Microinverters explained: the part of a plug-in solar kit the law actually regulates
The new UK law caps plug-in solar at 800 watts of AC output. Panels do not make AC. The microinverter is the component every legal number attaches to, and here is what the government specification actually demands of one.
Rules and product details last checked on .
Key takeaways
- The law regulates the microinverter, not the panels. The statutory limit is 800 W of AC output, and the microinverter is the only component in a kit that produces any AC at all.
- The government specification is stricter than the law. It caps a device at 800 VA of apparent power and 3.5 A of current, while allowing up to 2,000 W of panel capacity on the DC side.
- A compliant inverter must disconnect within 100 milliseconds of losing mains supply, and drop the voltage at its plug pins below 34 V in the same window.
- Type testing is checkable by anyone. The ENA Type Test Register is publicly searchable, though its public listings stop in April 2024 and newer entries live on Connect Direct.
- The only microinverter we found sold in the UK expressly for this purpose is the EcoFlow STREAM 800 W, at £122.55 on 23 August 2026.
Every guide tells you to check the microinverter. Almost none tells you what you are checking, or why the law points at that box and nowhere else.
The reason is arithmetic. A solar panel produces direct current. Your home runs on alternating current. Something in the kit has to convert one into the other, and that thing is the microinverter. When the law says a plug-in microgenerator must have “a maximum rated alternating current output not exceeding 800 watts”, it is describing a component the panels do not have. The panels could be rated at anything. The number that decides whether your kit is legal is printed on the inverter.
This page explains what the box does, what the government’s product specification demands of it, and how to check that a specific model has been type tested. If you are new to the category altogether, start with what the law actually permits.
What the box actually does
A microinverter is a small power converter, roughly the size of a hardback book, that sits behind or beside a solar panel instead of on a loft wall. It does three things continuously while the sun is up:
- It tracks the panel’s best operating point. A panel’s output voltage and current move with light and temperature. The inverter constantly adjusts the electrical load it presents so the panel delivers the most power available at that moment. This is called maximum power point tracking, MPPT, and you will see the term on every product page.
- It converts DC to AC. Power electronics inside the unit chop the panel’s direct current up and rebuild it as a 230 V, 50 Hz alternating current matched to the grid.
- It synchronises and protects. The inverter phase-locks onto the grid’s waveform before feeding anything in, and monitors voltage and frequency the whole time it runs. If the grid fails, it stops. That behaviour is not courtesy; the specification demands it, and we quote the numbers below.
Because each panel, or pair of panels, gets its own microinverter, each one works independently. Shade on one panel from a neighbouring building or the balcony above does not drag the others down, the way it can on a traditional string inverter shared by a whole rooftop array.
Why the legal numbers are the inverter’s numbers
Plug-in solar becomes legal to connect through a socket on 27 August 2026. The statute sets the headline limit, but the document that does the real work is the government’s Plug-in Solar Device Interim Product Specification, version 2.0, which a compliant kit must be certified against as a complete package. Its clause 4.1 says a device “shall be designed such that the maximum apparent power Smax supplied to the mains installation does not exceed 800 VA and the maximum current does not exceed 3.5 A”.
Three numbers there are worth unpacking, because sellers will quote whichever one flatters them:
- 800 VA, not 800 W. Apparent power is measured in volt-amperes. For a well-behaved inverter the two are close, but they are not the same quantity, and the specification deliberately uses the stricter one. A listing that says “800 W” without a VA figure has not answered the question.
- 3.5 A is a second, independent cap. Even a device under 800 VA must not push more than 3.5 A into the installation at the point of connection. The inverter is required to control itself so that “under all test conditions” it stays inside this, tested at supply voltages of 0.94, 1.0 and 1.1 times the nominal 230 V.
- 2,000 W of panels is allowed. The specification permits the sum of the panels’ DC output to reach 2,000 W, with a note that anyone above 960 W of panel capacity should “consider professional assessment of their existing electrical installation”. Panels overhanging the inverter’s rating are not illegal; the inverter simply clips, delivering no more than its ceiling.
Here is every number in one place, with the clause it comes from:
| Limit | Value | Applies to | Source |
|---|---|---|---|
| Rated AC output | 800 W maximum | The inverter | SI 2026/848, condition (b) |
| Apparent power (Smax) | 800 VA maximum | The device | Specification, clause 4.1 |
| Current at connection | 3.5 A maximum | The inverter | Specification, clause 4.1 |
| Total panel capacity | 2,000 W maximum | The DC side | Specification, clause 4.1 |
| Professional assessment advised | Above 960 W panels | The DC side | Specification, clause 4.1 |
| Disconnect on loss of mains | Within 100 ms | The inverter | Specification, clause 6.2.3.3 |
| Voltage at plug pins after disconnect | Below 34 V within 100 ms | The inverter | Specification, clause 6.2.3.3 |
| Open-circuit voltage at inputs | 120 V maximum | The DC side | Specification, section 4.2.2 |
That last point is the one most listings get backwards. A kit with two 500 W panels and an 800 W inverter is a legal configuration. A kit with one 400 W panel and a 1,000 W inverter is not, whatever the total suggests.
