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 943 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: £765, Upfront: £10,173, 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 | 1886 kWh | 754 kWh | 1132 kWh | £193 | £113 | £306 | £4,069 | 13.3 yrs | £2,050 |
| 3 kW | 2829 kWh | 1132 kWh | 1698 kWh | £289 | £170 | £459 | £6,104 | 13.3 yrs | £3,075 |
| 4 kW | 3772 kWh | 1509 kWh | 2263 kWh | £386 | £226 | £612 | £8,138 | 13.3 yrs | £4,100 |
| 5 kW | 4716 kWh | 1886 kWh | 2829 kWh | £482 | £283 | £765 | £10,173 | 13.3 yrs | £5,125 |
| 6 kW | 5659 kWh | 2263 kWh | 3395 kWh | £578 | £340 | £918 | £12,207 | 13.3 yrs | £6,150 |
| 7 kW | 6602 kWh | 2641 kWh | 3961 kWh | £675 | £396 | £1,071 | £14,242 | 13.3 yrs | £7,175 |
| 8 kW | 7545 kWh | 3018 kWh | 4527 kWh | £771 | £453 | £1,224 | £16,276 | 13.3 yrs | £8,200 |
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: £912, Upfront: £12,273, Break-even: 13.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1886 kWh | 1132 kWh | 754 kWh | £289 | £75 | £365 | £6,169 | 16.9 yrs | £1,123 |
| 3 kW | 2829 kWh | 1698 kWh | 1132 kWh | £434 | £113 | £547 | £8,204 | 15.0 yrs | £2,735 |
| 4 kW | 3772 kWh | 2263 kWh | 1509 kWh | £578 | £151 | £729 | £10,238 | 14.0 yrs | £4,346 |
| 5 kW | 4716 kWh | 2829 kWh | 1886 kWh | £723 | £189 | £912 | £12,273 | 13.5 yrs | £5,958 |
| 6 kW | 5659 kWh | 3395 kWh | 2263 kWh | £867 | £226 | £1,094 | £14,307 | 13.1 yrs | £7,570 |
| 7 kW | 6602 kWh | 3961 kWh | 2641 kWh | £1,012 | £264 | £1,276 | £16,342 | 12.8 yrs | £9,181 |
| 8 kW | 7545 kWh | 4527 kWh | 3018 kWh | £1,157 | £302 | £1,458 | £18,376 | 12.6 yrs | £10,793 |
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: £985, Upfront: £13,673, 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 | 1886 kWh | 1320 kWh | 566 kWh | £337 | £57 | £394 | £7,569 | 19.2 yrs | £310 |
| 3 kW | 2829 kWh | 1981 kWh | 849 kWh | £506 | £85 | £591 | £9,604 | 16.3 yrs | £2,215 |
| 4 kW | 3772 kWh | 2641 kWh | 1132 kWh | £675 | £113 | £788 | £11,638 | 14.8 yrs | £4,120 |
| 5 kW | 4716 kWh | 3301 kWh | 1415 kWh | £843 | £141 | £985 | £13,673 | 13.9 yrs | £6,025 |
| 6 kW | 5659 kWh | 3961 kWh | 1698 kWh | £1,012 | £170 | £1,182 | £15,707 | 13.3 yrs | £7,929 |
| 7 kW | 6602 kWh | 4621 kWh | 1981 kWh | £1,181 | £198 | £1,379 | £17,742 | 12.9 yrs | £9,834 |
| 8 kW | 7545 kWh | 5281 kWh | 2263 kWh | £1,349 | £226 | £1,576 | £19,776 | 12.6 yrs | £11,739 |
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: £1,007, Upfront: £15,423, 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 | 1886 kWh | 1377 kWh | 509 kWh | £352 | £51 | £403 | £9,319 | 23.1 yrs | £-1,264 |
| 3 kW | 2829 kWh | 2065 kWh | 764 kWh | £528 | £76 | £604 | £11,354 | 18.8 yrs | £729 |
| 4 kW | 3772 kWh | 2754 kWh | 1019 kWh | £704 | £102 | £805 | £13,388 | 16.6 yrs | £2,722 |
| 5 kW | 4716 kWh | 3442 kWh | 1273 kWh | £880 | £127 | £1,007 | £15,423 | 15.3 yrs | £4,714 |
| 6 kW | 5659 kWh | 4131 kWh | 1528 kWh | £1,055 | £153 | £1,208 | £17,457 | 14.4 yrs | £6,707 |
| 7 kW | 6602 kWh | 4819 kWh | 1782 kWh | £1,231 | £178 | £1,410 | £19,492 | 13.8 yrs | £8,700 |
| 8 kW | 7545 kWh | 5508 kWh | 2037 kWh | £1,407 | £204 | £1,611 | £21,526 | 13.4 yrs | £10,693 |
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: £1,022, Upfront: £17,173, Break-even: 16.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1886 kWh | 1415 kWh | 472 kWh | £361 | £47 | £409 | £11,069 | 27.1 yrs | £-2,897 |
| 3 kW | 2829 kWh | 2122 kWh | 707 kWh | £542 | £71 | £613 | £13,104 | 21.4 yrs | £-845 |
| 4 kW | 3772 kWh | 2829 kWh | 943 kWh | £723 | £94 | £817 | £15,138 | 18.5 yrs | £1,206 |
| 5 kW | 4716 kWh | 3537 kWh | 1179 kWh | £904 | £118 | £1,022 | £17,173 | 16.8 yrs | £3,258 |
| 6 kW | 5659 kWh | 4244 kWh | 1415 kWh | £1,084 | £141 | £1,226 | £19,207 | 15.7 yrs | £5,309 |
| 7 kW | 6602 kWh | 4951 kWh | 1650 kWh | £1,265 | £165 | £1,430 | £21,242 | 14.9 yrs | £7,361 |
| 8 kW | 7545 kWh | 5659 kWh | 1886 kWh | £1,446 | £189 | £1,634 | £23,276 | 14.2 yrs | £9,412 |
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: £1,036, Upfront: £19,623, Break-even: 18.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1886 kWh | 1452 kWh | 434 kWh | £371 | £43 | £414 | £13,519 | 32.6 yrs | £-5,230 |
| 3 kW | 2829 kWh | 2179 kWh | 651 kWh | £557 | £65 | £622 | £15,554 | 25.0 yrs | £-3,119 |
| 4 kW | 3772 kWh | 2905 kWh | 868 kWh | £742 | £87 | £829 | £17,588 | 21.2 yrs | £-1,009 |
| 5 kW | 4716 kWh | 3631 kWh | 1085 kWh | £928 | £108 | £1,036 | £19,623 | 18.9 yrs | £1,101 |
| 6 kW | 5659 kWh | 4357 kWh | 1302 kWh | £1,113 | £130 | £1,243 | £21,657 | 17.4 yrs | £3,211 |
| 7 kW | 6602 kWh | 5083 kWh | 1518 kWh | £1,299 | £152 | £1,451 | £23,692 | 16.3 yrs | £5,322 |
| 8 kW | 7545 kWh | 5810 kWh | 1735 kWh | £1,484 | £174 | £1,658 | £25,726 | 15.5 yrs | £7,432 |
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.