Geothermal Electricity Production by Means of the Low Temperature Difference Stirling Engine

Abstract

The first low-temperature difference Stirling engine was presented at the International University Center in Dubrovnik, as early as 1983. During the last 16 years, numerous low temperature difference engines were built all over the world, mostly for solar energy application. However, hot water from flat solar collectors has nearly the same temperature as hot water from geothermal sources. As the engine power depends upon the cube of temperature difference, geothermal wells of elevated temperatures, approaching the boiling point, are particularly suitable for Stirling engines. When compared to the classic Clausius-Rankine cycle, mostly used in the present geothermal plants, Stirling cycle offers many theoretical and practical advantages. From thermodynamic point of view, Stirling cycle is equivalent to the optimal Carnot cycle, having the highest possible efficiency. From the technical point of view, Stirling plant is cheaper, having no condenser and no turbine blades exposed to aggressive influences of geothermal steam. Due to the external, instead of internal heating, there is no need neither for specific materials, nor for tube exchangers. The latest performance of low temperature difference Stirling engine using hot water, was made by Japanese group at Saitama University, showing additional possibilities for use of geothermal sources.