Improving the Annual Net Power Output of Geothermal Binary Power Plants

Abstract

Geothermal binary power plants that use hot fluid with temperatures between 100 and 200 °C can be applied for both, the extended use of high-enthalpy geothermal resources as well as the exploitation of low-enthalpy geothermal systems even far away from volcanically active areas. Even though geothermal low temperature power plants offer a huge potential and have been installed at more than 100 sites, techno-economic challenges still prevent a broader use. Current research activities in the field of low temperature power plant technology mainly aim for an enhanced performance of the power plant cycle at the design point by means of improving conversion cycle set-up (e.g. trans-critical cycles or multi-pressure cycles), selecting more suitable working fluids (e.g. new pure fluids or working fluid mixtures) or developing plant components with higher performance (e.g. turbines or heat exchanging equipment). Experience from running power plants, however, shows that improving the design point performance is not the only issue since plant operation can deviate significantly from the design conditions, esp. due to variable ambient conditions. In comparison to site- and plant-specific investigations, which have been carried out for existing power plants, this contribution will discuss general aspects of improving operational plant performance and hence the annual net power output. The cooling system thereby plays the central role since geothermal binary plants typically need to remove relatively large amounts of waste heat by means of power consuming cooling equipment (e.g. forced-draught wet cooling towers or air-cooled condensers). Referring to the annual net power output, improvement potential especially exists for the design of the interface between power plant cycle and cooling system, for the component specification within the power plant cycle (e.g. recuperator, condenser and turbine) and for the cooling system operation strategy.