A bunch of solar panels installed in the 1990’s have undergone testing; the results of which indicate maximum degradation levels stipulated in long performance warranties are realistic.
What’s The Difference Between A Product And Performance Warranty?
A product warranty covers defects in manufacturing (materials, workmanship). Most decent panels come with a 25 – to 30- year product warranty these days.
The performance warranty (usually 25 – 30 years) is separate coverage relating to the remaining percentage of the module’s original nameplate power output rating throughout the warranty, and with a maximum annual degradation rate.
For example, the SolarQuotes solar panel comparison table indicates the Aiko Neostar 2SÂ has warranted power at year 25 of 90.6% and a warranted annual performance degradation during years 2 – 25 of 0.35% loss each year.
It used to be that solar panel product warranties were far shorter than performance warranties (e.g. 10Â vs 25 years); and the performance warranty has often been treated with a degree of suspicion as to whether the figures can be achieved.
Researchers from Switzerland, Austria and Germany have looked at the long-term performance of six solar systems in Switzerland over thirty years, with high-quality monitoring data for more than 20 years of that period.
What Were The Solar Panel Brands Tested?
All PV installations used modules from the same product family; being ARCO AM55, Siemens SM55 (and high output variant SM55-HO), and Siemens SM75. And all used Al-BSF cells.
All of the panels were manufactured and installed between 1987 and 1993. The nominal maximum power for most modules was 55 Watts (48 W for the SM75), with an open-circuit voltage (Voc) of 21.7 V and a short-circuit current (Isc) of 3.45 .
Separate from the systems, there were also two Siemens M55 (SM55) modules set aside. These were stored in a controlled indoor environment at the Photovoltaic Laboratory of the Bern University of Applied Sciences (PV-Lab of BFH).
“These unexposed modules serve as reference samples to evaluate material stability and potential ageing effects, independent of outdoor environmental stressors,” state the researchers.
Climate zones
The panel locations were categorised into three climate zones; which were based on their altitude: low-, mid-, or high-altitude.
“Altitude is a primary factor influencing climate variability in Switzerland, as it significantly affects temperature, irradiance, and weather patterns,” state the researchers.
The categories also corresponded to distinct Köppen-Geiger climate classifications for the sites.
Findings
Generally speaking, it looks like good quality solar panels — at least those manufactured in the 1990’s — can quite easily pass the performance warranty sniff test.
Performance promises kept.
The panels had seen an average performance loss of just −0.24 ± 0.16% per year The performance warranties of solar panels made today often have an allowable loss of 0.35% – 0.50% per year in years 2 – 25.
Power Output Good
Indoor laboratory measurements confirmed most modules retained over 80% of their initial nominal power after 30–35 years in the field. Today’s panels often promise a figure in the 80% – 90% range.
Thermal Stress At Lower Altitudes A Problem
The researchers also discovered higher thermal stress in low-altitude system locations, where it is up to 20C warmer, led to accelerated encapsulant (glue) degradation and acetic acid formation, causing localised corrosion and higher performance losses.
Solar Panels Then And Now
” These findings highlight the durability of early 1990s module designs featuring EVA encapsulants, Tedlar backsheets, and robust framed glass/foil structures, supporting lower levelised cost of energy (LCOE), reduced carbon footprints, and extended performance warranties,” the researchers state.
Panels back in the 1990’s were a really solid affair in terms of framing and glass thickness. Those components in more modern solar panels are far lighter and thinner. For example, the panels in the study had front-face glass 3.3 ± 0.1 mm thickness. Some of today’s solar panels may have a sheet as thin as 2mm, or perhaps even 1.6mm.
The EVA glue is still in use today, but it seems polyolefin (PO) encapsulants have gaining market share recently, particularly in the manufacturing of TOPCon bifacial modules that have glass front and back.
As for Tedlar backsheet use1, this material is still widely used and renowned for durability.
A New Hope?
As solar technology has only evolved since those systems were installed, it seems to hark well for the super-long product and performance warranties accompanying modules today. The good solar panels anyway.
But the researchers point out most degradation paths seen in the advanced solar cell technology nowadays such as PERC, TOPCon, and SHJ are not present in the Al-BSF cells used in the old solar panels.
And what it doesn’t guarantee is that the companies offering long warranties will hang around that long to honour them. Example: Siemens no longer manufactures solar panels directly, having exited manufacturing them around 2012-2013 due to market challenges,
Another crucial element making for a good solar panel is how well it’s installed. Lousy installation can make a mess of the best gear.
But the researchers say analysis such as they have carried out remains essential for guiding improvements in the design, manufacturing standards, and sustainability of solar panels.
” Ultimately, well-designed modules and systems have the potential to operate well beyond conventional warranty periods, contributing to lower LCOE, a reduced carbon footprint, and extended service lifetimes for PV systems.”
If you want to delve into the study’s nitty gritties, it can be accessed here. But perhaps pack a lunch first; you’ll be a while.
The World’s Oldest Functioning Solar Panel System?
The oldest functioning solar panel system I’ve come across to date is also in Switzerland. The 10kW installation known as “TISO 10kW“ was installed in Lugano in 1982 and was also the first grid-connected PV plant in Europe. So, that’s 43 years of operations.
This system’s 10kW capacity was huge for its day. Nowadays many Australians have 10 kW solar power systems installed on their rooftops for pennies on the 1980’s solar dollar.
Related:
Footnotes
- Tedlar is the trading name used by DuPont to market, sell and support these backsheets — and they are the only ones who can sell under the Tedlar name. ↩
About Michael Bloch
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I had 1kW of BP Solarex 80W installed around 2000 for silly money, but little Johnny Howard gave me an $8000 rebate that helped.
Still going strong. Sadly hard to quantify the degradation as I added a second array in 2008.
I have a 1.5kw system from 2010.
It is delivering 80 percent of the original output over the year. But trees have grown up so it is getting shade in the morning, so this is probably the cause.