A theoretical investigation of radiative cooling as a supplemental cooling option for dry-cooled concentrating solar power plants
“We have investigated using daytime radiative cooling to enhance performance of dry-cooled Concentrating Solar Power (CSP) plants. Water scarcity and environmental concerns are the driving forces for CSP plants to use dry cooling systems. In order to overcome the efficiency penalties associated with using air-cooled technologies several supplemental cooling techniques have been proposed. Recent advancements in manufacturing structures with selective radiative properties using plasmonic nanostructures have made the day-time radiative heat transfer to cold outer space practically applicable. In this work, we explored the efficiency improvement of air-cooled advanced supercritical carbon dioxide CSP plants using the supplemental radiative cooler.
CSP plants require abundant direct solar radiation in order to work efficiently. For this reason, best locations for CSP plants are hot and dry regions that make available water for cooling more scarce. During recent years environmental concerns, higher water demand as a result of population growth and climate change have made the water consumption for power plant cooling to go under increasing scrutiny. In 2011, ‘SunShot Concentrating Solar Power R&D’ initiated by US Department of Energy. The target of SunShot is to develop more efficient and reliable technologies with lower cost than existing CSP plants. The DOE aims to develop high efficiency, dry-cooled power cycles with a net efficiency greater than 50%.
Tailored thermal radiative structures have found many applications in energy applications such as local heating, thermo-photovoltaics, chemical analysis, spectroscopy, incandescent light sources, and cooling systems. Structures can passively cool themselves by radiation of heat to outer space if the right radiative properties are applied. The structure should reflect short wavelengths of visible and near IR up to 5 μm and emits in the mid-IR wavelengths about 8-13 μm that is called the ‘atmospheric window’ to achieve daytime radiative cooling. The day-time radiative cooling has been investigated by different researchers and successful numerical, and experimental results have been reported. The radiative cooling can be employed as supplemental cooling approach reducing the sink temperature in a dry-cooled thermal power cycle to overcome the performance disadvantage compared to a wet-cooled cycle.
It is shown that for simple and recompression supercritical CO2 cycles operating at hot source temperature value equal 550 °C, by adding 14.02 m2/kWe and 18.26 m2/kWe plasmonic radiative cooler it is possible to overcome the efficiency loss due to air cooling and the net output of the cycle increases by 5.0% and 3.1% respectively. For hot source temperature equal 800 °C, the required cooling areas are 4.38 m2/kWe and 10.46 m2/kWe and increase in net output of the cycles would be 7.5% and 4.9% respectively.”