A free-piston Stirling generator integrated with a parabolic trough collector for thermal-to-electric conversion of solar energy

Concentrated solar power (CSP) has attracted increasing attention as a renewable energy source with zero carbon emission. For efficient conversion of the externally concentrated heat, a suitable electric generator is crucial. In contrast to the currently widely used steam turbine, the free-piston Stirling electric generator (FPSG) features a flexible power range, high reliability, and zero water consumption. To date, most Stirling electric generators have been integrated with a parabolic dish concentrator in a dish-Stirling system. However, this configuration faces great difficulties in incorporating thermal energy storage or an auxiliary heating facility. To address this, a trough-Stirling concentrated solar power system, in which the parabolic dish concentrator is replaced with a parabolic trough collector (PTC), might be a good candidate. In this study, a free-piston Stirling electric generator integrated with a parabolic trough collector is constructed and tested for solar thermal power generation for the first time, and the performance of the generator and the overall system are experimentally investigated, with Therminol VP-1 being used as the circulating heat transfer fluid. The preliminary on-sun test results show that a maximum output electric power of 2008 W with a thermal-to-electric efficiency of 15% on the free-piston Stirling electric generator can be obtained at a heater head temperature of 300 °C, accompanied by a maximum overall efficiency of 3.0%. Loss analysis indicates that the dominant losses are the end loss and cosine loss of the parabolic trough collector, and that heat loss occurs in the heat collection elements and pipelines, thus providing indications as to where further improvements can be made.