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 926 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: £752, Upfront: £10,173, Break-even: 13.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1852 kWh | 741 kWh | 1111 kWh | £190 | £111 | £301 | £4,069 | 13.5 yrs | £1,951 |
| 3 kW | 2777 kWh | 1111 kWh | 1666 kWh | £285 | £167 | £451 | £6,104 | 13.5 yrs | £2,926 |
| 4 kW | 3703 kWh | 1481 kWh | 2222 kWh | £380 | £222 | £602 | £8,138 | 13.5 yrs | £3,901 |
| 5 kW | 4629 kWh | 1852 kWh | 2777 kWh | £475 | £278 | £752 | £10,173 | 13.5 yrs | £4,877 |
| 6 kW | 5555 kWh | 2222 kWh | 3333 kWh | £570 | £333 | £903 | £12,207 | 13.5 yrs | £5,852 |
| 7 kW | 6480 kWh | 2592 kWh | 3888 kWh | £665 | £389 | £1,053 | £14,242 | 13.5 yrs | £6,827 |
| 8 kW | 7406 kWh | 2962 kWh | 4444 kWh | £760 | £444 | £1,204 | £16,276 | 13.5 yrs | £7,803 |
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: £897, Upfront: £12,273, 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 | 1852 kWh | 1111 kWh | 741 kWh | £285 | £74 | £359 | £6,169 | 17.2 yrs | £1,009 |
| 3 kW | 2777 kWh | 1666 kWh | 1111 kWh | £427 | £111 | £538 | £8,204 | 15.2 yrs | £2,564 |
| 4 kW | 3703 kWh | 2222 kWh | 1481 kWh | £570 | £148 | £718 | £10,238 | 14.3 yrs | £4,118 |
| 5 kW | 4629 kWh | 2777 kWh | 1852 kWh | £712 | £185 | £897 | £12,273 | 13.7 yrs | £5,673 |
| 6 kW | 5555 kWh | 3333 kWh | 2222 kWh | £855 | £222 | £1,077 | £14,307 | 13.3 yrs | £7,227 |
| 7 kW | 6480 kWh | 3888 kWh | 2592 kWh | £997 | £259 | £1,256 | £16,342 | 13.0 yrs | £8,782 |
| 8 kW | 7406 kWh | 4444 kWh | 2962 kWh | £1,139 | £296 | £1,436 | £18,376 | 12.8 yrs | £10,336 |
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: £970, Upfront: £13,673, 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 | 1852 kWh | 1296 kWh | 555 kWh | £332 | £56 | £388 | £7,569 | 19.5 yrs | £188 |
| 3 kW | 2777 kWh | 1944 kWh | 833 kWh | £498 | £83 | £582 | £9,604 | 16.5 yrs | £2,032 |
| 4 kW | 3703 kWh | 2592 kWh | 1111 kWh | £665 | £111 | £776 | £11,638 | 15.0 yrs | £3,876 |
| 5 kW | 4629 kWh | 3240 kWh | 1389 kWh | £831 | £139 | £970 | £13,673 | 14.1 yrs | £5,720 |
| 6 kW | 5555 kWh | 3888 kWh | 1666 kWh | £997 | £167 | £1,164 | £15,707 | 13.5 yrs | £7,565 |
| 7 kW | 6480 kWh | 4536 kWh | 1944 kWh | £1,163 | £194 | £1,358 | £17,742 | 13.1 yrs | £9,409 |
| 8 kW | 7406 kWh | 5184 kWh | 2222 kWh | £1,329 | £222 | £1,551 | £19,776 | 12.7 yrs | £11,253 |
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: £991, Upfront: £15,423, Break-even: 15.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1852 kWh | 1352 kWh | 500 kWh | £347 | £50 | £397 | £9,319 | 23.5 yrs | £-1,388 |
| 3 kW | 2777 kWh | 2027 kWh | 750 kWh | £520 | £75 | £595 | £11,354 | 19.1 yrs | £543 |
| 4 kW | 3703 kWh | 2703 kWh | 1000 kWh | £693 | £100 | £793 | £13,388 | 16.9 yrs | £2,474 |
| 5 kW | 4629 kWh | 3379 kWh | 1250 kWh | £866 | £125 | £991 | £15,423 | 15.6 yrs | £4,405 |
| 6 kW | 5555 kWh | 4055 kWh | 1500 kWh | £1,040 | £150 | £1,190 | £17,457 | 14.7 yrs | £6,336 |
| 7 kW | 6480 kWh | 4731 kWh | 1750 kWh | £1,213 | £175 | £1,388 | £19,492 | 14.0 yrs | £8,267 |
| 8 kW | 7406 kWh | 5406 kWh | 2000 kWh | £1,386 | £200 | £1,586 | £21,526 | 13.6 yrs | £10,198 |
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: £1,006, Upfront: £17,173, Break-even: 17.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1852 kWh | 1389 kWh | 463 kWh | £356 | £46 | £402 | £11,069 | 27.5 yrs | £-3,022 |
| 3 kW | 2777 kWh | 2083 kWh | 694 kWh | £534 | £69 | £604 | £13,104 | 21.7 yrs | £-1,033 |
| 4 kW | 3703 kWh | 2777 kWh | 926 kWh | £712 | £93 | £805 | £15,138 | 18.8 yrs | £956 |
| 5 kW | 4629 kWh | 3472 kWh | 1157 kWh | £890 | £116 | £1,006 | £17,173 | 17.1 yrs | £2,944 |
| 6 kW | 5555 kWh | 4166 kWh | 1389 kWh | £1,068 | £139 | £1,207 | £19,207 | 15.9 yrs | £4,933 |
| 7 kW | 6480 kWh | 4860 kWh | 1620 kWh | £1,246 | £162 | £1,408 | £21,242 | 15.1 yrs | £6,922 |
| 8 kW | 7406 kWh | 5555 kWh | 1852 kWh | £1,424 | £185 | £1,609 | £23,276 | 14.5 yrs | £8,911 |
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: £1,020, Upfront: £19,623, Break-even: 19.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1852 kWh | 1426 kWh | 426 kWh | £366 | £43 | £408 | £13,519 | 33.1 yrs | £-5,356 |
| 3 kW | 2777 kWh | 2139 kWh | 639 kWh | £548 | £64 | £612 | £15,554 | 25.4 yrs | £-3,310 |
| 4 kW | 3703 kWh | 2851 kWh | 852 kWh | £731 | £85 | £816 | £17,588 | 21.5 yrs | £-1,263 |
| 5 kW | 4629 kWh | 3564 kWh | 1065 kWh | £914 | £106 | £1,020 | £19,623 | 19.2 yrs | £784 |
| 6 kW | 5555 kWh | 4277 kWh | 1278 kWh | £1,097 | £128 | £1,224 | £21,657 | 17.7 yrs | £2,831 |
| 7 kW | 6480 kWh | 4990 kWh | 1490 kWh | £1,279 | £149 | £1,428 | £23,692 | 16.6 yrs | £4,878 |
| 8 kW | 7406 kWh | 5703 kWh | 1703 kWh | £1,462 | £170 | £1,633 | £25,726 | 15.8 yrs | £6,924 |
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.