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 1002 kWh per year on a south-facing roof. We value self-used electricity at 26.9p 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: £840, Upfront: £10,173, Break-even: 12.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2004 kWh | 801 kWh | 1202 kWh | £216 | £120 | £336 | £4,069 | 12.1 yrs | £2,650 |
| 3 kW | 3005 kWh | 1202 kWh | 1803 kWh | £324 | £180 | £504 | £6,104 | 12.1 yrs | £3,975 |
| 4 kW | 4007 kWh | 1603 kWh | 2404 kWh | £431 | £240 | £672 | £8,138 | 12.1 yrs | £5,300 |
| 5 kW | 5009 kWh | 2004 kWh | 3005 kWh | £539 | £301 | £840 | £10,173 | 12.1 yrs | £6,625 |
| 6 kW | 6011 kWh | 2404 kWh | 3606 kWh | £647 | £361 | £1,008 | £12,207 | 12.1 yrs | £7,950 |
| 7 kW | 7012 kWh | 2805 kWh | 4207 kWh | £755 | £421 | £1,176 | £14,242 | 12.1 yrs | £9,275 |
| 8 kW | 8014 kWh | 3206 kWh | 4809 kWh | £863 | £481 | £1,344 | £16,276 | 12.1 yrs | £10,600 |
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: £1,009, Upfront: £12,273, 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 | 2004 kWh | 1202 kWh | 801 kWh | £324 | £80 | £404 | £6,169 | 15.3 yrs | £1,906 |
| 3 kW | 3005 kWh | 1803 kWh | 1202 kWh | £485 | £120 | £606 | £8,204 | 13.5 yrs | £3,909 |
| 4 kW | 4007 kWh | 2404 kWh | 1603 kWh | £647 | £160 | £808 | £10,238 | 12.7 yrs | £5,912 |
| 5 kW | 5009 kWh | 3005 kWh | 2004 kWh | £809 | £200 | £1,009 | £12,273 | 12.2 yrs | £7,915 |
| 6 kW | 6011 kWh | 3606 kWh | 2404 kWh | £971 | £240 | £1,211 | £14,307 | 11.8 yrs | £9,918 |
| 7 kW | 7012 kWh | 4207 kWh | 2805 kWh | £1,133 | £280 | £1,413 | £16,342 | 11.6 yrs | £11,921 |
| 8 kW | 8014 kWh | 4809 kWh | 3206 kWh | £1,294 | £321 | £1,615 | £18,376 | 11.4 yrs | £13,925 |
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: £1,094, Upfront: £13,673, Break-even: 12.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2004 kWh | 1402 kWh | 601 kWh | £378 | £60 | £438 | £7,569 | 17.3 yrs | £1,184 |
| 3 kW | 3005 kWh | 2104 kWh | 902 kWh | £566 | £90 | £656 | £9,604 | 14.6 yrs | £3,526 |
| 4 kW | 4007 kWh | 2805 kWh | 1202 kWh | £755 | £120 | £875 | £11,638 | 13.3 yrs | £5,868 |
| 5 kW | 5009 kWh | 3506 kWh | 1503 kWh | £944 | £150 | £1,094 | £13,673 | 12.5 yrs | £8,210 |
| 6 kW | 6011 kWh | 4207 kWh | 1803 kWh | £1,133 | £180 | £1,313 | £15,707 | 12.0 yrs | £10,552 |
| 7 kW | 7012 kWh | 4909 kWh | 2104 kWh | £1,321 | £210 | £1,532 | £17,742 | 11.6 yrs | £12,894 |
| 8 kW | 8014 kWh | 5610 kWh | 2404 kWh | £1,510 | £240 | £1,751 | £19,776 | 11.3 yrs | £15,237 |
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: £1,120, Upfront: £15,423, Break-even: 13.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2004 kWh | 1463 kWh | 541 kWh | £394 | £54 | £448 | £9,319 | 20.8 yrs | £-362 |
| 3 kW | 3005 kWh | 2194 kWh | 811 kWh | £591 | £81 | £672 | £11,354 | 16.9 yrs | £2,081 |
| 4 kW | 4007 kWh | 2925 kWh | 1082 kWh | £787 | £108 | £896 | £13,388 | 14.9 yrs | £4,525 |
| 5 kW | 5009 kWh | 3656 kWh | 1352 kWh | £984 | £135 | £1,120 | £15,423 | 13.8 yrs | £6,969 |
| 6 kW | 6011 kWh | 4388 kWh | 1623 kWh | £1,181 | £162 | £1,343 | £17,457 | 13.0 yrs | £9,413 |
| 7 kW | 7012 kWh | 5119 kWh | 1893 kWh | £1,378 | £189 | £1,567 | £19,492 | 12.4 yrs | £11,856 |
| 8 kW | 8014 kWh | 5850 kWh | 2164 kWh | £1,575 | £216 | £1,791 | £21,526 | 12.0 yrs | £14,300 |
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: £1,137, Upfront: £17,173, Break-even: 15.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2004 kWh | 1503 kWh | 501 kWh | £405 | £50 | £455 | £11,069 | 24.3 yrs | £-1,977 |
| 3 kW | 3005 kWh | 2254 kWh | 751 kWh | £607 | £75 | £682 | £13,104 | 19.2 yrs | £535 |
| 4 kW | 4007 kWh | 3005 kWh | 1002 kWh | £809 | £100 | £909 | £15,138 | 16.6 yrs | £3,046 |
| 5 kW | 5009 kWh | 3757 kWh | 1252 kWh | £1,011 | £125 | £1,137 | £17,173 | 15.1 yrs | £5,558 |
| 6 kW | 6011 kWh | 4508 kWh | 1503 kWh | £1,214 | £150 | £1,364 | £19,207 | 14.1 yrs | £8,069 |
| 7 kW | 7012 kWh | 5259 kWh | 1753 kWh | £1,416 | £175 | £1,591 | £21,242 | 13.4 yrs | £10,581 |
| 8 kW | 8014 kWh | 6011 kWh | 2004 kWh | £1,618 | £200 | £1,818 | £23,276 | 12.8 yrs | £13,093 |
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: £1,153, Upfront: £19,623, Break-even: 17.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2004 kWh | 1543 kWh | 461 kWh | £415 | £46 | £461 | £13,519 | 29.3 yrs | £-4,291 |
| 3 kW | 3005 kWh | 2314 kWh | 691 kWh | £623 | £69 | £692 | £15,554 | 22.5 yrs | £-1,712 |
| 4 kW | 4007 kWh | 3085 kWh | 922 kWh | £831 | £92 | £923 | £17,588 | 19.1 yrs | £867 |
| 5 kW | 5009 kWh | 3857 kWh | 1152 kWh | £1,038 | £115 | £1,153 | £19,623 | 17.0 yrs | £3,447 |
| 6 kW | 6011 kWh | 4628 kWh | 1382 kWh | £1,246 | £138 | £1,384 | £21,657 | 15.6 yrs | £6,026 |
| 7 kW | 7012 kWh | 5400 kWh | 1613 kWh | £1,454 | £161 | £1,615 | £23,692 | 14.7 yrs | £8,606 |
| 8 kW | 8014 kWh | 6171 kWh | 1843 kWh | £1,661 | £184 | £1,846 | £25,726 | 13.9 yrs | £11,185 |
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.