Sun-tracking

Sun-tracking is necessary to get the high power densities desired for Solar Concentrators.

Feedback based tracking
Feedback based tracking relies upon a light sensitive electronic circuit which adjusts the inclination of the reflectors to maximize the amount of light received by the circuit.

The Redrok tracker is an example of this. However, the redrok circuit is a non-optical tracker, and adjusts itself to point towards the direction of the highest average light level. On a perfectly clear day, this would be directly at the sun. On a cloudy day (even when the sun is not obstructed), or in the presence of a snow covered hillside, house, etc., this direction would be towards some point in between the sun and the other sources of light (white cloud, snow bank, etc.)

I am told by the designer of the Redrok circuit that it would not perform adequately in a situation where the receiver aperture is about the same size as the reflected image due to this error. His circuit is used by (point focusing) solar cookers where the reflector target is 3 times the diameter of the solar image.

According to the Redrok engineer, an alternative to this would be an optical feedback circuit, where a lens focuses light on the photo sensor. this way, the focusable rays of the sun would give a very strong signal when the circuit is correctly aligned. This setup would be run in parallel with a non-optical tracker, which would track close enough to the sun for the lensing apparatus to begin to be effective and thus overpower the averaged signal of the non-optical sensors. For a linear collector arrangement, this would require a linear lens.

The redrok engineer however was once given the advise "don't try to invent to many things at once", and since he hasn't ever built a linear optical tracker (and doesn't have a source for linear lenses), his initial advise is to avoid trying to develop this technique right now.

Sun's path calculation based trackers
Rather than relying on feedback, this method uses an equation (or tables of values) to calculate the sun's path and the appropriate rotation of the mirrors. Such could be implemented through a computer running a program with output to a stepper motor or linear actuator via parallel or serial port. It could also be implemented with a microcontroller (Arduino board), which would be a much lower power solution.

This is the current recommendation of the Redrok engineer for our project.

Related pages
Heliostat, Open Heliostat Array Project