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By aiming a solar generating source at the sun throughout the solar day, tracking systems increase energy harvest more than any other BOS components. Given their highly prominent role in squeezing as many usable electrons out of a group of solar panels as possible, why do some solar integrators, financiers and developers shy away from specifying tracker systems? Why do some consider trackers obsolete and prime candidates for the cost-chopping guillotine on the race to grid parity?
Trackers beautifully illustrate human ingenuity and applications engineering. A solar tracker can elegantly remove a significant constraint on a PV panel’s ability to capture light and convert it to electricity. So what is the deal? Are the naysayer’s arguments valid or just a case of efficiency envy? Are trackers the best answer for large ground-mounted PV arrays? The answer is fairly common in the dynamic and diverse solar industry—it depends.
My goal here is to help demystify trackers for on-site power generation. Because print resources on this subject are limited, I interviewed many industry subject matter experts and share their insights along with my own. The pros and cons of tracking systems must be communicated transparently. This requires realistic cost and performance numbers. At the same time, customers need guidance to understand site-specific requirements. When this due diligence is not followed, the results can be embarrassing. Tobin Booth, president and CEO of Blue Oak Energy, cautions: “Be aware that trackers may become fixed-tilt arrays before you are finished with the design.” However, diligence in matters regarding site-specific requirements ensures that viable projects move forward from concept to completion, which is the best way to further the acceptance of trackers throughout the solar industry.
Solar trackers have been around for almost 50 years. Steve Baer, a founder and former president of Zomeworks, says he built his first passive tracker in 1968. “We only began manufacturing passive trackers for sale in the late 1970s, when we figured Willard Geer’s patent on the idea had expired.” Track Rack, still in production today, is a nonmotorized pole-top tracker that uses refrigerant and aluminum channel reflectors to shift PV panels toward the sun. In the 1980s, Array Technologies—which, like Zomeworks, is based in Albuquerque, New Mexico—began offering closedloop, optically controlled Wattsun solar trackers that are still produced today.
Before the US grid-tied PV market developed, the Track Rack and Wattsun products were primarily sold to the residential off-grid market where trackers were a particularly good match for summer peak loads. Baer points to stock watering as an example: “A tracker enables greater use of a pump, well and water trough.” As described by Wattsun founder Ron Corio in Solar Cells and Their Applications (see Publications), in the 1980s and 1990s the evolution of the PV tracker market “exhibited slow but steady growth.”
The first large-scale solar trackers were built in 1983 on the Carrizo Plains in California. (This happens to be the same area chosen more recently by industry behemoths First Solar and SunPower for 750 MW of proposed solar power plants.) In 1977, ARCO Solar began manufacturing solar panels in response to the oil and energy crisis. A few years later, ARCO leased land on the Carrizo Plains and assembled two intricately designed and controlled dual-axis tracker PV power plants, totaling 5.2 MW. However, power from these plants was sold to the grid at a mere $0.04 per kilowatt-hour. Since the plants were not economically viable, they were eventually sold off and disassembled.
New tracker design for PV power plants stagnated during most of the Reagan era. As the solar market started its phoenix-like rise in the 1990s, a few tracker products came to market. Early 1990s designs lacked the standardization, reliability and, most importantly, the cost structure to be implemented on a large scale. Solar economics were (and still are) driven by the nature of various subsidy programs. Prevalent programs in the 1990s were based on system peak ratings (kWp) and not performance (kWh), so the increased capital investment for a tracker design made less financial sense.
This all changed in Germany during the late 1990s. A grassroots effort towards energy independence spurred the creation of the Renewable Energy Sources Act. This landmark policy eventually highlighted a feed-in-tariff (FIT) program, a highly effective policy framework for accelerating the deployment of renewable energy. The key to its success is that a FIT provides a guaranteed financial return on investment based on the sale of energy to the utility grid.