The name SoCRatus stands for “Solar Concentrator with a Rectangular Flat Focus“. This test facility was developed for experimental studies with photocatalytic and photoelectrochemical systems under concentrated solar irradiation and was installed in 2012/2013.
The two-axis tracking concentrator consists of 22 planar mirror facets made of aluminium, which concentrate the incident solar irradiation in the focal plane. Owing to the special design of the concentrator, a uniform flux density distribution is achieved in a rectangular focal area of 2500 mm x 100 mm. Here, solar reactors such as suspension reactors or photoelectrochemical cells can be mounted and operated under homogenously concentrated solar irradiation.
The geometric concentration factor equals 20.2, and if necessary, this can be reduced by covering single facets. Respecting the solar-weighted hemispheric reflectance of the mirror material of 87%, solar radiation is concentrated by a factor of 17.5 when all facets are used. The hemispheric reflectance of the mirrors regarding the UV part (UV-A, UV-B) ranges from 80% to 90%. Thus, also a major part of the short-wave terrestrial solar radiation reaches the focal plane and solar reactors mounted there. Further specifications of the SoCRatus are:
The spectral irradiance in the focal plane is measured by a spectrometer in a wavelength range from 250 nm to 850 nm. Moreover, the direct normal irradiance is assessed by a pyrheliometer fixed on the concentrator support structure.
Four identical fluid cycles are available for the integration of reactors. In each one of these fluid cycles, a liquid containing water and an electrolyte – and if required also suspended photocatalytic particles as well as other substances – are transported from a tank to the reactors. In order to adjust the temperature, the mixture passes a heat exchanger, which is connected to a temperature controller with 5 kW heating and cooling power, before entering the reactor.
The product gas resulting from photocatalytic or photoelectrochemical reactions is separated from the liquid phase in the tank together with inert gas introduced to the system downstream the reactor. After sample gas conditioning the gas composition is analysed with respect to H2, O2, N2, CH4, CO and CO2 by micro gas-phase chromatographs. The activity of tested systems can be estimated by relating the quantity of product gases, particularly concerning hydrogen as a promising energy carrier, to the provided solar power with the assessed spectral characteristics.
In addition to the use of concentrated solar radiation in the focal plane, it is also possible to test reactors under non-concentrated solar irradiation. In this case, the reactors are mounted on the concentrator structure and tracked according to the demand (one-axis / two-axis) or held in a defined position.
The construction of the test facility was sponsored by the Federal Ministry of Education and Research of Germany within the scope of the project HyCats.