What angle of bend can be designed for the solar array to be effective/not break?

• Solar cell limitations.

• Optimal angles for absorption.

The best-case scenario for a solar array to absorb energy is when it is perpendicular to the sun. Different seasons have different angles that the array should be tilted based on the sun's position to the earth, but since we are racing in the summer months (when the sun will be highest in the sky), the optimal angle for the solar panels is around 20degrees from the horizon. Panel arrays can be placed anywhere on the vehicle, but the best spot to put them would be on the southern-most facing side of the vehicle, under the assumption that the equator is south of where we will be racing.

Maxeon Solar Cells

https://sunpower.maxeon.com/int/solar-panel-products/flexible-solar-panels

^the same company that manufactures the Maxeon Gen 3 Solar cells we use on our car made a panel out of Gen 2 cells for consumers to purchase, advertising that the 5lb, 46x22 inch, 110 W array can flex up to 30degrees.

E-FLEX-110W - SunTech Solar Enterprises ($350) per panel

It should be noted that the optimization of where the solar panels are laid out on the vehicle should be considered of before/after and during the race. It is important to lay out the arrays so that during the race we can absorb the most sun while driving.

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Gochermann Solar Cells / Encapsulation

Semi-flexible Modules – Gochermann Solar Technology

“If the design of your application demands an arched plane for the PV mounting area, our PV panels are bendable to follow the curvature. Bending is possible over either axis, comparable to a piece of paper. The maximum bending radius is 30 cm without breaking cells. A panel fixed to a radius will never present all the cells at the optimum angle to the solar irradiation, so a reduction in power output is inevitable. The more a panel is arched the less power will be available. Thus, we strongly recommend using flat mounting areas as much as possible to achieve full power output.”

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Seeing as MSXIV bought these, and the technology has not changed, it would make sense to reuse/ repurpose them. Compared to the consumer available ones, these will be significantly smaller and therefore much more manipulatable in terms of the layout that we want. Note that the cells were said to be quite dirty after the race, although Gochermann provided instructions on cleaning, so they are expected to be relatively clean now and most likely not losing much efficiency.

Plenty of information can be found on the MSXIV confluence page regarding mounting procedure, how to clean, and other information from Gochermann.

Pages 97-100 of The Winning Solar Car: PDF Library - Mechanical - Confluence (atlassian.net)

Pages 39-45 of A Solar Car Primer: PDF Library - Mechanical - Confluence (atlassian.net)

Solar Array Type

An assumption can be made that there are different limitations depending on solar cell type.

Type 1 - Silicon Based Solar Cell

• Monocrystalline vs Polycrystalline:

  • Mono cells are made of one single fragment of silicon, are more efficient (about 4%) and are recommended when space is a limitation.

  • Poly cells consist of multiple fragments of silicon melted together, and although they are less expensive than mono, they are less efficient.

  • MS will use mono.

• Sunpower and Azur Space (mostly multijunction) seem to be the leading solar cell companies.

  • Sunpower Maxeon Gen III was used for MSXIV (efficiency of 24.3%)

• Looked through the Gochermann solar technology page, as they were who was used for encapsulation for MSXIV.

  • Maximum 30 degree bend, although with more bend, the power output decreases significantly. Always better to have a flatter surface to achieve the optimal angle with all cells.

    • This bend can happen in both axis, although since 3D curvature is very difficult to achieve, we will be staying with 2D curvature of the array as per Catherine’s recommendation.

  • They offer a non-reflective surface which decreases the light reflection fro 4% to 0.3% when compared to smooth surfaces.

• After brief research, could not find viable competition to Gochermann for a lightweight encapsulation company.

Type 2 - Thin Film GaAs - Will not be using due to cost

• Lightweight and thin

• The most efficient (electrons travel six times faster through it)

• Very expensive (1000x more than silicon counterparts)

Type 3 - Multi-junction - Will not be using due to cost

Resources/links:

https://www.sciencedirect.com/science/article/pii/S266693582030001X

New Stanford manufacturing process could yield better solar cells, faster chips