Inverters help combat PID as solar technology evolves

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Yaskawa Solectria string inverter in a thin film solar project.

Potentially induced degradation (PID) has plagued the solar industry since its inception. This phenomenon occurs when the high voltage DC side of a solar project is installed next to other equipment with different voltages. This mismatch can cause sodium migration that allows electrons trapped in the glass of the module to escape and hasten module degradation.

“Inherent large magnitudes drive this PID behavior unless the module or power electronics are designed in a specific way to mitigate this,” said senior director of technology and design at large development firm Origis Energy. Stephen Marsh says.

Thin-film modules are more susceptible to PID due to their higher voltage and material composition, while crystalline silicon panels are more susceptible to PID. are also at risk If the wafer has defects. Developer Silicon Ranch prioritizes the anti-PID feature of string inverters in both types of projects.

“They are made differently, but they have the same overarching concerns that solar designers need to have. It’s these little weaknesses of solar panels that the inverter’s anti-PID feature defends against. ,” said Nick de Vries, SVP. Technology and asset management expert at Silicon Ranch.

As new panel technologies emerge, it often takes time to refine the product to reduce the risk of PID. Earlier models of glass-on-glass bifacial modules had problems with his PID, but manufacturers have made progress since then, Marsh says.

“[PID] I come back from time to time as technology evolves, just because it’s so new and evolving. It’s a very tough condition that the module has to go through,” he said.

A central inverter is a safety net to avoid PID. They contain negative grounded internal transformers to separate the DC and AC sides of the system.

However, as transformerless string inverters are increasingly being deployed in large projects such as thin film panels for O&M simplification, project owners should consider PID mitigation.

“There are several important ways to achieve galvanic isolation, and transformers are one of them. “PV arrays are left floating, which typically means that about half the modules in the total system are negatively biased with respect to ground.”

Several methods can be used to avoid PID in transformerless string inverters. The installer can add a grounded isolating transformer or ground the step-up transformer on the AC side. Also, manufacturers are now adding special hardware and software to their string inverters to deal with PID.

According to Marsh, there are two categories of PID mitigation for string inverters: active anti-PID schemes and passive PID recovery modes. Active anti-PID hardware and software solutions take the DC side of the system and boost the voltage so that all modules are above ground. On the other hand, the PID recovery method works at night to restore his PID accumulated during the day. However, thin-film maker First Solar says its modules react more favorably to its active anti-PID feature than his PID recovery.

SMA string inverter from Silicon Ranch thin film project.

Several string inverter manufacturers on the market now incorporate anti-PID hardware and accompanying software to protect against degradation, or sell separate accessories that perform the protection function. For example, CPS America CPS Energy Balancer, Sungrow incorporates anti-PID hardware into its SG125HV and SG250HX string inverters. Sungrow started offering anti-PID string inverter around 2018.

Daniel Friberg, Sungrow’s Director of Products and Engineering, said:

Yaskawa Solectria recently announced an anti-PID version of its XGI 1500-250 series string inverter tuned to work with First Solar thin film modules.

“This requires a small change inside the inverter. It’s not a big deal, but it does require engineering time and list updates for new specific models in this series, so the best we have to prove it in the lab. in,” said product director Miles Russell. Managed by Yaskawa Solectria Solar.

Both Solectria and First Solar manufacture their products in the United States, offering installers an easy pairing to meet the national content incentive goals included in the IRA. But they were discussing his PID mitigation well before the IRA was created.

Alex Kamerer, Project Manager at First Solar, said: “We go the extra mile to ensure compatibility with system providers and benefit our customers.”

According to Marsh of Origis, more inverter manufacturers are starting to build anti-PID features into their string inverters, but engineers may have to dig through datasheets to check for anti-PID features in their products.

“We found that there are some options out there, but they are not necessarily a big factor in the initial capital cost of the inverter,” he said. “But these don’t tend to be hyped as inverter features. Perhaps the topic is very very technical or even [because] The PID itself is rather difficult to detect in the field. So we certainly see transformerless inverters that do not have this feature. ”

But mitigating PID becomes even more important now that solar companies can now take advantage of the production tax credit (PTC) on their IRAs. Reducing degradation so that modules produce maximum power for as long as possible is critical to tax credit certainty.

“I think there is probably a need for a broader industry understanding of what causes PID, education about when a module is prone to PID and how to detect it,” Marsh said.

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