Stationary solar array mounting systems are the most common form used in the business, but for a photovoltaic panel to produce its rated wattage for the entire day it needs to be continually aligned with the sun.
To solve this problem and enhance power output, a device called a tracker has been developed.
So what is a tracker? The name invokes an image of a hunter with his eyes scanning the ground working his way through the underbrush in search of his quarry. In this case, the tracker refers to a mechanism that can keep an array pointed at the sun all during the day, compensating for the different elevations in sun position during the different seasons; low in to the horizon in winter and higher overhead during the summer.
Trackers are mounted on an eight-inch pipe and use a computer chip, electric actuators and mechanical pivots to provide the sun-tracking motion. They keep the array at the optimum angle using an electronic device called an optical sensor. Two of these devices are mounted on the frame holding the panels to the tracker head and they use the variance in sunlight strength to accurately position the panels at the optimum angle, perpendicular to the sun, no matter the hour or day of the year.
Good quality trackers use azimuth and elevation tracking to maximize the amount of solar gain, adding approximately 40 per cent to the power produced by an array. This significant increase in electrical production speeds cost recovery of the system whether it is a grid-tied home or an off-grid home.
A good quality tracking unit also has the ability to protect against wind damage by manoeuvring the PV array into a horizontal position and reducing the surface area exposed and thus wind load.
In winter, it positions the array at a 17-degree vertical angle above the horizon. This is the angle required by the sun’s position in the winter, but it has the added advantage of being a steep enough angle to keep the snow sliding off. In the event snow does stick to the array, the tracker has a shake ability for removing it.
In June, at our latitude of 52 degrees, the sun travels in an arc starting at a six-degree vertical angle above the horizon in the morning, hitting a high of a 61-degrees vertical above the horizon at noon and returning to 4.5 degrees at sunset.
Azimuth is direction by degree, with east being 90 degrees, south 180 degrees, west 270 degrees and north 360 degrees (or zero degrees).
In June, at our latitude, sunrise is 60 degrees (east northeast) and sunset is 300 degrees (west northwest).
In December, the vertical angle above the horizon at noon is 15 degrees and its Azimuth for sunrise and sunset are 136 degrees (southeast) and 230° (southwest) respectively.
Because of this wide variation in sun position, tracking the sun makes sense, both for energy gain and cost recovery.
Lorne Oja is an energy consultant, power engineer and a partner in a company that installs solar panels, wind turbines and energy control products in Central Alberta. He built his first off-grid home in 2003 and is in the planning stage for his second. His column appears every second Friday in the Advocate.