Small scale organic Rankine cycle for solar applications

Lombard, H. J. ; Dobson, Robert Thomas (2015)


The global demand for energy has risen dramatically in recent years and the cost of electricity has risen considerably. Local electricity sales prices followed the global trend, increasing by an average of 25% per annum from 2008 to 2014. This upward trend has opened the market for new technologies, such as renewable energy alternatives, better use of waste streams and low temperature power generation. The Organic Rankine Cycle is an example of a low temperature power generation cycle that can utilize a renewably energy source or recover waste heat. The Organic Rankine Cycle is in essence a Rankine Cycle that employs a different working fluid than water. The primary objective was to build a functioning ORC. The cycle utilized a low temperature (< 120°C) and pressure heat source to generate electricity. This temperature is easy achieved using solar collectors which will make the system suitable to operate using solar radiation as a heat source. To meet the temperature, pressure and global warming potential requirements, refrigerant R123 is used as a working fluid. The system consisted of a rotary vane pump, some plate heat exchangers, a scroll expander and a natural convection condenser. The scroll expander was a modified Copeland scroll compressor. The system demonstrated a cycle efficiency of 13% compared to the Carnot cycle efficiency of 25% and a modified Carnot efficiency of 14%. Due to excessive heat loss and poor conversion from mechanical to electrical energy the electrical output was 40 W. The conversion efficiency could be greatly improved if the electric generator was changed to a DC generator.

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