Carbon Footprint and Solar: Search for Studies

Dale Chihuly's "The Sun" at the Desert Botanical Garden in Phoenix, Ariz.

I’ve been asking around for references to any life-cycle analysis of a solar power plant. Many executives I’ve talked to at Intersolar in San Francisco say they haven’t seen any. Jason Liu, vice president of Yingli Green Energy, tells me the company has done such an assessment, but the numbers aren’t verified by an independent source, so they aren’t available publicly.

I started to wonder about life cycle analysis of solar manufacturing and power plant operations after reading a Pacific Gas and Electric blog post last month that talked about the utility’s effort to study the carbon footprint of the products and services it buys. I asked PG&E about the assessment, and I got an email from Fiona Chan. Fiona said the utility, UC Berkeley and Climate Earth began the assessment on June 1 this year, and they expect to complete it in about a year. PG&E launched a “green supply chain program” last year.

Companies don’t do carbon footprint analyses just for fun. Whatever results they get from the reports will influence their buying decisions, and that in turn could have a big impact on their suppliers. When WalMart announced in July last year that it would start to ask its suppliers to track their greenhouse gas emissions, many of these suppliers were worried about fulfilling the requirement. Earlier this year, WalMart set a goal of getting rid of 20 million tons of greenhouse gas emissions from manufacturing and transporting the products they sell by 2015.

The United States has no national regulations requiring companies, be they power plant operators or retailers, to track their greenhouse gas emissions. Federal lawmakers certainly have debated over a proposal to cap emissions and penalize those who emit more than allowed. But the proposal is controversial and faces no shortage of opposition from heavy polluters and their Congressional representatives.

I have found some carbon footprint studies on solar. A 2008 study led by Brookhaven National Laboratory looked at four types of solar panel-based systems: multicrystalline silicon, monocrystalline silicon, ribbon silicon and cadmium-telluride. Here is an excerpt from the summary:

“Among the current vintage of PV technologies, thin-film cadmium telluride (CdTe) PV emits the least amount of harmful air emissions as it requires the least amount of energy during the module production. However, the differences in the emissions between different PV technologies are very small in comparison to the emissions from conventional energy technologies that PV could displace … At least 89% of air emissions associated with electricity generation could be prevented if electricity from photovoltaics displaces electricity from the grid.”

Here is a link to a 2006 study by the University of Michigan on a 33-kilowatt system, which was made up of multicrystalline silicon solar panels from Kyocera and amorphous-silicon thin films from Uni-Solar. You should try to read the whole paper to get the details, but here is one of the conclusions:

“These results demonstrate that multi-crystalline modules are more energy intensive when compared to thin film laminates.”

There is a life cycle analysis of crystalline silicon solar panels on a website. It’s only three pages and has an easy-to-read table showing the results. One of the conclusions is that, over their lifetime, “crystalline silicon solar panels generate 9-17 times the energy required to produce them.”

And finally, here is a link to the International Energy Agency’s 2009 guide for carrying out a life cycle analysis of solar electricity.

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2 Responses to Carbon Footprint and Solar: Search for Studies

  1. ECD Fan says:

    The reason why such public studies are rare is because they are very complicated and require detailed knowledge of manufacturing processes that are, at least in part, proprietary. I have not reviewed the other studies you mentioned, but I can tell you that the so-called “study by the University of Michigan” is absolutely bogus.

    For example, the authors can’t even calculate efficiency properly. Take a look at page 23 – they have the arrogance to claim there that the PVL62 is 6.6% efficient. If they knew how to calculate efficiency, they would have figured out it is just 6.0% efficient (62/(2.609*0.394)/1000).

    But, more importantly, the study essentially relies on an incomplete (and very likely fraudulent) Table 6 provided by Unisolar (see page 29) – that table, for example, does not list Germane or Germanium, which is interesting since two of the three junctions in Unisolar’s laminates contain Germanium!

    In other words, the Center for Sustainable Studies at UMich and Unisolar should both be ashamed of this shoddy (if not intentionally misleading) piece of work.

  2. I found the best PV Carbon footprint study in my Making Silicon Metal for Solar post. Mariska de Wild-Scholten with ECN presented the “Life Cycle Assessment of Photovoltaics: from cradle to cradleat the 1st International Conference on PV Module Recycling held in January 2010.

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