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 1016 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: £826, Upfront: £10,173, 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 | 2032 kWh | 813 kWh | 1219 kWh | £208 | £122 | £330 | £4,069 | 12.3 yrs | £2,536 |
| 3 kW | 3048 kWh | 1219 kWh | 1829 kWh | £312 | £183 | £495 | £6,104 | 12.3 yrs | £3,803 |
| 4 kW | 4064 kWh | 1626 kWh | 2438 kWh | £417 | £244 | £660 | £8,138 | 12.3 yrs | £5,071 |
| 5 kW | 5080 kWh | 2032 kWh | 3048 kWh | £521 | £305 | £826 | £10,173 | 12.3 yrs | £6,339 |
| 6 kW | 6096 kWh | 2438 kWh | 3657 kWh | £625 | £366 | £991 | £12,207 | 12.3 yrs | £7,607 |
| 7 kW | 7112 kWh | 2845 kWh | 4267 kWh | £729 | £427 | £1,156 | £14,242 | 12.3 yrs | £8,875 |
| 8 kW | 8128 kWh | 3251 kWh | 4877 kWh | £833 | £488 | £1,321 | £16,276 | 12.3 yrs | £10,142 |
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: £984, Upfront: £12,273, Break-even: 12.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2032 kWh | 1219 kWh | 813 kWh | £312 | £81 | £394 | £6,169 | 15.7 yrs | £1,706 |
| 3 kW | 3048 kWh | 1829 kWh | 1219 kWh | £469 | £122 | £591 | £8,204 | 13.9 yrs | £3,609 |
| 4 kW | 4064 kWh | 2438 kWh | 1626 kWh | £625 | £163 | £787 | £10,238 | 13.0 yrs | £5,512 |
| 5 kW | 5080 kWh | 3048 kWh | 2032 kWh | £781 | £203 | £984 | £12,273 | 12.5 yrs | £7,415 |
| 6 kW | 6096 kWh | 3657 kWh | 2438 kWh | £937 | £244 | £1,181 | £14,307 | 12.1 yrs | £9,318 |
| 7 kW | 7112 kWh | 4267 kWh | 2845 kWh | £1,094 | £284 | £1,378 | £16,342 | 11.9 yrs | £11,221 |
| 8 kW | 8128 kWh | 4877 kWh | 3251 kWh | £1,250 | £325 | £1,575 | £18,376 | 11.7 yrs | £13,124 |
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: £1,064, Upfront: £13,673, 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 | 2032 kWh | 1422 kWh | 610 kWh | £365 | £61 | £426 | £7,569 | 17.8 yrs | £941 |
| 3 kW | 3048 kWh | 2134 kWh | 914 kWh | £547 | £91 | £638 | £9,604 | 15.0 yrs | £3,162 |
| 4 kW | 4064 kWh | 2845 kWh | 1219 kWh | £729 | £122 | £851 | £11,638 | 13.7 yrs | £5,382 |
| 5 kW | 5080 kWh | 3556 kWh | 1524 kWh | £911 | £152 | £1,064 | £13,673 | 12.9 yrs | £7,603 |
| 6 kW | 6096 kWh | 4267 kWh | 1829 kWh | £1,094 | £183 | £1,277 | £15,707 | 12.3 yrs | £9,823 |
| 7 kW | 7112 kWh | 4978 kWh | 2134 kWh | £1,276 | £213 | £1,489 | £17,742 | 11.9 yrs | £12,044 |
| 8 kW | 8128 kWh | 5689 kWh | 2438 kWh | £1,458 | £244 | £1,702 | £19,776 | 11.6 yrs | £14,265 |
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: £1,088, Upfront: £15,423, 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 | 2032 kWh | 1483 kWh | 549 kWh | £380 | £55 | £435 | £9,319 | 21.4 yrs | £-618 |
| 3 kW | 3048 kWh | 2225 kWh | 823 kWh | £570 | £82 | £653 | £11,354 | 17.4 yrs | £1,698 |
| 4 kW | 4064 kWh | 2967 kWh | 1097 kWh | £760 | £110 | £870 | £13,388 | 15.4 yrs | £4,013 |
| 5 kW | 5080 kWh | 3708 kWh | 1372 kWh | £950 | £137 | £1,088 | £15,423 | 14.2 yrs | £6,329 |
| 6 kW | 6096 kWh | 4450 kWh | 1646 kWh | £1,141 | £165 | £1,305 | £17,457 | 13.4 yrs | £8,645 |
| 7 kW | 7112 kWh | 5192 kWh | 1920 kWh | £1,331 | £192 | £1,523 | £19,492 | 12.8 yrs | £10,961 |
| 8 kW | 8128 kWh | 5933 kWh | 2194 kWh | £1,521 | £219 | £1,740 | £21,526 | 12.4 yrs | £13,277 |
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: £1,103, Upfront: £17,173, Break-even: 15.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2032 kWh | 1524 kWh | 508 kWh | £391 | £51 | £441 | £11,069 | 25.1 yrs | £-2,241 |
| 3 kW | 3048 kWh | 2286 kWh | 762 kWh | £586 | £76 | £662 | £13,104 | 19.8 yrs | £138 |
| 4 kW | 4064 kWh | 3048 kWh | 1016 kWh | £781 | £102 | £883 | £15,138 | 17.1 yrs | £2,517 |
| 5 kW | 5080 kWh | 3810 kWh | 1270 kWh | £976 | £127 | £1,103 | £17,173 | 15.6 yrs | £4,897 |
| 6 kW | 6096 kWh | 4572 kWh | 1524 kWh | £1,172 | £152 | £1,324 | £19,207 | 14.5 yrs | £7,276 |
| 7 kW | 7112 kWh | 5334 kWh | 1778 kWh | £1,367 | £178 | £1,545 | £21,242 | 13.7 yrs | £9,656 |
| 8 kW | 8128 kWh | 6096 kWh | 2032 kWh | £1,562 | £203 | £1,766 | £23,276 | 13.2 yrs | £12,035 |
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: £1,119, Upfront: £19,623, Break-even: 17.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2032 kWh | 1565 kWh | 467 kWh | £401 | £47 | £448 | £13,519 | 30.2 yrs | £-4,564 |
| 3 kW | 3048 kWh | 2347 kWh | 701 kWh | £602 | £70 | £672 | £15,554 | 23.2 yrs | £-2,121 |
| 4 kW | 4064 kWh | 3129 kWh | 935 kWh | £802 | £93 | £895 | £17,588 | 19.6 yrs | £322 |
| 5 kW | 5080 kWh | 3911 kWh | 1168 kWh | £1,003 | £117 | £1,119 | £19,623 | 17.5 yrs | £2,764 |
| 6 kW | 6096 kWh | 4694 kWh | 1402 kWh | £1,203 | £140 | £1,343 | £21,657 | 16.1 yrs | £5,207 |
| 7 kW | 7112 kWh | 5476 kWh | 1636 kWh | £1,404 | £164 | £1,567 | £23,692 | 15.1 yrs | £7,650 |
| 8 kW | 8128 kWh | 6258 kWh | 1869 kWh | £1,604 | £187 | £1,791 | £25,726 | 14.4 yrs | £10,093 |
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.