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 1074 kWh per year on a south-facing roof. We value self-used electricity at 26.5p 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: £891, Upfront: £10,173, Break-even: 11.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2148 kWh | 859 kWh | 1289 kWh | £227 | £129 | £356 | £4,069 | 11.4 yrs | £3,057 |
| 3 kW | 3221 kWh | 1289 kWh | 1933 kWh | £341 | £193 | £534 | £6,104 | 11.4 yrs | £4,586 |
| 4 kW | 4295 kWh | 1718 kWh | 2577 kWh | £455 | £258 | £713 | £8,138 | 11.4 yrs | £6,115 |
| 5 kW | 5369 kWh | 2148 kWh | 3221 kWh | £569 | £322 | £891 | £10,173 | 11.4 yrs | £7,643 |
| 6 kW | 6443 kWh | 2577 kWh | 3866 kWh | £682 | £387 | £1,069 | £12,207 | 11.4 yrs | £9,172 |
| 7 kW | 7516 kWh | 3007 kWh | 4510 kWh | £796 | £451 | £1,247 | £14,242 | 11.4 yrs | £10,701 |
| 8 kW | 8590 kWh | 3436 kWh | 5154 kWh | £910 | £515 | £1,425 | £16,276 | 11.4 yrs | £12,230 |
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: £1,068, Upfront: £12,273, Break-even: 11.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2148 kWh | 1289 kWh | 859 kWh | £341 | £86 | £427 | £6,169 | 14.4 yrs | £2,373 |
| 3 kW | 3221 kWh | 1933 kWh | 1289 kWh | £512 | £129 | £641 | £8,204 | 12.8 yrs | £4,610 |
| 4 kW | 4295 kWh | 2577 kWh | 1718 kWh | £682 | £172 | £854 | £10,238 | 12.0 yrs | £6,846 |
| 5 kW | 5369 kWh | 3221 kWh | 2148 kWh | £853 | £215 | £1,068 | £12,273 | 11.5 yrs | £9,083 |
| 6 kW | 6443 kWh | 3866 kWh | 2577 kWh | £1,024 | £258 | £1,281 | £14,307 | 11.2 yrs | £11,319 |
| 7 kW | 7516 kWh | 4510 kWh | 3007 kWh | £1,194 | £301 | £1,495 | £16,342 | 10.9 yrs | £13,556 |
| 8 kW | 8590 kWh | 5154 kWh | 3436 kWh | £1,365 | £344 | £1,708 | £18,376 | 10.8 yrs | £15,792 |
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: £1,156, Upfront: £13,673, Break-even: 11.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2148 kWh | 1503 kWh | 644 kWh | £398 | £64 | £462 | £7,569 | 16.4 yrs | £1,681 |
| 3 kW | 3221 kWh | 2255 kWh | 966 kWh | £597 | £97 | £694 | £9,604 | 13.8 yrs | £4,271 |
| 4 kW | 4295 kWh | 3007 kWh | 1289 kWh | £796 | £129 | £925 | £11,638 | 12.6 yrs | £6,862 |
| 5 kW | 5369 kWh | 3758 kWh | 1611 kWh | £995 | £161 | £1,156 | £13,673 | 11.8 yrs | £9,452 |
| 6 kW | 6443 kWh | 4510 kWh | 1933 kWh | £1,194 | £193 | £1,387 | £15,707 | 11.3 yrs | £12,043 |
| 7 kW | 7516 kWh | 5261 kWh | 2255 kWh | £1,393 | £225 | £1,619 | £17,742 | 11.0 yrs | £14,633 |
| 8 kW | 8590 kWh | 6013 kWh | 2577 kWh | £1,592 | £258 | £1,850 | £19,776 | 10.7 yrs | £17,223 |
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: £1,183, Upfront: £15,423, Break-even: 13.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2148 kWh | 1568 kWh | 580 kWh | £415 | £58 | £473 | £9,319 | 19.7 yrs | £143 |
| 3 kW | 3221 kWh | 2352 kWh | 870 kWh | £623 | £87 | £710 | £11,354 | 16.0 yrs | £2,840 |
| 4 kW | 4295 kWh | 3135 kWh | 1160 kWh | £830 | £116 | £946 | £13,388 | 14.1 yrs | £5,536 |
| 5 kW | 5369 kWh | 3919 kWh | 1450 kWh | £1,038 | £145 | £1,183 | £15,423 | 13.0 yrs | £8,233 |
| 6 kW | 6443 kWh | 4703 kWh | 1740 kWh | £1,245 | £174 | £1,419 | £17,457 | 12.3 yrs | £10,930 |
| 7 kW | 7516 kWh | 5487 kWh | 2029 kWh | £1,453 | £203 | £1,656 | £19,492 | 11.8 yrs | £13,626 |
| 8 kW | 8590 kWh | 6271 kWh | 2319 kWh | £1,661 | £232 | £1,892 | £21,526 | 11.4 yrs | £16,323 |
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: £1,200, Upfront: £17,173, 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 | 2148 kWh | 1611 kWh | 537 kWh | £427 | £54 | £480 | £11,069 | 23.1 yrs | £-1,465 |
| 3 kW | 3221 kWh | 2416 kWh | 805 kWh | £640 | £81 | £720 | £13,104 | 18.2 yrs | £1,302 |
| 4 kW | 4295 kWh | 3221 kWh | 1074 kWh | £853 | £107 | £960 | £15,138 | 15.8 yrs | £4,070 |
| 5 kW | 5369 kWh | 4027 kWh | 1342 kWh | £1,066 | £134 | £1,200 | £17,173 | 14.3 yrs | £6,837 |
| 6 kW | 6443 kWh | 4832 kWh | 1611 kWh | £1,280 | £161 | £1,441 | £19,207 | 13.3 yrs | £9,604 |
| 7 kW | 7516 kWh | 5637 kWh | 1879 kWh | £1,493 | £188 | £1,681 | £21,242 | 12.6 yrs | £12,372 |
| 8 kW | 8590 kWh | 6443 kWh | 2148 kWh | £1,706 | £215 | £1,921 | £23,276 | 12.1 yrs | £15,139 |
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: £1,218, Upfront: £19,623, Break-even: 16.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2148 kWh | 1654 kWh | 494 kWh | £438 | £49 | £487 | £13,519 | 27.7 yrs | £-3,774 |
| 3 kW | 3221 kWh | 2480 kWh | 741 kWh | £657 | £74 | £731 | £15,554 | 21.3 yrs | £-935 |
| 4 kW | 4295 kWh | 3307 kWh | 988 kWh | £876 | £99 | £975 | £17,588 | 18.0 yrs | £1,903 |
| 5 kW | 5369 kWh | 4134 kWh | 1235 kWh | £1,095 | £123 | £1,218 | £19,623 | 16.1 yrs | £4,741 |
| 6 kW | 6443 kWh | 4961 kWh | 1482 kWh | £1,314 | £148 | £1,462 | £21,657 | 14.8 yrs | £7,579 |
| 7 kW | 7516 kWh | 5788 kWh | 1729 kWh | £1,533 | £173 | £1,705 | £23,692 | 13.9 yrs | £10,417 |
| 8 kW | 8590 kWh | 6614 kWh | 1976 kWh | £1,751 | £198 | £1,949 | £25,726 | 13.2 yrs | £13,255 |
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.