A typical roof here lands around 6.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 1110 kWh per year on a south-facing roof. We value self-used electricity at 26.9p 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: £931, Upfront: £10,173, Break-even: 10.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2220 kWh | 888 kWh | 1332 kWh | £239 | £133 | £372 | £4,069 | 10.9 yrs | £3,375 |
| 3 kW | 3330 kWh | 1332 kWh | 1998 kWh | £359 | £200 | £558 | £6,104 | 10.9 yrs | £5,063 |
| 4 kW | 4440 kWh | 1776 kWh | 2664 kWh | £478 | £266 | £744 | £8,138 | 10.9 yrs | £6,750 |
| 5 kW | 5549 kWh | 2220 kWh | 3330 kWh | £598 | £333 | £931 | £10,173 | 10.9 yrs | £8,438 |
| 6 kW | 6659 kWh | 2664 kWh | 3996 kWh | £717 | £400 | £1,117 | £12,207 | 10.9 yrs | £10,126 |
| 7 kW | 7769 kWh | 3108 kWh | 4662 kWh | £837 | £466 | £1,303 | £14,242 | 10.9 yrs | £11,813 |
| 8 kW | 8879 kWh | 3552 kWh | 5327 kWh | £956 | £533 | £1,489 | £16,276 | 10.9 yrs | £13,501 |
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: £1,118, Upfront: £12,273, Break-even: 11.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2220 kWh | 1332 kWh | 888 kWh | £359 | £89 | £447 | £6,169 | 13.8 yrs | £2,778 |
| 3 kW | 3330 kWh | 1998 kWh | 1332 kWh | £538 | £133 | £671 | £8,204 | 12.2 yrs | £5,216 |
| 4 kW | 4440 kWh | 2664 kWh | 1776 kWh | £717 | £178 | £895 | £10,238 | 11.4 yrs | £7,655 |
| 5 kW | 5549 kWh | 3330 kWh | 2220 kWh | £896 | £222 | £1,118 | £12,273 | 11.0 yrs | £10,094 |
| 6 kW | 6659 kWh | 3996 kWh | 2664 kWh | £1,076 | £266 | £1,342 | £14,307 | 10.7 yrs | £12,533 |
| 7 kW | 7769 kWh | 4662 kWh | 3108 kWh | £1,255 | £311 | £1,566 | £16,342 | 10.4 yrs | £14,972 |
| 8 kW | 8879 kWh | 5327 kWh | 3552 kWh | £1,434 | £355 | £1,789 | £18,376 | 10.3 yrs | £17,410 |
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: £1,212, Upfront: £13,673, Break-even: 11.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2220 kWh | 1554 kWh | 666 kWh | £418 | £67 | £485 | £7,569 | 15.6 yrs | £2,129 |
| 3 kW | 3330 kWh | 2331 kWh | 999 kWh | £627 | £100 | £727 | £9,604 | 13.2 yrs | £4,943 |
| 4 kW | 4440 kWh | 3108 kWh | 1332 kWh | £837 | £133 | £970 | £11,638 | 12.0 yrs | £7,758 |
| 5 kW | 5549 kWh | 3885 kWh | 1665 kWh | £1,046 | £166 | £1,212 | £13,673 | 11.3 yrs | £10,572 |
| 6 kW | 6659 kWh | 4662 kWh | 1998 kWh | £1,255 | £200 | £1,455 | £15,707 | 10.8 yrs | £13,386 |
| 7 kW | 7769 kWh | 5438 kWh | 2331 kWh | £1,464 | £233 | £1,697 | £17,742 | 10.5 yrs | £16,201 |
| 8 kW | 8879 kWh | 6215 kWh | 2664 kWh | £1,673 | £266 | £1,940 | £19,776 | 10.2 yrs | £19,015 |
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: £1,240, Upfront: £15,423, Break-even: 12.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2220 kWh | 1620 kWh | 599 kWh | £436 | £60 | £496 | £9,319 | 18.8 yrs | £604 |
| 3 kW | 3330 kWh | 2431 kWh | 899 kWh | £654 | £90 | £744 | £11,354 | 15.3 yrs | £3,531 |
| 4 kW | 4440 kWh | 3241 kWh | 1199 kWh | £872 | £120 | £992 | £13,388 | 13.5 yrs | £6,458 |
| 5 kW | 5549 kWh | 4051 kWh | 1498 kWh | £1,091 | £150 | £1,240 | £15,423 | 12.4 yrs | £9,385 |
| 6 kW | 6659 kWh | 4861 kWh | 1798 kWh | £1,309 | £180 | £1,488 | £17,457 | 11.7 yrs | £12,312 |
| 7 kW | 7769 kWh | 5672 kWh | 2098 kWh | £1,527 | £210 | £1,737 | £19,492 | 11.2 yrs | £15,239 |
| 8 kW | 8879 kWh | 6482 kWh | 2397 kWh | £1,745 | £240 | £1,985 | £21,526 | 10.8 yrs | £18,166 |
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: £1,259, Upfront: £17,173, 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 | 2220 kWh | 1665 kWh | 555 kWh | £448 | £55 | £504 | £11,069 | 22.0 yrs | £-996 |
| 3 kW | 3330 kWh | 2497 kWh | 832 kWh | £672 | £83 | £756 | £13,104 | 17.3 yrs | £2,007 |
| 4 kW | 4440 kWh | 3330 kWh | 1110 kWh | £896 | £111 | £1,007 | £15,138 | 15.0 yrs | £5,009 |
| 5 kW | 5549 kWh | 4162 kWh | 1387 kWh | £1,120 | £139 | £1,259 | £17,173 | 13.6 yrs | £8,011 |
| 6 kW | 6659 kWh | 4995 kWh | 1665 kWh | £1,345 | £166 | £1,511 | £19,207 | 12.7 yrs | £11,013 |
| 7 kW | 7769 kWh | 5827 kWh | 1942 kWh | £1,569 | £194 | £1,763 | £21,242 | 12.0 yrs | £14,015 |
| 8 kW | 8879 kWh | 6659 kWh | 2220 kWh | £1,793 | £222 | £2,015 | £23,276 | 11.6 yrs | £17,017 |
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: £1,278, Upfront: £19,623, Break-even: 15.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2220 kWh | 1709 kWh | 511 kWh | £460 | £51 | £511 | £13,519 | 26.4 yrs | £-3,295 |
| 3 kW | 3330 kWh | 2564 kWh | 766 kWh | £690 | £77 | £767 | £15,554 | 20.3 yrs | £-218 |
| 4 kW | 4440 kWh | 3418 kWh | 1021 kWh | £920 | £102 | £1,022 | £17,588 | 17.2 yrs | £2,859 |
| 5 kW | 5549 kWh | 4273 kWh | 1276 kWh | £1,150 | £128 | £1,278 | £19,623 | 15.4 yrs | £5,936 |
| 6 kW | 6659 kWh | 5128 kWh | 1532 kWh | £1,380 | £153 | £1,534 | £21,657 | 14.1 yrs | £9,014 |
| 7 kW | 7769 kWh | 5982 kWh | 1787 kWh | £1,610 | £179 | £1,789 | £23,692 | 13.2 yrs | £12,091 |
| 8 kW | 8879 kWh | 6837 kWh | 2042 kWh | £1,840 | £204 | £2,045 | £25,726 | 12.6 yrs | £15,168 |
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.