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 897 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: £733, 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 | 1795 kWh | 718 kWh | 1077 kWh | £186 | £108 | £293 | £4,069 | 13.9 yrs | £1,795 |
| 3 kW | 2692 kWh | 1077 kWh | 1615 kWh | £278 | £162 | £440 | £6,104 | 13.9 yrs | £2,693 |
| 4 kW | 3590 kWh | 1436 kWh | 2154 kWh | £371 | £215 | £586 | £8,138 | 13.9 yrs | £3,591 |
| 5 kW | 4487 kWh | 1795 kWh | 2692 kWh | £464 | £269 | £733 | £10,173 | 13.9 yrs | £4,488 |
| 6 kW | 5385 kWh | 2154 kWh | 3231 kWh | £557 | £323 | £880 | £12,207 | 13.9 yrs | £5,386 |
| 7 kW | 6282 kWh | 2513 kWh | 3769 kWh | £649 | £377 | £1,026 | £14,242 | 13.9 yrs | £6,284 |
| 8 kW | 7180 kWh | 2872 kWh | 4308 kWh | £742 | £431 | £1,173 | £16,276 | 13.9 yrs | £7,181 |
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: £875, Upfront: £12,273, Break-even: 14.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1795 kWh | 1077 kWh | 718 kWh | £278 | £72 | £350 | £6,169 | 17.6 yrs | £833 |
| 3 kW | 2692 kWh | 1615 kWh | 1077 kWh | £417 | £108 | £525 | £8,204 | 15.6 yrs | £2,299 |
| 4 kW | 3590 kWh | 2154 kWh | 1436 kWh | £557 | £144 | £700 | £10,238 | 14.6 yrs | £3,765 |
| 5 kW | 4487 kWh | 2692 kWh | 1795 kWh | £696 | £179 | £875 | £12,273 | 14.0 yrs | £5,232 |
| 6 kW | 5385 kWh | 3231 kWh | 2154 kWh | £835 | £215 | £1,050 | £14,307 | 13.6 yrs | £6,698 |
| 7 kW | 6282 kWh | 3769 kWh | 2513 kWh | £974 | £251 | £1,225 | £16,342 | 13.3 yrs | £8,164 |
| 8 kW | 7180 kWh | 4308 kWh | 2872 kWh | £1,113 | £287 | £1,400 | £18,376 | 13.1 yrs | £9,630 |
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: £946, Upfront: £13,673, Break-even: 14.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1795 kWh | 1256 kWh | 538 kWh | £325 | £54 | £379 | £7,569 | 20.0 yrs | £1 |
| 3 kW | 2692 kWh | 1885 kWh | 808 kWh | £487 | £81 | £568 | £9,604 | 16.9 yrs | £1,752 |
| 4 kW | 3590 kWh | 2513 kWh | 1077 kWh | £649 | £108 | £757 | £11,638 | 15.4 yrs | £3,502 |
| 5 kW | 4487 kWh | 3141 kWh | 1346 kWh | £812 | £135 | £946 | £13,673 | 14.4 yrs | £5,253 |
| 6 kW | 5385 kWh | 3769 kWh | 1615 kWh | £974 | £162 | £1,136 | £15,707 | 13.8 yrs | £7,004 |
| 7 kW | 6282 kWh | 4398 kWh | 1885 kWh | £1,136 | £188 | £1,325 | £17,742 | 13.4 yrs | £8,754 |
| 8 kW | 7180 kWh | 5026 kWh | 2154 kWh | £1,299 | £215 | £1,514 | £19,776 | 13.1 yrs | £10,505 |
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: £968, Upfront: £15,423, Break-even: 15.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1795 kWh | 1310 kWh | 485 kWh | £339 | £48 | £387 | £9,319 | 24.1 yrs | £-1,578 |
| 3 kW | 2692 kWh | 1965 kWh | 727 kWh | £508 | £73 | £581 | £11,354 | 19.6 yrs | £258 |
| 4 kW | 3590 kWh | 2621 kWh | 969 kWh | £677 | £97 | £774 | £13,388 | 17.3 yrs | £2,094 |
| 5 kW | 4487 kWh | 3276 kWh | 1212 kWh | £846 | £121 | £968 | £15,423 | 15.9 yrs | £3,930 |
| 6 kW | 5385 kWh | 3931 kWh | 1454 kWh | £1,016 | £145 | £1,161 | £17,457 | 15.0 yrs | £5,765 |
| 7 kW | 6282 kWh | 4586 kWh | 1696 kWh | £1,185 | £170 | £1,355 | £19,492 | 14.4 yrs | £7,601 |
| 8 kW | 7180 kWh | 5241 kWh | 1939 kWh | £1,354 | £194 | £1,548 | £21,526 | 13.9 yrs | £9,437 |
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: £982, Upfront: £17,173, Break-even: 17.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1795 kWh | 1346 kWh | 449 kWh | £348 | £45 | £393 | £11,069 | 28.2 yrs | £-3,214 |
| 3 kW | 2692 kWh | 2019 kWh | 673 kWh | £522 | £67 | £589 | £13,104 | 22.2 yrs | £-1,322 |
| 4 kW | 3590 kWh | 2692 kWh | 897 kWh | £696 | £90 | £785 | £15,138 | 19.3 yrs | £571 |
| 5 kW | 4487 kWh | 3365 kWh | 1122 kWh | £870 | £112 | £982 | £17,173 | 17.5 yrs | £2,464 |
| 6 kW | 5385 kWh | 4039 kWh | 1346 kWh | £1,044 | £135 | £1,178 | £19,207 | 16.3 yrs | £4,357 |
| 7 kW | 6282 kWh | 4712 kWh | 1571 kWh | £1,217 | £157 | £1,375 | £21,242 | 15.5 yrs | £6,249 |
| 8 kW | 7180 kWh | 5385 kWh | 1795 kWh | £1,391 | £179 | £1,571 | £23,276 | 14.8 yrs | £8,142 |
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: £996, Upfront: £19,623, Break-even: 19.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1795 kWh | 1382 kWh | 413 kWh | £357 | £41 | £398 | £13,519 | 33.9 yrs | £-5,551 |
| 3 kW | 2692 kWh | 2073 kWh | 619 kWh | £536 | £62 | £598 | £15,554 | 26.0 yrs | £-3,601 |
| 4 kW | 3590 kWh | 2764 kWh | 826 kWh | £714 | £83 | £797 | £17,588 | 22.1 yrs | £-1,651 |
| 5 kW | 4487 kWh | 3455 kWh | 1032 kWh | £893 | £103 | £996 | £19,623 | 19.7 yrs | £298 |
| 6 kW | 5385 kWh | 4146 kWh | 1238 kWh | £1,071 | £124 | £1,195 | £21,657 | 18.1 yrs | £2,248 |
| 7 kW | 6282 kWh | 4837 kWh | 1445 kWh | £1,250 | £144 | £1,394 | £23,692 | 17.0 yrs | £4,197 |
| 8 kW | 7180 kWh | 5528 kWh | 1651 kWh | £1,429 | £165 | £1,594 | £25,726 | 16.1 yrs | £6,147 |
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.