Invited Talk: Reaching Beyond 1’500°C with the Synhelion Absorbing Gas Solar Receiver: Results of Experimental Campaign

We report about the development and testing of a novel high-temperature solar receiver for generating process heat beyond 1’500°C. The receiver operation principle is similar to the “greenhouse effect” and exploits the ability of molecular gases such as water vapor and carbon dioxide to absorb a significant fraction of longer wavelength thermal radiation while being mostly transparent to terrestrial solar radiation. The receiver is constituted by an absorbing cavity with a windowed aperture. The cavity is filled with a streaming participating gas flowing from the aperture towards the back of the cavity. The incoming solar radiation enters the aperture, passes with minimal absorption through the gas, and is successively absorbed by the black surfaces of the cavity. The surfaces in turn thermalize and re-radiate with a blackbody spectrum. The gas absorbs to a large extent the thermal re-emission and is heated up, acting as heat transfer fluid (HTF). At the same time, the gas shields the aperture from the re-emission [1]. The left side of Figure 1 depicts schematically the system. The receiver works with radiation only as heat transfer mechanism and does not require, a priori, any convective contribution.
To assess the potential of the approach we modelled the system with the most accurate method available, spectral line-by-line photon Monte Carlo raytracing (MC-LBL) with the absorption coefficients derived from the HITEMP 2010 spectroscopic database [1]. With a solar irradiation flux of 1’200 kW/m2 at the aperture and a gas inlet temperature of 1’000 K, the receiver efficiency (defined as the ratio of thermal power absorbed by the HTF to the solar power incident on the receiver aperture) remained above 80% for gas outlet temperatures up to 1’800 K for receivers operated with steam [1].
To demonstrate in practice the system capabilities and to validate the models developed we built a large 250 kW input power receiver prototype operating with steam. The cylindrical cavity of the receiver prototype had an internal diameter of 0.8 m and a clear aperture diameter of 0.56 m. We tested the setup between summer 2019 and spring 2020 at DLR’s Synlight solar simulator facility. The system was operated “on-lamp” for almost 150 hours. Steam outlet temperatures in excess of 1’550°C were reached. The system after test is shown on the right side in Figure 1.

Fig. 1: (Left) Schematic illustration of the Synhelion absorbing gas receiver. (Right) Photograph of the receiver front taken after testing.

References
[1] G. Ambrosetti and P. Good, A novel approach to high temperature solar receivers with an absorbing gas as heat transfer fluid and reduced radiative losses. Solar Energy 183, 521–531 (2019).