Comparison and analysis of performance using Low Temperature Power Cycles

Low Temperature Power Cycles have become increasingly interesting means of increasing energy efficiency of processes as well as for base load power generation from solar, and geothermal, heat. Theoretical understanding of the various processes, components and limitations is constantly increasing through extensive research. Practical utilisation of this knowledge is also increasing steadily though properly published field data is scarce. In this article a number of different solutions for power generation from low temperature heat sources have been gathered and analysed. Some of the studied units have not previously been described. A method for general evaluation of LTPC's is proposed and the outcome of the analysis is discussed as well as how to use it for practical purposes. By separating thermodynamic potential from irreversibilities the analysis indicates that the irreversibilities show limited dependency on temperature, size, thermodynamic cycle or working fluid. Instead performance of the studied units follows a relatively simple correlation with utilisation of the thermal potential. This correlation is defined and discussed. One conclusion is that the correlation allows for a possibility to express the maximum expected real power generation with knowledge of the characteristics of the heat source and heat sink only. ► We present field data from power generating units using low temperature heat. ► We explain how data from fundamentally different units can be compared. ► We describe a correlation between performance and utilisation of a heat source. ► We demonstrate a simplified method to estimate total power generation with information on heat source and sink only.