When a reader told me to take a look at the March cover story for Environmental Science & Technology, "Life-Cycle Emissions from Photovoltaics," I expected the kind of head-scratcher seemingly designed to send environmentalists straight to the nearest bottle of (organic, locally-distilled) bourbon -- something along the lines of how the energy consumed and toxic emissions produced by purifying silicon would negate the renewable benefits of using the sun directly as fuel.

I couldn't have been more wrong. The result of the data crunching by three researchers who studied four different photovoltaic technologies employed by 11 different European manufacturers between 2004-6 could hardly be more definitive: "At least 89 percent of air emissions associated with electricity generation could be prevented if electricity from photovoltaics displaces electricity from the grid."

The four technologies under review were ribbon-silicon, multicrystalline silicon, monocrystalline silicon, and thin-film cadmium telluride. Of the four, thin-film cadmium telluride was the clear winner, for the simple reason that it requires the least amount of energy to produce. And the numbers get even better if solar power is used to provide some portion of the electricity necessary for the various stages of solar panel construction (from mining and smelting the ore all the way to factory assembly.)

So next time you hear someone wondering how a complete life-cycle assessment of solar power and greenhouse gas emissions stacks up against oil or coal, (don't laugh -- commenters on this very blog have asked that very question) send 'em to the March issue of Environmental Science & Technology. And I should relax -- not every assessment of the environmental friendliness of new technologies need get bogged down in irresolvable paradox. Sometimes, there is real reason for optimism:

To wit:

It is noted that the environmental profiles of photovoltaics are further improving as efficiencies and material utilization rates increase and this kind of analysis needs to be updated periodically.