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 830 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: £678, Upfront: £10,173, Break-even: 15.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1661 kWh | 664 kWh | 996 kWh | £172 | £100 | £271 | £4,069 | 15.0 yrs | £1,357 |
| 3 kW | 2491 kWh | 996 kWh | 1495 kWh | £257 | £149 | £407 | £6,104 | 15.0 yrs | £2,036 |
| 4 kW | 3322 kWh | 1329 kWh | 1993 kWh | £343 | £199 | £543 | £8,138 | 15.0 yrs | £2,714 |
| 5 kW | 4152 kWh | 1661 kWh | 2491 kWh | £429 | £249 | £678 | £10,173 | 15.0 yrs | £3,393 |
| 6 kW | 4982 kWh | 1993 kWh | 2989 kWh | £515 | £299 | £814 | £12,207 | 15.0 yrs | £4,071 |
| 7 kW | 5813 kWh | 2325 kWh | 3488 kWh | £601 | £349 | £950 | £14,242 | 15.0 yrs | £4,750 |
| 8 kW | 6643 kWh | 2657 kWh | 3986 kWh | £687 | £399 | £1,085 | £16,276 | 15.0 yrs | £5,429 |
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: £810, 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 | 1661 kWh | 996 kWh | 664 kWh | £257 | £66 | £324 | £6,169 | 19.0 yrs | £309 |
| 3 kW | 2491 kWh | 1495 kWh | 996 kWh | £386 | £100 | £486 | £8,204 | 16.9 yrs | £1,514 |
| 4 kW | 3322 kWh | 1993 kWh | 1329 kWh | £515 | £133 | £648 | £10,238 | 15.8 yrs | £2,719 |
| 5 kW | 4152 kWh | 2491 kWh | 1661 kWh | £644 | £166 | £810 | £12,273 | 15.2 yrs | £3,924 |
| 6 kW | 4982 kWh | 2989 kWh | 1993 kWh | £772 | £199 | £972 | £14,307 | 14.7 yrs | £5,128 |
| 7 kW | 5813 kWh | 3488 kWh | 2325 kWh | £901 | £233 | £1,134 | £16,342 | 14.4 yrs | £6,333 |
| 8 kW | 6643 kWh | 3986 kWh | 2657 kWh | £1,030 | £266 | £1,296 | £18,376 | 14.2 yrs | £7,538 |
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: £876, Upfront: £13,673, Break-even: 15.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1661 kWh | 1163 kWh | 498 kWh | £300 | £50 | £350 | £7,569 | 21.6 yrs | £-564 |
| 3 kW | 2491 kWh | 1744 kWh | 747 kWh | £451 | £75 | £525 | £9,604 | 18.3 yrs | £903 |
| 4 kW | 3322 kWh | 2325 kWh | 996 kWh | £601 | £100 | £700 | £11,638 | 16.6 yrs | £2,371 |
| 5 kW | 4152 kWh | 2906 kWh | 1246 kWh | £751 | £125 | £876 | £13,673 | 15.6 yrs | £3,839 |
| 6 kW | 4982 kWh | 3488 kWh | 1495 kWh | £901 | £149 | £1,051 | £15,707 | 14.9 yrs | £5,307 |
| 7 kW | 5813 kWh | 4069 kWh | 1744 kWh | £1,051 | £174 | £1,226 | £17,742 | 14.5 yrs | £6,774 |
| 8 kW | 6643 kWh | 4650 kWh | 1993 kWh | £1,202 | £199 | £1,401 | £19,776 | 14.1 yrs | £8,242 |
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: £895, Upfront: £15,423, Break-even: 17.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1661 kWh | 1212 kWh | 448 kWh | £313 | £45 | £358 | £9,319 | 26.0 yrs | £-2,157 |
| 3 kW | 2491 kWh | 1819 kWh | 673 kWh | £470 | £67 | £537 | £11,354 | 21.1 yrs | £-610 |
| 4 kW | 3322 kWh | 2425 kWh | 897 kWh | £627 | £90 | £716 | £13,388 | 18.7 yrs | £937 |
| 5 kW | 4152 kWh | 3031 kWh | 1121 kWh | £783 | £112 | £895 | £15,423 | 17.2 yrs | £2,484 |
| 6 kW | 4982 kWh | 3637 kWh | 1345 kWh | £940 | £135 | £1,074 | £17,457 | 16.2 yrs | £4,030 |
| 7 kW | 5813 kWh | 4243 kWh | 1569 kWh | £1,096 | £157 | £1,253 | £19,492 | 15.6 yrs | £5,577 |
| 8 kW | 6643 kWh | 4850 kWh | 1794 kWh | £1,253 | £179 | £1,432 | £21,526 | 15.0 yrs | £7,124 |
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: £908, Upfront: £17,173, Break-even: 18.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1661 kWh | 1246 kWh | 415 kWh | £322 | £42 | £363 | £11,069 | 30.5 yrs | £-3,801 |
| 3 kW | 2491 kWh | 1868 kWh | 623 kWh | £483 | £62 | £545 | £13,104 | 24.0 yrs | £-2,202 |
| 4 kW | 3322 kWh | 2491 kWh | 830 kWh | £644 | £83 | £727 | £15,138 | 20.8 yrs | £-603 |
| 5 kW | 4152 kWh | 3114 kWh | 1038 kWh | £805 | £104 | £908 | £17,173 | 18.9 yrs | £997 |
| 6 kW | 4982 kWh | 3737 kWh | 1246 kWh | £966 | £125 | £1,090 | £19,207 | 17.6 yrs | £2,596 |
| 7 kW | 5813 kWh | 4360 kWh | 1453 kWh | £1,127 | £145 | £1,272 | £21,242 | 16.7 yrs | £4,195 |
| 8 kW | 6643 kWh | 4982 kWh | 1661 kWh | £1,287 | £166 | £1,454 | £23,276 | 16.0 yrs | £5,795 |
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: £922, Upfront: £19,623, Break-even: 21.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1661 kWh | 1279 kWh | 382 kWh | £330 | £38 | £369 | £13,519 | 36.7 yrs | £-6,146 |
| 3 kW | 2491 kWh | 1918 kWh | 573 kWh | £496 | £57 | £553 | £15,554 | 28.1 yrs | £-4,494 |
| 4 kW | 3322 kWh | 2558 kWh | 764 kWh | £661 | £76 | £737 | £17,588 | 23.9 yrs | £-2,842 |
| 5 kW | 4152 kWh | 3197 kWh | 955 kWh | £826 | £95 | £922 | £19,623 | 21.3 yrs | £-1,190 |
| 6 kW | 4982 kWh | 3836 kWh | 1146 kWh | £991 | £115 | £1,106 | £21,657 | 19.6 yrs | £462 |
| 7 kW | 5813 kWh | 4476 kWh | 1337 kWh | £1,157 | £134 | £1,290 | £23,692 | 18.4 yrs | £2,114 |
| 8 kW | 6643 kWh | 5115 kWh | 1528 kWh | £1,322 | £153 | £1,475 | £25,726 | 17.4 yrs | £3,765 |
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.