Extreme Efficiency: Secrets Behind Miserly Solar Cars Part I
[Image Credit: MIT]
Recently I wrote about my visit to the MIT solar car team; this post is the first in a follow-up series that addresses the phenomenal efficiency of solar cars, and how innovative vehicle design techniques used in solar car development might influence design of future production cars.
Solar cars are amazingly efficient. The have to be if they are to drive continuously, powered only by the sun. If they have no other power source, solar cars must operate on only they power they can collect from their solar arrays (which is pretty limited). Let’s look at some rough numbers. When conditions are good, a horizontal square meter of ground receives about 1000 Watts of power from the sun. Photovoltaic cells are semiconductors that harness the sun’s radiation and convert it directly to electricity. The cells used on the MIT solar car are 21% efficient. That means 21% of the sun’s energy hitting the solar array is converted to electricity. Suppose we have a car with a solar array that has six square meters of area pointed directly at the sun. This array then has 6 m2 x 1000 W/m2 = 6000 Watts of solar radiation hitting it, and produces 0.21 x 6000 W = 1260 Watts of electrical power available to power the car. This is not much at all (about as much power as a hairdryer uses). 1260 Watts is best-case scenario as well; clouds or low sun angles early or late in the day reduce power production significantly. For comparison, a typical 150 horsepower car engine produces almost 112,000 Watts, or almost ninety times the peak power of our 6 m2 solar array. A solar car needs to squeeze every last bit of efficiency it can from all its systems to make it possible to run a car on such little power.
So how solar car designers develop a car that drives at freeway speeds with less than one horsepower? We will look at five main factors in vehicle energy consumption: air resistance, tire rolling resistance, vehicle mass, powertrain efficiency, and system design. I’ll explore the differences between solar cars and conventional cars along these five dimensions in a series of upcoming posts. While it’s impractical to start building production passenger cars the way solar cars are built, we can incorporate many elements of solar car design in future vehicle designs.
Have any of you seen a solar car? On the road? Or even better, have you actually driven one?
Posted: June 8th, 2009 | Filed under: Design, Energy, Transportation |
[...] Original post: Extreme Efficiency: Secrets Behind Miserly Solar Cars Part I [...]
You have stated all the correct reasons why solar cells/panels are not the future solution to solar cars. The future is coverage, the future is solar liquid paint and coatings. MIT has some every expensive and wonderful ideas. I too have met many folks from there and admire them. The thought that must enter the equation is “responsibly design to achieve maximum efficiency and usability within an affordable purchase model”. Dreaming large is great and often, but if you are trying to positively affect society in the renewable and greentech worlds, you must have thoughtfully considered usability as presented. dlinman@suntco.com
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Thanks Dr. Linman for your insights regarding PV liquids and practical considerations. I appreciate your perspective. There are obviously some great applications for PV liquids that could really help increase solar power production.
Yes, the MIT car is expensive, and definitely not practical as a passenger car replacement. (It’s definitely a race car.) There are other solar race cars that are actually far more expensive than the MIT car, mainly due to the use of satellite-grade PV cells.
In this post I described the power produced by a mobile PV array as a challenging design constraint. Solar car designers somehow have to make do with this meager amount of power. What I plan to discuss in subsequent posts in this series is more the mechanical and system integration aspects of vehicle design (not necessarily how to get more power from a PV array). In other words, I want to explore the question “if you really had to get a car to work on 1-2 magnitudes less power than current production cars, how might you go about doing it?” Even if solar race cars have limited usefulness, some of the things solar car designers have learned that help them get their cars to work could be applied to production vehicles to improve energy efficiency significantly.
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Eventually the entire car will be solar…including the glass.
Hence….
http://www.solarcarwindshield.com
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