Solar Panel System Maker Uses Micro PLCs

Background
Local utilities often offer incentives for companies to generate their own power, sometimes paying 20 to 30 cents per kilowatt hour. In addition, to conserve limited resources, more and more companies are placing a premium on efficiently capturing and generating as much renewable energy as possible.

Patriot Solar Group PSG helps these end users reach their renewable-energy goals by providing the solar tracking, as well as solar tracking equipment needed to fuel this growing trend. One of the company's hero products is a solar tracker that automatically tilts photovoltaic panels to follow the sun wherever it goes.

An up-and-coming application of PSG's Solar tracker is utilized in an area that often goes to waste: flat-roofed car ports at schools, universities and large businesses. Car-ports equipped with a solar-panel control system do double duty. They protect the vehicles from the elements and collect energy – either to fuel electric cars parked below or to return power to the building's energy grid.

Challenge
Chasing the sun is a major challenge because it is a moving target. But the reward is substantial. Solar panels operated by automatic control systems can generate up to 30 percent more power than static panels.

To meet this challenge, PSG originally devised a system based on a proprietary black-box solution that many manufacturers still use today.

“In the past, we used sun-based sensors in a simplified box that sat on top of our trackers and worked by trying to follow the brightest part of the sky,” said Jeff Mathie, president at PSG. “The good news – the system was inexpensive; the bad news – it was unreliable.”

Cloud cover or competing reflective light confused the tracker, sending it off-course in a frantic search for the sun. In turn, the system not only failed to collect solar energy, but it also needlessly burned up its own power to run the motors, wearing down its equipment in the process.

Solutions
Recognizing the need for better technology, PSG's team met with a local Rockwell Automation representative who shed light on an alternative control system that virtually eliminated the downfalls of the previous black-box solution.

“We decided to work with Rockwell Automation because they make a leading programmable logic controller (PLC) in the U.S.,” Mathie said. “We knew we could trust them. Their products lend credibility to our systems because customers are already familiar with the name and the reliable components behind it.”

Each new PSG tracker comes equipped with the company's Sun Scout control system. The brain of the system is the Allen-Bradley® MicroLogix™ 1400 controller from Rockwell Automation. Instead of relying on the unpredictability of the weather, the controller uses software pre-programmed with data from National Renewable Energy Labs (NREL). This data automatically provides accurate information on exactly where the sun is – anywhere, anytime.

“Using programmable controllers for the solar industry is somewhat of a new concept, but anyone who knows drives will understand the logic behind them,” Mathie said. “Plus, the MicroLogix controller is a cost-effective, powerful controller that can fit into a small form factor, so coupling it with the preprogrammed software transforms the system into a ‘smart' application.”

To create further efficiencies and protect the system's hardware, the software also alerts the control system when the sun has set for the day. After 30 minutes of darkness, the PLC tells the system to shift into “stow” or “birdbath” mode, putting the panels in a protective position facing straight up at the sky. That way, they will not be damaged if high winds whip up at night. Likewise, if the controller detects gusts reaching 35 mph or higher during the day, the system will transition into protective mode. After a minute of winds under 35 mph passes, the Sun Scout system redeploys the trackers to resume their prime, sun-tracking positioning.

The control system resides in a completely sealed plastic box on top of the car-port next to the solar panels. The controllers communicate over an EtherNet/IP™ network, which provides reliable, high-speed communications.

The unit arrives on-site entirely integrated with preset controls including latitude and longitude information specific to its location. The end user only needs to enter the date and time of day before the system instantly starts autonomously tracking the sun with laser-sharp accuracy – regardless of external conditions.

Results
PSG's new system has dramatically streamlined system development and operation compared to its previous solar-tracking solution.

“We've moved leaps and bounds in terms of improving the overall quality of our products,” said Ed Stuart, director of sales at Patriot Solar Group. “We introduced the PLCs and shifted from hand-soldered solutions to factory settings. Other control systems use off-the-shelf controllers that look like they came out of Einstein's laboratory. It's nice to deliver a polished product that does what it is intended to do.”

One PLC can drive 500 feet of panels that can generate 110 kilowatts of power per hour in perfect sun conditions. Previous systems required one sun sensor per panel.

“The old sun sensors might appear cheaper up front, but the MicroLogix controllers are powerful little devices,” Mathie said. “By networking the PLCs, we can deploy them for multiple drive systems – much less expensive than our past approach.”

This next-generation system has proven so successful that PSG has already used it to retrofit 18 projects. Customers are especially eager for this solution once they hear about the long-term cost benefits. Furthermore, with minimized equipment wear and tear, the new controller extends product longevity.

“Partnering with Rockwell Automation has given us an advantage in the market because we now deliver one of the highest-quality systems at a comparably lower price,” Mathie said. “This is a significant advance in the solar industry – one that both small and large customers can capitalize on.”