Solar Retrofit to Combined Cycle Power Plant With Thermal Energy Storage

Solar thermal power plants have been constructed over the past two decades to reduce harmful emissions and provide a long-term solution for oil independent electricity generation. Of the solar power plant solutions, Rankine cycle based machines have most widespread uses. This study focuses on the modeling of a solar retrofit to a typical combined cycle power plant. The goal is to operate the plant 17 hours per day, making use of thermal storage capability so that the plant may operate even during a portion of the night time. The plant will be located in Orlando, Florida to take advantage of the abundance of sun in that geographic location. On the cycle side, the amount of solar collectors, the working fluid, and the turbine are considered. The thermal storage system, on the other hand, must be designed based upon a balance between cost and storage density. A decision will be made from existing sensible heat solid storage materials. The storage material evens out the energy supplied to the turbine working fluid between the peak solar radiation of the day time and the absence of solar radiation at night. This plant can be implemented in two ways: as a completely newly constructed power plant or as an addition to a HRSG (Heat Recovery Steam Generation) configuration, which can be retrofitted to an existing combined cycle power plant to increase its overall efficiency. In this study, the addition of a solar air collection system with a storage unit to a HRSG combined cycle power plant is proposed. The HRSG will be designed using a series of energy balances for each component. This proposed plant will then be compared with a similar solar plant to examine its feasibility in terms of land area. The storage unit devised comprises 1377 m3 and stores approximately 3900 GJ of thermal energy, which equates to 8 hours of run time when solar radiation is not available. The benefit of this addition to the plant is that the storage reduces the gas turbine run time necessary to provide hot gas to the HRSG. The total cost of the storage medium is approximately $8 million.Copyright © 2010 by ASME