A typical roof here lands around 4.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 932 kWh per year on a south-facing roof. We value self-used electricity at 25.3p 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: £752, Upfront: £10,173, Break-even: 13.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1864 kWh | 746 kWh | 1118 kWh | £189 | £112 | £301 | £4,069 | 13.5 yrs | £1,944 |
| 3 kW | 2796 kWh | 1118 kWh | 1677 kWh | £283 | £168 | £451 | £6,104 | 13.5 yrs | £2,916 |
| 4 kW | 3728 kWh | 1491 kWh | 2237 kWh | £378 | £224 | £601 | £8,138 | 13.5 yrs | £3,889 |
| 5 kW | 4659 kWh | 1864 kWh | 2796 kWh | £472 | £280 | £752 | £10,173 | 13.5 yrs | £4,861 |
| 6 kW | 5591 kWh | 2237 kWh | 3355 kWh | £567 | £335 | £902 | £12,207 | 13.5 yrs | £5,833 |
| 7 kW | 6523 kWh | 2609 kWh | 3914 kWh | £661 | £391 | £1,052 | £14,242 | 13.5 yrs | £6,805 |
| 8 kW | 7455 kWh | 2982 kWh | 4473 kWh | £755 | £447 | £1,203 | £16,276 | 13.5 yrs | £7,777 |
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: £895, 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 | 1864 kWh | 1118 kWh | 746 kWh | £283 | £75 | £358 | £6,169 | 17.2 yrs | £987 |
| 3 kW | 2796 kWh | 1677 kWh | 1118 kWh | £425 | £112 | £537 | £8,204 | 15.3 yrs | £2,531 |
| 4 kW | 3728 kWh | 2237 kWh | 1491 kWh | £567 | £149 | £716 | £10,238 | 14.3 yrs | £4,074 |
| 5 kW | 4659 kWh | 2796 kWh | 1864 kWh | £708 | £186 | £895 | £12,273 | 13.7 yrs | £5,618 |
| 6 kW | 5591 kWh | 3355 kWh | 2237 kWh | £850 | £224 | £1,073 | £14,307 | 13.3 yrs | £7,161 |
| 7 kW | 6523 kWh | 3914 kWh | 2609 kWh | £991 | £261 | £1,252 | £16,342 | 13.0 yrs | £8,705 |
| 8 kW | 7455 kWh | 4473 kWh | 2982 kWh | £1,133 | £298 | £1,431 | £18,376 | 12.8 yrs | £10,249 |
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: £966, Upfront: £13,673, Break-even: 14.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1864 kWh | 1305 kWh | 559 kWh | £330 | £56 | £386 | £7,569 | 19.6 yrs | £159 |
| 3 kW | 2796 kWh | 1957 kWh | 839 kWh | £496 | £84 | £580 | £9,604 | 16.6 yrs | £1,988 |
| 4 kW | 3728 kWh | 2609 kWh | 1118 kWh | £661 | £112 | £773 | £11,638 | 15.1 yrs | £3,817 |
| 5 kW | 4659 kWh | 3262 kWh | 1398 kWh | £826 | £140 | £966 | £13,673 | 14.2 yrs | £5,646 |
| 6 kW | 5591 kWh | 3914 kWh | 1677 kWh | £991 | £168 | £1,159 | £15,707 | 13.6 yrs | £7,476 |
| 7 kW | 6523 kWh | 4566 kWh | 1957 kWh | £1,157 | £196 | £1,352 | £17,742 | 13.1 yrs | £9,305 |
| 8 kW | 7455 kWh | 5219 kWh | 2237 kWh | £1,322 | £224 | £1,546 | £19,776 | 12.8 yrs | £11,134 |
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: £987, Upfront: £15,423, Break-even: 15.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1864 kWh | 1361 kWh | 503 kWh | £345 | £50 | £395 | £9,319 | 23.6 yrs | £-1,420 |
| 3 kW | 2796 kWh | 2041 kWh | 755 kWh | £517 | £75 | £592 | £11,354 | 19.2 yrs | £495 |
| 4 kW | 3728 kWh | 2721 kWh | 1006 kWh | £689 | £101 | £790 | £13,388 | 16.9 yrs | £2,410 |
| 5 kW | 4659 kWh | 3401 kWh | 1258 kWh | £862 | £126 | £987 | £15,423 | 15.6 yrs | £4,325 |
| 6 kW | 5591 kWh | 4082 kWh | 1510 kWh | £1,034 | £151 | £1,185 | £17,457 | 14.7 yrs | £6,240 |
| 7 kW | 6523 kWh | 4762 kWh | 1761 kWh | £1,206 | £176 | £1,382 | £19,492 | 14.1 yrs | £8,155 |
| 8 kW | 7455 kWh | 5442 kWh | 2013 kWh | £1,379 | £201 | £1,580 | £21,526 | 13.6 yrs | £10,070 |
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: £1,002, Upfront: £17,173, Break-even: 17.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1864 kWh | 1398 kWh | 466 kWh | £354 | £47 | £401 | £11,069 | 27.6 yrs | £-3,056 |
| 3 kW | 2796 kWh | 2097 kWh | 699 kWh | £531 | £70 | £601 | £13,104 | 21.8 yrs | £-1,084 |
| 4 kW | 3728 kWh | 2796 kWh | 932 kWh | £708 | £93 | £801 | £15,138 | 18.9 yrs | £889 |
| 5 kW | 4659 kWh | 3495 kWh | 1165 kWh | £885 | £116 | £1,002 | £17,173 | 17.1 yrs | £2,861 |
| 6 kW | 5591 kWh | 4194 kWh | 1398 kWh | £1,062 | £140 | £1,202 | £19,207 | 16.0 yrs | £4,833 |
| 7 kW | 6523 kWh | 4892 kWh | 1631 kWh | £1,239 | £163 | £1,402 | £21,242 | 15.1 yrs | £6,805 |
| 8 kW | 7455 kWh | 5591 kWh | 1864 kWh | £1,416 | £186 | £1,603 | £23,276 | 14.5 yrs | £8,777 |
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: £1,016, Upfront: £19,623, Break-even: 19.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1864 kWh | 1435 kWh | 429 kWh | £364 | £43 | £406 | £13,519 | 33.3 yrs | £-5,391 |
| 3 kW | 2796 kWh | 2153 kWh | 643 kWh | £545 | £64 | £610 | £15,554 | 25.5 yrs | £-3,362 |
| 4 kW | 3728 kWh | 2870 kWh | 857 kWh | £727 | £86 | £813 | £17,588 | 21.6 yrs | £-1,333 |
| 5 kW | 4659 kWh | 3588 kWh | 1072 kWh | £909 | £107 | £1,016 | £19,623 | 19.3 yrs | £696 |
| 6 kW | 5591 kWh | 4305 kWh | 1286 kWh | £1,091 | £129 | £1,219 | £21,657 | 17.8 yrs | £2,726 |
| 7 kW | 6523 kWh | 5023 kWh | 1500 kWh | £1,272 | £150 | £1,422 | £23,692 | 16.7 yrs | £4,755 |
| 8 kW | 7455 kWh | 5740 kWh | 1715 kWh | £1,454 | £171 | £1,626 | £25,726 | 15.8 yrs | £6,784 |
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.