The Solar Tracker
The idea behind adding a solar tracker for a residential solar power system is to get more electricity power without increasing the solar panel size The assumption is that the cost to add a solar panel tracker is less than the cost of adding more solar panels. Tracking the Sun The ultimate direction for a given solar panel plane, if we want to get from it the maximum electricity 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 conceivable to consider 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 might not be a practical proposition If the tracker mounted on a mast can be squeezed into the site, it is wise to calculate the added cost versus the cost of bigger solar panels mounted on a fixed direction mount 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)
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
Solar Trackers for Large Size Solar Power PlantsThe natural choice for large size plants is to use solar trackers in conjunction with concentrated solar
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