It’s a reasonable thing to wonder, “How green is Green Energy, really?” Critical thinking and skepticism certainly deserve a place at the table as we plan for our energy future. But before reaching temptingly ironic conclusions, maybe we should revisit our commitment to data and facts, lest we throw the baby out with the solar-heated bathwater!

Take the issue of possible waste materials from photovoltaic solar panels (PVs).  Recently we encountered commentary concerned with the possibility that we are transitioning from an energy source (fossil fuels) that produces one kind of waste to one (PVs) that just produces a different kind of waste.

The commentary implied that the two power sources are equally bad since they both produce harmful waste.  But there was no quantitative analysis. How much waste from each? What is the relative difficulty of dealing with their wastes?

Here are some concerns we have heard: 1) Solar panels release sulfur hexafluoride (SF6,), harmless to humans, but a much worse greenhouse gas than CO2;  2)The solid waste from discarded PVs will create huge problems in the future; 3) One of the current PV technologies uses cadmium telluride. Cadmium is a highly toxic substance that definitely requires regulation.

So let’s try to get a handle on this by comparing this waste to a conventional energy source such as coal.

SF6 is mostly used as an insulator in electrical equipment, and about 7% of worldwide SF6 is attributable to photovoltaic manufacture. Solar panels in the field do not release SF6, but leakage from electrical equipment worldwide annually results in around 0.5% as much greenhouse warming potential  as CO2 emissions.  A molecule of SF6 does have 23,500 times the warming potential of a CO2 molecule,  but since CO2 is 41 million times more concentrated in the atmosphere, the net atmospheric warming from CO2 is more than 1,700 times that from SF6.

A legitimate concern is that since its use is growing, SF6 could become a more significant contributor to greenhouse warming.  Regulatory agencies and industry are aware of this problem and are developing ways to mitigate SF6 release and to find alternatives. Controlling SF6 is a relatively straightforward problem compared to the difficult and energy-intensive process of capturing and storing CO2 at scale.  At this time, there are no successful, cost-effective CO2 capture-and-storage processes in existence.

Now let’s compare the solid waste and CO2 produced through generating electricity with coal to that from PVs.  The energy payback time for 1000W of photovoltaics (3 typical panels) is 3 to 4 years: in this time it will produce as much energy as it takes to manufacture, install and decommission; after this, it is carbon neutral.

Here in Maine it will produce around 44,000 kWh of energy in its expected 30-year lifetime. Its total weight is under 150 lbs, 80% of which is glass and aluminum, which are relatively easily separated and recycled or reused, leaving 30 lbs of more difficult, but mostly recyclable, material.

Over its life cycle the panel will be responsible for between 1,000 and 2,000 lbs of CO2. Producing that same electrical energy from coal would require about 35,000 lbs of coal, which would produce about 90,000 lbs. of CO2 and 2,000-9,000 lbs of coal ash.

According to the EPA coal ash is the second largest source of solid waste in the US after household trash, and it contains a variety of toxic materials, including arsenic. Coal electricity is also the largest producer of atmospheric mercury pollution in the U.S.  While some coal ash is recycled in uses such as concrete, about half of it is stored in landfills and wet storage lagoons, which have produced very significant and deadly spills in the past.

So how would you choose to get those 44,000 kWh of electricity? 30 lbs of waste and 1,500 lbs of CO2, or 5,000 lbs of waste and 90,000 lbs of CO2?

As for the cadmium content of these two fuel options: One of the most efficient and lowest-CO2 PVs contains a thin film of cadmium telluride that could leach from a broken panel in some circumstances, in an amount of up to 5 grams for a 1,000W panel. Coal ash contains cadmium, in amounts that vary by type of coal from 0.1 to 5.0 parts per million according to a USGS report, so 5,000 lbs of coal ash would contain between .25 and 12.5 grams of cadmium.

The two might look potentially comparable in cadmium levels, but whereas the PV panel would only leach cadmium if it were pulverized and abandoned, the cadmium from the coal ash just enters the waste stream, wherever that goes.

Admittedly, coal is the most profligate of polluters as a source of electricity, but comparisons with oil and gas will yield a similar range of issues, and the brighter the lights of quantitative analysis that we shine on them, the more glaring their drawbacks in comparison with good old-fashioned, updated solar power.

So keep that bathwater, and the baby too!

Paul Stancioff, PhD., is a professor of Physics at the University of Maine Farmington who studies energy economics on the side.  He can be reached at [email protected]  Cynthia Stancioff is a one-time English major who likes to re-word things. Previous columns can be found at

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