A typical roof here lands around 4.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 928 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: £754, Upfront: £10,173, 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 | 1856 kWh | 742 kWh | 1113 kWh | £190 | £111 | £302 | £4,069 | 13.5 yrs | £1,964 |
| 3 kW | 2784 kWh | 1113 kWh | 1670 kWh | £285 | £167 | £453 | £6,104 | 13.5 yrs | £2,947 |
| 4 kW | 3712 kWh | 1485 kWh | 2227 kWh | £381 | £223 | £603 | £8,138 | 13.5 yrs | £3,929 |
| 5 kW | 4639 kWh | 1856 kWh | 2784 kWh | £476 | £278 | £754 | £10,173 | 13.5 yrs | £4,911 |
| 6 kW | 5567 kWh | 2227 kWh | 3340 kWh | £571 | £334 | £905 | £12,207 | 13.5 yrs | £5,893 |
| 7 kW | 6495 kWh | 2598 kWh | 3897 kWh | £666 | £390 | £1,056 | £14,242 | 13.5 yrs | £6,876 |
| 8 kW | 7423 kWh | 2969 kWh | 4454 kWh | £761 | £445 | £1,207 | £16,276 | 13.5 yrs | £7,858 |
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: £899, Upfront: £12,273, Break-even: 13.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1856 kWh | 1113 kWh | 742 kWh | £285 | £74 | £360 | £6,169 | 17.1 yrs | £1,025 |
| 3 kW | 2784 kWh | 1670 kWh | 1113 kWh | £428 | £111 | £540 | £8,204 | 15.2 yrs | £2,588 |
| 4 kW | 3712 kWh | 2227 kWh | 1485 kWh | £571 | £148 | £719 | £10,238 | 14.2 yrs | £4,151 |
| 5 kW | 4639 kWh | 2784 kWh | 1856 kWh | £714 | £186 | £899 | £12,273 | 13.6 yrs | £5,714 |
| 6 kW | 5567 kWh | 3340 kWh | 2227 kWh | £856 | £223 | £1,079 | £14,307 | 13.3 yrs | £7,276 |
| 7 kW | 6495 kWh | 3897 kWh | 2598 kWh | £999 | £260 | £1,259 | £16,342 | 13.0 yrs | £8,839 |
| 8 kW | 7423 kWh | 4454 kWh | 2969 kWh | £1,142 | £297 | £1,439 | £18,376 | 12.8 yrs | £10,402 |
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: £972, Upfront: £13,673, Break-even: 14.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1856 kWh | 1299 kWh | 557 kWh | £333 | £56 | £389 | £7,569 | 19.5 yrs | £206 |
| 3 kW | 2784 kWh | 1949 kWh | 835 kWh | £500 | £84 | £583 | £9,604 | 16.5 yrs | £2,059 |
| 4 kW | 3712 kWh | 2598 kWh | 1113 kWh | £666 | £111 | £777 | £11,638 | 15.0 yrs | £3,912 |
| 5 kW | 4639 kWh | 3248 kWh | 1392 kWh | £833 | £139 | £972 | £13,673 | 14.1 yrs | £5,765 |
| 6 kW | 5567 kWh | 3897 kWh | 1670 kWh | £999 | £167 | £1,166 | £15,707 | 13.5 yrs | £7,618 |
| 7 kW | 6495 kWh | 4547 kWh | 1949 kWh | £1,166 | £195 | £1,361 | £17,742 | 13.0 yrs | £9,471 |
| 8 kW | 7423 kWh | 5196 kWh | 2227 kWh | £1,332 | £223 | £1,555 | £19,776 | 12.7 yrs | £11,324 |
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: £994, Upfront: £15,423, Break-even: 15.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1856 kWh | 1355 kWh | 501 kWh | £347 | £50 | £397 | £9,319 | 23.4 yrs | £-1,370 |
| 3 kW | 2784 kWh | 2032 kWh | 752 kWh | £521 | £75 | £596 | £11,354 | 19.0 yrs | £570 |
| 4 kW | 3712 kWh | 2709 kWh | 1002 kWh | £695 | £100 | £795 | £13,388 | 16.8 yrs | £2,510 |
| 5 kW | 4639 kWh | 3387 kWh | 1253 kWh | £868 | £125 | £994 | £15,423 | 15.5 yrs | £4,450 |
| 6 kW | 5567 kWh | 4064 kWh | 1503 kWh | £1,042 | £150 | £1,192 | £17,457 | 14.6 yrs | £6,390 |
| 7 kW | 6495 kWh | 4742 kWh | 1754 kWh | £1,216 | £175 | £1,391 | £19,492 | 14.0 yrs | £8,330 |
| 8 kW | 7423 kWh | 5419 kWh | 2004 kWh | £1,389 | £200 | £1,590 | £21,526 | 13.5 yrs | £10,270 |
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: £1,008, Upfront: £17,173, Break-even: 17.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1856 kWh | 1392 kWh | 464 kWh | £357 | £46 | £403 | £11,069 | 27.4 yrs | £-3,004 |
| 3 kW | 2784 kWh | 2088 kWh | 696 kWh | £535 | £70 | £605 | £13,104 | 21.7 yrs | £-1,006 |
| 4 kW | 3712 kWh | 2784 kWh | 928 kWh | £714 | £93 | £807 | £15,138 | 18.8 yrs | £992 |
| 5 kW | 4639 kWh | 3480 kWh | 1160 kWh | £892 | £116 | £1,008 | £17,173 | 17.0 yrs | £2,990 |
| 6 kW | 5567 kWh | 4176 kWh | 1392 kWh | £1,071 | £139 | £1,210 | £19,207 | 15.9 yrs | £4,989 |
| 7 kW | 6495 kWh | 4871 kWh | 1624 kWh | £1,249 | £162 | £1,411 | £21,242 | 15.0 yrs | £6,987 |
| 8 kW | 7423 kWh | 5567 kWh | 1856 kWh | £1,427 | £186 | £1,613 | £23,276 | 14.4 yrs | £8,985 |
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: £1,023, Upfront: £19,623, Break-even: 19.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1856 kWh | 1429 kWh | 427 kWh | £366 | £43 | £409 | £13,519 | 33.0 yrs | £-5,338 |
| 3 kW | 2784 kWh | 2143 kWh | 640 kWh | £550 | £64 | £614 | £15,554 | 25.3 yrs | £-3,282 |
| 4 kW | 3712 kWh | 2858 kWh | 854 kWh | £733 | £85 | £818 | £17,588 | 21.5 yrs | £-1,225 |
| 5 kW | 4639 kWh | 3572 kWh | 1067 kWh | £916 | £107 | £1,023 | £19,623 | 19.2 yrs | £831 |
| 6 kW | 5567 kWh | 4287 kWh | 1280 kWh | £1,099 | £128 | £1,227 | £21,657 | 17.6 yrs | £2,887 |
| 7 kW | 6495 kWh | 5001 kWh | 1494 kWh | £1,282 | £149 | £1,432 | £23,692 | 16.5 yrs | £4,943 |
| 8 kW | 7423 kWh | 5716 kWh | 1707 kWh | £1,466 | £171 | £1,636 | £25,726 | 15.7 yrs | £6,999 |
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.