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 1004 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: £816, Upfront: £10,173, Break-even: 12.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2008 kWh | 803 kWh | 1205 kWh | £206 | £121 | £326 | £4,069 | 12.5 yrs | £2,459 |
| 3 kW | 3013 kWh | 1205 kWh | 1808 kWh | £309 | £181 | £490 | £6,104 | 12.5 yrs | £3,689 |
| 4 kW | 4017 kWh | 1607 kWh | 2410 kWh | £412 | £241 | £653 | £8,138 | 12.5 yrs | £4,918 |
| 5 kW | 5021 kWh | 2008 kWh | 3013 kWh | £515 | £301 | £816 | £10,173 | 12.5 yrs | £6,148 |
| 6 kW | 6025 kWh | 2410 kWh | 3615 kWh | £618 | £362 | £979 | £12,207 | 12.5 yrs | £7,377 |
| 7 kW | 7029 kWh | 2812 kWh | 4218 kWh | £721 | £422 | £1,142 | £14,242 | 12.5 yrs | £8,607 |
| 8 kW | 8034 kWh | 3213 kWh | 4820 kWh | £824 | £482 | £1,306 | £16,276 | 12.5 yrs | £9,836 |
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: £973, 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 | 2008 kWh | 1205 kWh | 803 kWh | £309 | £80 | £389 | £6,169 | 15.9 yrs | £1,615 |
| 3 kW | 3013 kWh | 1808 kWh | 1205 kWh | £463 | £121 | £584 | £8,204 | 14.1 yrs | £3,472 |
| 4 kW | 4017 kWh | 2410 kWh | 1607 kWh | £618 | £161 | £778 | £10,238 | 13.2 yrs | £5,329 |
| 5 kW | 5021 kWh | 3013 kWh | 2008 kWh | £772 | £201 | £973 | £12,273 | 12.6 yrs | £7,187 |
| 6 kW | 6025 kWh | 3615 kWh | 2410 kWh | £927 | £241 | £1,168 | £14,307 | 12.3 yrs | £9,044 |
| 7 kW | 7029 kWh | 4218 kWh | 2812 kWh | £1,081 | £281 | £1,362 | £16,342 | 12.0 yrs | £10,901 |
| 8 kW | 8034 kWh | 4820 kWh | 3213 kWh | £1,235 | £321 | £1,557 | £18,376 | 11.8 yrs | £12,759 |
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: £1,051, 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 | 2008 kWh | 1406 kWh | 603 kWh | £360 | £60 | £421 | £7,569 | 18.0 yrs | £842 |
| 3 kW | 3013 kWh | 2109 kWh | 904 kWh | £540 | £90 | £631 | £9,604 | 15.2 yrs | £3,014 |
| 4 kW | 4017 kWh | 2812 kWh | 1205 kWh | £721 | £121 | £841 | £11,638 | 13.8 yrs | £5,185 |
| 5 kW | 5021 kWh | 3515 kWh | 1506 kWh | £901 | £151 | £1,051 | £13,673 | 13.0 yrs | £7,356 |
| 6 kW | 6025 kWh | 4218 kWh | 1808 kWh | £1,081 | £181 | £1,262 | £15,707 | 12.4 yrs | £9,527 |
| 7 kW | 7029 kWh | 4921 kWh | 2109 kWh | £1,261 | £211 | £1,472 | £17,742 | 12.1 yrs | £11,699 |
| 8 kW | 8034 kWh | 5623 kWh | 2410 kWh | £1,441 | £241 | £1,682 | £19,776 | 11.8 yrs | £13,870 |
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: £1,075, 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 | 2008 kWh | 1466 kWh | 542 kWh | £376 | £54 | £430 | £9,319 | 21.7 yrs | £-719 |
| 3 kW | 3013 kWh | 2199 kWh | 813 kWh | £564 | £81 | £645 | £11,354 | 17.6 yrs | £1,546 |
| 4 kW | 4017 kWh | 2932 kWh | 1085 kWh | £752 | £108 | £860 | £13,388 | 15.6 yrs | £3,812 |
| 5 kW | 5021 kWh | 3665 kWh | 1356 kWh | £939 | £136 | £1,075 | £15,423 | 14.3 yrs | £6,077 |
| 6 kW | 6025 kWh | 4398 kWh | 1627 kWh | £1,127 | £163 | £1,290 | £17,457 | 13.5 yrs | £8,342 |
| 7 kW | 7029 kWh | 5131 kWh | 1898 kWh | £1,315 | £190 | £1,505 | £19,492 | 13.0 yrs | £10,608 |
| 8 kW | 8034 kWh | 5864 kWh | 2169 kWh | £1,503 | £217 | £1,720 | £21,526 | 12.5 yrs | £12,873 |
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: £1,091, 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 | 2008 kWh | 1506 kWh | 502 kWh | £386 | £50 | £436 | £11,069 | 25.4 yrs | £-2,344 |
| 3 kW | 3013 kWh | 2259 kWh | 753 kWh | £579 | £75 | £654 | £13,104 | 20.0 yrs | £-15 |
| 4 kW | 4017 kWh | 3013 kWh | 1004 kWh | £772 | £100 | £873 | £15,138 | 17.3 yrs | £2,313 |
| 5 kW | 5021 kWh | 3766 kWh | 1255 kWh | £965 | £126 | £1,091 | £17,173 | 15.7 yrs | £4,641 |
| 6 kW | 6025 kWh | 4519 kWh | 1506 kWh | £1,158 | £151 | £1,309 | £19,207 | 14.7 yrs | £6,969 |
| 7 kW | 7029 kWh | 5272 kWh | 1757 kWh | £1,351 | £176 | £1,527 | £21,242 | 13.9 yrs | £9,297 |
| 8 kW | 8034 kWh | 6025 kWh | 2008 kWh | £1,544 | £201 | £1,745 | £23,276 | 13.3 yrs | £11,626 |
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: £1,106, 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 | 2008 kWh | 1546 kWh | 462 kWh | £396 | £46 | £443 | £13,519 | 30.5 yrs | £-4,668 |
| 3 kW | 3013 kWh | 2320 kWh | 693 kWh | £595 | £69 | £664 | £15,554 | 23.4 yrs | £-2,277 |
| 4 kW | 4017 kWh | 3093 kWh | 924 kWh | £793 | £92 | £885 | £17,588 | 19.9 yrs | £114 |
| 5 kW | 5021 kWh | 3866 kWh | 1155 kWh | £991 | £115 | £1,106 | £19,623 | 17.7 yrs | £2,505 |
| 6 kW | 6025 kWh | 4639 kWh | 1386 kWh | £1,189 | £139 | £1,328 | £21,657 | 16.3 yrs | £4,896 |
| 7 kW | 7029 kWh | 5413 kWh | 1617 kWh | £1,387 | £162 | £1,549 | £23,692 | 15.3 yrs | £7,287 |
| 8 kW | 8034 kWh | 6186 kWh | 1848 kWh | £1,585 | £185 | £1,770 | £25,726 | 14.5 yrs | £9,678 |
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.