Lesson 5 Activity

Lesson 5 Activity
ActivityDetails
Assignment

Scenario 1

Assume you are designing a system with the same module counts on the rooftop as shown in the video shown below. The Module used is Trina Solar TSM-500NEG18R.28/20. You may choose the SOLARMOUNT rail based options that can serve the purpose from Unirac (a racking manufacturer). You have standard 12” spaced rafters for a residential roof.

Video: How Solar Works SSI (0:58)

How Solar Works SSI

As shown in the video, a solar array can be installed on a rooftop for residential application. After all mechanical holding structures are installed on the roof, the solar panels can be fastened to it [0:05-0:10]. When the sun shines on PV panels, photons are converted into electrons that form electrical current when it moves towards the circuit terminals [0:11-0:20]. The electrical DC current then travels through conduits down towards a power conditioning unit (AKA inverter) [0:21-0:29]. The current is converted to AC electrical current and travels through an AC disconnect box [0:30-0:33]. When the AC current exits the disconnect box, it goes through a PV production meter to count energy generated [0:30-0:36]. After that, the current is back fed to the lower side of the Main distribution panel (MDP), where all load circuits are connected, through a protection breaker [0:37-0:39]. When the PV array is generating power, the load circuits draw power from the PV array instead of the grid [0:40-0:43]. While the PV array is generating power, the monitoring device is transmitting the data to an online portfolio, where clients can see their instantaneous PV array performance online [0:44-0:51]. Finally, the excess energy generated from the PV array is returned to the utility grid [0:52-0:58].

Credit: Sam Fortune
  • Find how many rails, stand-offs with L-foot, splices, mid-clamps, and end clamps are required.
  • What is the dead structural load and the PSF? (Hint: wind and snow load add weights. Dead load doesn't consider them. PSF is the per squre foot load)?
  • Based on the number of L-foot points you came up with, what is the Point Dead Load? (Hint: the dead load will be divided on the roof rafter based on the number of attachment point).
  • In case the roof is built with trusses spaced at 24” (instead of 12"). How does this affect the attachments to the PV system in terms PSF? (Hint: use the analogy of a table with three legs instead of four!)

Scenario 2

Assuming the roof is flat, the installation to flat roof with ballasted system from Unirac, taking the average cement weight of 32 lb. and considering the following:

  • Wind speed for State College, PA to be 90 mph

  • Exposure category to be "B"

  • Roof height is 15' for residential installations
  • How many concrete blocks do you need per module to have a safe installation?
  • Hints for both Scenarios:
    • Design with safety factor according to the manufacturer's specification.
    • Use UNIRAC DESIGN TOOL (create a free account to access it)

Deliverable

Prepare a report that includes your findings for each of the scenarios. The report should be no more than one double-spaced page in a 12 point font.

Submission Instructions and GradingPlease visit the Lesson Activity page in Canvas for submission instructions and grading information.