Plug-in solar microinverter safety in the UK
A good microinverter is a major part of making plug-in solar safe, but there is an important point that is going to catch people out after 27 August.
A G98-compliant microinverter is not, by itself, a compliant UK plug-in solar product. The new rules apply to the complete product as supplied by the manufacturer, including the inverter, panels, plug and lead, mounting arrangement, protection and instructions.
The mistake I would avoid: buying a microinverter that appears on an ENA/G98 list, buying a BS 1363 lead separately and assuming that combination automatically qualifies under the new plug-in solar legislation.
The final UK framework is written around a complete compliant product. The microinverter is only one part of it.
Why the microinverter matters
The microinverter sits between the solar panels and the house supply. It takes DC from the modules and converts it into AC that can operate in parallel with the grid.
That means it has two very different jobs to do safely: manage the DC input from the panels and control its behaviour on the AC network side.
On a plug-in product, the fact that the AC connection ends in a normal-looking household plug can make the equipment look simpler than it really is. Electrically, it is still generation operating in parallel with the public network.
What does G98 actually tell me?
G98 is the Engineering Recommendation used for connecting small generating equipment to the distribution network. A suitable inverter needs the correct network protection behaviour, including voltage and frequency limits and loss-of-mains protection.
That is important. But G98 is not the same thing as the new plug-in solar product specification.
A microinverter can have suitable G98 characteristics and still not prove that a home-made combination of panels, cable, plug and brackets meets the new consumer-product route.
A useful way to separate it:
G98: can the generating equipment operate safely in parallel with the electricity network?
Plug-in Solar IPS: does the complete consumer product meet the additional requirements for this socket-connected route?
What is anti-islanding?
Anti-islanding is one of the most important safety functions in a grid-connected inverter.
If the street supply fails, the inverter must not continue trying to energise the house wiring. Network engineers may be working on equipment that is expected to be dead.
A compliant grid-connected microinverter detects loss of mains and stops supplying power. This also means normal plug-in solar is not a backup supply during a power cut.
The new UK product has extra safety requirements
The final Interim Product Specification goes much further than simply saying “use a G98 inverter”. The complete product has requirements around:
- 800VA maximum continuous AC output,
- 3.5A maximum continuous AC current,
- a manufacturer-supplied non-rewireable BS 1363 plug,
- a 5A fuse in that plug,
- the connection lead and complete product arrangement,
- consumer-unit and residual-current-protection checks,
- safe mounting and mechanical installation,
- DNO notification instructions, and
- instructions explaining where and how the product may be connected.
That is why “the inverter is approved” is too simplistic.
Can I fit my own plug lead?
Not if the argument is that doing so turns a separately purchased microinverter into the compliant product described by the new IPS.
The specification calls for a manufacturer-supplied non-rewireable BS 1363 plug fitted with a 5A fuse. That wording matters.
The same microinverter may be perfectly suitable in another type of PV installation, but that is different from saying a user-made lead converts it into the new self-install product.
What about the DC side?
Every microinverter input has electrical limits, including maximum input voltage, MPPT operating range, maximum input current, short-circuit current and the module arrangements the manufacturer permits.
Panel wattage alone does not tell you whether a combination is safe.
Why wiring panels in series can be dangerous
When panels are connected in series, their voltages add together.
If one panel has an open-circuit voltage around 40V, two similar panels in series can be around 80V before allowing for the increase in panel voltage in cold weather. If the microinverter input was designed for one low-voltage module, that can put it well outside its rating.
Do not use “the inverter only outputs 800W” as a reason to ignore DC voltage. The AC output rating tells you virtually nothing about whether an improvised series string is within the inverter's DC input limits.
What about panels in parallel?
Parallel connection behaves differently: voltage stays broadly similar while available current increases. That may avoid the high-voltage problem of series wiring, but the input and connectors still have current limits.
Again, use the exact product design and instructions rather than guessing.
But the new rules allow up to 2,000W of panels
They do. The final IPS allows up to 2,000W connected PV module capacity while AC output remains limited to 800VA.
That does not make the DC side open-ended. A manufacturer can design and test a compliant product using an oversized array while keeping every input within its ratings. That is very different from a homeowner deciding that any four panels can be wired into any 800W microinverter.
The 800W / 800VA guide explains the 2,000W and 960W figures.
Why have two-panel microinverters been so common?
Many balcony-solar products use two independent DC inputs, often one module per input. It keeps each panel in a relatively low-voltage arrangement and allows the inverter to track the modules independently.
But the final UK rules do not say every compliant product must be a two-panel design. Manufacturers can use other arrangements if the complete product meets the specification.
What should I check before buying?
| Check | Why it matters |
|---|---|
| Complete UK-compliant product? | A suitable inverter alone does not establish IPS compliance. |
| Exact inverter and network reference | You need the correct G98 information for the product you own. |
| Panel model and permitted arrangement | Confirms voltage, current and module compatibility. |
| Factory-supplied BS 1363 lead | The IPS specifies a manufacturer-supplied non-rewireable plug with a 5A fuse. |
| Mounting supplied or approved | The new route covers the complete product, not just the electronics. |
| Circuit/protection instructions | The user needs to establish whether the intended connection is suitable. |
| DNO/G98 instructions | Network notification still applies. |
Can I use an APsystems, Hoymiles or another existing microinverter?
The right question is not simply whether the inverter has G98 credentials.
For the new plug-in route the question is: has a manufacturer placed a complete product on the UK market using that inverter which meets the final IPS as a whole?
An inverter that is perfectly good in a conventional PV installation does not automatically become a legal self-install plug-in product when somebody buys a cable for it.
This is particularly relevant to the APsystems EZ1 guide.
Does unplugging make everything dead?
No. Follow the manufacturer's shutdown and disconnection sequence. Solar modules can produce DC whenever sufficient light is present, even when the AC plug has been removed.
The DC side does not become electrically dead just because the house connection has been unplugged.
What about batteries?
The final UK plug-in solar IPS does not cover plug-in battery systems or plug-in solar products incorporating electrical energy storage.
See the plug-in battery storage guide.
My practical view:
Microinverters are a sensible way of keeping the DC side of small solar relatively low voltage, and proper G98 protection makes the network side safer. But the new legislation is not an invitation to build your own product from individually decent components.
If you want the new DIY plug-in route, buy the complete compliant product and use the panels, lead, mounting and wiring arrangement it was actually designed and supplied with.
Sources
Common questions
If my microinverter is G98 approved, is my plug-in solar system legal?
Not automatically. G98 suitability matters, but the new plug-in route applies to the complete product and its additional IPS requirements.
Can I buy a plug lead separately?
Do not assume that makes the system IPS compliant. The final specification calls for a manufacturer-supplied non-rewireable BS 1363 plug fitted with a 5A fuse.
Can I wire two panels in series?
Only if the exact manufacturer design allows it. Series wiring adds panel voltages and can exceed the input rating of microinverters designed for one module per input.
Does anti-islanding give me power in a blackout?
No. Normal grid-connected generation shuts down when the mains supply is lost.
Related guides
General guidance only. Always use the exact electrical limits, module arrangements and connection instructions supplied by the manufacturer of the product you own.