Yaskawa Solectria string inverters on a thin-film solar project.
Potential induced degradation (PID) has haunted the solar industry since its origin. This phenomenon happens when the high-voltage DC side of a solar project is installed next to other equipment with differing voltage. The discrepancy can induce sodium migration, where electrons enclosed in module glass escape and speed up module degradation.
“That inherent big magnitude drives this PID behavior, if the modules or the power electronics are not designed in a particular way to mitigate this,” said Steven Marsh, senior director of technology and design at large-scale developer Origis Energy.
Thin-film modules are more susceptible to PID because of their higher voltage and material makeup, but crystalline silicon panels are also at risk if there are any flaws in the wafers. Developer Silicon Ranch prioritizes anti-PID functionality for string inverters on both types of projects.
“They’re made different, but it’s the same overarching worry that a solar designer has to have, which is these minor weaknesses in the solar panels, you guard against with anti-PID features in your inverters,” said Nick de Vries, SVP of technology and asset management at Silicon Ranch.
When new panel technology comes out, it often takes some time to hone the product to reduce the risk of PID. Early models of glass-on-glass bifacial modules had issues with PID, but manufacturers have made strides since then, Marsh said.
“[PID] comes back from time to time as the technology evolves, just because it’s very new and it’s evolving. It’s a very demanding condition that modules have to go through,” he said.
Central inverters are a safe bet for avoiding PID. They include built-in transformers that are negatively grounded, isolating the DC and AC sides of the system.
But as transformerless string inverters are increasingly deployed on larger projects for their O&M simplicity, with thin-film panels and otherwise, project owners must now consider PID mitigation.
“There are a few key ways that you can achieve galvanic isolation, and a transformer is one of them. Making that change to transformerless unfortunately creates that issue,” Marsh said. “The PV array will end up floating, and usually what that means is about half the modules in the entire system will experience a negative bias relative to ground.”
A few methods can be used to help avoid PID in transformerless string inverters. Installers can add a grounded isolation transformer or ground the step-up transformer on the AC side. And manufacturers are now adding special hardware and software to string inverters to combat PID.
Marsh said there are two categories of PID mitigation in string inverters — active anti-PID methods and passive PID recovery modes. Active anti-PID hardware and software solutions take the DC side of the system and elevate the voltage so all modules are above ground. On the other end, PID recovery methods work at night to undo the PID accumulated during the day. However, thin-film manufacturer First Solar says its modules respond more favorably to active anti-PID functionality rather than PID recovery.
SMA string inverters on a Silicon Ranch thin-film project.
A few string inverter manufacturers on the market now include anti-PID hardware and accompanying software to protect from degradation, or sell separate accessories to perform the protective functions. For example, CPS America offers the CPS Energy Balancer, whereas Sungrow builds anti-PID {hardware} into its SG125HV and SG250HX string inverters. Sungrow began providing anti-PID string inverters round 2018.
“There have been questions in regards to the degradation charges of panels generally on the time, so we developed the answer,” mentioned Daniel Friberg, director of product and engineering at Sungrow.
Yaskawa Solectria lately introduced an anti-PID model of its XGI 1500-250 sequence string inverter that’s tailor-made to work with First Photo voltaic thin-film modules.
“That takes a couple of small adjustments inside to the inverter. It’s not an enormous deal, however it does require some engineering time and an inventory replace for a brand-new particular mannequin on this sequence, so we’re within the midst of proving that out within the lab,” mentioned Miles Russell, director of product administration at Yaskawa Solectria Photo voltaic.
Each Solectria and First Photo voltaic make their merchandise in america, giving installers a straightforward pairing to attain home content material incentive objectives included within the IRA. However they mentioned PID mitigation nicely earlier than the IRA was written.
“We began that relationship two years in the past, with simply purely the purpose on a technical degree to attain a product which is well appropriate with our product,” mentioned Alex Kamerer, undertaking supervisor at First Photo voltaic. “We go that additional step to making sure that we have now compatibility with our system suppliers, which advantages our prospects.”
Though extra inverter producers are beginning to incorporate anti-PID features in string inverters because the expertise is more and more utilized in bigger tasks, engineers nonetheless generally should dig by way of knowledge sheets to test on a product’s anti-PID capabilities, in response to Origis’s Marsh.
“We discover that there are a couple of choices on the market, and so they’re not essentially a giant driver within the capital preliminary value of the inverter,” he mentioned. “Nonetheless, these don’t are typically closely publicized inverter options, possibly as a result of the subject could be very, very technical, and even [because] PID itself is fairly arduous to detect within the discipline. So we actually see some transformerless inverters that come with out this operate.”
However mitigating PID goes to develop into much more essential as photo voltaic firms now have the choice to take the manufacturing tax credit score (PTC) within the IRA. Holding degradation in test so the modules produce most energy for so long as doable shall be essential for tax credit score certainty.
“I feel having a widespread business understanding of the elements in PID might be what wants to extend — schooling in regards to the occasions that your modules could also be liable to PID, in addition to detection strategies,” Marsh mentioned.
