Vehicle Electrification - October 24, 2013 - 11

The key innovations started to come together a year ago, he recalled, when the team
learned of a rule change that all the entries
were to have four wheels.
"We had been planning a solar-powered
motorbike at the time, so even though it was
a dead-end, we were already thinking radically," he explained.
Another change was that drivers must be
seated in an upright position, unlike in the
past where they could lie prone for better
aerodynamics.
"We hit the drawing board with a clean
sheet, but we did take from that earlier work
the key idea of minimizing the size and
weight of the design as much as possible,"
Mario-Ghae said. "We went through 20 different sketches and finally hit upon the idea
of decoupling the aerodynamic performance
from the solar performance, which would allow us to improve them both without detriment to the other."
CUER's design philosophy, he explained,
was to compress the car in all directions to
make it as small, lightweight, and aerodynamic
as possible and then to use solar-tracking
plates housed beneath a transparent canopy
that transmits 95% of the wavelengths that the
solar cells use. The need to minimize the frontal area to cut drag led to the bullet nose, and
the streamlined teardrop canopy at the back
worked well to enclose the tilting solar panels.

Design trade-offs
Of course, "increased complexity is a risk of
this approach, so it's no surprise that we've
been spending a lot of time getting the
tracking system to operate correctly," he reported. During the effort, the team developed
the means to model the sunlight and the panel positions in any arbitrary geometry so

SAE Vehicle Electrification evsae.com

A Tokai University student shows his
solar-powered car to U.S. Navy sailors in
Ayase, Japan.
members could simulate how the sun moves
across the sky. That helped them produce
software that triangulates the vehicle's GPS
position and direction of travel with the time
of day to track the sun.
Mario-Ghae noted that CUER had opted to
use satellite-grade gallium arsenide photovoltaic (PV) cells, which provide high (36%) conversion efficiencies. The rules allow teams to
choose either 3 m2 of high-efficiency gallium
arsenide or 6 m2 of silicon cells, which offer
less efficiency (22%) but provide around a
fifth more total solar power.
Resolution's carbon-fiber monocoque
structure, a one-piece shell that weighs only
35 kg (77 lb), was built in collaboration with
the U.K.'s National Composites Centre. The
solar array is connected to a lithium-ion battery pack and a 97%-efficient electric motor
that is mounted in the hub of one of the rear
wheels, thus avoiding gears or chains.
The CUER team captain acknowledged
that his team benefited from considerable
technical support from its U.K. industry sponsors, such as Jaguar and Land Rover.

Steven Ashley

October 24, 2013

http://www.evsae.com

Vehicle Electrification - October 24, 2013

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