Solar Array Knowledge Transfer

Owned by Calder Kitagawa
Jan 21, 2017

High Level:

  • Specs allow for 4, 5 or 6 m^2  of Si cells
  • Si is much cheaper than GaAs
  • Sunpower is leader in Si efficiency
    • Not released to the public (no information for residential users)
    • Can't directly buy. Go through supplier:
      • SunCat Solar
        • American
        • Better encapsulation as of a year ago
        • Really good technique
        • Frustrated with Gocherman (marketing)
        • Cheaper encapsulation with better cells pays off usually
        • A little cheaper
        • USD
        • Per module
      • Gocherman
        • German
        • Price based on area
        • Efficient and serious
        • Euros
        • Can get anything (pyramid encapsulation)
        • More rigid less flexible
  • Get cell number based on spec sheet, space and power. 
    • Get max number.
    • Note the corners are rounded so you can use this to get more cells
  • A module is a group of cells and they are connected together into a string


Goals

  • Max cells
  • 1 MPPT per string
  • Locate each shaded area and group into a string (Logically).
  • Goal is to separate strings to defend against shadows.
  • Less cells per string = lower voltage (MPPTs lose some efficiency)
  • MPPTs have a minimum operating voltage. String sizes need to be calculated based on this. Research the MPPTs to determine strings.
  • You can design your own MPPTs (Good teams make their own, most buy from Australian Research Labs)
  • These MPPTs are off 1% - 5% of the time to poll the array
  • Divide into modules (4x5, 5x5) make as even as possible withing the string. (No bias on bypass diodes). 
  • You could have bonus cells on a separate string (vulnerable) only activate under ideal conditions. 
  • 1 bypass diode per module. (Some cells Gocherman, includes these in the modules but if they do get damaged they are hard to repair).

Encapsulation

  • When cells are raw they have an efficiency of 25 - 29%
  • Encapsulating (polymer coating) them causes a loss of 1-3% based on dampening/attenuation effects. Used to protect cell from elements
  • Currently pyramids are used to maximize the efficiency +3% by angling light to 90 degrees.

Procurement

  • Order in advance 3-6 months shipped in crate
  • 50% up front and 50% at the end
  • 40K - 50K

Diodes

  • Bypass diode in parallel with the module.
  • Let the module be shut off automatically under shading.
  • ~5$ per diode (specific to usecase, study the datasheets).
  • Diodes have active elements so this can interfere with testing equipment.
  • Be very careful about direction of the diodes.

MPPTs

  • AERL
  • Look at the requirements
  • Consider just using the most popular one
  • You can get data out of the MPPTs.

Details

  • When CADing the car be very confident the car will be the correct size.
  • Removable panels.
  • Cells have minimum clearances between them
  • Compound curves are terrible for solar surfaces
  • Wiring, avoid shorting, nice diode wiring.
  • Cable management.
  • Purchase +1 module of each size (or more)
  • Attach with double sided tape kind of worked. 
  • Use a silicon with window mesh to get beaded silicon
  • Weigh down in place.
  • Use lots of insulating tape.
  • Use circuit breakers for safety.
  • Prevent the array from being damaged as much as possible.

Software

  • Disconnect, MPPTs from the array before shutting them off. Vice versa for turn on

Safety

  • Array is dangerous. Can't turn it off.
  • Cover with a blanket, build safety into the car.
  • Electrically isolate the driver.
  • Cover the array when wiring.

Grades

  • Ordered by bin of how well they do, we have bin J. Usually we can get highest or second highest.
  • Check approvals.