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 820 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: £690, Upfront: £10,173, Break-even: 14.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1640 kWh | 656 kWh | 984 kWh | £178 | £98 | £276 | £4,069 | 14.7 yrs | £1,450 |
| 3 kW | 2460 kWh | 984 kWh | 1476 kWh | £266 | £148 | £414 | £6,104 | 14.7 yrs | £2,175 |
| 4 kW | 3280 kWh | 1312 kWh | 1968 kWh | £355 | £197 | £552 | £8,138 | 14.7 yrs | £2,899 |
| 5 kW | 4100 kWh | 1640 kWh | 2460 kWh | £444 | £246 | £690 | £10,173 | 14.7 yrs | £3,624 |
| 6 kW | 4920 kWh | 1968 kWh | 2952 kWh | £533 | £295 | £828 | £12,207 | 14.7 yrs | £4,349 |
| 7 kW | 5740 kWh | 2296 kWh | 3444 kWh | £621 | £344 | £966 | £14,242 | 14.7 yrs | £5,074 |
| 8 kW | 6561 kWh | 2624 kWh | 3936 kWh | £710 | £394 | £1,104 | £16,276 | 14.7 yrs | £5,799 |
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: £830, Upfront: £12,273, Break-even: 14.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1640 kWh | 984 kWh | 656 kWh | £266 | £66 | £332 | £6,169 | 18.6 yrs | £469 |
| 3 kW | 2460 kWh | 1476 kWh | 984 kWh | £399 | £98 | £498 | £8,204 | 16.5 yrs | £1,753 |
| 4 kW | 3280 kWh | 1968 kWh | 1312 kWh | £533 | £131 | £664 | £10,238 | 15.4 yrs | £3,038 |
| 5 kW | 4100 kWh | 2460 kWh | 1640 kWh | £666 | £164 | £830 | £12,273 | 14.8 yrs | £4,322 |
| 6 kW | 4920 kWh | 2952 kWh | 1968 kWh | £799 | £197 | £996 | £14,307 | 14.4 yrs | £5,607 |
| 7 kW | 5740 kWh | 3444 kWh | 2296 kWh | £932 | £230 | £1,162 | £16,342 | 14.1 yrs | £6,891 |
| 8 kW | 6561 kWh | 3936 kWh | 2624 kWh | £1,065 | £262 | £1,328 | £18,376 | 13.8 yrs | £8,176 |
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: £900, Upfront: £13,673, 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 | 1640 kWh | 1148 kWh | 492 kWh | £311 | £49 | £360 | £7,569 | 21.0 yrs | £-371 |
| 3 kW | 2460 kWh | 1722 kWh | 738 kWh | £466 | £74 | £540 | £9,604 | 17.8 yrs | £1,193 |
| 4 kW | 3280 kWh | 2296 kWh | 984 kWh | £621 | £98 | £720 | £11,638 | 16.2 yrs | £2,757 |
| 5 kW | 4100 kWh | 2870 kWh | 1230 kWh | £777 | £123 | £900 | £13,673 | 15.2 yrs | £4,321 |
| 6 kW | 4920 kWh | 3444 kWh | 1476 kWh | £932 | £148 | £1,080 | £15,707 | 14.5 yrs | £5,886 |
| 7 kW | 5740 kWh | 4018 kWh | 1722 kWh | £1,087 | £172 | £1,260 | £17,742 | 14.1 yrs | £7,450 |
| 8 kW | 6561 kWh | 4592 kWh | 1968 kWh | £1,243 | £197 | £1,440 | £19,776 | 13.7 yrs | £9,014 |
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: £921, Upfront: £15,423, Break-even: 16.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1640 kWh | 1197 kWh | 443 kWh | £324 | £44 | £368 | £9,319 | 25.3 yrs | £-1,954 |
| 3 kW | 2460 kWh | 1796 kWh | 664 kWh | £486 | £66 | £552 | £11,354 | 20.6 yrs | £-305 |
| 4 kW | 3280 kWh | 2395 kWh | 886 kWh | £648 | £89 | £737 | £13,388 | 18.2 yrs | £1,343 |
| 5 kW | 4100 kWh | 2993 kWh | 1107 kWh | £810 | £111 | £921 | £15,423 | 16.8 yrs | £2,991 |
| 6 kW | 4920 kWh | 3592 kWh | 1329 kWh | £972 | £133 | £1,105 | £17,457 | 15.8 yrs | £4,639 |
| 7 kW | 5740 kWh | 4191 kWh | 1550 kWh | £1,134 | £155 | £1,289 | £19,492 | 15.1 yrs | £6,288 |
| 8 kW | 6561 kWh | 4789 kWh | 1771 kWh | £1,296 | £177 | £1,473 | £21,526 | 14.6 yrs | £7,936 |
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: £935, Upfront: £17,173, Break-even: 18.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1640 kWh | 1230 kWh | 410 kWh | £333 | £41 | £374 | £11,069 | 29.6 yrs | £-3,592 |
| 3 kW | 2460 kWh | 1845 kWh | 615 kWh | £499 | £62 | £561 | £13,104 | 23.4 yrs | £-1,887 |
| 4 kW | 3280 kWh | 2460 kWh | 820 kWh | £666 | £82 | £748 | £15,138 | 20.2 yrs | £-183 |
| 5 kW | 4100 kWh | 3075 kWh | 1025 kWh | £832 | £103 | £935 | £17,173 | 18.4 yrs | £1,521 |
| 6 kW | 4920 kWh | 3690 kWh | 1230 kWh | £999 | £123 | £1,122 | £19,207 | 17.1 yrs | £3,225 |
| 7 kW | 5740 kWh | 4305 kWh | 1435 kWh | £1,165 | £144 | £1,309 | £21,242 | 16.2 yrs | £4,929 |
| 8 kW | 6561 kWh | 4920 kWh | 1640 kWh | £1,331 | £164 | £1,495 | £23,276 | 15.6 yrs | £6,634 |
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: £949, Upfront: £19,623, Break-even: 20.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1640 kWh | 1263 kWh | 377 kWh | £342 | £38 | £379 | £13,519 | 35.6 yrs | £-5,930 |
| 3 kW | 2460 kWh | 1894 kWh | 566 kWh | £513 | £57 | £569 | £15,554 | 27.3 yrs | £-4,170 |
| 4 kW | 3280 kWh | 2526 kWh | 754 kWh | £683 | £75 | £759 | £17,588 | 23.2 yrs | £-2,409 |
| 5 kW | 4100 kWh | 3157 kWh | 943 kWh | £854 | £94 | £949 | £19,623 | 20.7 yrs | £-649 |
| 6 kW | 4920 kWh | 3789 kWh | 1132 kWh | £1,025 | £113 | £1,138 | £21,657 | 19.0 yrs | £1,111 |
| 7 kW | 5740 kWh | 4420 kWh | 1320 kWh | £1,196 | £132 | £1,328 | £23,692 | 17.8 yrs | £2,871 |
| 8 kW | 6561 kWh | 5052 kWh | 1509 kWh | £1,367 | £151 | £1,518 | £25,726 | 16.9 yrs | £4,631 |
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.