Murphy’s study found that aerosols reduce direct sunlight much more than total sunlight. Each 1% reduction in the Earth’s sunlight due to aerosols will cause a 4-10% loss in output from concentrating solar power applications, depending on what measure is used for electrical output.

In the past, the increased aerosols resulting from the 1991 eruption of Mt. Pinatubo in the Philippines reduced global sunlight by less than three percent but decreased output from some solar generating plants by about 20%.

Because flat solar hot water and photovoltaic panels utilize diffuse as well as direct sunlight, the performance losses are not as large as for concentrating solar collectors. However, the performance loss will still exceed the reduction in total sunlight because a tilted panel does not capture diffuse sunlight as efficiently as direct sunlight. A potentially important effect is that any shift from direct to diffuse sunlight makes a passive solar design less effective: in winter diffuse sunlight is harder to capture with south-facing windows, and in summer shading windows with overhangs is less effective.

Although only stratospheric aerosols are explicitly considered here, any cooling of the earth that relies on light scattering by particles, including tropospheric aerosol scattering and increased cloudiness, will also result in reductions in direct sunlight that are several times the reductions in total sunlight.

—Daniel Murphy

Resources

• Daniel M. Murphy (2009) Effect of Stratospheric Aerosols on Direct Sunlight and Implications for Concentrating Solar Power. Environ. Sci. Technol., 43 (8), pp 2784–2786 doi: 10.1021/es802206b