Geothermal Energy for Small-Scale Power Generation Using an Organic Rankine Cycle

Geothermal power generation is achieved by feeding the harnessed geothermal heat into the boiler of an ORC (Organic Rankine Cycle) based engine which uses an organic working fluid characterised by its low boiling temperature. For the purpose of this study, such a system was designed, built and operated to verify the concept of small-scale power generation using heat from a low temperature source. This experimental facility used hot water as the source of heat, brazed plate heat exchangers as the boiler and the condenser, an automotive inline fuel pump for circulation and a Scroll compressor operated in reverse to act as the expander. The working fluid was R245fa with a boiling point of 80°C at a pressure of 790kPa (or 40°C at 250kPa). A Prony Brake was fitted on the shaft of the expander to determine its power output. Experimental investigations found that ∼600W of power could be produced under optimum conditions at a rotational speed of ∼2000RPM. The details of the experimental facility as well as the results of the experiments are provided in this paper.