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 878 kWh per year on a south-facing roof. We value self-used electricity at 25.8p 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: £717, Upfront: £10,173, Break-even: 14.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1756 kWh | 702 kWh | 1053 kWh | £181 | £105 | £287 | £4,069 | 14.2 yrs | £1,667 |
| 3 kW | 2633 kWh | 1053 kWh | 1580 kWh | £272 | £158 | £430 | £6,104 | 14.2 yrs | £2,500 |
| 4 kW | 3511 kWh | 1404 kWh | 2107 kWh | £363 | £211 | £574 | £8,138 | 14.2 yrs | £3,334 |
| 5 kW | 4389 kWh | 1756 kWh | 2633 kWh | £454 | £263 | £717 | £10,173 | 14.2 yrs | £4,167 |
| 6 kW | 5267 kWh | 2107 kWh | 3160 kWh | £544 | £316 | £860 | £12,207 | 14.2 yrs | £5,001 |
| 7 kW | 6145 kWh | 2458 kWh | 3687 kWh | £635 | £369 | £1,004 | £14,242 | 14.2 yrs | £5,834 |
| 8 kW | 7022 kWh | 2809 kWh | 4213 kWh | £726 | £421 | £1,147 | £16,276 | 14.2 yrs | £6,668 |
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: £856, Upfront: £12,273, Break-even: 14.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1756 kWh | 1053 kWh | 702 kWh | £272 | £70 | £342 | £6,169 | 18.0 yrs | £679 |
| 3 kW | 2633 kWh | 1580 kWh | 1053 kWh | £408 | £105 | £514 | £8,204 | 16.0 yrs | £2,069 |
| 4 kW | 3511 kWh | 2107 kWh | 1404 kWh | £544 | £140 | £685 | £10,238 | 14.9 yrs | £3,459 |
| 5 kW | 4389 kWh | 2633 kWh | 1756 kWh | £680 | £176 | £856 | £12,273 | 14.3 yrs | £4,848 |
| 6 kW | 5267 kWh | 3160 kWh | 2107 kWh | £817 | £211 | £1,027 | £14,307 | 13.9 yrs | £6,238 |
| 7 kW | 6145 kWh | 3687 kWh | 2458 kWh | £953 | £246 | £1,198 | £16,342 | 13.6 yrs | £7,628 |
| 8 kW | 7022 kWh | 4213 kWh | 2809 kWh | £1,089 | £281 | £1,370 | £18,376 | 13.4 yrs | £9,017 |
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: £926, Upfront: £13,673, Break-even: 14.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1756 kWh | 1229 kWh | 527 kWh | £318 | £53 | £370 | £7,569 | 20.4 yrs | £-165 |
| 3 kW | 2633 kWh | 1843 kWh | 790 kWh | £476 | £79 | £555 | £9,604 | 17.3 yrs | £1,503 |
| 4 kW | 3511 kWh | 2458 kWh | 1053 kWh | £635 | £105 | £740 | £11,638 | 15.7 yrs | £3,171 |
| 5 kW | 4389 kWh | 3072 kWh | 1317 kWh | £794 | £132 | £926 | £13,673 | 14.8 yrs | £4,839 |
| 6 kW | 5267 kWh | 3687 kWh | 1580 kWh | £953 | £158 | £1,111 | £15,707 | 14.1 yrs | £6,506 |
| 7 kW | 6145 kWh | 4301 kWh | 1843 kWh | £1,111 | £184 | £1,296 | £17,742 | 13.7 yrs | £8,174 |
| 8 kW | 7022 kWh | 4916 kWh | 2107 kWh | £1,270 | £211 | £1,481 | £19,776 | 13.4 yrs | £9,842 |
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: £946, Upfront: £15,423, Break-even: 16.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1756 kWh | 1282 kWh | 474 kWh | £331 | £47 | £379 | £9,319 | 24.6 yrs | £-1,748 |
| 3 kW | 2633 kWh | 1922 kWh | 711 kWh | £497 | £71 | £568 | £11,354 | 20.0 yrs | £4 |
| 4 kW | 3511 kWh | 2563 kWh | 948 kWh | £662 | £95 | £757 | £13,388 | 17.7 yrs | £1,755 |
| 5 kW | 4389 kWh | 3204 kWh | 1185 kWh | £828 | £119 | £946 | £15,423 | 16.3 yrs | £3,506 |
| 6 kW | 5267 kWh | 3845 kWh | 1422 kWh | £993 | £142 | £1,136 | £17,457 | 15.4 yrs | £5,257 |
| 7 kW | 6145 kWh | 4486 kWh | 1659 kWh | £1,159 | £166 | £1,325 | £19,492 | 14.7 yrs | £7,008 |
| 8 kW | 7022 kWh | 5126 kWh | 1896 kWh | £1,325 | £190 | £1,514 | £21,526 | 14.2 yrs | £8,759 |
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: £960, Upfront: £17,173, Break-even: 17.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1756 kWh | 1317 kWh | 439 kWh | £340 | £44 | £384 | £11,069 | 28.8 yrs | £-3,386 |
| 3 kW | 2633 kWh | 1975 kWh | 658 kWh | £510 | £66 | £576 | £13,104 | 22.7 yrs | £-1,580 |
| 4 kW | 3511 kWh | 2633 kWh | 878 kWh | £680 | £88 | £768 | £15,138 | 19.7 yrs | £227 |
| 5 kW | 4389 kWh | 3292 kWh | 1097 kWh | £851 | £110 | £960 | £17,173 | 17.9 yrs | £2,034 |
| 6 kW | 5267 kWh | 3950 kWh | 1317 kWh | £1,021 | £132 | £1,152 | £19,207 | 16.7 yrs | £3,841 |
| 7 kW | 6145 kWh | 4609 kWh | 1536 kWh | £1,191 | £154 | £1,344 | £21,242 | 15.8 yrs | £5,648 |
| 8 kW | 7022 kWh | 5267 kWh | 1756 kWh | £1,361 | £176 | £1,537 | £23,276 | 15.1 yrs | £7,454 |
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: £974, Upfront: £19,623, Break-even: 20.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1756 kWh | 1352 kWh | 404 kWh | £349 | £40 | £390 | £13,519 | 34.7 yrs | £-5,725 |
| 3 kW | 2633 kWh | 2028 kWh | 606 kWh | £524 | £61 | £585 | £15,554 | 26.6 yrs | £-3,863 |
| 4 kW | 3511 kWh | 2704 kWh | 808 kWh | £699 | £81 | £779 | £17,588 | 22.6 yrs | £-2,000 |
| 5 kW | 4389 kWh | 3380 kWh | 1009 kWh | £873 | £101 | £974 | £19,623 | 20.1 yrs | £-138 |
| 6 kW | 5267 kWh | 4055 kWh | 1211 kWh | £1,048 | £121 | £1,169 | £21,657 | 18.5 yrs | £1,724 |
| 7 kW | 6145 kWh | 4731 kWh | 1413 kWh | £1,223 | £141 | £1,364 | £23,692 | 17.4 yrs | £3,587 |
| 8 kW | 7022 kWh | 5407 kWh | 1615 kWh | £1,397 | £162 | £1,559 | £25,726 | 16.5 yrs | £5,449 |
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.