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 751 kWh per year on a south-facing roof. We value self-used electricity at 27.1p 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: £632, Upfront: £10,173, 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 | 1503 kWh | 601 kWh | 902 kWh | £163 | £90 | £253 | £4,069 | 16.1 yrs | £987 |
| 3 kW | 2254 kWh | 902 kWh | 1352 kWh | £244 | £135 | £379 | £6,104 | 16.1 yrs | £1,481 |
| 4 kW | 3005 kWh | 1202 kWh | 1803 kWh | £325 | £180 | £506 | £8,138 | 16.1 yrs | £1,975 |
| 5 kW | 3757 kWh | 1503 kWh | 2254 kWh | £407 | £225 | £632 | £10,173 | 16.1 yrs | £2,468 |
| 6 kW | 4508 kWh | 1803 kWh | 2705 kWh | £488 | £270 | £758 | £12,207 | 16.1 yrs | £2,962 |
| 7 kW | 5260 kWh | 2104 kWh | 3156 kWh | £569 | £316 | £885 | £14,242 | 16.1 yrs | £3,456 |
| 8 kW | 6011 kWh | 2404 kWh | 3607 kWh | £651 | £361 | £1,011 | £16,276 | 16.1 yrs | £3,949 |
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: £760, Upfront: £12,273, 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 | 1503 kWh | 902 kWh | 601 kWh | £244 | £60 | £304 | £6,169 | 20.3 yrs | £-87 |
| 3 kW | 2254 kWh | 1352 kWh | 902 kWh | £366 | £90 | £456 | £8,204 | 18.0 yrs | £919 |
| 4 kW | 3005 kWh | 1803 kWh | 1202 kWh | £488 | £120 | £608 | £10,238 | 16.8 yrs | £1,926 |
| 5 kW | 3757 kWh | 2254 kWh | 1503 kWh | £610 | £150 | £760 | £12,273 | 16.1 yrs | £2,932 |
| 6 kW | 4508 kWh | 2705 kWh | 1803 kWh | £732 | £180 | £912 | £14,307 | 15.7 yrs | £3,938 |
| 7 kW | 5260 kWh | 3156 kWh | 2104 kWh | £854 | £210 | £1,064 | £16,342 | 15.4 yrs | £4,945 |
| 8 kW | 6011 kWh | 3607 kWh | 2404 kWh | £976 | £240 | £1,216 | £18,376 | 15.1 yrs | £5,951 |
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: £824, Upfront: £13,673, Break-even: 16.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1503 kWh | 1052 kWh | 451 kWh | £285 | £45 | £330 | £7,569 | 23.0 yrs | £-974 |
| 3 kW | 2254 kWh | 1578 kWh | 676 kWh | £427 | £68 | £495 | £9,604 | 19.4 yrs | £288 |
| 4 kW | 3005 kWh | 2104 kWh | 902 kWh | £569 | £90 | £659 | £11,638 | 17.6 yrs | £1,551 |
| 5 kW | 3757 kWh | 2630 kWh | 1127 kWh | £712 | £113 | £824 | £13,673 | 16.6 yrs | £2,814 |
| 6 kW | 4508 kWh | 3156 kWh | 1352 kWh | £854 | £135 | £989 | £15,707 | 15.9 yrs | £4,077 |
| 7 kW | 5260 kWh | 3682 kWh | 1578 kWh | £996 | £158 | £1,154 | £17,742 | 15.4 yrs | £5,339 |
| 8 kW | 6011 kWh | 4208 kWh | 1803 kWh | £1,139 | £180 | £1,319 | £19,776 | 15.0 yrs | £6,602 |
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: £844, Upfront: £15,423, Break-even: 18.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1503 kWh | 1097 kWh | 406 kWh | £297 | £41 | £337 | £9,319 | 27.6 yrs | £-2,571 |
| 3 kW | 2254 kWh | 1645 kWh | 609 kWh | £445 | £61 | £506 | £11,354 | 22.4 yrs | £-1,231 |
| 4 kW | 3005 kWh | 2194 kWh | 811 kWh | £594 | £81 | £675 | £13,388 | 19.8 yrs | £109 |
| 5 kW | 3757 kWh | 2742 kWh | 1014 kWh | £742 | £101 | £844 | £15,423 | 18.3 yrs | £1,448 |
| 6 kW | 4508 kWh | 3291 kWh | 1217 kWh | £891 | £122 | £1,012 | £17,457 | 17.2 yrs | £2,788 |
| 7 kW | 5260 kWh | 3839 kWh | 1420 kWh | £1,039 | £142 | £1,181 | £19,492 | 16.5 yrs | £4,128 |
| 8 kW | 6011 kWh | 4388 kWh | 1623 kWh | £1,187 | £162 | £1,350 | £21,526 | 15.9 yrs | £5,467 |
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: £856, Upfront: £17,173, Break-even: 20.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1503 kWh | 1127 kWh | 376 kWh | £305 | £38 | £343 | £11,069 | 32.3 yrs | £-4,218 |
| 3 kW | 2254 kWh | 1691 kWh | 564 kWh | £457 | £56 | £514 | £13,104 | 25.5 yrs | £-2,827 |
| 4 kW | 3005 kWh | 2254 kWh | 751 kWh | £610 | £75 | £685 | £15,138 | 22.1 yrs | £-1,436 |
| 5 kW | 3757 kWh | 2818 kWh | 939 kWh | £762 | £94 | £856 | £17,173 | 20.1 yrs | £-45 |
| 6 kW | 4508 kWh | 3381 kWh | 1127 kWh | £915 | £113 | £1,028 | £19,207 | 18.7 yrs | £1,346 |
| 7 kW | 5260 kWh | 3945 kWh | 1315 kWh | £1,067 | £131 | £1,199 | £21,242 | 17.7 yrs | £2,737 |
| 8 kW | 6011 kWh | 4508 kWh | 1503 kWh | £1,220 | £150 | £1,370 | £23,276 | 17.0 yrs | £4,128 |
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: £869, Upfront: £19,623, Break-even: 22.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1503 kWh | 1157 kWh | 346 kWh | £313 | £35 | £348 | £13,519 | 38.9 yrs | £-6,566 |
| 3 kW | 2254 kWh | 1736 kWh | 518 kWh | £470 | £52 | £522 | £15,554 | 29.8 yrs | £-5,123 |
| 4 kW | 3005 kWh | 2314 kWh | 691 kWh | £626 | £69 | £695 | £17,588 | 25.3 yrs | £-3,681 |
| 5 kW | 3757 kWh | 2893 kWh | 864 kWh | £783 | £86 | £869 | £19,623 | 22.6 yrs | £-2,239 |
| 6 kW | 4508 kWh | 3471 kWh | 1037 kWh | £939 | £104 | £1,043 | £21,657 | 20.8 yrs | £-797 |
| 7 kW | 5260 kWh | 4050 kWh | 1210 kWh | £1,096 | £121 | £1,217 | £23,692 | 19.5 yrs | £645 |
| 8 kW | 6011 kWh | 4628 kWh | 1383 kWh | £1,252 | £138 | £1,391 | £25,726 | 18.5 yrs | £2,088 |
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.