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Medium-Temperature Stirling Technology

Over the last decades mainstream Stirling development has been focusing on high-temperature (>800°C) and high-frequency (>50Hz) engines in order to achieve good efficiencies.

BSR Solar Technologies GmbH is pursuing a radically different approach with the development of medium-temperature (200°C to 500°C), low-pressure (about 10 bar) and low-frequency (0.5 to 5 Hz) Stirling engines. Due to this relatively low temperature/pressure/frequency constellation, the percentage of the ideal Carnot efficiency achieved for a given temperature difference is much higher than that realized by high-temperature Stirling engines. For temperatures of 300°C (and 30°C on the cold side) the ideal Carnot efficiency is about 48% of which 75% is realized by SUNPULSE^TM engines, that is 36% (see graph below). This equals the value achieved by conventional Stirling engines at a temperature of 800°C and higher.

BSRsolar's medium-temperature Stirling technology brings very favorable economics to the design and construction of Stirling engines. In conventional high-temperature Stirling engines the displacer and the piston are synchronized. To maintain a momentum of both at all times, costly crankshafts, heavy flywheels and other devices are necessary for temporary storage of mechanical energy. In addition, they need very expensive material.

With the introduction of an innovative Stirling valve the SUNPULSE^TM technology decouples the movement of the displacer and the power piston, thus making crankshafts or flywheels superfluous. The phase between displacer and power piston is variable and adjusts automatically to the respective pressure/frequency constellation of the total system. The engine adjusts optimally to varying energy supply levels of the system and changes in mechanical performance can be accommodated for short intervals.

For a detailed description of BSRsolar's Stirling technology, please click here.