Description
Humanity’s need to transition from fossil fuel-based power generation to more environmentally friendly renewable sources has contributed to huge progress in solar energy research. Concentrated solar power (CSP) can store large amounts of energy for peak shifting and potentially will operate at higher overall efficiencies than photovoltaics. Amongst the various CSP technologies, power tower systems show the most promise in the long-term when paired with a thermal energy storage system (TES). A numerical code, modeling a rock-filled TES system, to be used in conjunction with a CSP power tower plant, was developed. This porous media bed storage is being applied from a successful model solving a set of two coupled partial differential equations modeling the temperature of the solid and fluid at various nodes throughout the volume. The goal of this project is to integrate this numerical model of a high-temperature rock bed sensible heat storage system into hybrid solar combined cycle previously developed at the Combustion and Solar Energy Lab. The strategy explored here is to put the storage unit after the gas turbine in a combined cycle plant, since storage prior to the gas turbine still requires substantial research due to the high temperatures involved. The initial strategy is to have the gas turbine operate while the sun is providing solar input. Using the National Renewable Energy Lab’s System Advisor Model, approximations of useful solar input were made. During the daylight operation, the storage will capture the exhaust from the gas turbine through heat transfer from the gas to the rocks inside the storage. Once the solar resource drops to zero at night, ambient air will be blown back up the storage unit, acquiring the heat from the rocks. This heated air then enters a heat recovery steam generator where steam is produced to power the bottoming Rankine cycle. Temperature profiles for charge and discharge cycles of the storage unit as well as 24-hour operation power results are presented. A comparison between the properties of dry air and a combustion gas is made. The resulting storage profiles of the TES comparing these two inputs are also shown.
