The inverter turns the direct current from your panels into the alternating current your house and the grid use. Replacing it on a Feed-in Tariff system is normal work, and Ofgem treats the inverter as part of your generating equipment, along with the panels.
Ofgem's guidance says you may repair or replace all or some of your generating equipment without affecting the compliance of an accredited installation. What can cause problems is a change in capacity, and silence towards the people who need to be told.
Key Points
- For solar, Ofgem defines generating equipment as the solar panels and inverters. So an inverter is covered by the replacement rules.
- Replacement does not, in itself, affect the compliance of an accredited installation. Ofgem's supplier guidance says the same, and adds that it may affect total installed capacity.
- The installation must still meet the scheme rules: capacity at or below 5 MW, same eligible technology, not decommissioned and not moved to another site.
- Changes to total installed capacity do not change your tariff rate. But added capacity is an extension and gets no FIT support.
- You must contact your FIT licensee if the work increases or decreases total installed capacity. MCS-FIT generators should also tell their licensee about other modifications.
- If the generation meter is replaced during the work, that has to be reported too. Ofgem tells licensees the generator should notify them when a generation or export meter has been replaced or removed.
- The Energy Networks Association lists informing your network operator when you remove or replace a generating unit as an ongoing duty of the owner.
- For an existing G99 connection, the guide says you must notify the network operator before making changes. A small change means confirming the new part complies. A significant change, such as a capacity increase, often means a new application.
- You cannot claim FIT payments for a period when the system is not generating.
Common Misconceptions
- Replacing a failed inverter has no effect on my FIT and needs no paperwork. The first half is broadly right and the second half is not. Ofgem says replacement does not in itself affect compliance. But capacity changes must be notified. Your network operator must also be told about a replaced generating unit.
- A bigger inverter means bigger FIT payments. No. Capacity above your accredited figure earns nothing under FIT, and your rate per kWh does not change.
- My inverter is the generation meter. It is not. The generation meter is a separate approved meter. Ofgem says a generation meter must measure the electricity generated separately from any other source.
- Any electrician can swap it. For FIT and SEG purposes the certification of the installation and installer matters. Ofgem's supplier guidance also expects the network operator notification to have been made.
- I can leave the old inverter connected as a spare. That changes what is connected to the network, and what your meter sees. Ask first.
Real-World Advice
We repair and replace inverters on systems fitted by other companies, not just our own. One Polegate customer's older solar had faults and he could not reach the original installers. We made his system safe, then upgraded the whole thing.
UK-Specific Considerations
Capacity is the trap. A replacement inverter with a higher output can raise your total installed capacity. Ofgem treats that as an extension, and an extension commissioned on or after 15 January 2016 receives no FIT support. Ofgem specifically names repowering, where older equipment is replaced with equipment of greater capacity, as a way an installation gets extended.
Removing an output limit counts too. Ofgem names de-rating removal as an extension. If your old inverter was software limited and the new one is not, that is a capacity increase.
Connection rules depend on the original route. Under G98, connect and notify applies and the installer submits the Installation Document within 28 days of commissioning. Above 16 A per phase the G99 process applies. That is 3.68 kW on a single phase supply and 11.04 kW on a three phase supply.
Older systems may be on G83 or G59. Many 2010 to 2015 systems were connected under the earlier recommendations. The Energy Networks Association guide covers replacing a generating unit installed under G59. You need to discuss it with the network operator. They decide whether the new equipment should comply with G59 or be upgraded to G99.
Protection settings matter as much as the inverter. The same guide covers interface protection on a G59 installation. Tell the network operator if you replace all or part of it. They will want confirmation that the new protection complies. They may want to witness the commissioning.
A hybrid inverter is a bigger change than a like for like swap. A hybrid unit is chosen so a battery can be added. That brings the battery metering rules into play as well. Our guide to adding a battery to a FIT system covers those.
The generation meter is separate from the inverter. Do not let an installer relocate or replace the generation meter as a convenience without telling your licensee.
Keep, notify or apply
| Situation | FIT effect | Who to tell |
|---|---|---|
| Same rated capacity, new inverter | Compliance and tariff unchanged | FIT licensee, as a modification. Network operator, as a replaced generating unit |
| Higher rated capacity | Original capacity keeps its rate. The increase gets no FIT support | FIT licensee, because capacity changed. Network operator, by G98 notification or G99 application |
| Lower rated capacity | Accreditation continues. Ofgem says tariff rate and eligibility period are unaffected | FIT licensee. Take a meter reading on the date of the change |
| Hybrid inverter fitted ready for a battery | Depends on the metering arrangement | FIT licensee, with a diagram. Network operator |
| Generation meter changed at the same time | Readings must still measure only your installation | FIT licensee, as a meter replacement |
When This Isn't Right For You
- The panels themselves are the problem and the inverter is fine.
- Your eligibility period is nearly over and the system is close to the end of its useful life. Then a full replacement may be the better question.
- The system is leased or under a rent a roof agreement, so the equipment is not yours to change.
Before You Spend Money
- Get the old and new inverter ratings side by side, in kW. Then compare with the accredited capacity on your FIT statement.
- Ask whether the fault is really the inverter. Isolators, fuses, string faults and monitoring failures all look like a dead inverter from the ground.
- Ask which connection route applies, and whether it is notify or apply. A G99 application has to happen before the work.
- Ask who submits the network operator paperwork, and get a copy. Ofgem expects your licensee to be able to verify the network operator was told.
- Take a generation meter reading on the day. It marks the boundary between old and new for your licensee.
- Ask about the warranty and about monitoring. A new inverter usually brings better monitoring, which makes the next fault easier to spot.
Frequently Asked Questions
Q: Will I lose my Feed-in Tariff if I replace the inverter?
A: In most cases no. Ofgem says replacing generating equipment does not, in itself, affect the compliance of an accredited installation. Your FIT licensee still has to be told, and the paperwork has to be right.
Q: Does a more powerful inverter earn me more FIT?
A: No. Extra capacity is an extension, and Ofgem says extensions commissioned on or after 15 January 2016 get no FIT support. Your rate per kWh is unchanged.
Q: Do I need a new grid connection application?
A: It depends on size and on your existing agreement. Under G98 the installer notifies within 28 days of commissioning. Above 16 A per phase the G99 process applies, and for an existing G99 connection you must notify before making changes.
Q: What happens to my payments while the inverter is out?
A: The system is not generating, so there is nothing to claim for that period. Ofgem's supplier guidance says FIT payments cannot be claimed while works are taking place.
Q: My system was installed in 2011. Which rules apply to it?
A: Older systems were connected under G83 or G59. The Energy Networks Association guide says you should discuss with the network operator whether replacement equipment stays under the old recommendation or moves to G99.
Summary
An inverter swap is one of the most common jobs on a FIT era system, and it does not end your tariff. Two things decide how smooth it is. First, the rating of the new unit: match the accredited capacity and there is nothing to argue about. Second, the paperwork: tell your FIT licensee, tell your network operator, and take a meter reading on the day. If the new inverter is a hybrid ready for a battery, treat the metering as a separate decision and settle it before the work.