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 986 kWh per year on a south-facing roof. We value self-used electricity at 27.1p 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 | 1972 kWh | 789 kWh | 1183 kWh | £214 | £118 | £332 | £4,069 | 12.2 yrs | £2,576 |
| 3 kW | 2959 kWh | 1183 kWh | 1775 kWh | £321 | £178 | £498 | £6,104 | 12.2 yrs | £3,863 |
| 4 kW | 3945 kWh | 1578 kWh | 2367 kWh | £428 | £237 | £664 | £8,138 | 12.2 yrs | £5,151 |
| 5 kW | 4931 kWh | 1972 kWh | 2959 kWh | £535 | £296 | £831 | £10,173 | 12.2 yrs | £6,439 |
| 6 kW | 5917 kWh | 2367 kWh | 3550 kWh | £642 | £355 | £997 | £12,207 | 12.2 yrs | £7,727 |
| 7 kW | 6903 kWh | 2761 kWh | 4142 kWh | £749 | £414 | £1,163 | £14,242 | 12.2 yrs | £9,015 |
| 8 kW | 7890 kWh | 3156 kWh | 4734 kWh | £856 | £473 | £1,329 | £16,276 | 12.2 yrs | £10,302 |
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: £999, 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 | 1972 kWh | 1183 kWh | 789 kWh | £321 | £79 | £400 | £6,169 | 15.4 yrs | £1,826 |
| 3 kW | 2959 kWh | 1775 kWh | 1183 kWh | £481 | £118 | £600 | £8,204 | 13.7 yrs | £3,788 |
| 4 kW | 3945 kWh | 2367 kWh | 1578 kWh | £642 | £158 | £799 | £10,238 | 12.8 yrs | £5,751 |
| 5 kW | 4931 kWh | 2959 kWh | 1972 kWh | £802 | £197 | £999 | £12,273 | 12.3 yrs | £7,714 |
| 6 kW | 5917 kWh | 3550 kWh | 2367 kWh | £962 | £237 | £1,199 | £14,307 | 11.9 yrs | £9,677 |
| 7 kW | 6903 kWh | 4142 kWh | 2761 kWh | £1,123 | £276 | £1,399 | £16,342 | 11.7 yrs | £11,639 |
| 8 kW | 7890 kWh | 4734 kWh | 3156 kWh | £1,283 | £316 | £1,599 | £18,376 | 11.5 yrs | £13,602 |
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: £1,084, 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 | 1972 kWh | 1381 kWh | 592 kWh | £374 | £59 | £433 | £7,569 | 17.5 yrs | £1,100 |
| 3 kW | 2959 kWh | 2071 kWh | 888 kWh | £561 | £89 | £650 | £9,604 | 14.8 yrs | £3,401 |
| 4 kW | 3945 kWh | 2761 kWh | 1183 kWh | £749 | £118 | £867 | £11,638 | 13.4 yrs | £5,701 |
| 5 kW | 4931 kWh | 3452 kWh | 1479 kWh | £936 | £148 | £1,084 | £13,673 | 12.6 yrs | £8,001 |
| 6 kW | 5917 kWh | 4142 kWh | 1775 kWh | £1,123 | £178 | £1,300 | £15,707 | 12.1 yrs | £10,301 |
| 7 kW | 6903 kWh | 4832 kWh | 2071 kWh | £1,310 | £207 | £1,517 | £17,742 | 11.7 yrs | £12,602 |
| 8 kW | 7890 kWh | 5523 kWh | 2367 kWh | £1,497 | £237 | £1,734 | £19,776 | 11.4 yrs | £14,902 |
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: £1,109, 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 | 1972 kWh | 1440 kWh | 533 kWh | £390 | £53 | £444 | £9,319 | 21.0 yrs | £-447 |
| 3 kW | 2959 kWh | 2160 kWh | 799 kWh | £586 | £80 | £665 | £11,354 | 17.1 yrs | £1,954 |
| 4 kW | 3945 kWh | 2880 kWh | 1065 kWh | £781 | £107 | £887 | £13,388 | 15.1 yrs | £4,356 |
| 5 kW | 4931 kWh | 3600 kWh | 1331 kWh | £976 | £133 | £1,109 | £15,423 | 13.9 yrs | £6,757 |
| 6 kW | 5917 kWh | 4320 kWh | 1598 kWh | £1,171 | £160 | £1,331 | £17,457 | 13.1 yrs | £9,159 |
| 7 kW | 6903 kWh | 5039 kWh | 1864 kWh | £1,366 | £186 | £1,553 | £19,492 | 12.6 yrs | £11,560 |
| 8 kW | 7890 kWh | 5759 kWh | 2130 kWh | £1,561 | £213 | £1,774 | £21,526 | 12.1 yrs | £13,962 |
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: £1,126, 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 | 1972 kWh | 1479 kWh | 493 kWh | £401 | £49 | £450 | £11,069 | 24.6 yrs | £-2,062 |
| 3 kW | 2959 kWh | 2219 kWh | 740 kWh | £602 | £74 | £676 | £13,104 | 19.4 yrs | £407 |
| 4 kW | 3945 kWh | 2959 kWh | 986 kWh | £802 | £99 | £901 | £15,138 | 16.8 yrs | £2,876 |
| 5 kW | 4931 kWh | 3698 kWh | 1233 kWh | £1,003 | £123 | £1,126 | £17,173 | 15.3 yrs | £5,345 |
| 6 kW | 5917 kWh | 4438 kWh | 1479 kWh | £1,203 | £148 | £1,351 | £19,207 | 14.2 yrs | £7,814 |
| 7 kW | 6903 kWh | 5178 kWh | 1726 kWh | £1,404 | £173 | £1,576 | £21,242 | 13.5 yrs | £10,283 |
| 8 kW | 7890 kWh | 5917 kWh | 1972 kWh | £1,604 | £197 | £1,801 | £23,276 | 12.9 yrs | £12,752 |
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: £1,143, 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 | 1972 kWh | 1519 kWh | 454 kWh | £412 | £45 | £457 | £13,519 | 29.6 yrs | £-4,377 |
| 3 kW | 2959 kWh | 2278 kWh | 680 kWh | £618 | £68 | £686 | £15,554 | 22.7 yrs | £-1,841 |
| 4 kW | 3945 kWh | 3037 kWh | 907 kWh | £823 | £91 | £914 | £17,588 | 19.2 yrs | £696 |
| 5 kW | 4931 kWh | 3797 kWh | 1134 kWh | £1,029 | £113 | £1,143 | £19,623 | 17.2 yrs | £3,232 |
| 6 kW | 5917 kWh | 4556 kWh | 1361 kWh | £1,235 | £136 | £1,371 | £21,657 | 15.8 yrs | £5,769 |
| 7 kW | 6903 kWh | 5316 kWh | 1588 kWh | £1,441 | £159 | £1,600 | £23,692 | 14.8 yrs | £8,305 |
| 8 kW | 7890 kWh | 6075 kWh | 1815 kWh | £1,647 | £181 | £1,828 | £25,726 | 14.1 yrs | £10,842 |
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.