PV solar panels and degradation
This degradation issue of photovoltaic should be a minor consideration. Degradation rates of solar panels are so small that they should be of little consideration. The cost of your solar installation is more worthy of your investigative powers.
Investigating the panel degradation issue, it’s important to know exactly what the terms “degradation” and/or “Performance Warranties” mean. These terms will be used when presenting systems for your consideration.
Degradation is the term used to describe the deterioration due to weathering, UV exposure, and pollution effects. By default, PV manufacturers give customers a twenty-five-year performance warranty. A linear degradation is a set amount per annum. Typically between 0.4% and 0.9% per year. This doesn’t mean PV solar panels actually degrade at that level, that’s merely the warranty specification.
Warranties give an average that may be higher or lower depending on lifetime factors. Neither you nor your installer expects panels to degrade by more than that stated. A warranty specification is there in the unlikely event it does.
A good PV installation company, when projecting the performance, will input an annual degradation rate of 1%. They’ll take the yearly kilowatts generated in year one, e.g. 3500 kilowatts, and reduce by 1% per year to 2730 in the last year of the generation tariff.
Factoring inflation rates for the export tariff, energy prices rise in the cost of electricity to give potential payback times and likely earnings with savings expected. This is standard practice for all PV solar companies. Additionally, a comprehensive study by the National Renewable Energy Laboratories clearly shows PV degradation levels are much less than stated in specification data.
They pulled together over 40 years of published literature, covering nearly 2000 degradation measurements. The results were interesting.
They found the “1% per year rule” was far too pessimistic for solar panels produced before 1999. Today’s PV solar panels are manufactured better with rare-earth elements, thus, lasting longer than their predecessors.
The most commonly installed photovoltaic solar panels in the UK are Monocrystalline with degradation rates as little as 0.5 percent before 1999 and as low as 0.4 percent after that pivotal year.
Photovoltaic panels manufactured today produce 92% of their original performance figures after twenty years of service. This rate is higher than the 80 percent given by the default specified “1% rule”.
Photovoltaic arrays installed in warmer climates, such as equatorial regions show much quicker degradation rates.
PV systems installed in our more moderate climate, had degradation rates as low as 0.2 percent per year, so on this basis, you can assume that your UK-based panels could retain 96 percent of the original performance rate after twenty years of service life. Amazingly, this pre-sales data is understating your return-on-investment.
Overstating the degradation rate should be viewed as a good thing. The earliest satellite solar panels are still working fine today, even in a high UV environment in low Earth orbit.
This allows enthusiasts to make contact with retired 36-year-old satellites today. This is the proof of the pudding. But, the real heroes in our thirst for knowledge comes from the Mars rovers Spirit and Opportunity.
After ten years of service, their solar panels are subject to high doses of UV radiation. Enduring the sandblasting from Martian winds and seasonal extremes and it’s only their wheels that died! These brave pioneers should be the only endorsement that you need.
Actually it is not certain that PV panels degrade much faster in hotter climates, although it is possible that the degradation rate is a little higher, especially for lower quality panels (some experts estimate a median degradation rate of around .5 or .6% for moderate climates and around .8% for hot climates). Recent research (also by NREL) has found that a lot of low quality studies, with only one data point, comes out of areas with hotter climates and that there is statistical significance for one-data point studies to find higher degradation rates, but the climate difference for hot climates vs. more moderate climates was not statistically significant, just a mild trend. Either way, you can stack the odds in your favor by buying certified panels from reputable companies (a newer certification process is called Qualification Plus, developed by NREL, etc. to help maintain continuous manufacturing standards and longevity). Also allow some inches for airflow underneath on roofs to keep them cooler and maximize production and longevity.
My 3·84 kw system was installed in October 2010 and at one point today (11th April 2015) was reading 4kw. I have seen it hit 4kw before but this would seem to suggest that there hasn’t been any degradation over the last four and a half years.
Great Article
Degradation is a factor by how much is the million dollar question. When quoting, I tend to stick with manufactures guide lines, most will give a guide of .7% per year and starting 97% when first installed.
Some manufactures will state higher degradation and some lower. The problem we face is we are heavily governed, which is a good thing as far as I’m concerned. If the customer has the worse case and it comes up better, happy customer. That’s important and is better than over stating the returns.
Well done Stuart for all the love and hard work that has gone into building this site.
This is a handy article indeed about solar panel degradation. Still the Solar Panels I’ve got are spot on and I’ve never had any problems with them and yeah, I’m expecting them to last over 25 years.
Like you say, thanks to modern tech these modern panels are a lot better than the old ones and what’s best is getting them fitted with a decent firm for a fair price.