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 902 kWh per year on a south-facing roof. We value self-used electricity at 25.8p 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: £737, Upfront: £10,173, Break-even: 13.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1804 kWh | 722 kWh | 1082 kWh | £186 | £108 | £295 | £4,069 | 13.8 yrs | £1,825 |
| 3 kW | 2706 kWh | 1082 kWh | 1624 kWh | £280 | £162 | £442 | £6,104 | 13.8 yrs | £2,738 |
| 4 kW | 3608 kWh | 1443 kWh | 2165 kWh | £373 | £216 | £589 | £8,138 | 13.8 yrs | £3,650 |
| 5 kW | 4510 kWh | 1804 kWh | 2706 kWh | £466 | £271 | £737 | £10,173 | 13.8 yrs | £4,563 |
| 6 kW | 5412 kWh | 2165 kWh | 3247 kWh | £559 | £325 | £884 | £12,207 | 13.8 yrs | £5,475 |
| 7 kW | 6314 kWh | 2526 kWh | 3788 kWh | £653 | £379 | £1,031 | £14,242 | 13.8 yrs | £6,388 |
| 8 kW | 7216 kWh | 2886 kWh | 4330 kWh | £746 | £433 | £1,179 | £16,276 | 13.8 yrs | £7,300 |
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: £880, Upfront: £12,273, Break-even: 14.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1804 kWh | 1082 kWh | 722 kWh | £280 | £72 | £352 | £6,169 | 17.5 yrs | £868 |
| 3 kW | 2706 kWh | 1624 kWh | 1082 kWh | £420 | £108 | £528 | £8,204 | 15.5 yrs | £2,352 |
| 4 kW | 3608 kWh | 2165 kWh | 1443 kWh | £559 | £144 | £704 | £10,238 | 14.5 yrs | £3,836 |
| 5 kW | 4510 kWh | 2706 kWh | 1804 kWh | £699 | £180 | £880 | £12,273 | 14.0 yrs | £5,320 |
| 6 kW | 5412 kWh | 3247 kWh | 2165 kWh | £839 | £216 | £1,056 | £14,307 | 13.6 yrs | £6,804 |
| 7 kW | 6314 kWh | 3788 kWh | 2526 kWh | £979 | £253 | £1,231 | £16,342 | 13.3 yrs | £8,288 |
| 8 kW | 7216 kWh | 4330 kWh | 2886 kWh | £1,119 | £289 | £1,407 | £18,376 | 13.1 yrs | £9,772 |
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: £951, Upfront: £13,673, Break-even: 14.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1804 kWh | 1263 kWh | 541 kWh | £326 | £54 | £380 | £7,569 | 19.9 yrs | £40 |
| 3 kW | 2706 kWh | 1894 kWh | 812 kWh | £489 | £81 | £571 | £9,604 | 16.8 yrs | £1,809 |
| 4 kW | 3608 kWh | 2526 kWh | 1082 kWh | £653 | £108 | £761 | £11,638 | 15.3 yrs | £3,579 |
| 5 kW | 4510 kWh | 3157 kWh | 1353 kWh | £816 | £135 | £951 | £13,673 | 14.4 yrs | £5,349 |
| 6 kW | 5412 kWh | 3788 kWh | 1624 kWh | £979 | £162 | £1,141 | £15,707 | 13.8 yrs | £7,119 |
| 7 kW | 6314 kWh | 4420 kWh | 1894 kWh | £1,142 | £189 | £1,331 | £17,742 | 13.3 yrs | £8,888 |
| 8 kW | 7216 kWh | 5051 kWh | 2165 kWh | £1,305 | £216 | £1,522 | £19,776 | 13.0 yrs | £10,658 |
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: £973, Upfront: £15,423, Break-even: 15.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1804 kWh | 1317 kWh | 487 kWh | £340 | £49 | £389 | £9,319 | 24.0 yrs | £-1,539 |
| 3 kW | 2706 kWh | 1975 kWh | 731 kWh | £510 | £73 | £584 | £11,354 | 19.5 yrs | £316 |
| 4 kW | 3608 kWh | 2634 kWh | 974 kWh | £681 | £97 | £778 | £13,388 | 17.2 yrs | £2,172 |
| 5 kW | 4510 kWh | 3292 kWh | 1218 kWh | £851 | £122 | £973 | £15,423 | 15.9 yrs | £4,027 |
| 6 kW | 5412 kWh | 3951 kWh | 1461 kWh | £1,021 | £146 | £1,167 | £17,457 | 15.0 yrs | £5,883 |
| 7 kW | 6314 kWh | 4609 kWh | 1705 kWh | £1,191 | £170 | £1,362 | £19,492 | 14.3 yrs | £7,738 |
| 8 kW | 7216 kWh | 5268 kWh | 1948 kWh | £1,361 | £195 | £1,556 | £21,526 | 13.8 yrs | £9,594 |
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: £987, Upfront: £17,173, Break-even: 17.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1804 kWh | 1353 kWh | 451 kWh | £350 | £45 | £395 | £11,069 | 28.0 yrs | £-3,175 |
| 3 kW | 2706 kWh | 2030 kWh | 676 kWh | £524 | £68 | £592 | £13,104 | 22.1 yrs | £-1,262 |
| 4 kW | 3608 kWh | 2706 kWh | 902 kWh | £699 | £90 | £789 | £15,138 | 19.2 yrs | £651 |
| 5 kW | 4510 kWh | 3382 kWh | 1128 kWh | £874 | £113 | £987 | £17,173 | 17.4 yrs | £2,563 |
| 6 kW | 5412 kWh | 4059 kWh | 1353 kWh | £1,049 | £135 | £1,184 | £19,207 | 16.2 yrs | £4,476 |
| 7 kW | 6314 kWh | 4736 kWh | 1578 kWh | £1,224 | £158 | £1,382 | £21,242 | 15.4 yrs | £6,388 |
| 8 kW | 7216 kWh | 5412 kWh | 1804 kWh | £1,398 | £180 | £1,579 | £23,276 | 14.7 yrs | £8,301 |
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: £1,001, Upfront: £19,623, Break-even: 19.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1804 kWh | 1389 kWh | 415 kWh | £359 | £41 | £400 | £13,519 | 33.8 yrs | £-5,510 |
| 3 kW | 2706 kWh | 2084 kWh | 622 kWh | £538 | £62 | £601 | £15,554 | 25.9 yrs | £-3,541 |
| 4 kW | 3608 kWh | 2778 kWh | 830 kWh | £718 | £83 | £801 | £17,588 | 22.0 yrs | £-1,571 |
| 5 kW | 4510 kWh | 3473 kWh | 1037 kWh | £897 | £104 | £1,001 | £19,623 | 19.6 yrs | £399 |
| 6 kW | 5412 kWh | 4167 kWh | 1245 kWh | £1,077 | £124 | £1,201 | £21,657 | 18.0 yrs | £2,369 |
| 7 kW | 6314 kWh | 4862 kWh | 1452 kWh | £1,256 | £145 | £1,402 | £23,692 | 16.9 yrs | £4,339 |
| 8 kW | 7216 kWh | 5556 kWh | 1660 kWh | £1,436 | £166 | £1,602 | £25,726 | 16.1 yrs | £6,308 |
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.