A typical roof here lands around 6.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 992 kWh per year on a south-facing roof. We value self-used electricity at 26.8p 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: £830, Upfront: £10,173, Break-even: 12.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1984 kWh | 793 kWh | 1190 kWh | £213 | £119 | £332 | £4,069 | 12.3 yrs | £2,567 |
| 3 kW | 2975 kWh | 1190 kWh | 1785 kWh | £319 | £179 | £498 | £6,104 | 12.3 yrs | £3,851 |
| 4 kW | 3967 kWh | 1587 kWh | 2380 kWh | £426 | £238 | £664 | £8,138 | 12.3 yrs | £5,134 |
| 5 kW | 4959 kWh | 1984 kWh | 2975 kWh | £532 | £298 | £830 | £10,173 | 12.3 yrs | £6,418 |
| 6 kW | 5951 kWh | 2380 kWh | 3570 kWh | £638 | £357 | £995 | £12,207 | 12.3 yrs | £7,701 |
| 7 kW | 6942 kWh | 2777 kWh | 4165 kWh | £745 | £417 | £1,161 | £14,242 | 12.3 yrs | £8,985 |
| 8 kW | 7934 kWh | 3174 kWh | 4760 kWh | £851 | £476 | £1,327 | £16,276 | 12.3 yrs | £10,268 |
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: £996, Upfront: £12,273, Break-even: 12.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1984 kWh | 1190 kWh | 793 kWh | £319 | £79 | £399 | £6,169 | 15.5 yrs | £1,802 |
| 3 kW | 2975 kWh | 1785 kWh | 1190 kWh | £479 | £119 | £598 | £8,204 | 13.7 yrs | £3,752 |
| 4 kW | 3967 kWh | 2380 kWh | 1587 kWh | £638 | £159 | £797 | £10,238 | 12.8 yrs | £5,703 |
| 5 kW | 4959 kWh | 2975 kWh | 1984 kWh | £798 | £198 | £996 | £12,273 | 12.3 yrs | £7,654 |
| 6 kW | 5951 kWh | 3570 kWh | 2380 kWh | £958 | £238 | £1,196 | £14,307 | 12.0 yrs | £9,605 |
| 7 kW | 6942 kWh | 4165 kWh | 2777 kWh | £1,117 | £278 | £1,395 | £16,342 | 11.7 yrs | £11,555 |
| 8 kW | 7934 kWh | 4760 kWh | 3174 kWh | £1,277 | £317 | £1,594 | £18,376 | 11.5 yrs | £13,506 |
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: £1,080, Upfront: £13,673, Break-even: 12.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1984 kWh | 1388 kWh | 595 kWh | £372 | £60 | £432 | £7,569 | 17.5 yrs | £1,069 |
| 3 kW | 2975 kWh | 2083 kWh | 893 kWh | £559 | £89 | £648 | £9,604 | 14.8 yrs | £3,353 |
| 4 kW | 3967 kWh | 2777 kWh | 1190 kWh | £745 | £119 | £864 | £11,638 | 13.5 yrs | £5,638 |
| 5 kW | 4959 kWh | 3471 kWh | 1488 kWh | £931 | £149 | £1,080 | £13,673 | 12.7 yrs | £7,922 |
| 6 kW | 5951 kWh | 4165 kWh | 1785 kWh | £1,117 | £179 | £1,296 | £15,707 | 12.1 yrs | £10,206 |
| 7 kW | 6942 kWh | 4860 kWh | 2083 kWh | £1,303 | £208 | £1,512 | £17,742 | 11.7 yrs | £12,491 |
| 8 kW | 7934 kWh | 5554 kWh | 2380 kWh | £1,490 | £238 | £1,728 | £19,776 | 11.4 yrs | £14,775 |
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: £1,105, Upfront: £15,423, Break-even: 14.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1984 kWh | 1448 kWh | 536 kWh | £388 | £54 | £442 | £9,319 | 21.1 yrs | £-481 |
| 3 kW | 2975 kWh | 2172 kWh | 803 kWh | £583 | £80 | £663 | £11,354 | 17.1 yrs | £1,903 |
| 4 kW | 3967 kWh | 2896 kWh | 1071 kWh | £777 | £107 | £884 | £13,388 | 15.1 yrs | £4,288 |
| 5 kW | 4959 kWh | 3620 kWh | 1339 kWh | £971 | £134 | £1,105 | £15,423 | 14.0 yrs | £6,672 |
| 6 kW | 5951 kWh | 4344 kWh | 1607 kWh | £1,165 | £161 | £1,326 | £17,457 | 13.2 yrs | £9,057 |
| 7 kW | 6942 kWh | 5068 kWh | 1874 kWh | £1,359 | £187 | £1,547 | £19,492 | 12.6 yrs | £11,441 |
| 8 kW | 7934 kWh | 5792 kWh | 2142 kWh | £1,553 | £214 | £1,768 | £21,526 | 12.2 yrs | £13,826 |
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: £1,121, Upfront: £17,173, Break-even: 15.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1984 kWh | 1488 kWh | 496 kWh | £399 | £50 | £449 | £11,069 | 24.7 yrs | £-2,098 |
| 3 kW | 2975 kWh | 2231 kWh | 744 kWh | £598 | £74 | £673 | £13,104 | 19.5 yrs | £354 |
| 4 kW | 3967 kWh | 2975 kWh | 992 kWh | £798 | £99 | £897 | £15,138 | 16.9 yrs | £2,805 |
| 5 kW | 4959 kWh | 3719 kWh | 1240 kWh | £997 | £124 | £1,121 | £17,173 | 15.3 yrs | £5,256 |
| 6 kW | 5951 kWh | 4463 kWh | 1488 kWh | £1,197 | £149 | £1,346 | £19,207 | 14.3 yrs | £7,707 |
| 7 kW | 6942 kWh | 5207 kWh | 1736 kWh | £1,396 | £174 | £1,570 | £21,242 | 13.5 yrs | £10,159 |
| 8 kW | 7934 kWh | 5951 kWh | 1984 kWh | £1,596 | £198 | £1,794 | £23,276 | 13.0 yrs | £12,610 |
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: £1,138, Upfront: £19,623, Break-even: 17.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1984 kWh | 1527 kWh | 456 kWh | £410 | £46 | £455 | £13,519 | 29.7 yrs | £-4,414 |
| 3 kW | 2975 kWh | 2291 kWh | 684 kWh | £614 | £68 | £683 | £15,554 | 22.8 yrs | £-1,896 |
| 4 kW | 3967 kWh | 3055 kWh | 912 kWh | £819 | £91 | £910 | £17,588 | 19.3 yrs | £622 |
| 5 kW | 4959 kWh | 3818 kWh | 1141 kWh | £1,024 | £114 | £1,138 | £19,623 | 17.2 yrs | £3,140 |
| 6 kW | 5951 kWh | 4582 kWh | 1369 kWh | £1,229 | £137 | £1,366 | £21,657 | 15.9 yrs | £5,658 |
| 7 kW | 6942 kWh | 5346 kWh | 1597 kWh | £1,434 | £160 | £1,593 | £23,692 | 14.9 yrs | £8,176 |
| 8 kW | 7934 kWh | 6109 kWh | 1825 kWh | £1,638 | £182 | £1,821 | £25,726 | 14.1 yrs | £10,694 |
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.