In short
Not always G99: a replacement inverter must meet today's rules for your system, G98 for most homes and G99 for larger ones, and the exact model must show as compliant on the ENA's Connect Direct register. Going bigger, or to a hybrid, can move a home system into G99.
Your inverter is showing an error code or a red light, or it has been condemned, and the quote for a new one mentions G98 or G99. Before anything is ordered, it helps to know which rules the new inverter has to meet and who needs telling.
Do I need a G99 compliant inverter? The short rule
Not always. A replacement inverter has to meet today's connection rules for your system, not the rules it was first connected under, and which rules apply depends on the size of the system.
Most homes: G98. Systems up to 16 amps per phase, about 3.68 kW on a normal single-phase supply, come under G98, which covers "Fully Type Tested" equipment. Our G98 vs G99 explainer covers where that line sits and why.
Larger systems: G99. Above that line, the new inverter has to meet G99. The ENA's connection guide says that if you replace a component, you "must notify the DNO before making changes".
Systems connected before 27 April 2019. Older home systems were connected under the G83 rules, and they don't stay on them. G98 says that where "a significant piece of equipment, such as an inverter, is replaced", the system has to comply with G98.
For larger systems on the old G59 rules, the ENA guide says you discuss with the network operator whether the new equipment can stay on G59 or must be upgraded to G99.
Either way, the network operator is told. On a G98 system the installer notifies it within 28 days of commissioning. On a G99 system the notice goes in before the work.
What to check before a G99 compliant inverter is ordered
The exact model, on Connect Direct. Inverter makers register their models with the Energy Networks Association. The old ENA Type Test Register closed on 16 April 2024, and its data moved to the ENA's Connect Direct platform, which now shows "the latest compliance status for all devices" (ENA).
What to do: search Connect Direct by manufacturer and model, not just the brand, or ask your installer to show you the result.
The status wording. "Compliant" is what you want. In September 2022 the ENA added a status called "Non-compliant for new installations", for devices that were compliant before the standards changed and no longer are.
What to do: don't re-buy the same model as your old inverter without checking it. A model that was fine when your system went in may now carry that status.
Compliant is a guide, not a promise. The ENA calls its compliance status "indicative only" and says network operators keep the right to review whether a device suits their network. Government guidance adds that a network operator may ask for extra documents if a device isn't type tested.
What to do: use an installer who deals with the network operator's questions, not one who just fits the box.
The size, compared with the old one. A bigger inverter, or a hybrid that runs a battery as well, can take a home system over the G98 line and into G99. The ENA guide gives increasing capacity as an example of a significant change, which you agree with the network operator first and which in many cases means a new application form.
What to do: decide about a battery before the inverter is ordered. Our G98, G99 and DNO approval guide explains how approval works.
What was notified before. The paperwork for the new inverter builds on what was sent when the system was first connected. If that was never done, the system can be notified retrospectively.
What to do: find your MCS certificate and any network operator paperwork before you ask for quotes.
The Feed-in Tariff, if you're on it. Ofgem says you "may repair or replace all or some generating equipment" without affecting your accreditation, as long as the installation still meets the scheme rules. If the change increases or reduces the installation's capacity, you must contact your FIT licensee, and capacity added on or after 15 January 2016 doesn't get FIT payments (Ofgem).
What to do: check with your FIT licensee before you choose a bigger inverter.
Settings and labels on the day. G98 says no setting covered by the type test can be changed unless agreed in writing with the network operator, and the installer checks the loss of mains protection at commissioning. A summary of the protection settings is displayed with the labels at the supply point.
What to do: make sure the labels and settings summary show the new inverter. G98 makes keeping that safety information up to date the owner's responsibility.
What we see on real jobs
The step that gets skipped is telling the network operator. Tony Beckett, our director, says: "there's some installers out there who don't even put the forms in, which is crazy because you can face large fines."
We work out which route applies before anything is ordered, because the choice of inverter can change the answer. That starts with what was originally notified for the site.
Customers sign a letter of authorisation so we can speak to the network operator on their behalf. You get copies of everything for your records, which matter later for export payments, insurance and selling the house.
We do the same on systems we didn't install, including ones that were never notified.
When an inverter has to be replaced anyway, we'll tell you whether a hybrid is worth it. It lets a battery go on later without a second round of work.
What an inverter replacement costs
Our inverter replacements typically cost £1,200 to £2,000 fitted, depending on the size and type of inverter. We keep some in stock and source others for the job.
We prepare and submit the network operator notification or application that the replacement needs. Our servicing page covers inverter repairs and replacement.
When to call someone, and what to send
Get the fault confirmed before you buy anything. In a Which? survey of solar owners, "claiming the inverter needs changing" was among the most common cold calls.
Call an MCS certified installer if:
- the inverter shows an error code, a red light or a blank screen in daylight
- you're thinking of a bigger or hybrid inverter, or a battery
- you can't find any paperwork for the original connection
- you're on the Feed-in Tariff and the capacity might change
What to send us on WhatsApp:
- a photo of the inverter and its rating label
- a photo of any error code on the screen
- a screenshot from your monitoring app
- your MCS certificate and any network operator paperwork from the original install
- whether you want a battery, now or later
- your postcode
- for a business site: the MPAN, supply capacity and any export limit
DB Energy is MCS certified (NIC-601172). We're based in Warrington and work across the UK.
Key points
Not always G99. The new inverter has to meet today's rules for your system: G98 for most homes, G99 for larger systems.
Check the exact model on Connect Direct. The ENA Type Test Register closed on 16 April 2024. Avoid models marked "Non-compliant for new installations".
Old G83 systems move to G98. Replacing the inverter brings an older home system under G98.
The network operator is told. Within 28 days of commissioning on G98, before the work on G99. Keep a copy.
Bigger means more paperwork. A larger or hybrid inverter can move a home system into G99, which is agreed before the work.
Questions people also ask
Where can I check if an inverter is G98 or G99 compliant?
On the Energy Networks Association's Connect Direct platform, which took over from the ENA Type Test Register on 16 April 2024. Search by manufacturer and model, and check the status says compliant.
Can I replace my inverter with the same model?
Only if that model still shows as compliant on Connect Direct. Some older models now carry the status "Non-compliant for new installations", which the ENA added in September 2022.
Does my network operator need to know I've replaced my inverter?
Yes. On a G98 system the installer notifies it within 28 days of commissioning, and on a G99 system the operator is told before the change is made.
Does an old G83 system have to meet G98 when the inverter is replaced?
Yes. G98 says that when a significant piece of equipment such as an inverter is replaced, a system installed under G83 must then comply with G98.
Can I fit a bigger inverter than my old one?
You can, but it may take a home system over the G98 line and into G99. The ENA treats extra capacity as a significant change, agreed with the network operator before the work, and it can mean a new application.
Send us a photo of your inverter and its label on WhatsApp, and we'll tell you what the replacement has to meet.
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