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 865 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: £706, Upfront: £10,173, 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 | 1730 kWh | 692 kWh | 1038 kWh | £179 | £104 | £283 | £4,069 | 14.4 yrs | £1,582 |
| 3 kW | 2595 kWh | 1038 kWh | 1557 kWh | £268 | £156 | £424 | £6,104 | 14.4 yrs | £2,373 |
| 4 kW | 3459 kWh | 1384 kWh | 2076 kWh | £358 | £208 | £565 | £8,138 | 14.4 yrs | £3,164 |
| 5 kW | 4324 kWh | 1730 kWh | 2595 kWh | £447 | £259 | £706 | £10,173 | 14.4 yrs | £3,955 |
| 6 kW | 5189 kWh | 2076 kWh | 3113 kWh | £536 | £311 | £848 | £12,207 | 14.4 yrs | £4,747 |
| 7 kW | 6054 kWh | 2422 kWh | 3632 kWh | £626 | £363 | £989 | £14,242 | 14.4 yrs | £5,538 |
| 8 kW | 6919 kWh | 2767 kWh | 4151 kWh | £715 | £415 | £1,130 | £16,276 | 14.4 yrs | £6,329 |
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: £843, Upfront: £12,273, Break-even: 14.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1730 kWh | 1038 kWh | 692 kWh | £268 | £69 | £337 | £6,169 | 18.3 yrs | £578 |
| 3 kW | 2595 kWh | 1557 kWh | 1038 kWh | £402 | £104 | £506 | £8,204 | 16.2 yrs | £1,917 |
| 4 kW | 3459 kWh | 2076 kWh | 1384 kWh | £536 | £138 | £675 | £10,238 | 15.2 yrs | £3,256 |
| 5 kW | 4324 kWh | 2595 kWh | 1730 kWh | £670 | £173 | £843 | £12,273 | 14.6 yrs | £4,595 |
| 6 kW | 5189 kWh | 3113 kWh | 2076 kWh | £805 | £208 | £1,012 | £14,307 | 14.1 yrs | £5,934 |
| 7 kW | 6054 kWh | 3632 kWh | 2422 kWh | £939 | £242 | £1,181 | £16,342 | 13.8 yrs | £7,273 |
| 8 kW | 6919 kWh | 4151 kWh | 2767 kWh | £1,073 | £277 | £1,349 | £18,376 | 13.6 yrs | £8,612 |
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: £912, Upfront: £13,673, Break-even: 15.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1730 kWh | 1211 kWh | 519 kWh | £313 | £52 | £365 | £7,569 | 20.8 yrs | £-274 |
| 3 kW | 2595 kWh | 1816 kWh | 778 kWh | £469 | £78 | £547 | £9,604 | 17.6 yrs | £1,339 |
| 4 kW | 3459 kWh | 2422 kWh | 1038 kWh | £626 | £104 | £730 | £11,638 | 16.0 yrs | £2,952 |
| 5 kW | 4324 kWh | 3027 kWh | 1297 kWh | £782 | £130 | £912 | £13,673 | 15.0 yrs | £4,565 |
| 6 kW | 5189 kWh | 3632 kWh | 1557 kWh | £939 | £156 | £1,094 | £15,707 | 14.4 yrs | £6,178 |
| 7 kW | 6054 kWh | 4238 kWh | 1816 kWh | £1,095 | £182 | £1,277 | £17,742 | 13.9 yrs | £7,791 |
| 8 kW | 6919 kWh | 4843 kWh | 2076 kWh | £1,251 | £208 | £1,459 | £19,776 | 13.6 yrs | £9,404 |
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: £932, Upfront: £15,423, Break-even: 16.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1730 kWh | 1263 kWh | 467 kWh | £326 | £47 | £373 | £9,319 | 25.0 yrs | £-1,860 |
| 3 kW | 2595 kWh | 1894 kWh | 701 kWh | £489 | £70 | £559 | £11,354 | 20.3 yrs | £-164 |
| 4 kW | 3459 kWh | 2525 kWh | 934 kWh | £653 | £93 | £746 | £13,388 | 17.9 yrs | £1,531 |
| 5 kW | 4324 kWh | 3157 kWh | 1168 kWh | £816 | £117 | £932 | £15,423 | 16.5 yrs | £3,226 |
| 6 kW | 5189 kWh | 3788 kWh | 1401 kWh | £979 | £140 | £1,119 | £17,457 | 15.6 yrs | £4,921 |
| 7 kW | 6054 kWh | 4419 kWh | 1635 kWh | £1,142 | £163 | £1,305 | £19,492 | 14.9 yrs | £6,617 |
| 8 kW | 6919 kWh | 5051 kWh | 1868 kWh | £1,305 | £187 | £1,492 | £21,526 | 14.4 yrs | £8,312 |
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: £946, Upfront: £17,173, Break-even: 18.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1730 kWh | 1297 kWh | 432 kWh | £335 | £43 | £378 | £11,069 | 29.2 yrs | £-3,500 |
| 3 kW | 2595 kWh | 1946 kWh | 649 kWh | £503 | £65 | £568 | £13,104 | 23.1 yrs | £-1,750 |
| 4 kW | 3459 kWh | 2595 kWh | 865 kWh | £670 | £86 | £757 | £15,138 | 20.0 yrs | £0 |
| 5 kW | 4324 kWh | 3243 kWh | 1081 kWh | £838 | £108 | £946 | £17,173 | 18.2 yrs | £1,750 |
| 6 kW | 5189 kWh | 3892 kWh | 1297 kWh | £1,006 | £130 | £1,135 | £19,207 | 16.9 yrs | £3,500 |
| 7 kW | 6054 kWh | 4540 kWh | 1513 kWh | £1,173 | £151 | £1,325 | £21,242 | 16.0 yrs | £5,250 |
| 8 kW | 6919 kWh | 5189 kWh | 1730 kWh | £1,341 | £173 | £1,514 | £23,276 | 15.4 yrs | £7,000 |
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: £960, Upfront: £19,623, Break-even: 20.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1730 kWh | 1332 kWh | 398 kWh | £344 | £40 | £384 | £13,519 | 35.2 yrs | £-5,840 |
| 3 kW | 2595 kWh | 1998 kWh | 597 kWh | £516 | £60 | £576 | £15,554 | 27.0 yrs | £-4,036 |
| 4 kW | 3459 kWh | 2664 kWh | 796 kWh | £688 | £80 | £768 | £17,588 | 22.9 yrs | £-2,231 |
| 5 kW | 4324 kWh | 3330 kWh | 995 kWh | £860 | £99 | £960 | £19,623 | 20.4 yrs | £-426 |
| 6 kW | 5189 kWh | 3996 kWh | 1193 kWh | £1,032 | £119 | £1,152 | £21,657 | 18.8 yrs | £1,379 |
| 7 kW | 6054 kWh | 4661 kWh | 1392 kWh | £1,205 | £139 | £1,344 | £23,692 | 17.6 yrs | £3,184 |
| 8 kW | 6919 kWh | 5327 kWh | 1591 kWh | £1,377 | £159 | £1,536 | £25,726 | 16.8 yrs | £4,989 |
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.