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 1126 kWh per year on a south-facing roof. We value self-used electricity at 26.9p 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: £944, Upfront: £10,173, Break-even: 10.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2252 kWh | 901 kWh | 1351 kWh | £243 | £135 | £378 | £4,069 | 10.8 yrs | £3,484 |
| 3 kW | 3379 kWh | 1351 kWh | 2027 kWh | £364 | £203 | £567 | £6,104 | 10.8 yrs | £5,227 |
| 4 kW | 4505 kWh | 1802 kWh | 2703 kWh | £485 | £270 | £755 | £8,138 | 10.8 yrs | £6,969 |
| 5 kW | 5631 kWh | 2252 kWh | 3379 kWh | £606 | £338 | £944 | £10,173 | 10.8 yrs | £8,711 |
| 6 kW | 6757 kWh | 2703 kWh | 4054 kWh | £728 | £405 | £1,133 | £12,207 | 10.8 yrs | £10,453 |
| 7 kW | 7883 kWh | 3153 kWh | 4730 kWh | £849 | £473 | £1,322 | £14,242 | 10.8 yrs | £12,195 |
| 8 kW | 9009 kWh | 3604 kWh | 5406 kWh | £970 | £541 | £1,511 | £16,276 | 10.8 yrs | £13,938 |
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: £1,135, Upfront: £12,273, Break-even: 10.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2252 kWh | 1351 kWh | 901 kWh | £364 | £90 | £454 | £6,169 | 13.6 yrs | £2,909 |
| 3 kW | 3379 kWh | 2027 kWh | 1351 kWh | £546 | £135 | £681 | £8,204 | 12.0 yrs | £5,413 |
| 4 kW | 4505 kWh | 2703 kWh | 1802 kWh | £728 | £180 | £908 | £10,238 | 11.3 yrs | £7,918 |
| 5 kW | 5631 kWh | 3379 kWh | 2252 kWh | £909 | £225 | £1,135 | £12,273 | 10.8 yrs | £10,422 |
| 6 kW | 6757 kWh | 4054 kWh | 2703 kWh | £1,091 | £270 | £1,362 | £14,307 | 10.5 yrs | £12,926 |
| 7 kW | 7883 kWh | 4730 kWh | 3153 kWh | £1,273 | £315 | £1,589 | £16,342 | 10.3 yrs | £15,431 |
| 8 kW | 9009 kWh | 5406 kWh | 3604 kWh | £1,455 | £360 | £1,816 | £18,376 | 10.1 yrs | £17,935 |
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: £1,230, Upfront: £13,673, Break-even: 11.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2252 kWh | 1577 kWh | 676 kWh | £424 | £68 | £492 | £7,569 | 15.4 yrs | £2,271 |
| 3 kW | 3379 kWh | 2365 kWh | 1014 kWh | £637 | £101 | £738 | £9,604 | 13.0 yrs | £5,157 |
| 4 kW | 4505 kWh | 3153 kWh | 1351 kWh | £849 | £135 | £984 | £11,638 | 11.8 yrs | £8,042 |
| 5 kW | 5631 kWh | 3942 kWh | 1689 kWh | £1,061 | £169 | £1,230 | £13,673 | 11.1 yrs | £10,928 |
| 6 kW | 6757 kWh | 4730 kWh | 2027 kWh | £1,273 | £203 | £1,476 | £15,707 | 10.6 yrs | £13,813 |
| 7 kW | 7883 kWh | 5518 kWh | 2365 kWh | £1,486 | £236 | £1,722 | £17,742 | 10.3 yrs | £16,699 |
| 8 kW | 9009 kWh | 6307 kWh | 2703 kWh | £1,698 | £270 | £1,968 | £19,776 | 10.0 yrs | £19,584 |
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: £1,259, Upfront: £15,423, 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 | 2252 kWh | 1644 kWh | 608 kWh | £443 | £61 | £503 | £9,319 | 18.5 yrs | £750 |
| 3 kW | 3379 kWh | 2466 kWh | 912 kWh | £664 | £91 | £755 | £11,354 | 15.0 yrs | £3,749 |
| 4 kW | 4505 kWh | 3288 kWh | 1216 kWh | £885 | £122 | £1,007 | £13,388 | 13.3 yrs | £6,749 |
| 5 kW | 5631 kWh | 4111 kWh | 1520 kWh | £1,107 | £152 | £1,259 | £15,423 | 12.3 yrs | £9,749 |
| 6 kW | 6757 kWh | 4933 kWh | 1824 kWh | £1,328 | £182 | £1,510 | £17,457 | 11.6 yrs | £12,749 |
| 7 kW | 7883 kWh | 5755 kWh | 2128 kWh | £1,549 | £213 | £1,762 | £19,492 | 11.1 yrs | £15,749 |
| 8 kW | 9009 kWh | 6577 kWh | 2433 kWh | £1,770 | £243 | £2,014 | £21,526 | 10.7 yrs | £18,749 |
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: £1,278, Upfront: £17,173, 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 | 2252 kWh | 1689 kWh | 563 kWh | £455 | £56 | £511 | £11,069 | 21.7 yrs | £-848 |
| 3 kW | 3379 kWh | 2534 kWh | 845 kWh | £682 | £84 | £767 | £13,104 | 17.1 yrs | £2,228 |
| 4 kW | 4505 kWh | 3379 kWh | 1126 kWh | £909 | £113 | £1,022 | £15,138 | 14.8 yrs | £5,304 |
| 5 kW | 5631 kWh | 4223 kWh | 1408 kWh | £1,137 | £141 | £1,278 | £17,173 | 13.4 yrs | £8,380 |
| 6 kW | 6757 kWh | 5068 kWh | 1689 kWh | £1,364 | £169 | £1,533 | £19,207 | 12.5 yrs | £11,456 |
| 7 kW | 7883 kWh | 5912 kWh | 1971 kWh | £1,592 | £197 | £1,789 | £21,242 | 11.9 yrs | £14,532 |
| 8 kW | 9009 kWh | 6757 kWh | 2252 kWh | £1,819 | £225 | £2,044 | £23,276 | 11.4 yrs | £17,608 |
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: £1,297, Upfront: £19,623, Break-even: 15.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2252 kWh | 1734 kWh | 518 kWh | £467 | £52 | £519 | £13,519 | 26.1 yrs | £-3,145 |
| 3 kW | 3379 kWh | 2601 kWh | 777 kWh | £700 | £78 | £778 | £15,554 | 20.0 yrs | £7 |
| 4 kW | 4505 kWh | 3469 kWh | 1036 kWh | £934 | £104 | £1,037 | £17,588 | 17.0 yrs | £3,159 |
| 5 kW | 5631 kWh | 4336 kWh | 1295 kWh | £1,167 | £130 | £1,297 | £19,623 | 15.1 yrs | £6,311 |
| 6 kW | 6757 kWh | 5203 kWh | 1554 kWh | £1,401 | £155 | £1,556 | £21,657 | 13.9 yrs | £9,464 |
| 7 kW | 7883 kWh | 6070 kWh | 1813 kWh | £1,634 | £181 | £1,815 | £23,692 | 13.1 yrs | £12,616 |
| 8 kW | 9009 kWh | 6937 kWh | 2072 kWh | £1,867 | £207 | £2,075 | £25,726 | 12.4 yrs | £15,768 |
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.