- Where potential-induced degradation shows up in the design
- PID beside ordinary wear
- What to ask, without a fake loss percentage
- Frequently asked questions
- Does every transformerless inverter cause potential-induced degradation?
- How much power does PID remove?
- Can I see PID on the monitoring portal?
- Sources and references
Potential-induced degradation is a loss of photovoltaic module power that can appear when the module sits at a high voltage relative to ground for a long time, and the module’s materials allow leakage current to drive damaging effects in the cell. It is not ordinary soiling, and it is not the slow median aging reported in field surveys of all modules. Whether it happens depends on the module and on the electrical system the module is tied to. A transformerless inverter with a floating ground is one of the designs that has to be checked against the module. That is the practical point. A universal percentage of “PID loss” is not.
Where potential-induced degradation shows up in the design
A 2017 comparison of central and string inverters, written by ICF, notes that string inverters of that period were typically transformerless and operated with a floating ground, and that potential-induced degradation risk on those designs has to be checked on the module. Large central inverters in the same comparison typically included an isolation transformer and a grounded array. The capacity numbers in that paper are from 2017 and should not be reused as a catalog. The grounding contrast is the part that still tells you what to ask. The architectural comparison is in central versus string solar inverters.
Pacific Northwest National Laboratory makes the same hardware split in plainer language: large central inverters often contain a transformer, while smaller central inverters and microinverters are typically transformerless. Transformerless does not mean “PID will happen.” It means you do not get to skip the module manufacturer’s guidance on system grounding, polarity, and whether the module is rated for the inverter topology you are buying. Microinverters put a small inverter on each module. They are typically transformerless. They also avoid a long series string at high DC voltage, which is one of the stresses PID discussions care about. That is a reason to ask, not a certificate that PID cannot occur. String versus micro layouts are in string inverter versus microinverter.
The module datasheet or the installation manual is where the check lives. Some modules are sold as PID-resistant or PID-free under a stated test. A test passed on one bill of materials is not a property of every module with a similar cell. PERC, heterojunction, and thin film are not interchangeable here. Do not copy a PID claim from one chemistry onto another. What a PERC cell is, including issues that are not PID, is in what a PERC solar cell is.
PID beside ordinary wear
It is not the temperature loss you see every hot afternoon. That loss follows the module’s temperature coefficient and reverses when the cell cools. PID does not reverse because a cloud arrived. Heat is in how heat affects a solar module.
It is not shade, dirt, or snow. Those move with the hour or the weather, and a wash or a melt changes them. If one string is low only in the late afternoon, look at a shadow before you look at leakage current. Sorting weather from faults is in solar inverter faults and the weather.
It is not the Jordan and Kurtz median of about 0.5 percent per year. That figure is a literature median across many reported rates, and the authors warn it is not a random sample. PID, when it is severe, is one of the mechanisms that can sit in the bad tail of such surveys. It is not the median itself. Using the median as “expected PID” invents a number this page will not print. How long panels last, and how not to misuse that median, is in how long solar panels last.
What to ask, without a fake loss percentage
| Ask | Why |
|---|---|
| Is the inverter transformerless and floating? | ICF flagged PID risk as something to check on that topology. The check is the module’s requirement, not a ban on transformerless inverters. |
| What does the module manual say about grounding and PID? | The module maker’s instruction is the one that matches the bill of materials. A forum rule is not. |
| Is the array voltage high for long hours? | PID is associated with voltage stress over time. A design choice that raises string voltage is part of the question. No threshold voltage is given here. |
| Is the loss uniform and permanent? | If it washes off, melts, or follows the sun, it is not PID. If a tested module has lost power against its flash file, then investigate. |
Recovery techniques exist in the trade, including grounding schemes and, on some systems, applying a reverse voltage under controlled conditions. This page does not give that procedure. Done wrong, it is an electrical hazard and a warranty problem. If you suspect PID, the next step is a measurement against the flash test and a reading of the module and inverter manuals, by someone qualified to work on live DC. Modules are producing in daylight. Pacific Northwest National Laboratory’s rule stands: trained people disconnect the wiring.
Warranty language matters more than a nickname. A performance warranty may or may not treat PID as a covered defect. Read the exclusions. How those contracts are structured is in what a solar panel warranty covers.
Frequently asked questions
Does every transformerless inverter cause potential-induced degradation?
No. The ICF paper says the risk on floating-ground transformerless designs has to be checked against the module. Some modules are built and warranted for those systems. The check is mandatory. The failure is not.
How much power does PID remove?
This page does not state a percentage. Published cases vary, and a single number would pretend they do not. Compare a suspect module with its own flash file after it is clean, at a translated test condition, rather than with a rule of thumb.
Can I see PID on the monitoring portal?
You can see a string that is low and stays low after you have ruled out shade, dirt, snow, and a failed diode or connector. The portal does not label the cause PID. The label comes from a test and from the module’s known behavior, not from the daily total.
Sources and references
PID risk to be checked on floating-ground transformerless string designs, in a 2017 architecture comparison whose capacity bands are dated: ICF, September 2017. Transformers typical on large central inverters, transformerless typical on smaller central inverters and microinverters: Pacific Northwest National Laboratory. Median degradation near 0.5 percent per year in a literature survey, which is not a PID rate: Jordan and Kurtz, 2012. No recovery procedure and no loss percentage are given.
