The difficulty with solar panels is that they are static (i.e., mounted in fixed position) while the sun isn’t. As a result, the sun doesn’t always strike them in such a way as to maximize solar energy capture. This is especially true in the morning or evening, and (to a lesser degree) in winter, when the sun’s angle relative to earth decreases.
Ideally, the sun’s rays should be perpendicular to the panels, with sunlight reaching the panels at a 90 degree angle. To visualize a 90 degree angle, draw a (right or left) isosceles triangle and tilt it so that the long side faces up. This is optimum solar panel positioning.
In winter, in states at 45 degrees latitude (Minnesota, S. Dakota, Wisconsin, Maine), solar panel optimization is worsened by the fact that the sun’s rays strike the earth at about 23 degrees, rather than the optimum 90 degrees found in summer.
Solar trackers, which angle the panels as the sun moves across the sky, are an attempt to solve these problems. These trackers can increase solar output by 50 percent in the summer and up to 20 percent in the winter. In fact, solar experts like Paula Mints, a principal analyst at Navigant Consulting (which offers technological expertise to the construction industry, among others), predicts that tracking systems will find use in at least 85 percent of commercial installations by 2012.
This is supported by comments from Miguel de Anguin, vice president of solar installer Premier Power, who notes that about 70 percent of the company’s ground-mounted commercial projects involve trackers, as compared to about 20 to 30 percent just four years ago.
The conversion to tracking systems is largely due to government policies which offer premium feed-in tariffs for alternative energy systems like solar. In California, where solar rebates are beginning to decrease from their 2006 values as installation rises, project developers are continually seeking ways to maximize the output of their solar projects.
The tracking systems themselves are aiding this conversion. Once bulky and unreliable, more modern systems – equipped with batteries in the event of a power failure or “brownout”, and able to realign themselves electronically via GPS monitoring – perform admirably. And, while tracker technology still has room for improvement, most people understand that tracking systems are going to be the key to solar energy success.
Tracking systems come in two basic categories: single-axis trackers move east and west to follow the sun. Dual-axis trackers also incline, or tilt, to accommodate the difference between winter and summer solstice sun angles. In 2007, SunPower Corp. launched a single-axis tracker that tilts panels up to 25 degrees, and uses algorithms to keep the panels from shading one another – an innovation that allows SunPower to lead the nation in the tracking manufacture arena.
While trackers offer varying benefits at different latitudes (best in California, less in Maine), the combination of improved solar cell efficiencies, more reliable and flexible solar trackers, and innovative solar advances like thin film promise to move solar energy into the grid-parity zone within a few years at most. This is good for solar users, solar system manufacturers, and America as a whole.