Array Tracking Systems for PV Power Plants
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IHS Technology’s “PV Balance of System Equipment Report—2015” forecasts 9 GW of single-axis tracker installations worldwide in 2019, with the US the largest market, accounting for 36% of global single-axis tracker installations. The projected growth in the deployment of systems using horizontal single-axis trackers has focused the attention of existing manufacturers that are scaling their technologies for multimegawatt tracked PV plants and influenced manufacturers that have historically offered fixed racking systems to dedicate resources to tracker technology acquisition and development. This article presents manufacturer and equipment profiles that provide insight into the backgrounds, products and development efforts of ten companies that offer single-axis or dual-axis trackers for utility-scale and large commercial applications.
Founded in 2008 by David Blittersdorf, AllEarth Solar is a privately held corporation headquartered in Williston, Vermont. Blittersdorf has a long history of entrepreneurship in the renewable energy industry and related fields. After receiving a mechanical engineering degree from the University of Vermont in 1981, he founded NRG Systems, a manufacturer of wind and solar resource assessment equipment. In 2004 Blittersdorf stepped down as CEO of NRG Systems to found AllEarth Renewables. Initially, the company’s focus was the development of residential and farm-scale wind turbines. However, the rapid decrease in PV module prices that was occurring at the time created a challenging market for grid-tied small-scale wind systems in the US. Due to these changing market dynamics, Blittersdorf decided to make a full-scale shift in AllEarth’s product focus and began developing dual-axis solar trackers in 2008. Five months later, AllEarth’s first tracker models were in production.
While integrators most often deploy AllEarth’s trackers in commercial and residential installations, they have also used the single-pole dual-axis tracker system in megawatt-scale projects, such as the 2.1 MW South Burlington Solar Farm commissioned in 2011 and the 2.2 MW Claire Solar Farm commissioned in October 2014. Both plants are located in South Burlington, Vermont. AllEarth served as the EPC firm for the Claire Solar Farm project and deployed 366 solar trackers on the site.
Unique aspects of the solar tracker include the way that AllEarth has designed all its components, with the exception of the pole, to fit on a single pallet, streamlining procurement and shipping. In addition, AllEarth typically packages the tracker as part of a pre-engineered system that includes modules, a string inverter and associated mounting hardware. AllEarth’s approach to distributed power processing, with a string inverter mounted to each tracker, is an early example of a shift toward decentralized power conditioning systems that utilize high-power string inverters rather than central inverters.
AllEarth trackers are compatible with precast or pour-in-place concrete, steel riser and helical pile foundations. The trackers are certified to ASCE 7–10 for 120 mph wind loads. A 180 W hydraulic motor drives a ring/worm gear yaw drive (azimuth) with a 360° movement range. A hydraulic cylinder automatically adjusts the tracker’s tilt from 0° to 60°. A GPS-based microprocessor controller regulates both tracking mechanisms (azimuth and tilt). To protect the tracker during high-wind events, the system relies on an anemometer sensor and associated algorithm that stows the array flat when wind speed reaches 30 mph. The system includes wireless communication and visualization software for tracker plant management. AllEarth manufactures its trackers in the US, and they carry a 10-year warranty.
Array Technologies (ATI) is a privately held company that has been manufacturing solar trackers in Albuquerque, New Mexico, since 1992. Its founder and CEO, Ron Corio, patented his first solar tracking system in 1990 while working for Wattsun. SolarPro’s publishing partner, Home Power, ran an early and very favorable review of Corio’s first dual-axis tracker in its October/November 1991 issue. The magazine’s publisher, Richard Perez, concluded, “I have never been excited enough by a PV tracker to install one in our system. The mechanical vagaries seemed to decrease the inherent reliability of the PV system. Wattsun has changed my mind. They have made a PV tracker we can rely on.” The reviewed tracker is still operational 26 years later (as are its eight Kyocera K51 modules).
ATI has continually evolved, redesigned and scaled its solar tracking equipment, systems and services in pace with the growth of the solar industry, especially with regard to the utility-scale PV plant market segment. Corio serves as the company’s chief engineer and is still actively involved in product engineering and development. Over the company’s history, ATI has delivered more than 4 GW of array tracking systems.
ATI currently offers single- and dual-axis DuraTrack pole-mounted trackers for residential and small commercial applications, as well as two models of DuraTrack single-axis horizontal trackers that are well suited to large residential and small commercial projects.
With a sharpened focus on multimegawatt utility-scale PV plants, ATI launched its third-generation DuraTrack HZ v3 horizontal single-axis tracker at Intersolar North America 2015 in San Francisco. The tracker features two-stage gearing and a flexible rotary drive shaft. Each 2 hp 3-phase 480 Vac motor can drive up to 28 rows of 80 c-Si modules each, with only two motors required per MWac. The DuraTrack HZ v3 minimizes driveline and module gaps to maximize array density and site utilization, while requiring half as many motors as the previous DuraTrack HZ v2.5 model.
The DuraTrack HZ v3 has an algorithm with a GPS input tracking method and a ±52° tracking range of motion with backtracking functionality. The system’s drivetrain has sealed gearboxes designed to be maintenance free for the life of the plant. The DuraTrack HZ v3 has a 135 mph 3-second gust exposure C (IBC 2012) allowable wind-load rating. A passive mechanical wind protection system that does not require power to operate protects the tracker during high-wind events and eliminates the maintenance requirements associated with active stow components.
Configurations for c-Si modules include one-up in portrait orientation, two-up in landscape orientation, and four-up in landscape for thin-film modules. To speed module deployment, ATI has developed a single-fastener module clamp with integrated grounding. The DuraTrack HZ v3 is certified to UL 2703 and to the UL 3703 standard for solar trackers. It has a 5-year parts-only warranty. A 10-year extended warranty is available.