Think of solar panels and you're likely to envision them fixed in a single position. But the sun travels from east to west every day -- at least from the perspective of the Earth -- and also moves from north to south as the seasons change. And solar panels make the most electricity when they are positioned 90 degrees from incoming sunlight.

Solar trackers attempt to solve this problem. They follow the sun, so that the panels mounted on them can catch more rays and make more electricity. Companies claim trackers can increase solar arrays' efficiency by up to 40 percent in some regions. So as developers chase higher returns on their solar investments, trackers have been gaining popularity. Paula Mints, a principal analyst at Navigant Consulting, projects that tracking systems will be used in at least 85 percent of commercial installations with more than 1 megawatt (MW) of capacity between 2009 and 2012.

Several companies say they are seeing tracker growth. Miguel de Anquin, vice president of Premier Power, a solar installer in El Dorado Hills, Calif., says that about 70 percent of its ground-mounted commercial projects involve trackers today. That compares to only 20 to 30 percent of a far smaller pool of projects just four years ago, he says. (See image of the solar trackers at the West County Wastewater District implementation in Richmond, CA that were installed by Premier Power, below.)

And in Spain — which overtook Germany as the world's largest solar market last year — tracker projects went from making up an insignificant part of the market in 2006 to perhaps 25 to 30 percent of new projects in 2008, estimates Maria Lahuerta Antoune, international marketing manager for ADES, a Zaragoza, Spain-based tracker manufacturer. (Lead photo, top of page, shows an ADES installation in Spain.)

Policies Push Trackers

The companies attribute much of this growth to different government policies. In Spain, a feed-in tariff offering a high price for solar electricity sparked the market in 2007. The 400-MW program didn't distinguish between systems installed on rooftops or on the ground, and because ground-mounted systems — which can use trackers — are cheaper per watt, those projects became more popular. And because developers get paid for the electricity their projects generate, they have turned increasingly to trackers to try to eke out as many kilowatt-hours as they can from each panel, Lahuerta says. Tracker projects ballooned alongside the country's estimated 3.1 gigawatts of new capacity last year, and ADES saw a 40 percent increase in production, she says.

Meanwhile, California offers solar rebates that automatically decrease, in steps, as more projects take advantage of them. The idea is to gradually reduce the price of solar until it is competitive with conventional electricity prices. The shrinking rebates mean that developers of new solar projects need to find ways to increase capacity at a lower cost to continue to make a profit, and that has pushed them to adopt trackers, de Anquin says. When the incentive program began in 2006, companies didn't need to use trackers to make a return on their investments, and preferred to use more tried-and-true technology, he says. "Now, as the rebate comes down, you need to take a little bit of risk to hit the [return on investment] numbers," he said.

As companies accumulate more experience in the field and prove their technologies, confidence in trackers also is growing. Trackers also are becoming hardier and more reliable as a result of the added experience, Lahuerta says. ADES, for example, designed a tractor clamp to keep its trackers from moving after hearing news of a tracker system that blew away during a storm, she says. "Imagine a tracker that flies because of the wind. That's something that really happened in Spain." The company also added batteries to keep its trackers, well, on track during power outages after grid failures and fluctuations resulted in misaligned and less accurate tracking for some of its earlier projects, she says.

Tracker Technologies

New technologies could make trackers more effective, as well. A number of startups and established players alike are developing ways to control them more precisely, for example. Larger projects tend to use GPS-controlled trackers, which use the Global Positioning System to determine where trackers should point at different times, while smaller projects are more likely to use sensors to seek the sun, de Anquin says.

Trackers fall into two basic categories. They have either a single-axis, meaning they move east and west, or a double-axis, meaning they move in all four directions. In 2007, SunPower Corp. launched a single-axis tracker that — aside from moving panels east and west — also tilts the panels up to 25 degrees to maintain the best angle (south in the Northern Hemisphere, or north in the Southern Hemisphere) toward the sun, and uses algorithms to enable the panels to change direction to avoid shading each other. SunPower's "very clever" design has made it the largest single-axis manufacturer, Lahuerta says. ADES claims it's the biggest installer of two-axis trackers, with some 150 MW already installed, followed by Meca Solar, which is an ET Solar partner, and Solon.

Trackers deliver different benefits in different geographies. In Northern California, for example, regular single-axis trackers usually increase electricity output by about 20 percent, compared to fixed systems, tilted single-axis trackers boost output between 27 and 32 percent and dual-axis trackers see a gain of 35 to 40 percent, de Anquin says.

