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 1123 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: £940, Upfront: £10,173, Break-even: 10.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2247 kWh | 899 kWh | 1348 kWh | £241 | £135 | £376 | £4,069 | 10.8 yrs | £3,448 |
| 3 kW | 3370 kWh | 1348 kWh | 2022 kWh | £362 | £202 | £564 | £6,104 | 10.8 yrs | £5,172 |
| 4 kW | 4494 kWh | 1797 kWh | 2696 kWh | £482 | £270 | £752 | £8,138 | 10.8 yrs | £6,896 |
| 5 kW | 5617 kWh | 2247 kWh | 3370 kWh | £603 | £337 | £940 | £10,173 | 10.8 yrs | £8,620 |
| 6 kW | 6741 kWh | 2696 kWh | 4044 kWh | £723 | £404 | £1,128 | £12,207 | 10.8 yrs | £10,344 |
| 7 kW | 7864 kWh | 3146 kWh | 4718 kWh | £844 | £472 | £1,315 | £14,242 | 10.8 yrs | £12,068 |
| 8 kW | 8987 kWh | 3595 kWh | 5392 kWh | £964 | £539 | £1,503 | £16,276 | 10.8 yrs | £13,792 |
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: £1,129, Upfront: £12,273, Break-even: 10.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2247 kWh | 1348 kWh | 899 kWh | £362 | £90 | £451 | £6,169 | 13.7 yrs | £2,860 |
| 3 kW | 3370 kWh | 2022 kWh | 1348 kWh | £542 | £135 | £677 | £8,204 | 12.1 yrs | £5,340 |
| 4 kW | 4494 kWh | 2696 kWh | 1797 kWh | £723 | £180 | £903 | £10,238 | 11.3 yrs | £7,820 |
| 5 kW | 5617 kWh | 3370 kWh | 2247 kWh | £904 | £225 | £1,129 | £12,273 | 10.9 yrs | £10,299 |
| 6 kW | 6741 kWh | 4044 kWh | 2696 kWh | £1,085 | £270 | £1,354 | £14,307 | 10.6 yrs | £12,779 |
| 7 kW | 7864 kWh | 4718 kWh | 3146 kWh | £1,265 | £315 | £1,580 | £16,342 | 10.3 yrs | £15,259 |
| 8 kW | 8987 kWh | 5392 kWh | 3595 kWh | £1,446 | £359 | £1,806 | £18,376 | 10.2 yrs | £17,739 |
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: £1,223, Upfront: £13,673, Break-even: 11.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2247 kWh | 1573 kWh | 674 kWh | £422 | £67 | £489 | £7,569 | 15.5 yrs | £2,216 |
| 3 kW | 3370 kWh | 2359 kWh | 1011 kWh | £633 | £101 | £734 | £9,604 | 13.1 yrs | £5,073 |
| 4 kW | 4494 kWh | 3146 kWh | 1348 kWh | £844 | £135 | £978 | £11,638 | 11.9 yrs | £7,931 |
| 5 kW | 5617 kWh | 3932 kWh | 1685 kWh | £1,055 | £169 | £1,223 | £13,673 | 11.2 yrs | £10,789 |
| 6 kW | 6741 kWh | 4718 kWh | 2022 kWh | £1,265 | £202 | £1,468 | £15,707 | 10.7 yrs | £13,647 |
| 7 kW | 7864 kWh | 5505 kWh | 2359 kWh | £1,476 | £236 | £1,712 | £17,742 | 10.4 yrs | £16,505 |
| 8 kW | 8987 kWh | 6291 kWh | 2696 kWh | £1,687 | £270 | £1,957 | £19,776 | 10.1 yrs | £19,362 |
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: £1,251, Upfront: £15,423, Break-even: 12.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2247 kWh | 1640 kWh | 607 kWh | £440 | £61 | £501 | £9,319 | 18.6 yrs | £692 |
| 3 kW | 3370 kWh | 2460 kWh | 910 kWh | £660 | £91 | £751 | £11,354 | 15.1 yrs | £3,664 |
| 4 kW | 4494 kWh | 3280 kWh | 1213 kWh | £880 | £121 | £1,001 | £13,388 | 13.4 yrs | £6,635 |
| 5 kW | 5617 kWh | 4101 kWh | 1517 kWh | £1,100 | £152 | £1,251 | £15,423 | 12.3 yrs | £9,606 |
| 6 kW | 6741 kWh | 4921 kWh | 1820 kWh | £1,320 | £182 | £1,502 | £17,457 | 11.6 yrs | £12,577 |
| 7 kW | 7864 kWh | 5741 kWh | 2123 kWh | £1,540 | £212 | £1,752 | £19,492 | 11.1 yrs | £15,548 |
| 8 kW | 8987 kWh | 6561 kWh | 2427 kWh | £1,760 | £243 | £2,002 | £21,526 | 10.8 yrs | £18,519 |
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: £1,270, Upfront: £17,173, 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 | 2247 kWh | 1685 kWh | 562 kWh | £452 | £56 | £508 | £11,069 | 21.8 yrs | £-906 |
| 3 kW | 3370 kWh | 2528 kWh | 843 kWh | £678 | £84 | £762 | £13,104 | 17.2 yrs | £2,140 |
| 4 kW | 4494 kWh | 3370 kWh | 1123 kWh | £904 | £112 | £1,016 | £15,138 | 14.9 yrs | £5,187 |
| 5 kW | 5617 kWh | 4213 kWh | 1404 kWh | £1,130 | £140 | £1,270 | £17,173 | 13.5 yrs | £8,234 |
| 6 kW | 6741 kWh | 5055 kWh | 1685 kWh | £1,356 | £169 | £1,524 | £19,207 | 12.6 yrs | £11,281 |
| 7 kW | 7864 kWh | 5898 kWh | 1966 kWh | £1,582 | £197 | £1,778 | £21,242 | 11.9 yrs | £14,327 |
| 8 kW | 8987 kWh | 6741 kWh | 2247 kWh | £1,808 | £225 | £2,033 | £23,276 | 11.5 yrs | £17,374 |
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: £1,289, Upfront: £19,623, 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 | 2247 kWh | 1730 kWh | 517 kWh | £464 | £52 | £516 | £13,519 | 26.2 yrs | £-3,205 |
| 3 kW | 3370 kWh | 2595 kWh | 775 kWh | £696 | £78 | £774 | £15,554 | 20.1 yrs | £-83 |
| 4 kW | 4494 kWh | 3460 kWh | 1034 kWh | £928 | £103 | £1,031 | £17,588 | 17.1 yrs | £3,039 |
| 5 kW | 5617 kWh | 4325 kWh | 1292 kWh | £1,160 | £129 | £1,289 | £19,623 | 15.2 yrs | £6,162 |
| 6 kW | 6741 kWh | 5190 kWh | 1550 kWh | £1,392 | £155 | £1,547 | £21,657 | 14.0 yrs | £9,284 |
| 7 kW | 7864 kWh | 6055 kWh | 1809 kWh | £1,624 | £181 | £1,805 | £23,692 | 13.1 yrs | £12,406 |
| 8 kW | 8987 kWh | 6920 kWh | 2067 kWh | £1,856 | £207 | £2,063 | £25,726 | 12.5 yrs | £15,529 |
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.