Design and Selection of Turbo-Machinery for Solar and Geothermal Power Plants

Several important sources of renewable energy, such as biomass, concentrated solar panels, waste heat, geothermal, or tidal, use different types of turbo-machinery for conversion to electrical power. The diverse nature of the heat sources and their cyclic behavior make the design of the turbo-machinery power generation equipment quite different than that of the steam turbines used in conventional power plants. The high capital cost of these renewable facilities and the limited hours of operation are powerful drivers to increase the turbo-machinery efficiency. The paper reviews the state-of-the-art hardware designs for each application from an engineering, procurement, and construction (EPC) Contractor’s perspective. Specifically for geothermal power, the discussion covers the application of working fluids other than steam, organic fluid, various mixtures of fluids etc. The benefits and limitations of each method are addressed, along with the impact of geothermal source flow and temperature on the cycle efficiency. The paper also covers the special requirements for single- and multiple-stage arrangements for geothermal applications. For concentrated thermal solar either in high-temperature applications, such as the power tower, or in medium-temperature applications, such as the solar troughs collector field, the paper addresses the unique requirements for performance, integration, and fast startup of the turbines, including the impact of various thermal storage options. Since most of the concentrated thermal solar applications are in arid regions, the paper discusses the heat sink selection (air-cooled condenser [ACC], hybrid, Heller tower, etc.) and how it impacts the plant design and performance. In conclusion, the paper deals with practical issues of achieving a balance between the economics of generation and cost of equipment and reliability for renewable power plants.