PRODUCTS & SERVICES
Chasing the sun
The smallest measurable improvements in efficiency can make the difference
between winning and losing a solar-powered car race across Australia
The 3,020km (1,876 mile)
Bridgestone World Solar Team
Challenge, which took place in
October 2019 in Australia, from
Darwin to Adelaide, was won this
year with an average speed of
86.6km/h (53.8mph), seeing an
improvement of 5.4km/h (3.3mph)
or 6.6% compared to 2017. This
biannual event is the ultimate racing
challenge for cars powered entirely
by the sun.
The basic design of all cars in the
race is similar: an aerodynamic wing
shape covered in arrays of
photovoltaic panels to convert the
sun’s light into electric power, which
is fed directly to a motor driving the
wheels, with any excess stored in a
small on-board battery.
To win the World Solar Challenge,
the race car must capture as much
solar energy as possible and convert
the electricity it generates as
e iciently as possible into
mechanical power delivered to the
wheels. At the same time, it must
keep energy losses to a minimum,
with race teams paying minute
attention to aerodynamic design to
keep wind resistance to a minimum.
One of the most important
engineering challenges is to
optimize the e iciency of the motor
and battery management systems.
The aim is to achieve better than
99% e iciency in the various power
conversion circuits, the most
important being the solar panels, the
battery and its management system,
the inverter, which converts the DC
output from the solar converter to
the AC supplied to the motor, and
the motor itself.
Typically, a DC solar conversion
circuit consists of a Maximum Power
Point Tracking (MPPT) algorithm,
to optimize the panel’s voltage with
reference to the sun’s brightness
and angle of incidence, as well the
solar cell temperature, and a
Solar Team Twente from the Netherlands entered its Red E car in the World Solar Team Challenge, which sets entrants the goal
of fi nishing a 3,020km (1,876 mile) race using only power harvested from the sun and generated into electricity
converter circuit to boost the voltage
from the solar array to the required
input voltage of the inverter.
The goal of every team is to finish
the race with zero energy remaining
in the battery, so the state of the
battery’s charge must also be
precisely regulated. This will,
therefore, enable the driver to
maximize total energy usage and
achieve the highest possible speed
for the longest possible distance
144 // January 2020 // www.electrichybridvehicletechnology.com
without running out of power. The
more accurately the charging state
can be measured, the more
confidently the driver and race team
can set the optimum speed, given
the prevailing and forecasted
weather conditions.
Given that the di erence in the
average speeds between this year’s
winner and second place was just
0.5km/h (0.6%), it is even clearer
why even the smallest improvement
in conversion e iciency could make
a di erence between winning and
losing, both for the race and our
global e orts to maximize the
potential of solar power.
To be able to measure potentially
small improvements in e iciency
requires a sensitive and accurate
power measurement system. The
accuracy needs to be high because
it needs to be better than the very
small percentage improvement that
Photo: Jerome Wassenaar
/www.electrichybridvehicletechnology.com