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 1011 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: £821, Upfront: £10,173, 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 | 2021 kWh | 808 kWh | 1213 kWh | £207 | £121 | £328 | £4,069 | 12.4 yrs | £2,500 |
| 3 kW | 3032 kWh | 1213 kWh | 1819 kWh | £311 | £182 | £493 | £6,104 | 12.4 yrs | £3,750 |
| 4 kW | 4042 kWh | 1617 kWh | 2425 kWh | £414 | £243 | £657 | £8,138 | 12.4 yrs | £5,000 |
| 5 kW | 5053 kWh | 2021 kWh | 3032 kWh | £518 | £303 | £821 | £10,173 | 12.4 yrs | £6,251 |
| 6 kW | 6063 kWh | 2425 kWh | 3638 kWh | £622 | £364 | £985 | £12,207 | 12.4 yrs | £7,501 |
| 7 kW | 7074 kWh | 2829 kWh | 4244 kWh | £725 | £424 | £1,150 | £14,242 | 12.4 yrs | £8,751 |
| 8 kW | 8084 kWh | 3234 kWh | 4851 kWh | £829 | £485 | £1,314 | £16,276 | 12.4 yrs | £10,001 |
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: £979, Upfront: £12,273, 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 | 2021 kWh | 1213 kWh | 808 kWh | £311 | £81 | £392 | £6,169 | 15.8 yrs | £1,664 |
| 3 kW | 3032 kWh | 1819 kWh | 1213 kWh | £466 | £121 | £587 | £8,204 | 14.0 yrs | £3,546 |
| 4 kW | 4042 kWh | 2425 kWh | 1617 kWh | £622 | £162 | £783 | £10,238 | 13.1 yrs | £5,428 |
| 5 kW | 5053 kWh | 3032 kWh | 2021 kWh | £777 | £202 | £979 | £12,273 | 12.5 yrs | £7,310 |
| 6 kW | 6063 kWh | 3638 kWh | 2425 kWh | £932 | £243 | £1,175 | £14,307 | 12.2 yrs | £9,191 |
| 7 kW | 7074 kWh | 4244 kWh | 2829 kWh | £1,088 | £283 | £1,371 | £16,342 | 11.9 yrs | £11,073 |
| 8 kW | 8084 kWh | 4851 kWh | 3234 kWh | £1,243 | £323 | £1,567 | £18,376 | 11.7 yrs | £12,955 |
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: £1,058, Upfront: £13,673, Break-even: 12.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2021 kWh | 1415 kWh | 606 kWh | £363 | £61 | £423 | £7,569 | 17.9 yrs | £896 |
| 3 kW | 3032 kWh | 2122 kWh | 909 kWh | £544 | £91 | £635 | £9,604 | 15.1 yrs | £3,093 |
| 4 kW | 4042 kWh | 2829 kWh | 1213 kWh | £725 | £121 | £846 | £11,638 | 13.7 yrs | £5,291 |
| 5 kW | 5053 kWh | 3537 kWh | 1516 kWh | £906 | £152 | £1,058 | £13,673 | 12.9 yrs | £7,489 |
| 6 kW | 6063 kWh | 4244 kWh | 1819 kWh | £1,088 | £182 | £1,270 | £15,707 | 12.4 yrs | £9,687 |
| 7 kW | 7074 kWh | 4952 kWh | 2122 kWh | £1,269 | £212 | £1,481 | £17,742 | 12.0 yrs | £11,885 |
| 8 kW | 8084 kWh | 5659 kWh | 2425 kWh | £1,450 | £243 | £1,693 | £19,776 | 11.7 yrs | £14,082 |
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: £1,082, 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 | 2021 kWh | 1475 kWh | 546 kWh | £378 | £55 | £433 | £9,319 | 21.5 yrs | £-665 |
| 3 kW | 3032 kWh | 2213 kWh | 819 kWh | £567 | £82 | £649 | £11,354 | 17.5 yrs | £1,628 |
| 4 kW | 4042 kWh | 2951 kWh | 1091 kWh | £756 | £109 | £865 | £13,388 | 15.5 yrs | £3,920 |
| 5 kW | 5053 kWh | 3688 kWh | 1364 kWh | £945 | £136 | £1,082 | £15,423 | 14.3 yrs | £6,213 |
| 6 kW | 6063 kWh | 4426 kWh | 1637 kWh | £1,134 | £164 | £1,298 | £17,457 | 13.4 yrs | £8,505 |
| 7 kW | 7074 kWh | 5164 kWh | 1910 kWh | £1,323 | £191 | £1,514 | £19,492 | 12.9 yrs | £10,798 |
| 8 kW | 8084 kWh | 5901 kWh | 2183 kWh | £1,513 | £218 | £1,731 | £21,526 | 12.4 yrs | £13,090 |
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: £1,098, Upfront: £17,173, 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 | 2021 kWh | 1516 kWh | 505 kWh | £388 | £51 | £439 | £11,069 | 25.2 yrs | £-2,289 |
| 3 kW | 3032 kWh | 2274 kWh | 758 kWh | £583 | £76 | £659 | £13,104 | 19.9 yrs | £67 |
| 4 kW | 4042 kWh | 3032 kWh | 1011 kWh | £777 | £101 | £878 | £15,138 | 17.2 yrs | £2,423 |
| 5 kW | 5053 kWh | 3789 kWh | 1263 kWh | £971 | £126 | £1,098 | £17,173 | 15.6 yrs | £4,779 |
| 6 kW | 6063 kWh | 4547 kWh | 1516 kWh | £1,165 | £152 | £1,317 | £19,207 | 14.6 yrs | £7,134 |
| 7 kW | 7074 kWh | 5305 kWh | 1768 kWh | £1,360 | £177 | £1,537 | £21,242 | 13.8 yrs | £9,490 |
| 8 kW | 8084 kWh | 6063 kWh | 2021 kWh | £1,554 | £202 | £1,756 | £23,276 | 13.3 yrs | £11,846 |
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: £1,113, Upfront: £19,623, Break-even: 17.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2021 kWh | 1556 kWh | 465 kWh | £399 | £46 | £445 | £13,519 | 30.4 yrs | £-4,612 |
| 3 kW | 3032 kWh | 2334 kWh | 697 kWh | £598 | £70 | £668 | £15,554 | 23.3 yrs | £-2,193 |
| 4 kW | 4042 kWh | 3112 kWh | 930 kWh | £798 | £93 | £891 | £17,588 | 19.7 yrs | £226 |
| 5 kW | 5053 kWh | 3891 kWh | 1162 kWh | £997 | £116 | £1,113 | £19,623 | 17.6 yrs | £2,645 |
| 6 kW | 6063 kWh | 4669 kWh | 1395 kWh | £1,197 | £139 | £1,336 | £21,657 | 16.2 yrs | £5,063 |
| 7 kW | 7074 kWh | 5447 kWh | 1627 kWh | £1,396 | £163 | £1,559 | £23,692 | 15.2 yrs | £7,482 |
| 8 kW | 8084 kWh | 6225 kWh | 1859 kWh | £1,595 | £186 | £1,781 | £25,726 | 14.4 yrs | £9,901 |
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.