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 954 kWh per year on a south-facing roof. We value self-used electricity at 25.6p 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 | 1909 kWh | 764 kWh | 1145 kWh | £196 | £115 | £310 | £4,069 | 13.1 yrs | £2,137 |
| 3 kW | 2863 kWh | 1145 kWh | 1718 kWh | £294 | £172 | £465 | £6,104 | 13.1 yrs | £3,206 |
| 4 kW | 3818 kWh | 1527 kWh | 2291 kWh | £392 | £229 | £621 | £8,138 | 13.1 yrs | £4,275 |
| 5 kW | 4772 kWh | 1909 kWh | 2863 kWh | £489 | £286 | £776 | £10,173 | 13.1 yrs | £5,343 |
| 6 kW | 5727 kWh | 2291 kWh | 3436 kWh | £587 | £344 | £931 | £12,207 | 13.1 yrs | £6,412 |
| 7 kW | 6681 kWh | 2673 kWh | 4009 kWh | £685 | £401 | £1,086 | £14,242 | 13.1 yrs | £7,481 |
| 8 kW | 7636 kWh | 3054 kWh | 4582 kWh | £783 | £458 | £1,241 | £16,276 | 13.1 yrs | £8,550 |
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 | 1909 kWh | 1145 kWh | 764 kWh | £294 | £76 | £370 | £6,169 | 16.7 yrs | £1,232 |
| 3 kW | 2863 kWh | 1718 kWh | 1145 kWh | £441 | £115 | £555 | £8,204 | 14.8 yrs | £2,897 |
| 4 kW | 3818 kWh | 2291 kWh | 1527 kWh | £587 | £153 | £740 | £10,238 | 13.8 yrs | £4,563 |
| 5 kW | 4772 kWh | 2863 kWh | 1909 kWh | £734 | £191 | £925 | £12,273 | 13.3 yrs | £6,229 |
| 6 kW | 5727 kWh | 3436 kWh | 2291 kWh | £881 | £229 | £1,110 | £14,307 | 12.9 yrs | £7,895 |
| 7 kW | 6681 kWh | 4009 kWh | 2673 kWh | £1,028 | £267 | £1,295 | £16,342 | 12.6 yrs | £9,561 |
| 8 kW | 7636 kWh | 4582 kWh | 3054 kWh | £1,175 | £305 | £1,480 | £18,376 | 12.4 yrs | £11,227 |
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: £1,000, 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 | 1909 kWh | 1336 kWh | 573 kWh | £343 | £57 | £400 | £7,569 | 18.9 yrs | £429 |
| 3 kW | 2863 kWh | 2004 kWh | 859 kWh | £514 | £86 | £600 | £9,604 | 16.0 yrs | £2,393 |
| 4 kW | 3818 kWh | 2673 kWh | 1145 kWh | £685 | £115 | £800 | £11,638 | 14.6 yrs | £4,358 |
| 5 kW | 4772 kWh | 3341 kWh | 1432 kWh | £857 | £143 | £1,000 | £13,673 | 13.7 yrs | £6,322 |
| 6 kW | 5727 kWh | 4009 kWh | 1718 kWh | £1,028 | £172 | £1,200 | £15,707 | 13.1 yrs | £8,286 |
| 7 kW | 6681 kWh | 4677 kWh | 2004 kWh | £1,199 | £200 | £1,400 | £17,742 | 12.7 yrs | £10,251 |
| 8 kW | 7636 kWh | 5345 kWh | 2291 kWh | £1,370 | £229 | £1,600 | £19,776 | 12.4 yrs | £12,215 |
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: £1,022, 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 | 1909 kWh | 1394 kWh | 515 kWh | £357 | £52 | £409 | £9,319 | 22.8 yrs | £-1,142 |
| 3 kW | 2863 kWh | 2090 kWh | 773 kWh | £536 | £77 | £613 | £11,354 | 18.5 yrs | £912 |
| 4 kW | 3818 kWh | 2787 kWh | 1031 kWh | £715 | £103 | £818 | £13,388 | 16.4 yrs | £2,966 |
| 5 kW | 4772 kWh | 3484 kWh | 1289 kWh | £893 | £129 | £1,022 | £15,423 | 15.1 yrs | £5,020 |
| 6 kW | 5727 kWh | 4181 kWh | 1546 kWh | £1,072 | £155 | £1,227 | £17,457 | 14.2 yrs | £7,074 |
| 7 kW | 6681 kWh | 4877 kWh | 1804 kWh | £1,251 | £180 | £1,431 | £19,492 | 13.6 yrs | £9,128 |
| 8 kW | 7636 kWh | 5574 kWh | 2062 kWh | £1,429 | £206 | £1,635 | £21,526 | 13.2 yrs | £11,182 |
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: £1,037, 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 | 1909 kWh | 1432 kWh | 477 kWh | £367 | £48 | £415 | £11,069 | 26.7 yrs | £-2,773 |
| 3 kW | 2863 kWh | 2148 kWh | 716 kWh | £551 | £72 | £622 | £13,104 | 21.1 yrs | £-659 |
| 4 kW | 3818 kWh | 2863 kWh | 954 kWh | £734 | £95 | £830 | £15,138 | 18.2 yrs | £1,455 |
| 5 kW | 4772 kWh | 3579 kWh | 1193 kWh | £918 | £119 | £1,037 | £17,173 | 16.6 yrs | £3,568 |
| 6 kW | 5727 kWh | 4295 kWh | 1432 kWh | £1,101 | £143 | £1,244 | £19,207 | 15.4 yrs | £5,682 |
| 7 kW | 6681 kWh | 5011 kWh | 1670 kWh | £1,285 | £167 | £1,452 | £21,242 | 14.6 yrs | £7,796 |
| 8 kW | 7636 kWh | 5727 kWh | 1909 kWh | £1,468 | £191 | £1,659 | £23,276 | 14.0 yrs | £9,909 |
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: £1,052, 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 | 1909 kWh | 1470 kWh | 439 kWh | £377 | £44 | £421 | £13,519 | 32.1 yrs | £-5,103 |
| 3 kW | 2863 kWh | 2205 kWh | 659 kWh | £565 | £66 | £631 | £15,554 | 24.6 yrs | £-2,930 |
| 4 kW | 3818 kWh | 2940 kWh | 878 kWh | £754 | £88 | £842 | £17,588 | 20.9 yrs | £-757 |
| 5 kW | 4772 kWh | 3675 kWh | 1098 kWh | £942 | £110 | £1,052 | £19,623 | 18.7 yrs | £1,417 |
| 6 kW | 5727 kWh | 4410 kWh | 1317 kWh | £1,131 | £132 | £1,262 | £21,657 | 17.2 yrs | £3,590 |
| 7 kW | 6681 kWh | 5145 kWh | 1537 kWh | £1,319 | £154 | £1,473 | £23,692 | 16.1 yrs | £5,764 |
| 8 kW | 7636 kWh | 5880 kWh | 1756 kWh | £1,508 | £176 | £1,683 | £25,726 | 15.3 yrs | £7,937 |
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.