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 998 kWh per year on a south-facing roof. We value self-used electricity at 26.8p 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: £835, Upfront: £10,173, Break-even: 12.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1996 kWh | 798 kWh | 1197 kWh | £214 | £120 | £334 | £4,069 | 12.2 yrs | £2,608 |
| 3 kW | 2993 kWh | 1197 kWh | 1796 kWh | £321 | £180 | £501 | £6,104 | 12.2 yrs | £3,911 |
| 4 kW | 3991 kWh | 1597 kWh | 2395 kWh | £428 | £239 | £668 | £8,138 | 12.2 yrs | £5,215 |
| 5 kW | 4989 kWh | 1996 kWh | 2993 kWh | £535 | £299 | £835 | £10,173 | 12.2 yrs | £6,519 |
| 6 kW | 5987 kWh | 2395 kWh | 3592 kWh | £642 | £359 | £1,002 | £12,207 | 12.2 yrs | £7,823 |
| 7 kW | 6985 kWh | 2794 kWh | 4191 kWh | £749 | £419 | £1,168 | £14,242 | 12.2 yrs | £9,127 |
| 8 kW | 7983 kWh | 3193 kWh | 4790 kWh | £856 | £479 | £1,335 | £16,276 | 12.2 yrs | £10,431 |
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: £1,002, Upfront: £12,273, Break-even: 12.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1996 kWh | 1197 kWh | 798 kWh | £321 | £80 | £401 | £6,169 | 15.4 yrs | £1,850 |
| 3 kW | 2993 kWh | 1796 kWh | 1197 kWh | £482 | £120 | £601 | £8,204 | 13.6 yrs | £3,826 |
| 4 kW | 3991 kWh | 2395 kWh | 1597 kWh | £642 | £160 | £802 | £10,238 | 12.8 yrs | £5,801 |
| 5 kW | 4989 kWh | 2993 kWh | 1996 kWh | £803 | £200 | £1,002 | £12,273 | 12.2 yrs | £7,776 |
| 6 kW | 5987 kWh | 3592 kWh | 2395 kWh | £963 | £239 | £1,203 | £14,307 | 11.9 yrs | £9,751 |
| 7 kW | 6985 kWh | 4191 kWh | 2794 kWh | £1,124 | £279 | £1,403 | £16,342 | 11.6 yrs | £11,726 |
| 8 kW | 7983 kWh | 4790 kWh | 3193 kWh | £1,285 | £319 | £1,604 | £18,376 | 11.5 yrs | £13,701 |
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: £1,086, Upfront: £13,673, Break-even: 12.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1996 kWh | 1397 kWh | 599 kWh | £375 | £60 | £435 | £7,569 | 17.4 yrs | £1,122 |
| 3 kW | 2993 kWh | 2095 kWh | 898 kWh | £562 | £90 | £652 | £9,604 | 14.7 yrs | £3,433 |
| 4 kW | 3991 kWh | 2794 kWh | 1197 kWh | £749 | £120 | £869 | £11,638 | 13.4 yrs | £5,743 |
| 5 kW | 4989 kWh | 3492 kWh | 1497 kWh | £937 | £150 | £1,086 | £13,673 | 12.6 yrs | £8,054 |
| 6 kW | 5987 kWh | 4191 kWh | 1796 kWh | £1,124 | £180 | £1,304 | £15,707 | 12.0 yrs | £10,365 |
| 7 kW | 6985 kWh | 4889 kWh | 2095 kWh | £1,311 | £210 | £1,521 | £17,742 | 11.7 yrs | £12,676 |
| 8 kW | 7983 kWh | 5588 kWh | 2395 kWh | £1,499 | £239 | £1,738 | £19,776 | 11.4 yrs | £14,987 |
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: £1,112, Upfront: £15,423, 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 | 1996 kWh | 1457 kWh | 539 kWh | £391 | £54 | £445 | £9,319 | 21.0 yrs | £-427 |
| 3 kW | 2993 kWh | 2185 kWh | 808 kWh | £586 | £81 | £667 | £11,354 | 17.0 yrs | £1,985 |
| 4 kW | 3991 kWh | 2914 kWh | 1078 kWh | £781 | £108 | £889 | £13,388 | 15.1 yrs | £4,396 |
| 5 kW | 4989 kWh | 3642 kWh | 1347 kWh | £977 | £135 | £1,112 | £15,423 | 13.9 yrs | £6,808 |
| 6 kW | 5987 kWh | 4370 kWh | 1616 kWh | £1,172 | £162 | £1,334 | £17,457 | 13.1 yrs | £9,219 |
| 7 kW | 6985 kWh | 5099 kWh | 1886 kWh | £1,368 | £189 | £1,556 | £19,492 | 12.5 yrs | £11,631 |
| 8 kW | 7983 kWh | 5827 kWh | 2155 kWh | £1,563 | £216 | £1,778 | £21,526 | 12.1 yrs | £14,042 |
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: £1,128, Upfront: £17,173, Break-even: 15.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1996 kWh | 1497 kWh | 499 kWh | £401 | £50 | £451 | £11,069 | 24.5 yrs | £-2,043 |
| 3 kW | 2993 kWh | 2245 kWh | 748 kWh | £602 | £75 | £677 | £13,104 | 19.4 yrs | £436 |
| 4 kW | 3991 kWh | 2993 kWh | 998 kWh | £803 | £100 | £903 | £15,138 | 16.8 yrs | £2,915 |
| 5 kW | 4989 kWh | 3742 kWh | 1247 kWh | £1,004 | £125 | £1,128 | £17,173 | 15.2 yrs | £5,393 |
| 6 kW | 5987 kWh | 4490 kWh | 1497 kWh | £1,204 | £150 | £1,354 | £19,207 | 14.2 yrs | £7,872 |
| 7 kW | 6985 kWh | 5239 kWh | 1746 kWh | £1,405 | £175 | £1,580 | £21,242 | 13.4 yrs | £10,351 |
| 8 kW | 7983 kWh | 5987 kWh | 1996 kWh | £1,606 | £200 | £1,805 | £23,276 | 12.9 yrs | £12,829 |
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: £1,145, Upfront: £19,623, Break-even: 17.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1996 kWh | 1537 kWh | 459 kWh | £412 | £46 | £458 | £13,519 | 29.5 yrs | £-4,358 |
| 3 kW | 2993 kWh | 2305 kWh | 689 kWh | £618 | £69 | £687 | £15,554 | 22.6 yrs | £-1,813 |
| 4 kW | 3991 kWh | 3073 kWh | 918 kWh | £824 | £92 | £916 | £17,588 | 19.2 yrs | £733 |
| 5 kW | 4989 kWh | 3842 kWh | 1148 kWh | £1,030 | £115 | £1,145 | £19,623 | 17.1 yrs | £3,279 |
| 6 kW | 5987 kWh | 4610 kWh | 1377 kWh | £1,236 | £138 | £1,374 | £21,657 | 15.8 yrs | £5,825 |
| 7 kW | 6985 kWh | 5378 kWh | 1607 kWh | £1,442 | £161 | £1,603 | £23,692 | 14.8 yrs | £8,371 |
| 8 kW | 7983 kWh | 6147 kWh | 1836 kWh | £1,649 | £184 | £1,832 | £25,726 | 14.0 yrs | £10,916 |
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.