Feasibility of fully solar-powered cars
The Sunday Nation
Nairobi,
15 May 2022
After reading the
article about electric vehicles in this column a few weeks ago, Joseph
Ngure wondered whether there are cars “that are fully powered by solar
panels mounted on the roof of the vehicle.”
The answer is yes!
Such vehicles do exist but they are not yet commercially viable. They
are mostly made for solar car races in different countries around the
world. On the longest is the World Solar Challenge where 100 per cent
solar powered cars traverse over 3,000km across Australia.
The greatest design
hurdle is that a large area is needed to generate any meaningful energy
from sunlight. Think about it: a typical car measures about 2m wide by
5m long. This makes 10 square metres. However, about 3sq.m need to be
cut out from the front and rear windscreens, leaving only 7sq.m
available for solar panels.
The intensity of
solar energy reaching the earth when the sun is directly overhead is
about 1,000 watts per square metre. Thus, the 7sq.m on a car receives
7,000W at peak time. Of course, this power is only available for a short
time and it immediately begins to decrease as the sun drifts across the
sky.
With current level of
technology, solar panels convert about 20 per cent of sunlight into
electricity. The energy conversion rate has been at that level for the
last 30 years! I think this is an area that requires disruptive thinking
to push the efficiency to much higher levels. Nevertheless, we can get
only about 350W at peak time from the panels on the roof, bonnet and
boot of a car.
Due to the variation
in intensity of sunlight from morning through the day till evening, the
average output of any solar panel is about a half of the peak power.
Thus, in the case of a car, it would be about 175W.
The total energy
generated depends on where in the world the car is being used. In
Nairobi, we get an average of about 7 hours of sunshine daily, so, the
car would generate approximately 1.225kWh in a day. The question, then,
is how far one car drive on such an amount of electricity.
1.225kWh is not much!
In my house, we consume over 10kWh daily. For that reason, the car must
be made with very light materials and have a well-streamlined design to
reduce air resistance to its motion to the lowest possible minimum.
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