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 826 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: £674, Upfront: £10,173, 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 | 1651 kWh | 660 kWh | 991 kWh | £171 | £99 | £270 | £4,069 | 15.1 yrs | £1,325 |
| 3 kW | 2476 kWh | 991 kWh | 1486 kWh | £256 | £149 | £405 | £6,104 | 15.1 yrs | £1,988 |
| 4 kW | 3302 kWh | 1321 kWh | 1981 kWh | £341 | £198 | £539 | £8,138 | 15.1 yrs | £2,650 |
| 5 kW | 4128 kWh | 1651 kWh | 2476 kWh | £427 | £248 | £674 | £10,173 | 15.1 yrs | £3,313 |
| 6 kW | 4953 kWh | 1981 kWh | 2972 kWh | £512 | £297 | £809 | £12,207 | 15.1 yrs | £3,975 |
| 7 kW | 5778 kWh | 2311 kWh | 3467 kWh | £597 | £347 | £944 | £14,242 | 15.1 yrs | £4,638 |
| 8 kW | 6604 kWh | 2642 kWh | 3962 kWh | £683 | £396 | £1,079 | £16,276 | 15.1 yrs | £5,301 |
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: £805, Upfront: £12,273, Break-even: 15.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1651 kWh | 991 kWh | 660 kWh | £256 | £66 | £322 | £6,169 | 19.2 yrs | £271 |
| 3 kW | 2476 kWh | 1486 kWh | 991 kWh | £384 | £99 | £483 | £8,204 | 17.0 yrs | £1,457 |
| 4 kW | 3302 kWh | 1981 kWh | 1321 kWh | £512 | £132 | £644 | £10,238 | 15.9 yrs | £2,642 |
| 5 kW | 4128 kWh | 2476 kWh | 1651 kWh | £640 | £165 | £805 | £12,273 | 15.2 yrs | £3,828 |
| 6 kW | 4953 kWh | 2972 kWh | 1981 kWh | £768 | £198 | £966 | £14,307 | 14.8 yrs | £5,014 |
| 7 kW | 5778 kWh | 3467 kWh | 2311 kWh | £896 | £231 | £1,127 | £16,342 | 14.5 yrs | £6,199 |
| 8 kW | 6604 kWh | 3962 kWh | 2642 kWh | £1,024 | £264 | £1,288 | £18,376 | 14.3 yrs | £7,385 |
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: £870, Upfront: £13,673, Break-even: 15.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1651 kWh | 1156 kWh | 495 kWh | £299 | £50 | £348 | £7,569 | 21.7 yrs | £-606 |
| 3 kW | 2476 kWh | 1734 kWh | 743 kWh | £448 | £74 | £522 | £9,604 | 18.4 yrs | £841 |
| 4 kW | 3302 kWh | 2311 kWh | 991 kWh | £597 | £99 | £696 | £11,638 | 16.7 yrs | £2,288 |
| 5 kW | 4128 kWh | 2889 kWh | 1238 kWh | £747 | £124 | £870 | £13,673 | 15.7 yrs | £3,736 |
| 6 kW | 4953 kWh | 3467 kWh | 1486 kWh | £896 | £149 | £1,044 | £15,707 | 15.0 yrs | £5,183 |
| 7 kW | 5778 kWh | 4045 kWh | 1734 kWh | £1,045 | £173 | £1,219 | £17,742 | 14.6 yrs | £6,630 |
| 8 kW | 6604 kWh | 4623 kWh | 1981 kWh | £1,195 | £198 | £1,393 | £19,776 | 14.2 yrs | £8,077 |
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: £890, Upfront: £15,423, Break-even: 17.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1651 kWh | 1205 kWh | 446 kWh | £311 | £45 | £356 | £9,319 | 26.2 yrs | £-2,199 |
| 3 kW | 2476 kWh | 1808 kWh | 669 kWh | £467 | £67 | £534 | £11,354 | 21.3 yrs | £-673 |
| 4 kW | 3302 kWh | 2410 kWh | 892 kWh | £623 | £89 | £712 | £13,388 | 18.8 yrs | £852 |
| 5 kW | 4128 kWh | 3013 kWh | 1114 kWh | £779 | £111 | £890 | £15,423 | 17.3 yrs | £2,378 |
| 6 kW | 4953 kWh | 3616 kWh | 1337 kWh | £934 | £134 | £1,068 | £17,457 | 16.3 yrs | £3,903 |
| 7 kW | 5778 kWh | 4218 kWh | 1560 kWh | £1,090 | £156 | £1,246 | £19,492 | 15.6 yrs | £5,429 |
| 8 kW | 6604 kWh | 4821 kWh | 1783 kWh | £1,246 | £178 | £1,424 | £21,526 | 15.1 yrs | £6,955 |
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: £903, Upfront: £17,173, Break-even: 19.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1651 kWh | 1238 kWh | 413 kWh | £320 | £41 | £361 | £11,069 | 30.6 yrs | £-3,844 |
| 3 kW | 2476 kWh | 1857 kWh | 619 kWh | £480 | £62 | £542 | £13,104 | 24.2 yrs | £-2,266 |
| 4 kW | 3302 kWh | 2476 kWh | 826 kWh | £640 | £83 | £722 | £15,138 | 21.0 yrs | £-688 |
| 5 kW | 4128 kWh | 3096 kWh | 1032 kWh | £800 | £103 | £903 | £17,173 | 19.0 yrs | £889 |
| 6 kW | 4953 kWh | 3715 kWh | 1238 kWh | £960 | £124 | £1,084 | £19,207 | 17.7 yrs | £2,467 |
| 7 kW | 5778 kWh | 4334 kWh | 1445 kWh | £1,120 | £144 | £1,264 | £21,242 | 16.8 yrs | £4,045 |
| 8 kW | 6604 kWh | 4953 kWh | 1651 kWh | £1,280 | £165 | £1,445 | £23,276 | 16.1 yrs | £5,623 |
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: £916, Upfront: £19,623, Break-even: 21.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1651 kWh | 1271 kWh | 380 kWh | £328 | £38 | £366 | £13,519 | 36.9 yrs | £-6,190 |
| 3 kW | 2476 kWh | 1907 kWh | 570 kWh | £493 | £57 | £550 | £15,554 | 28.3 yrs | £-4,559 |
| 4 kW | 3302 kWh | 2543 kWh | 759 kWh | £657 | £76 | £733 | £17,588 | 24.0 yrs | £-2,929 |
| 5 kW | 4128 kWh | 3178 kWh | 949 kWh | £821 | £95 | £916 | £19,623 | 21.4 yrs | £-1,299 |
| 6 kW | 4953 kWh | 3814 kWh | 1139 kWh | £985 | £114 | £1,099 | £21,657 | 19.7 yrs | £331 |
| 7 kW | 5778 kWh | 4449 kWh | 1329 kWh | £1,150 | £133 | £1,283 | £23,692 | 18.5 yrs | £1,961 |
| 8 kW | 6604 kWh | 5085 kWh | 1519 kWh | £1,314 | £152 | £1,466 | £25,726 | 17.5 yrs | £3,591 |
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.