Over 50 teams, composed of students from high schools and colleges in over 30 countries, will soon compete in the Bridgestone World Solar Challenge (BWSC), a solar-powered car race. The road race is over 30 years old, held every two years in the Australian outback, and covers a route more than 3000 km (1864 mi) long from Darwin to Adelaide. The race rules mandate that the cars must be designed, built, and raced by the teams and run primarily on solar power, with very limited use of stored energy.
Team Sonnenwagen from RWTH Aachen University and University of Applied Science Aachen, which is participating in the Challenger class for the first time, will also be taking part. (The Challenger class features a smaller solar collector area and broader design envelope than the Cruiser class, which allows a greater design variety.) Covestro, a materials supplier for the automotive industry, is supporting the project as main sponsor this year and is a key team member.
To make the Sonnenwagen as light and aerodynamic as possible, the development team chose the energy-absorbing polyurethane foam system Baysafe from Covestro, which is used in the crash box at the front of the solar car. The team chose Baysafe because it resolved the conflict between low weight and impact resistance: The crash box foamed with Baysafe absorbs impact accelerations of up to 5g.
Another team competing in the BWSC, a Dutch solar car team from the University of Twente and Saxion Hogeschool, selected silicon carbide (SiC) devices from UnitedSiC, a manufacturer of SiC power semiconductors. UnitedSiC provided product samples of its FAST Series of SiC FETs to the team for use in its new solar car, RED E. Solar Team Twente consists of students of different disciplines ranging from mechanical and electrical engineers to marketing students.
“At Solar Team Twente we try to make everything as efficient as possible. Since most commercial electronics do not meet our high demands, we develop our own,” said Devon Screever, Electrical Engineer at Solar Team Twente. “At the moment, Solar Team Twente develops and produces the entire electrical system of the vehicle, from solar panel, battery, and even the drivetrain. The motor controller and electrical motor are also developed by the team. To ensure we get the best possible performance, we are continuously looking to new technologies, including silicon carbide. With SiC we can reduce our switching losses drastically, while reliability and robustness remain guaranteed.”
SiC FETs from UnitedSiC are based on a cascode circuit configuration, in which a normally-on SiC JFET is co-packaged with a Si MOSFET to produce a normally-off SiC FET device. With its standard gate-drive characteristics, the SiC FETs offer a “drop-in replacement” capability for higher performance in existing designs that use Silicon (Si) IGBTs, Si FETs, SiC MOSFETs, or Si super junction devices.
“For new designs such as this solar car project, UnitedSiC FAST Series SiC FETs will offer the designers significant system benefits from the device’s increased switching frequencies, such as increased efficiency and reduction in the size and cost of passive components,” said Anup Bhalla, VP of Engineering at UnitedSiC. “The FAST Series devices offer not only ultra-low gate charge, but also the best reverse recovery characteristics of any device of similar ratings.
The UnitedSiC UF3C FAST SiC series, which now totals 14 devices, is available in a range of TO247-3L, TO247-4L, TO220-3L and D2PAK7-3L packages, with four 1200V and ten 650V options.
Flexible, glass-free solar technology from Alta Devices will be employed in the Stanford Solar Car competing in the challenge.
“For solar to be realistic for the broad auto market, it needs to have several important characteristics,” said Jian Ding, Alta Devices CEO. “It must be flexible enough to conform to the surfaces of innovative vehicle designs, maintain high efficiency even in the hottest weather conditions, and be manufacturable at scale.”
To date, solar technology used on solar race cars, luxury cars, or concept vehicles has typically been silicon solar or specialized solar developed for space applications. Silicon solar, while low-cost, is very brittle, which makes it difficult to handle and integrate into curved automotive surfaces. Silicon has relatively low energy conversion efficiency compared with other materials, making it harder to generate the desired amount of power from the limited area of a car roof. In addition, silicon solar quickly becomes warm during operation and loses efficiency as temperatures rise. Overall, this results in less vehicle range or available power per day. Space solar cells are high efficiency, but like silicon, very brittle and don’t manage heat well. In addition, the traditional complex and time-consuming manufacturing process makes them expensive.
Alta Devices thin-film gallium arsenide solar technology is a newer technology relative to silicon and space solar. It is flexible, lightweight, high-efficiency, and has structural properties that allow it to run much cooler. It can also reportedly be produced at mass-market scale.
The 2019 SSCP solar car, Black Mamba, has a new sleek design versus previous team cars, and the Stanford team built a custom oven to cure the large shell composites. The car is the 14th solar car that the Stanford team has designed. This year’s design is asymmetrical with a single aerodynamic shell covering the body. Alta Devices solar cells have been integrated onto the top surface of the vehicle.
Due to the ability of the solar to flex, the curves of the vehicle design were preserved. Ding explained, “In the future, mass-market electric vehicles will be designed for long-range, as well as safety, and sustainability. They will use extremely light-weight and aerodynamic materials. Solar will be incorporated to seamlessly cover the body of the car, maximize range, and power auxiliary systems. Whenever there is sunlight, the car will always be charging.”