Efficiency of radiative cooling and cold storage in solar power plants

In a recent article published in the journal Energy storage and savingthe researchers presented a detailed discussion of the usefulness of radiative cooling and cold storage in concentrated solar power plants.

Study: Radiative cooling and cold storage for concentrated solar power plants. Image Credit: Novikov Aleksey/Shutterstock.com

context

Concentrating solar power plants (CSP) are rapidly becoming one of the main sources of renewable energy. Traditional thermal power plant cooling solutions, such as less efficient dry cooling and water-intensive wet cooling, are not appropriate choices in such severe situations because most CSP plants are built in places sunny, hot and dry with a limited water supply.

Unlike traditional thermal power plants, where output power generation and input thermal power can be easily controlled, CSP power plants are less flexible due to the limitations imposed by the availability of solar irradiation, unless be aided by thermal storage devices or additional thermal energy sources.

A recirculating wet-cooled (CSP) concentrated solar power plant additionally cooled by a radiative cooling system.  (a) Schematic of a parabolic trough CSP plant with a wet evaporative cooling tower and an additional radiative cooling system placed before the cooling tower.  (b) Schematic of a single radiative cooling module laminated with a highly reflective and selectively emissive radiative cooling film.  It also highlights the determining meteorological conditions, as well as the heat transfer processes associated with this radiative cooling module.  (c) Spectral emissivity of radiative cooling film and atmosphere (PW?=?5mm, zenith?=?45o) as well as spectral solar irradiance and blackbody radiation.

A recirculating wet-cooled (CSP) concentrated solar power plant additionally cooled by a radiative cooling system. (a) Schematic of a parabolic trough CSP plant with a wet evaporative cooling tower and an additional radiative cooling system placed before the cooling tower. (b) Schematic of a single radiative cooling module laminated with a highly reflective and selectively emissive radiative cooling film. It also highlights the determining meteorological conditions, as well as the heat transfer processes associated with this radiative cooling module. (c) Spectral emissivity of radiative cooling film and atmosphere (PW=5mm, zenith=45oh) as well as spectral solar irradiance and black body radiation. Image Credit: Aili, A et al., Energy Storage and Saving

To solve the water-related problems that CSP plants face, additional cooling solutions must be developed to reduce the dependence of CSP plants on water while maintaining thermal efficiency at the level achieved with channel cooling. recirculating wet. Radiative cooling is another potential supplemental cooling solution that has recently garnered a lot of attention.

Even under direct sunlight, new radiative cooling materials have been shown to make objects sub-ambient in temperature. Water cooling systems using radiative cooling materials have been created that have been shown to cool water to temperatures below ambient with minimal evaporative water loss and electricity consumption. In certain meteorological circumstances, radiant cooling is offered for CSP installations; however, it is not clear how the water saving potential differs from region to region.

About the study

In the present study, the authors investigated the possibility of reducing water consumption in wet-cooled concentrated solar power (CSP) installations by combining supplemental cold storage and radiative cooling. They discussed the importance of solar-rich but hot and water-stressed areas for CSP systems.

They also assessed the impact of waterless air cooling and water-intensive wet cooling on the operation of CSP plants. The impact of recirculating evaporative cooling on the thermal efficiency and water availability/temperature of CSP systems was illustrated. Additionally, the importance of effective supplemental cooling to reduce water loss while maintaining the thermal efficiency of CSP installations was determined.

The daytime radiative cooling only and the annual potential water saving in the warm southwestern United States were determined when the radiative cooling system operated day and night with cold storage, using a power plant model Reference CSP with an additional radiative cooling system as large as the plant solar field. For recirculating wet-cooled CSP plants, the authors investigated the use of cold storage and radiative cooling as auxiliary cooling technologies.

The cooling capacity of the proposed radiative cooling system was modeled in terms of the capacity and size of water storage tanks for a reference CSP plant operating under various weather conditions across the contiguous United States. Annual water savings maps for the continental United States were produced using two cooling strategies: continuous day and night operation and day-only operation.

Cooling strategies of the supplemental radiative cooling system for a wet-cooled CSP plant without thermal storage.  (a) Daytime only operation without cold room.  This strategy is also applicable if the plant is operational 24 hours a day with thermal storage or an additional thermal energy source.  (b) Day-night operation with cold room.  This strategy assumes that the power of the CSP plant operates only during the day without thermal storage or an additional thermal energy source.

Cooling strategies of the supplemental radiative cooling system for a wet-cooled CSP plant without thermal storage. (a) Daytime only operation without cold room. This strategy is also applicable if the plant is operational 24 hours a day with thermal storage or an additional thermal energy source. (b) Day-night operation with cold room. This strategy assumes that the power of the CSP plant operates only during the day without thermal storage or an additional thermal energy source. Image Credit: Aili, A et al., Energy Storage and Saving

Comments

In this study, researchers observed that when wet-cooled CSP plants were supplemented with radiative cooling, the amount of evaporative water used was reduced. It was also observed that daytime radiative cooling alone could save 40% to 60% of the annual water consumption in the warm southwestern region of the United States, while the annual potential water saving reached 65% to 85% when radiative cooling system worked day and night with cold room.

In addition, the annual potential water savings with the radiative-only daytime cooling system were determined to be nearly 40% to 60% in the rather hot and arid region of the southwestern United States, where the simultaneous management of the water shortage and the cooling of the thermal power plant was difficult. The potential annual water savings with the day-night radiative cooling system has also been shown to be as high as 65-85%.

Annual Contiguous United States Water Savings Maps for Wet-Cooled CSP Plants.  (a) Daytime radiative cooling system only.  (b) The day-night radiative cooling system.  The day-only radiative cooling system potentially reduces water loss from CSP plants in the Southwest region of the United States by 40-60%, while the day-night radiative cooling system reduces water loss 65 to 85% in the same region.

Annual Contiguous United States Water Savings Maps for Wet-Cooled CSP Plants. (a) Daytime radiative cooling system only. (b) The day-night radiative cooling system. The day-only radiative cooling system potentially reduces water loss from CSP plants in the Southwest region of the United States by 40-60%, while the day-night radiative cooling system reduces water loss 65 to 85% in the same region. Image Credit: Aili, A et al., Energy Storage and Saving

conclusion

In conclusion, this article has elucidated the water saving potentials of day-only and day-night radiative cooling by combining a radiative cooling system with the evaporative cooling tower of a benchmark CSP facility – the Mojave Solar Project . The model has also been applied to the benchmark CSP plant at over 3,000 locations across the United States under varying weather conditions. The authors demonstrated the water saving maps of the contiguous United States for day and day-night radiative cooling systems by projecting how much water loss through evaporation can be avoided under such conditions.

For recirculating wet-cooled CSP plants, the authors pointed out that radiative cooling and cold storage can be used as auxiliary cooling technologies. The authors also believe that the current findings open up the possibility of increasing the thermal efficiency of wet-cooled CSP plants while reducing their water consumption through evaporation, which is essential in water-stressed and hot locations. with arid and desert climates.

Source

Aili, A., Tan, G., Yin, X., et al. Radiative cooling and cold storage for concentrated solar power plants. Storage and energy saving (2022). https://www.sciencedirect.com/science/article/pii/S2772683522000024

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