Albuquerque, NM | 11/2/15 –
Michael Orshan, Director of Sales, Array Technologies, Inc.
As an industry we have accepted the benefits of using single-axis trackers in utility-scale solar power plants. There is now a clear understanding of the processes, technologies and risks associated with developing and building utility-scale power plants with solar trackers. But this wasn’t always the case.
Beginning around 2005 the tracker vs. fixed-tilt debate started for utility-scale solar plants. Was it better to stick with the well-known standard fixed-tilt option or switch to a lesser known technology to boost production? From the beginning, tracker maintenance was on the minds of project developers, owners and utilities everywhere. How often do these moving parts fail? How much does it cost per watt to service these systems over 30 years? The questions were plentiful. To address these fears, there was a tendency to overbuild tracking systems to appease the risk averse. Large trackers were often moved with oversized motors. Extra steel was added on the pilings and torque tubes. Gears were oversized. Module interface brackets were large and over designed while attachment methods were clumsy. An abundance of inclinometers, optical sensors and other components added complexity.
Reducing the number of components
Today, tracking systems are optimized to reduce component requirements – minimizing motors, controllers and sensors – and promoting a hands-off operations and maintenance approach. By using wind tunnels and other testing mechanisms, optimizing steel is down to a science. The arrays are simpler, easier to install and still protect against wind and other weather events over their 30-year design lives. Gears are smaller and more efficient, some are even sealed and lubricated for life. Sensors are compact, using modern SCADA and monitoring technology with larger command sets. Module interface brackets are sleek, simpler to install and often times do not require specialized tools.
Early on, nearly all trackers received power from the grid. Few arrays protected motors and controllers from surges. Two of the chief failure causes with early tracking systems turned out to be lightning strikes and installation mistakes. Today, mainly due to use of UL standards, tracker electronics are better designed and able to withstand years of inclement weather. When required, some fields even feature high current diodes to protect electronics from recurring lightning storms. Tracker controllers feature UL standard disconnect buttons to kill power in an emergency situation.
Cutting the switch
While single-axis trackers have come a long way in the last decade, there is always room for technological improvement and innovation. Electrical limit switches ensure a tracker cannot exceed its pre-determined range of motion. Limit switches are prone to improper installation or operator error that cause failures. In addition to this, if power to the site is interrupted, for example due to inclement weather in the area affecting the grid, limit switches are unable to function and the tracker may suffer damages. A limited number of modern trackers have eliminated the use of these switches using mechanical hard-stops located at each row, removing this complexity altogether.
Tracker maintenance is also at the forefront of every development and design discussion. Some trackers require the greasing of slew drives, actuators or motor units. Others have batteries that expire. The primary goal for a 30-year solar plant is to achieve the lowest maintenance possible. Some vendors are moving in this direction, while others are adding complexity that ultimately increases long-term maintenance.
Wind and inclement weather events also spark intense conversation. Many trackers have a wind sensor that forces an array to stow in a horizontal position at a certain wind speed. Most trackers on the market have an inclinometer that measures the angle of the modules to figure out where the modules should stow. An inclinometer requires an uninterrupted power source to function properly. If power is lost, trackers not designed to withstand severe weather events may suffer damage. A select few manufacturers eliminate these electronic components altogether and focus on designing their systems to each project’s wind load requirements. That way if power is lost at a remote power plant, the structural integrity of the tracker will not be compromised by inclement weather.
Ease of installation is another hot topic and provides more room for innovation. Setting up multiple motion devices such as motors and actuators can be tricky. Some tracking systems take time to align, others need a reference position, however more advanced systems have mechanical solutions to automatically calibrate rows and maintain accuracy. Another often overlooked piece of the tracking system is component kitting. Some manufacturers go through extensive assembly at the factory to make implementation intuitive as well as to allow installers to repurpose hours that would otherwise be used assembling nuts and bolts in the field. During the installation process various tracking products require specialized tools that are often cumbersome and difficult to obtain and maintain. The most optimized trackers are those designed to be installed using off-the-shelf tools sold at your nearest hardware store.
When building a solar power plant with solar trackers, stability and long-term reliability are key. With such large long-term investments on the table, solar project developers, owners and utilities alike need to be focused on reducing ownership cost and system complexity at every turn. Details matter and simplicity is critical to success.
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