A typical roof here lands around 6.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 811 kWh per year on a south-facing roof. We value self-used electricity at 25.8p 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: £663, Upfront: £10,173, Break-even: 15.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1623 kWh | 649 kWh | 974 kWh | £168 | £97 | £265 | £4,069 | 15.3 yrs | £1,233 |
| 3 kW | 2434 kWh | 974 kWh | 1460 kWh | £252 | £146 | £398 | £6,104 | 15.3 yrs | £1,849 |
| 4 kW | 3246 kWh | 1298 kWh | 1947 kWh | £335 | £195 | £530 | £8,138 | 15.3 yrs | £2,466 |
| 5 kW | 4057 kWh | 1623 kWh | 2434 kWh | £419 | £243 | £663 | £10,173 | 15.3 yrs | £3,082 |
| 6 kW | 4868 kWh | 1947 kWh | 2921 kWh | £503 | £292 | £795 | £12,207 | 15.3 yrs | £3,699 |
| 7 kW | 5680 kWh | 2272 kWh | 3408 kWh | £587 | £341 | £928 | £14,242 | 15.3 yrs | £4,315 |
| 8 kW | 6491 kWh | 2596 kWh | 3895 kWh | £671 | £389 | £1,060 | £16,276 | 15.3 yrs | £4,931 |
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: £791, Upfront: £12,273, Break-even: 15.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1623 kWh | 974 kWh | 649 kWh | £252 | £65 | £317 | £6,169 | 19.5 yrs | £161 |
| 3 kW | 2434 kWh | 1460 kWh | 974 kWh | £377 | £97 | £475 | £8,204 | 17.3 yrs | £1,292 |
| 4 kW | 3246 kWh | 1947 kWh | 1298 kWh | £503 | £130 | £633 | £10,238 | 16.2 yrs | £2,422 |
| 5 kW | 4057 kWh | 2434 kWh | 1623 kWh | £629 | £162 | £791 | £12,273 | 15.5 yrs | £3,553 |
| 6 kW | 4868 kWh | 2921 kWh | 1947 kWh | £755 | £195 | £950 | £14,307 | 15.1 yrs | £4,683 |
| 7 kW | 5680 kWh | 3408 kWh | 2272 kWh | £881 | £227 | £1,108 | £16,342 | 14.8 yrs | £5,814 |
| 8 kW | 6491 kWh | 3895 kWh | 2596 kWh | £1,006 | £260 | £1,266 | £18,376 | 14.5 yrs | £6,944 |
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: £856, Upfront: £13,673, Break-even: 16.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1623 kWh | 1136 kWh | 487 kWh | £294 | £49 | £342 | £7,569 | 22.1 yrs | £-725 |
| 3 kW | 2434 kWh | 1704 kWh | 730 kWh | £440 | £73 | £513 | £9,604 | 18.7 yrs | £663 |
| 4 kW | 3246 kWh | 2272 kWh | 974 kWh | £587 | £97 | £684 | £11,638 | 17.0 yrs | £2,050 |
| 5 kW | 4057 kWh | 2840 kWh | 1217 kWh | £734 | £122 | £856 | £13,673 | 16.0 yrs | £3,438 |
| 6 kW | 4868 kWh | 3408 kWh | 1460 kWh | £881 | £146 | £1,027 | £15,707 | 15.3 yrs | £4,825 |
| 7 kW | 5680 kWh | 3976 kWh | 1704 kWh | £1,027 | £170 | £1,198 | £17,742 | 14.8 yrs | £6,213 |
| 8 kW | 6491 kWh | 4544 kWh | 1947 kWh | £1,174 | £195 | £1,369 | £19,776 | 14.4 yrs | £7,601 |
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: £875, Upfront: £15,423, Break-even: 17.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1623 kWh | 1185 kWh | 438 kWh | £306 | £44 | £350 | £9,319 | 26.6 yrs | £-2,321 |
| 3 kW | 2434 kWh | 1777 kWh | 657 kWh | £459 | £66 | £525 | £11,354 | 21.6 yrs | £-856 |
| 4 kW | 3246 kWh | 2369 kWh | 876 kWh | £612 | £88 | £700 | £13,388 | 19.1 yrs | £609 |
| 5 kW | 4057 kWh | 2962 kWh | 1095 kWh | £765 | £110 | £875 | £15,423 | 17.6 yrs | £2,073 |
| 6 kW | 4868 kWh | 3554 kWh | 1314 kWh | £918 | £131 | £1,050 | £17,457 | 16.6 yrs | £3,538 |
| 7 kW | 5680 kWh | 4146 kWh | 1534 kWh | £1,071 | £153 | £1,225 | £19,492 | 15.9 yrs | £5,003 |
| 8 kW | 6491 kWh | 4738 kWh | 1753 kWh | £1,224 | £175 | £1,400 | £21,526 | 15.4 yrs | £6,467 |
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: £888, Upfront: £17,173, Break-even: 19.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1623 kWh | 1217 kWh | 406 kWh | £314 | £41 | £355 | £11,069 | 31.2 yrs | £-3,968 |
| 3 kW | 2434 kWh | 1826 kWh | 609 kWh | £472 | £61 | £533 | £13,104 | 24.6 yrs | £-2,452 |
| 4 kW | 3246 kWh | 2434 kWh | 811 kWh | £629 | £81 | £710 | £15,138 | 21.3 yrs | £-936 |
| 5 kW | 4057 kWh | 3043 kWh | 1014 kWh | £786 | £101 | £888 | £17,173 | 19.3 yrs | £580 |
| 6 kW | 4868 kWh | 3651 kWh | 1217 kWh | £943 | £122 | £1,065 | £19,207 | 18.0 yrs | £2,097 |
| 7 kW | 5680 kWh | 4260 kWh | 1420 kWh | £1,101 | £142 | £1,243 | £21,242 | 17.1 yrs | £3,613 |
| 8 kW | 6491 kWh | 4868 kWh | 1623 kWh | £1,258 | £162 | £1,420 | £23,276 | 16.4 yrs | £5,129 |
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: £901, Upfront: £19,623, Break-even: 21.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1623 kWh | 1250 kWh | 373 kWh | £323 | £37 | £360 | £13,519 | 37.5 yrs | £-6,315 |
| 3 kW | 2434 kWh | 1874 kWh | 560 kWh | £484 | £56 | £540 | £15,554 | 28.8 yrs | £-4,748 |
| 4 kW | 3246 kWh | 2499 kWh | 746 kWh | £646 | £75 | £720 | £17,588 | 24.4 yrs | £-3,180 |
| 5 kW | 4057 kWh | 3124 kWh | 933 kWh | £807 | £93 | £901 | £19,623 | 21.8 yrs | £-1,613 |
| 6 kW | 4868 kWh | 3749 kWh | 1120 kWh | £969 | £112 | £1,081 | £21,657 | 20.0 yrs | £-45 |
| 7 kW | 5680 kWh | 4373 kWh | 1306 kWh | £1,130 | £131 | £1,261 | £23,692 | 18.8 yrs | £1,522 |
| 8 kW | 6491 kWh | 4998 kWh | 1493 kWh | £1,292 | £149 | £1,441 | £25,726 | 17.9 yrs | £3,090 |
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.