Saturday, March 7, 2015

Solar panel seasonal tracking

My workshop with solar arrays
A couple of years ago after I had installed my west facing solar array, I realized there was still some space above my south facing solar collectors that are used to heat the building.  So I decided to install two additional 245W panels.  Each panel feeds an Enphase microinverter that converts the DC solar power to 240VAC that feeds into the main breaker panel.

Solar panels perform optimally when they are pointed directly at the sun and their energy output drops significantly when they are off by as much as 20°.   Since the sun elevation changes from 42° in the winter to 66° in the summer here in Maine (a change of 42°) I felt it would be wise to engineer the panels to track the seasonal changes.

I researched DC linear actuators and found one that had a 24 inch stroke, this means that it could change length from 28 inches to 52 inches.  This would allow me to lower the panel to meet the lowest sun angle in the winter and raise it relatively close to the 66° summer elevation angle.  I am more concerned with optimizing winter power since the days are so much shorter.
Progressive Automations PA-14
I used Google SketchUp to optimize the geometry of the installation.
In order to get the panels to accurately track the sun's position, I designed a servo control system (here is my schematic) and connected it to a timer that activates the electronics several times a day for a minute.  Here is a photo showing the timer mounted above my handmade control panel that allows me to operate it in automatic or manual modes.
Moving the panels in manual override
I designed a solar tracking sensor and built it into a small red plastic dome.  There are two small photocells mounted above and below a black painted metal divider.  When the sun shines unequally on the two sensors a signal is sent to my controller to move the motor until the brightness is equal on both sensors.
Sun tracking sensor with 2 photocells
It is early March now and the actuators are approaching their maximum extension in order to catch the higher angle of the sun.  Due to limitations of the length of throw of the actuators, they only actively track the sun from the fall solstice through the winter until the spring solstice.  This improves performance during the shortest solar days in the year.
Solar panels with linear actuators extended part way
To be honest, I am not sure how much more energy I am gaining by tracking the seasonal solar elevation changes, but it was a lot of fun to engineer this project.  I am reminded that this system is working because the linear actuators are loud enough that I can hear them when they move.  The timer is programmed to activate the system at noon and 2:00pm for a minute every day.

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