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 1091 kWh per year on a south-facing roof. We value self-used electricity at 26.9p 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: £915, Upfront: £10,173, Break-even: 11.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2182 kWh | 873 kWh | 1309 kWh | £235 | £131 | £366 | £4,069 | 11.1 yrs | £3,248 |
| 3 kW | 3273 kWh | 1309 kWh | 1964 kWh | £352 | £196 | £549 | £6,104 | 11.1 yrs | £4,872 |
| 4 kW | 4364 kWh | 1746 kWh | 2618 kWh | £470 | £262 | £732 | £8,138 | 11.1 yrs | £6,496 |
| 5 kW | 5455 kWh | 2182 kWh | 3273 kWh | £587 | £327 | £915 | £10,173 | 11.1 yrs | £8,120 |
| 6 kW | 6546 kWh | 2618 kWh | 3927 kWh | £705 | £393 | £1,098 | £12,207 | 11.1 yrs | £9,745 |
| 7 kW | 7637 kWh | 3055 kWh | 4582 kWh | £822 | £458 | £1,281 | £14,242 | 11.1 yrs | £11,369 |
| 8 kW | 8728 kWh | 3491 kWh | 5237 kWh | £940 | £524 | £1,463 | £16,276 | 11.1 yrs | £12,993 |
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: £1,099, Upfront: £12,273, Break-even: 11.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2182 kWh | 1309 kWh | 873 kWh | £352 | £87 | £440 | £6,169 | 14.0 yrs | £2,625 |
| 3 kW | 3273 kWh | 1964 kWh | 1309 kWh | £529 | £131 | £660 | £8,204 | 12.4 yrs | £4,987 |
| 4 kW | 4364 kWh | 2618 kWh | 1746 kWh | £705 | £175 | £879 | £10,238 | 11.6 yrs | £7,350 |
| 5 kW | 5455 kWh | 3273 kWh | 2182 kWh | £881 | £218 | £1,099 | £12,273 | 11.2 yrs | £9,712 |
| 6 kW | 6546 kWh | 3927 kWh | 2618 kWh | £1,057 | £262 | £1,319 | £14,307 | 10.8 yrs | £12,075 |
| 7 kW | 7637 kWh | 4582 kWh | 3055 kWh | £1,233 | £305 | £1,539 | £16,342 | 10.6 yrs | £14,437 |
| 8 kW | 8728 kWh | 5237 kWh | 3491 kWh | £1,410 | £349 | £1,759 | £18,376 | 10.4 yrs | £16,800 |
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: £1,192, Upfront: £13,673, Break-even: 11.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2182 kWh | 1527 kWh | 655 kWh | £411 | £65 | £477 | £7,569 | 15.9 yrs | £1,963 |
| 3 kW | 3273 kWh | 2291 kWh | 982 kWh | £617 | £98 | £715 | £9,604 | 13.4 yrs | £4,695 |
| 4 kW | 4364 kWh | 3055 kWh | 1309 kWh | £822 | £131 | £953 | £11,638 | 12.2 yrs | £7,427 |
| 5 kW | 5455 kWh | 3818 kWh | 1636 kWh | £1,028 | £164 | £1,192 | £13,673 | 11.5 yrs | £10,158 |
| 6 kW | 6546 kWh | 4582 kWh | 1964 kWh | £1,233 | £196 | £1,430 | £15,707 | 11.0 yrs | £12,890 |
| 7 kW | 7637 kWh | 5346 kWh | 2291 kWh | £1,439 | £229 | £1,668 | £17,742 | 10.6 yrs | £15,621 |
| 8 kW | 8728 kWh | 6109 kWh | 2618 kWh | £1,645 | £262 | £1,906 | £19,776 | 10.4 yrs | £18,353 |
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: £1,219, Upfront: £15,423, Break-even: 12.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2182 kWh | 1593 kWh | 589 kWh | £429 | £59 | £488 | £9,319 | 19.1 yrs | £435 |
| 3 kW | 3273 kWh | 2389 kWh | 884 kWh | £643 | £88 | £732 | £11,354 | 15.5 yrs | £3,277 |
| 4 kW | 4364 kWh | 3186 kWh | 1178 kWh | £858 | £118 | £975 | £13,388 | 13.7 yrs | £6,120 |
| 5 kW | 5455 kWh | 3982 kWh | 1473 kWh | £1,072 | £147 | £1,219 | £15,423 | 12.6 yrs | £8,962 |
| 6 kW | 6546 kWh | 4778 kWh | 1767 kWh | £1,286 | £177 | £1,463 | £17,457 | 11.9 yrs | £11,804 |
| 7 kW | 7637 kWh | 5575 kWh | 2062 kWh | £1,501 | £206 | £1,707 | £19,492 | 11.4 yrs | £14,647 |
| 8 kW | 8728 kWh | 6371 kWh | 2356 kWh | £1,715 | £236 | £1,951 | £21,526 | 11.0 yrs | £17,489 |
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: £1,238, Upfront: £17,173, Break-even: 13.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2182 kWh | 1636 kWh | 545 kWh | £441 | £55 | £495 | £11,069 | 22.4 yrs | £-1,168 |
| 3 kW | 3273 kWh | 2455 kWh | 818 kWh | £661 | £82 | £743 | £13,104 | 17.6 yrs | £1,749 |
| 4 kW | 4364 kWh | 3273 kWh | 1091 kWh | £881 | £109 | £990 | £15,138 | 15.3 yrs | £4,665 |
| 5 kW | 5455 kWh | 4091 kWh | 1364 kWh | £1,101 | £136 | £1,238 | £17,173 | 13.9 yrs | £7,581 |
| 6 kW | 6546 kWh | 4909 kWh | 1636 kWh | £1,322 | £164 | £1,485 | £19,207 | 12.9 yrs | £10,497 |
| 7 kW | 7637 kWh | 5727 kWh | 1909 kWh | £1,542 | £191 | £1,733 | £21,242 | 12.3 yrs | £13,414 |
| 8 kW | 8728 kWh | 6546 kWh | 2182 kWh | £1,762 | £218 | £1,980 | £23,276 | 11.8 yrs | £16,330 |
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: £1,256, Upfront: £19,623, 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 | 2182 kWh | 1680 kWh | 502 kWh | £452 | £50 | £502 | £13,519 | 26.9 yrs | £-3,470 |
| 3 kW | 3273 kWh | 2520 kWh | 753 kWh | £678 | £75 | £754 | £15,554 | 20.6 yrs | £-480 |
| 4 kW | 4364 kWh | 3360 kWh | 1004 kWh | £905 | £100 | £1,005 | £17,588 | 17.5 yrs | £2,510 |
| 5 kW | 5455 kWh | 4200 kWh | 1255 kWh | £1,131 | £125 | £1,256 | £19,623 | 15.6 yrs | £5,500 |
| 6 kW | 6546 kWh | 5040 kWh | 1506 kWh | £1,357 | £151 | £1,507 | £21,657 | 14.4 yrs | £8,490 |
| 7 kW | 7637 kWh | 5880 kWh | 1756 kWh | £1,583 | £176 | £1,759 | £23,692 | 13.5 yrs | £11,480 |
| 8 kW | 8728 kWh | 6720 kWh | 2007 kWh | £1,809 | £201 | £2,010 | £25,726 | 12.8 yrs | £14,470 |
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.