8 kW | 7418 kWh | 5563 kWh | 1854 kWh | £1,426 | £185 | £1,612 | £23,276 | 14.4 yrs | £8,962 |
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: £1,022, Upfront: £19,623, Break-even: 19.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1854 kWh | 1428 kWh | 427 kWh | £366 | £43 | £409 | £13,519 | 33.1 yrs | £-5,344 |
| 3 kW | 2782 kWh | 2142 kWh | 640 kWh | £549 | £64 | £613 | £15,554 | 25.4 yrs | £-3,290 |
| 4 kW | 3709 kWh | 2856 kWh | 853 kWh | £732 | £85 | £818 | £17,588 | 21.5 yrs | £-1,237 |
| 5 kW | 4636 kWh | 3570 kWh | 1066 kWh | £915 | £107 | £1,022 | £19,623 | 19.2 yrs | £816 |
| 6 kW | 5563 kWh | 4284 kWh | 1280 kWh | £1,098 | £128 | £1,226 | £21,657 | 17.7 yrs | £2,869 |
| 7 kW | 6491 kWh | 4998 kWh | 1493 kWh | £1,281 | £149 | £1,431 | £23,692 | 16.6 yrs | £4,922 |
| 8 kW | 7418 kWh | 5712 kWh | 1706 kWh | £1,464 | £171 | £1,635 | £25,726 | 15.7 yrs | £6,976 |
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.