UK PLUG-IN SOLAR
Plug-In Solar Savings Calculator
Enter the panel capacity you are considering and how it will be mounted. The calculator scales the government's two modelled 800W installations and returns generation, the electricity your home actually uses, the annual saving and simple payback.
Your kit
2,000W across four modules is the legal maximum for a plug-in kit. Most compliant kits sold today sit between 400W and 1,000W.
The assessment assumes 25.7p/kWh and a £400–£600 kit. Use your own figures if you know them.
What it returns
- Generated a year
- 690 kWh
- Direct current from the panels, converted by the inverter.
- Used at home
- 428 kWh
- 62% of generation, at the moment it is made.
- Annual saving
- £110
- At 25.7p/kWh on the electricity you avoid buying.
- Simple payback
- 4.5 years
- Kit price divided by the annual saving, with no inflation or degradation.
262 kWh would flow back to the grid over the year and is not counted as a saving, because a plug-in kit is not paid for export. That works out at £0.63 per panel watt for the kit price you entered.
| Mounting | Generated | Used at home | Annual saving | Payback |
|---|---|---|---|---|
| 30° tilt, roof or garden frame | 690 kWh | 428 kWh | £110 | 4.5 years |
| Vertical, wall or balcony rail | 378 kWh | 272 kWh | £70 | 7.2 years |
Both rows use 800W of panels, 25.7p/kWh and a £500 kit.
WHAT THE NUMBER CANNOT TELL YOU
Four Things This Calculator Leaves Out
- Shading and orientation. The assessment models two fixed mountings in one location. A tree, a north-facing wall or a chimney can take a large share of the generation away, and no online calculator can see your home.
- The inverter ceiling. Panels above roughly 1,000W are clipped at 800VA in strong summer sun. The extra capacity mostly helps in weak winter light, so treat any figure above the 800W the assessment modelled as an upper bound.
- Your load pattern. The saving assumes the share of generation the assessment says a household uses. Working from home raises it; a household that is out all day lowers it.
- Installation extras. A compliant kit plugs into a socket, but the assessment's £400–£600 excludes electrical work such as a dedicated circuit or a Type A RCD upgrade.
NEXT
Before You Buy
A saving is only real if the kit is legal to plug in. The hub carries the rules, the surfaces a kit may go on, and the checks to make before paying.
The 800VA limit and specification
The legal definition, the panel cap and what notification involves.
Read the rulesPlacementWhere a kit can legally go
Permitted development limits and the surfaces the rules out.
Check placementBuyingPriced, checkable kits
What each kit costs per panel watt, and the register that decides compliance.
Compare kitsMETHOD
Where These Figures Come From
Two published rows, scaled. Nothing else is assumed.
- The 30° tilt column is the assessment's 690 kWh generated, 428 kWh used and £110 saved on an 800W installation.
- The vertical column is its 378 kWh generated, 272 kWh used and £70 saved on the same 800W.
- Generation scales in proportion to panel capacity. The used-at-home share is held at the assessment's ratio for each mounting, and the saving is that share multiplied by your tariff.
- Payback is the kit price divided by the annual saving: no tariff inflation, no panel degradation, no maintenance. It is a first-pass figure, not a forecast.
Source: the UK government's plug-in solar impact assessment, as cited on the UK plug-in solar hub.
QUESTIONS
Plug-In Solar Calculator FAQ
How the figures are built, and what an 800W kit realistically returns.
How much does plug-in solar save in the UK?
The government impact assessment models an 800W system saving about £110 a year when mounted at a 30° tilt, and about £70 a year when mounted vertically on a wall or balcony. Those figures assume 25.7p/kWh and count only the electricity the household uses as it is generated.
How much electricity does an 800W plug-in solar kit generate?
The same assessment puts generation at 690 kWh a year for a 30° tilted installation and 378 kWh a year for a vertical one. Of that, 428 kWh and 272 kWh respectively are used in the home, with the rest flowing to the grid unpaid.
How long does a plug-in solar kit take to pay for itself?
At the assessment’s £400–£600 kit cost and its £70–£110 annual saving, simple payback falls between roughly four and eight years. A higher kit price, a lower tariff or more shade pushes payback out; using more of the generation at home brings it in.
Does a bigger panel array save proportionally more?
No. A plug-in kit is capped at 800VA of output, so panels above roughly 1,000W are clipped in strong summer sun. Extra panel capacity mainly helps in weak winter light, which is why the calculator labels results above the modelled 800W as an upper bound.
Does the calculator include payments for exported electricity?
No. A plug-in kit is not paid for export under the 2026 rules, so electricity that flows back to the grid is not counted as a saving. Only the share used in the home at the moment it is generated reduces a bill.
Why is less electricity used at home than generated?
Generation peaks in the middle of the day, while most households use more electricity in the morning and evening. The assessment assumes about 62% of tilted generation and 72% of vertical generation is used on site, and a vertical array scores higher because its output is flatter across the day.
WHICHWATTS
Check the kit before you check the payback
Only kits on the ENA Type Test Register may be self-installed. Read the rules, then compare what each listed kit costs per panel watt.