A plug in solar calculator should tell you what a kit is worth in your home, not in a brochure. Enter your region, panels, shade, daytime use and the price you pay, and you get yearly generation, savings and payback. The result is an estimate, and we show you every assumption behind it.
Plug-in solar calculator
Your estimate per year
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- Panels produce
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- You use at home
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- Inverter limit
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- Payback
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DESNZ says households could save "up to £110 a year". Treat that as a ceiling, not a typical result.
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Data and assumptions
- Sun: yearly output per kW of south-facing panels, PVGIS 5.3, European Commission JRC, 14% system losses, read 9 Nov 2026.
- Price: Ofgem price cap, GB average, direct debit, 1 Oct 2026 to 31 Dec 2026. Overwrite it with the rate on your bill.
- Inverter limit: 800 W AC by law in Great Britain. Panel power above 1.3 times the limit (1.6 times for upright panels, which rarely reach full power) is counted as lost.
- Shade cuts output by 20% (partial) or 45% (heavy). Your share used at home is our assumption: 45%, 60% or 75% by daytime use. Power you do not use goes to the grid unpaid.
- An estimate, not a quote. It cannot see your roofline, trees or appliances.
How the Calculator Works
Four steps sit behind the result.
- Generation. From your region, panel size, orientation, tilt and shade, we estimate what the panels produce over a year.
- The 800 W cap. The inverter may put out no more than 800 W AC, even though up to 2,000 W of panels can be connected. SI 2026/848 EM §5.1 The calculator clips generation at that limit, so a bigger array only helps on weak-light days.
- What you use. We keep only the share of generation that your home consumes at the time.
- Money. That share multiplied by your price per kWh is the yearly saving. Your kit price divided by the saving is the payback.
We label every data source with its name and date on the calculator itself. Regional sunshine figures and the starting unit price come from named, dated sources, and the share of power you use at home is our own assumption, shown as such and editable. You can overwrite the price per kWh and the kit price with your own figures at any time.
Why Your Savings Depend on Daytime Use
Solar only helps while the sun is up. If the panels make more than your home is using at that moment, the surplus flows out to the grid.
You are not paid for that surplus by default. The Smart Export Guarantee needs an installation by an MCS-certified installer using certified products. MCS, SEG for consumers, 2026 MCS says plug-in solar, as a do-it-yourself system, is outside the scope of MCS. MCS, 14 Sep 2026 So we find no documented route to export payments today, and the calculator counts only what you use.
That is why the daytime-use setting moves your result more than most other inputs. A fridge, router and standby loads run all day and soak up solar power. A house that is empty from morning to evening, with the oven and washing machine on at night, uses much less of what the panels make.
Practical ways to raise your share: run the dishwasher or washing machine in the middle of the day, charge devices while the sun is out, and work from home when you can.
A Reality Check
On 26 August 2026 the Department for Energy Security and Net Zero (DESNZ) said households could save up to £110 a year, and that a kit could provide up to 20% of an average home’s electricity use. DESNZ news, 26 Aug 2026
Treat both as ceilings. They describe a good case, not the typical one. We show the £110 figure beside your result so you can see how your home compares.
If your estimate lands well below it, that is normal for a shaded spot, a north-facing wall or an empty house. If it lands above it, check your inputs, because the DESNZ figure is described as the most a household could save.
Payback follows the same logic. A cheap kit with good sun and daytime use pays back faster. An expensive kit in the shade may not pay back at all within its life, and we would rather the calculator told you that than hid it.
What the Calculator Can’t Know
Some things only you can see.
Shade You Have Not Measured
The shade setting is a choice of none, partial or heavy. A tree that blocks the panel only in the afternoon, or a neighbour’s extension, can cut output more than you expect. Stand where the panels will go at different times of day before you trust a result.
Whether You Are Allowed
The calculator estimates money, not permission. If you rent, no law gives you a right to install plug-in solar, and your landlord or freeholder can say no. Tick “I rent” and we will point you to the right next step. Our renters guide explains how to ask.
The Rules Behind the 800 W
The plug-in limit, the one-per-home rule and the registration on myplugin.solar before use are covered in the full legal guide. The calculator assumes you meet them. It also assumes Great Britain: the 2026 change does not reach Northern Ireland in practice, and we could not confirm a decision there. SI 2026/848 reg. 1
Your Real Usage
Your usage profile is a simple one. A smart meter, an energy display or a few weeks of notes will tell you more about your daytime load than any default.
For a wider picture of the rules, savings and who can use a kit, start with our main guide to plug in solar in the UK.
Sources
Each one opened and checked on 10 November 2026.
Questions people ask
How much power will 800 watts of solar panels produce?
It depends on where the panels are, which way they face, how much shade they get and the time of year. A rating of 800 W is the peak in ideal light, not a steady output. In Great Britain the plug-in limit is also 800 W AC, so the calculator caps the result at that figure.
Do plug-in solar panels actually save money?
They can, but only on electricity you use while the panels are generating. Surplus goes to the grid and is not paid for by default. A home with steady daytime use in a sunny, unshaded spot saves more than an empty house with shaded panels. The calculator shows your own range.
How is my result worked out?
The calculator estimates how much your panels generate in your region, cuts it at the 800 W AC limit, then counts only the share you use in the home. That share, multiplied by your price per kWh, is your yearly saving. Dividing your kit price by it gives the payback.