Tracked: Page 2 of 3

Tracking Cons

One of the benefits of PV technology is that the modules don’t need to move to produce electricity—it’s one of the reasons why solar electricity is such a reliable form of power. Whenever moving parts are introduced, the likelihood of component failure—and the need for periodic maintenance—increases.

If a tracker stops functioning, to keep your array producing optimally, you’ll need to manually position the array at an appropriate tilt angle and face it to solar south. Defunct electronically controlled trackers can be positioned with manual controls (an option at purchase). A passive tracker can be positioned by hand and secured into place by attaching ropes or ratcheting straps to fixed points provided at the four corners of the rack and tying down to fixed points placed on either the pole or in the concrete pad.

A potential disadvantage of purchasing a tracked system is that some PV rebate programs are based on the size of the PV array (installed watts) rather than PV array energy production. This means that the overall cost benefit of the tracking system could be reduced, depending on how incentive programs are structured. For example, at your site you might calculate that a 3 kW tracked array will produce as much power as a 4 kW fixed array. However, your local utility offers a $4 per installed watt rebate. Here’s the catch: Even though the up-front cost of the tracked system is lower, instead of a rebate check for $16,000, you’ll get only $12,000, since the rated wattage of your array is smaller. In this case, while the energy production of each array would be about the same, the system cost after the rebate would be less for the fixed PV array. Note that many areas have or are moving to production-based incentive programs, which make payments based on energy produced instead of installed watts. Check on available incentives with the Database of State Incentives for Renewables & Efficiency (www.dsireusa.org).

Best Applications

Extra power is only beneficial if you can use it, sell it, or store it as it is produced. A grid-connected system with a wide-open solar window can be a good candidate for a tracked array, since every kilowatt-hour gets used and, in net-metered situations, is credited to your utility bill. An off-grid system with daytime summer-dominated loads (like irrigation) is another good candidate for a tracking array.

Water-pumping systems are also ideal candidates for PV-direct tracked arrays. Because these systems often do not have batteries that would allow for water-pumping when the sun is unavailable, there is a need to pump as much water during daylight hours as possible, and a tracking array can take full advantage of the available sunlight. These systems offer inherent synergy, matching the seasonal needs for water pumping (for livestock and crops) with the longest daylight hours.

If you have an off-grid system with winter-dominated loads, a tracked system may not yield the best cost benefit. This is largely due to two issues. First, off-grid systems often cannot put excess power to work—if the batteries are full, the charge controller will simply shut off the PV array. Second, for most off-grid homes, energy use is highest in the wintertime—so systems are often sized for that season—yet the extra energy from a tracking array is most available in the summertime.