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 | £1,356 |
| 3 kW | 2491 kWh | 996 kWh | 1494 kWh | £257 | £149 | £407 | £6,104 | 15.0 yrs | £2,034 |
| 4 kW | 3321 kWh | 1328 kWh | 1993 kWh | £343 | £199 | £543 | £8,138 | 15.0 yrs | £2,713 |
| 5 kW | 4151 kWh | 1661 kWh | 2491 kWh | £429 | £249 | £678 | £10,173 | 15.0 yrs | £3,391 |
| 6 kW | 4982 kWh | 1993 kWh | 2989 kWh | £515 | £299 | £814 | £12,207 | 15.0 yrs | £4,069 |
| 7 kW | 5812 kWh | 2325 kWh | 3487 kWh | £601 | £349 | £949 | £14,242 | 15.0 yrs | £4,747 |
| 8 kW | 6642 kWh | 2657 kWh | 3985 kWh | £687 | £399 | £1,085 | £16,276 | 15.0 yrs | £5,425 |
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 | £308 |
| 3 kW | 2491 kWh | 1494 kWh | 996 kWh | £386 | £100 | £486 | £8,204 | 16.9 yrs | £1,513 |
| 4 kW | 3321 kWh | 1993 kWh | 1328 kWh | £515 | £133 | £648 | £10,238 | 15.8 yrs | £2,717 |
| 5 kW | 4151 kWh | 2491 kWh | 1661 kWh | £644 | £166 | £810 | £12,273 | 15.2 yrs | £3,921 |
| 6 kW | 4982 kWh | 2989 kWh | 1993 kWh | £772 | £199 | £972 | £14,307 | 14.7 yrs | £5,125 |
| 7 kW | 5812 kWh | 3487 kWh | 2325 kWh | £901 | £232 | £1,134 | £16,342 | 14.4 yrs | £6,329 |
| 8 kW | 6642 kWh | 3985 kWh | 2657 kWh | £1,030 | £266 | £1,295 | £18,376 | 14.2 yrs | £7,534 |
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: £875, 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 | 1162 kWh | 498 kWh | £300 | £50 | £350 | £7,569 | 21.6 yrs | £-566 |
| 3 kW | 2491 kWh | 1744 kWh | 747 kWh | £451 | £75 | £525 | £9,604 | 18.3 yrs | £902 |
| 4 kW | 3321 kWh | 2325 kWh | 996 kWh | £601 | £100 | £700 | £11,638 | 16.6 yrs | £2,369 |
| 5 kW | 4151 kWh | 2906 kWh | 1245 kWh | £751 | £125 | £875 | £13,673 | 15.6 yrs | £3,836 |
| 6 kW | 4982 kWh | 3487 kWh | 1494 kWh | £901 | £149 | £1,051 | £15,707 | 15.0 yrs | £5,303 |
| 7 kW | 5812 kWh | 4068 kWh | 1744 kWh | £1,051 | £174 | £1,226 | £17,742 | 14.5 yrs | £6,771 |
| 8 kW | 6642 kWh | 4650 kWh | 1993 kWh | £1,201 | £199 | £1,401 | £19,776 | 14.1 yrs | £8,238 |
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 | £-2,158 |
| 3 kW | 2491 kWh | 1818 kWh | 673 kWh | £470 | £67 | £537 | £11,354 | 21.1 yrs | £-612 |
| 4 kW | 3321 kWh | 2424 kWh | 897 kWh | £626 | £90 | £716 | £13,388 | 18.7 yrs | £935 |
| 5 kW | 4151 kWh | 3030 kWh | 1121 kWh | £783 | £112 | £895 | £15,423 | 17.2 yrs | £2,481 |
| 6 kW | 4982 kWh | 3637 kWh | 1345 kWh | £940 | £135 | £1,074 | £17,457 | 16.3 yrs | £4,027 |
| 7 kW | 5812 kWh | 4243 kWh | 1569 kWh | £1,096 | £157 | £1,253 | £19,492 | 15.6 yrs | £5,573 |
| 8 kW | 6642 kWh | 4849 kWh | 1793 kWh | £1,253 | £179 | £1,432 | £21,526 | 15.0 yrs | £7,119 |
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 | 1245 kWh | 415 kWh | £322 | £42 | £363 | £11,069 | 30.5 yrs | £-3,802 |
| 3 kW | 2491 kWh | 1868 kWh | 623 kWh | £483 | £62 | £545 | £13,104 | 24.0 yrs | £-2,204 |
| 4 kW | 3321 kWh | 2491 kWh | 830 kWh | £644 | £83 | £727 | £15,138 | 20.8 yrs | £-605 |
| 5 kW | 4151 kWh | 3114 kWh | 1038 kWh | £805 | £104 | £908 | £17,173 | 18.9 yrs | £994 |
| 6 kW | 4982 kWh | 3736 kWh | 1245 kWh | £965 | £125 | £1,090 | £19,207 | 17.6 yrs | £2,593 |
| 7 kW | 5812 kWh | 4359 kWh | 1453 kWh | £1,126 | £145 | £1,272 | £21,242 | 16.7 yrs | £4,191 |
| 8 kW | 6642 kWh | 4982 kWh | 1661 kWh | £1,287 | £166 | £1,453 | £23,276 | 16.0 yrs | £5,790 |
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: £921, 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 | £-6,147 |
| 3 kW | 2491 kWh | 1918 kWh | 573 kWh | £496 | £57 | £553 | £15,554 | 28.1 yrs | £-4,496 |
| 4 kW | 3321 kWh | 2557 kWh | 764 kWh | £661 | £76 | £737 | £17,588 | 23.9 yrs | £-2,845 |
| 5 kW | 4151 kWh | 3197 kWh | 955 kWh | £826 | £95 | £921 | £19,623 | 21.3 yrs | £-1,193 |
| 6 kW | 4982 kWh | 3836 kWh | 1146 kWh | £991 | £115 | £1,106 | £21,657 | 19.6 yrs | £458 |
| 7 kW | 5812 kWh | 4475 kWh | 1337 kWh | £1,156 | £134 | £1,290 | £23,692 | 18.4 yrs | £2,110 |
| 8 kW | 6642 kWh | 5114 kWh | 1528 kWh | £1,322 | £153 | £1,474 | £25,726 | 17.4 yrs | £3,761 |
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.