In this article, I build a simple solar tracking system using a Raspberry Pi and a stepper motor, with the purpose of experimentally verifying the gain in power from a solar panel that is tracking the sun compared with a fixed solar panel. Oh – and it looks cool in time-lapse video .
Over the past few years I have built a lot of solar-powered systems: Project Curacao, SunAirPlus, WeatherPi, and the recent solar-powered ESP8266 . Although I've fooled around with sun tracking systems, I have never built one all the way out and then gathered the data to figure out if it was worth it. Now that the sun has returned to the Pacific Northwest, the time is right.
A single solar cell never seems to put out quite enough power to run a Raspberry Pi all the time, and the new Raspberry Pis take even more power. One improvement you can make is to add the hardware to track the sun with your solar panels, which could increase your solar power generation by 20 to 30 percent.
Sunlight has two components: the "direct beam," which carries about 90% of the solar energy, and the "diffuse sunlight," which carries the remainder. The diffuse portion is the blue sky on a clear day and increases proportionately on cloudy days. Because the majority of energy is in the direct beam, maximizing collection requires the sun to be visible to the panels as long as possible.
At any fixed location, the visible sun tracks across 180 degrees during an average half-day period (more in spring and summer; less in fall and winter). Local horizon effects reduce this tracking motion somewhat, making the effective track somewhere about 150 degrees. A solar panel in a fixed orientation between the dawn and sunset extremes sees a motion of 75 degrees to either side so will lose roughly 75 percent of the energy in the morning and evening. Rotating the panels to the east and west can help recapture those losses; thus the statement that tracking the sun can improve your total output by about 20 to 30 percent.
To determine whether those power improvement numbers are correct, I will endeavor to verify by experimentation!