Solar trackers are devices that automatically orient solar panel arrays and other solar payloads to the sun or to the brightest source of reflected light to increase energy production.
While solar panel tracking is maybe the most common tracking system in use, solar reflector mirrors (heliostats) and optical lenses can also be tracked. Heliostats, for instance, can reflect sunlight in a constant direction, while optical lenses can focus the sun's rays to a fixed target such as an array of solar panels.
In this article we'll examine the types of solar trackers and how they function.
When installing solar panel modules, the common practice has been to install them in a fixed position tilted at the optimal "angle of incidence" for their point of latitude. For instance, when the rays of sunlight are perpendicular (90°) to the photovoltaic cells in a solar panel, maximum energy is captured.
However, the calculated angle of incidence for installed fixed panels has of necessity been optimized, and depending on your location (latitude) can vary 30° or more over the course of a year, as the sun traverses its east to west path higher or lower in the sky. Even so, when compared to laying the solar modules flat, fixing panels at the optimum angle can yield an approximate 15% increase in power output efficiency.
Trackers, however, are used in solar power systems to position the panels near perpendicular to the streaming rays of sunlight at the minimal angle of incidence; they can adapt to both the daily passage of the sun and the changing seasons.
By pointing the solar panel array directly at the brightest light source, either reflected light or the sun itself, energy produced from the solar panels is greatly increased. Annual electrical power output can be increased by up to 30% or more. This represents a significant increase revenue earned compared to fixed angle modules.
A solar panel tracker can offer a much quicker payoff period for a solar power installation. Under a high-rate Feed-in Tariff program like Ontario's microFIT program that rewards PV producers per kWh delivered to the grid, trackers can help generate significant income to offset solar panel installation costs, especially in northern climates. Maximizing system power output simply makes economic sense.
Tracking systems are classified by the number and orientation of their axes. There are two basic tracker types: single axis and two axis (also called dual or double axis). Photovoltaic trackers that operate with a single axis can increase solar power output 25-30%, while a two axis tracker can further increase output by up to 10% and possibly more when compared to a fixed solar panel system.
Considering that the solar PV industry continually strives to improve solar cell conversion performance by a single percentage point, or less, an increase of 40% over fixed panel performance is impressive. Solar trackers can boost daily energy production significantly.
Choosing what solar tracker to install simply comes down to comparing the extra investment and cost of maintenance over time against the increased solar energy and financial yield delivered by the unit.
Trackers with a single axis can either rotate on a horizontal or a vertical axis that's positioned on a north-south alignment. Most are programmed to automatically follow the east-to-west path of the sun throughout the course of the day. Some units permit manual adjustment of the tilt on the polar axis in response to seasonal changes in the sun's orbit.
There are three common types of single axis trackers:
This system's axis of rotation is horizontal to the ground with the upper surface of the solar panel array positioned parallel to it. The tracking system rotates the panels along a cylindrical arc to track the visible path of the sun throughout the course of the day.
The benefit of the one axis design is that support posts at either end of the single axis of rotation can be shared between tracking systems to lower the cost of installation. Trackers can be closely positioned for commercial large scale solar power applications.
This system's axis of rotation is neither horizontal or vertical to the ground; its any angle between horizontal and vertical with the face of the solar panel array positioned parallel to the axis of rotation. The tracking system rotates the panels along a cylindrical-like arc to follow the visible motion of the sun throughout the day.
This system's axis of rotation is vertical to the ground with the upper surface of the solar panel array positioned at an angle to it. The tracking system rotates the panels around the supporting pole along a distinctive cone-shaped arc to track the visible motion of the sun throughout the day.
Two axis trackers operate on two axes of rotation coordinated to work together. The vertical axis fixed to the ground is considered the primary axis, and the secondary axis is coordinated to it.
Most dual axis solar trackers are programmed to automatically follow the sun's orbit throughout the course of the day while compensating for the seasons of the year.
There are two common types of dual axis trackers:
This versatile tracking system has its main axis of rotation vertical to the ground with its secondary axis coordinated to it. The axes of these trackers are normally aligned either north-south or east-west, but they are very flexible and through programming can be aligned in any key direction desired to best follow the sun's path as explained in the following video:
The patented Deger Tracker (above) is German engineered and manufactured by DEGERenergie of Germany. It's the perfect example of a dual axis tracker designed to increase the electrical yield of a standard solar power installation up to 45%. If you need a quality solar panel pole mount tracker, the Deger Trackers offer a superb solution for both residential and commercial installations.
This type of tracking system is similar to the tilt-top system with its main axis of rotation positioned vertical to the ground, and its secondary axis coordinated to it. Like a telescope mount, the system is vertically supported on a large circular track resting on the ground, allowing the rolling mechanism to orient to a compass point while the second axis is a horizontal pivot, enabling the solar panel array to tip and point to any sky location.
As it's a non-precision orientation, this type of tracker only works best with solar panel systems instead of some types of concentrating PV collectors; however, its advantage is the much larger PV arrays it can support over the pole mount system.
There are two tracker drive systems in common use: passive and active. Passive trackers are ideal in southern-latitude locations experiencing long sunny days whereas active trackers are best used for northern-latitude locations where cloud cover and colder weather is common.
Passive trackers depend on Earth's gravity and radiant heat from the sun for their operation. The sun's heat moves a liquid gas (freon) from side-to-side in its container and the shift in weight slowly rotates the solar panel array.
Pros: Proven simplicity of operation without the need of motors or electricity. Cons: Operates with less precision than an active system, especially in cloudy sky conditions and during cold weather. Tends to be overpowered by strong winds and is slow to reset for morning sun.
Active trackers depend on low-power electric motors, often solar driven, and precision gear trains to position the solar panel array automatically to the brightest source of light as determined by the system. A pair of photosensors will determine the brightest source of light, usually the sun.
Pros: Panel array is always positioned perpendicular to the brightest light source ensuring maximum energy gathering and revenue. Cons: Higher initial cost and maintenance owed to its greater complexity of parts.
Single axis tracking systems can be more cost-effective for large commercial power installations. Their simpler components lead to less maintenance and installation costs, and their lower profile creates less shadow thereby permitting closer positioning of solar modules. They offer a definite energy yield advantage over fixed angle solar installations.
Double axis trackers are more cost-effective for smaller, residential solar power installations when coupled with high Feed-in Tariff programs. Their greater number of moving parts results in additional installation and maintenance costs, and their higher profile requires greater space between units, but this can be offset by the increased efficiency they offer, especially in northern climates.
Unfortunately, not all residential solar panel installers promote the
benefits of solar tracking systems claiming they are prone to breakdowns
and over expensive. Neither is the case! Today's tracker technology
ensures near trouble free operation, and the significant increase in
energy they produce results in a quicker system payback.
Some solar installation companies that discourage tracking don't have the know-how to install trackers, or they cannot supply them, or they opt for quick profits by hurrying to their next job not willing to spend the extra time connecting them. If you live in a northern climate and the installer won't recommend solar trackers, dump him and find one that's better-qualified who will. You'll benefit in the long run.
The benefit of solar trackers like DEGERenergie Tracking Systems can no longer be ignored, as the gain in solar energy production results in less payback time and greater profits.
Photo credit: ©Flagstone Solar Power International
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