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 959 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: £776, 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 | 1918 kWh | 767 kWh | 1151 kWh | £195 | £115 | £310 | £4,069 | 13.1 yrs | £2,135 |
| 3 kW | 2877 kWh | 1151 kWh | 1726 kWh | £293 | £173 | £465 | £6,104 | 13.1 yrs | £3,203 |
| 4 kW | 3836 kWh | 1535 kWh | 2302 kWh | £390 | £230 | £620 | £8,138 | 13.1 yrs | £4,271 |
| 5 kW | 4796 kWh | 1918 kWh | 2877 kWh | £488 | £288 | £776 | £10,173 | 13.1 yrs | £5,338 |
| 6 kW | 5755 kWh | 2302 kWh | 3453 kWh | £585 | £345 | £931 | £12,207 | 13.1 yrs | £6,406 |
| 7 kW | 6714 kWh | 2686 kWh | 4028 kWh | £683 | £403 | £1,086 | £14,242 | 13.1 yrs | £7,473 |
| 8 kW | 7673 kWh | 3069 kWh | 4604 kWh | £780 | £460 | £1,241 | £16,276 | 13.1 yrs | £8,541 |
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: £924, 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 | 1918 kWh | 1151 kWh | 767 kWh | £293 | £77 | £369 | £6,169 | 16.7 yrs | £1,219 |
| 3 kW | 2877 kWh | 1726 kWh | 1151 kWh | £439 | £115 | £554 | £8,204 | 14.8 yrs | £2,879 |
| 4 kW | 3836 kWh | 2302 kWh | 1535 kWh | £585 | £153 | £739 | £10,238 | 13.9 yrs | £4,538 |
| 5 kW | 4796 kWh | 2877 kWh | 1918 kWh | £732 | £192 | £924 | £12,273 | 13.3 yrs | £6,198 |
| 6 kW | 5755 kWh | 3453 kWh | 2302 kWh | £878 | £230 | £1,108 | £14,307 | 12.9 yrs | £7,858 |
| 7 kW | 6714 kWh | 4028 kWh | 2686 kWh | £1,024 | £269 | £1,293 | £16,342 | 12.6 yrs | £9,517 |
| 8 kW | 7673 kWh | 4604 kWh | 3069 kWh | £1,171 | £307 | £1,478 | £18,376 | 12.4 yrs | £11,177 |
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: £998, 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 | 1918 kWh | 1343 kWh | 575 kWh | £341 | £58 | £399 | £7,569 | 19.0 yrs | £411 |
| 3 kW | 2877 kWh | 2014 kWh | 863 kWh | £512 | £86 | £599 | £9,604 | 16.0 yrs | £2,367 |
| 4 kW | 3836 kWh | 2686 kWh | 1151 kWh | £683 | £115 | £798 | £11,638 | 14.6 yrs | £4,322 |
| 5 kW | 4796 kWh | 3357 kWh | 1439 kWh | £854 | £144 | £998 | £13,673 | 13.7 yrs | £6,278 |
| 6 kW | 5755 kWh | 4028 kWh | 1726 kWh | £1,024 | £173 | £1,197 | £15,707 | 13.1 yrs | £8,233 |
| 7 kW | 6714 kWh | 4700 kWh | 2014 kWh | £1,195 | £201 | £1,397 | £17,742 | 12.7 yrs | £10,189 |
| 8 kW | 7673 kWh | 5371 kWh | 2302 kWh | £1,366 | £230 | £1,596 | £19,776 | 12.4 yrs | £12,145 |
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: £1,020, 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 | 1918 kWh | 1400 kWh | 518 kWh | £356 | £52 | £408 | £9,319 | 22.8 yrs | £-1,161 |
| 3 kW | 2877 kWh | 2100 kWh | 777 kWh | £534 | £78 | £612 | £11,354 | 18.6 yrs | £883 |
| 4 kW | 3836 kWh | 2801 kWh | 1036 kWh | £712 | £104 | £816 | £13,388 | 16.4 yrs | £2,927 |
| 5 kW | 4796 kWh | 3501 kWh | 1295 kWh | £890 | £129 | £1,020 | £15,423 | 15.1 yrs | £4,972 |
| 6 kW | 5755 kWh | 4201 kWh | 1554 kWh | £1,068 | £155 | £1,224 | £17,457 | 14.3 yrs | £7,016 |
| 7 kW | 6714 kWh | 4901 kWh | 1813 kWh | £1,246 | £181 | £1,428 | £19,492 | 13.7 yrs | £9,061 |
| 8 kW | 7673 kWh | 5601 kWh | 2072 kWh | £1,424 | £207 | £1,632 | £21,526 | 13.2 yrs | £11,105 |
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: £1,035, 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 | 1918 kWh | 1439 kWh | 480 kWh | £366 | £48 | £414 | £11,069 | 26.7 yrs | £-2,793 |
| 3 kW | 2877 kWh | 2158 kWh | 719 kWh | £549 | £72 | £621 | £13,104 | 21.1 yrs | £-689 |
| 4 kW | 3836 kWh | 2877 kWh | 959 kWh | £732 | £96 | £828 | £15,138 | 18.3 yrs | £1,414 |
| 5 kW | 4796 kWh | 3597 kWh | 1199 kWh | £915 | £120 | £1,035 | £17,173 | 16.6 yrs | £3,518 |
| 6 kW | 5755 kWh | 4316 kWh | 1439 kWh | £1,098 | £144 | £1,241 | £19,207 | 15.5 yrs | £5,621 |
| 7 kW | 6714 kWh | 5035 kWh | 1678 kWh | £1,280 | £168 | £1,448 | £21,242 | 14.7 yrs | £7,725 |
| 8 kW | 7673 kWh | 5755 kWh | 1918 kWh | £1,463 | £192 | £1,655 | £23,276 | 14.1 yrs | £9,829 |
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: £1,049, 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 | 1918 kWh | 1477 kWh | 441 kWh | £376 | £44 | £420 | £13,519 | 32.2 yrs | £-5,124 |
| 3 kW | 2877 kWh | 2216 kWh | 662 kWh | £563 | £66 | £630 | £15,554 | 24.7 yrs | £-2,962 |
| 4 kW | 3836 kWh | 2954 kWh | 882 kWh | £751 | £88 | £839 | £17,588 | 21.0 yrs | £-799 |
| 5 kW | 4796 kWh | 3693 kWh | 1103 kWh | £939 | £110 | £1,049 | £19,623 | 18.7 yrs | £1,364 |
| 6 kW | 5755 kWh | 4431 kWh | 1324 kWh | £1,127 | £132 | £1,259 | £21,657 | 17.2 yrs | £3,527 |
| 7 kW | 6714 kWh | 5170 kWh | 1544 kWh | £1,315 | £154 | £1,469 | £23,692 | 16.1 yrs | £5,689 |
| 8 kW | 7673 kWh | 5908 kWh | 1765 kWh | £1,502 | £176 | £1,679 | £25,726 | 15.3 yrs | £7,852 |
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.