19 July 2012

Invited research lecture throws light on the environmental performance of Photovoltaics

On Monday 18th July, Dr Marco Raugei, UNESCO Chair in Life Cycle and Climate change of ESCI, delivered a lecture on the Environmental Performance of Photovoltaics (PV), as part of the 2012 Research Lecture Series.

Dr Raugei was invited to speak by Dr Brian Azzopardi of the Department of Mechanical Engineering and Mathematical Sciences at Oxford Brookes University and the lecture Environmental Performance of Photovoltaics: the devil is in the details was the 4th Invited Research Lecture in the series. Marco Raugei is currently a senior researcher with Pompeu Fabra University, Barcelona, Spain. He is also a collaborator of the Center for Life Cycle Analysis, Columbia University, New York (USA), and a technical representative in the International Energy Agency Photovoltaic Power Systems Programme (PVPS) Task 12 - Life Cycle Analysis component.

The lecture examined Marco's in-depth analysis of cadmium telluride (CdTe) thin film PV. This analysis has special reference to key metrics such as energy pay-back time (EPBT), Energy return on investment (EROI) and cadmium emissions. Photovoltaics or PV are among the fastest growing renewable energy technologies and they have improved notably over the last few decades. This research wanted to look at estimating and predicting various aspects of their present and future environmental performance. A careful multi-pronged methodological approach was required that would identify potentially misleading scenarios.

Energy Pay-Back Time or EPBT is defined as the ratio of the primary energy required for the construction and end-of-life of a PV system to its net yearly energy output (expressed in terms of equivalent primary energy). EPBT has almost universally been adopted as the indicator of choice to express the energy performance of PV. Over the last few decades, technological improvements have produced an almost order of magnitude reduction in the EPBT of PV. However, due to the details of how EPBT is operationally defined, it may be shown that foreseeable reductions in cumulative energy demand for PV manufacturing and concomitant increases in grid efficiencies will likely result in a rather severe curtailment, or even a possible reversal, of this trend.

Energy Return on Investment or EROI is defined as the amount of energy gained from an energy production process compared to the amount of energy (or its equivalent from some other source) required to produce a new unit of the energy in question. The EROI metric has been used since the 1970's to gauge the ultimate viability of a range of diverse energy sources. The EROI of PV has traditionally been viewed as much lower than that of conventional fossil fuel life cycles.

Cadmium emissions – The introduction to the market of a novel cadmium-based PV technology caused understandable concern because of the metal's well-known toxicity. However, a careful prospective analysis of CdTe PV's potential contribution to yearly global Cd emissions into air and water has shown that the latter may well be orders-of-magnitude lower than the current Cd emissions rates in Europe. Also, results indicate that while CdTe PV may account for a large percentage of future global Cd demand, its role in terms of Cd sequestration may prove beneficial, rather than detrimental to the environment.