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 885 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: £746, Upfront: £10,173, Break-even: 13.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1770 kWh | 708 kWh | 1062 kWh | £192 | £106 | £298 | £4,069 | 13.6 yrs | £1,895 |
| 3 kW | 2656 kWh | 1062 kWh | 1593 kWh | £288 | £159 | £447 | £6,104 | 13.6 yrs | £2,843 |
| 4 kW | 3541 kWh | 1416 kWh | 2125 kWh | £384 | £212 | £596 | £8,138 | 13.6 yrs | £3,790 |
| 5 kW | 4426 kWh | 1770 kWh | 2656 kWh | £480 | £266 | £746 | £10,173 | 13.6 yrs | £4,738 |
| 6 kW | 5311 kWh | 2125 kWh | 3187 kWh | £576 | £319 | £895 | £12,207 | 13.6 yrs | £5,686 |
| 7 kW | 6196 kWh | 2479 kWh | 3718 kWh | £672 | £372 | £1,044 | £14,242 | 13.6 yrs | £6,633 |
| 8 kW | 7082 kWh | 2833 kWh | 4249 kWh | £768 | £425 | £1,193 | £16,276 | 13.6 yrs | £7,581 |
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: £897, Upfront: £12,273, Break-even: 13.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1770 kWh | 1062 kWh | 708 kWh | £288 | £71 | £359 | £6,169 | 17.2 yrs | £1,007 |
| 3 kW | 2656 kWh | 1593 kWh | 1062 kWh | £432 | £106 | £538 | £8,204 | 15.2 yrs | £2,560 |
| 4 kW | 3541 kWh | 2125 kWh | 1416 kWh | £576 | £142 | £718 | £10,238 | 14.3 yrs | £4,114 |
| 5 kW | 4426 kWh | 2656 kWh | 1770 kWh | £720 | £177 | £897 | £12,273 | 13.7 yrs | £5,667 |
| 6 kW | 5311 kWh | 3187 kWh | 2125 kWh | £864 | £212 | £1,076 | £14,307 | 13.3 yrs | £7,221 |
| 7 kW | 6196 kWh | 3718 kWh | 2479 kWh | £1,008 | £248 | £1,256 | £16,342 | 13.0 yrs | £8,774 |
| 8 kW | 7082 kWh | 4249 kWh | 2833 kWh | £1,152 | £283 | £1,435 | £18,376 | 12.8 yrs | £10,327 |
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: £973, Upfront: £13,673, Break-even: 14.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1770 kWh | 1239 kWh | 531 kWh | £336 | £53 | £389 | £7,569 | 19.5 yrs | £213 |
| 3 kW | 2656 kWh | 1859 kWh | 797 kWh | £504 | £80 | £584 | £9,604 | 16.5 yrs | £2,069 |
| 4 kW | 3541 kWh | 2479 kWh | 1062 kWh | £672 | £106 | £778 | £11,638 | 15.0 yrs | £3,925 |
| 5 kW | 4426 kWh | 3098 kWh | 1328 kWh | £840 | £133 | £973 | £13,673 | 14.1 yrs | £5,782 |
| 6 kW | 5311 kWh | 3718 kWh | 1593 kWh | £1,008 | £159 | £1,167 | £15,707 | 13.5 yrs | £7,638 |
| 7 kW | 6196 kWh | 4338 kWh | 1859 kWh | £1,176 | £186 | £1,362 | £17,742 | 13.0 yrs | £9,494 |
| 8 kW | 7082 kWh | 4957 kWh | 2125 kWh | £1,344 | £212 | £1,556 | £19,776 | 12.7 yrs | £11,351 |
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: £995, Upfront: £15,423, 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 | 1770 kWh | 1292 kWh | 478 kWh | £350 | £48 | £398 | £9,319 | 23.4 yrs | £-1,356 |
| 3 kW | 2656 kWh | 1939 kWh | 717 kWh | £526 | £72 | £597 | £11,354 | 19.0 yrs | £592 |
| 4 kW | 3541 kWh | 2585 kWh | 956 kWh | £701 | £96 | £796 | £13,388 | 16.8 yrs | £2,539 |
| 5 kW | 4426 kWh | 3231 kWh | 1195 kWh | £876 | £120 | £995 | £15,423 | 15.5 yrs | £4,486 |
| 6 kW | 5311 kWh | 3877 kWh | 1434 kWh | £1,051 | £143 | £1,195 | £17,457 | 14.6 yrs | £6,433 |
| 7 kW | 6196 kWh | 4523 kWh | 1673 kWh | £1,226 | £167 | £1,394 | £19,492 | 14.0 yrs | £8,381 |
| 8 kW | 7082 kWh | 5170 kWh | 1912 kWh | £1,401 | £191 | £1,593 | £21,526 | 13.5 yrs | £10,328 |
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: £1,011, Upfront: £17,173, Break-even: 17.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1770 kWh | 1328 kWh | 443 kWh | £360 | £44 | £404 | £11,069 | 27.4 yrs | £-2,984 |
| 3 kW | 2656 kWh | 1992 kWh | 664 kWh | £540 | £66 | £606 | £13,104 | 21.6 yrs | £-977 |
| 4 kW | 3541 kWh | 2656 kWh | 885 kWh | £720 | £89 | £808 | £15,138 | 18.7 yrs | £1,031 |
| 5 kW | 4426 kWh | 3320 kWh | 1107 kWh | £900 | £111 | £1,011 | £17,173 | 17.0 yrs | £3,039 |
| 6 kW | 5311 kWh | 3983 kWh | 1328 kWh | £1,080 | £133 | £1,213 | £19,207 | 15.8 yrs | £5,047 |
| 7 kW | 6196 kWh | 4647 kWh | 1549 kWh | £1,260 | £155 | £1,415 | £21,242 | 15.0 yrs | £7,055 |
| 8 kW | 7082 kWh | 5311 kWh | 1770 kWh | £1,440 | £177 | £1,617 | £23,276 | 14.4 yrs | £9,062 |
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: £1,026, Upfront: £19,623, Break-even: 19.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1770 kWh | 1363 kWh | 407 kWh | £370 | £41 | £410 | £13,519 | 32.9 yrs | £-5,313 |
| 3 kW | 2656 kWh | 2045 kWh | 611 kWh | £554 | £61 | £615 | £15,554 | 25.3 yrs | £-3,245 |
| 4 kW | 3541 kWh | 2726 kWh | 814 kWh | £739 | £81 | £821 | £17,588 | 21.4 yrs | £-1,176 |
| 5 kW | 4426 kWh | 3408 kWh | 1018 kWh | £924 | £102 | £1,026 | £19,623 | 19.1 yrs | £892 |
| 6 kW | 5311 kWh | 4090 kWh | 1222 kWh | £1,109 | £122 | £1,231 | £21,657 | 17.6 yrs | £2,960 |
| 7 kW | 6196 kWh | 4771 kWh | 1425 kWh | £1,293 | £143 | £1,436 | £23,692 | 16.5 yrs | £5,029 |
| 8 kW | 7082 kWh | 5453 kWh | 1629 kWh | £1,478 | £163 | £1,641 | £25,726 | 15.7 yrs | £7,097 |
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.