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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Thanks for watching and have a great day.