Parabolic trough collectors for industrial process heat
Sheep graze next to parabolic trough collectors on the collector field in Turnhout, which supply process heat at up to 400 °C to the Avery Dennison chemical plant.
Various technologies are available for generating solar thermal heat with concentrating collectors. Linear concentrating collectors such as parabolic troughs are well suited for use in industrial processes up to 400 degrees Celsius and heating networks. Higher temperatures, such as those required in metal processing, can be provided by solar towers.
Parabolic troughs have elongated, curved reflectors that concentrate sunlight onto an absorber pipe along the focal line. A heat transfer medium circulates in this pipe, which is heated to high temperatures by the concentrated solar radiation. Water or oil are used as working fluids, or saturated steam is generated directly in the solar field. At the commercial scale, parabolic trough collectors are the most well-established technology among concentrating solar process heat systems. They achieve operating temperatures ranging from 80 to 400 degrees Celsius.
Linear Fresnel reflectors (LFR) consist of several flat mirrors set up on the ground and arranged at specific angles to concentrate sunlight onto a receiver above. Compared with parabolic trough collectors, linear Fresnel reflector (LFR) systems exhibit significantly lower efficiency. Their fixed receiver tubes are intended to reduce manufacturing costs. They also achieve operating temperatures ranging from 80 to 400 degrees Celsius.
Solar towers use a large number of computer-controlled mirrors (heliostats) that individually track the sun along two axes. This concentrates the sun's rays onto a central receiver at the top of the tower. Solar tower plants generally reach higher temperatures than parabolic trough or LFR systems. They reach operating temperatures of 500-1000 degrees Celsius.
Further information on the various technologies can be found at our Website.
Collector technologies
Illustration of various concentrating collector technologies.
Parabolic trough collectors are named after the parabolic curvature of their mirrors. This curvature enables the incoming solar radiation to be concentrated from every point of the mirror onto an absorber tube, thereby heating it. The absorber pipe is usually surrounded by a glass vacuum tube, which minimises heat loss. A heat transfer medium (for example water or thermal oil) flows through the absorber tube, absorbing the heat and transferring it to the consumer either directly or via a heat exchanger. Parabolic trough collectors are tracked towards the sun using a single-axis tracking mechanism, so that the mirrors follow the position of the sun. It is also possible to move the collector away from the sun using the tracking system, which allows the collector output to be regulated.
Parabolic trough collectors
Structure and function of parabolic trough collectors.
Compared to flat-plate collectors and vacuum tubes, linear concentrating collectors such as parabolic troughs can only utilise direct solar radiation. However, a parabolic trough collector compensates for this through its tracking system, which ensures that the sun is already at a favourable angle relative to the collector in the morning and evening during summer, as well as through its comparatively lower heat losses. As a result, the collector achieves similar annual yields even at an operating temperature of approximately 80 degrees Celsius. At higher operating temperatures, the parabolic trough achieves higher annual yields compared to the two non-concentrating technologies. This makes the use of parabolic trough collectors attractive even in Germany, where they are particularly suitable for use in heating networks and process heat.
Possible applications for parabolic troughs
Thanks to the different collector types and their controllability, parabolic troughs are very versatile and can cover a wide temperature range, which means they can be used in a variety of areas.
For electricity generation: A heat transfer fluid is heated using high temperatures, which can then drive turbines via steam generation. This works in a similar way to conventional power stations.
For the generation of industrial process heat: Many industrial processes (for example in the chemical, drinks or food production sectors) require heat in excess of 80 degrees Celsius. This heat can be provided by parabolic trough collectors, which can supply processes requiring temperatures of up to 400 degrees Celsius.
For heat supply: Heat generated by parabolic trough collectors can also be used in local and district heating networks, for example to heat buildings and neighbourhoods.
Contact
Dr.-Ing. Eckhard Lüpfert
Head of Concentrating Solar Technologies Department
