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 687 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: £578, Upfront: £10,173, 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 | 1374 kWh | 550 kWh | 825 kWh | £149 | £82 | £231 | £4,069 | 17.6 yrs | £555 |
| 3 kW | 2061 kWh | 825 kWh | 1237 kWh | £223 | £124 | £347 | £6,104 | 17.6 yrs | £833 |
| 4 kW | 2749 kWh | 1099 kWh | 1649 kWh | £298 | £165 | £462 | £8,138 | 17.6 yrs | £1,110 |
| 5 kW | 3436 kWh | 1374 kWh | 2061 kWh | £372 | £206 | £578 | £10,173 | 17.6 yrs | £1,388 |
| 6 kW | 4123 kWh | 1649 kWh | 2474 kWh | £446 | £247 | £694 | £12,207 | 17.6 yrs | £1,666 |
| 7 kW | 4810 kWh | 1924 kWh | 2886 kWh | £521 | £289 | £809 | £14,242 | 17.6 yrs | £1,943 |
| 8 kW | 5497 kWh | 2199 kWh | 3298 kWh | £595 | £330 | £925 | £16,276 | 17.6 yrs | £2,221 |
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: £695, Upfront: £12,273, 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 | 1374 kWh | 825 kWh | 550 kWh | £223 | £55 | £278 | £6,169 | 22.2 yrs | £-607 |
| 3 kW | 2061 kWh | 1237 kWh | 825 kWh | £335 | £82 | £417 | £8,204 | 19.7 yrs | £140 |
| 4 kW | 2749 kWh | 1649 kWh | 1099 kWh | £446 | £110 | £556 | £10,238 | 18.4 yrs | £886 |
| 5 kW | 3436 kWh | 2061 kWh | 1374 kWh | £558 | £137 | £695 | £12,273 | 17.7 yrs | £1,633 |
| 6 kW | 4123 kWh | 2474 kWh | 1649 kWh | £669 | £165 | £834 | £14,307 | 17.1 yrs | £2,379 |
| 7 kW | 4810 kWh | 2886 kWh | 1924 kWh | £781 | £192 | £973 | £16,342 | 16.8 yrs | £3,126 |
| 8 kW | 5497 kWh | 3298 kWh | 2199 kWh | £893 | £220 | £1,112 | £18,376 | 16.5 yrs | £3,872 |
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: £754, Upfront: £13,673, Break-even: 18.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1374 kWh | 962 kWh | 412 kWh | £260 | £41 | £302 | £7,569 | 25.1 yrs | £-1,538 |
| 3 kW | 2061 kWh | 1443 kWh | 618 kWh | £390 | £62 | £452 | £9,604 | 21.2 yrs | £-557 |
| 4 kW | 2749 kWh | 1924 kWh | 825 kWh | £521 | £82 | £603 | £11,638 | 19.3 yrs | £424 |
| 5 kW | 3436 kWh | 2405 kWh | 1031 kWh | £651 | £103 | £754 | £13,673 | 18.1 yrs | £1,405 |
| 6 kW | 4123 kWh | 2886 kWh | 1237 kWh | £781 | £124 | £905 | £15,707 | 17.4 yrs | £2,386 |
| 7 kW | 4810 kWh | 3367 kWh | 1443 kWh | £911 | £144 | £1,055 | £17,742 | 16.8 yrs | £3,367 |
| 8 kW | 5497 kWh | 3848 kWh | 1649 kWh | £1,041 | £165 | £1,206 | £19,776 | 16.4 yrs | £4,348 |
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: £771, Upfront: £15,423, Break-even: 20.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1374 kWh | 1003 kWh | 371 kWh | £271 | £37 | £309 | £9,319 | 30.2 yrs | £-3,147 |
| 3 kW | 2061 kWh | 1505 kWh | 557 kWh | £407 | £56 | £463 | £11,354 | 24.5 yrs | £-2,096 |
| 4 kW | 2749 kWh | 2006 kWh | 742 kWh | £543 | £74 | £617 | £13,388 | 21.7 yrs | £-1,045 |
| 5 kW | 3436 kWh | 2508 kWh | 928 kWh | £679 | £93 | £771 | £15,423 | 20.0 yrs | £7 |
| 6 kW | 4123 kWh | 3010 kWh | 1113 kWh | £814 | £111 | £926 | £17,457 | 18.9 yrs | £1,058 |
| 7 kW | 4810 kWh | 3511 kWh | 1299 kWh | £950 | £130 | £1,080 | £19,492 | 18.0 yrs | £2,109 |
| 8 kW | 5497 kWh | 4013 kWh | 1484 kWh | £1,086 | £148 | £1,234 | £21,526 | 17.4 yrs | £3,161 |
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: £783, Upfront: £17,173, Break-even: 21.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1374 kWh | 1031 kWh | 344 kWh | £279 | £34 | £313 | £11,069 | 35.3 yrs | £-4,804 |
| 3 kW | 2061 kWh | 1546 kWh | 515 kWh | £418 | £52 | £470 | £13,104 | 27.9 yrs | £-3,705 |
| 4 kW | 2749 kWh | 2061 kWh | 687 kWh | £558 | £69 | £627 | £15,138 | 24.2 yrs | £-2,607 |
| 5 kW | 3436 kWh | 2577 kWh | 859 kWh | £697 | £86 | £783 | £17,173 | 21.9 yrs | £-1,509 |
| 6 kW | 4123 kWh | 3092 kWh | 1031 kWh | £837 | £103 | £940 | £19,207 | 20.4 yrs | £-411 |
| 7 kW | 4810 kWh | 3608 kWh | 1203 kWh | £976 | £120 | £1,096 | £21,242 | 19.4 yrs | £687 |
| 8 kW | 5497 kWh | 4123 kWh | 1374 kWh | £1,116 | £137 | £1,253 | £23,276 | 18.6 yrs | £1,786 |
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: £795, Upfront: £19,623, Break-even: 24.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1374 kWh | 1058 kWh | 316 kWh | £286 | £32 | £318 | £13,519 | 42.5 yrs | £-7,160 |
| 3 kW | 2061 kWh | 1587 kWh | 474 kWh | £430 | £47 | £477 | £15,554 | 32.6 yrs | £-6,015 |
| 4 kW | 2749 kWh | 2116 kWh | 632 kWh | £573 | £63 | £636 | £17,588 | 27.7 yrs | £-4,870 |
| 5 kW | 3436 kWh | 2646 kWh | 790 kWh | £716 | £79 | £795 | £19,623 | 24.7 yrs | £-3,725 |
| 6 kW | 4123 kWh | 3175 kWh | 948 kWh | £859 | £95 | £954 | £21,657 | 22.7 yrs | £-2,579 |
| 7 kW | 4810 kWh | 3704 kWh | 1106 kWh | £1,002 | £111 | £1,113 | £23,692 | 21.3 yrs | £-1,434 |
| 8 kW | 5497 kWh | 4233 kWh | 1264 kWh | £1,145 | £126 | £1,272 | £25,726 | 20.2 yrs | £-289 |
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.