How to Prevent PID losses In Advance
UL International Germany
- Jan 14, 2019 7:15 am GMT
- 614 views
Why is it smarter and cheaper to use PID preventive measure from planning stage?
After years PID has been severely damaging the performance of PV plants, 2017 was the turning point in both perspective and execution, as PV developers, EPC's, PV plants owners, banks and insurance companies, have reached the conclusion, after years of experience, that PID damages are deeper than perceived in the past and that PID should be avoided by default preventive measure from planning stage of the plant, just like inverters and modules, and not only after nonrefundable financial losses and physical damages already occurred.
First, what is PID?
In short, PID is Potential Induced Degradation; a common phenomenon where negative potential can occur within photovoltaic modules. Due to the grounded module frames a potential between the cells (negative pole) and the frame (positive pole) can occur, which leads to an electric field. The electric field forces the ions to move out of the glass, through the encapsulant and into the solar cell. Inside the cell, a short circuit of the PN-Junction of the cell leads to a decrease of the parallel resistance, followed by a drop of the power output and a decrease of the other module parameters. Performance losses of over 80% and more could be already observed in numerous PV plants.
PID can be found in Thin-Film modules (irreversible degradation called transparent conductive oxide [TCO] corrosion), in N-type modules (reversible, until a no return point, polarization due to positive potential and in P-type (most common C-SI & M-SI) also reversible, until a no return point.
It is well established that the higher the negative voltage, the faster and more severe the degradation.
According to that, will the new 1500V PV modules will be more or less likely to be prone to PID?
1500V modules will definitely be more likely to have PID, as the negative pole voltage will be 50% higher than the 1000V modules. That only shows that PID will be more and more common and extreme.
What was the old way of dealing with PID?
The old way was to install the PV plant without PID preventive measure, and hope for the best.
Sometimes it worked; in other times it had a significant, sometimes crushing effect on the project financing and revenues.
In what way PID have an effect on the project financing?
It usually takes about two years in order to clearly diagnose the PID phenomenon;
at the beginning when comparing YoY yields, the PID degradation effect can be explained by different possible reasons like weather, soiling, maintenance, irradiation levels, LID Etc.
Once the degradation is too severe to explain otherwise, on-site or lab testing is done to locate the degradation source (STC, IR, EL, IV_Curve, and Lab).
The main problem is that by that time the PID affects the overall plant by 10%-20%, the PV modules on the negative side of the strings are already severely degraded, and all of the modules on the negative side of the strings are affected.
At this point in time, treating the PID and restoring the plant will have high and non-refundable costs.
The impact on the project financing & revenues at this stage can already be critical, and could have been prevented in advance.
So what changed in the past year?
In the past years PID preventive measures were taken only at PV plants using PID FREE modules, combined with internal transformer central inverters, by connecting a grounding kit.
Yet, plants using string inverters or TL central inverter where left for pure luck, and the risk of PID was not prevented in advance, that until 2017, when PID became a widespread phenomenon and could not be ignored anymore.
That raised a lot of red flags for all involved parties as a risk management issue.
Since two years ago, Vigdu Technologies has been receiving on-going orders for new & existing plants, for our PID prevention solution.
How risk management is coming into the picture?
It is actually a pure risk management issue.
Today not only EPC companies, but also investors, banks and insurance companies look at PID preventive measures from a risk management point of view. The preventive approach significantly reduces the investment risk, and can shorten the ROI period while increasing profits.
That keeps the investment on track as planned.
Furthermore, project financing, bankability, yield and revenue insurance, due diligence Etc. are easier when PID prevention actions have been taken at the planning stage of projects.
So, it is a type of “insurance” or protection layer?
Exactly! since not all the plants will be affected by PID, and the Vigdu PID preventive solution is a one-time low-cost investment, the use of it as preventive measure can be easily perceived as a one-time protection layer or a type of “insurance” for the lifetime of the plant.
Today most PV modules are PID FREE, so why worry?
There are few relevant facts to answer this question.
The first point is PID FREE modules, according to IEC IEC62804 standard test undergo at best a 96-hour PID stress test under the conditions of 85℃ degrees and 85% relative humidity ("double 85") at +/-1,000V, with a degradation of up to 5%. We don’t think anyone is willing to give up on ~ 5% of the plant lifetime overall yield and profit. Furthermore, it is in contradiction or as extra degradation to the PV modules manufacture production warranty.
The second point is that we see numerous cases that PID FREE TIER 1 modules with “Approved” PID testing are extremely sensitive to PID, and in many cases are strongly affected by PID.
That was proven by third party laboratories worldwide.
There are two reasons for that: First, the modules manufacturers certify a module type by third party accredited labs with a specific BOM, yet they may use many uncertified and/or different components during manufacturing of the same module type.
The second reason is that overbooked order pipelines, force the manufacturers to purchase PV modules from other OEM’s.
So what happens when PID is detected in a PV plant without preventive measures?
When PID is detected the following occurs:
- The plant has already suffered significant losses that will not be returned to the plant owner.
- The PV modules manufacturer needs to be convinced by a third party accredited laboratory that the lower production is indeed from PID. That involves many manpower hours, testing costs etc.
- Negotiations time period with the modules manufacturer in some cases take two years or more.
It is even more complicated when the modules manufacturer is also the EPC.
- Disassembling, packing and recycling of the PID affected modules, as agreed with the module's manufacturer. In the absolute majority of the cases 20% of each PID affected string will be replaced – less than half of the PID affected modules.
The modules manufacturer will try to replace modules in order to improve the plant production to the average production in other plants in the same geographical area, which is far from optimizing the plant.
- Inland transportation of the old PV modules for recycling and new PV modules from the manufacture warehouse.
- Installation of the new modules.
- A permanent mismatch of the old and new modules at all strings.
- Installation of the Vigdu solution in order to prevent further development of PID.
All the above costs will not be returned to the investor, owner, EPC etc.!
Experience shows that PID FREE modules cannot be a sufficient protection against direct and indirect PID losses.
To avoid the above mentioned losses, a Vigdu PID preventive
device should be installed from day 1 of the PV plant