A typical roof here lands around 3.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 1000 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: £812, 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 | 1999 kWh | 800 kWh | 1199 kWh | £205 | £120 | £325 | £4,069 | 12.5 yrs | £2,429 |
| 3 kW | 2999 kWh | 1199 kWh | 1799 kWh | £307 | £180 | £487 | £6,104 | 12.5 yrs | £3,643 |
| 4 kW | 3998 kWh | 1599 kWh | 2399 kWh | £410 | £240 | £650 | £8,138 | 12.5 yrs | £4,858 |
| 5 kW | 4998 kWh | 1999 kWh | 2999 kWh | £512 | £300 | £812 | £10,173 | 12.5 yrs | £6,072 |
| 6 kW | 5997 kWh | 2399 kWh | 3598 kWh | £615 | £360 | £975 | £12,207 | 12.5 yrs | £7,287 |
| 7 kW | 6997 kWh | 2799 kWh | 4198 kWh | £717 | £420 | £1,137 | £14,242 | 12.5 yrs | £8,501 |
| 8 kW | 7997 kWh | 3199 kWh | 4798 kWh | £820 | £480 | £1,300 | £16,276 | 12.5 yrs | £9,716 |
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: £968, 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 | 1999 kWh | 1199 kWh | 800 kWh | £307 | £80 | £387 | £6,169 | 15.9 yrs | £1,579 |
| 3 kW | 2999 kWh | 1799 kWh | 1199 kWh | £461 | £120 | £581 | £8,204 | 14.1 yrs | £3,418 |
| 4 kW | 3998 kWh | 2399 kWh | 1599 kWh | £615 | £160 | £775 | £10,238 | 13.2 yrs | £5,258 |
| 5 kW | 4998 kWh | 2999 kWh | 1999 kWh | £769 | £200 | £968 | £12,273 | 12.7 yrs | £7,097 |
| 6 kW | 5997 kWh | 3598 kWh | 2399 kWh | £922 | £240 | £1,162 | £14,307 | 12.3 yrs | £8,937 |
| 7 kW | 6997 kWh | 4198 kWh | 2799 kWh | £1,076 | £280 | £1,356 | £16,342 | 12.1 yrs | £10,776 |
| 8 kW | 7997 kWh | 4798 kWh | 3199 kWh | £1,230 | £320 | £1,550 | £18,376 | 11.9 yrs | £12,615 |
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: £1,047, Upfront: £13,673, Break-even: 13.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1999 kWh | 1399 kWh | 600 kWh | £359 | £60 | £419 | £7,569 | 18.1 yrs | £804 |
| 3 kW | 2999 kWh | 2099 kWh | 900 kWh | £538 | £90 | £628 | £9,604 | 15.3 yrs | £2,956 |
| 4 kW | 3998 kWh | 2799 kWh | 1199 kWh | £717 | £120 | £837 | £11,638 | 13.9 yrs | £5,108 |
| 5 kW | 4998 kWh | 3498 kWh | 1499 kWh | £897 | £150 | £1,047 | £13,673 | 13.1 yrs | £7,259 |
| 6 kW | 5997 kWh | 4198 kWh | 1799 kWh | £1,076 | £180 | £1,256 | £15,707 | 12.5 yrs | £9,411 |
| 7 kW | 6997 kWh | 4898 kWh | 2099 kWh | £1,255 | £210 | £1,465 | £17,742 | 12.1 yrs | £11,563 |
| 8 kW | 7997 kWh | 5598 kWh | 2399 kWh | £1,435 | £240 | £1,675 | £19,776 | 11.8 yrs | £13,715 |
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: £1,070, 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 | 1999 kWh | 1459 kWh | 540 kWh | £374 | £54 | £428 | £9,319 | 21.8 yrs | £-759 |
| 3 kW | 2999 kWh | 2189 kWh | 810 kWh | £561 | £81 | £642 | £11,354 | 17.7 yrs | £1,487 |
| 4 kW | 3998 kWh | 2919 kWh | 1080 kWh | £748 | £108 | £856 | £13,388 | 15.6 yrs | £3,733 |
| 5 kW | 4998 kWh | 3648 kWh | 1349 kWh | £935 | £135 | £1,070 | £15,423 | 14.4 yrs | £5,978 |
| 6 kW | 5997 kWh | 4378 kWh | 1619 kWh | £1,122 | £162 | £1,284 | £17,457 | 13.6 yrs | £8,224 |
| 7 kW | 6997 kWh | 5108 kWh | 1889 kWh | £1,309 | £189 | £1,498 | £19,492 | 13.0 yrs | £10,469 |
| 8 kW | 7997 kWh | 5837 kWh | 2159 kWh | £1,496 | £216 | £1,712 | £21,526 | 12.6 yrs | £12,715 |
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: £1,086, 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 | 1999 kWh | 1499 kWh | 500 kWh | £384 | £50 | £434 | £11,069 | 25.5 yrs | £-2,384 |
| 3 kW | 2999 kWh | 2249 kWh | 750 kWh | £576 | £75 | £651 | £13,104 | 20.1 yrs | £-76 |
| 4 kW | 3998 kWh | 2999 kWh | 1000 kWh | £769 | £100 | £869 | £15,138 | 17.4 yrs | £2,232 |
| 5 kW | 4998 kWh | 3748 kWh | 1249 kWh | £961 | £125 | £1,086 | £17,173 | 15.8 yrs | £4,541 |
| 6 kW | 5997 kWh | 4498 kWh | 1499 kWh | £1,153 | £150 | £1,303 | £19,207 | 14.7 yrs | £6,849 |
| 7 kW | 6997 kWh | 5248 kWh | 1749 kWh | £1,345 | £175 | £1,520 | £21,242 | 14.0 yrs | £9,157 |
| 8 kW | 7997 kWh | 5997 kWh | 1999 kWh | £1,537 | £200 | £1,737 | £23,276 | 13.4 yrs | £11,465 |
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: £1,101, 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 | 1999 kWh | 1539 kWh | 460 kWh | £395 | £46 | £441 | £13,519 | 30.7 yrs | £-4,709 |
| 3 kW | 2999 kWh | 2309 kWh | 690 kWh | £592 | £69 | £661 | £15,554 | 23.5 yrs | £-2,338 |
| 4 kW | 3998 kWh | 3079 kWh | 920 kWh | £789 | £92 | £881 | £17,588 | 20.0 yrs | £32 |
| 5 kW | 4998 kWh | 3848 kWh | 1150 kWh | £986 | £115 | £1,101 | £19,623 | 17.8 yrs | £2,403 |
| 6 kW | 5997 kWh | 4618 kWh | 1379 kWh | £1,184 | £138 | £1,322 | £21,657 | 16.4 yrs | £4,774 |
| 7 kW | 6997 kWh | 5388 kWh | 1609 kWh | £1,381 | £161 | £1,542 | £23,692 | 15.4 yrs | £7,144 |
| 8 kW | 7997 kWh | 6157 kWh | 1839 kWh | £1,578 | £184 | £1,762 | £25,726 | 14.6 yrs | £9,515 |
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.