Solar Powered Car Can Get Close To 60 mph 119
Jason Sahler writes with this excerpt from Inhabit: "The World Solar Challenge across the Australian outback is coming up, and we're already seeing some truly incredible vehicles going for the gold. Take the Bethany, a solar powered vehicle designed by Cambridge University students. The vehicle is capable of achieving close to 60 miles per hour. Doesn't sound too impressive? Try doing it by using the power required to run a hairdryer."
No, not impressed. (Score:5, Informative)
I work on Purdue's Solar team and have first hand experience with these vehicles on the highway.
www.PurdueSolar.org
60mph Average (Score:5, Informative)
I think (the article is badly written) that the key development is that this car can average almost 60mph. 60mph burst speeds are pretty easily reached in many solar cars. I remember doing about 65 mph back in 1993 in our cars (Dartmouth College's Sunvox I and IV)
Let's do the math (Score:3, Informative)
Let's do the math on this one.
A hair dryer draws around 750 watts, which is a convenient number too, as that's about 1 horsepower. Let's assume the electric motor is 100% efficient too, just for simplicity.
So you're saying the car can do 60MPH on one horsepower.
That's quite doable with a very aerodynamic design and low-friction tires.
But the hill-climbing ability is mighty weak.
One horsepower can lift 550 pounds one foot per second.
So if this vehicle and rider weight 550 pounds, it's going to slow down to 70.7% of 60 MPH if it encounters a hill with a 60 foot rise per mile, just a bit under 1% slope. A 3% slope is going to slow it to a crawl. Not too good anyplace but Kansas.
And no, you don't get it all back on the downhill slope.
Re:Pushing the limits of tech (Score:3, Informative)
Sorry, but not with current physics.
A typical streamlined EV, like the Volt, the MiEV, or the Roadster, will use about 200Wh/mi. Let's go with 220Wh/mi wall to wheels, since some is lost in charging. Let's assume a very efficient panel (20% *after* accounting for the cells not all fitting perfectly together) and a large, flat area (2' x 4' ~= 0.74 square meters). Let's say that it's perfectly sunny (1000W/m^2), there's no shade, and let's be optimistic and say that the cosine-weighted average angle of the sun to your car is 50 degrees over the course of a 9 hour work day. Ready? 1000W/m^2 * 0.74m^2 * cos(50 degrees) * 20% efficiency * 9 hours / (220Wh/mi) = 3.9 miles.
Not exactly a long distance for this very favorable case, ne?
Put solar cells on the roof where they belong -- where they're not requiring space/aero compromises, weighing your vehicle down, more likely to be shaded, and more likely to be at the wrong angle.
Re:Let's do the math (Score:3, Informative)
A hair dryer draws around 750 watts
That's one weak hairdryer.
it's going to slow down to 70.7%
If there were no batteries to average out the ups and downs.