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 1003 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: £814, Upfront: £10,173, 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 | 2007 kWh | 803 kWh | 1204 kWh | £205 | £120 | £326 | £4,069 | 12.5 yrs | £2,442 |
| 3 kW | 3010 kWh | 1204 kWh | 1806 kWh | £308 | £181 | £488 | £6,104 | 12.5 yrs | £3,662 |
| 4 kW | 4014 kWh | 1606 kWh | 2408 kWh | £410 | £241 | £651 | £8,138 | 12.5 yrs | £4,883 |
| 5 kW | 5017 kWh | 2007 kWh | 3010 kWh | £513 | £301 | £814 | £10,173 | 12.5 yrs | £6,104 |
| 6 kW | 6021 kWh | 2408 kWh | 3613 kWh | £615 | £361 | £977 | £12,207 | 12.5 yrs | £7,325 |
| 7 kW | 7024 kWh | 2810 kWh | 4215 kWh | £718 | £421 | £1,139 | £14,242 | 12.5 yrs | £8,545 |
| 8 kW | 8028 kWh | 3211 kWh | 4817 kWh | £820 | £482 | £1,302 | £16,276 | 12.5 yrs | £9,766 |
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: £970, Upfront: £12,273, Break-even: 12.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2007 kWh | 1204 kWh | 803 kWh | £308 | £80 | £388 | £6,169 | 15.9 yrs | £1,590 |
| 3 kW | 3010 kWh | 1806 kWh | 1204 kWh | £462 | £120 | £582 | £8,204 | 14.1 yrs | £3,435 |
| 4 kW | 4014 kWh | 2408 kWh | 1606 kWh | £615 | £161 | £776 | £10,238 | 13.2 yrs | £5,280 |
| 5 kW | 5017 kWh | 3010 kWh | 2007 kWh | £769 | £201 | £970 | £12,273 | 12.7 yrs | £7,125 |
| 6 kW | 6021 kWh | 3613 kWh | 2408 kWh | £923 | £241 | £1,164 | £14,307 | 12.3 yrs | £8,970 |
| 7 kW | 7024 kWh | 4215 kWh | 2810 kWh | £1,077 | £281 | £1,358 | £16,342 | 12.0 yrs | £10,815 |
| 8 kW | 8028 kWh | 4817 kWh | 3211 kWh | £1,231 | £321 | £1,552 | £18,376 | 11.8 yrs | £12,660 |
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: £1,048, Upfront: £13,673, 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 | 2007 kWh | 1405 kWh | 602 kWh | £359 | £60 | £419 | £7,569 | 18.1 yrs | £814 |
| 3 kW | 3010 kWh | 2107 kWh | 903 kWh | £538 | £90 | £629 | £9,604 | 15.3 yrs | £2,971 |
| 4 kW | 4014 kWh | 2810 kWh | 1204 kWh | £718 | £120 | £838 | £11,638 | 13.9 yrs | £5,128 |
| 5 kW | 5017 kWh | 3512 kWh | 1505 kWh | £897 | £151 | £1,048 | £13,673 | 13.0 yrs | £7,285 |
| 6 kW | 6021 kWh | 4215 kWh | 1806 kWh | £1,077 | £181 | £1,257 | £15,707 | 12.5 yrs | £9,442 |
| 7 kW | 7024 kWh | 4917 kWh | 2107 kWh | £1,256 | £211 | £1,467 | £17,742 | 12.1 yrs | £11,599 |
| 8 kW | 8028 kWh | 5619 kWh | 2408 kWh | £1,436 | £241 | £1,677 | £19,776 | 11.8 yrs | £13,756 |
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: £1,071, Upfront: £15,423, Break-even: 14.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2007 kWh | 1465 kWh | 542 kWh | £374 | £54 | £429 | £9,319 | 21.7 yrs | £-749 |
| 3 kW | 3010 kWh | 2198 kWh | 813 kWh | £561 | £81 | £643 | £11,354 | 17.7 yrs | £1,502 |
| 4 kW | 4014 kWh | 2930 kWh | 1084 kWh | £749 | £108 | £857 | £13,388 | 15.6 yrs | £3,753 |
| 5 kW | 5017 kWh | 3663 kWh | 1355 kWh | £936 | £135 | £1,071 | £15,423 | 14.4 yrs | £6,003 |
| 6 kW | 6021 kWh | 4395 kWh | 1626 kWh | £1,123 | £163 | £1,286 | £17,457 | 13.6 yrs | £8,254 |
| 7 kW | 7024 kWh | 5128 kWh | 1897 kWh | £1,310 | £190 | £1,500 | £19,492 | 13.0 yrs | £10,505 |
| 8 kW | 8028 kWh | 5860 kWh | 2168 kWh | £1,497 | £217 | £1,714 | £21,526 | 12.6 yrs | £12,755 |
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: £1,087, Upfront: £17,173, Break-even: 15.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2007 kWh | 1505 kWh | 502 kWh | £385 | £50 | £435 | £11,069 | 25.5 yrs | £-2,374 |
| 3 kW | 3010 kWh | 2258 kWh | 753 kWh | £577 | £75 | £652 | £13,104 | 20.1 yrs | £-61 |
| 4 kW | 4014 kWh | 3010 kWh | 1003 kWh | £769 | £100 | £870 | £15,138 | 17.4 yrs | £2,252 |
| 5 kW | 5017 kWh | 3763 kWh | 1254 kWh | £961 | £125 | £1,087 | £17,173 | 15.8 yrs | £4,565 |
| 6 kW | 6021 kWh | 4516 kWh | 1505 kWh | £1,154 | £151 | £1,304 | £19,207 | 14.7 yrs | £6,878 |
| 7 kW | 7024 kWh | 5268 kWh | 1756 kWh | £1,346 | £176 | £1,522 | £21,242 | 14.0 yrs | £9,191 |
| 8 kW | 8028 kWh | 6021 kWh | 2007 kWh | £1,538 | £201 | £1,739 | £23,276 | 13.4 yrs | £11,505 |
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: £1,102, Upfront: £19,623, Break-even: 17.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2007 kWh | 1545 kWh | 462 kWh | £395 | £46 | £441 | £13,519 | 30.7 yrs | £-4,699 |
| 3 kW | 3010 kWh | 2318 kWh | 692 kWh | £592 | £69 | £661 | £15,554 | 23.5 yrs | £-2,324 |
| 4 kW | 4014 kWh | 3091 kWh | 923 kWh | £790 | £92 | £882 | £17,588 | 19.9 yrs | £52 |
| 5 kW | 5017 kWh | 3863 kWh | 1154 kWh | £987 | £115 | £1,102 | £19,623 | 17.8 yrs | £2,427 |
| 6 kW | 6021 kWh | 4636 kWh | 1385 kWh | £1,185 | £138 | £1,323 | £21,657 | 16.4 yrs | £4,803 |
| 7 kW | 7024 kWh | 5409 kWh | 1616 kWh | £1,382 | £162 | £1,543 | £23,692 | 15.3 yrs | £7,178 |
| 8 kW | 8028 kWh | 6181 kWh | 1846 kWh | £1,579 | £185 | £1,764 | £25,726 | 14.6 yrs | £9,554 |
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.