Solar Turbine with Optical Coupling of Radiation into the Turbine Casing

A solar concentrator/gas turbine is described in which solar radiation is directed by mirrors, etc, through windows in the turbine casing. This radiation is used to heat absorbing surfaces inside the turbine, thus heating the circulating gas. This hot gas then produces a thermodynamic (Brayton) cycle, which is used to drive a generator. The optical properties of solar selective surfaces for the windows were considered, in order to minimize re-radiation losses. Film coatings were deposited onto glass, and their optical transmission was measured, to assess their effectiveness as solar selective surfaces. Suitable distribution of incoming radiation between the turbine discs is used to perform turbine reheat, without recirculating hot gas to an external heat source. This allows a larger number of reheat stages, with a consequent improvement in efficiency. The ideal and non-ideal efficiencies were calculated by computer models, as a function of the number of stages. A generator connected directly to the high-speed turbine shaft was considered, with a rectifier-inverter to produce output at line frequency (50/60 Hz). The losses in the electronics were compared to those incurred in the gearbox of a conventional transmission.