kubler articles

Sensors For Solar Thermal Plants

Kubler 1/1/2014

Sensors For Solar Thermal PlantsConstant growth can be observed in the solar branch essentially in the area of solar thermal plants. CSP - Concentrated Solar Power is a key technology in the area of alternative energy generation that achieves its full potential in sunny regions. Today, solar thermal plants are installed mainly in Europe and in the USA, reaching a total power of about 5 GW.

A quick increase is expected in the coming years, especially in India and in the Middle East countries. In 2020, solar thermal plants with a power exceeding 25 GW will be installed. Various technologies such as the tower system using heliostats, the parabolic trough system and the Fresnel system are equipped with Kubler sensors. With their accuracy, robustness and long service life, these sensors ensure optimal plant efficiency.

Requirements for Sensors

Solar power plants manufacturers place high demands on the sensor manufacturers. Despite extreme weather conditions, sensors must ensure reliability and long service life. Accurate sensors allow an exact positioning of the mirrors, ensuring a maximum efficiency of the plant. The sensors must nevertheless remain cost-effective, as the plant manufacturers are under cost pressure.

Encoders with Competence in Solar Technology

Kubler's Sendix encoders stand for highest reliability and service life. With their robust design (die-cast zinc housing) for a wide temperature range (from -40°C up to 85°C) and their high protection level (IP67), they are particularly suitable for outdoor applications. This technology furthermore protects them against faulty installation.

Optical accuracy is guaranteed; a resolution reaching 5000 imp/rev. for incremental encoders and a resolution reaching 17 bits singleturn and 24 bits multiturn for absolute encoders are available. The Intelligent Scan Technology is the answer for fundamental trends in automation: cost-efficiency, robustness and accuracy.

Elevation and Azimuth Adjustment for Heliostats

In tower systems equipped with heliostats, individually controlled mirrors concentrate the sunlight on a tower housing an absorber. A heat transfer fluid or molten salt heated in the absorber is used to produce steam that generates electricity in a turbine generator.

The efficiency of the system depends mainly on the elevation and azimuth positioning accuracy of the heliostats. This highaccuracy positioning is guaranteed by the used incremental and absolute Sendix encoders. 
Highest adjustment accuracy of the individual mirrors, exceeding 0.05°, is required. This has been achieved within short time in a 50 MW solar tower project in South Africa.

Adjustment of the Angular Position of Parabolic Trough Systems

The curved surface of a parabolic mirror concentrates the solar energy on a receiving pipe located in the focal line. This energy heats up a heat transfer fluid circulating in the pipe and generating electricity with a steam generator. With this technology, focus is set on a simple, robust and flexible measuring system rather than on accurate positioning.

This is due to the fact that the pipe to heat is located close to the mirror. This application uses sturdy absolute magnetic Sendix encoders with a singleturn resolution reaching 12 bits. In case of applications offering restricted installation space, the incremental linear measuring system Limes with customerspecific magnetic tapes is the solution.

The sensor head is made of a particularly sturdy aluminium housing with the maximum protection level of IP69. The sensor has to resist the local climatic conditions of the desert site, as in India, with heat or sandstorms. Simple installation and flexible operation are ensured by the Kubler IS inclinometers. Thanks to they extremely compact and robust design, they are suitable for restricted installation space. The IS inclinometers feature zero point setting, a measuring range reaching 360° and various interfaces such as for example CANopen.

Solutions through Cooperation - Everything from one Source

The construction of a Fresnel plant is very simple: a steel frame carries flat primary mirrors arranged in rows behind one another. The absorber pipe is located at a height of few metres above the primary mirrors. This height is about 50 metres in the case of a current customer project. This application requires first of all high mirror positioning accuracy; otherwise, the efficiency of the plant would be drastically reduced.

In this example, the demand is: highest mirror positioning accuracy < 0.01°. The standard high accuracy of the Sendix F36 absolute encoder has been optimised thanks to the collaboration with a cooperation partner from the drives branch. This collaboration led to a both highly accurate and cost-efficient drive system - the comprehensive solution for the customer.