Why plug-in solar uses microinverters, not string inverters
A conventional rooftop array strings its panels together in DC and feeds one big inverter fixed near the consumer unit. That architecture assumes someone qualified is running the DC wiring, and DC wiring in a home is regulated work.
The specification takes the opposite path. It defines a plug-in solar device as a package of “at least one PV module, a grid-following inverter, a factory assembled connection line fitted by the manufacturer with a plug designed to BS 1363”, and a mounting system. The conversion happens at the panel, so the only cable entering your home is ordinary mains cable carrying AC. It sorts the possible layouts into one-component devices, where the inverter is integrated into the panel, two-component kits, and multi-component kits with up to four panels on one inverter.
Two safety limits shape those layouts. No more than two panels may be wired in series in any string, and the open-circuit voltage at the inverter’s inputs must not exceed 120 V, because series-connected panels “can produce harmful DC voltages at the inverter input leading to an electrocution risk and the possibility of DC arcing”. The specification also requires that any unused AC output, provided for paralleling a second inverter, “shall be closed with a cap that can only be removed with a tool”. Each of those sentences is the shadow of a German balcony-solar accident report, borrowed through the parent standard DIN VDE V 0126-95.
What it must do when the grid fails
A plug-in solar inverter is grid-following: it does not create the waveform, it follows the one already there. When that waveform disappears, the specification’s clause 6.2.3.3 imposes two clocks.
First, the anti-islanding clock. An inverter feeding power into cables an engineer believes are dead is a genuine hazard, so on loss of mains the unit “shall automatically disconnect from the mains supply within 100 ms”. Second, the discharge clock: capacitors inside the unit can hold a charge after disconnection, so “the voltage at accessible plug pins shall decrease to below 34 V within 100 ms”, and any capacitor above 100 nF must fall below 34 V within one second.
This is why an uncertified marketplace microinverter is not a bargain but a hazard. A unit without working anti-islanding will happily back-feed a dead grid. The specification also requires the inverter to meet BS EN IEC 62109-1 and -2 for safety, BS EN 62116 specifically for its islanding prevention, and BS EN IEC 62109-3 where the inverter is integrated into the panel. Those standard numbers, not the word “compliant” on a listing, are what you are looking for.
How to check one is type tested
Before a network operator will accept a microgenerator, its inverter must appear in the industry type-test register, which exists because notifying your DNO is a real duty, not a formality. The register is run by the Energy Networks Association and is publicly searchable at the ENA Generator Type Test Register. You do not need an account to look a device up: filter by manufacturer, category and type, and each entry shows a system reference, the model, its registered capacity and phases, and a compliance status of “Compliant”, “Awaiting assessment” or “Further information required”.
Two things we verified on 23 August 2026 are worth knowing before you rely on it:
- The public listings stop on 16 April 2024. The register’s own note says newer devices are recorded on Connect Direct, the industry portal, and the public list has not carried them since. A device absent from the public register is not therefore unregistered; it may simply be newer than the cutoff. Ask the seller for the system reference rather than concluding anything from a blank search.
- The compliance status is the field that matters, and it is per model reference, including its version suffix. Two otherwise identical entries can carry different statuses. Check the exact reference you are being sold, not the family name.
EcoFlow, Hoymiles, Enphase and Deye all appear as manufacturers in the register, which covers G98, G99 and G100 devices. The reference you want for a plug-in kit is a G98 one, since that is the engineering recommendation for microgeneration at this scale.
What is on sale today
We have already documented what you can actually buy in the UK, and the picture has not changed. The one microinverter we found sold expressly for this purpose is the EcoFlow STREAM 800 W, listed at £122.55 on 23 August 2026, with bundles adding two rigid panels at £329 to £419 depending on wattage. It is rated at the full 800 W, carries an IP67 rating and is designed to pair with the STREAM app.
What its product page still did not carry, when we checked, is a type-test system reference. That is not evidence of non-compliance; it is an absence of evidence, and it is the exact question to put to any seller before buying: which reference, in which register, under which status?
For what a working kit actually yields through a British year, see our modelled output figures.
What we have verified, and what we have not
Verified against primary sources. The 800 W AC condition in SI 2026/848; clause 4.1’s 800 VA and 3.5 A limits, the 2,000 W panel ceiling and the 960 W assessment threshold; the 100 ms and 34 V disconnection requirements; the 62109 and 62116 standard references; the device-type definitions; the ENA register’s public cutoff of 16 April 2024; and the EcoFlow price. All checked on 23 August 2026.
Not verified. Whether any specific product on sale has completed type testing under the new specification. We have not tested hardware and have not seen a certificate. When a manufacturer publishes a reference we can check against the register, it goes in.
Our editorial policy explains how we handle claims we cannot check.
This page carries the date it was last checked. The specification and the register will both move in the first months of this new category; if you spot something that has changed, tell us and we will verify it against the source and update the date.