The Challenge And Opportunity Of Cadmium Telluride, Solar Photovoltaic Film
There's plenty of buzz in the startup world about faster-to-make, cheaper, highly efficient, thin-film solar photo-voltaic technology. For a sample, check out "Painting solar Bloo" about a solar panel startup company balled "Bloo" which is deploying nano-tech methods to up the cost effectiveness of Cadmium Telluride based solar collection devices. We're all for innovation, don't get us wrong; but Cadmium Telluride or "CdTe" solar panels are a troubling innovation pathway. This post presents a high-level summary of the risk management areas of concern and a closing comment on how to potentially relieve concerns about cadmium coating our rooftops.
Tellurium, although very rare, even in comparison to the other noble metals such as gold, is available as a byproduct of copper and lead smelting, and is already produced in North American for variety of non-solar applications. Tellurium metal is only of moderate toxicity. This is the good news part of the story.Cadmium: not so good. Per the US Geological Survey, Cadmium Statistics and Information page, "Cadmium is produced mainly as a byproduct from mining, smelting, and refining sulfide ores of zinc, and to a lesser degree, lead and copper. Small amounts of cadmium, about 10% of consumption, are produced from secondary sources, mainly from dust generated by recycling of iron and steel scrap."
In recent decades, there have been extensive efforts to eliminate all elemental cadmium from personal electronics and from batteries and switching devices in general. RoHS specifically focuses on eliminating cadmium-based items exported into Europe, for example.
A major US toymaker recently reported plans for phasing out cadmium-based NiCad batteries in their products, citing high occupational exposures in China for mining and battery making employees as well as landfill disposal issues in the US. May have something to do with the recent publicity about lead in toys.
More evidence of Cadmium's departure from consumer applications:- for decades, the phasing out of cadmium based paints in highway striping and in oil paints has been underway in the developed world (with Europe of course ahead of the US and Canada on replacing the highway stripe Cadmium yellow).
Here's the interesting part. With consumer applications of cadmium on the way out, where does the unused cadmium produced by Zinc and Copper companies go? Sounds eerily reminiscent of the mercury disposal problem, no?
To expand on this analogy a bit: no nation with a decent understanding of chemical risk wants the waste mercury from old thermometers; and if they do want it, that's reason it enough not to send it to them. What happens when the US' planned "Clean Coal" gasification plants all go on line and each regularly generates hundreds of additional Kilos of elemental mercury waste per year....then what?
Same issue with Cadmium byproduct from Zinc, Lead, and Copper smelting. What to do with it?
Some clever wag, presumably prior to the emergence of CdTe solar panels as a hopeful technology, proposed that pure cadmium sculptures be commissioned and paid for by the mining and minerals companies, and the Cd statuary so produced be erected around the mine perimeters as permanent tributes to a risk preventive (exposure control) strategy. Talk about a short lived artistic career.
Perhaps there is an alternative way to sequester the byproduct Cadmium, and even put it to good use making electricity in artful designs?
Before we proceed, we should mention that tire-making consumes huge quantities of zinc. Lead batteries won't be going away any time soon either. And we're still not at Peak Copper. So, don't expect the cadmium production rate to decrease for other reasons.
As you would expect, things get a little dicey when you put Cd together with Te. From Wikipedia we pasted a very nice summary of the hazard and risk management issue.
The toxicity is not solely due to the cadmium content. One study found that the highly reactive surface of cadmium telluride quantum dots triggers extensive reactive oxygen damage to the cell membrane, mitochondria, and cell nucleus.
The disposal life-cycle and long term safety of cadmium telluride could become an issue in the large scale commercialization of cadmium telluride solar panels. A document hosted by the U.S. National Institutes of Health dated 2003 discloses that:
Brookhaven National Laboratory (BNL) and the U.S. Department of Energy (DOE) are nominating Cadmium Telluride (CdTe) for inclusion in the National Toxicology Program (NTP). This nomination is strongly supported by the National Renewable Energy Laboratory (NREL) and First Solar Inc. The material has the potential for widespread applications in photovoltaic energy generation that will involve extensive human interfaces. Hence, we consider that a definitive toxicological study of the effects of long-term exposure to CdTe is a necessity.
Health and Environmental Risks Researchers from the U.S. Department of Energy Brookhaven National Laboratory have found that: Large-scale use of CdTe PV modules does not present any risks to health and the environment, and recycling the modules at the end of their useful life completely resolves any environmental concerns. During their operation, these modules do not produce any pollutants, and furthermore, by displacing fossil fuels, they offer great environmental benefits. CdTe PV modules appear to be more environmentally friendly than all other current uses of Cd.
Here's the nub of the matter. How can we conscionably posit that cadmium telluride is fine in solar panels just because that technology is "green" relative to electricity production, without having seen a full-blown risk management evaluation that encompasses how cadmium is produced and incorporated into the CdTe matrix, and, then, how it will be reclaimed at product end of life?
Well,...."we" can't do that, is the answer.
The next question is, who's going to be responsible for doing the risk management evaluation (not just human toxicity studies - we mean conventional human and eco-tox hazard updates, plus an assessment of all reasonably anticipated exposures).
Will it be the startup investors? No way.
Will potential customers trust the US Department of Energy Labs to perform the kind of studies that are needed to really delve into full product life cycle risk? Doesn't seem like the best option.
Having completely overlooked the global food availability and cost impacts of corn-based ethanol, for example, US government agencies with an indirect stake in the outcome (those which give research grants) don't seem trustworthy. That includes all DOE funded labs.
Given the track record of frequent political interventions by US executive branch in matters of Federally sponsored scientific research, it even seems doubtful that USEPA can be trusted to perform the necessary evaluation for at least several years past a new Administration coming in.
TreeHugger characteristically likes to go beyond merely flagging an environmental problem and nagging about it. Keeping on the sunny side of the street really does make you feel better about life. So, what's the solution?
The assessment challenge is not technically difficult. Communication is. As long as the hazard and the exposure data are honestly and openly presented, it comes down to trust and the ability to communicate the findings without spin and political intervention.
The time to do this is now, before the sunk costs become large and before investor risk piles up high enough to build political backlash and cause an outbreak of 'messenger shooting' (blaming TreeHugger for bringing up the subject, for example).
What might work, is an NGO facilitated revaluation - with formal participation by industry sectors, scientific academies, and public health scientists from all the developed nations. This time, wouldn't it be nice to let the general public link in to postings of all the proceedings while they are underway. Think webcams, daily blog posting from tech meetings, etc.
Perhaps our rooftops can be those works of art that sequester Cadmium. We can only hope that no Cd leaches into the stormwater, should that come to pass.
Image credit::Comic Book Periodic Table Of The Elements, "Dr Solar" - Cadmium