A very popular question about solar electric photovoltaic panels is "How long do solar electric PV panels last - what is their life expectancy?".
It takes a lot of energy and money to produce PV panels, therefore financial and carbon payback times under UK conditions are long and a very long lifetime is important to make the technology attractive, both in economic and ecological terms.
What government and manufacturers say
UK Feed-in Tariffs for PV are calculated for an economic lifetime of 25 years, indicating that the Department of Energy and Climate Change believes that panels will produce for at least that long. The warranty conditions for PV panels typically guarantee that panels can still produce at least 80% of their initial rated peak output after 20 (or sometimes 25) years. So manufactures expect that their panels last at least 20 years, and that the efficiency decreases by no more than 1% per year.
What makes talking about lifetimes for PV panels difficult is the fact that very few panels have been installed for long enough. In the UK, more panels have been installed between 2006 and 2008 than in all previous years together. Globally, only a small proportion of all PV panels installed is older than 10 years.
What we found at CAT
Here at the Centre for Alternative Technology we installed our first integrated PV roof of 180 panels, rated at 75W peak output, in 1997. In spring 2010 we did some refurbishment on that roof and used the opportunity to inspect and test each of the panels. We performed a so-called “flash test” for each individual panel to establish how much of the original rated peak output of 75W the panel can still achieve. The result averaged to around 68.5W – only around 9% decrease over 13 years (0.7% per year). There were some differences between individual panels, but even the lowest performing panels still produced around 60W (20% decrease).
We did find some damage to some of the panels - there was laminate peeling off at the back and some colour changes (yellowing) at the front – but none of the 180 panels was in a condition that required replacement.
While 13 years is old for a PV roof in the UK, it is not a lot in terms of PV panel lifespan. Fortunately, there are some examples of very early PV roof installations which tell us more about the long-term durability and performance of solar electric panels.
Research from Switzerland: Still good after 20 years
The LEE-TISO testing centre for PV components at the University of Applied Sciences of Southern Switzerland installed Europe’s first grid-connected PV plant, a 10kW roof, in May 1982. They analysed the performance of the panels in 2002 and published the results in a scientific paper (Chianese et al, 2003). The PV plant was installed with 288 monocrystalline modules and an initial nominal plant power raring of 10.7kW, or an average of 37W peak rating per panel. Interestingly, when the panels were tested in 1983, the peak power output of the panels came to an average of 34W, 9% less than the initial rated peak output. This steep initial drop is normal – even with modern PV panels a loss of 5% over the first 12 months is not uncommon.
When the panels were tested in 2002, the average peak output of the panels was 32.9W – 11% lower than the nominal value in 1982 and only 3.2% lower than the measured value in 1983. In other words, between 1983 and 2002 the panels peak output had only degraded by around 0.2% per year since 1983 (0.5% per year against initial nominal rating).
Just as in the case of CAT’s PV roof, the LEE-TISO researchers found significant amounts of mechanical degradation of their panels. In 2002, 98% of their modules showed signs of yellowing, and 92% had issues with lamination peeling off. However, the impact of delamination on the overall plant performance was limited and only one single panel (less than 0.4%) was replaced.
Overall, the picture is very encouraging: Both our own experience at CAT and the research by LEE-TISO suggest that PV panel power output decreases by less than 1% per year. Panels do experience a significant amount of physical decay (yellowing, laminate peeling off) if they are exposed to the elements for 10 or 20 years, but the effect on their performance is limited. This suggests a PV installation should produce electricity for 30 years or longer. Take a look at our Solar Calculator to see roughly how much energy a household system could produce.
Introduction to Renewable Energy Systems
Friday, November 6, 2015