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 953 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: £773, Upfront: £10,173, Break-even: 13.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1906 kWh | 763 kWh | 1144 kWh | £195 | £114 | £309 | £4,069 | 13.2 yrs | £2,115 |
| 3 kW | 2859 kWh | 1144 kWh | 1716 kWh | £292 | £172 | £464 | £6,104 | 13.2 yrs | £3,173 |
| 4 kW | 3813 kWh | 1525 kWh | 2288 kWh | £390 | £229 | £618 | £8,138 | 13.2 yrs | £4,230 |
| 5 kW | 4766 kWh | 1906 kWh | 2859 kWh | £487 | £286 | £773 | £10,173 | 13.2 yrs | £5,288 |
| 6 kW | 5719 kWh | 2288 kWh | 3431 kWh | £584 | £343 | £928 | £12,207 | 13.2 yrs | £6,345 |
| 7 kW | 6672 kWh | 2669 kWh | 4003 kWh | £682 | £400 | £1,082 | £14,242 | 13.2 yrs | £7,403 |
| 8 kW | 7625 kWh | 3050 kWh | 4575 kWh | £779 | £458 | £1,237 | £16,276 | 13.2 yrs | £8,460 |
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: £921, 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 | 1906 kWh | 1144 kWh | 763 kWh | £292 | £76 | £368 | £6,169 | 16.7 yrs | £1,201 |
| 3 kW | 2859 kWh | 1716 kWh | 1144 kWh | £438 | £114 | £553 | £8,204 | 14.8 yrs | £2,851 |
| 4 kW | 3813 kWh | 2288 kWh | 1525 kWh | £584 | £153 | £737 | £10,238 | 13.9 yrs | £4,502 |
| 5 kW | 4766 kWh | 2859 kWh | 1906 kWh | £731 | £191 | £921 | £12,273 | 13.3 yrs | £6,152 |
| 6 kW | 5719 kWh | 3431 kWh | 2288 kWh | £877 | £229 | £1,105 | £14,307 | 12.9 yrs | £7,802 |
| 7 kW | 6672 kWh | 4003 kWh | 2669 kWh | £1,023 | £267 | £1,290 | £16,342 | 12.7 yrs | £9,453 |
| 8 kW | 7625 kWh | 4575 kWh | 3050 kWh | £1,169 | £305 | £1,474 | £18,376 | 12.5 yrs | £11,103 |
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: £995, 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 | 1906 kWh | 1334 kWh | 572 kWh | £341 | £57 | £398 | £7,569 | 19.0 yrs | £394 |
| 3 kW | 2859 kWh | 2002 kWh | 858 kWh | £511 | £86 | £597 | £9,604 | 16.1 yrs | £2,341 |
| 4 kW | 3813 kWh | 2669 kWh | 1144 kWh | £682 | £114 | £796 | £11,638 | 14.6 yrs | £4,287 |
| 5 kW | 4766 kWh | 3336 kWh | 1430 kWh | £852 | £143 | £995 | £13,673 | 13.7 yrs | £6,234 |
| 6 kW | 5719 kWh | 4003 kWh | 1716 kWh | £1,023 | £172 | £1,194 | £15,707 | 13.2 yrs | £8,181 |
| 7 kW | 6672 kWh | 4670 kWh | 2002 kWh | £1,193 | £200 | £1,393 | £17,742 | 12.7 yrs | £10,128 |
| 8 kW | 7625 kWh | 5338 kWh | 2288 kWh | £1,364 | £229 | £1,593 | £19,776 | 12.4 yrs | £12,075 |
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: £1,018, Upfront: £15,423, Break-even: 15.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1906 kWh | 1392 kWh | 515 kWh | £356 | £51 | £407 | £9,319 | 22.9 yrs | £-1,178 |
| 3 kW | 2859 kWh | 2087 kWh | 772 kWh | £533 | £77 | £611 | £11,354 | 18.6 yrs | £857 |
| 4 kW | 3813 kWh | 2783 kWh | 1029 kWh | £711 | £103 | £814 | £13,388 | 16.4 yrs | £2,893 |
| 5 kW | 4766 kWh | 3479 kWh | 1287 kWh | £889 | £129 | £1,018 | £15,423 | 15.2 yrs | £4,929 |
| 6 kW | 5719 kWh | 4175 kWh | 1544 kWh | £1,067 | £154 | £1,221 | £17,457 | 14.3 yrs | £6,965 |
| 7 kW | 6672 kWh | 4871 kWh | 1801 kWh | £1,244 | £180 | £1,425 | £19,492 | 13.7 yrs | £9,000 |
| 8 kW | 7625 kWh | 5566 kWh | 2059 kWh | £1,422 | £206 | £1,628 | £21,526 | 13.2 yrs | £11,036 |
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: £1,032, 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 | 1906 kWh | 1430 kWh | 477 kWh | £365 | £48 | £413 | £11,069 | 26.8 yrs | £-2,810 |
| 3 kW | 2859 kWh | 2145 kWh | 715 kWh | £548 | £71 | £619 | £13,104 | 21.2 yrs | £-715 |
| 4 kW | 3813 kWh | 2859 kWh | 953 kWh | £731 | £95 | £826 | £15,138 | 18.3 yrs | £1,380 |
| 5 kW | 4766 kWh | 3574 kWh | 1191 kWh | £913 | £119 | £1,032 | £17,173 | 16.6 yrs | £3,475 |
| 6 kW | 5719 kWh | 4289 kWh | 1430 kWh | £1,096 | £143 | £1,239 | £19,207 | 15.5 yrs | £5,570 |
| 7 kW | 6672 kWh | 5004 kWh | 1668 kWh | £1,279 | £167 | £1,445 | £21,242 | 14.7 yrs | £7,665 |
| 8 kW | 7625 kWh | 5719 kWh | 1906 kWh | £1,461 | £191 | £1,652 | £23,276 | 14.1 yrs | £9,760 |
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: £1,047, 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 | 1906 kWh | 1468 kWh | 438 kWh | £375 | £44 | £419 | £13,519 | 32.3 yrs | £-5,141 |
| 3 kW | 2859 kWh | 2202 kWh | 658 kWh | £563 | £66 | £628 | £15,554 | 24.8 yrs | £-2,987 |
| 4 kW | 3813 kWh | 2936 kWh | 877 kWh | £750 | £88 | £838 | £17,588 | 21.0 yrs | £-833 |
| 5 kW | 4766 kWh | 3670 kWh | 1096 kWh | £938 | £110 | £1,047 | £19,623 | 18.7 yrs | £1,322 |
| 6 kW | 5719 kWh | 4404 kWh | 1315 kWh | £1,125 | £132 | £1,257 | £21,657 | 17.2 yrs | £3,476 |
| 7 kW | 6672 kWh | 5138 kWh | 1535 kWh | £1,313 | £153 | £1,466 | £23,692 | 16.2 yrs | £5,630 |
| 8 kW | 7625 kWh | 5871 kWh | 1754 kWh | £1,500 | £175 | £1,676 | £25,726 | 15.4 yrs | £7,785 |
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.