Electric cars and solar panels seem like a
match made in heaven, free clean power as
long as the sun shines. A self reliant, solar
car that’s not dependent on the power grid
could recharge sustainably from anywhere you
dare to venture, as long it’s not a cloudy
day.
So, have you ever wondered about bolting solar
panels on your Tesla? And why don’t all
electric cars come equipped with solar panels
for a sleek charge-on-the-go solution? In
fact, with improving solar technology and
clever ground-up engineering, a few self-charging
solar cars are just at the point of coming
to market. In this video we’ll delve into
the practicalities of solar power for vehicles
and have a look at some of the early adopters
of this emerging technology.
In 2017, Elon Musk suggested that Tesla would
offer optional solar tiles on the roof of
the model 3. But later retracted the statement,
saying that putting solar panels on a car
is "Not that helpful, because the actual surface
of the car is not that much, and cars are
often inside. The least efficient place to
put solar is on the car.”
Did you know that every hour the earth is
hit with more energy from the sun than the
entire world consumes in a year? The problem
is the total surface area of the earth is
about 197 million square miles, and The roof
of you car is… a lot less than that, about
3-10 square meters of usable space.
It does make a lot more sense to utilize the
large surface area of your home with a solar
power system like the Tesla solar roof, and
charge your car from there. The only problem
is, you have to be home to use it.
A car with integrated solar panels can recharge
from any sunny parking lot in the world. And,
if you happen to be driving in perfect midday
conditions, you can even charge on the go,
extending the range of your vehicle as you
drive.
Potentially, the extra incoming power from
the solar system could even allow for a smaller,
lighter battery system than in a comparable
conventional electric car, leading to lower
vehicle mass and energy use in driving.
To understand if a solar car could really
work, we need to find out how much solar energy
the surface of a car can capture, and how
much range that energy will provide under
realistic driving conditions.
Solar radiation is often measured in kilowatts
per square meter, so let's assume a 1 meter
square panel is being hit with about 1 kW
of energy in direct sunlight.
Unfortunately, nothing in this world is perfectly
efficient, especially devices that take raw
energy and transform it into useful work:
that’s just thermodynamics.
The most efficient modern silicon solar cells
you'd find on a home system only work at best
around 20% efficiency, but unlike a house,
cars move. This creates unpredictable conditions
and can lead to suboptimal solar panel angles.
You can technically cover every square inch
of the car in panels, but for example, covering
the lower door panels isn’t going do you
much good, as they won’t get much sunlight,
and the proximity to the road will have them
covered in a thick layer of dirt and dust
every time you drive.
So let’s take a sedan the size of a Tesla
Model S, almost 5 m long and 2 m wide, and
put a totally impractical, hypothetical array
of solar cells covering the whole plan-view
rectangular area of 10 square meters. In direct
sunlight, it could charge its battery with,
at best, 20% of the 10 kilowatts of solar
energy hitting it, about 2 kW.
With full sun for about 5 hours per day – just
as an approximation, – that’s 10kWh of
battery charge per day, at best. For comparison,
the long range plus battery option on the
Model S is 100 kWh, so our giant imaginary
square solar panel could charge up to 10%
of its lithium ion battery per day. This model
has an EPA estimated range of 402 miles or
647 km, so we could be looking at gaining
up to 40 miles, or 65 km of range with this
exceedingly optimistic and frankly unrealistic
estimate - potentially a useful extra distance.
In a more practical scenario, the solar panels
would only partially cover the top surfaces
of the vehicle, and have a much smaller surface
area.
Now, no one’s saying you’ll get 100% of
your power from an integrated solar panel
system, in the foreseeable future any solar
tesla would still require the standard battery
charging apparatus, but solar could be a useful
supplement.
Tesla’s commitment to solar energy is well
known, and the Palo Alto behemoth offers solar
roof tiles in addition to the Tesla Power
wall line of energy storage products.
According to the 2019 Impact report from Tesla
the average lifecycle emissions from the Model
3 are less than half those of a equivalent
mid sized ICE car, and if you install a solar
power system on your home, and charge your
EV with that, your carbon footprint can be
reduced to almost nothing.
