Thin-film residential solar panels experiences.  - Page 1
Forum section: electronics / general

author: Fflint
author_rank: Frequent Contributor
timestamp: December 21, 2021, 11:43:42 am
content: I have an opportunity to cheaply buy some thin-film CIGS solar panels that were made ~4 years ago. They were never used. They are still in original packaging.The panels were made by a now bankrupt German company Solibro.The price is pretty low. I have an inverter that can work with high voltage thin-film solar panels, but I'm worried about their possible existing deterioration because of storage and during later use.Does anyone here have any long term experience with thin-film solar panels (preferably Cigs). I was given all sorts of testing certificates that certify panels resilience to impact, abrasion, chemical corrosives etc. They have good paperwork.The price is good enough that if they are at 50% of their output in 15 years that's fine, but if they drop to 50% in 5 years I'll probably loose money in comparison with silicone panels.What do you think? For me at this moment it is not a question of buying new-old-stock thin film or new silicone panels, but buying new-old-stock or nothing. Alternatively, finding used silicone panels at right price and quality. Unfortunately the used panels I already saw looked like they may fail any moment.Edit:Well, I don't think I'll buy them. I could've gotten double the wattage for the same cost compared with polycrystalline silicon panels. Also, they have great advantages like not being so sensitive to shadows (see Dave's video when an antenna mast guy wire shadow causes major output drop!). Being a simple device to produce, and is made locally in Europe.Unfortunately, they have one huge, humongous disadvantage. They absolutely have to have their negative output terminal (in a string) grounded or they will deteriorate within a year irreversibly. Look up PID (potential induced damage).PID happens to all solar panels more or less when they are used in a system where the negative DC side floats way below the ground potential. Back in the day (few years ago) there were isolated transformer based inverters available that allowed the DC side to be grounded. Now, pretty much all models that meet the new EU grid requirements and are not horribly overpriced are transformerless (non isolated) designs. This means that the DC side floats up and down by hundreds of volts and grounding the dc side to prevent it would cause inverter descruction. For people interested in more about why that is : look up grid tie inverter design in H5 or heric configuration. They are efficient and cheap devices, but the potentials on the DC side look like this:And this kills thin film solar panels :-(As I mentioned all solar panels experience this degradation. I read somewhere 30% of all recent warranty claims on solar panels is because of that very thing. However, in polycrystalline silicone panels it can reversed if it didn't etoo far.It did cross my mind to stick a huge 20kg 3kW isolation transformer in front of my inverter and ground the DC side, but I decided against it for obvious reasons (AC on the chassis)So I'll probably get half the size system with silicone panels instead. Pity.Edit2: After lots of research and after weighting some options how to prevent PID (with extra devices) I did decide to buy those panels. Unfortunately poly Silicone has a too long ROI for me so I took a chance on thin film Cigs. I also heard IKEA is currently marketing(or planning to shortly) their own CIGS panels made by the same process.

author: Toolworker
author_rank: Contributor
timestamp: January 08, 2022, 04:54:29 am
content: I have 18 Sanyo HIP-190BA3 panels installed in 2006. I'm not sure they qualify as thin-film, but just in case:When I bought them, there was some concern about fall-off in power. In 2007 they produced 5561 kWh. In 2021, 4923 kWh.

author: NiHaoMike
author_rank: Super Contributor
timestamp: January 08, 2022, 01:12:29 pm
content: Might it be possible to isolate the frames from the mounting and connect each one to its own negative via a high value resistor with a GDT to ground for lightning protection?