Some companies are working to make trackers more energy- and cost-efficient. Portasol Trackers in Australia, for instance, has developed a "passive" tracker technology that uses hydraulics to turn solar panels based on temperature changes throughout the day. The company claims the tracker consumes no electricity, as it doesn't have any electronics, motors or gearboxes.

Challenges Ahead

Of course, trackers aren't seeing universal growth. Some government policies favor rooftop projects over ground-mounted projects, or only offer incentives for projects too small to make most trackers worthwhile, Lahuerta says. 

Trackers also don't make financial sense for the growing number of thin-film solar projects, de Anquin says. Thin-film panels take up more space per watt of capacity, meaning a thin-film project would require more trackers, increasing the relative cost of trackers to the rest of the project, he says. Thin films also capture more diffuse light than conventional panels, so they stand to gain less generating capacity from tracking the sun.

And in general, trackers are still perceived as more risky than fixed photovoltaic systems, which could be a disadvantage in today's risk-averse financial environment. "It's not that it's a risky proposition, but it's more risk than if it's fixed," de Anquin says. Jenny Chase, a senior associate at London-based research firm New Energy Finance, says trackers are more prone to failure than any other component of a photovoltaic system except for the inverters.

Operations and maintenance costs also are higher with trackers than with fixed mounts, which require almost no maintenance, said Brian Yerger, CEO of ARDA Advisors, an alternative-energy consulting firm in Wilmington, Del. "Problems do exist," he said. "While trackers can increase returns, each motor enabling the tracker is an isolated unit and can cause a plethora of problems from simply breaking down and not working for mechanical reasons to not properly aligning the panel toward the sun."

While companies are working to improve both the trackers and the perceptions about them — and the most reliable products prove themselves — they could face additional challenges on the horizon. The economy certainly hasn't helped, reducing the money available for all sorts of projects, and Spain's new incentive program has hit the solar market even harder. After a boom last year, Spain capped its market at 500 MW this year and limited ground-mounted systems to less than half of that. That has considerably slowed a market that had already had 300 to 400 MW of ground projects under construction before the new policy was announced.

At the same time, prices for solar panels have been declining — partly also due to the Spanish slowdown — and Lahuerta says that low panel prices could make trackers less attractive. The idea is that if panel prices get too low, it could become as cost-effective just to cover more space with fixed panels as to make the panels move.

The Next Big Thing

Lahuerta believes the tracker market will move from conventional panels to concentrating-photovoltaic systems, which are far more dependent on good trackers, she says. Concentrating PV uses mirrors or lenses to magnify sunlight onto solar cells, enabling systems to capture sun from a larger area than covered by the cells. They require more direct sunlight than flat panels, meaning they need more accurate trackers to work. Trackers stand to have far greater impact on CPV systems than on conventional solar-panel systems because while a good panel would produce electricity even with an ineffective tracker, even a very efficient CPV module won't produce anything with a bad tracker, Lahuerta says.

Of course, CPV is still a tiny part of the market today, with most technologies still in the development phase. The technologies made up less than 1 percent, or 4.8 MW, of total U.S. photovoltaic shipments in 2007, according to the Energy Information Administration. But ADES, which is finishing the development of a CPV tracker with a precision sensor now, sees CPV as a huge potential opportunity for the tracker market, Lahuerta says. "Until today, the tracker was the ugly duck in the industry," she says. "Now things are changing because of CPV. People are understanding that the tracker is going to be [key] to the success of CPV. We are becoming an important part of the industry."

Others also apparently expect trackers' place in the solar industry to grow. Energy Innovations earlier this month spun out its tracking business as its own company, RayTracker, after introducing the GPS-controlled single-axis tracker last year. Overall, demand for trackers "should increase dramatically over the next few years," ARDA's Yerger says. While tracker technology is still evolving and needs to improve, "benefits could be substantial if design and performance can be stabilized," he adds.

Freelancer Jennifer Kho has been covering green technology since 2004, when she was a reporter at Red Herring magazine. She has more than nine years of reporting experience, most recently serving as the editor of Greentech Media. Her stories have appeared in such publications as The Wall Street Journal, the Los Angeles Times, BusinessWeek.com, CNN.com, Earth2Tech, Cleantechnica, MIT's Technology Review, and TheStreet.com.