This was Elon Musk’s idea in 2017 – that
car roofs are small and inefficiently angled
platforms for viable solar installations,
and charging from a home solar installation
made more sense. You could even charge at
night on stored solar and cheaper off peak
electricity.
However, Elon might have changed his mind,
confirming that the Cybertruck will offer
a solar roof option on the truck’s bed.
On twitter Elon said, “Will be an option
to add solar power that generates 15 miles
per day, possibly more. Would love this to
be self-powered. Adding fold out solar wings
would generate 30 to 40 miles per day. Avg
miles per day in US is 30.”
In a previous video, we envisioned what a
foldable solar array might look like on a
Cybertruck, and you may have noticed, we envisioned
it as a… military cybertruck and equipped
it with some extra goodies.
Researchers at NASA’s Jet Propulsion Laboratory,
and Brigham Young University collaborated
to construct a prototype of a solar panel
array that folds origami style, to be used
in space. Such a technology might be an interesting
concept to explore in the automotive world
on earth, where the greater surface area could
increase solar production of stationary vehicles.
When it comes down to it, solar vehicles are
all about efficiency. It’s a matter of energy
to weight. A practical solar car would really
need to be designed from the ground up with
reduced weight and low aerodynamic drag, to
create a vehicle with more favorable energy
density.
For as far as electric cars have come in the
last decade, the energy density of gasoline
is still far greater than lithium ion batteries.
1 kilogram of gasoline contains about 48 megajoule’s
of energy, and lithium ion battery packs only
contain about .3 megajoules of energy per
kilogram. Gasoline still has more than 100
times the energy density of the batteries
used in most electric cars. This is why planes
still use fuel, and why we’re not likely
to see an electric 787 unless a radical breakthrough
in commercially viable battery technology
comes into service.
Teams gather each year in Australia to race
pure solar cars across the continent from
Darwin to Adelaide under the scorching desert
sun. Back in 2013, a new class of racer was
brought into the competition: the Cruiser
Class. Whereas previously the race was simply
about building stripped down single-seaters,
now designs were welcomed for vehicles which
could carry passengers, with additional points
were scored for ‘practicality’ – passenger
cars which could perform under normal driving
conditions. Consistent winners of this class
have been the evolving Stella series from
the University of Eindhoven, the team from
which Lightyear sprang in 2016. This young
start-up is one of the most prominent automotive
companies pursuing solar powered vehicles.
This is a perfect example of engineering competitions
and racing fueling innovation for consumer
products, as the lessons learned in the playground
of the Australian outback have been incorporated
directly into Lightyear One, the first car
offered by the company, which sports 5 square
meters of integrated solar cells along its
low, sweeping roof and hood.
Lightyear one reevaluated every component
of the car and used lighter materials like
aluminum and carbon fiber, to build a lighter
vehicle with the best aerodynamic coefficient
of any car on the market. Four independently
driven in-wheel motors also lower the cars
weight, and improve powertrain efficiency.
In an interview with ‘AutomotiveEV’ magazine,
CEO Lex Hoefsloot described the positive feedback
loop of weight reduction:
‘By concentrating on efficiency and light
weight, we can use batteries that are about
half the size and weight of a conventional
EV, and half the energy consumption of an
EV in the same segment. We have a battery
pack that is two-thirds the size of that of
a Tesla Model S and we can drive further than
the Model S - up to 800 kilometres with good
sunlight, and a minimum range of 400 kilometres
without any solar top-up and with heating,
air conditioning all being used and doing
high-speed driving’.
Stop-start and initial acceleration demands
power and wastes energy in proportion to mass, typical
in urban, low speed situations, whereas the
power required for overcoming air resistance
increases proportionally to speed cubed, sapping
energy at high speeds. How effective the solar
charging will be therefore depends largely
on how you use the car to balance the energy
usage. As Hoefsloot notes, the lightyear one
is an electric vehicle capable of 250 miles
or 400 km of high energy use driving, even
at night, and is expected to achieve a rated
range of 450 miles or 725 km even without
its solar panels trickling in their 1.25kW
of extra juice, which the company equates
to 10-12 km, or 6-7 miles for each hour of
charging, even while driving. This means that,
while this car is self-charging, it is primarily
a highly capable battery electric vehicle
with a small solar capability. Lightyear points
out this solar charge adds up to 10,000 km
or 6,200 miles of free motoring per year in
the Netherlands, and up to 20,000km or 12,400
miles in sunnier regions like Australia or
California.
