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 904 kWh per year on a south-facing roof. We value self-used electricity at 25.4p 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: £731, Upfront: £10,173, Break-even: 13.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1809 kWh | 723 kWh | 1085 kWh | £184 | £109 | £292 | £4,069 | 13.9 yrs | £1,781 |
| 3 kW | 2713 kWh | 1085 kWh | 1628 kWh | £276 | £163 | £439 | £6,104 | 13.9 yrs | £2,671 |
| 4 kW | 3617 kWh | 1447 kWh | 2170 kWh | £368 | £217 | £585 | £8,138 | 13.9 yrs | £3,561 |
| 5 kW | 4522 kWh | 1809 kWh | 2713 kWh | £460 | £271 | £731 | £10,173 | 13.9 yrs | £4,452 |
| 6 kW | 5426 kWh | 2170 kWh | 3255 kWh | £552 | £326 | £877 | £12,207 | 13.9 yrs | £5,342 |
| 7 kW | 6330 kWh | 2532 kWh | 3798 kWh | £644 | £380 | £1,024 | £14,242 | 13.9 yrs | £6,233 |
| 8 kW | 7234 kWh | 2894 kWh | 4341 kWh | £736 | £434 | £1,170 | £16,276 | 13.9 yrs | £7,123 |
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: £871, Upfront: £12,273, Break-even: 14.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1809 kWh | 1085 kWh | 723 kWh | £276 | £72 | £348 | £6,169 | 17.7 yrs | £797 |
| 3 kW | 2713 kWh | 1628 kWh | 1085 kWh | £414 | £109 | £522 | £8,204 | 15.7 yrs | £2,245 |
| 4 kW | 3617 kWh | 2170 kWh | 1447 kWh | £552 | £145 | £697 | £10,238 | 14.7 yrs | £3,694 |
| 5 kW | 4522 kWh | 2713 kWh | 1809 kWh | £690 | £181 | £871 | £12,273 | 14.1 yrs | £5,142 |
| 6 kW | 5426 kWh | 3255 kWh | 2170 kWh | £828 | £217 | £1,045 | £14,307 | 13.7 yrs | £6,591 |
| 7 kW | 6330 kWh | 3798 kWh | 2532 kWh | £966 | £253 | £1,219 | £16,342 | 13.4 yrs | £8,039 |
| 8 kW | 7234 kWh | 4341 kWh | 2894 kWh | £1,104 | £289 | £1,393 | £18,376 | 13.2 yrs | £9,488 |
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: £941, Upfront: £13,673, Break-even: 14.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1809 kWh | 1266 kWh | 543 kWh | £322 | £54 | £376 | £7,569 | 20.1 yrs | £-45 |
| 3 kW | 2713 kWh | 1899 kWh | 814 kWh | £483 | £81 | £564 | £9,604 | 17.0 yrs | £1,683 |
| 4 kW | 3617 kWh | 2532 kWh | 1085 kWh | £644 | £109 | £752 | £11,638 | 15.5 yrs | £3,410 |
| 5 kW | 4522 kWh | 3165 kWh | 1356 kWh | £805 | £136 | £941 | £13,673 | 14.5 yrs | £5,138 |
| 6 kW | 5426 kWh | 3798 kWh | 1628 kWh | £966 | £163 | £1,129 | £15,707 | 13.9 yrs | £6,865 |
| 7 kW | 6330 kWh | 4431 kWh | 1899 kWh | £1,127 | £190 | £1,317 | £17,742 | 13.5 yrs | £8,593 |
| 8 kW | 7234 kWh | 5064 kWh | 2170 kWh | £1,288 | £217 | £1,505 | £19,776 | 13.1 yrs | £10,320 |
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: £961, Upfront: £15,423, Break-even: 16.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1809 kWh | 1320 kWh | 488 kWh | £336 | £49 | £385 | £9,319 | 24.2 yrs | £-1,627 |
| 3 kW | 2713 kWh | 1980 kWh | 732 kWh | £504 | £73 | £577 | £11,354 | 19.7 yrs | £184 |
| 4 kW | 3617 kWh | 2641 kWh | 977 kWh | £671 | £98 | £769 | £13,388 | 17.4 yrs | £1,995 |
| 5 kW | 4522 kWh | 3301 kWh | 1221 kWh | £839 | £122 | £961 | £15,423 | 16.0 yrs | £3,806 |
| 6 kW | 5426 kWh | 3961 kWh | 1465 kWh | £1,007 | £146 | £1,154 | £17,457 | 15.1 yrs | £5,618 |
| 7 kW | 6330 kWh | 4621 kWh | 1709 kWh | £1,175 | £171 | £1,346 | £19,492 | 14.5 yrs | £7,429 |
| 8 kW | 7234 kWh | 5281 kWh | 1953 kWh | £1,343 | £195 | £1,538 | £21,526 | 14.0 yrs | £9,240 |
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: £975, Upfront: £17,173, Break-even: 17.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1809 kWh | 1356 kWh | 452 kWh | £345 | £45 | £390 | £11,069 | 28.4 yrs | £-3,266 |
| 3 kW | 2713 kWh | 2035 kWh | 678 kWh | £517 | £68 | £585 | £13,104 | 22.4 yrs | £-1,399 |
| 4 kW | 3617 kWh | 2713 kWh | 904 kWh | £690 | £90 | £780 | £15,138 | 19.4 yrs | £468 |
| 5 kW | 4522 kWh | 3391 kWh | 1130 kWh | £862 | £113 | £975 | £17,173 | 17.6 yrs | £2,335 |
| 6 kW | 5426 kWh | 4069 kWh | 1356 kWh | £1,035 | £136 | £1,170 | £19,207 | 16.4 yrs | £4,203 |
| 7 kW | 6330 kWh | 4748 kWh | 1583 kWh | £1,207 | £158 | £1,366 | £21,242 | 15.6 yrs | £6,070 |
| 8 kW | 7234 kWh | 5426 kWh | 1809 kWh | £1,380 | £181 | £1,561 | £23,276 | 14.9 yrs | £7,937 |
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: £989, Upfront: £19,623, Break-even: 19.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1809 kWh | 1393 kWh | 416 kWh | £354 | £42 | £396 | £13,519 | 34.2 yrs | £-5,604 |
| 3 kW | 2713 kWh | 2089 kWh | 624 kWh | £531 | £62 | £594 | £15,554 | 26.2 yrs | £-3,681 |
| 4 kW | 3617 kWh | 2785 kWh | 832 kWh | £708 | £83 | £791 | £17,588 | 22.2 yrs | £-1,758 |
| 5 kW | 4522 kWh | 3482 kWh | 1040 kWh | £885 | £104 | £989 | £19,623 | 19.8 yrs | £165 |
| 6 kW | 5426 kWh | 4178 kWh | 1248 kWh | £1,062 | £125 | £1,187 | £21,657 | 18.2 yrs | £2,087 |
| 7 kW | 6330 kWh | 4874 kWh | 1456 kWh | £1,240 | £146 | £1,385 | £23,692 | 17.1 yrs | £4,010 |
| 8 kW | 7234 kWh | 5570 kWh | 1664 kWh | £1,417 | £166 | £1,583 | £25,726 | 16.3 yrs | £5,933 |
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.