Repairs · Guide
Solar panel optimisers: what they do and how to spot a fault
A power optimiser is a small box fixed behind a solar panel, usually one for each panel. It helps each panel produce as much as it can, and it can also report how each panel is doing.
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What they do
What a power optimiser does.
Optimisers live on the roof through heat, cold and rain. When one fails you may see low or no production, and replacing it means someone has to get to that panel safely. This guide explains what optimisers do, how to tell if one has failed, and what a repair involves.
- Gets the most from each panel. An optimiser is a DC-to-DC converter. It tracks the best operating point of its own panel, which SolarEdge calls module-level maximum power point tracking. The Energy Saving Trust puts it simply: if one panel is shaded, it doesn’t affect how much electricity the other panels can generate.
- Reports each panel. SolarEdge optimisers send each panel’s performance data over the DC cables, so the monitoring can show every panel separately and pick out ones that are underperforming. If the whole system shows as offline, see solar monitoring offline?
- Drops to a safe voltage. SolarEdge’s SafeDC feature cuts each optimiser’s output to about 1 volt when the inverter is switched off, its AC breaker is off, the optimisers are disconnected from the inverter, or there’s a fault. SolarEdge’s datasheets give 1 ± 0.1 V per optimiser. Once the inverter is switched back on, the cables carry high voltage again.
SafeDC doesn’t switch the panels off. They still generate in daylight, so the roof wiring is never something to touch.
Which systems
Which systems use optimisers.
- SolarEdge optimisers and inverters are designed as one system. The optimisers stay at their 1 V safety level until they’re connected to a SolarEdge inverter, and SolarEdge describes its inverters as “specifically designed to work with power optimizers”. So a SolarEdge system is repaired as a SolarEdge system. See SolarEdge inverter repair.
- Tigo makes optimisers designed to work with other makes of inverter. Tigo says its products are “virtually compatible with any inverter”. They can be fitted to selected panels only, such as the shaded ones, and panel-level monitoring needs Tigo’s own kit (a CCA and a TAP).
- Many homes have no optimisers at all: just a string inverter, or microinverters.
Your handover paperwork, or the name on your inverter and monitoring app, tells you which you have.
Optimisers vs microinverters
Optimisers or microinverters?
Both work at panel level, but they do different jobs. An optimiser conditions the DC power from its panel and sends it on to one central inverter, which turns it into AC for your home. A microinverter is a small inverter on the back of each panel, turning that panel’s output into AC on the roof.
The Energy Saving Trust notes that if one microinverter fails, it won’t affect the whole system. The drawback it points to applies to optimisers too: replacing one needs roof access.
Warning signs
Signs an optimiser has failed.
- A panel looks wrong in the monitoring. SolarEdge’s monitoring has a site layout with every panel on it. A panel showing no data, or much less than its neighbours on the same roof, can point to a failed optimiser.
- A “No communication with Power Optimizer” alert. SolarEdge’s monitoring raises this when an optimiser has stopped sending data.
- Low or no production. SolarEdge lists low or no production, and patchy or lost communication, as signs of a faulty optimiser.
- A connector safety event. Newer SolarEdge optimisers can detect a connector heating up. The monitoring shows it as a safety event for “increased temperature at Power Optimizer’s connector”. Call an engineer promptly.
- Output well down on last year, with no new shading or heavy dirt to explain it.
An alert doesn’t always mean a failed optimiser. If the whole system shows offline, a new router or Wi-Fi password is the usual cause. SolarEdge’s own troubleshooting guide also shows that a faulty panel can look like a faulty optimiser, so it takes testing to tell them apart. For other checks, see solar panels not working?
If you ever notice a burning smell, smoke or scorch marks, keep clear. Follow the emergency shutdown procedure on the label near your inverter only if it is safe to do so. If there is any sign of fire, call 999.
Access
Why replacing one needs safe roof access.
An optimiser is fixed to the mounting rails behind its panel, so it can only be reached from the roof. Please don’t go up yourself, and don’t touch the panels, connectors or cables.
HSE says almost one in five deaths in construction work involve roof work, and that sloping roofs need scaffolding to stop people or materials falling from the edge. For very short jobs, measured in minutes, it accepts properly secured ladders and roof ladders. So the right access depends on your roof and the job. For an optimiser replacement that means scaffold, a tower or a roof ladder, depending on your roof, planned before the visit.
If access is going up anyway, it’s a sensible time to check the rest of the array, clean the panels or deal with pigeons at the same visit.
Replacements
Replacements and compatibility.
- Check the series. When replacing an optimiser, SolarEdge says to check the series of the original unit and follow its compatibility rules. Different models can share a string only if they meet those rules, and S-series and P-series optimisers must not be mixed in the same string on new installations.
- Service models. SolarEdge makes service versions of some optimisers specifically for replacing older units.
- Matching connectors. Solar Energy UK warns that mismatched connectors at panel level could affect the manufacturer’s cover for both the panel and the optimiser.
- Paperwork. Check your handover pack. The optimiser may still be within the manufacturer’s terms.
What we do
What we do.
- Test on site. We make the system safe and test the suspect optimiser and panel, following SolarEdge’s own test procedures, to find which one has failed.
- Replace the failed unit with a compatible optimiser, or the panel if that’s the fault.
- Recommission. We pair the new optimiser with the inverter and check every panel is reporting again.
We repair SolarEdge and Tigo optimiser systems fitted by any installer, including installers who are no longer trading, across England, Wales and southern Scotland. You get a clear written quote before any work starts. See inverter repair, isolator switches and solar panel repair.
Sources: SolarEdge installation guides and datasheets; Energy Saving Trust; HSE.
Questions
The things people ask before they ring.
Not answered here? Call 0800 156 0191, Monday to Friday, 9:00am–5:00pm.
Do I need solar panel optimisers?
Not always. They help most where some panels are shaded for part of the day or face different ways. The Energy Saving Trust says a string inverter works most efficiently when all the panels are the same and working in the same conditions, so an unshaded roof facing one way may not need them.
How do I know if a solar optimiser has failed?
Look at your monitoring. A panel showing no data or much less than its neighbours, a “No communication” alert, or output well down on last year can all point to an optimiser. A faulty panel or a lost internet connection can look similar, so an engineer tests before replacing anything.
Can I use SolarEdge optimisers with a different inverter?
Standard SolarEdge optimisers are designed as part of a SolarEdge system and stay at a safe 1 V until they’re connected to a SolarEdge inverter. If your SolarEdge inverter fails, talk to an engineer about a compatible replacement before buying anything. Tigo optimisers, by contrast, are made to work with most makes.
Why does replacing an optimiser need scaffolding?
Optimisers are fixed behind the panels, so the only way to reach one is from the roof. HSE says sloping roofs need scaffolding to stop people or materials falling from the edge, though very short jobs can use properly secured ladders and roof ladders. The right access depends on your roof and the job.
Ready when you are
Panel missing from your monitoring?
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