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 1002 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: £833, 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 | 2005 kWh | 802 kWh | 1203 kWh | £213 | £120 | £333 | £4,069 | 12.2 yrs | £2,591 |
| 3 kW | 3007 kWh | 1203 kWh | 1804 kWh | £319 | £180 | £500 | £6,104 | 12.2 yrs | £3,887 |
| 4 kW | 4009 kWh | 1604 kWh | 2406 kWh | £425 | £241 | £666 | £8,138 | 12.2 yrs | £5,183 |
| 5 kW | 5012 kWh | 2005 kWh | 3007 kWh | £532 | £301 | £833 | £10,173 | 12.2 yrs | £6,478 |
| 6 kW | 6014 kWh | 2406 kWh | 3608 kWh | £638 | £361 | £999 | £12,207 | 12.2 yrs | £7,774 |
| 7 kW | 7016 kWh | 2807 kWh | 4210 kWh | £745 | £421 | £1,166 | £14,242 | 12.2 yrs | £9,069 |
| 8 kW | 8019 kWh | 3207 kWh | 4811 kWh | £851 | £481 | £1,332 | £16,276 | 12.2 yrs | £10,365 |
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: £998, 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 | 2005 kWh | 1203 kWh | 802 kWh | £319 | £80 | £399 | £6,169 | 15.5 yrs | £1,817 |
| 3 kW | 3007 kWh | 1804 kWh | 1203 kWh | £479 | £120 | £599 | £8,204 | 13.7 yrs | £3,775 |
| 4 kW | 4009 kWh | 2406 kWh | 1604 kWh | £638 | £160 | £799 | £10,238 | 12.8 yrs | £5,733 |
| 5 kW | 5012 kWh | 3007 kWh | 2005 kWh | £798 | £200 | £998 | £12,273 | 12.3 yrs | £7,692 |
| 6 kW | 6014 kWh | 3608 kWh | 2406 kWh | £957 | £241 | £1,198 | £14,307 | 11.9 yrs | £9,650 |
| 7 kW | 7016 kWh | 4210 kWh | 2807 kWh | £1,117 | £281 | £1,398 | £16,342 | 11.7 yrs | £11,609 |
| 8 kW | 8019 kWh | 4811 kWh | 3207 kWh | £1,276 | £321 | £1,597 | £18,376 | 11.5 yrs | £13,567 |
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: £1,081, Upfront: £13,673, Break-even: 12.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2005 kWh | 1403 kWh | 601 kWh | £372 | £60 | £432 | £7,569 | 17.5 yrs | £1,079 |
| 3 kW | 3007 kWh | 2105 kWh | 902 kWh | £558 | £90 | £649 | £9,604 | 14.8 yrs | £3,369 |
| 4 kW | 4009 kWh | 2807 kWh | 1203 kWh | £745 | £120 | £865 | £11,638 | 13.5 yrs | £5,659 |
| 5 kW | 5012 kWh | 3508 kWh | 1503 kWh | £931 | £150 | £1,081 | £13,673 | 12.6 yrs | £7,949 |
| 6 kW | 6014 kWh | 4210 kWh | 1804 kWh | £1,117 | £180 | £1,297 | £15,707 | 12.1 yrs | £10,238 |
| 7 kW | 7016 kWh | 4911 kWh | 2105 kWh | £1,303 | £210 | £1,513 | £17,742 | 11.7 yrs | £12,528 |
| 8 kW | 8019 kWh | 5613 kWh | 2406 kWh | £1,489 | £241 | £1,730 | £19,776 | 11.4 yrs | £14,818 |
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: £1,106, Upfront: £15,423, Break-even: 13.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2005 kWh | 1463 kWh | 541 kWh | £388 | £54 | £442 | £9,319 | 21.1 yrs | £-472 |
| 3 kW | 3007 kWh | 2195 kWh | 812 kWh | £582 | £81 | £664 | £11,354 | 17.1 yrs | £1,917 |
| 4 kW | 4009 kWh | 2927 kWh | 1083 kWh | £776 | £108 | £885 | £13,388 | 15.1 yrs | £4,307 |
| 5 kW | 5012 kWh | 3659 kWh | 1353 kWh | £971 | £135 | £1,106 | £15,423 | 13.9 yrs | £6,696 |
| 6 kW | 6014 kWh | 4390 kWh | 1624 kWh | £1,165 | £162 | £1,327 | £17,457 | 13.2 yrs | £9,085 |
| 7 kW | 7016 kWh | 5122 kWh | 1894 kWh | £1,359 | £189 | £1,548 | £19,492 | 12.6 yrs | £11,474 |
| 8 kW | 8019 kWh | 5854 kWh | 2165 kWh | £1,553 | £217 | £1,769 | £21,526 | 12.2 yrs | £13,863 |
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: £1,122, 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 | 2005 kWh | 1503 kWh | 501 kWh | £399 | £50 | £449 | £11,069 | 24.7 yrs | £-2,089 |
| 3 kW | 3007 kWh | 2255 kWh | 752 kWh | £598 | £75 | £673 | £13,104 | 19.5 yrs | £366 |
| 4 kW | 4009 kWh | 3007 kWh | 1002 kWh | £798 | £100 | £898 | £15,138 | 16.9 yrs | £2,822 |
| 5 kW | 5012 kWh | 3759 kWh | 1253 kWh | £997 | £125 | £1,122 | £17,173 | 15.3 yrs | £5,277 |
| 6 kW | 6014 kWh | 4510 kWh | 1503 kWh | £1,197 | £150 | £1,347 | £19,207 | 14.3 yrs | £7,733 |
| 7 kW | 7016 kWh | 5262 kWh | 1754 kWh | £1,396 | £175 | £1,571 | £21,242 | 13.5 yrs | £10,188 |
| 8 kW | 8019 kWh | 6014 kWh | 2005 kWh | £1,596 | £200 | £1,796 | £23,276 | 13.0 yrs | £12,643 |
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: £1,139, 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 | 2005 kWh | 1544 kWh | 461 kWh | £410 | £46 | £456 | £13,519 | 29.7 yrs | £-4,407 |
| 3 kW | 3007 kWh | 2315 kWh | 692 kWh | £614 | £69 | £683 | £15,554 | 22.8 yrs | £-1,885 |
| 4 kW | 4009 kWh | 3087 kWh | 922 kWh | £819 | £92 | £911 | £17,588 | 19.3 yrs | £637 |
| 5 kW | 5012 kWh | 3859 kWh | 1153 kWh | £1,024 | £115 | £1,139 | £19,623 | 17.2 yrs | £3,159 |
| 6 kW | 6014 kWh | 4631 kWh | 1383 kWh | £1,229 | £138 | £1,367 | £21,657 | 15.8 yrs | £5,680 |
| 7 kW | 7016 kWh | 5403 kWh | 1614 kWh | £1,433 | £161 | £1,595 | £23,692 | 14.9 yrs | £8,202 |
| 8 kW | 8019 kWh | 6174 kWh | 1844 kWh | £1,638 | £184 | £1,822 | £25,726 | 14.1 yrs | £10,724 |
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.