Energy Leverage Of Photovoltaics

In an argument between economics and thermodynamics, thermodynamics wins.

Numerous studies have been made to compare the energy that it takes to make photovoltaic solar cells versus the amount of energy that they produce over time. For example:

Considering that solar panels typically have useful lives of 20 years or more, the electric energy recovery will range from 400% (in the case of a 5 year energy payback) to 2000% (in the case of a 1 year energy payback).

These figures demonstrate that a barrel of oil [equivalent] invested in making solar panels can effectively generate sufficient electricity to recover the investment of that barrel of oil with 4 barrels of oil [equivalent] as a minimum and up to 20 barrels of oil in the optimistic scenario. This is like investing in a savings account at an interest rate ranging from 20% to 100%. At the low end, this is a healthy return on investment!

Crystalline flat plate photovoltaic panels do not fare quite as well as thin-film panels in terms of energy payback time ("EPBT"). For example, at the above-mentioned 1997 conference, system EPBT values ranging from 5 to 10 years were reported for present-day mono-crystalline silicon modules.

While this analysis is more pessimistic than some of the other studies cited, this helps to explain why photovoltaic systems have not been as attractive as other energy investments and thus have been limited to remote applications where transportation of other energy resources (such as combustible fuels) is expensive.

As technology improves, energy performance improves. For example, concentrator systems perform better than crystalline wafer flat plate panels, yielding energy paybacks on the order of 1.5 - 3 years (depending on the specific technology). [This information is based on interviews with professionals in the field. Citations from the scientific literature are being researched.] As energy payback time improves, photovoltaics will achieve economic payback in the general electricity marketplace. For another example, read about more energy-efficient "PV Grade" or "Electronic Grade" Green Silicon.

As another example, in "Photovoltaic Technology: The Case for Thin-Film Solar Cells," the authors state "Wafer-based crystalline silicon solar modules dominate in terms of production, but amorphous silicon solar cells have the potential to undercut costs owing, for example, to the roll-to-roll production possibilities for modules. Recent developments suggest that thin-film crystalline silicon (especially microcrystalline silicon) is becoming a prime candidate for future photovoltaics. [A. Shah, P. Torres, R. Tscharner, N. Wyrsch, & H. Keppner, Science Magazine, July 30, 1999. Abstract is free to registered users, full article is available online by subscription.]

While economic payback does not correlate exactly to energy payback, and may not reach the same remarkable level of three years, these figures demonstrate why prices have been falling and how the underlying fundamentals of electricity produced from solar cells can lead to wise investment. How does EPBT for PV stack up against fossil fuels? It might be surprising to discover that the energy payback for oil has been declining steadily for many decades. See figure 2.15 in Beyond Oil, Gevers et al, 1991]. As the energy payback improves for PV and declines for oil, the attractiveness of PV will only continue to get better.

How PV works.

Home Apollo2 updated 2000 July 27
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