Advanced Binary Cycles: Optimum Working Fluids

Research output: Contribution to conferencePaper


A computer model (Cycle Analysis Simulation Tool, CAST) and a methodology have been developed to perform value analysis for small, low- to moderate-temperature binary geothermal power plants. The value analysis method allows for incremental changes in the levelized electricity cost (LEC) to be determined between a baseline plant and a modified plant. Thermodynamic cycle analyses and componentsizing are carried out in the model followed by economic analysis which provides LEC results. The; emphasis of the present work is on evaluating the effect of mixed working fluids instead of pure fluids on the LEC of a geothermal binary plant that uses a simple Organic Rankine Cycle. Four resources were studied spanning the range of 265 degrees F to 375 degrees F. A variety of isobutane andpropane based mixtures, in addition to pure fluids, were used as working fluids. This study shows that the use of propane mixtures at a 265 degrees F resource can reduce the LEC by 24% when compared to a base case value that utilizes commercial isobutane as its working fluid. The cost savings drop to 6% for a 375 degrees F resource, where an isobutane mixture is favored. Supercritical cycleswere found to have the lowest cost at all resources.
Original languageAmerican English
Number of pages9
StatePublished - 1998
EventGeothermal Resources Council 1998 - San Diego, California
Duration: 20 Sep 199823 Sep 1998


ConferenceGeothermal Resources Council 1998
CitySan Diego, California

NREL Publication Number

  • NREL/CP-550-26209


  • cast
  • cycle analysis simulation tool
  • isobutane
  • organic Rankine cycle (ORC)
  • thermal power plants
  • thermodynamic cycle analyses


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