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 878 kWh per year on a south-facing roof. We value self-used electricity at 0.0p 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: £263, Upfront: £10,173, Break-even: 38.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1756 kWh | 702 kWh | 1054 kWh | £0 | £105 | £105 | £4,069 | 38.6 yrs | £-1,962 |
| 3 kW | 2634 kWh | 1054 kWh | 1581 kWh | £0 | £158 | £158 | £6,104 | 38.6 yrs | £-2,942 |
| 4 kW | 3512 kWh | 1405 kWh | 2107 kWh | £0 | £211 | £211 | £8,138 | 38.6 yrs | £-3,923 |
| 5 kW | 4390 kWh | 1756 kWh | 2634 kWh | £0 | £263 | £263 | £10,173 | 38.6 yrs | £-4,904 |
| 6 kW | 5269 kWh | 2107 kWh | 3161 kWh | £0 | £316 | £316 | £12,207 | 38.6 yrs | £-5,885 |
| 7 kW | 6147 kWh | 2459 kWh | 3688 kWh | £0 | £369 | £369 | £14,242 | 38.6 yrs | £-6,866 |
| 8 kW | 7025 kWh | 2810 kWh | 4215 kWh | £0 | £421 | £421 | £16,276 | 38.6 yrs | £-7,846 |
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: £176, Upfront: £12,273, Break-even: 69.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1756 kWh | 1054 kWh | 702 kWh | £0 | £70 | £70 | £6,169 | 87.8 yrs | £-4,764 |
| 3 kW | 2634 kWh | 1581 kWh | 1054 kWh | £0 | £105 | £105 | £8,204 | 77.9 yrs | £-6,096 |
| 4 kW | 3512 kWh | 2107 kWh | 1405 kWh | £0 | £140 | £140 | £10,238 | 72.9 yrs | £-7,428 |
| 5 kW | 4390 kWh | 2634 kWh | 1756 kWh | £0 | £176 | £176 | £12,273 | 69.9 yrs | £-8,760 |
| 6 kW | 5269 kWh | 3161 kWh | 2107 kWh | £0 | £211 | £211 | £14,307 | 67.9 yrs | £-10,092 |
| 7 kW | 6147 kWh | 3688 kWh | 2459 kWh | £0 | £246 | £246 | £16,342 | 66.5 yrs | £-11,424 |
| 8 kW | 7025 kWh | 4215 kWh | 2810 kWh | £0 | £281 | £281 | £18,376 | 65.4 yrs | £-12,756 |
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: £132, Upfront: £13,673, Break-even: 103.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1756 kWh | 1229 kWh | 527 kWh | £0 | £53 | £53 | £7,569 | 143.7 yrs | £-6,515 |
| 3 kW | 2634 kWh | 1844 kWh | 790 kWh | £0 | £79 | £79 | £9,604 | 121.5 yrs | £-8,023 |
| 4 kW | 3512 kWh | 2459 kWh | 1054 kWh | £0 | £105 | £105 | £11,638 | 110.4 yrs | £-9,531 |
| 5 kW | 4390 kWh | 3073 kWh | 1317 kWh | £0 | £132 | £132 | £13,673 | 103.8 yrs | £-11,038 |
| 6 kW | 5269 kWh | 3688 kWh | 1581 kWh | £0 | £158 | £158 | £15,707 | 99.4 yrs | £-12,546 |
| 7 kW | 6147 kWh | 4303 kWh | 1844 kWh | £0 | £184 | £184 | £17,742 | 96.2 yrs | £-14,054 |
| 8 kW | 7025 kWh | 4917 kWh | 2107 kWh | £0 | £211 | £211 | £19,776 | 93.8 yrs | £-15,561 |
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: £119, Upfront: £15,423, Break-even: 130.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1756 kWh | 1282 kWh | 474 kWh | £0 | £47 | £47 | £9,319 | 196.5 yrs | £-8,371 |
| 3 kW | 2634 kWh | 1923 kWh | 711 kWh | £0 | £71 | £71 | £11,354 | 159.6 yrs | £-9,931 |
| 4 kW | 3512 kWh | 2564 kWh | 948 kWh | £0 | £95 | £95 | £13,388 | 141.2 yrs | £-11,491 |
| 5 kW | 4390 kWh | 3205 kWh | 1185 kWh | £0 | £119 | £119 | £15,423 | 130.1 yrs | £-13,052 |
| 6 kW | 5269 kWh | 3846 kWh | 1423 kWh | £0 | £142 | £142 | £17,457 | 122.7 yrs | £-14,612 |
| 7 kW | 6147 kWh | 4487 kWh | 1660 kWh | £0 | £166 | £166 | £19,492 | 117.4 yrs | £-16,172 |
| 8 kW | 7025 kWh | 5128 kWh | 1897 kWh | £0 | £190 | £190 | £21,526 | 113.5 yrs | £-17,733 |
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: £110, Upfront: £17,173, Break-even: 156.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1756 kWh | 1317 kWh | 439 kWh | £0 | £44 | £44 | £11,069 | 252.1 yrs | £-10,191 |
| 3 kW | 2634 kWh | 1976 kWh | 659 kWh | £0 | £66 | £66 | £13,104 | 199.0 yrs | £-11,786 |
| 4 kW | 3512 kWh | 2634 kWh | 878 kWh | £0 | £88 | £88 | £15,138 | 172.4 yrs | £-13,382 |
| 5 kW | 4390 kWh | 3293 kWh | 1098 kWh | £0 | £110 | £110 | £17,173 | 156.5 yrs | £-14,977 |
| 6 kW | 5269 kWh | 3951 kWh | 1317 kWh | £0 | £132 | £132 | £19,207 | 145.8 yrs | £-16,573 |
| 7 kW | 6147 kWh | 4610 kWh | 1537 kWh | £0 | £154 | £154 | £21,242 | 138.2 yrs | £-18,168 |
| 8 kW | 7025 kWh | 5269 kWh | 1756 kWh | £0 | £176 | £176 | £23,276 | 132.5 yrs | £-19,764 |
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: £101, Upfront: £19,623, Break-even: 194.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1756 kWh | 1352 kWh | 404 kWh | £0 | £40 | £40 | £13,519 | 334.7 yrs | £-12,711 |
| 3 kW | 2634 kWh | 2028 kWh | 606 kWh | £0 | £61 | £61 | £15,554 | 256.7 yrs | £-14,342 |
| 4 kW | 3512 kWh | 2705 kWh | 808 kWh | £0 | £81 | £81 | £17,588 | 217.7 yrs | £-15,972 |
| 5 kW | 4390 kWh | 3381 kWh | 1010 kWh | £0 | £101 | £101 | £19,623 | 194.3 yrs | £-17,603 |
| 6 kW | 5269 kWh | 4057 kWh | 1212 kWh | £0 | £121 | £121 | £21,657 | 178.7 yrs | £-19,234 |
| 7 kW | 6147 kWh | 4733 kWh | 1414 kWh | £0 | £141 | £141 | £23,692 | 167.6 yrs | £-20,864 |
| 8 kW | 7025 kWh | 5409 kWh | 1616 kWh | £0 | £162 | £162 | £25,726 | 159.2 yrs | £-22,495 |
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.