New Scientist 23 Apr 09;
PUMPING aerosol particles into the atmosphere to create a sunshade could take a heavier toll on solar power generation than expected.
For every 1 per cent of the sun's rays deflected into space, the average output of solar systems that rely on direct sunlight would drop by 4 to 5 per cent, says Daniel Murphy at the US National Oceanic and Atmospheric Administration in Boulder, Colorado. Geoengineers propose scattering 1 to 2 per cent of sunlight.
Aerosols scatter the light that hits them, but only 20 to 25 per cent of that is reflected into space. The rest reaches the ground as diffuse light. Since this light doesn't come directly from the sun, it isn't collected by solar systems that concentrate sunlight onto thermal power generators or high-efficiency solar cells. Their optics track the sun during the day and focus an image of it onto the power-generating elements, so they can produce much more power than flat solar cells.
Losses could reach 20 per cent in the late afternoon during summer, Murphy warns, because more light is scattered when the sun is lower (Environmental Science and Technology, vol 43, p 2784).
Research has previously shown a sunshade could also trigger droughts in some regions.
