Climate-Saving Sunshade Would Screw up Climate-Saving Solar Facilities

By Eliza Strickland | March 18, 2009 11:38 am

solar-thermalAs global warming‘s effects become evident researchers have turned to geoengineering schemes that could slow the warming process, like a global “sunshade” produced by spraying sulfur aerosols into the atmosphere to reflect sunlight back into space. But a new study points out an (obvious in retrospect) drawback of that idea: It would seriously reduce the effectiveness of some solar energy facilities, which proponents hope would reduce our dependence on fossil fuels and thus prevent further global warming.

Researchers from the National Oceanic and Atmospheric Administration went back and examined data from 1991, when Mount Pinatubo erupted. The Philippine volcano ejected about 15 million metric tons of sulfur-dioxide–laden dust into the air, cooling the planet’s average temperature by about 0.6°C for nearly 2 years [ScienceNOW Daily News]. The researchers found that the eruption also reduced peak power output at a California solar-thermal plant by 20 percent. Solar thermal plants use arrays of mirrors to concentrate sunlight and turn it into a heat source for a conventional power plant; they are generally cheaper than traditional photovoltaic systems.

Lead author Daniel Murphy explains that particles in the stratosphere reduce the amount and change the nature of the sunlight that strikes the Earth. Though a fraction of the incoming sunlight bounces back to space (the cooling effect), a much larger amount becomes diffuse, or scattered, light. On average, for every watt of sunlight the particles reflect away from the Earth, another three watts of direct sunlight are converted to diffuse sunlight [Photonics Online].

While that switch to diffuse sunlight has little impact on the photovoltaic systems, it seriously interferes with solar-thermal systems. “The sensitivity of concentrating solar systems to stratospheric particles may seem surprising,” said Murphy. “But because these systems use only direct sunlight, increasing stratospheric particles has a disproportionately large effect on them” [The Register].

Researchers say the study‘s results, published in the journal Environmental Science and Technology, should serve as a cautionary reminder. Such a reduction [in the power plant's effectiveness] demonstrates the need to pay careful attention “to the potential unintended consequences of employing geoengineering concepts” [ScienceNOW Daily News], says NOAA researcher A. R. Ravishankara. Other researchers have questioned how sulfur particles would impact the ozone layer, while still others point out that the sulfur sunshade would have to be constantly replenished to avoid a sudden spike in temperatures.

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Image: National Renewable Energy Laboratory

CATEGORIZED UNDER: Environment, Technology
  • Damian

    “The researchers found that the eruption also reduced peak power output at a California solar-thermal plant by 20 percent.”

    I’m not surprised peak output was strongly affected. But what about average output? Even if the system couldn’t produce as much energy at noon on a sunny day, how did it do during the overall balance of a year?

  • http://blogs.discovermagazine.com/80beats/ Eliza Strickland

    Good question, and the Register has the answer: the annual energy output “fell by 16 per cent the year after Mt Pinatubo.”

  • Doug

    If I could manage thunderous applause all on my own, this post would receive it. As it stands, I will say thank you very much for pointing out that, in a system as chaotic and complex as the ecosphere, the law of unintended consequences is rarely given the voice it needs.

    I always thought the sulphur aerosol idea was laughable anyway, especially since it would set the stage for global acid rain as a by-product. I am glad that this plan is starting to have holes poked in it, and would hope that more realistic approaches – population controls and a global culture of efficiency, for example – will soon come to the fore.

  • http://clubneko.net Nick

    Pollution has messed up our atmosphere. I know, lets pollute it some more to fix it!!

    Some of these so-called geoengineering schemes are the stupidest ideas I’ve ever heard. THE SUN IS NOT THE PROBLEM. Our pollution is the problem and until we tidy up that waste stream everything else is worthless.

    Like Doug said, acid rain. Other unforseen effects will occur. This mess has started because of the excess crap we’ve dumped into our atmosphere, oceans and lands. Adding extra is not going to re-balance the system. It’s like having 200lbs at one end of a teeter totter and 20 lbs at the other, and to try to lift the 200lbs you add 20 extra pounds to the 200lbs side and wonder why it’s suddenly sinking into the ground.

  • Mark

    This discovery doesn’t bode well for a switch away from fossil fuels on a global scale. Imagine a time in the future when the vast majority of the planet has weaned itself off carbon-based energy sources.

    Now a major volcanic eruption – or several – happens AGAIN.

    With a global population approaching 10B, with water resources at an all time low, with shorelines changing constantly resulting in constant pan-migrations inland, no human population could tolerate a dramatic reduction in a naturally-occurring energy source. It would cause total economic collapse.

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