A SUNTRACKER (illustrated in figure1), is a Concentrating Solar Power (CSP) unit, in the category of solar dish engines. The novel solar dish engine module (shown in figure 2) is designed to provide 10.1kW electric power (measured at the engine output electric power lugs), from a conversion of 21kW solar energy from the solar dish reflective sun light to the high temperature receiver focal point. Total electric power output from the solar dish engine module is attributed to combined cycles, closed brayton cycle (CBC) and a organic rankine cycle (ORC), both of which are hermetically sealed to atmosphere. The CBC engine receives 21kW solar energy from a solar dish, estimated to have 27 square meters (291 square feet) reflective surface area. However, unlike the photovoltaic (PV) units, the SUNTRACKER will provide increased use of available solar energy from sunlight. Concentrated sunlight from the dish will focus on the CBC engine receiver, which in turn heats the working fluid media to as much as 1600F, pending the ratio of solar dish to receiver areas. A specific gas mixture of xenon/helium, with excellent thermodynamic properties is used for the high temperature application. Turbomachinery in the CBC engine has one moving part / assembly (compressor impeller, alternator rotor and turbine rotor), mounted on compliant foil bearings. Reference figure 4 as an example. The engine operates with a compressor impeller stage pressure ratio 1.6, and is recuperated. Electric power, measured at the CBC engine electric power lugs, is 6.4kW. The CBC engine is not new, (a closed Brayton cycle, sealed to atmosphere) [1], [4], [8], [18], [19]. However, the application to extract thermal energy from the sunlight and provide electric power in commercial and residential use is (patented). In addition, to increase the efficiency of solar energy conversion to electric power, waste heat from the CBC engine provides thermal energy to an ORC engine, to generate an additional electrical output of 3.7kW (measured at the output electric power lugs). With use of an ORC system, the size of the radiator (CBC unit) for heat rejection is reduced significantly. Working fluid HFC-RC245fa [10] was selected for the ORC unit, based on the low temperature application. Also, as with the CBC turbomachinery, the ORC rotor assembly has one moving part, comprised of a pump impeller, alternator rotor and turbine rotor. With the two engines combined, total system thermal efficiency is 48% (10.1kW electric power out / 21kW solar energy in). However, power electronics are needed for conversion of high frequency voltage at the engine output electric power leads to 60/50 Hz power, for customer use. Power electronics losses for this machine, debits the power 0.5 kW. Thus total electric power to the customer, as measured at power electronics output terminals, is 9.6kW. With solar energy, from the reflective sunlight solar dish 21kW and measured output power from the power electronics 9.6kW, the conversion of solar energy to useful electric power an efficiency 46% (i.e. 9.6kW / 21kW). In addition, the design does not require external water / liquid for cooling.
Degradation of thermal interface materials for high-temperature power electronics applications
