Solar Powered Car Can Get Close To 60 mph

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."

Comments

But how does it do in the crash test?

[InsaneProcessor]

And I don't think my entire family will fit either.

Re:But how does it do in the crash test?

[Thanshin]

does it do in the crash test? And I don't think my entire family will fit either.

Are you looking for a car? Or for an alibi.

Re:But how does it do in the crash test?

[Nutria]

And I don't think my entire family will fit either.

Or groceries or luggage, or run on a cloudy day.

Solar auto challenges should be viewed as nothing more than useful engineer training that serves no immediate practical purpose, just as having my CompSci prof give me a large Senior Project, that I haven't used in my professional life, but gave me a solid foundation on which to grow.

Re:But how does it do in the crash test?

[cool_story_bro]

I think you have a shaky grasp on the term immediate practical purpose. I'm fairly certain the GP meant that these solar powered race cars aren't going to finish their race and go straight into production for retail consumption

Re:But how does it do in the crash test?

[Simon Brooke]

Solar auto challenges should be viewed as nothing more than useful engineer training that serves no immediate practical purpose...

Disagree.

Granted solar power is not suitable for actual every day transportation in most parts of the world, a great deal of the engineering of these cars will move into the mainstream - and sooner than you think. As fuel gets more expensive, cars will have to get much lighter, much more aerodynamic, and have much lower rolling resistance. Many of them will use battery or hybrid power systems, and regenerative braking will become commonplace. Solar cars are pioneering all these technologies.

Re:But how does it do in the crash test?

[Alioth]

It's a racing car. Your family and your groceries won't fit in a Formula 1 car or Indy car either. It's not supposed to be a family car or anything approximating that, it's for racing.

Re:But how does it do in the crash test?

[Endo13]

And I don't think my entire family will fit either.

Imagine a beowulf cluster of them!

Pushing the limits of tech

[peterdaly]

This is very interesting technology. These solar races really produce odd looking vehicles. Three wheels makes sense in terms of rolling resistance, but I can help but think what might happen if it needed to take a turn fast.

Programs like this are great, and help push the technology envelope. Although it's neat that it can hit 60Mph...the article really does not have much real information in it.

I hope to see some of this technology filter down into production cars. I've always wondered how much power could result from the sunlight hitting the roof of my car all day long when I'm at work. Seems like there is potential missed opportunity there.

-Pete

Re:Pushing the limits of tech

[cplusplus]

I've had the same thought. I'd love to be able to drive to work in a plug-in vehicle of some sort, park the car in the sun all day and let it passively recharge, and then drive home using that free power. The only thing the sun does for my car now is make the interior too damn hot (even with window tint and a sun shade).

Re:Pushing the limits of tech

[hedwards]

If you need to turn that fast you're probably screwed anyways. The friction on the front tires hasn't been the limiting factor for quite some time.

The much bigger problems are weight distribution and the rate at which the wheels spin with respect to each other. Hence the addition of http://en.wikipedia.org/wiki/Electronic_stability_control for more information.

And with only 3 wheels, that latter concern is easier to deal with than with the extra wheel.

Re:Pushing the limits of tech

[Rei]

This is very interesting technology. These solar races really produce odd looking vehicles. Three wheels makes sense in terms of rolling resistance, but I can help but think what might happen if it needed to take a turn fast.

Just because it's three wheeled, or because it's this specific car? Three wheelers can be extremely stable.

I've always wondered how much power could result from the sunlight hitting the roof of my car all day long when I'm at work. Seems like there is potential missed opportunity there.

The missed opportunity would be to put those precious solar cells on top of a car where you have to carry the weight around and the angles are poor rather than on a rooftop where you don't have to haul the weight around and where they can be positioned at an optimum angle.

Re:Pushing the limits of tech

[Rei]

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.

No, not impressed.

[gblackwo]

Most of the North American Solar Challenge vehicles and World Solar Challenge Vehicles easily exceed 60 mph.

