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 1028 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: £860, Upfront: £10,173, Break-even: 11.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2056 kWh | 822 kWh | 1234 kWh | £221 | £123 | £344 | £4,069 | 11.8 yrs | £2,810 |
| 3 kW | 3084 kWh | 1234 kWh | 1851 kWh | £331 | £185 | £516 | £6,104 | 11.8 yrs | £4,215 |
| 4 kW | 4112 kWh | 1645 kWh | 2467 kWh | £441 | £247 | £688 | £8,138 | 11.8 yrs | £5,620 |
| 5 kW | 5140 kWh | 2056 kWh | 3084 kWh | £551 | £308 | £860 | £10,173 | 11.8 yrs | £7,026 |
| 6 kW | 6169 kWh | 2467 kWh | 3701 kWh | £662 | £370 | £1,032 | £12,207 | 11.8 yrs | £8,431 |
| 7 kW | 7197 kWh | 2879 kWh | 4318 kWh | £772 | £432 | £1,204 | £14,242 | 11.8 yrs | £9,836 |
| 8 kW | 8225 kWh | 3290 kWh | 4935 kWh | £882 | £493 | £1,376 | £16,276 | 11.8 yrs | £11,241 |
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: £1,033, Upfront: £12,273, Break-even: 11.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2056 kWh | 1234 kWh | 822 kWh | £331 | £82 | £413 | £6,169 | 14.9 yrs | £2,094 |
| 3 kW | 3084 kWh | 1851 kWh | 1234 kWh | £496 | £123 | £620 | £8,204 | 13.2 yrs | £4,190 |
| 4 kW | 4112 kWh | 2467 kWh | 1645 kWh | £662 | £164 | £826 | £10,238 | 12.4 yrs | £6,287 |
| 5 kW | 5140 kWh | 3084 kWh | 2056 kWh | £827 | £206 | £1,033 | £12,273 | 11.9 yrs | £8,384 |
| 6 kW | 6169 kWh | 3701 kWh | 2467 kWh | £993 | £247 | £1,239 | £14,307 | 11.5 yrs | £10,481 |
| 7 kW | 7197 kWh | 4318 kWh | 2879 kWh | £1,158 | £288 | £1,446 | £16,342 | 11.3 yrs | £12,578 |
| 8 kW | 8225 kWh | 4935 kWh | 3290 kWh | £1,324 | £329 | £1,653 | £18,376 | 11.1 yrs | £14,674 |
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: £1,119, Upfront: £13,673, Break-even: 12.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2056 kWh | 1439 kWh | 617 kWh | £386 | £62 | £448 | £7,569 | 16.9 yrs | £1,385 |
| 3 kW | 3084 kWh | 2159 kWh | 925 kWh | £579 | £93 | £672 | £9,604 | 14.3 yrs | £3,828 |
| 4 kW | 4112 kWh | 2879 kWh | 1234 kWh | £772 | £123 | £895 | £11,638 | 13.0 yrs | £6,271 |
| 5 kW | 5140 kWh | 3598 kWh | 1542 kWh | £965 | £154 | £1,119 | £13,673 | 12.2 yrs | £8,713 |
| 6 kW | 6169 kWh | 4318 kWh | 1851 kWh | £1,158 | £185 | £1,343 | £15,707 | 11.7 yrs | £11,156 |
| 7 kW | 7197 kWh | 5038 kWh | 2159 kWh | £1,351 | £216 | £1,567 | £17,742 | 11.3 yrs | £13,599 |
| 8 kW | 8225 kWh | 5757 kWh | 2467 kWh | £1,544 | £247 | £1,791 | £19,776 | 11.0 yrs | £16,041 |
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: £1,145, Upfront: £15,423, 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 | 2056 kWh | 1501 kWh | 555 kWh | £403 | £56 | £458 | £9,319 | 20.3 yrs | £-157 |
| 3 kW | 3084 kWh | 2252 kWh | 833 kWh | £604 | £83 | £687 | £11,354 | 16.5 yrs | £2,389 |
| 4 kW | 4112 kWh | 3002 kWh | 1110 kWh | £805 | £111 | £916 | £13,388 | 14.6 yrs | £4,936 |
| 5 kW | 5140 kWh | 3753 kWh | 1388 kWh | £1,006 | £139 | £1,145 | £15,423 | 13.5 yrs | £7,482 |
| 6 kW | 6169 kWh | 4503 kWh | 1666 kWh | £1,208 | £167 | £1,374 | £17,457 | 12.7 yrs | £10,028 |
| 7 kW | 7197 kWh | 5254 kWh | 1943 kWh | £1,409 | £194 | £1,603 | £19,492 | 12.2 yrs | £12,575 |
| 8 kW | 8225 kWh | 6004 kWh | 2221 kWh | £1,610 | £222 | £1,832 | £21,526 | 11.7 yrs | £15,121 |
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: £1,163, Upfront: £17,173, 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 | 2056 kWh | 1542 kWh | 514 kWh | £414 | £51 | £465 | £11,069 | 23.8 yrs | £-1,769 |
| 3 kW | 3084 kWh | 2313 kWh | 771 kWh | £620 | £77 | £698 | £13,104 | 18.8 yrs | £847 |
| 4 kW | 4112 kWh | 3084 kWh | 1028 kWh | £827 | £103 | £930 | £15,138 | 16.3 yrs | £3,462 |
| 5 kW | 5140 kWh | 3855 kWh | 1285 kWh | £1,034 | £129 | £1,163 | £17,173 | 14.8 yrs | £6,078 |
| 6 kW | 6169 kWh | 4626 kWh | 1542 kWh | £1,241 | £154 | £1,395 | £19,207 | 13.8 yrs | £8,694 |
| 7 kW | 7197 kWh | 5398 kWh | 1799 kWh | £1,448 | £180 | £1,628 | £21,242 | 13.1 yrs | £11,309 |
| 8 kW | 8225 kWh | 6169 kWh | 2056 kWh | £1,654 | £206 | £1,860 | £23,276 | 12.5 yrs | £13,925 |
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: £1,180, Upfront: £19,623, Break-even: 16.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2056 kWh | 1583 kWh | 473 kWh | £425 | £47 | £472 | £13,519 | 28.6 yrs | £-4,080 |
| 3 kW | 3084 kWh | 2375 kWh | 709 kWh | £637 | £71 | £708 | £15,554 | 22.0 yrs | £-1,396 |
| 4 kW | 4112 kWh | 3167 kWh | 946 kWh | £849 | £95 | £944 | £17,588 | 18.6 yrs | £1,289 |
| 5 kW | 5140 kWh | 3958 kWh | 1182 kWh | £1,062 | £118 | £1,180 | £19,623 | 16.6 yrs | £3,974 |
| 6 kW | 6169 kWh | 4750 kWh | 1419 kWh | £1,274 | £142 | £1,416 | £21,657 | 15.3 yrs | £6,659 |
| 7 kW | 7197 kWh | 5541 kWh | 1655 kWh | £1,486 | £166 | £1,652 | £23,692 | 14.3 yrs | £9,343 |
| 8 kW | 8225 kWh | 6333 kWh | 1892 kWh | £1,699 | £189 | £1,888 | £25,726 | 13.6 yrs | £12,028 |
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.