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 964 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: £777, Upfront: £10,173, Break-even: 13.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1927 kWh | 771 kWh | 1156 kWh | £195 | £116 | £311 | £4,069 | 13.1 yrs | £2,148 |
| 3 kW | 2891 kWh | 1156 kWh | 1734 kWh | £293 | £173 | £466 | £6,104 | 13.1 yrs | £3,223 |
| 4 kW | 3854 kWh | 1542 kWh | 2312 kWh | £390 | £231 | £622 | £8,138 | 13.1 yrs | £4,297 |
| 5 kW | 4818 kWh | 1927 kWh | 2891 kWh | £488 | £289 | £777 | £10,173 | 13.1 yrs | £5,371 |
| 6 kW | 5781 kWh | 2312 kWh | 3469 kWh | £586 | £347 | £933 | £12,207 | 13.1 yrs | £6,445 |
| 7 kW | 6745 kWh | 2698 kWh | 4047 kWh | £683 | £405 | £1,088 | £14,242 | 13.1 yrs | £7,519 |
| 8 kW | 7708 kWh | 3083 kWh | 4625 kWh | £781 | £462 | £1,243 | £16,276 | 13.1 yrs | £8,594 |
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: £925, Upfront: £12,273, Break-even: 13.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1927 kWh | 1156 kWh | 771 kWh | £293 | £77 | £370 | £6,169 | 16.7 yrs | £1,230 |
| 3 kW | 2891 kWh | 1734 kWh | 1156 kWh | £439 | £116 | £555 | £8,204 | 14.8 yrs | £2,895 |
| 4 kW | 3854 kWh | 2312 kWh | 1542 kWh | £586 | £154 | £740 | £10,238 | 13.8 yrs | £4,560 |
| 5 kW | 4818 kWh | 2891 kWh | 1927 kWh | £732 | £193 | £925 | £12,273 | 13.3 yrs | £6,225 |
| 6 kW | 5781 kWh | 3469 kWh | 2312 kWh | £879 | £231 | £1,110 | £14,307 | 12.9 yrs | £7,890 |
| 7 kW | 6745 kWh | 4047 kWh | 2698 kWh | £1,025 | £270 | £1,295 | £16,342 | 12.6 yrs | £9,555 |
| 8 kW | 7708 kWh | 4625 kWh | 3083 kWh | £1,171 | £308 | £1,480 | £18,376 | 12.4 yrs | £11,220 |
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: £999, Upfront: £13,673, 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 | 1927 kWh | 1349 kWh | 578 kWh | £342 | £58 | £399 | £7,569 | 18.9 yrs | £421 |
| 3 kW | 2891 kWh | 2023 kWh | 867 kWh | £513 | £87 | £599 | £9,604 | 16.0 yrs | £2,381 |
| 4 kW | 3854 kWh | 2698 kWh | 1156 kWh | £683 | £116 | £799 | £11,638 | 14.6 yrs | £4,342 |
| 5 kW | 4818 kWh | 3372 kWh | 1445 kWh | £854 | £145 | £999 | £13,673 | 13.7 yrs | £6,302 |
| 6 kW | 5781 kWh | 4047 kWh | 1734 kWh | £1,025 | £173 | £1,198 | £15,707 | 13.1 yrs | £8,263 |
| 7 kW | 6745 kWh | 4721 kWh | 2023 kWh | £1,196 | £202 | £1,398 | £17,742 | 12.7 yrs | £10,223 |
| 8 kW | 7708 kWh | 5396 kWh | 2312 kWh | £1,367 | £231 | £1,598 | £19,776 | 12.4 yrs | £12,183 |
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: £1,021, Upfront: £15,423, Break-even: 15.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1927 kWh | 1407 kWh | 520 kWh | £356 | £52 | £408 | £9,319 | 22.8 yrs | £-1,152 |
| 3 kW | 2891 kWh | 2110 kWh | 780 kWh | £534 | £78 | £613 | £11,354 | 18.5 yrs | £897 |
| 4 kW | 3854 kWh | 2813 kWh | 1041 kWh | £713 | £104 | £817 | £13,388 | 16.4 yrs | £2,946 |
| 5 kW | 4818 kWh | 3517 kWh | 1301 kWh | £891 | £130 | £1,021 | £15,423 | 15.1 yrs | £4,995 |
| 6 kW | 5781 kWh | 4220 kWh | 1561 kWh | £1,069 | £156 | £1,225 | £17,457 | 14.2 yrs | £7,044 |
| 7 kW | 6745 kWh | 4924 kWh | 1821 kWh | £1,247 | £182 | £1,429 | £19,492 | 13.6 yrs | £9,093 |
| 8 kW | 7708 kWh | 5627 kWh | 2081 kWh | £1,425 | £208 | £1,633 | £21,526 | 13.2 yrs | £11,142 |
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: £1,036, Upfront: £17,173, Break-even: 16.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1927 kWh | 1445 kWh | 482 kWh | £366 | £48 | £414 | £11,069 | 26.7 yrs | £-2,784 |
| 3 kW | 2891 kWh | 2168 kWh | 723 kWh | £549 | £72 | £621 | £13,104 | 21.1 yrs | £-676 |
| 4 kW | 3854 kWh | 2891 kWh | 964 kWh | £732 | £96 | £829 | £15,138 | 18.3 yrs | £1,433 |
| 5 kW | 4818 kWh | 3613 kWh | 1204 kWh | £915 | £120 | £1,036 | £17,173 | 16.6 yrs | £3,541 |
| 6 kW | 5781 kWh | 4336 kWh | 1445 kWh | £1,098 | £145 | £1,243 | £19,207 | 15.5 yrs | £5,649 |
| 7 kW | 6745 kWh | 5058 kWh | 1686 kWh | £1,281 | £169 | £1,450 | £21,242 | 14.7 yrs | £7,757 |
| 8 kW | 7708 kWh | 5781 kWh | 1927 kWh | £1,464 | £193 | £1,657 | £23,276 | 14.0 yrs | £9,865 |
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: £1,050, Upfront: £19,623, Break-even: 18.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1927 kWh | 1484 kWh | 443 kWh | £376 | £44 | £420 | £13,519 | 32.2 yrs | £-5,116 |
| 3 kW | 2891 kWh | 2226 kWh | 665 kWh | £564 | £66 | £630 | £15,554 | 24.7 yrs | £-2,948 |
| 4 kW | 3854 kWh | 2968 kWh | 886 kWh | £752 | £89 | £840 | £17,588 | 20.9 yrs | £-781 |
| 5 kW | 4818 kWh | 3710 kWh | 1108 kWh | £940 | £111 | £1,050 | £19,623 | 18.7 yrs | £1,386 |
| 6 kW | 5781 kWh | 4451 kWh | 1330 kWh | £1,128 | £133 | £1,261 | £21,657 | 17.2 yrs | £3,553 |
| 7 kW | 6745 kWh | 5193 kWh | 1551 kWh | £1,315 | £155 | £1,471 | £23,692 | 16.1 yrs | £5,721 |
| 8 kW | 7708 kWh | 5935 kWh | 1773 kWh | £1,503 | £177 | £1,681 | £25,726 | 15.3 yrs | £7,888 |
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.