In TaiyangNews’s 1st Solar Tracker survey we’ve also looked at their tools to control the tracking.  All drive system components are activated by a control and communication system. Solar trackers are mostly equipped with a programmable logic controller (PLC), which is driving the motors of the solar tracker to an optimal position depending on the actual irradiation and weather conditions. The PLC can use inputs from several sensors such as GPS receiver, an inclinometer, a GMT clock, irradiation and wind sensors, PV inverters to determine the optimal position in closed-loop or open-loop control algorithm.
Closed-loop controls, also called feedback controllers, use solar sensors or the inverter output to determine the sun’s position. The input data from the sensors come into the controller unit, which drives the motors and actuators to position the tracker. The majority of the participants in our market survey offer closed-loop control systems. Four companies offer artificial intelligence (AI) based controllers to allow for self-learning control routines. In this case, trackers can calculate the optimal tilt angle for various weather conditions and terrains, which results in increase of a system’s bifacial gain by differentiating between overcast skies and few scattered clouds. Four of 19 companies in our survey, Arctech, GameChange, PVH and TrinaTracker have equipped their solar trackers with AI-based controllers.
Open-loop control systems use a microcontroller and do not need any sensors to detect the sun’s position. The sun’s path is predicted by astronomic relationships programmed in a microprocessor which calculates the sun’s position at any time. Some devices use for accurate tracking a solar map, which depending on the location gives information on where the sun is at different times of day throughout the year. This is solution used by Ideematec, Mechatron, Big Sun Energy, Nexans and STI. Furthermore, some tracker suppliers, such as Schletter, use GPS signals to determine the tracker’s latitude and longitude, as well as the date and time. With this information, the tracker will know the position of the sun for any given time and orient itself to face the sun. The tracker will be facing the sun even during cloudy periods; and when the clouds part the tracker will already be positioned to maximize power production without any delays to reposition itself.
Some trackers use both, sensors and a solar map; when the weather is sunny, the sensors are used to track the sun and during cloudy days, the information from the solar map is used. In order to maximize the energy yield, shading should be obviously avoided. However, sometimes a shadow-free module position might not be optimal in terms of module sun alignment. Some solar tracker manufacturers use smart control algorithms to detect when tracker self-shading between the module rows occur and update the current rotation angle for eliminate shading by module alignment for maximized solar generated electricity yield. This is the so-called backtracking, which is implemented by almost all participants in our survey.
Solar trackers integrate either active or passive mechanisms to reduce the impact of high wind and snow loads as well as hailstorms. In such extreme weather conditions, the trackers move from the operational to a more favourable stow position. Ideally, the stow position is not the same for all extreme weather conditions. As an example, 0° stow position, which is advantageous for reducing the sailing effect at high-wind speeds might lead to module damages in case of hailstorms. Just a few tracker suppliers offer different stowing strategies for different potential weather risks.
The text is an excerpt from the TaiyangNews Report Solar Trackers: First Comprehensive Technology Overview with Product Specs For A Key Component With Increasing Share In Utility-Scale Solar Power Plants – The TaiyangNews Market Survey Report can be downloaded for free here.
A comprehensive overview on Solar Trackers  was provided by Dr Olga Papathanasiou, TaiyangNews, during the TaiyangNews Solar Tracker Conference; the recording can be viewed here.