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: £831, 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 | 2002 kWh | 801 kWh | 1201 kWh | £212 | £120 | £333 | £4,069 | 12.2 yrs | £2,583 |
| 3 kW | 3003 kWh | 1201 kWh | 1802 kWh | £319 | £180 | £499 | £6,104 | 12.2 yrs | £3,874 |
| 4 kW | 4004 kWh | 1602 kWh | 2403 kWh | £425 | £240 | £665 | £8,138 | 12.2 yrs | £5,166 |
| 5 kW | 5005 kWh | 2002 kWh | 3003 kWh | £531 | £300 | £831 | £10,173 | 12.2 yrs | £6,457 |
| 6 kW | 6006 kWh | 2403 kWh | 3604 kWh | £637 | £360 | £998 | £12,207 | 12.2 yrs | £7,748 |
| 7 kW | 7007 kWh | 2803 kWh | 4204 kWh | £744 | £420 | £1,164 | £14,242 | 12.2 yrs | £9,040 |
| 8 kW | 8008 kWh | 3203 kWh | 4805 kWh | £850 | £481 | £1,330 | £16,276 | 12.2 yrs | £10,331 |
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 | 2002 kWh | 1201 kWh | 801 kWh | £319 | £80 | £399 | £6,169 | 15.5 yrs | £1,807 |
| 3 kW | 3003 kWh | 1802 kWh | 1201 kWh | £478 | £120 | £598 | £8,204 | 13.7 yrs | £3,760 |
| 4 kW | 4004 kWh | 2403 kWh | 1602 kWh | £637 | £160 | £798 | £10,238 | 12.8 yrs | £5,713 |
| 5 kW | 5005 kWh | 3003 kWh | 2002 kWh | £797 | £200 | £997 | £12,273 | 12.3 yrs | £7,667 |
| 6 kW | 6006 kWh | 3604 kWh | 2403 kWh | £956 | £240 | £1,196 | £14,307 | 12.0 yrs | £9,620 |
| 7 kW | 7007 kWh | 4204 kWh | 2803 kWh | £1,115 | £280 | £1,396 | £16,342 | 11.7 yrs | £11,573 |
| 8 kW | 8008 kWh | 4805 kWh | 3203 kWh | £1,275 | £320 | £1,595 | £18,376 | 11.5 yrs | £13,527 |
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 | 2002 kWh | 1401 kWh | 601 kWh | £372 | £60 | £432 | £7,569 | 17.5 yrs | £1,069 |
| 3 kW | 3003 kWh | 2102 kWh | 901 kWh | £558 | £90 | £648 | £9,604 | 14.8 yrs | £3,353 |
| 4 kW | 4004 kWh | 2803 kWh | 1201 kWh | £744 | £120 | £864 | £11,638 | 13.5 yrs | £5,637 |
| 5 kW | 5005 kWh | 3504 kWh | 1502 kWh | £930 | £150 | £1,080 | £13,673 | 12.7 yrs | £7,921 |
| 6 kW | 6006 kWh | 4204 kWh | 1802 kWh | £1,115 | £180 | £1,296 | £15,707 | 12.1 yrs | £10,206 |
| 7 kW | 7007 kWh | 4905 kWh | 2102 kWh | £1,301 | £210 | £1,512 | £17,742 | 11.7 yrs | £12,490 |
| 8 kW | 8008 kWh | 5606 kWh | 2403 kWh | £1,487 | £240 | £1,728 | £19,776 | 11.4 yrs | £14,774 |
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 | 2002 kWh | 1462 kWh | 541 kWh | £388 | £54 | £442 | £9,319 | 21.1 yrs | £-483 |
| 3 kW | 3003 kWh | 2192 kWh | 811 kWh | £582 | £81 | £663 | £11,354 | 17.1 yrs | £1,901 |
| 4 kW | 4004 kWh | 2923 kWh | 1081 kWh | £775 | £108 | £884 | £13,388 | 15.2 yrs | £4,284 |
| 5 kW | 5005 kWh | 3654 kWh | 1351 kWh | £969 | £135 | £1,105 | £15,423 | 14.0 yrs | £6,668 |
| 6 kW | 6006 kWh | 4385 kWh | 1622 kWh | £1,163 | £162 | £1,325 | £17,457 | 13.2 yrs | £9,051 |
| 7 kW | 7007 kWh | 5115 kWh | 1892 kWh | £1,357 | £189 | £1,546 | £19,492 | 12.6 yrs | £11,435 |
| 8 kW | 8008 kWh | 5846 kWh | 2162 kWh | £1,551 | £216 | £1,767 | £21,526 | 12.2 yrs | £13,818 |
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 | 2002 kWh | 1502 kWh | 501 kWh | £398 | £50 | £448 | £11,069 | 24.7 yrs | £-2,101 |
| 3 kW | 3003 kWh | 2252 kWh | 751 kWh | £598 | £75 | £673 | £13,104 | 19.5 yrs | £349 |
| 4 kW | 4004 kWh | 3003 kWh | 1001 kWh | £797 | £100 | £897 | £15,138 | 16.9 yrs | £2,799 |
| 5 kW | 5005 kWh | 3754 kWh | 1251 kWh | £996 | £125 | £1,121 | £17,173 | 15.3 yrs | £5,249 |
| 6 kW | 6006 kWh | 4505 kWh | 1502 kWh | £1,195 | £150 | £1,345 | £19,207 | 14.3 yrs | £7,698 |
| 7 kW | 7007 kWh | 5256 kWh | 1752 kWh | £1,394 | £175 | £1,569 | £21,242 | 13.5 yrs | £10,148 |
| 8 kW | 8008 kWh | 6006 kWh | 2002 kWh | £1,593 | £200 | £1,794 | £23,276 | 13.0 yrs | £12,598 |
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 | 2002 kWh | 1542 kWh | 460 kWh | £409 | £46 | £455 | £13,519 | 29.7 yrs | £-4,418 |
| 3 kW | 3003 kWh | 2312 kWh | 691 kWh | £613 | £69 | £683 | £15,554 | 22.8 yrs | £-1,902 |
| 4 kW | 4004 kWh | 3083 kWh | 921 kWh | £818 | £92 | £910 | £17,588 | 19.3 yrs | £614 |
| 5 kW | 5005 kWh | 3854 kWh | 1151 kWh | £1,022 | £115 | £1,138 | £19,623 | 17.2 yrs | £3,130 |
| 6 kW | 6006 kWh | 4625 kWh | 1381 kWh | £1,227 | £138 | £1,365 | £21,657 | 15.9 yrs | £5,646 |
| 7 kW | 7007 kWh | 5396 kWh | 1612 kWh | £1,431 | £161 | £1,593 | £23,692 | 14.9 yrs | £8,161 |
| 8 kW | 8008 kWh | 6167 kWh | 1842 kWh | £1,636 | £184 | £1,820 | £25,726 | 14.1 yrs | £10,677 |
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.