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 1033 kWh per year on a south-facing roof. We value self-used electricity at 26.5p 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: £858, Upfront: £10,173, Break-even: 11.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2066 kWh | 826 kWh | 1240 kWh | £219 | £124 | £343 | £4,069 | 11.9 yrs | £2,795 |
| 3 kW | 3099 kWh | 1240 kWh | 1859 kWh | £329 | £186 | £515 | £6,104 | 11.9 yrs | £4,193 |
| 4 kW | 4132 kWh | 1653 kWh | 2479 kWh | £438 | £248 | £686 | £8,138 | 11.9 yrs | £5,590 |
| 5 kW | 5165 kWh | 2066 kWh | 3099 kWh | £548 | £310 | £858 | £10,173 | 11.9 yrs | £6,988 |
| 6 kW | 6198 kWh | 2479 kWh | 3719 kWh | £658 | £372 | £1,030 | £12,207 | 11.9 yrs | £8,385 |
| 7 kW | 7231 kWh | 2892 kWh | 4339 kWh | £767 | £434 | £1,201 | £14,242 | 11.9 yrs | £9,783 |
| 8 kW | 8264 kWh | 3306 kWh | 4958 kWh | £877 | £496 | £1,373 | £16,276 | 11.9 yrs | £11,180 |
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: £1,029, Upfront: £12,273, Break-even: 11.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2066 kWh | 1240 kWh | 826 kWh | £329 | £83 | £412 | £6,169 | 15.0 yrs | £2,061 |
| 3 kW | 3099 kWh | 1859 kWh | 1240 kWh | £493 | £124 | £617 | £8,204 | 13.3 yrs | £4,142 |
| 4 kW | 4132 kWh | 2479 kWh | 1653 kWh | £658 | £165 | £823 | £10,238 | 12.4 yrs | £6,222 |
| 5 kW | 5165 kWh | 3099 kWh | 2066 kWh | £822 | £207 | £1,029 | £12,273 | 11.9 yrs | £8,303 |
| 6 kW | 6198 kWh | 3719 kWh | 2479 kWh | £987 | £248 | £1,235 | £14,307 | 11.6 yrs | £10,383 |
| 7 kW | 7231 kWh | 4339 kWh | 2892 kWh | £1,151 | £289 | £1,440 | £16,342 | 11.3 yrs | £12,464 |
| 8 kW | 8264 kWh | 4958 kWh | 3306 kWh | £1,315 | £331 | £1,646 | £18,376 | 11.2 yrs | £14,544 |
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: £1,114, Upfront: £13,673, Break-even: 12.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2066 kWh | 1446 kWh | 620 kWh | £384 | £62 | £446 | £7,569 | 17.0 yrs | £1,344 |
| 3 kW | 3099 kWh | 2169 kWh | 930 kWh | £576 | £93 | £668 | £9,604 | 14.4 yrs | £3,766 |
| 4 kW | 4132 kWh | 2892 kWh | 1240 kWh | £767 | £124 | £891 | £11,638 | 13.1 yrs | £6,188 |
| 5 kW | 5165 kWh | 3615 kWh | 1550 kWh | £959 | £155 | £1,114 | £13,673 | 12.3 yrs | £8,610 |
| 6 kW | 6198 kWh | 4339 kWh | 1859 kWh | £1,151 | £186 | £1,337 | £15,707 | 11.7 yrs | £11,032 |
| 7 kW | 7231 kWh | 5062 kWh | 2169 kWh | £1,343 | £217 | £1,560 | £17,742 | 11.4 yrs | £13,454 |
| 8 kW | 8264 kWh | 5785 kWh | 2479 kWh | £1,535 | £248 | £1,783 | £19,776 | 11.1 yrs | £15,876 |
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: £1,140, Upfront: £15,423, 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 | 2066 kWh | 1508 kWh | 558 kWh | £400 | £56 | £456 | £9,319 | 20.4 yrs | £-201 |
| 3 kW | 3099 kWh | 2262 kWh | 837 kWh | £600 | £84 | £684 | £11,354 | 16.6 yrs | £2,324 |
| 4 kW | 4132 kWh | 3016 kWh | 1116 kWh | £800 | £112 | £912 | £13,388 | 14.7 yrs | £4,848 |
| 5 kW | 5165 kWh | 3770 kWh | 1395 kWh | £1,000 | £139 | £1,140 | £15,423 | 13.5 yrs | £7,373 |
| 6 kW | 6198 kWh | 4525 kWh | 1673 kWh | £1,200 | £167 | £1,368 | £17,457 | 12.8 yrs | £9,897 |
| 7 kW | 7231 kWh | 5279 kWh | 1952 kWh | £1,400 | £195 | £1,596 | £19,492 | 12.2 yrs | £12,422 |
| 8 kW | 8264 kWh | 6033 kWh | 2231 kWh | £1,600 | £223 | £1,824 | £21,526 | 11.8 yrs | £14,946 |
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: £1,157, Upfront: £17,173, Break-even: 14.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2066 kWh | 1550 kWh | 516 kWh | £411 | £52 | £463 | £11,069 | 23.9 yrs | £-1,814 |
| 3 kW | 3099 kWh | 2324 kWh | 775 kWh | £617 | £77 | £694 | £13,104 | 18.9 yrs | £778 |
| 4 kW | 4132 kWh | 3099 kWh | 1033 kWh | £822 | £103 | £925 | £15,138 | 16.4 yrs | £3,371 |
| 5 kW | 5165 kWh | 3874 kWh | 1291 kWh | £1,028 | £129 | £1,157 | £17,173 | 14.8 yrs | £5,964 |
| 6 kW | 6198 kWh | 4648 kWh | 1550 kWh | £1,233 | £155 | £1,388 | £19,207 | 13.8 yrs | £8,557 |
| 7 kW | 7231 kWh | 5423 kWh | 1808 kWh | £1,439 | £181 | £1,620 | £21,242 | 13.1 yrs | £11,150 |
| 8 kW | 8264 kWh | 6198 kWh | 2066 kWh | £1,644 | £207 | £1,851 | £23,276 | 12.6 yrs | £13,743 |
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: £1,174, Upfront: £19,623, Break-even: 16.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2066 kWh | 1591 kWh | 475 kWh | £422 | £48 | £470 | £13,519 | 28.8 yrs | £-4,128 |
| 3 kW | 3099 kWh | 2386 kWh | 713 kWh | £633 | £71 | £704 | £15,554 | 22.1 yrs | £-1,467 |
| 4 kW | 4132 kWh | 3182 kWh | 950 kWh | £844 | £95 | £939 | £17,588 | 18.7 yrs | £1,194 |
| 5 kW | 5165 kWh | 3977 kWh | 1188 kWh | £1,055 | £119 | £1,174 | £19,623 | 16.7 yrs | £3,856 |
| 6 kW | 6198 kWh | 4772 kWh | 1426 kWh | £1,266 | £143 | £1,409 | £21,657 | 15.4 yrs | £6,517 |
| 7 kW | 7231 kWh | 5568 kWh | 1663 kWh | £1,477 | £166 | £1,643 | £23,692 | 14.4 yrs | £9,178 |
| 8 kW | 8264 kWh | 6363 kWh | 1901 kWh | £1,688 | £190 | £1,878 | £25,726 | 13.7 yrs | £11,839 |
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.