Trackers Optimize Yield of Utility-Scale Solar Plants

The utility-scale solar market is rapidly growing in North America, representing a large area of opportunity for project and product developers alike. The market more than doubled in size between 2012 and 2013 alone, propelling the solar racking and tracking sector to revenue of $8 billion. Analysts are projecting this strong growth to continue in the coming years.

Solar trackers—motorized structures that orient photovoltaic (PV) panels toward the sun throughout the day—in particular are an increasingly important aspect of utility-scale project development (Figure 1). With substantial research and development advancements in recent years, trackers are no longer cost prohibitive due to high manufacturing or operations and maintenance costs. For many utility-scale projects, trackers can significantly increase yield by optimizing the angle of incidence between a module and incoming solar rays.

1. The Langelé solar plant in France utilizes solar trackers. Solar trackers have been proven to increase plant production compared to fixed-tilt systems. Courtesy: Exosun

This article takes an in-depth look at the potential benefits of horizontal, single-axis solar trackers, the most commonly implemented tracker design, and examine the considerations installers face throughout the system design and construction processes.

“Tracking” Return on Investment

Solar trackers enable large-scale PV installations to better capture solar irradiance as the sun moves across the sky (Figure 2). Output gains will vary, depending on both project site and tracker technology, with higher-performing models achieving as much as a 25% performance increase compared to fixed-tilt systems.

2. A unique drive mechanism. The balanced design of Exosun horizontal single-axis solar trackers reduces stress on the motor and requires no maintenance. Courtesy: Exosun

Furthermore, utilities across the U.S. are increasingly implementing time-of-use (TOU) rate structures, where electricity prices rise during periods of peak demand—typically in the late afternoon hours. As seen in Figure 3—a case study from a PV system located in Chowchilla, Calif.—a tracker-equipped project will capture increased sunlight during peak use hours, leading to increased revenue and rates of return. Additionally, as electricity rates increase and TOU rates become a mandatory consideration in project financing contracts, trackers will become a system asset that helps secure financing.

3. Performance and price relationships. This graph shows energy yields during an average June day in comparison to time-of-use prices. Courtesy: Exosun

For systems under a power purchase agreement, irradiance is also a key factor, further providing reason for trackers to be integrated in systems to expedite return on investment.

Designing an Optimal System

Installers should be prepared to do their homework to find a tracker that offers the ideal combination of affordability, performance, and reliability. World-renowned certification bodies, from Underwriters Laboratories to the Canadian Standards Association, perform tests related to product safety, performance, and durability in extreme environments. The highest quality trackers on the market meet or exceed evaluation criteria in areas ranging from accelerated aging to wind resistance, and are fully compliant with safety-focused manufacturing codes. Strong product warranties also speak volumes to a tracker provider’s commitment to customers. If a PV system is expected to return dividends for a minimum of 25 years, its trackers should be held to those same standards of longevity.

Of course, smart system configuration is essential to achieving maximum performance. As with any ground-mounted project, site assessment begins with an evaluation of land size, cost, topography, and weather patterns. When evaluating whether trackers are right for a project, developers must weigh additional considerations.

An essential design aspect of tracker-equipped PV systems is ground cover ratio (GCR), which is the ratio between the PV modules’ area and the total ground area. An increase in GCR negatively affects system output (Figure 4). This is because the higher the GCR, the smaller the distance between the tables, thus increasing panel-on-panel shading. Unlike fixed-tilt systems, trackers with an integrated backtracking program can position tables to avoid shading adjacent panels.

4. Ground coverage ratio (GCR) affects performance more than panel orientation. Results are based on data from the Chowchilla, Calif., system. Courtesy: Exosun

Once we’ve selected the technology, site, and layout, it’s time for installation. The latest advanced trackers are far less cumbersome and complex to install than their predecessors. High-quality trackers offer a low-stress system, optimized for a fast and easy installation process. Modular designs also significantly decrease the amount of time, tools, and manpower required at a job site.

Seasonal Yield Variance

With a smart tracker system in place, PV plant developers and investors should expect to see immediate financial benefits. Figure 5 shows the annual performance of the PV plant in Chowchilla, comparing results with and without trackers installed. Fixed-tilt systems offer a minor performance advantage in the winter months, when the sun is low in the sky, because a fixed-tilt installation is always tilted toward the south. Single-axis trackers follow the movement of the sun throughout the day; therefore, tracker-equipped plants will achieve significant gains throughout the summer. In this particular case, the average annual production increase was 20.16%.

5. Summer gains offset winter losses. Increased output during summer months more than offsets lost production during the winter, resulting in a total yield increase with trackers. Courtesy: Exosun

Solar tracker technologies have come a long way in recent years. Today’s solutions offer the simplicity and reliability PV plant developers require, at a desirable price point. With the right tracker technology and an optimized implementation, installers can offer their customers a safe, long-term solar investment opportunity.

Jay Johnson is vice president of business development for Exosun Inc., a leading developer and supplier of solar tracking systems.