Residential Solar Panel Actuation
A theoretical project building a solar actuation system to track the sun over the course of a day
Summary
What was this project?
I successfully designed and analyzed the machine components for a solar panel actuation system. This system required a power screw, motor, gearbox, and a robust structural frame. Tailored for Boston, I ensured it effectively addressed the region's climatic conditions throughout the year.
How was it executed?
The initial component requirements were clearly defined, and the layout of these components was determined. Calculations were conducted to evaluate the maximum Von Mises stress, fatigue life, and potential failure modes of the system. Each component was designed using SolidWorks CAD and then assembled to ensure optimal manufacturability, ease of assembly, and system motion.
What was the results?
A theoretical system was developed that could improve solar panel power delivery by over 50% under ideal conditions. A single prototype is estimated to cost around $1,200.
Why build this?
Research indicates that a dual-axis solar panel tracker can increase power output by 82% over the course of a three-month measurement period. This technology is widespread in industrial solar power plants, but the goal was to design a system for residential use. A system like this flattens the power curve of the solar system, providing more power in the mornings and evenings—precisely when the power demand of a household is highest. In areas at higher (and lower) latitudes, it can boost the produced power during the darker months, enhancing the viability of solar energy as a household power source.
Design Constraints
01.
Withstand environmental loads
02.
2-axis motion
03.
Accommodate standard residential solar panels
04.
Minimize Mass
Design Goals
01
Minimize Mass
Minimizing the system's mass was crucial, as applying it on a large scale to a roof could negatively impact the roof's structural integrity due to the added weight. Additionally, a lighter system is more convenient for transportation and installation.
02
Lifespan greater than 25 years
To ensure adequate return on investment for this product, reduce the environmental impact and improve ease of use, I design this system to last more than 25 years - particularly by focusing on the fatigue life of mechanical components and ensuring the materials selected can withstand weathering.
03
Range of Motion
The system was designed to have a targeted range of motion of 45 degrees around both the x and y axes, with the z-axis perpendicular to the roof. Preliminary calculations indicated that this range of motion is optimal for tracking the sun without casting a shadow that would entirely obstruct the other panels in the system.
The System
The system was designed to have an actuation plate which was driven by lead-screws and lead-nuts. This controlled the rotation of the panel, by pivoting about a central ball-and-socket joint. NEMA stepper motors drove this system through a gearbox. As precision and power were more important than speed in this application, a cheaper alternative was to use these off-the-shelf motors through a gear box to achieve the required force and precision.*
*This is not the most efficient design for this task, but it was necessary for the project
Powertrain
The powertrain for this system consisted of three assemblies: a lead nut inside a swivel bearing, which was connected to a 20-inch long, 0.25-inch ACME leadscrew driven by a worm gear at its base. This assembly was constrained by two bearings in the housing. The rest of the powertrain comprised of two planetary gear trains in series to achieve the required torque without using custom gears. Shaft reducers connected these to the NEMA stepper motor and worm gear.
Actuation
Movement into the connection plate is translated to the panel through three actuation arms. Each arm has a rod-end bearing on either end with 20 degrees of travel. These are connected with Grade 5 1/4" - 20 bolts to support the snow and wind loads expected on the panel.
Solar Plate
The solar panel plate was design to fit two standard residential solar panels (5.5 ft by 3 ft). It is design for medium scale production, using sheet metal and anodization.
Actuation
Movement into the connection plate is translated into the panel through three actuation arms. Each arm had a rod-end bearing on either end with 20 degrees of travel. This was connected with a Grade 5 1/4" - 20 bolt to support the snow and wind loads expected on the panel
Analysis
The bolted connections in this design were examined to assess their lifespan, failure strength, suitable preload, and resistance to loosening.
The first step in this analysis was to determine the loading on the bolt pattern and, in the process, identify the critical bolts. Next, an M8 bolt of SAE Grade 8 was selected and analyzed under this load case.
To determine the preload, the bolt was assessed using its proof strength and the condition that it was a permanent fastener (as these components never need to be separated). From this value, the bolt pre-tension was calculated.
The next step was to determine the bolt stiffness and the stiffness of the component. In the component, the first, second, and third frustums were dictated by the thickness of the adjoining plate and beam. This indicated the bolt stiffness accounted for about 65% of the stiffness of the connection.
Finally, the safety factors against overload, loosening, and infinite life were all established. In this case, the preload was more than adequate, producing a safety factor against joint loosening of approximately 24. The safety factor against bolt overload was approximately 4.5, which was not concerning in this application. Finally, the bolt was most at risk of fatigue failure, with the safety factor for infinite life coming in at 2.26.