Blue Sky Cooling for Parabolic Trough Plants

Abstract

At most locations with sufficient solar resources for a viable exploitation of solar power plants water is too precious to be wasted in cooling towers. However, application of air cooling increases the levelized cost of electricity up to 16%. An alternative for air cooling is radiation cooling. A new function is given to the parabolic trough mirror, which is the realization of optical contact between a radiating plane and the sky. The sky is cold, therefore the radiating plane cools down. This cooling is available day and night and can supply most of the cooling power that is needed for the condenser of the Rankine cycle. When there is wind, the radiating plane also dissipates heat. Radiation cooling and wind are sufficient for cooling the solar thermal power plant.Storage of cold in a water basin is an essential component, because wind cooling and radiation cooling are more effective at night, when the air temperature is low. Pumping the cold night-air through heat exchangers in the basin is an alternative when wind speeds are generally low.An additional function is given to the water basin, namely the support of a floating parabolic mirror field. A field of floating parabolic trough mirrors that are stationary with respect to each other rotates collectively around a vertical axis in order to follow the sun. We expect that this simple concept will lead to a substantial cost reduction, in spite of the less favorable average angular orientation of the mirrors. Floating parabolic trough fields are most suited for applying radiation cooling in solar power plants.