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 921 kWh per year on a south-facing roof. We value self-used electricity at 25.4p 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: £745, Upfront: £10,173, 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 | 1843 kWh | 737 kWh | 1106 kWh | £187 | £111 | £298 | £4,069 | 13.7 yrs | £1,892 |
| 3 kW | 2764 kWh | 1106 kWh | 1659 kWh | £281 | £166 | £447 | £6,104 | 13.7 yrs | £2,837 |
| 4 kW | 3686 kWh | 1474 kWh | 2211 kWh | £375 | £221 | £596 | £8,138 | 13.7 yrs | £3,783 |
| 5 kW | 4607 kWh | 1843 kWh | 2764 kWh | £469 | £276 | £745 | £10,173 | 13.7 yrs | £4,729 |
| 6 kW | 5529 kWh | 2211 kWh | 3317 kWh | £562 | £332 | £894 | £12,207 | 13.7 yrs | £5,675 |
| 7 kW | 6450 kWh | 2580 kWh | 3870 kWh | £656 | £387 | £1,043 | £14,242 | 13.7 yrs | £6,621 |
| 8 kW | 7372 kWh | 2949 kWh | 4423 kWh | £750 | £442 | £1,192 | £16,276 | 13.7 yrs | £7,566 |
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: £887, Upfront: £12,273, Break-even: 13.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1843 kWh | 1106 kWh | 737 kWh | £281 | £74 | £355 | £6,169 | 17.4 yrs | £929 |
| 3 kW | 2764 kWh | 1659 kWh | 1106 kWh | £422 | £111 | £532 | £8,204 | 15.4 yrs | £2,444 |
| 4 kW | 3686 kWh | 2211 kWh | 1474 kWh | £562 | £147 | £710 | £10,238 | 14.4 yrs | £3,958 |
| 5 kW | 4607 kWh | 2764 kWh | 1843 kWh | £703 | £184 | £887 | £12,273 | 13.8 yrs | £5,473 |
| 6 kW | 5529 kWh | 3317 kWh | 2211 kWh | £844 | £221 | £1,065 | £14,307 | 13.4 yrs | £6,987 |
| 7 kW | 6450 kWh | 3870 kWh | 2580 kWh | £984 | £258 | £1,242 | £16,342 | 13.2 yrs | £8,502 |
| 8 kW | 7372 kWh | 4423 kWh | 2949 kWh | £1,125 | £295 | £1,420 | £18,376 | 12.9 yrs | £10,016 |
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: £958, Upfront: £13,673, 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 | 1843 kWh | 1290 kWh | 553 kWh | £328 | £55 | £383 | £7,569 | 19.7 yrs | £98 |
| 3 kW | 2764 kWh | 1935 kWh | 829 kWh | £492 | £83 | £575 | £9,604 | 16.7 yrs | £1,897 |
| 4 kW | 3686 kWh | 2580 kWh | 1106 kWh | £656 | £111 | £767 | £11,638 | 15.2 yrs | £3,695 |
| 5 kW | 4607 kWh | 3225 kWh | 1382 kWh | £820 | £138 | £958 | £13,673 | 14.3 yrs | £5,494 |
| 6 kW | 5529 kWh | 3870 kWh | 1659 kWh | £984 | £166 | £1,150 | £15,707 | 13.7 yrs | £7,293 |
| 7 kW | 6450 kWh | 4515 kWh | 1935 kWh | £1,148 | £194 | £1,342 | £17,742 | 13.2 yrs | £9,092 |
| 8 kW | 7372 kWh | 5160 kWh | 2211 kWh | £1,312 | £221 | £1,533 | £19,776 | 12.9 yrs | £10,891 |
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: £980, Upfront: £15,423, 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 | 1843 kWh | 1345 kWh | 498 kWh | £342 | £50 | £392 | £9,319 | 23.8 yrs | £-1,482 |
| 3 kW | 2764 kWh | 2018 kWh | 746 kWh | £513 | £75 | £588 | £11,354 | 19.3 yrs | £403 |
| 4 kW | 3686 kWh | 2691 kWh | 995 kWh | £684 | £100 | £784 | £13,388 | 17.1 yrs | £2,287 |
| 5 kW | 4607 kWh | 3363 kWh | 1244 kWh | £855 | £124 | £980 | £15,423 | 15.7 yrs | £4,171 |
| 6 kW | 5529 kWh | 4036 kWh | 1493 kWh | £1,026 | £149 | £1,176 | £17,457 | 14.8 yrs | £6,055 |
| 7 kW | 6450 kWh | 4709 kWh | 1742 kWh | £1,197 | £174 | £1,372 | £19,492 | 14.2 yrs | £7,939 |
| 8 kW | 7372 kWh | 5381 kWh | 1990 kWh | £1,368 | £199 | £1,567 | £21,526 | 13.7 yrs | £9,823 |
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: £994, Upfront: £17,173, Break-even: 17.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1843 kWh | 1382 kWh | 461 kWh | £351 | £46 | £398 | £11,069 | 27.8 yrs | £-3,118 |
| 3 kW | 2764 kWh | 2073 kWh | 691 kWh | £527 | £69 | £596 | £13,104 | 22.0 yrs | £-1,177 |
| 4 kW | 3686 kWh | 2764 kWh | 921 kWh | £703 | £92 | £795 | £15,138 | 19.0 yrs | £764 |
| 5 kW | 4607 kWh | 3455 kWh | 1152 kWh | £879 | £115 | £994 | £17,173 | 17.3 yrs | £2,705 |
| 6 kW | 5529 kWh | 4146 kWh | 1382 kWh | £1,054 | £138 | £1,193 | £19,207 | 16.1 yrs | £4,646 |
| 7 kW | 6450 kWh | 4838 kWh | 1613 kWh | £1,230 | £161 | £1,391 | £21,242 | 15.3 yrs | £6,587 |
| 8 kW | 7372 kWh | 5529 kWh | 1843 kWh | £1,406 | £184 | £1,590 | £23,276 | 14.6 yrs | £8,528 |
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: £1,008, Upfront: £19,623, Break-even: 19.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1843 kWh | 1419 kWh | 424 kWh | £361 | £42 | £403 | £13,519 | 33.5 yrs | £-5,454 |
| 3 kW | 2764 kWh | 2129 kWh | 636 kWh | £541 | £64 | £605 | £15,554 | 25.7 yrs | £-3,456 |
| 4 kW | 3686 kWh | 2838 kWh | 848 kWh | £722 | £85 | £806 | £17,588 | 21.8 yrs | £-1,458 |
| 5 kW | 4607 kWh | 3548 kWh | 1060 kWh | £902 | £106 | £1,008 | £19,623 | 19.5 yrs | £540 |
| 6 kW | 5529 kWh | 4257 kWh | 1272 kWh | £1,083 | £127 | £1,210 | £21,657 | 17.9 yrs | £2,537 |
| 7 kW | 6450 kWh | 4967 kWh | 1484 kWh | £1,263 | £148 | £1,411 | £23,692 | 16.8 yrs | £4,535 |
| 8 kW | 7372 kWh | 5676 kWh | 1695 kWh | £1,443 | £170 | £1,613 | £25,726 | 15.9 yrs | £6,533 |
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.