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 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 | 1971 kWh | 788 kWh | 1182 kWh | £201 | £118 | £320 | £4,069 | 12.7 yrs | £2,324 |
| 3 kW | 2956 kWh | 1182 kWh | 1774 kWh | £302 | £177 | £479 | £6,104 | 12.7 yrs | £3,485 |
| 4 kW | 3941 kWh | 1576 kWh | 2365 kWh | £403 | £236 | £639 | £8,138 | 12.7 yrs | £4,647 |
| 5 kW | 4926 kWh | 1971 kWh | 2956 kWh | £503 | £296 | £799 | £10,173 | 12.7 yrs | £5,809 |
| 6 kW | 5912 kWh | 2365 kWh | 3547 kWh | £604 | £355 | £959 | £12,207 | 12.7 yrs | £6,971 |
| 7 kW | 6897 kWh | 2759 kWh | 4138 kWh | £705 | £414 | £1,119 | £14,242 | 12.7 yrs | £8,132 |
| 8 kW | 7882 kWh | 3153 kWh | 4729 kWh | £806 | £473 | £1,279 | £16,276 | 12.7 yrs | £9,294 |
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 | 1971 kWh | 1182 kWh | 788 kWh | £302 | £79 | £381 | £6,169 | 16.2 yrs | £1,449 |
| 3 kW | 2956 kWh | 1774 kWh | 1182 kWh | £453 | £118 | £571 | £8,204 | 14.4 yrs | £3,224 |
| 4 kW | 3941 kWh | 2365 kWh | 1576 kWh | £604 | £158 | £762 | £10,238 | 13.4 yrs | £4,998 |
| 5 kW | 4926 kWh | 2956 kWh | 1971 kWh | £755 | £197 | £952 | £12,273 | 12.9 yrs | £6,773 |
| 6 kW | 5912 kWh | 3547 kWh | 2365 kWh | £906 | £236 | £1,143 | £14,307 | 12.5 yrs | £8,548 |
| 7 kW | 6897 kWh | 4138 kWh | 2759 kWh | £1,057 | £276 | £1,333 | £16,342 | 12.3 yrs | £10,322 |
| 8 kW | 7882 kWh | 4729 kWh | 3153 kWh | £1,208 | £315 | £1,524 | £18,376 | 12.1 yrs | £12,097 |
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 | 1971 kWh | 1379 kWh | 591 kWh | £352 | £59 | £412 | £7,569 | 18.4 yrs | £662 |
| 3 kW | 2956 kWh | 2069 kWh | 887 kWh | £529 | £89 | £617 | £9,604 | 15.6 yrs | £2,743 |
| 4 kW | 3941 kWh | 2759 kWh | 1182 kWh | £705 | £118 | £823 | £11,638 | 14.1 yrs | £4,824 |
| 5 kW | 4926 kWh | 3449 kWh | 1478 kWh | £881 | £148 | £1,029 | £13,673 | 13.3 yrs | £6,905 |
| 6 kW | 5912 kWh | 4138 kWh | 1774 kWh | £1,057 | £177 | £1,235 | £15,707 | 12.7 yrs | £8,986 |
| 7 kW | 6897 kWh | 4828 kWh | 2069 kWh | £1,234 | £207 | £1,440 | £17,742 | 12.3 yrs | £11,067 |
| 8 kW | 7882 kWh | 5518 kWh | 2365 kWh | £1,410 | £236 | £1,646 | £19,776 | 12.0 yrs | £13,148 |
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 | 1971 kWh | 1439 kWh | 532 kWh | £368 | £53 | £421 | £9,319 | 22.1 yrs | £-904 |
| 3 kW | 2956 kWh | 2158 kWh | 798 kWh | £551 | £80 | £631 | £11,354 | 18.0 yrs | £1,269 |
| 4 kW | 3941 kWh | 2877 kWh | 1064 kWh | £735 | £106 | £841 | £13,388 | 15.9 yrs | £3,442 |
| 5 kW | 4926 kWh | 3596 kWh | 1330 kWh | £919 | £133 | £1,052 | £15,423 | 14.7 yrs | £5,615 |
| 6 kW | 5912 kWh | 4316 kWh | 1596 kWh | £1,103 | £160 | £1,262 | £17,457 | 13.8 yrs | £7,788 |
| 7 kW | 6897 kWh | 5035 kWh | 1862 kWh | £1,286 | £186 | £1,473 | £19,492 | 13.2 yrs | £9,961 |
| 8 kW | 7882 kWh | 5754 kWh | 2128 kWh | £1,470 | £213 | £1,683 | £21,526 | 12.8 yrs | £12,134 |
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 | 1971 kWh | 1478 kWh | 493 kWh | £378 | £49 | £427 | £11,069 | 25.9 yrs | £-2,531 |
| 3 kW | 2956 kWh | 2217 kWh | 739 kWh | £566 | £74 | £640 | £13,104 | 20.5 yrs | £-297 |
| 4 kW | 3941 kWh | 2956 kWh | 985 kWh | £755 | £99 | £854 | £15,138 | 17.7 yrs | £1,937 |
| 5 kW | 4926 kWh | 3695 kWh | 1232 kWh | £944 | £123 | £1,067 | £17,173 | 16.1 yrs | £4,171 |
| 6 kW | 5912 kWh | 4434 kWh | 1478 kWh | £1,133 | £148 | £1,281 | £19,207 | 15.0 yrs | £6,406 |
| 7 kW | 6897 kWh | 5173 kWh | 1724 kWh | £1,322 | £172 | £1,494 | £21,242 | 14.2 yrs | £8,640 |
| 8 kW | 7882 kWh | 5912 kWh | 1971 kWh | £1,510 | £197 | £1,708 | £23,276 | 13.6 yrs | £10,874 |
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: £1,083, 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 | 1971 kWh | 1517 kWh | 453 kWh | £388 | £45 | £433 | £13,519 | 31.2 yrs | £-4,859 |
| 3 kW | 2956 kWh | 2276 kWh | 680 kWh | £582 | £68 | £650 | £15,554 | 23.9 yrs | £-2,563 |
| 4 kW | 3941 kWh | 3035 kWh | 906 kWh | £775 | £91 | £866 | £17,588 | 20.3 yrs | £-268 |
| 5 kW | 4926 kWh | 3793 kWh | 1133 kWh | £969 | £113 | £1,083 | £19,623 | 18.1 yrs | £2,028 |
| 6 kW | 5912 kWh | 4552 kWh | 1360 kWh | £1,163 | £136 | £1,299 | £21,657 | 16.7 yrs | £4,323 |
| 7 kW | 6897 kWh | 5311 kWh | 1586 kWh | £1,357 | £159 | £1,516 | £23,692 | 15.6 yrs | £6,619 |
| 8 kW | 7882 kWh | 6069 kWh | 1813 kWh | £1,551 | £181 | £1,732 | £25,726 | 14.9 yrs | £8,914 |
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.