Double Axis Tracker

Definition

Two axis tracking dish system – or Stirling Engine – tracks the Sun from East to West, and North to South using two pivot points (1).

 

Stirling engine is a renewable energy technology that transforms natural resource, solar energy, into useful energy form, electricity (7).

 

This system tracks the Sun in two axes, horizontally and vertically, such that the Sun vector is normal to the aperture as to achieve 100% energy collection efficiency. Solar panels are normally positioned perpendicular to the Sun’s rays to attain a greater total power output (2). 

 

 

The dish system convert the solar energy to mechanical energy and then to electrical energy. Dish systems use a mirror array (parabolic dish reflector) to reflect and concentrate incoming insolation to a receiver (Stirling cycle engine/generator), to achieve the desired temperature to convert heat into work (6). The working fluid in the receiver is heated to 250-750 degrees Celcius and then used by the Stirling engine to generate power (3).

 

 

There are two main tracking systems with two axes: Azimuth-Elevation Tracker and Polar Tracker. In Azimuth-Elevation system, dish rotates in two planes, one parallel and the other perpendicular to earth. For the polar system, concentrator rotates parallel to Earth’s rotation, west to east (5).

Stirling engine is very versatile and have a wide range of applications. It is capable of providing power from kilowatts up to gigawats. The output from many modules can be added together to produce a collective output of virtually any desired amount of energy. In addition, more dish systems can be added to respond to increase in demand (4). 

Sun tracking methods with good accuracy can be expensive and complicated. Conventional on-axis sun tracking adopt two common configurations: azimuth-elevation and polar tracking (or tilt-roll). In the Azimuth-Elevation, solar collector is free to rotate about the azimuth (plane parallel to earth) and elevation (plane perpendicular to earth) axes, and the sun-tracking axes must be aligned with both zenith (direct overhead angle) and real north, as it can be seem In picture 1 below.

 

On the other hand, polar system sets the collector to follow the sun path – rising in the east and setting in west – as well as changing the tilting angle to follow the Sun elevation through the seasons of the year. For this system, the sun-tracking axes must be aligned with the latitude angle and real north (5).

 

 

The tracking accuracy requirement is much dependent on the design and application of the solar collector. The longer the distance between the solar concentrator (parabolic dish reflector) and the receiver (Stirling cycle engine/generator) the higher the tracking accuracy required will be, because the solar image becomes more sensitive to the movement of the solar concentrator (5).

 

 

Sun tracking algorithms used for sun-tracking are accurate and cost effective, and can prevent misalignments or defects. For each period of time, the path of the sun is determined by referencing to this algorithm (5). Another tracking system is the dynamic tracking, which uses a sensor to search for sun’s position constantly for the entire day (8). These algorithms are integrated to microprocessor or computer based controller (electro-optical controller), which controls the sun tracking system (5).