In the Bindlacher Berg solar farm in Germany, the 229 solar systems track the sun fully automatically, resulting in an almost 30% improvement in yield for the solar power plant. The ‘trackers’ are controlled by individual controllers and the ‘Solar Tracking Toolbox’ from Siemens.
Its outstanding performance has made the Bindlacher Berg solar farm number three among the Germany’s photovoltaic plants. What has made this achievement possible is the fact that every one of the 229 systems installed on the 7,3 hectare site of a former military barracks can be individually aligned on two axes directly towards the sun.
The Bindlacher Berg solar power farm consists of a total of 229 dual-axis tracking units in three networked fields. The total output is around 2.4 megawatt peak (MWp).
With an overall output totaling 2,4 megawatt peak (MWp), the plant is able to supply up to 1 000 households, which is 30% more power compared to fixed installations. This increase in efficiency was made possible by the use of Simatic S7-1200 type programmable logic controllers from Siemens, the modular Solar Tracking Toolbox and cooperation with Gerlitz elektro-gmbh from Bayreuth as system integrator.
The Siemens Solar Tracking Toolbox is a collection of pre-assembled functions for tracking tasks, including the ‘backtracking’ system used to prevent solar modules placing each other in shadow when the sun is low in the sky, in other words, one tracker shading the one behind it, so reducing yield. The Simatic is designed for operating temperatures of between -20° and +60° C and is therefore suitable for use in on-site control boxes mounted on the trackers used all year round.
The selected PLC control module CPU 1212C is also powerful enough for online calculation of the necessary tracking guidance, based on a high-precision solar position algorithm (SPA) provided by the National Renewable Energy Laboratory (NREL) in the USA. This algorithm determines the sun's position with an accuracy of 0,0003 degrees over the next 6,000 years.
Performing the calculation in the respective controller allows the trackers to be commissioned and operated autonomously without any higher-level automation. By means of absolute value encoders connected to the Simatic by a communication module, the controllers recognise the position of the respective trackers, even after an interruption of the power supply, and can move them to the optimum position automatically after a restart. Configuration, project engineering and programming of the Simatic S7-1200 are all carried out using the TIA Portal. The same applies to the Simatic HMI Comfort Panel, which is used to observe the solar power plant from the “control center”.
The ‘head PC’ for the entire solar farm is a Simatic industrial PC IPC 427C. A standardised communication algorithm runs on the PC which polls the tracker controllers via several channels over an Ethernet link and visualises their operating status. Any error messages can be sent by email or SMS to freely definable recipients. Log-in from home is also possible over VPN and the WinCC-Option Sm@artServer.
Author: Gerhard Stauss