Fall 2016 Solar Panels: Motor Trade-Off Study

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By Jose Rodriguez (Electronics and Control)

Approved By Inna Echual (Project Manager)

Objective: Motors we need to select must be able to hold the panel at different angles with precision with maximum 12 volts and 2 amps to fulfill the sun tracking requirement. In order to do this, a minimum torque of 50 oz/in is required based on our calculations. 

Stepper Motor:

Need to consider the positioning resolution because the number of steps per revolution range from 4 to 400.

Note: Resolution is expressed in degrees. Example- 1.8⁰ is 1.8360= 200 step/rev motor

  • Higher resolution torque effects the speed and torque by decreasing both as resolution increase
  • Gearing can help to increase resolution without having to loose torque
  • In addition, torque can be increased, but the tradeoff will be speed

Pros

  • Precise positioning
  • Low Speed Torque

Cons

  • Low Efficiency- draw the most current when not doing any work
  • Less Torque at high speed
  • No feedback- Limit switches or detectors typically required for safety and establishing a reference position
  • Require a stepper controller to energize
  • Cost more
  • Four inputs

DC Motor:

Pros

  • Cheap
  • Efficient
  • Can be controlled using an H-Bridge circuit
  • Only need two inputs

Cons

  • Can’t be used for precision
  • Noise is introduced if not brushless
  • Brushless DC motors- require a separate controller, ESC

Based on the two key differences on these two motors, we concluded that we will need to use 2 stepper motors to control the sun tracking on the solar panels. Precision is needed and the stepper motor is the only motor that can be controlled to fulfill that precision requirement. In addition, a constant-holding torque is required to hold the panels and the stepper motors are able to provide this. Since the other panels do not require any precision or holding torque, DC motors are more acceptable to be used than stepper motors. The following table shown in Figure 1 will show the motors that I compared and based on my needs I picked one of the 6.

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Figure 1: Stepper Motor Comparisons

Final Decision:

The final decision for making the sun tracking possible are the two stepper motors SY57STH41-1006A. They are my choice because it draws only 1 amp and has a holding torque of 55 oz/in, which is required to articulate the panels efficiently.