Solar thermal power station powered by SIKO GmbH

Optimal utilisation of solar energy

SIKO GmbH: Since the subsidies for new photovoltaic installations on rooftops and open areas were recently severely curtailed or abolished by some governments, taking a closer look at thermal solar power plants is all the more promising for companies in the solar sector. The technology of heat recovery from solar radiation can be realized in the form of large arrays, in particularly sunny areas, in quite a profitable manner. The available solar energy is optimally utilised here when the solar collectors flexibly adapt to the position of the sun. SIKO GmbH offers magnetic measuring systems that help catch each beam of sunlight.

Fig. 2: Solar collector with SIKO feedback system at solar power station Manchasol, Spain Application image

SIKO GmbH manufactures innovative length and angle measurement systems for a wide variety of applications. Solar thermal power stations utilize a measurement system that belongs to the MagLine product group. These sensors work according to the magnetic measuring principle completely without physical contact.

Magnetic instead of mechanical

Magnetic measurement devices increasingly replace mechanical systems and are used to record linear and radial positions, angle values and revolutions. A magnetic band solidly mounted to the respective machine represents the core element of such a measurement system. This magnetic band is equipped with a code which is scanned by a magnetic sensor during the measurement - completely without physical contact - and the location of the band is thus determined. The integrated electronics then calculates the path or angle information and makes it available either as absolute value or incremental signals.

"Because of the contactless process of the measurement no wear occurs whatsoever on our devices", summarizes Andreas Wiessler, MagLine department manager of SIKO GmbH. This saves maintenance and replacement costs and makes the measurement systems particularly economic and profitable.

Two different system types

The magnetic measuring systems of the MagLine product group are divided into two categories: incremental or absolute. The incremental system requires an absolute reference point. The mirrors must therefore first be moved as far as they will go and referenced there. With the absolute system, by contrast, the current position value is stored "absolute" at each point in the coded magnetic tape and is therefore immediately available again after switching on the system.

Capturing the beams of sunlight

In solar-thermal power stations, the MagLine sensors measure the angle of the reflectors thus providing the downstream control system with the required position message, that is, the actual value. The required angles (= set value) are stored in the controller according to the time of day and thus the position of the sun. The collectors can assume any position, thereby following the movement of the sun in an ideal manner.

The result of the measurement is available in real time and is very precise up to 10 µm. SIKO sensors are distinguished by their high system and repeat accuracy. The mirrors can therefore be aligned quickly and dynamically with the position of the sun and capture as much solar heat as possible. The direct radiation of the sun is then reflected by the collectors to so-called absorbers where it is bundled and absorbed.

Generating power with mirrors

The two most advanced power station systems are solar towers and parabolic trough power plants. The latter utilise curved through-type mirrors to bundle the sunlight onto an absorber tube which runs along their centre. Because of the shape of the mirrors the sun shines 30 to 60 times stronger on the tube than normally. The concentrated energy heats a liquid heat transfer medium running through the tube. This liquid is used to generate steam which, in turn, powers a turbine. Power is thus generated via an electric generator.

Solar towers, by contrast, function with thousands of individual concave mirrors reflecting the sunrays onto a central absorber on a tall tower. The absorber, again, concentrates the solar heat onto a liquid heat transfer medium.

SIKO measurement systems in Spain

SIKO measurement systems are suitable for both types of power stations. "Our devices are already employed in several parabolic trough power plants in Spain providing optimal alignment of the solar collectors", reports Andreas Wiessler. The power stations Extresol, located in the Extremadura, as well as Manchasol in the Castile region use approx. 2500 MSK5000 sensors. The MSK5000 is a contactless measuring sensor with integrated evaluation module and a digital signal output. In combination with the magnetic band MB500, it forms an open measuring system with very high resolution.

SIKO magnetic sensors are also used in the Sonova power stations near Seville:magnetic sensors -in this case approx.1100 units of the type MSK320. This sensor is also equipped with an evaluation module as well as a direct, digital signal output and is used in combination with the magnetic band MB320.

Andreas Wiessler explains: "The magnetic bands can be installed very easily by gluing and are solidly joined with a steel carrier strip."

Application under difficult conditions

Because of the demand for many sunny days, solar thermal plants are primarily located in warm regions such as Spain or Australia and in the Californian desert. The measuring devices from SIKO GmbH are optimally equipped for the challenging climates: temperatures up to 70 °C pose no problems. In addition, because of their compact design, the measuring systems are extremely robust against shocks or vibration as well as impervious to sand; another key criterion for use in desert areas. Apart from the compact design, which gives the device a small practical footprint, its simple handling contributes to the renown of SIKO measurement systems as optimal solution for difficult applications. "We continuously develop our devices to reflect the state of the art in (measurement) technology and are always on the lookout for challenging applications, in this case, in the solar sector", explains Andreas Wiessler.

Info box:

SIKO GmbH in Buchenbach was founded in 1963 by Dr. Ing. G. Wandres and is now headed by Dipl. Ing. Horst Wandres. The company develops and manufactures mechanical and electronic angle and position measuring devices; the company considers itself to be the market leader in the mechanical digital display product group. Magnetic length measuring systems, handwheels with position indicators, incremental encoders and absolute encoders are just as much part of the programme as electronic displays and geared potentiometers. Wire-actuated encoders complement the product offering. Users can be found in the whole field of machine construction; with the manufacturers of wood, glass and sheet metal processing machines, in textile and printing machines as well as in packaging devices and machine tools.