Both solar water systems and photovoltaic (PV) solar systems can be installed into racks or trackers (rotating racks), able to follow the sun’s path throughout the year (and the day...).
The idea behind solar rack systems and solar trackers is simple: to allow sunlight to hit the collectors at a better angle, for a longer period; they can improve the efficiency of solar powered systems by up to 20% or 30%.
The problem with sophisticated solar rack systems is that they are expensive and prone to problems (from high winds or heavy winter snow-loads). That is: they are prone to damage and require regular maintenance, which can offset the benefits.
Besides, they may be obstructive, when installed on the ground, and many of them can't be used on roofs.
Fixed racks: the most common solar rack systems
Obviously, fixed racks do not share the problems of rotating racks. They are simple, cheap and strong; they are by far the most common choice for rooftops and ground applications.
Fixed roof rack systems can be advantageous on roofs with a low pitch, or when a variable pitch adjustment is needed to align collectors for maximum efficiency. Solar panels should face the sun as directly as possible. To that purpose, fixed rack systems should provide an angle matching the latitude of your place (see image from Energy.gov).
Manually adjustable solar racks to follow the sun’s altitude during the year
The problem with fixed racks is that... they do not rotate... The orientation of the solar panels is kept unchanged during the entire year.
They are typically installed in a south facing position (or in a north one, in the southern hemisphere) to get more sunlight during the winter, but small adjustments would be advantageous.
And that's where manually adjustable racks enter. They are as simple and as strong and easy to manage as fixed racks, but they allow small adjustments during the year; they just have to be installed in an easy-to-access location, or on the ground.
They are typically fixed at due south (north, in the southern hemisphere), but homeowners can adjust them manually a certain number of times along the year (say, every two or every three months) to keep them aligned with the sun’s changing path. These adjustments can provide gains up to 10% or slightly more.
Single-Axis rotating Solar trackers
We all know that the sun’s daily path changes from morning to night, and that it rises at the east and sets in the west. And it’s this path that single-axis rotating trackers follow.
Their goal is to have the collectors always facing the sun. They have a small motor, usually driven by a photocell system, and they can improve the output of a solar PV system by up to 20 or 25%, which is a significant amount.
As mentioned earlier, the problem with them is their higher price and the fact that they aren't so strong or so free-maintenance as fixed-rack solar systems.
Dual-axis solar rotating trackers
Dual-axis solar rotating trackers are similar to single-axis.
They just have a second axis to allow them to also follow the variation of the sun’s altitude during the year. They share the same advantages of single-axis solar rotating trackers (they can provide output improvements up to 25-30%) and the same disadvantages.