Compared with a real installation

Plug-in solar or a proper installation?

Short answer

An 800 VA plug-in kit generates roughly 650 to 800 kWh a year. A typical 4kWp roof array generates 3,400 to 4,200 kWh. That is a factor of five in output on a capital difference of far less than five. If you own a suitable roof, a plug-in kit is not a cheaper version of solar: it is a different and much smaller thing.

Plug-in (800 VA)
650–800 kWh/yr
Rooftop (4kWp)
3,400–4,200 kWh/yr
Ratio
About 5:1
Export income
Rooftop only
By the UKSolars editorial team Updated 2026-09-02
Sources checked 2026-09-02

Since plug-in solar became legal in Great Britain on 27 August 2026, a lot of coverage has framed it as the affordable alternative to a rooftop installation. For people who cannot have a rooftop installation, that is exactly right. For people who can, it is misleading in a way that is worth spelling out with numbers.

The output gap

~5×

A 4kWp roof array against an 800 VA plug-in kit, in annual generation

Derived from the 800 VA cap in the DESNZ Interim Product Specification v2.0 and a typical UK yield of 850 kWh per kWp

| | Plug-in kit | Rooftop array | | --- | --- | --- | | Capacity | 800 VA (capped) | 4,000 W typical | | Annual generation | 650–800 kWh | 3,400–4,200 kWh | | Typical cost | £400–£700 | £6,000–£7,800 | | Paid for export? | No | Yes, via the Smart Export Guarantee | | Needs an installer? | No | Yes, MCS-certified | | Grant-eligible? | No | Yes, in principle | | Adds to home value? | No: it is portable | Generally neutral to positive |

The cost ratio is roughly ten to one. The output ratio is roughly five to one. On that basis the plug-in kit looks like the better deal per pound, and on a pure payback calculation it is: three to four years against eight to sixteen.

Why the payback figure is the wrong lens here

Payback measures how quickly you recover the money. It says nothing about how much money there is to recover.

A plug-in kit saves you perhaps £190 a year and then stops, because it is capped at 800 VA by law. There is no version where it saves more. A roof array saves several times that and keeps doing so for two decades, and it earns on top of that through an export tariff that the plug-in kit cannot access at all.

The way to think about it

A plug-in kit is a fast, small, complete answer. A roof array is a slow, large, compounding one. If you can only have the first, it is a good thing and worth having. If you can have the second, choosing the first because it pays back faster is optimising the wrong number.

Where a plug-in kit works well

Four situations, and they are not marginal: they cover a large fraction of UK households.

Choose plug-in

  • You rent. A tenant cannot install a roof array without the landlord as applicant.
  • You live in a flat. Permitted development does not apply, and a leasehold flat rarely has the roof rights.
  • You expect to move within a few years. A plug-in kit goes with you; an array does not.
  • Your usable space is a balcony, a wall or a fence rather than a roof slope.

Choose rooftop

  • You own a house with a pitched roof facing anywhere but due north.
  • You want to be paid for what you export.
  • You have or plan a heat pump or an EV: 800 VA will not touch that load.
  • You might qualify for grant funding, which a plug-in kit cannot access.

If you own a roof, here is the actual question

It is not “plug-in or rooftop”. It is whether a rooftop installation pays on your roof, which depends on orientation, shading, your consumption pattern and your export rate, and which depends on the property and local rules.

The payback calculator puts all six of those inputs on screen and lets you change every one, including the ones we have defaulted conservatively. It runs entirely in your browser and asks for nothing.

If the answer comes back at fourteen years and you were hoping for eight, that is useful information, and it is worth having before anyone knocks on your door with a quote.

Common questions

Can I have both?
The rules permit one plug-in device per household, and it would sit alongside a rooftop system rather than replacing part of it. In practice, if you are installing a roof array there is no reason to add a plug-in kit: the money is better spent on one more panel or on storage.
Is a plug-in kit a good way to test whether solar suits my house?
Not really, and this is worth being clear about. A plug-in kit tells you almost nothing about how a roof array would perform, because the orientation, tilt, shading and scale are all different. If you want to know what your roof would do, model it: that is free and takes two minutes.
Do plug-in kits get paid for export?
Generally no. The Smart Export Guarantee requires an MCS-certified installation and a smart meter set up for half-hourly export readings, which a plug-in kit does not have. Anything you are not consuming at the moment it is generated is given away.
What about payback?
A £400 to £700 plug-in kit saving £175 to £215 a year may pay back in three to four years. Its output is limited. A roof array costs more and usually takes longer to repay, but generates several times as much electricity.

Sources

Checked 2026-09-02. Rates, rules and eligibility can change. Confirm current terms before signing a contract or applying for funding.

Read next

Model a real installation→

Your roof, your bill, your numbers: no email needed.

Is your roof suitable?→

Six factors, and only two of them are dealbreakers.

If you rent→

Then this comparison does not apply and the kit is your answer.

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