This blog had mentioned before how better computerized tracking improved solar energy. Renewable Energy World now reports how dual axis tracking increases output.
“Because it can tilt on both azimuth and zenith axes, a dual-axis tracking system follows the sun daily and seasonally, always positioning the solar array so that it optimally faces the sun.”
While a tremendous amount of research and funding is going into trying to increase the efficiency of photovoltaic cells by a few percentage points, there is a readily available solution that yields a 40% increase in produced power today – dual-axis tracking [1]. By simply moving the PV array so that it is aligned with the sun throughout the day and seasons, you get a large boost in produced power at a small incremental cost. Of course the cost depends on the design of the tracking system. In today’s market, this cost ranges from under a $1.00/produced watt, to around $3.00/produced watt. We are talking about produced watts rather than rated watts.
The key to understanding the benefits of tracking is the significance of the incident angle, the angle at which the sun’s rays strike the PV array. To see how the incident angle affects solar intensity and power production, we use the formula Intensity = Constant x cos ? where ? is the incident angle measured from perpendicular (Fig. 1). So intensity is at its maximum when ? = 0?this is when the arriving energy strikes a PV panel perpendicularly. The greater the incident angle, the smaller the amount of energy reaching the panel.
Another consequence of a large incident angle is reflection. As the incident angle increases, the glass on the front of the PV panels begins to reflect energy away from the panels, reducing the power produced. The combination of reflection and reduced available surface area is why fixed solar systems produce very little power in the morning and afternoon. Figure 2 is a representational daily energy production graph for a fixed array. For a fixed array, the incident angle changes throughout the day, from highly acute to highly obtuse. The result is that very little energy is produced during the morning and afternoon.
“One of the drawbacks of most dual-axis trackers has been the pole-mounted design. Most tracking systems are pole-mounted in a manner similar to satellite or radar dishes. Because the array is hung from a single point, gravity is always trying to pull them over and their wind load factor is quite high. This requires heavy-duty mechanisms to hold and position the array and massive, heavy concrete foundations, heavy-duty earth moving equipment and cranes to set the array in place ? all increasing the cost of installation. Another disadvantage to pole mounting is the height which can be anywhere from 12′ to 20′, forcing the arrays to be widely spaced to avoid shading.”
The Renewable Energy World article suggests, “A better design would be lightweight, low wind resistance, and no requirement for an extensive foundation to support it.”
One solution is the InteliTrack (Fig. 5), which holds the PV panels in balance, like a gimbaled ship’s compass, allowing the panels to tilt in two directions around their own axes. This design eliminates the need for a huge foundation since there is no stress from gravity or a high wind load on the supports. It is made of aluminum so it is lightweight and, without a heavy foundation, suitable for rooftops and parking lot shade structures as well as for large ground-mounted utility projects. Wind loading is greatly diminished because of its low profile and the fact that the panels can be louvered to present only a thin edge to the wind.
Commentator SeeNovak disagrees.
The economics does not bear out the installation of a dual-tracking mechanism for commercial sites. If the solar panels are permanently aligned to the “best-average” azimuth, you can initially install MORE solar panels, which are getting progressively cheaper and more efficient (not to mention less reflective) in lieu of a complex tracking system.
Also, bear in mind every mount is something that will eventually need maintenance/repair. At a 1 MW or larger facility, you’d have to hire a crew just to operate and maintain the mounts and directing apparatus.
This blog agrees with the commentator. For utility-scale solar PV installations, we see greater investment in optics that concentrate solar power and / or solar cells (e.g., multi-junction) that capture more photons. And, site selection still plays a crucial role.
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Speaking of multi-junction solar cells, Treehugger Michael Graham Richard relays an announcement from Spectrolab, a subsidiary of Boeing. They have begun mass-production of a very efficient concentrating solar cell, the C3MJ+, which reportedly has an efficiency at converting sunlight into electricity of 39.2%. This would make it the most efficient on the market.
And, speaking of squeezing more energy out of solar panels, IEEE Spectrumz Peter Fairley says to do it with distributed intelligence.