author: Fflint
author_rank: Frequent Contributor
timestamp: January 09, 2022, 08:13:41 am
content: Quote from: Toolworker on January 08, 2022, 04:54:29 amThank you for the info. That's not bad at all. Yes, I believe your panels do classify as thin film silicon. My panels are thin film CIGS (sometimes called CIS). It is a different technology. Silicon panels too experience PID (potential Induced degradation), but it is more reversible in silicon.Also, I would be very interested in hearing what inverter do you use? Being deployed in 2006 it is likely an isolated (transformer) design.Quote from: NiHaoMike on January 08, 2022, 01:12:29 pmThere are no frames :-) These are frame less panels. This picture from one study shows the mechanism of the problem with glass backed panel.In the same research there was another picture showing how they were making PID faster by applying a potential of 50V to an aluminium foil glued to the back of the panel.Seeing the above I thought. Why not use their idea, but in reverse to protect panels?So I bought a roll of single side metallised mylar. It is a foil that conducts electricity on one side and is a dielectric on the other. And I plan to glue that mylar foil to the back of my panels, then to connect the mylar back through a high value resistor (500k, 1M etc) to the minus of each individual panel or the - of the string. The first way would make the potential difference to disappear, the second would create an opposite potential difference.I decided on using mylar because this way the back of the panels will not be floating at a couple of hundred volts just waiting for a person to touch it.I'm just looking for what kind of glue to use. Ideally I would like the kind of glue they use to tint car back windows as one can use a bit of water to make thd gluing process much easier. The foil can be repositioned before the glue dries etc.Mylar I have shows few ohms per 10cm (4in) distance so it should be ideal. Also such high value resistors can be used because the mechanism is electrostatic and very little actual current flows.I also calculated capacitance this extra foil will bring to the system and it is far less than the capacitance of panels themselves. So adding it shouldn't cause any issues with leakage of current etc.I also have an isolation transformer I could stick in front of my transformerless inverter, but I prefer the mylar approach.I characterised all panels in (winter blue sky) sun. And I'll repeat it every few days after the install to ensure PID is not happening. One can see it on the IV curve. A damaged panel looses its "sharp-ish corner" in its IV curve. It becomes flattened. One can monitor the condition this way and act quickly before permanent damage is made.Here is how it looks:This is a study that I took pictures from:https://uu.diva-portal.org/smash/get/diva2:730877/FULLTEXT01.pdfAlso, please note if you are reading this and you are considering not buying new made CIGS Solar panels, because of PID, consider that there are construction techniques that make panels resistant to it. However, the panels I have (cheap) acess to are not new ones. They were made in 2017 and quite likely would become degraded within a year of use with a modern transformerless inverter.

author: Toolworker
author_rank: Contributor
timestamp: January 09, 2022, 05:37:24 pm
content: Quote from: Fflint on January 09, 2022, 08:13:41 amYes, I am pretty happy with that. I reroofed a year and a half ago, and didn't have time to analyze whether to put the same system back up or get a new one. But I think that turned out OK so far. I may regret it if and when I go to add a battery system.QuoteIt's an SMA SB-3800U.

author: Fflint
author_rank: Frequent Contributor
timestamp: April 25, 2022, 07:58:21 am
content: Quote from: Toolworker on January 09, 2022, 05:37:24 pmI've looked up your inverter and in the manual it says that the PV array operates in "negative grounding configuration". I suspect this is the reason why you haven't seen much deterioration in output.Unfortunately all the inverters that met regulatory requirements in EU when I did my install were transformerless designs where the PV array is not grounded. Both DC rails swing +-400V matching grid frequency.So in the end I've implemented my "mylar foil" fix. Essentially it provides another electrode on the bottom side of the glass that is at the same potential as DC- (of each panel). The connection is made via 1MegOhm resistors for safety reasons.So far it has been a month and the output seems to be as expected. Before each panel was mounted I recorded its IV curve (on a sunny winter day) and I plan to repeat the measurement every 6 months or so to hopefully detect any deterioration if it happens. According to various science articles I saw it is pretty easy to see the damage because of the shape of the IV curve.

author: Fflint
author_rank: Frequent Contributor
timestamp: April 27, 2023, 06:03:29 am
content: An update after a year in operation.The 2kW thin film array has produced 2.4MWh of electricity :-)The foil on the back just started peeling off a couple of weeks ago. So far on 3 panels, always a corner 10cm * 15cm or so (4in*6in) flapping in the wind. I used the same 3m 77 spray on adhesive I used initially to install it to reattach all 3I can see no deterioration in output so far (the system produces a peak of 2300W in good weather 2h before noon - it is facing slightly east). I've benefited quite a bit in winter from these being thin film panels, by the system still providing usable amounts of power on medium-overcast days.I'll have to wait at least 5 years to determine if my foil-protection method works to prevent PID for sure, after just a year I can tell it isn't causing any additional problems.