American Institute of Aeronautics and Astronautics 1 Spray-Cooling for Wind-Based Compressed Air Energy Storage Chao Qin 1 and Eric Loth 2 University of Virginia, Charlottesville, VA, 22904 Perry Y. Li 3 , Terrence W. Simon 4 , and James D. Van de Ven 5 University of Minnesota, Minneapolis, MN, 55455 and Stephen E. Crane 6 and Amir Pourmousa 7 LightSail Energy, Inc., Oakland, CA, 94607 Energy systems can benefit from compact and efficient energy storage technologies. In particular, energy storage is well suited for off-shore wind turbines whose output energy variability is typically inconsistent with grid power demand. Furthermore, accommodating peak power generation can lead to over-sizing of electrical generator and transmission lines. It would be more efficient and economical if off-shore wind turbines could be sized for average power and could produce this power on a continuous basis. This would allow the traditional wind turbine generator and transmission lines can be replaced by a smaller, lower-cost, constant-speed generator and a transmission system sized for average power output. This study analyzes a compressor to build and maintain compressed air energy storage for a 35-MPa accumulator sized for a 5 MW off-shore wind turbine. The compressor employs a liquid piston for compression and water spray for heat transfer to achieve near isothermal behavior and efficiency. The overall compression is achieved in three stages with pressure ratios of 10:1, 7:1, and 5:1 under 1-Hz working frequency. The results indicate that droplet surface area plays a critical role in system performance and that high mass loading and small drops can increase overall system efficiency by as much as 50%, as compared to conventional air compressor systems. I. Introduction URRENT wind turbine systems are conventionally designed based on rated wind speed and peak output power. However, the actual energy produced averaged over long times (e.g. one year) is typically 20-40% of the rated power, which means that the generator and transmission lines are over-sized by three-fold relative to the average power generated. Furthermore, the wind turbine electrical output is based on the wind conditions (Fig. 1) rather than the grid energy consumption, indicating that peak generated power often does not occur at the same time as peak demand. For example, if there is little or no wind, the wind turbine will generally not provide enough electricity supply relative to average or expected consumption. This problem and that of over-sizing wind turbines could be alleviated if efficient energy storage and regeneration technologies are employed so that the net energy from the wind turbine and the storage/regeneration system is levelized. Various energy storage systems are being considered for this use including: pumped-hydroelectric storage (PHS), compressed-air energy storage (CAES), and batteries. 2, 8 The principal of those technologies shown in Fig. 2 is that, when energy produced is larger than required, energy is 1 Graduate Research Assistant, Department of Mechanical and Aerospace Engineering, AIAA Student Member 2 Professor, Department of Mechanical and Aerospace Engineering, AIAA Associate Fellow (corresponding author) 3 Professor, Department of Mechanical Engineering 4 Professor, Department of Mechanical Engineering 5 Professor, Department of Mechanical Engineering 6 President, Chief Executive Officer, Co-Founder, LightSail Energy, Inc. 7 Engineer, Scientist, LightSail Energy, Inc. C 11th International Energy Conversion Engineering Conference July 14 - 17, 2013, San Jose, CA AIAA 2013-3870 Joint Propulsion Conferences