4th Quarter 2011Electrical switching & drive systems & components
The Spanish company Mecasolar is a major supplier of high-tech solar tracking units. These align photovoltaic systems to the movement of the sun and can increase the yield of photovoltaic solar energy by more than 35%. The two-axis tracking system is controlled by Simatic S7-1200 CPUs from Siemens.
Rotating and tilting to ccordinates
The course of the sun changes constantly and is different everywhere in the world. The Simatic S7-1200 controllers enable the tracker not only to simulate the movement of the sun but also to adapt to climatic conditions, as well as allowing remote control. Astronomical information is converted into individually parameterisable control programs for any location in the world.
The controllers determine the optimum radiation coordinates on a daily basis so that the photovoltaic modules can follow the course of the sun and the sun’s rays always hit the surface of the modules at an angle which allows maximum conversion of the radiation.
When the incident angle is very flat and the shadow cast is long, as in the mornings and evenings, the controller automatically moves the modules into tilted position so that the modules do not cast shadows on each other and the efficiency stays as high as possible. At night, the panels adopt an almost horizontal position. The panels are immediately moved to a safe position in storms. This is all taken care of by the control program.
The photovoltaic modules are tilted azimuthally (vertically) and zenithally (horizontally) in relation to the sun. The azimuthal movement is performed by a gear rim which turns the complete carrier plate from east to west once a day. The second zenithal movement is made by a threaded rod or rack which tilts the carrier plate towards the sun.
All weather conditions
The PLC programming enables the tracking units to respond to all weather conditions. The solar panels can withstand wind speeds of up to 130 km/h, and a vertical position can be programmed for wind speeds up to 70 km/h. Both carrier axes are moved by 3-phase current motors. Every tracking system has its own PLC controller and an independent electrical switching system.
Automatic tracking with SIMATIC S7-1200
Parameters such as longitude, latitude and time are required to compute the necessary angle of inclination of the sun vector (azimuth-zenith) in short cycle times and to control the movements of the trackers. The position of the sun is determined exactly by an astronomical algorithm stored in every CPU and run from a Simatic library. The library outputs nominal values for controlling the motors which move each carrier plate. Accurate data for the various astronomical and geographical parameters can be saved in the control program for a broad time span with minimum uncertainty.
All the tracker movements of the solar park are visualised and monitored centrally with an OPC Server WinCC in a central station. The Simatic Library offers efficient engineering support for the Simatic.Net OPC Server WinCC visualisation system for this purpose.
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