Solar tracking devices, mounted with photovoltaic (PV) panels, allow the panels to exactly track the sun’s path across the sky and can increase the yield of solar energy installations by as much as 40 percent compared to stationary panels. Solar trackers have been around since about 1980, but their increasing use in both commercial-scale and residential solar energy projects is a direct result of proven, improved solar capture efficiencies. This increase, though largely driven by commercial-scale solar energy installations, has translated into lower costs and more reliable tracking systems for homeowners and small businesses as well.
Stationary solar panels are fixed, either by the installer or the homeowner, at the optimum angle for solar exposure; that is, in Australia, at 35 degrees latitude south, where the sun’s declination varies from 78.5 in the summer to 31.5 in the winter, most rooftop systems will rely on an approximately 52.3 degrees declination, allowing for a 22.6-roof tilt angle (or a 5/12 roof pitch). Unfortunately, in more northern climes, the angle of the sun’s rays in summer varies from winter by much more than 60 degrees, which means targeting summer sunlight makes winter solar energy generation somewhat iffy.
Solar trackers solve this problem. The basic solution, a single axis horizontal tracker, follows the sun across the sky from morning to evening, optimizing solar performance during spring and summer days, when the sun is higher in the sky. Unfortunately, they are less useful the farther north one goes, since (as noted above) the variance the sun’s angle is greater between summer and winter, so any setting along the horizontal diminishes performance the other 60 percent of the year.
Vertical axis trackers work better at higher latitudes, enabling solar panels or arrays to track the sun both at summer and winter declinations. Dual axis, or azimuth trackers solve both problems simultaneously, but can be very expensive, adding from $ 3,500 to $ 6,500 to the cost of solar installation, with the smaller figure accommodating about 125 square feet of solar panels and the larger supporting 225 square feet.
There are also dual axis trackers that rely on horizontal and vertical pivots guided by a controller, similar to that used for solar telescopes. These are so expensive that their use is commonly restricted to commercial solar energy systems that rely on a parabolic dish with an accompanying Stirling engine that produces energy onsite, rather than being grid-tied. This type of precise tracking is also used in concentrated solar applications (i.e., mirrors collecting sunlight directed onto receivers which convert sunlight to heat), which require minute accuracy to be effective, in that the focal point on which sunlight is directed is near the center of the reflector, or lens.
Trackers can also be divided into active and passive trackers, the first operating on an electric motor activated by a controller, the second using compressed gas which, when heated (by the sun’s rays) creates an imbalance in a chamber which causes the tracker to tilt.
In the early days of solar energy installation, maximizing yields was less important than developing technologies. With the advent of feed-in tariffs (where entities like utilities pay more for renewable energy generation, and the excess goes toward expanding renewable technologies), solar installations are finding profit in increasing the number of kilowatt hours delivered to the utility grid. The incentive is money, but the benefits result in improved technologies, not only in collection but in cost efficiencies (think thin-film solar).
The need to improve solar yields has, in recent years, driven the solar tracking market from about 2 percent in 1990 to more than 25 percent in 2008, and projections suggest that at least 85 percent of solar installations of more than one megawatt built in the future will use some form of tracking.
This increasing reliance on tracking will also result in improvements in tracking technology, as developers struggle to find new and better ways to improve and insure the reliability of the motors, gear drives, controllers and pivot systems that trackers rely on.
Cooler Planet is a leading solar resource for connecting consumers and commercial entities with local solar Installers. Cooler Planet’s solar energy resource page contains articles and tools about solar panels to help with your solar project.
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