A typical roof here lands around 5.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 782 kWh per year on a south-facing roof. We value self-used electricity at 27.1p 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: £658, Upfront: £10,173, Break-even: 15.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1564 kWh | 625 kWh | 938 kWh | £169 | £94 | £263 | £4,069 | 15.5 yrs | £1,193 |
| 3 kW | 2346 kWh | 938 kWh | 1407 kWh | £254 | £141 | £395 | £6,104 | 15.5 yrs | £1,789 |
| 4 kW | 3127 kWh | 1251 kWh | 1876 kWh | £339 | £188 | £526 | £8,138 | 15.5 yrs | £2,385 |
| 5 kW | 3909 kWh | 1564 kWh | 2346 kWh | £423 | £235 | £658 | £10,173 | 15.5 yrs | £2,981 |
| 6 kW | 4691 kWh | 1876 kWh | 2815 kWh | £508 | £281 | £789 | £12,207 | 15.5 yrs | £3,578 |
| 7 kW | 5473 kWh | 2189 kWh | 3284 kWh | £592 | £328 | £921 | £14,242 | 15.5 yrs | £4,174 |
| 8 kW | 6255 kWh | 2502 kWh | 3753 kWh | £677 | £375 | £1,052 | £16,276 | 15.5 yrs | £4,770 |
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: £791, Upfront: £12,273, Break-even: 15.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1564 kWh | 938 kWh | 625 kWh | £254 | £63 | £316 | £6,169 | 19.5 yrs | £160 |
| 3 kW | 2346 kWh | 1407 kWh | 938 kWh | £381 | £94 | £475 | £8,204 | 17.3 yrs | £1,290 |
| 4 kW | 3127 kWh | 1876 kWh | 1251 kWh | £508 | £125 | £633 | £10,238 | 16.2 yrs | £2,419 |
| 5 kW | 3909 kWh | 2346 kWh | 1564 kWh | £635 | £156 | £791 | £12,273 | 15.5 yrs | £3,549 |
| 6 kW | 4691 kWh | 2815 kWh | 1876 kWh | £762 | £188 | £949 | £14,307 | 15.1 yrs | £4,679 |
| 7 kW | 5473 kWh | 3284 kWh | 2189 kWh | £889 | £219 | £1,108 | £16,342 | 14.8 yrs | £5,809 |
| 8 kW | 6255 kWh | 3753 kWh | 2502 kWh | £1,016 | £250 | £1,266 | £18,376 | 14.5 yrs | £6,939 |
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: £858, Upfront: £13,673, 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 | 1564 kWh | 1095 kWh | 469 kWh | £296 | £47 | £343 | £7,569 | 22.1 yrs | £-707 |
| 3 kW | 2346 kWh | 1642 kWh | 704 kWh | £444 | £70 | £515 | £9,604 | 18.7 yrs | £690 |
| 4 kW | 3127 kWh | 2189 kWh | 938 kWh | £592 | £94 | £686 | £11,638 | 17.0 yrs | £2,086 |
| 5 kW | 3909 kWh | 2737 kWh | 1173 kWh | £740 | £117 | £858 | £13,673 | 15.9 yrs | £3,483 |
| 6 kW | 4691 kWh | 3284 kWh | 1407 kWh | £889 | £141 | £1,029 | £15,707 | 15.3 yrs | £4,880 |
| 7 kW | 5473 kWh | 3831 kWh | 1642 kWh | £1,037 | £164 | £1,201 | £17,742 | 14.8 yrs | £6,276 |
| 8 kW | 6255 kWh | 4378 kWh | 1876 kWh | £1,185 | £188 | £1,372 | £19,776 | 14.4 yrs | £7,673 |
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: £878, Upfront: £15,423, Break-even: 17.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1564 kWh | 1142 kWh | 422 kWh | £309 | £42 | £351 | £9,319 | 26.5 yrs | £-2,297 |
| 3 kW | 2346 kWh | 1712 kWh | 633 kWh | £463 | £63 | £527 | £11,354 | 21.6 yrs | £-820 |
| 4 kW | 3127 kWh | 2283 kWh | 844 kWh | £618 | £84 | £702 | £13,388 | 19.1 yrs | £657 |
| 5 kW | 3909 kWh | 2854 kWh | 1056 kWh | £772 | £106 | £878 | £15,423 | 17.6 yrs | £2,133 |
| 6 kW | 4691 kWh | 3425 kWh | 1267 kWh | £927 | £127 | £1,053 | £17,457 | 16.6 yrs | £3,610 |
| 7 kW | 5473 kWh | 3995 kWh | 1478 kWh | £1,081 | £148 | £1,229 | £19,492 | 15.9 yrs | £5,086 |
| 8 kW | 6255 kWh | 4566 kWh | 1689 kWh | £1,236 | £169 | £1,404 | £21,526 | 15.3 yrs | £6,563 |
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: £891, Upfront: £17,173, Break-even: 19.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1564 kWh | 1173 kWh | 391 kWh | £317 | £39 | £356 | £11,069 | 31.1 yrs | £-3,940 |
| 3 kW | 2346 kWh | 1759 kWh | 586 kWh | £476 | £59 | £535 | £13,104 | 24.5 yrs | £-2,410 |
| 4 kW | 3127 kWh | 2346 kWh | 782 kWh | £635 | £78 | £713 | £15,138 | 21.2 yrs | £-880 |
| 5 kW | 3909 kWh | 2932 kWh | 977 kWh | £793 | £98 | £891 | £17,173 | 19.3 yrs | £650 |
| 6 kW | 4691 kWh | 3518 kWh | 1173 kWh | £952 | £117 | £1,069 | £19,207 | 18.0 yrs | £2,180 |
| 7 kW | 5473 kWh | 4105 kWh | 1368 kWh | £1,111 | £137 | £1,248 | £21,242 | 17.0 yrs | £3,710 |
| 8 kW | 6255 kWh | 4691 kWh | 1564 kWh | £1,269 | £156 | £1,426 | £23,276 | 16.3 yrs | £5,240 |
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: £904, Upfront: £19,623, Break-even: 21.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1564 kWh | 1204 kWh | 360 kWh | £326 | £36 | £362 | £13,519 | 37.4 yrs | £-6,283 |
| 3 kW | 2346 kWh | 1806 kWh | 539 kWh | £489 | £54 | £543 | £15,554 | 28.7 yrs | £-4,700 |
| 4 kW | 3127 kWh | 2408 kWh | 719 kWh | £652 | £72 | £724 | £17,588 | 24.3 yrs | £-3,117 |
| 5 kW | 3909 kWh | 3010 kWh | 899 kWh | £815 | £90 | £904 | £19,623 | 21.7 yrs | £-1,533 |
| 6 kW | 4691 kWh | 3612 kWh | 1079 kWh | £977 | £108 | £1,085 | £21,657 | 20.0 yrs | £50 |
| 7 kW | 5473 kWh | 4214 kWh | 1259 kWh | £1,140 | £126 | £1,266 | £23,692 | 18.7 yrs | £1,633 |
| 8 kW | 6255 kWh | 4816 kWh | 1439 kWh | £1,303 | £144 | £1,447 | £25,726 | 17.8 yrs | £3,217 |
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.