The inverter turns the direct current from your panels into the alternating current your house uses. It is the only part of a solar system with a screen, and it is the part most likely to need attention first.
When one fails you have three choices. Repair it, replace it with the same kind of unit, or replace it with a hybrid inverter so a battery can be added. This guide sets out how to choose, and what to check before you spend anything.
Our service page for this work is inverter replacement.
Key Points
- Check the warranty before anything else. A unit still in warranty is the manufacturer's problem, not yours.
- The inverters we fit carry ten year warranties. The Anker SOLIX X1 power module datasheet states "10 Years Limited".
- Read the fault code. It is the fastest route to knowing whether the fault is in the inverter or in the array.
- Not every "inverter fault" is the inverter. Isolators, string faults and grid conditions all produce inverter alarms.
- Board level repair is rarely offered on domestic inverters. Most manufacturers replace the unit.
- A like for like replacement is the simplest route and usually keeps your paperwork unchanged.
- Going up in size is not a free choice. It can change your grid connection route.
- If your panels are on the Feed in Tariff, stop and read before you change anything.
| Situation | Usual answer | Why |
|---|---|---|
| Still in manufacturer warranty | Claim | The manufacturer covers it |
| Out of warranty, same size unit available | Replace like for like | Simplest, keeps the paperwork straight |
| Out of warranty, battery wanted | Replace with a hybrid | One box does both jobs |
| Fault code points at the array | Fix the array first | The inverter may not be at fault |
| System on the Feed in Tariff | Check the scheme rules first | Changes can affect what you are paid for |
Common Misconceptions
"The inverter is dead, so the panels are finished." Almost never true. Panels usually outlast several inverters.
"A repair is always cheaper." Not once a call out, a diagnosis and a part are added up. And not if the same unit fails again next year.
"Any inverter will do." It has to suit the array, the supply and the grid rules. It also has to be certified for use here.
"Replacing it will invalidate my Feed in Tariff." Not automatically. But it is a change that needs handling properly, which is why the separate article exists.
"Bigger is better." A larger inverter can push you into a different connection route and does not make the panels produce more.
Real-World Advice
Our published work shows what we fit as a replacement. The single phase hybrid inverters on our published installations are the Fox ESS H1-6.0-E-G2, the Fox ESS KH7 and the Fox ESS KH10. The other is the Anker SOLIX X1-H6K-S. See our published work for the full list.
UK-Specific Considerations
Grid rules matter here. ENA Engineering Recommendation G99 says a new application is required where a modification increases installed capacity above 16 A per phase. So swapping a small inverter for a bigger one is not always a straight exchange. See UK Power Networks and G99 timescales.
UK Power Networks is the network operator for the whole of East Sussex, so that rule is the same in Eastbourne, Hastings, Lewes and Uckfield.
If your solar was fitted under the Feed in Tariff, an inverter change is a moment to be careful. What you are paid for is tied to what was originally accredited. Read upgrading existing solar systems on the Feed in Tariff first. That article covers the rules, and this one does not repeat them.
Some older systems in this area were fitted by companies that no longer exist. That does not stop a replacement. It does mean the original paperwork may be missing, so allow time to track down the system details before the work is booked.
When This Isn't Right For You
Replacing the inverter is not the answer when the real problem is elsewhere. If output has been falling slowly for years, look at shading, soiling and the array before you buy a box. See why is my solar generating less.
It is also not the answer if the roof itself needs work. Do the roof first, because scaffolding twice costs more than scaffolding once.
Before You Spend Money
Find the commissioning paperwork and the warranty certificate. The install date decides most of this.
Write down the make, model and serial number, and the exact fault code.
Ask whether the fault has been proven to be in the inverter. Ask what test was done.
Ask for the replacement's warranty in writing, and check whether it covers labour as well as the part.
Ask whether the replacement changes your grid connection status.
If storage may follow, ask what a hybrid unit costs now. Compare that with a plain replacement now and a second job later. See AC coupled and DC coupled batteries compared.
Frequently Asked Questions
Q: How long should an inverter last?
A: The units we fit carry ten year warranties.
Q: Can a solar inverter be repaired?
A: Sometimes, but domestic units are usually replaced rather than repaired at board level. Ask what the manufacturer offers before assuming either.
Q: Will a new inverter make my system produce more?
A: Only if the old one was faulty or badly sized. A working inverter replaced with a similar one produces about the same.
Q: Do I need to tell anyone I have changed it?
A: Usually yes. The duty to notify the network operator sits with you as the owner. Your installer normally submits the paperwork, so ask them to confirm it was done.
Q: Can I fit a hybrid inverter now and add the battery later?
A: Yes. That is a normal way to spread the work and the cost.
Summary
Start with the warranty and the fault code, not with a quote. A unit inside its warranty is the manufacturer's problem. Out of warranty, most domestic inverters are replaced rather than repaired. A like for like swap is the simplest route. A hybrid unit makes sense if a battery is coming. Going up in size can change your grid connection route, and any change to a Feed in Tariff system needs handling carefully. Do not replace an inverter to fix a problem that is really shading, soiling or a faulty string.