LightYear believes that by eliminating the
steps between sun and wheel, it should be
possible to gain overall efficiency.
Lightyear, as Tesla did before them, are starting
at the top of the market, coming in at a premium
price point of $170,000 for their first full-size
luxury car with future plans to release smaller
more affordable vehicles in the future.
Sono Motors
Sono Motors on the other hand, are starting
with a more affordable $29,000 compact family
car designed for urban use. In designing the
Scion prototype, The German startup looked
at driving patterns of real world motorists
and found that a typical commute from home
to work and back in Europe or the US might
be up to 16 miles or 25 km.
Sono’s proudest new technology integrates
solar cells into polymer body panels to replace
conventional painted metal bodywork. These
weigh as little as 4-8 kilograms per square
meter2, compared to 5-12 kilograms per square
meter for metal, or the 10 or 20 kilograms
per square meter of flexible or glass-encased
solar panels respectively. Importantly, Sono
claims to be able to produce these at the
same cost as painted metal, although that
includes their initial expense of building
and operating a painting production line,
a cost which reduces per car panel as more
cars are produced. These robust, damage tolerant,
plastic body panels have the additional advantage
of being capable of mounting to the sides
of the vehicle, increasing the solar cell
area on a car where glass panels (as used
by Lightyear) might be risky. Vertical panels,
such as on doors, however, can rarely hope
to point directly towards the sun and achieve
their maximum potential and will often be
shaded entirely when parked next to walls
or other cars.
The Sono founders are exploring some other
intriguing ideas, including bi-directional
charging to allow solar generated power to
be fed into other cars or back into the grid,
or even used for grid-connected external renewable
energy storage and stabilization.
It’s not only relative newcomers who are
adapting to new technological innovations
in solar energy. Toyota has experimented with
a demonstration Prius with high efficiency
thin-film triple junction cells made by Sharp,
whose efficiency is claimed to be 34%, compared
to that of their commercially available silicon-based
solar panel of 22.5%.
Hanergy Solar, a Chinese manufacturer of thin
film panels, have also demonstrated prototype
cars with panels that can harvest 8-10 kWh
per day and supplied such panels to Aston
Martin for their GTE racing car.
Most solar panels rely on cells made from
semiconducting silicon crystals, which convert
sunlight to electricity at around 15%-19%,
but new technologies are in the works to create
higher efficiency solar cells utilizing new
materials.
Organic molecules such as polymers, can form
the light-absorbing layer in a photovoltaic
cell, and can potentially be semi-transparent.
Absorbing infrared light and letting visible
light pass through, which has intriguing implications
for automotive applications, such as windows.
Organic cells can also be flexible, which
can allow them to be fitted onto uneven surfaces
more effectively than traditional glass panels.
As the future unfolds, and more cutting edge
solar technologies come to market, we can
see self charging solar electric vehicles
become more and more practical, as cells get
more and more efficient. A future cell technology
with efficiencies above 50% would be a game
changer, and probably make solar cars ubiquitous.
Heavy batteries are a limiting factor in the
feasibility of solar cars. A breakthrough
battery with more favorable energy to weight
characteristics would revolutionize electric
transportation, and make solar cars far more
realistic.
Promising new technologies that utilize materials
like graphene, solid polymers, and ceramics
are currently in research and development,
and are poised to create the next generation
of powerful batteries with higher energy density,
greater service life, faster charging, improved
safety, and potentially even lower costs.
Most experts agree that we’re likely at
least a decade out from a fundamental commercial
disruption in battery chemistry, but there
is a massive amount of scientific and commercial
attention on this sector, and a lot at stake,
so stay tuned.
So should you mount a solar panel on your
Tesla? Well, we wouldn’t recommend a home-made
conversion with a heavy and delicate, aerodynamically
inefficient domestic panel. However, with
fresh design of new vehicles whose entire
architecture revolves around the solar cells
and a design philosophy of maximum efficiency
and lightweight construction, the future is
bright and this technology can be viable.
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