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 743 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: £625, Upfront: £10,173, Break-even: 16.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1487 kWh | 595 kWh | 892 kWh | £161 | £89 | £250 | £4,069 | 16.3 yrs | £933 |
| 3 kW | 2230 kWh | 892 kWh | 1338 kWh | £241 | £134 | £375 | £6,104 | 16.3 yrs | £1,400 |
| 4 kW | 2973 kWh | 1189 kWh | 1784 kWh | £322 | £178 | £500 | £8,138 | 16.3 yrs | £1,867 |
| 5 kW | 3717 kWh | 1487 kWh | 2230 kWh | £402 | £223 | £625 | £10,173 | 16.3 yrs | £2,334 |
| 6 kW | 4460 kWh | 1784 kWh | 2676 kWh | £483 | £268 | £750 | £12,207 | 16.3 yrs | £2,800 |
| 7 kW | 5204 kWh | 2081 kWh | 3122 kWh | £563 | £312 | £875 | £14,242 | 16.3 yrs | £3,267 |
| 8 kW | 5947 kWh | 2379 kWh | 3568 kWh | £644 | £357 | £1,001 | £16,276 | 16.3 yrs | £3,734 |
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: £752, Upfront: £12,273, Break-even: 16.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1487 kWh | 892 kWh | 595 kWh | £241 | £59 | £301 | £6,169 | 20.5 yrs | £-152 |
| 3 kW | 2230 kWh | 1338 kWh | 892 kWh | £362 | £89 | £451 | £8,204 | 18.2 yrs | £822 |
| 4 kW | 2973 kWh | 1784 kWh | 1189 kWh | £483 | £119 | £602 | £10,238 | 17.0 yrs | £1,796 |
| 5 kW | 3717 kWh | 2230 kWh | 1487 kWh | £603 | £149 | £752 | £12,273 | 16.3 yrs | £2,770 |
| 6 kW | 4460 kWh | 2676 kWh | 1784 kWh | £724 | £178 | £903 | £14,307 | 15.9 yrs | £3,744 |
| 7 kW | 5204 kWh | 3122 kWh | 2081 kWh | £845 | £208 | £1,053 | £16,342 | 15.5 yrs | £4,718 |
| 8 kW | 5947 kWh | 3568 kWh | 2379 kWh | £966 | £238 | £1,203 | £18,376 | 15.3 yrs | £5,692 |
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: £816, Upfront: £13,673, 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 | 1487 kWh | 1041 kWh | 446 kWh | £282 | £45 | £326 | £7,569 | 23.2 yrs | £-1,045 |
| 3 kW | 2230 kWh | 1561 kWh | 669 kWh | £422 | £67 | £489 | £9,604 | 19.6 yrs | £183 |
| 4 kW | 2973 kWh | 2081 kWh | 892 kWh | £563 | £89 | £652 | £11,638 | 17.8 yrs | £1,411 |
| 5 kW | 3717 kWh | 2602 kWh | 1115 kWh | £704 | £112 | £816 | £13,673 | 16.8 yrs | £2,638 |
| 6 kW | 4460 kWh | 3122 kWh | 1338 kWh | £845 | £134 | £979 | £15,707 | 16.0 yrs | £3,866 |
| 7 kW | 5204 kWh | 3642 kWh | 1561 kWh | £986 | £156 | £1,142 | £17,742 | 15.5 yrs | £5,094 |
| 8 kW | 5947 kWh | 4163 kWh | 1784 kWh | £1,126 | £178 | £1,305 | £19,776 | 15.2 yrs | £6,321 |
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: £835, Upfront: £15,423, Break-even: 18.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1487 kWh | 1085 kWh | 401 kWh | £294 | £40 | £334 | £9,319 | 27.9 yrs | £-2,643 |
| 3 kW | 2230 kWh | 1628 kWh | 602 kWh | £441 | £60 | £501 | £11,354 | 22.7 yrs | £-1,339 |
| 4 kW | 2973 kWh | 2171 kWh | 803 kWh | £587 | £80 | £668 | £13,388 | 20.1 yrs | £-35 |
| 5 kW | 3717 kWh | 2713 kWh | 1004 kWh | £734 | £100 | £835 | £15,423 | 18.5 yrs | £1,269 |
| 6 kW | 4460 kWh | 3256 kWh | 1204 kWh | £881 | £120 | £1,001 | £17,457 | 17.4 yrs | £2,572 |
| 7 kW | 5204 kWh | 3799 kWh | 1405 kWh | £1,028 | £140 | £1,168 | £19,492 | 16.7 yrs | £3,876 |
| 8 kW | 5947 kWh | 4341 kWh | 1606 kWh | £1,175 | £161 | £1,335 | £21,526 | 16.1 yrs | £5,180 |
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: £847, Upfront: £17,173, Break-even: 20.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1487 kWh | 1115 kWh | 372 kWh | £302 | £37 | £339 | £11,069 | 32.7 yrs | £-4,291 |
| 3 kW | 2230 kWh | 1673 kWh | 558 kWh | £453 | £56 | £508 | £13,104 | 25.8 yrs | £-2,937 |
| 4 kW | 2973 kWh | 2230 kWh | 743 kWh | £603 | £74 | £678 | £15,138 | 22.3 yrs | £-1,582 |
| 5 kW | 3717 kWh | 2788 kWh | 929 kWh | £754 | £93 | £847 | £17,173 | 20.3 yrs | £-228 |
| 6 kW | 4460 kWh | 3345 kWh | 1115 kWh | £905 | £112 | £1,017 | £19,207 | 18.9 yrs | £1,127 |
| 7 kW | 5204 kWh | 3903 kWh | 1301 kWh | £1,056 | £130 | £1,186 | £21,242 | 17.9 yrs | £2,481 |
| 8 kW | 5947 kWh | 4460 kWh | 1487 kWh | £1,207 | £149 | £1,356 | £23,276 | 17.2 yrs | £3,836 |
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: £860, Upfront: £19,623, Break-even: 22.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1487 kWh | 1145 kWh | 342 kWh | £310 | £34 | £344 | £13,519 | 39.3 yrs | £-6,640 |
| 3 kW | 2230 kWh | 1717 kWh | 513 kWh | £465 | £51 | £516 | £15,554 | 30.1 yrs | £-5,234 |
| 4 kW | 2973 kWh | 2290 kWh | 684 kWh | £620 | £68 | £688 | £17,588 | 25.6 yrs | £-3,829 |
| 5 kW | 3717 kWh | 2862 kWh | 855 kWh | £774 | £85 | £860 | £19,623 | 22.8 yrs | £-2,424 |
| 6 kW | 4460 kWh | 3434 kWh | 1026 kWh | £929 | £103 | £1,032 | £21,657 | 21.0 yrs | £-1,019 |
| 7 kW | 5204 kWh | 4007 kWh | 1197 kWh | £1,084 | £120 | £1,204 | £23,692 | 19.7 yrs | £386 |
| 8 kW | 5947 kWh | 4579 kWh | 1368 kWh | £1,239 | £137 | £1,376 | £25,726 | 18.7 yrs | £1,792 |
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.