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 883 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: £721, Upfront: £10,173, Break-even: 14.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1765 kWh | 706 kWh | 1059 kWh | £182 | £106 | £288 | £4,069 | 14.1 yrs | £1,699 |
| 3 kW | 2648 kWh | 1059 kWh | 1589 kWh | £274 | £159 | £433 | £6,104 | 14.1 yrs | £2,549 |
| 4 kW | 3531 kWh | 1412 kWh | 2119 kWh | £365 | £212 | £577 | £8,138 | 14.1 yrs | £3,398 |
| 5 kW | 4414 kWh | 1765 kWh | 2648 kWh | £456 | £265 | £721 | £10,173 | 14.1 yrs | £4,248 |
| 6 kW | 5296 kWh | 2119 kWh | 3178 kWh | £547 | £318 | £865 | £12,207 | 14.1 yrs | £5,097 |
| 7 kW | 6179 kWh | 2472 kWh | 3707 kWh | £639 | £371 | £1,009 | £14,242 | 14.1 yrs | £5,947 |
| 8 kW | 7062 kWh | 2825 kWh | 4237 kWh | £730 | £424 | £1,154 | £16,276 | 14.1 yrs | £6,796 |
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: £861, Upfront: £12,273, Break-even: 14.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1765 kWh | 1059 kWh | 706 kWh | £274 | £71 | £344 | £6,169 | 17.9 yrs | £718 |
| 3 kW | 2648 kWh | 1589 kWh | 1059 kWh | £411 | £106 | £517 | £8,204 | 15.9 yrs | £2,127 |
| 4 kW | 3531 kWh | 2119 kWh | 1412 kWh | £547 | £141 | £689 | £10,238 | 14.9 yrs | £3,535 |
| 5 kW | 4414 kWh | 2648 kWh | 1765 kWh | £684 | £177 | £861 | £12,273 | 14.3 yrs | £4,944 |
| 6 kW | 5296 kWh | 3178 kWh | 2119 kWh | £821 | £212 | £1,033 | £14,307 | 13.8 yrs | £6,353 |
| 7 kW | 6179 kWh | 3707 kWh | 2472 kWh | £958 | £247 | £1,205 | £16,342 | 13.6 yrs | £7,762 |
| 8 kW | 7062 kWh | 4237 kWh | 2825 kWh | £1,095 | £282 | £1,377 | £18,376 | 13.3 yrs | £9,171 |
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: £931, Upfront: £13,673, Break-even: 14.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1765 kWh | 1236 kWh | 530 kWh | £319 | £53 | £372 | £7,569 | 20.3 yrs | £-123 |
| 3 kW | 2648 kWh | 1854 kWh | 794 kWh | £479 | £79 | £558 | £9,604 | 17.2 yrs | £1,565 |
| 4 kW | 3531 kWh | 2472 kWh | 1059 kWh | £639 | £106 | £745 | £11,638 | 15.6 yrs | £3,254 |
| 5 kW | 4414 kWh | 3090 kWh | 1324 kWh | £798 | £132 | £931 | £13,673 | 14.7 yrs | £4,942 |
| 6 kW | 5296 kWh | 3707 kWh | 1589 kWh | £958 | £159 | £1,117 | £15,707 | 14.1 yrs | £6,631 |
| 7 kW | 6179 kWh | 4325 kWh | 1854 kWh | £1,118 | £185 | £1,303 | £17,742 | 13.6 yrs | £8,319 |
| 8 kW | 7062 kWh | 4943 kWh | 2119 kWh | £1,277 | £212 | £1,489 | £19,776 | 13.3 yrs | £10,008 |
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: £952, Upfront: £15,423, Break-even: 16.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1765 kWh | 1289 kWh | 477 kWh | £333 | £48 | £381 | £9,319 | 24.5 yrs | £-1,705 |
| 3 kW | 2648 kWh | 1933 kWh | 715 kWh | £500 | £72 | £571 | £11,354 | 19.9 yrs | £67 |
| 4 kW | 3531 kWh | 2578 kWh | 953 kWh | £666 | £95 | £761 | £13,388 | 17.6 yrs | £1,840 |
| 5 kW | 4414 kWh | 3222 kWh | 1192 kWh | £833 | £119 | £952 | £15,423 | 16.2 yrs | £3,612 |
| 6 kW | 5296 kWh | 3866 kWh | 1430 kWh | £999 | £143 | £1,142 | £17,457 | 15.3 yrs | £5,384 |
| 7 kW | 6179 kWh | 4511 kWh | 1668 kWh | £1,166 | £167 | £1,332 | £19,492 | 14.6 yrs | £7,157 |
| 8 kW | 7062 kWh | 5155 kWh | 1907 kWh | £1,332 | £191 | £1,523 | £21,526 | 14.1 yrs | £8,929 |
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: £966, Upfront: £17,173, Break-even: 17.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1765 kWh | 1324 kWh | 441 kWh | £342 | £44 | £386 | £11,069 | 28.7 yrs | £-3,343 |
| 3 kW | 2648 kWh | 1986 kWh | 662 kWh | £513 | £66 | £579 | £13,104 | 22.6 yrs | £-1,515 |
| 4 kW | 3531 kWh | 2648 kWh | 883 kWh | £684 | £88 | £773 | £15,138 | 19.6 yrs | £313 |
| 5 kW | 4414 kWh | 3310 kWh | 1103 kWh | £855 | £110 | £966 | £17,173 | 17.8 yrs | £2,142 |
| 6 kW | 5296 kWh | 3972 kWh | 1324 kWh | £1,026 | £132 | £1,159 | £19,207 | 16.6 yrs | £3,970 |
| 7 kW | 6179 kWh | 4634 kWh | 1545 kWh | £1,198 | £154 | £1,352 | £21,242 | 15.7 yrs | £5,798 |
| 8 kW | 7062 kWh | 5296 kWh | 1765 kWh | £1,369 | £177 | £1,545 | £23,276 | 15.1 yrs | £7,627 |
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: £980, Upfront: £19,623, Break-even: 20.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1765 kWh | 1359 kWh | 406 kWh | £351 | £41 | £392 | £13,519 | 34.5 yrs | £-5,682 |
| 3 kW | 2648 kWh | 2039 kWh | 609 kWh | £527 | £61 | £588 | £15,554 | 26.5 yrs | £-3,797 |
| 4 kW | 3531 kWh | 2719 kWh | 812 kWh | £703 | £81 | £784 | £17,588 | 22.4 yrs | £-1,913 |
| 5 kW | 4414 kWh | 3399 kWh | 1015 kWh | £878 | £102 | £980 | £19,623 | 20.0 yrs | £-29 |
| 6 kW | 5296 kWh | 4078 kWh | 1218 kWh | £1,054 | £122 | £1,176 | £21,657 | 18.4 yrs | £1,855 |
| 7 kW | 6179 kWh | 4758 kWh | 1421 kWh | £1,229 | £142 | £1,372 | £23,692 | 17.3 yrs | £3,740 |
| 8 kW | 7062 kWh | 5438 kWh | 1624 kWh | £1,405 | £162 | £1,568 | £25,726 | 16.4 yrs | £5,624 |
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.