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 1001 kWh per year on a south-facing roof. We value self-used electricity at 26.5p 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: £832, Upfront: £10,173, Break-even: 12.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2003 kWh | 801 kWh | 1202 kWh | £213 | £120 | £333 | £4,069 | 12.2 yrs | £2,585 |
| 3 kW | 3004 kWh | 1202 kWh | 1802 kWh | £319 | £180 | £499 | £6,104 | 12.2 yrs | £3,877 |
| 4 kW | 4005 kWh | 1602 kWh | 2403 kWh | £425 | £240 | £665 | £8,138 | 12.2 yrs | £5,169 |
| 5 kW | 5007 kWh | 2003 kWh | 3004 kWh | £531 | £300 | £832 | £10,173 | 12.2 yrs | £6,462 |
| 6 kW | 6008 kWh | 2403 kWh | 3605 kWh | £638 | £360 | £998 | £12,207 | 12.2 yrs | £7,754 |
| 7 kW | 7009 kWh | 2804 kWh | 4206 kWh | £744 | £421 | £1,164 | £14,242 | 12.2 yrs | £9,046 |
| 8 kW | 8011 kWh | 3204 kWh | 4806 kWh | £850 | £481 | £1,331 | £16,276 | 12.2 yrs | £10,339 |
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: £997, Upfront: £12,273, Break-even: 12.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2003 kWh | 1202 kWh | 801 kWh | £319 | £80 | £399 | £6,169 | 15.5 yrs | £1,809 |
| 3 kW | 3004 kWh | 1802 kWh | 1202 kWh | £478 | £120 | £598 | £8,204 | 13.7 yrs | £3,763 |
| 4 kW | 4005 kWh | 2403 kWh | 1602 kWh | £638 | £160 | £798 | £10,238 | 12.8 yrs | £5,718 |
| 5 kW | 5007 kWh | 3004 kWh | 2003 kWh | £797 | £200 | £997 | £12,273 | 12.3 yrs | £7,672 |
| 6 kW | 6008 kWh | 3605 kWh | 2403 kWh | £956 | £240 | £1,197 | £14,307 | 12.0 yrs | £9,627 |
| 7 kW | 7009 kWh | 4206 kWh | 2804 kWh | £1,116 | £280 | £1,396 | £16,342 | 11.7 yrs | £11,581 |
| 8 kW | 8011 kWh | 4806 kWh | 3204 kWh | £1,275 | £320 | £1,596 | £18,376 | 11.5 yrs | £13,535 |
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: £1,080, Upfront: £13,673, Break-even: 12.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2003 kWh | 1402 kWh | 601 kWh | £372 | £60 | £432 | £7,569 | 17.5 yrs | £1,071 |
| 3 kW | 3004 kWh | 2103 kWh | 901 kWh | £558 | £90 | £648 | £9,604 | 14.8 yrs | £3,356 |
| 4 kW | 4005 kWh | 2804 kWh | 1202 kWh | £744 | £120 | £864 | £11,638 | 13.5 yrs | £5,642 |
| 5 kW | 5007 kWh | 3505 kWh | 1502 kWh | £930 | £150 | £1,080 | £13,673 | 12.7 yrs | £7,927 |
| 6 kW | 6008 kWh | 4206 kWh | 1802 kWh | £1,116 | £180 | £1,296 | £15,707 | 12.1 yrs | £10,213 |
| 7 kW | 7009 kWh | 4907 kWh | 2103 kWh | £1,302 | £210 | £1,512 | £17,742 | 11.7 yrs | £12,498 |
| 8 kW | 8011 kWh | 5608 kWh | 2403 kWh | £1,488 | £240 | £1,728 | £19,776 | 11.4 yrs | £14,784 |
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: £1,105, Upfront: £15,423, 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 | 2003 kWh | 1462 kWh | 541 kWh | £388 | £54 | £442 | £9,319 | 21.1 yrs | £-480 |
| 3 kW | 3004 kWh | 2193 kWh | 811 kWh | £582 | £81 | £663 | £11,354 | 17.1 yrs | £1,904 |
| 4 kW | 4005 kWh | 2924 kWh | 1081 kWh | £776 | £108 | £884 | £13,388 | 15.1 yrs | £4,289 |
| 5 kW | 5007 kWh | 3655 kWh | 1352 kWh | £970 | £135 | £1,105 | £15,423 | 14.0 yrs | £6,674 |
| 6 kW | 6008 kWh | 4386 kWh | 1622 kWh | £1,164 | £162 | £1,326 | £17,457 | 13.2 yrs | £9,059 |
| 7 kW | 7009 kWh | 5117 kWh | 1893 kWh | £1,357 | £189 | £1,547 | £19,492 | 12.6 yrs | £11,443 |
| 8 kW | 8011 kWh | 5848 kWh | 2163 kWh | £1,551 | £216 | £1,768 | £21,526 | 12.2 yrs | £13,828 |
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: £1,121, Upfront: £17,173, Break-even: 15.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2003 kWh | 1502 kWh | 501 kWh | £398 | £50 | £449 | £11,069 | 24.7 yrs | £-2,098 |
| 3 kW | 3004 kWh | 2253 kWh | 751 kWh | £598 | £75 | £673 | £13,104 | 19.5 yrs | £353 |
| 4 kW | 4005 kWh | 3004 kWh | 1001 kWh | £797 | £100 | £897 | £15,138 | 16.9 yrs | £2,804 |
| 5 kW | 5007 kWh | 3755 kWh | 1252 kWh | £996 | £125 | £1,121 | £17,173 | 15.3 yrs | £5,255 |
| 6 kW | 6008 kWh | 4506 kWh | 1502 kWh | £1,195 | £150 | £1,346 | £19,207 | 14.3 yrs | £7,706 |
| 7 kW | 7009 kWh | 5257 kWh | 1752 kWh | £1,395 | £175 | £1,570 | £21,242 | 13.5 yrs | £10,157 |
| 8 kW | 8011 kWh | 6008 kWh | 2003 kWh | £1,594 | £200 | £1,794 | £23,276 | 13.0 yrs | £12,608 |
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: £1,138, Upfront: £19,623, Break-even: 17.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2003 kWh | 1542 kWh | 461 kWh | £409 | £46 | £455 | £13,519 | 29.7 yrs | £-4,416 |
| 3 kW | 3004 kWh | 2313 kWh | 691 kWh | £614 | £69 | £683 | £15,554 | 22.8 yrs | £-1,898 |
| 4 kW | 4005 kWh | 3084 kWh | 921 kWh | £818 | £92 | £910 | £17,588 | 19.3 yrs | £619 |
| 5 kW | 5007 kWh | 3855 kWh | 1152 kWh | £1,023 | £115 | £1,138 | £19,623 | 17.2 yrs | £3,136 |
| 6 kW | 6008 kWh | 4626 kWh | 1382 kWh | £1,227 | £138 | £1,366 | £21,657 | 15.9 yrs | £5,653 |
| 7 kW | 7009 kWh | 5397 kWh | 1612 kWh | £1,432 | £161 | £1,593 | £23,692 | 14.9 yrs | £8,170 |
| 8 kW | 8011 kWh | 6168 kWh | 1842 kWh | £1,636 | £184 | £1,821 | £25,726 | 14.1 yrs | £10,688 |
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.