The high-flux solar furnace and the xenon high-flux solar simulator are used for exploration and testing new technologies with concentrated sunlight and artificial light, whereat irradiances of up to 5 MW/m² and temperatures of above 2000 °C are possible to achieve.
The term solar furnace denotes a facility that allocates concentrated solar radiation. The energy of the concentrated solar light can be utilized to induce thermal or photonic effects on irradiated materials. Moreover, the xenon-high-flux emitter is considered to be a solar simulator and delivers quite similar radiant conditions as the solar furnace.
Since the start-up of the solar furnace operation in 1994 about 160 experimental campaigns have been carried out, reaching from the production of hydrogen to the implementation of tests under space-like conditions. The solar furnace laboratory building is constructed according to the low energy architectural rules.
Field of Application
The solar furnace and the high flux solar simulator give manifold opportunities to researchers and users in science and industry to develop and qualify sustainable procedures in which concentrated sunlight is crucial for the technical application. These procedures target the chemical storage of solar energy and the application in chemo-technical and metallurgical high-temperature processes. Moreover, irradiation of a wide variety of materials can be conducted under special conditions such as high vacuum down to 10-5 mbar.
Design of the Solar Furnace
The sunlight is reflected by a flat mirror (heliostat) onto a concentrator. The irradiation is turned out of the optical main axis and is focused in an experimental area of the solar furnace laboratory building. The total radiant power of up to 25 kW sums up to a flux density of 5 MW/m².The flux of the incoming, concentrated irradiation is adjusted by a shutter, thus the irradiation reaching the target can be controlled very accurately. This alignment is called off-axis and has the advantage that the focal point does not shadow the experimental set-up as it would be with on-axis geometry.
The heliostat is a plane mirror with an area of 57 m² that was originally used as one of 30 test series heliostats in a solar power tower in Almeria, Spain. It was modified for the DLR solar furnace, now tracking the sun, thus reflecting the incident solar radiation on the concentrator. The mirrors are made of float glass with a reflective layer of silver that is fixed on the back side because of the unavoidable weather conditions. In addition, the front side is coated with titanium oxide to guarantee the reflection of the UV spectrum of the solar radiation.
A Fresnel array of 159 hexagonal spherical mirrors concentrate the sun radiation into the laboratory building, where it can be directed to a test object. The total area of the concentrator is 42 m², its average focal length is 7.3 m, and the individual mirrors have an edge length of 32 cm. The concentrator mirrors are coated with aluminum on the front side and are protected by a vapor-deposited silicon oxide layer against weather impact.
A shutter at the entrance to the laboratory building is used for adjusting the concentrated solar radiation. Within 0.02s, the incident radiation can be varied from 0 to 100%. Despite the position of the shutter of about 1 m before the focal point it is exposed to considerable thermal stress. The irradiance here is already about 55-times higher than the plain solar radiation. The shutter may achieve temperatures of up to 300°C and is therefore coated with a heat-resistant paint.
Design of the Xenon High-Power Emitter
A high flux solar simulator based on elliptical reflectors with xenon short-arc lamps complement the solar furnace in times of low radiation and for long-term experiments. The emitted radiation is feasible for a wide field of applications. The radiant power of 20 kW is pointed on a target area of about 100cm² at a distance of 3m with an irradiance greater than 4.1 MW/m².Beyond the means of the solar furnace, it is possible to carry out experiments of several days duration under very stable radiant conditions and component tests on certification level.
The laboratory building of the solar furnace includes a test room to perform the experiments, a control room for the management and operation of the experiment, and a workshop to prepare the works and the test set-ups. In addition, the experimenters have access to chemical and material laboratories.
The experimental set-ups are installed in the test room on a positioning table in order to place them in the focus of the concentrated solar radiation. An extensive data acquisition system allows the control and analysis of the experiments; for example temperatures, voltages, cooling water flows and other signals can be visualized and recorded.For the non-contact measurement of high temperatures pyrometers and infrared camera systems are used. In addition, radiation flux density measurement systems provide information on the incident power that is exposed on the experiment. Moreover, the experimenters have different vacuum test facilities available that can be used to work under space-like conditions (see link on the right hand side).
Focus Solar Chemistry
The aim of the work in the field of solar chemistry is to identify and to qualify technically feasible solutions for the application of solar radiation in the chemical processing industries:
Focus Solar Materials
In comparison to the use of conventional resistance heating, induction furnaces, or the use of lasers for materials research, the use of a solar furnace offers significant advantages that have to be exploited. For special applications, simplification of material testing procedures, rapid heating and cooling rates improved material properties and material surfaces can be expected, when high temperatures and oxidizing environments are required:
Temperatures of up to 2,770 K possible
Information on high-power emitter
Solar Furnace and Laboratory measuring technique
A reasonable use of the solar furnace for scientific or technological experiments is inextricably linked to a powerful measurement technique. Some solar-typical problems in the measurement of temperatures and irradiances cannot be solved with standard methods or devices. Also, specially trained personnel and specially developed techniques are required.In order to optimize these techniques to accurately determine the important parameters, such as flux density distribution and temperature, the solar furnace has its own optical laboratory. There, for example the properties of measuring cameras, imaging systems and other detectors are tested and sample structures for new measurement methods are checked. Not least, because of these benefits in terms of measurement equipment and development, the solar furnace of the DLR enjoys an excellent international reputation and international recognition. A detailed listing of the instruments may be found in the download area.
The Solar Furnace is located on the site of the DLR in Cologne; Linder Höhe, 51147 Köln.