by Emil Morhardt
The main considerations in whether and where to install photovoltaic (PV) panels are how much sun there is, and how much the panels cost. Right? Not necessarily. Engineers at Arizona State University have just published a paper pointing out that if a goal of installing photovoltaics is to decrease greenhouse gas emissions, it would be prudent to consider the emissions from manufacturing—which vary significantly by panel type—how long they stay in the atmosphere, and whether or not the installation is competing with other renewable energy sources rather than with fossil fuel burning. Because of the greenhouse gases associated with manufacturing, all panel installations increase greenhouse effects in the short term, although the initial two-year effect is to reduce them owing to sulfur and nitrogen oxides released from power plants during manufacture.
In their lifecycle modeling, Ravikumar et al. (2014) concluded that in California and Wyoming it takes at least six years to get to the point that the panels are reducing the greenhouse effect, and it might take as long as eleven years in Wyoming and twelve years in California. This five-to-six-year difference has to do with the choice or technology and the primary energy source where the panels are installed. Chinese polycrystalline panels use more energy to refine the panel components than do the cadmium telluride panels made in Malaysia; China gets most of its energy from coal, whereas Malaysia gets about half of its energy from the less-polluting natural gas, and ten percent of it from hydroelectricity; and installations in California are competing with the equally-renewable hydroelectric energy which makes up a significant part of the electricity on the grid; Wyoming is more dependent on coal. In all cases however, the model calculates that the sooner photovoltaics are deployed, the better.
This blog summary greatly simplifies a complex and insightful lifecycle modeling effort that seems to me to serve as a good introduction to the process for the uninitiated. I’d recommend reading the whole paper.
Ravikumar, D.T., Seager, T., Chester, M., Fraser, M.P., 2014. Intertemporal Cumulative Radiative Forcing Effects of Photovoltaic Deployments. Environmental Science & Technology dx.doi.org/10.1021/es502542a Abstract and a figure at: http://bit.ly/1AF5fGK