Evaluating the Cleanliness of Solar Photovoltaics Can Be Complicated

June 19th, 2008 by Rod Adams

I am a frustrating individual who likes to delve deeply into decision making computations and hates easy answers that sound like sales pitches. One of the best compliments I ever received came from one of my division officers when I was serving as the Engineer Officer on a submarine – he told me “Eng, you ask hard questions.”

As vocal advocate for nuclear fission power I recognize that it has many associated questions, but I after 30 years of study, I have determined to my own satisfaction that most of the important questions have reasonably good answers. In contrast, I have not yet found reasonable answers for many of my questions related to other renewable energy sources. (Yes, I – perhaps controversially – classify fission as renewable, but that is a discussion for a different post.)

Solar photovoltaic (PV) cells are a popular and often discussed (see, for example Atlantic City Convention Center Plans Largest Solar Roof in U.S., 10% of U.S. Electricity From Solar by 2025, SF Passes Largest City Solar Program in U.S. (Finally), all of which were published within the past week) form of “renewable” or “green” energy, but a casual scratching of the surface knowledge that many people have about the technology reveals some troubling details.

Not only are the panels expensive sources of electricity, but they do not last as long as advertised, they do not provide as much energy as the nameplate capacity implies, they consume significant quantities of energy in their production, installation and transportation, and they often use some very nasty materials in their manufacturing process.

The longevity of a solar panel will vary greatly depending on where it is installed, but any customer should remember that they are buying a product that will inherently need to spend as much time as possible fully exposed to the sun and weather. Though there are no visibly moving parts in a solar PV panel, there are many parts of the system where continuous chemical and physical reactions take place that can eventually lead to system degradation and failure.

Take a good look at panels that have been installed for several years and you will notice discontinuities and shiny areas where the components have been damaged and where the power production is reduced. If you have any panels, might want keep a record of the current production so that you can see this effect – or perhaps you will not want to find out just how fast that long term investment is decaying.

The literature accompanying most solar panels provide customers with numbers related to their peak capacity – what I call “noon on a clear day at the Equator”. That quantity of power is only available when the sun is directly overhead, when the panel is perfectly clean and when there are no clouds shading the cells. The cleaning part is important, any panel owner that wants maximum performance needs to set up a routine for cleaning and clearing the panels of any debris.

Leaves and snow are particular nuisances for rooftop solar panels, but sand and bird droppings can be important in some areas as well. Not that the article was specifically discussing PV panels, but I recently read about the 4,000 gallon water tanker trucks that are part of the maintenance equipment at some desert solar power plants.

Some of the most energy efficient solar panels, in terms of both the energy required to produce the panel and the panel operating efficiency are made of a semiconductor material called CdTe (Cadmium Telluride). Companies that make CdTe cells like to brag about the quality of their products, but they have also recently had to warn their investors that they may not be able to sell their panels in the EU for much longer because of rules about using toxic heavy metals in electronics. What they have not made clear yet is what their long term liability is for the panels that they have already sold. What will happen in 5, 10 or 20 years when the panel output is no longer useful and the materials need disposal? Can they be recycled without releasing the heavy metals? Will their customers be able to return the panels to the original producer? Will they make the effort or simply take the systems to the dump like many consumers do with batteries made of similar materials? (Those are the kinds of questions that my former division officer was talking about.)

There are definitely answers to some of the questions that I have about solar PV, but that does not mean that the issues are fully solved. If you are in the market for solar PV systems, please ask the hard questions and realize that anyone who wants you to buy the systems without good answers is just a salesman who is not much different from any other salesman.

Photo credit – The Sun Works (photos to be shared)









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