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 985 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: £799, Upfront: £10,173, 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 | 1970 kWh | 788 kWh | 1182 kWh | £201 | £118 | £320 | £4,069 | 12.7 yrs | £2,322 |
| 3 kW | 2955 kWh | 1182 kWh | 1773 kWh | £302 | £177 | £479 | £6,104 | 12.7 yrs | £3,482 |
| 4 kW | 3940 kWh | 1576 kWh | 2364 kWh | £403 | £236 | £639 | £8,138 | 12.7 yrs | £4,643 |
| 5 kW | 4925 kWh | 1970 kWh | 2955 kWh | £503 | £295 | £799 | £10,173 | 12.7 yrs | £5,804 |
| 6 kW | 5910 kWh | 2364 kWh | 3546 kWh | £604 | £355 | £959 | £12,207 | 12.7 yrs | £6,965 |
| 7 kW | 6895 kWh | 2758 kWh | 4137 kWh | £705 | £414 | £1,118 | £14,242 | 12.7 yrs | £8,125 |
| 8 kW | 7880 kWh | 3152 kWh | 4728 kWh | £805 | £473 | £1,278 | £16,276 | 12.7 yrs | £9,286 |
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: £952, Upfront: £12,273, Break-even: 12.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1970 kWh | 1182 kWh | 788 kWh | £302 | £79 | £381 | £6,169 | 16.2 yrs | £1,447 |
| 3 kW | 2955 kWh | 1773 kWh | 1182 kWh | £453 | £118 | £571 | £8,204 | 14.4 yrs | £3,220 |
| 4 kW | 3940 kWh | 2364 kWh | 1576 kWh | £604 | £158 | £762 | £10,238 | 13.4 yrs | £4,994 |
| 5 kW | 4925 kWh | 2955 kWh | 1970 kWh | £755 | £197 | £952 | £12,273 | 12.9 yrs | £6,767 |
| 6 kW | 5910 kWh | 3546 kWh | 2364 kWh | £906 | £236 | £1,142 | £14,307 | 12.5 yrs | £8,541 |
| 7 kW | 6895 kWh | 4137 kWh | 2758 kWh | £1,057 | £276 | £1,333 | £16,342 | 12.3 yrs | £10,314 |
| 8 kW | 7880 kWh | 4728 kWh | 3152 kWh | £1,208 | £315 | £1,523 | £18,376 | 12.1 yrs | £12,087 |
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: £1,029, Upfront: £13,673, Break-even: 13.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1970 kWh | 1379 kWh | 591 kWh | £352 | £59 | £411 | £7,569 | 18.4 yrs | £660 |
| 3 kW | 2955 kWh | 2068 kWh | 886 kWh | £528 | £89 | £617 | £9,604 | 15.6 yrs | £2,739 |
| 4 kW | 3940 kWh | 2758 kWh | 1182 kWh | £705 | £118 | £823 | £11,638 | 14.1 yrs | £4,819 |
| 5 kW | 4925 kWh | 3447 kWh | 1477 kWh | £881 | £148 | £1,029 | £13,673 | 13.3 yrs | £6,899 |
| 6 kW | 5910 kWh | 4137 kWh | 1773 kWh | £1,057 | £177 | £1,234 | £15,707 | 12.7 yrs | £8,979 |
| 7 kW | 6895 kWh | 4826 kWh | 2068 kWh | £1,233 | £207 | £1,440 | £17,742 | 12.3 yrs | £11,058 |
| 8 kW | 7880 kWh | 5516 kWh | 2364 kWh | £1,409 | £236 | £1,646 | £19,776 | 12.0 yrs | £13,138 |
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: £1,052, Upfront: £15,423, Break-even: 14.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1970 kWh | 1438 kWh | 532 kWh | £367 | £53 | £421 | £9,319 | 22.2 yrs | £-907 |
| 3 kW | 2955 kWh | 2157 kWh | 798 kWh | £551 | £80 | £631 | £11,354 | 18.0 yrs | £1,265 |
| 4 kW | 3940 kWh | 2876 kWh | 1064 kWh | £735 | £106 | £841 | £13,388 | 15.9 yrs | £3,437 |
| 5 kW | 4925 kWh | 3595 kWh | 1330 kWh | £919 | £133 | £1,052 | £15,423 | 14.7 yrs | £5,608 |
| 6 kW | 5910 kWh | 4314 kWh | 1596 kWh | £1,102 | £160 | £1,262 | £17,457 | 13.8 yrs | £7,780 |
| 7 kW | 6895 kWh | 5033 kWh | 1862 kWh | £1,286 | £186 | £1,472 | £19,492 | 13.2 yrs | £9,952 |
| 8 kW | 7880 kWh | 5752 kWh | 2128 kWh | £1,470 | £213 | £1,682 | £21,526 | 12.8 yrs | £12,123 |
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: £1,067, Upfront: £17,173, Break-even: 16.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1970 kWh | 1477 kWh | 492 kWh | £377 | £49 | £427 | £11,069 | 25.9 yrs | £-2,534 |
| 3 kW | 2955 kWh | 2216 kWh | 739 kWh | £566 | £74 | £640 | £13,104 | 20.5 yrs | £-301 |
| 4 kW | 3940 kWh | 2955 kWh | 985 kWh | £755 | £98 | £853 | £15,138 | 17.7 yrs | £1,932 |
| 5 kW | 4925 kWh | 3694 kWh | 1231 kWh | £944 | £123 | £1,067 | £17,173 | 16.1 yrs | £4,165 |
| 6 kW | 5910 kWh | 4432 kWh | 1477 kWh | £1,132 | £148 | £1,280 | £19,207 | 15.0 yrs | £6,397 |
| 7 kW | 6895 kWh | 5171 kWh | 1724 kWh | £1,321 | £172 | £1,494 | £21,242 | 14.2 yrs | £8,630 |
| 8 kW | 7880 kWh | 5910 kWh | 1970 kWh | £1,510 | £197 | £1,707 | £23,276 | 13.6 yrs | £10,863 |
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: £1,082, Upfront: £19,623, Break-even: 18.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1970 kWh | 1517 kWh | 453 kWh | £388 | £45 | £433 | £13,519 | 31.2 yrs | £-4,862 |
| 3 kW | 2955 kWh | 2275 kWh | 680 kWh | £581 | £68 | £649 | £15,554 | 24.0 yrs | £-2,567 |
| 4 kW | 3940 kWh | 3034 kWh | 906 kWh | £775 | £91 | £866 | £17,588 | 20.3 yrs | £-273 |
| 5 kW | 4925 kWh | 3792 kWh | 1133 kWh | £969 | £113 | £1,082 | £19,623 | 18.1 yrs | £2,021 |
| 6 kW | 5910 kWh | 4551 kWh | 1359 kWh | £1,163 | £136 | £1,299 | £21,657 | 16.7 yrs | £4,315 |
| 7 kW | 6895 kWh | 5309 kWh | 1586 kWh | £1,356 | £159 | £1,515 | £23,692 | 15.6 yrs | £6,609 |
| 8 kW | 7880 kWh | 6067 kWh | 1812 kWh | £1,550 | £181 | £1,731 | £25,726 | 14.9 yrs | £8,903 |
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.