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Radiative Film for Supplemental Cooling

Palo Alto Research Center (PARC)
Metamaterials-Enhanced Passive Radiative Cooling Panels
ARPA-E Award: 
Palo Alto, CA
Project Term: 
08/06/2015 to 05/05/2017
Project Status: 
Technical Categories: 
Critical Need: 
In thermoelectric power generation, only about 40% of the energy in the fuel is converted into electricity. In other words, the power plant operates at about 40% efficiency. The remainder of the energy is converted to low-grade waste heat that must be removed to maintain the power plant's efficiency. Most power plants use water from nearby rivers, lakes, or the ocean for cooling. The water may pass directly over tubes containing the plant's heated condenser water, and then be returned, warmer, to the original source, or it may be evaporated to carry off the heat in water vapor. In areas with limited water or under drought conditions, dry-cooling systems use air to remove heat from the plant's condenser water. However, present dry-cooling technology reduces the power plant's efficiency and requires costly equipment. With water supplies becoming increasingly strained in many areas, economical dry-cooling approaches that do not reduce the efficiency of power plans are critically needed. Innovative methods to allow cooling below the daytime ambient air temperature and improve heat exchange between air and the plant's recirculating condenser water will provide the keys to ensuring the continued efficiency of power generation while decreasing the burden on water supplies.
Project Innovation + Advantages: 
PARC, working with SPX Cooling Technologies, is developing a low-cost, passive radiative cooling panel for supplemental dry cooling at power plants. PARC's envisioned end product is a cooling module, consisting of multiple radiative cooling panels tiled over large, enclosed water channels that carry water from an initial cooling system, such as a dry-cooling tower. The cooling panel consists of a two-layer structure in which a reflective film sits atop a unique metamaterial-based emitter. In this architecture, the top layer completely reflects sunlight while the bottom layer effectively emits infrared radiation through a spectral window in the earth's atmosphere. This combination enables radiative cooling of the water even in full illumination by the sun. The cooling panel will be made using a lithography-free process compatible with roll-to-roll fabrication. In a large-scale system, the water temperature at the outlet of the cooling module is expected to be 8oC cooler than the temperature of the water at the inlet, which will result in a 3% efficiency gain for the power plant.
Potential Impact: 
If successful, PARC will develop a low-cost, low-complexity, and scalable structure that can cool water to near-ambient temperatures.
PARC's structure could help power plants maintain energy efficiency by providing a low-cost means of supplemental dry cooling when water use is restricted.
The team's system could reduce water usage for cooling by 30%, which helps conserve water for other uses.
By applying low-cost and scalable manufacturing techniques, PARC estimates the system could be an economical option for radiative cooling.
ARPA-E Program Director: 
Dr. Michael Ohadi
Project Contact: 
Dr. Bernard Casse
Release Date: