Solar Rayce Car Materials

Outline

•What is solar raycing?

•Solar Car Design

•Materials

–Solar Cells

–Carbon Composites

–Batteries

•Results

Solar Raycing

World Solar Challenge

1987 first World Solar Challenge

Hans Tholstrup

Australia 3,000km

2015 new Cruiser Class at WSC

American Solar Challenge

1990 first Sunrayce

University teams

Route varies

2000 annual Formula Sun Grand Prix

Solar Car Design

Solar Cells

https://energyeducation.ca/encyclopedia/Photovoltaic_cell

Photovoltaic Cell

The absorption of the energy of a solar photon excites electrons to jump the p-n junction, creating holes. The flow of the electrons and holes creates electricity.

Shockley−Queisser limit sets the maximum efficiency for a solar collector

Balance of incoming photon flux and outgoing carrier flux

Shockley, W. & Queisser, H. J. "Detailed Balance Limit of Efficiency of p-n Junction Solar Cells." J. Appl. Phys. 1961, 32, 510–519.

Semiconductors

Band Theory of Bonding in Solids

Electrons distributed throughout the solid in extended orbitals with a continuum of energy levels. Metallic (conductors) have a partially filled valence band (a). Insulators have a filled valence band (b). Semiconductors have a small energy gap between the valence band and conduction band.

Silicon

Band Gap Energy of 1.11 eV @ 300K

GaAs

Band Gap Energy of 1.43 eV @ 300K

from P/N Junctions and Band Gaps

p-type semiconductor

Dope to add holes

n-type semiconductor

Dope to add electrons

Solar Spectrum at Earth's Surface

Sircar R, Tripathi B, Gupta S. 2011. Design and Simulation of Thin-Film Silicon Quantum Well Photovoltaic Cell. Journal of Nano- and Electronic Physics. 3: 11-18.

Multi-Junction PV

Up to 45% solar efficiency

(Single junction max. 33.5% solar efficiency)

However, current Solar Challenge regulations do not allow this type of solar collector since they contain toxic elements (e.g. arsenic).

Image from National Renewable Energy Lab.

Future of Solar Cells

Perovskite-based Dye Sensitized Solar Cells

Kim, J. Y.; Lee, J.-W.; Jung, H. S.; Shin, H.; Park, N.-G., "High-Efficiency Perovskite Solar Cells." Chem. Rev. (Washington, DC, U. S.) 2020, 120 (15), 7867-7918.

So far the highest PCE is 34.6% for a perovskite/Si tandem cell (multi-junction)

Liu, J.; He, Y.; Ding, L.; Zhang, H.; Li, Q.; Jia, L.; Yu, J.; Lau, T. W.; Li, M.; Qin, Y.; Gu, X.; Zhang, F.; Li, Q.; Yang, Y.; Zhao, S.; Wu, X.; Liu, J.; Liu, T.; Gao, Y.; Wang, Y.; Dong, X.; Chen, H.; Li, P.; Zhou, T.; Yang, M.; Ru, X.; Peng, F.; Yin, S.; Qu, M.; Zhao, D.; Zhao, Z.; Li, M.; Guo, P.; Yan, H.; Xiao, C.; Xiao, P.; Yin, J.; Zhang, X.; Li, Z.; He, B.; Xu, X. "Perovskite/silicon tandem solar cells with bilayer interface passivation" Nature 2024. https://doi.org/10.1038/s41586-024-07997-7

DSSC

https://www.gamry.com/application-notes/physechem/dssc-dye-sensitized-solar-cells/

Perovskite structure (ABX3)

photo by Angela Foster, UTC

DSSCs

Dye Sensitized Solar Cell manufacturing less environmental impact than semiconductor crystals

Gratzel, M., "Mesoporous oxide junctions and nanostructured solar cells." Curr. Opin. Colloid Interface Sci. 1999, 4 (4), 314-321.

Carbon Composites

Polymers

Monomer

single unit

Dimer

two units

Polymer

many units

Carbon Fiber

Polyacrylonitrile

PAN is the precursor, graphitized at high T & P.

Polyethylene oxide

PEO used as a protective coating for carbon fiber bundle.

Carbon cloth

Woven from carbon fibers.

From "How is Carbon Fiber Made?"

Resin

Cross-linked polymer to increase strength

Epoxy

Epoxide

pre-polymer

Amine

cross-linker

Amine + Alcohol

chemical cross-link

From Macrogalleria

Composites

Sandwich reinforcing material with carbon fiber sheets, fill with resin and cure into the desired shape.

Steel

Tensile strength of 400 - 550 MPa

@ 7.8 g/mL

Carbon Composite

Tensile strength of 4,000 - 6,000 MPa

@ 1.8 g/mL (Zoltek)

Momeni, Amir & Dehghani, Kamran & Zhang, X.. (2012). Mechanical and microstructural analysis of 2205 duplex stainless steel under hot working condition. Journal of Materials Science. 47. 2966-2974. 10.1007/s10853-011-6130-3.

However, exposure of epoxy composites to moisture and heat can significantly reduce their tensile strength over time.

Niu, Y. F.; Yan, Y.; Yao, J. W., Hygrothermal aging mechanism of carbon fiber/epoxy resin composites based on quantitative characterization of interface structure. Polymer Testing 2021, 94.

Batteries

Battery Chemistries

from the Clean Energy Institute at the University of Washington.

Lithium Ion Batteries

Chemical and Engineering News, 1998; pp 37-43

Nobel Prize in Chemistry, 2019

High potential energy: 3.6 V

High energy density: 150 - 250 W-hr/kg

High cycle life: 400 - 1200

Townsend, Ashleigh, and Rupert Gouws. 2022. "A Comparative Review of Lead-Acid, Lithium-Ion and Ultra-Capacitor Technologies and Their Degradation Mechanisms" Energies 15, no. 13: 4930. https://doi.org/10.3390/en15134930

But cobalt mining has negative human and environmental health implications (Kara, S., Cobalt Red: How the Blood of the Congo Powers Our Lives. St. Martin's Press: New York, 2023).

Image from ChemicalStructure.net

Lithium Iron Phosphate

Replace LiCoO2 with less toxic LiFePO4.

Tunnels (1D) of lithium ions instead of sheets (2D).

Less potential energy: 3.2 V

Less energy density: 90 - 120 W-hr/kg

High cycle life: about 750

Lithium Polymer

Replace electrolyte with polymer gel (e.g. PAN or PEO) to decrease weight

Future of Batteries

Replace PVDF (binder in battery composites)

https://www.sciencedirect.com/topics/engineering/polyvinylidene-fluoride

Type of Per- and Polyfluoroalkyl Substances (PFAS) that are persistent in the environment, "forever chemicals," EPA limits

https://www.epa.gov/pfas

Replace graphite anode with TiO2 or Si

Greater capacity

Higher current

But lower cycle stability

Opra, D. P.; Gnedenkov, S. V.; Sinebryukhov, S. L., Recent efforts in design of TiO2(B) anodes for high-rate lithium-ion batteries: A review. Journal of Power Sources 2019, 442, 227225.

Solid State Electrolyte (SSE)

Replace flammable organic solvents

Greater mechanical resistance to Li-dendrite formation

Wu, J, Rao, Z, Wang, H, Huang, Y. Order-structured solid-state electrolytes. SusMat. 2022; 2: 660– 678. https://doi.org/10.1002/sus2.93

Huawei to boost EV range with sulfide-based solid-state battery

Other lithium battery chemistries

Lithium Sulfur

Higher energy density (2600 Whr/kg but only 350 Whr/kg achieved)

Lee, B.-J.; Zhao, C.; Yu, J.-H.; Kang, T.-H.; Park, H.-Y.; Kang, J.; Jung, Y.; Liu, X.; Li, T.; Xu, W.; Zuo, X.-B.; Xu, G.-L.; Amine, K.; Yu, J.-S., Development of high-energy non-aqueous lithium-sulfur batteries via redox-active interlayer strategy. Nature Communications 2022, 13 (1), 4629.

Lithium Air

Highest energy density (1700 Whr/kg, comparable to gasoline)

But "sluggish" kinetics

Girishkumar, G.; McCloskey, B.; Luntz, A. C.; Swanson, S.; Wilcke, W., Lithium−Air Battery: Promise and Challenges. The Journal of Physical Chemistry Letters 2010, 1 (14), 2193-2203.

Liu, Y.; Li, Z.; Zhang, L.; Sun, P.; Wang, S.; Ji, C.; Duan, W.; Wang, L.; Niu, X., Role of Electrocatalysts in the Performance and Efficiency of Metal−Air Batteries. In Noble Metal-Free Electrocatalysts: Fundamentals and Recent Advances in Electrocatalysts for Energy Applications. Volume 1, American Chemical Society: 2022; Vol. 1431, pp 95-127.

Other Materials

Metals

Specialized alloys for lightweight and strength

Motors and frame materials

Rubber Tires

Specialized block co-polymers for

lightweight and traction

Future

Artificial Intelligence Materials Research

https://www.nist.gov/people/aaron-gilad-kusne

Results

Single-Occupant Vehicle (SOV)

Solar cars designed to carry a single occupant

Referred to as Challenger Class in WSC

Catamaran Design

Mono-hull Design

Multi-Occupant Vehicle (MOV)

Solar cars designed to carry more than one occupant that grid charge during the event

Referred to as Cruiser Class in WSC

Putting it all together

"Raycing"

https://solarcar.fandom.com/wiki/Main_Page

Future of Transportation?

Battery technology getting cheaper

https://news.wttw.com/2020/01/02/falling-battery-price-transforms-economics-green-energy

Recycling of Li-ion batteries

https://cen.acs.org/environment/recycling/Lithium-ion-battery-recycling-goes/101/i38

Contact

dungeychem@gmail.com

Twitter @dungeychem

YouTube: dungeychem