A typical roof here lands around 3.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 1006 kWh per year on a south-facing roof. We value self-used electricity at 25.6p 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: £817, Upfront: £10,173, Break-even: 12.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2011 kWh | 805 kWh | 1207 kWh | £206 | £121 | £327 | £4,069 | 12.4 yrs | £2,469 |
| 3 kW | 3017 kWh | 1207 kWh | 1810 kWh | £309 | £181 | £490 | £6,104 | 12.4 yrs | £3,704 |
| 4 kW | 4023 kWh | 1609 kWh | 2414 kWh | £412 | £241 | £654 | £8,138 | 12.4 yrs | £4,938 |
| 5 kW | 5029 kWh | 2011 kWh | 3017 kWh | £516 | £302 | £817 | £10,173 | 12.4 yrs | £6,173 |
| 6 kW | 6034 kWh | 2414 kWh | 3621 kWh | £619 | £362 | £981 | £12,207 | 12.4 yrs | £7,407 |
| 7 kW | 7040 kWh | 2816 kWh | 4224 kWh | £722 | £422 | £1,144 | £14,242 | 12.4 yrs | £8,642 |
| 8 kW | 8046 kWh | 3218 kWh | 4828 kWh | £825 | £483 | £1,308 | £16,276 | 12.4 yrs | £9,876 |
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: £974, Upfront: £12,273, Break-even: 12.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2011 kWh | 1207 kWh | 805 kWh | £309 | £80 | £390 | £6,169 | 15.8 yrs | £1,627 |
| 3 kW | 3017 kWh | 1810 kWh | 1207 kWh | £464 | £121 | £585 | £8,204 | 14.0 yrs | £3,490 |
| 4 kW | 4023 kWh | 2414 kWh | 1609 kWh | £619 | £161 | £780 | £10,238 | 13.1 yrs | £5,353 |
| 5 kW | 5029 kWh | 3017 kWh | 2011 kWh | £773 | £201 | £974 | £12,273 | 12.6 yrs | £7,217 |
| 6 kW | 6034 kWh | 3621 kWh | 2414 kWh | £928 | £241 | £1,169 | £14,307 | 12.2 yrs | £9,080 |
| 7 kW | 7040 kWh | 4224 kWh | 2816 kWh | £1,083 | £282 | £1,364 | £16,342 | 12.0 yrs | £10,943 |
| 8 kW | 8046 kWh | 4828 kWh | 3218 kWh | £1,237 | £322 | £1,559 | £18,376 | 11.8 yrs | £12,807 |
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: £1,053, Upfront: £13,673, Break-even: 13.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2011 kWh | 1408 kWh | 603 kWh | £361 | £60 | £421 | £7,569 | 18.0 yrs | £855 |
| 3 kW | 3017 kWh | 2112 kWh | 905 kWh | £541 | £91 | £632 | £9,604 | 15.2 yrs | £3,033 |
| 4 kW | 4023 kWh | 2816 kWh | 1207 kWh | £722 | £121 | £842 | £11,638 | 13.8 yrs | £5,211 |
| 5 kW | 5029 kWh | 3520 kWh | 1509 kWh | £902 | £151 | £1,053 | £13,673 | 13.0 yrs | £7,389 |
| 6 kW | 6034 kWh | 4224 kWh | 1810 kWh | £1,083 | £181 | £1,264 | £15,707 | 12.4 yrs | £9,566 |
| 7 kW | 7040 kWh | 4928 kWh | 2112 kWh | £1,263 | £211 | £1,474 | £17,742 | 12.0 yrs | £11,744 |
| 8 kW | 8046 kWh | 5632 kWh | 2414 kWh | £1,444 | £241 | £1,685 | £19,776 | 11.7 yrs | £13,922 |
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: £1,077, Upfront: £15,423, Break-even: 14.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2011 kWh | 1468 kWh | 543 kWh | £376 | £54 | £431 | £9,319 | 21.6 yrs | £-706 |
| 3 kW | 3017 kWh | 2203 kWh | 815 kWh | £565 | £81 | £646 | £11,354 | 17.6 yrs | £1,566 |
| 4 kW | 4023 kWh | 2937 kWh | 1086 kWh | £753 | £109 | £861 | £13,388 | 15.5 yrs | £3,838 |
| 5 kW | 5029 kWh | 3671 kWh | 1358 kWh | £941 | £136 | £1,077 | £15,423 | 14.3 yrs | £6,110 |
| 6 kW | 6034 kWh | 4405 kWh | 1629 kWh | £1,129 | £163 | £1,292 | £17,457 | 13.5 yrs | £8,382 |
| 7 kW | 7040 kWh | 5139 kWh | 1901 kWh | £1,317 | £190 | £1,507 | £19,492 | 12.9 yrs | £10,654 |
| 8 kW | 8046 kWh | 5874 kWh | 2172 kWh | £1,505 | £217 | £1,723 | £21,526 | 12.5 yrs | £12,926 |
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: £1,092, Upfront: £17,173, 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 | 2011 kWh | 1509 kWh | 503 kWh | £387 | £50 | £437 | £11,069 | 25.3 yrs | £-2,330 |
| 3 kW | 3017 kWh | 2263 kWh | 754 kWh | £580 | £75 | £655 | £13,104 | 20.0 yrs | £5 |
| 4 kW | 4023 kWh | 3017 kWh | 1006 kWh | £773 | £101 | £874 | £15,138 | 17.3 yrs | £2,340 |
| 5 kW | 5029 kWh | 3772 kWh | 1257 kWh | £967 | £126 | £1,092 | £17,173 | 15.7 yrs | £4,675 |
| 6 kW | 6034 kWh | 4526 kWh | 1509 kWh | £1,160 | £151 | £1,311 | £19,207 | 14.7 yrs | £7,010 |
| 7 kW | 7040 kWh | 5280 kWh | 1760 kWh | £1,353 | £176 | £1,529 | £21,242 | 13.9 yrs | £9,344 |
| 8 kW | 8046 kWh | 6034 kWh | 2011 kWh | £1,547 | £201 | £1,748 | £23,276 | 13.3 yrs | £11,679 |
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: £1,108, Upfront: £19,623, Break-even: 17.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2011 kWh | 1549 kWh | 463 kWh | £397 | £46 | £443 | £13,519 | 30.5 yrs | £-4,654 |
| 3 kW | 3017 kWh | 2323 kWh | 694 kWh | £595 | £69 | £665 | £15,554 | 23.4 yrs | £-2,257 |
| 4 kW | 4023 kWh | 3098 kWh | 925 kWh | £794 | £93 | £886 | £17,588 | 19.8 yrs | £141 |
| 5 kW | 5029 kWh | 3872 kWh | 1157 kWh | £992 | £116 | £1,108 | £19,623 | 17.7 yrs | £2,539 |
| 6 kW | 6034 kWh | 4647 kWh | 1388 kWh | £1,191 | £139 | £1,330 | £21,657 | 16.3 yrs | £4,937 |
| 7 kW | 7040 kWh | 5421 kWh | 1619 kWh | £1,389 | £162 | £1,551 | £23,692 | 15.3 yrs | £7,335 |
| 8 kW | 8046 kWh | 6195 kWh | 1851 kWh | £1,588 | £185 | £1,773 | £25,726 | 14.5 yrs | £9,732 |
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.