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 694 kWh per year on a south-facing roof. We value self-used electricity at 27.1p 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: £584, Upfront: £10,173, Break-even: 17.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1388 kWh | 555 kWh | 833 kWh | £150 | £83 | £233 | £4,069 | 17.4 yrs | £601 |
| 3 kW | 2082 kWh | 833 kWh | 1249 kWh | £225 | £125 | £350 | £6,104 | 17.4 yrs | £901 |
| 4 kW | 2776 kWh | 1110 kWh | 1665 kWh | £300 | £167 | £467 | £8,138 | 17.4 yrs | £1,202 |
| 5 kW | 3470 kWh | 1388 kWh | 2082 kWh | £376 | £208 | £584 | £10,173 | 17.4 yrs | £1,502 |
| 6 kW | 4164 kWh | 1665 kWh | 2498 kWh | £451 | £250 | £700 | £12,207 | 17.4 yrs | £1,802 |
| 7 kW | 4857 kWh | 1943 kWh | 2914 kWh | £526 | £291 | £817 | £14,242 | 17.4 yrs | £2,103 |
| 8 kW | 5551 kWh | 2221 kWh | 3331 kWh | £601 | £333 | £934 | £16,276 | 17.4 yrs | £2,403 |
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: £702, Upfront: £12,273, 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 | 1388 kWh | 833 kWh | 555 kWh | £225 | £56 | £281 | £6,169 | 22.0 yrs | £-552 |
| 3 kW | 2082 kWh | 1249 kWh | 833 kWh | £338 | £83 | £421 | £8,204 | 19.5 yrs | £222 |
| 4 kW | 2776 kWh | 1665 kWh | 1110 kWh | £451 | £111 | £562 | £10,238 | 18.2 yrs | £996 |
| 5 kW | 3470 kWh | 2082 kWh | 1388 kWh | £563 | £139 | £702 | £12,273 | 17.5 yrs | £1,770 |
| 6 kW | 4164 kWh | 2498 kWh | 1665 kWh | £676 | £167 | £843 | £14,307 | 17.0 yrs | £2,544 |
| 7 kW | 4857 kWh | 2914 kWh | 1943 kWh | £789 | £194 | £983 | £16,342 | 16.6 yrs | £3,317 |
| 8 kW | 5551 kWh | 3331 kWh | 2221 kWh | £901 | £222 | £1,123 | £18,376 | 16.4 yrs | £4,091 |
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: £761, Upfront: £13,673, Break-even: 18.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1388 kWh | 971 kWh | 416 kWh | £263 | £42 | £305 | £7,569 | 24.9 yrs | £-1,479 |
| 3 kW | 2082 kWh | 1457 kWh | 625 kWh | £394 | £62 | £457 | £9,604 | 21.0 yrs | £-468 |
| 4 kW | 2776 kWh | 1943 kWh | 833 kWh | £526 | £83 | £609 | £11,638 | 19.1 yrs | £543 |
| 5 kW | 3470 kWh | 2429 kWh | 1041 kWh | £657 | £104 | £761 | £13,673 | 18.0 yrs | £1,553 |
| 6 kW | 4164 kWh | 2914 kWh | 1249 kWh | £789 | £125 | £914 | £15,707 | 17.2 yrs | £2,564 |
| 7 kW | 4857 kWh | 3400 kWh | 1457 kWh | £920 | £146 | £1,066 | £17,742 | 16.6 yrs | £3,575 |
| 8 kW | 5551 kWh | 3886 kWh | 1665 kWh | £1,052 | £167 | £1,218 | £19,776 | 16.2 yrs | £4,586 |
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: £779, Upfront: £15,423, Break-even: 19.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1388 kWh | 1013 kWh | 375 kWh | £274 | £37 | £312 | £9,319 | 29.9 yrs | £-3,087 |
| 3 kW | 2082 kWh | 1520 kWh | 562 kWh | £411 | £56 | £467 | £11,354 | 24.3 yrs | £-2,005 |
| 4 kW | 2776 kWh | 2026 kWh | 749 kWh | £548 | £75 | £623 | £13,388 | 21.5 yrs | £-923 |
| 5 kW | 3470 kWh | 2533 kWh | 937 kWh | £685 | £94 | £779 | £15,423 | 19.8 yrs | £159 |
| 6 kW | 4164 kWh | 3039 kWh | 1124 kWh | £822 | £112 | £935 | £17,457 | 18.7 yrs | £1,240 |
| 7 kW | 4857 kWh | 3546 kWh | 1312 kWh | £960 | £131 | £1,091 | £19,492 | 17.9 yrs | £2,322 |
| 8 kW | 5551 kWh | 4052 kWh | 1499 kWh | £1,097 | £150 | £1,246 | £21,526 | 17.3 yrs | £3,404 |
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: £791, Upfront: £17,173, Break-even: 21.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1388 kWh | 1041 kWh | 347 kWh | £282 | £35 | £316 | £11,069 | 35.0 yrs | £-4,742 |
| 3 kW | 2082 kWh | 1561 kWh | 520 kWh | £422 | £52 | £475 | £13,104 | 27.6 yrs | £-3,613 |
| 4 kW | 2776 kWh | 2082 kWh | 694 kWh | £563 | £69 | £633 | £15,138 | 23.9 yrs | £-2,484 |
| 5 kW | 3470 kWh | 2602 kWh | 867 kWh | £704 | £87 | £791 | £17,173 | 21.7 yrs | £-1,355 |
| 6 kW | 4164 kWh | 3123 kWh | 1041 kWh | £845 | £104 | £949 | £19,207 | 20.2 yrs | £-226 |
| 7 kW | 4857 kWh | 3643 kWh | 1214 kWh | £986 | £121 | £1,107 | £21,242 | 19.2 yrs | £903 |
| 8 kW | 5551 kWh | 4164 kWh | 1388 kWh | £1,127 | £139 | £1,265 | £23,276 | 18.4 yrs | £2,033 |
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: £803, Upfront: £19,623, Break-even: 24.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1388 kWh | 1069 kWh | 319 kWh | £289 | £32 | £321 | £13,519 | 42.1 yrs | £-7,097 |
| 3 kW | 2082 kWh | 1603 kWh | 479 kWh | £434 | £48 | £482 | £15,554 | 32.3 yrs | £-5,921 |
| 4 kW | 2776 kWh | 2137 kWh | 638 kWh | £578 | £64 | £642 | £17,588 | 27.4 yrs | £-4,744 |
| 5 kW | 3470 kWh | 2672 kWh | 798 kWh | £723 | £80 | £803 | £19,623 | 24.4 yrs | £-3,568 |
| 6 kW | 4164 kWh | 3206 kWh | 958 kWh | £868 | £96 | £963 | £21,657 | 22.5 yrs | £-2,391 |
| 7 kW | 4857 kWh | 3740 kWh | 1117 kWh | £1,012 | £112 | £1,124 | £23,692 | 21.1 yrs | £-1,215 |
| 8 kW | 5551 kWh | 4275 kWh | 1277 kWh | £1,157 | £128 | £1,284 | £25,726 | 20.0 yrs | £-39 |
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.