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 583 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: £491, Upfront: £10,173, Break-even: 20.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1167 kWh | 467 kWh | 700 kWh | £126 | £70 | £196 | £4,069 | 20.7 yrs | £-144 |
| 3 kW | 1750 kWh | 700 kWh | 1050 kWh | £189 | £105 | £294 | £6,104 | 20.7 yrs | £-215 |
| 4 kW | 2333 kWh | 933 kWh | 1400 kWh | £253 | £140 | £393 | £8,138 | 20.7 yrs | £-287 |
| 5 kW | 2917 kWh | 1167 kWh | 1750 kWh | £316 | £175 | £491 | £10,173 | 20.7 yrs | £-359 |
| 6 kW | 3500 kWh | 1400 kWh | 2100 kWh | £379 | £210 | £589 | £12,207 | 20.7 yrs | £-431 |
| 7 kW | 4083 kWh | 1633 kWh | 2450 kWh | £442 | £245 | £687 | £14,242 | 20.7 yrs | £-503 |
| 8 kW | 4666 kWh | 1867 kWh | 2800 kWh | £505 | £280 | £785 | £16,276 | 20.7 yrs | £-574 |
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: £590, Upfront: £12,273, Break-even: 20.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1167 kWh | 700 kWh | 467 kWh | £189 | £47 | £236 | £6,169 | 26.1 yrs | £-1,447 |
| 3 kW | 1750 kWh | 1050 kWh | 700 kWh | £284 | £70 | £354 | £8,204 | 23.2 yrs | £-1,121 |
| 4 kW | 2333 kWh | 1400 kWh | 933 kWh | £379 | £93 | £472 | £10,238 | 21.7 yrs | £-795 |
| 5 kW | 2917 kWh | 1750 kWh | 1167 kWh | £474 | £117 | £590 | £12,273 | 20.8 yrs | £-469 |
| 6 kW | 3500 kWh | 2100 kWh | 1400 kWh | £568 | £140 | £708 | £14,307 | 20.2 yrs | £-142 |
| 7 kW | 4083 kWh | 2450 kWh | 1633 kWh | £663 | £163 | £826 | £16,342 | 19.8 yrs | £184 |
| 8 kW | 4666 kWh | 2800 kWh | 1867 kWh | £758 | £187 | £944 | £18,376 | 19.5 yrs | £510 |
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: £640, Upfront: £13,673, Break-even: 21.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1167 kWh | 817 kWh | 350 kWh | £221 | £35 | £256 | £7,569 | 29.6 yrs | £-2,449 |
| 3 kW | 1750 kWh | 1225 kWh | 525 kWh | £331 | £52 | £384 | £9,604 | 25.0 yrs | £-1,924 |
| 4 kW | 2333 kWh | 1633 kWh | 700 kWh | £442 | £70 | £512 | £11,638 | 22.7 yrs | £-1,399 |
| 5 kW | 2917 kWh | 2042 kWh | 875 kWh | £552 | £87 | £640 | £13,673 | 21.4 yrs | £-874 |
| 6 kW | 3500 kWh | 2450 kWh | 1050 kWh | £663 | £105 | £768 | £15,707 | 20.5 yrs | £-348 |
| 7 kW | 4083 kWh | 2858 kWh | 1225 kWh | £773 | £122 | £896 | £17,742 | 19.8 yrs | £177 |
| 8 kW | 4666 kWh | 3267 kWh | 1400 kWh | £884 | £140 | £1,024 | £19,776 | 19.3 yrs | £702 |
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: £655, Upfront: £15,423, Break-even: 23.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1167 kWh | 852 kWh | 315 kWh | £230 | £31 | £262 | £9,319 | 35.6 yrs | £-4,080 |
| 3 kW | 1750 kWh | 1277 kWh | 472 kWh | £346 | £47 | £393 | £11,354 | 28.9 yrs | £-3,495 |
| 4 kW | 2333 kWh | 1703 kWh | 630 kWh | £461 | £63 | £524 | £13,388 | 25.6 yrs | £-2,910 |
| 5 kW | 2917 kWh | 2129 kWh | 787 kWh | £576 | £79 | £655 | £15,423 | 23.6 yrs | £-2,325 |
| 6 kW | 3500 kWh | 2555 kWh | 945 kWh | £691 | £94 | £786 | £17,457 | 22.2 yrs | £-1,740 |
| 7 kW | 4083 kWh | 2981 kWh | 1102 kWh | £807 | £110 | £917 | £19,492 | 21.3 yrs | £-1,155 |
| 8 kW | 4666 kWh | 3407 kWh | 1260 kWh | £922 | £126 | £1,048 | £21,526 | 20.5 yrs | £-570 |
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: £665, Upfront: £17,173, Break-even: 25.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1167 kWh | 875 kWh | 292 kWh | £237 | £29 | £266 | £11,069 | 41.6 yrs | £-5,750 |
| 3 kW | 1750 kWh | 1312 kWh | 437 kWh | £355 | £44 | £399 | £13,104 | 32.8 yrs | £-5,126 |
| 4 kW | 2333 kWh | 1750 kWh | 583 kWh | £474 | £58 | £532 | £15,138 | 28.5 yrs | £-4,501 |
| 5 kW | 2917 kWh | 2187 kWh | 729 kWh | £592 | £73 | £665 | £17,173 | 25.8 yrs | £-3,876 |
| 6 kW | 3500 kWh | 2625 kWh | 875 kWh | £710 | £87 | £798 | £19,207 | 24.1 yrs | £-3,251 |
| 7 kW | 4083 kWh | 3062 kWh | 1021 kWh | £829 | £102 | £931 | £21,242 | 22.8 yrs | £-2,626 |
| 8 kW | 4666 kWh | 3500 kWh | 1167 kWh | £947 | £117 | £1,064 | £23,276 | 21.9 yrs | £-2,002 |
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: £675, Upfront: £19,623, Break-even: 29.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1167 kWh | 898 kWh | 268 kWh | £243 | £27 | £270 | £13,519 | 50.1 yrs | £-8,121 |
| 3 kW | 1750 kWh | 1347 kWh | 402 kWh | £365 | £40 | £405 | £15,554 | 38.4 yrs | £-7,456 |
| 4 kW | 2333 kWh | 1797 kWh | 537 kWh | £486 | £54 | £540 | £17,588 | 32.6 yrs | £-6,792 |
| 5 kW | 2917 kWh | 2246 kWh | 671 kWh | £608 | £67 | £675 | £19,623 | 29.1 yrs | £-6,127 |
| 6 kW | 3500 kWh | 2695 kWh | 805 kWh | £729 | £80 | £810 | £21,657 | 26.7 yrs | £-5,462 |
| 7 kW | 4083 kWh | 3144 kWh | 939 kWh | £851 | £94 | £945 | £23,692 | 25.1 yrs | £-4,798 |
| 8 kW | 4666 kWh | 3593 kWh | 1073 kWh | £972 | £107 | £1,080 | £25,726 | 23.8 yrs | £-4,133 |
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.