The Solar Tracker

The idea behind adding a solar tracker to a residential solar electric power systems is to get more electricity power from the existing solar panels.
The assumption is that the cost to add a solar panel tracker is less than the cost of adding more solar panels. Yet, very few homeowners add solar tracking systems. Click to view the common practical reasons not to add the trackers.

Tracking the Sun

The ultimate orientation for a given solar panel plane, if we want to get from it the maximum electrical power is perpendicular to the sun position. The most straight forward way to mount a solar panel is in a fixed direction. Since the sun apparently moves in the sky, having a fixed direction mounted panel is not the optimum. It is however a reasonable engineering compromise if site constraints and economical constraints are taken into account

An obvious situation where the panel must be mounted in a particular direction is on a slant roof in general and if solar tiles are used in particular.

On a flat roof or in a non shaded area in the yard one can consider the addition of a solar tracker. On offgrid solar systems sites it is a plausible that a suitable location for the tracker and the mounting mast can be found
In grid-tie solar systems, to fit a mast and the tracker into a typical suburban home and to comply with local planning restrictions is usually not a practical idea

If the tracker mounted on a mast can be squeezed into the site, it is wise to calculate the added cost of the tracker versus the cost of bigger solar panels mounted on a fixed direction mount. With the recent drop in solar panels price the relative economic advantage of solar trackers is less than what it used to be

A concentrator solar power system must have a tracker

The solar tracker orients a solar photovoltaic panel to face the sun while tracking the sun position. Accuracy is not terribly important for orienting flat solar panels. Comparing to fixed mounted panels, the extra power generation comes into effect early in the morning and late in the afternoon (around noon time the fixed mounted panel is anyhow facing South where the sun is)

Types of Solar Trackers

There are two types of trackers: the single axis tracker and the two (dual) axes tracker
In a single axis tracker, the tracker tracks the sun in azimuth only; elevation can be changed manually according to the season (higher angle in the summer season)
Most dual axis trackers can track in elevation and in azimuth; some have polar control
Compared to a fixed mount panel, a single axis tracker increases annual electrical power production by around 25-30%, a dual axis tracker might add 5% on top of that.
A single axis solar panel tracker is a good engineering compromise in most situations

You probably ask yourself how does the motors in the tracker “know” where the sun is? There are two solutions to the riddle.

A passive solution: since the azimuth and elevation are known for the location, date and hour the data can be stored as digital tables into the controller memory
An active solution: a clever optical sensor* senses the tracker axis deviation from the sun direction, and the tracker nulls the error (a closed loop servomechanism)

*The clever sensor is composed in essence from two sensors in 90 degrees offset (each one converts light strength to a DC voltage), in the correct orientation the light reading (DC voltage) in one is supposed to be equal to the light reading in the other. In all other positions one of the 2 will get stronger light than the other and the difference in signal strength (called error signal by control engineers) is used to steer the motor to the correct orientation

Practical Limitation to adding a Sun Tracker

The main practical reasons not to add sun trackers are:

Sun trackers has moving parts (motors) and use micro-controller. As such, they require higher maintenance than solar panels and they exhibit more opportunities to fail

Installation of a heavy sun tracker is not always feasible on a tilted roof due to geometric constraints and heavy weight. They also need to survive strong winds. It is more natural to install solar panels parallel to the roof even though the panels produce less electricity

With present prices of solar panels, prices that are getting lower and lower, it is not a clear cut conclusion that adding a solar tracker will reduce the overall price

Sun Trackers for Large Size Solar Power Plants

The natural choice for large size plants is to use solar trackers in conjunction with concentrated solar

Sun trackers and domestic concentrated photovoltaic

It is expected that concentrated photovoltaic technologies, technologies that use optic lenses or optic mirrors to focus more sun radiation on a given photovoltaic panels will find their way to the domestic market. Right now these technologies are mainly used in large scale solar plants. When this happens,tracking the sun is almost a must, and another issue of cooling the solar panels will need a solution.