High-Precision PC-Based Solar Tracking

Embedded PCs, solar tracking algorithms and advanced EtherCAT network architectures are offering new control solutions for concentrated solar (CSV) tracking systems. Large solar installations that include 3,500 troughs and 30,000 dishes, for example, are making use of conventional control approaches much more difficult.

"The solar industry is still an emerging technology area especially with new systems that are the size of nuclear power plants. But with the size and complexity of these new systems, it's not just a matter of using old technology," says Ed Schultz, renewable energy business development manager for Beckhoff Automation. "Companies are primarily migrating their controls from what they knew in the past, but concentrated solar applications in particular pose a different set of challenges."

With a solar field that includes 3,500 troughs covering 200 acres, or 30,000 dishes in one field, the problem is how to effectively communicate with all of the devices. Typically, companies have been using PLCs for control, but now the question is how to communicate with 30,000 PLCs that all need to be in phase and synchronized, which worked for photovoltaic (PV) sites but not for more sophisticated concentrated solar applications.

"Communication with the solar fields is where EtherCAT technology provides an ability to talk to more than 65,000 different devices," says Schultz. "Using an embedded PC allows the integration of various wireless solutions and provides an array of options such as connectivity to weather stations based on groupings to sense the wind and other environmental conditions."

With large systems that communicate with a large number of PLCs, there is a need for some type of Ethernet communication tool. As is the case with most Ethernet approaches, each device requires an IP address and needs to be wired into a switch. That, in turn, creates a large need for processing power to communicate with the large number of devices.

"With EtherCAT technology, however, we don't need Ethernet IP addresses, switches, routers or hubs which lends itself extremely well to the solar industry," says Schultz.

Diagnostics is also a major problem for these large installations. EtherCAT allows the user to remotely pinpoint details on specific faults, and resolve issues remotely if possible. EtherCAT master technology and support for "hot connecting" simplifies the replacement of devices in the field and makes it possible to cut a line and keep the system running because of redundancy in the media. A user can specify one master and 300 slave devices, or use dual-master redundancy which requires an additional PLC so that if one embedded controller stops, the second controller maintains control.
Beckhoff has also released a TwinCAT solar position algorithm library for use in these systems. This function block facilitates the exact calculation of sun angles anywhere in the world at any time, without the use of sensors. This solution is targeting parabolic mirror and photovoltaic systems, as well as other solar power plant designs that automatically track the sun's position for optimum utilization of the sun's rays.

The control algorithm calculates the zenith and azimuth angles of the sun with a precision of A plus or minus 0.001 degree, and can also be used for other applications such as in building automation or with wind turbines for shadow flicker calculations.

For solar tracking applications, EtherCAT networking provides low microsecond level communication speeds, full connectivity to higher level systems and to IEEE 802.3 Ethernet-based infrastructure. It facilitates web-based remote maintenance capabilities, and is compatible with copper and/or fiber optic cabling at distances up to 20 km (12.4 mi) for single mode fiber optics or 2 km (1.2 mi) for multimode fiber optics. It permits flexible wiring and via line, tree, star and/or mixed topologies.