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 845 kWh per year on a south-facing roof. We value self-used electricity at 25.8p 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: £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 | 1689 kWh | 676 kWh | 1014 kWh | £175 | £101 | £276 | £4,069 | 14.7 yrs | £1,450 |
| 3 kW | 2534 kWh | 1014 kWh | 1520 kWh | £262 | £152 | £414 | £6,104 | 14.7 yrs | £2,175 |
| 4 kW | 3379 kWh | 1351 kWh | 2027 kWh | £349 | £203 | £552 | £8,138 | 14.7 yrs | £2,901 |
| 5 kW | 4223 kWh | 1689 kWh | 2534 kWh | £437 | £253 | £690 | £10,173 | 14.7 yrs | £3,626 |
| 6 kW | 5068 kWh | 2027 kWh | 3041 kWh | £524 | £304 | £828 | £12,207 | 14.7 yrs | £4,351 |
| 7 kW | 5913 kWh | 2365 kWh | 3548 kWh | £611 | £355 | £966 | £14,242 | 14.7 yrs | £5,076 |
| 8 kW | 6757 kWh | 2703 kWh | 4054 kWh | £698 | £405 | £1,104 | £16,276 | 14.7 yrs | £5,801 |
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: £824, Upfront: £12,273, Break-even: 14.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1689 kWh | 1014 kWh | 676 kWh | £262 | £68 | £329 | £6,169 | 18.7 yrs | £421 |
| 3 kW | 2534 kWh | 1520 kWh | 1014 kWh | £393 | £101 | £494 | £8,204 | 16.6 yrs | £1,681 |
| 4 kW | 3379 kWh | 2027 kWh | 1351 kWh | £524 | £135 | £659 | £10,238 | 15.5 yrs | £2,941 |
| 5 kW | 4223 kWh | 2534 kWh | 1689 kWh | £655 | £169 | £824 | £12,273 | 14.9 yrs | £4,202 |
| 6 kW | 5068 kWh | 3041 kWh | 2027 kWh | £786 | £203 | £988 | £14,307 | 14.5 yrs | £5,462 |
| 7 kW | 5913 kWh | 3548 kWh | 2365 kWh | £917 | £237 | £1,153 | £16,342 | 14.2 yrs | £6,722 |
| 8 kW | 6757 kWh | 4054 kWh | 2703 kWh | £1,048 | £270 | £1,318 | £18,376 | 13.9 yrs | £7,983 |
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: £891, Upfront: £13,673, Break-even: 15.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1689 kWh | 1183 kWh | 507 kWh | £306 | £51 | £356 | £7,569 | 21.2 yrs | £-444 |
| 3 kW | 2534 kWh | 1774 kWh | 760 kWh | £458 | £76 | £534 | £9,604 | 18.0 yrs | £1,084 |
| 4 kW | 3379 kWh | 2365 kWh | 1014 kWh | £611 | £101 | £712 | £11,638 | 16.3 yrs | £2,612 |
| 5 kW | 4223 kWh | 2956 kWh | 1267 kWh | £764 | £127 | £891 | £13,673 | 15.4 yrs | £4,140 |
| 6 kW | 5068 kWh | 3548 kWh | 1520 kWh | £917 | £152 | £1,069 | £15,707 | 14.7 yrs | £5,668 |
| 7 kW | 5913 kWh | 4139 kWh | 1774 kWh | £1,069 | £177 | £1,247 | £17,742 | 14.2 yrs | £7,195 |
| 8 kW | 6757 kWh | 4730 kWh | 2027 kWh | £1,222 | £203 | £1,425 | £19,776 | 13.9 yrs | £8,723 |
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: £911, Upfront: £15,423, Break-even: 16.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1689 kWh | 1233 kWh | 456 kWh | £319 | £46 | £364 | £9,319 | 25.6 yrs | £-2,034 |
| 3 kW | 2534 kWh | 1850 kWh | 684 kWh | £478 | £68 | £546 | £11,354 | 20.8 yrs | £-425 |
| 4 kW | 3379 kWh | 2466 kWh | 912 kWh | £637 | £91 | £729 | £13,388 | 18.4 yrs | £1,183 |
| 5 kW | 4223 kWh | 3083 kWh | 1140 kWh | £797 | £114 | £911 | £15,423 | 16.9 yrs | £2,791 |
| 6 kW | 5068 kWh | 3700 kWh | 1368 kWh | £956 | £137 | £1,093 | £17,457 | 16.0 yrs | £4,399 |
| 7 kW | 5913 kWh | 4316 kWh | 1596 kWh | £1,115 | £160 | £1,275 | £19,492 | 15.3 yrs | £6,007 |
| 8 kW | 6757 kWh | 4933 kWh | 1824 kWh | £1,275 | £182 | £1,457 | £21,526 | 14.8 yrs | £7,616 |
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: £924, Upfront: £17,173, Break-even: 18.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1689 kWh | 1267 kWh | 422 kWh | £327 | £42 | £370 | £11,069 | 29.9 yrs | £-3,677 |
| 3 kW | 2534 kWh | 1900 kWh | 633 kWh | £491 | £63 | £554 | £13,104 | 23.6 yrs | £-2,015 |
| 4 kW | 3379 kWh | 2534 kWh | 845 kWh | £655 | £84 | £739 | £15,138 | 20.5 yrs | £-353 |
| 5 kW | 4223 kWh | 3167 kWh | 1056 kWh | £818 | £106 | £924 | £17,173 | 18.6 yrs | £1,309 |
| 6 kW | 5068 kWh | 3801 kWh | 1267 kWh | £982 | £127 | £1,109 | £19,207 | 17.3 yrs | £2,970 |
| 7 kW | 5913 kWh | 4434 kWh | 1478 kWh | £1,146 | £148 | £1,294 | £21,242 | 16.4 yrs | £4,632 |
| 8 kW | 6757 kWh | 5068 kWh | 1689 kWh | £1,310 | £169 | £1,478 | £23,276 | 15.7 yrs | £6,294 |
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: £937, Upfront: £19,623, Break-even: 20.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1689 kWh | 1301 kWh | 389 kWh | £336 | £39 | £375 | £13,519 | 36.1 yrs | £-6,020 |
| 3 kW | 2534 kWh | 1951 kWh | 583 kWh | £504 | £58 | £562 | £15,554 | 27.7 yrs | £-4,304 |
| 4 kW | 3379 kWh | 2602 kWh | 777 kWh | £672 | £78 | £750 | £17,588 | 23.5 yrs | £-2,589 |
| 5 kW | 4223 kWh | 3252 kWh | 971 kWh | £840 | £97 | £937 | £19,623 | 20.9 yrs | £-874 |
| 6 kW | 5068 kWh | 3902 kWh | 1166 kWh | £1,008 | £117 | £1,125 | £21,657 | 19.3 yrs | £841 |
| 7 kW | 5913 kWh | 4553 kWh | 1360 kWh | £1,176 | £136 | £1,312 | £23,692 | 18.1 yrs | £2,557 |
| 8 kW | 6757 kWh | 5203 kWh | 1554 kWh | £1,344 | £155 | £1,500 | £25,726 | 17.2 yrs | £4,272 |
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.