I work on Purdue's Solar team and have first hand experience with these vehicles on the highway.

www.PurdueSolar.org

Re:No, not impressed.

[oneiros27]

I was on the GW solar car team more than 10 years ago -- we could do 60mph back then, so I'm not impressed, either.

The important factors included: how much sun is there are the time, are you willing to drain the batteries, and are we going uphill?

If you've got good sun, don't have a screwed up array like we did in the '95 Sunrayce, and are willing to drain your batteries, it's easy to go over 60mph. And if you're going downhill, it's even easier.

Of course, that year they decided to put the finish line at the top of a mountain, and we had mostly clouds for the last few days, so just about everyone showed poorly overall.

Sponsorship

[ickleberry]

Those HP Logo's could have been solar cells and it would have actually got to 60 rather than close to it

Re:Which means for the greenies...

[CannedTurkey]

Get your SUV out of the way of my progress.

Big whoop

[djupedal]

>"Try doing it by using the power required to run a hairdryer."

Hair dryers pull 1000~2000 watts, right? That is a ton. Try having only a few watts to work with...on Mars.

"The transmitter on the lander has a broadcast power of about 14 watts, says Callas. For comparison, the beacon on the Mars Global Surveyor, which is currently in orbit 380 kilometers (228 miles) above the surface of the Red Planet, is weaker -- only 1 watt. Boding poorly for the mission is the fact that this week the sensitive Dish detected the weaker signal from the surveyor, but not the stronger signal from the lander.

But the main problem is the weakness of the signal. And signals weaken as they traverse the roughly 300 million kilometers (about 180 million miles) from Mars to Earth. "We expect a signal hitting the Dish to be something of the order of one billionth of a billionth of a milliwatt [one-thousandth of a watt] of power," says Callas. "It's extremely tiny. This is equivalent to listening to a cell phone from Mars.""

Re:Big whoop

[R3d M3rcury]

Hair dryers pull 1000~2000 watts, right? That is a ton. Try having only a few watts to work with...

You had a few watts?! LUXURY! Why, when I was a boy, we had to generate our own electricity by walking up hill to school! Both ways!

But try to explain that to the kids today...

60mph Average

[zlexiss]

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)

Going fast is easy.

[onion2k]

Actually going fast is pretty easy so long as your aerodynamics are sound. All you need is enough energy input to counter air resistance and friction from the wheels and you can maintain whatever speed you like. The difficult bit is accelerating to a high speed quickly. It'd be easier to wait until people get over wanting to go fast than design a solar vehicle that can accelerate from a standstill anything like a petrol car.

Fortunately I can see that happening. As the price of driving goes up people's priorities will change.

Re:Going fast is easy.

[prefect42]

But surely systems like KERS show that with only a small weight penalty (from around 25kg), and a decent amount of power (~80bhp), you can already get there. Now as long as you don't need to be using that often, and can simply clutch it out while not using it, it's just 25kg of dead weight while trying to be efficient.

This is assuming that you've got another much more efficient lower powered motor for the rest of the time.

25kg just isn't such a huge weight to carry in any vehicle intended to carry 2+ people, and you don't need that much power to make a car perfectly good to drive, as long as it's not stupidly heavy.

Re:Going fast is easy.

[Rei]

Yeah. Note what happens when you try to take these sort of concepts from "crazy hypercar" to "usable vehicle". Compare, for example, Pac Car II to the Aptera 2e. Same basic design philosophy, but the 2e has to be usable on city streets, hold two passengers and a good amount of cargo comfortably, be practical to mass produce, have proper acceleration and range, and in general have the amenities and safety people expect in a car. And the net result is that you go from a drag coefficient of 0.06-ish to one of 0.15-ish combined with a severalfold increase in cross-sectional area, while your weight increases from 66lbs to almost 1700lbs.

It's hard to say that Aptera wasn't going for as extreme as you can get while still meeting those basic consumer requirements; it's just that those basic consumer requirements really take a huge hit on your energy consumption. The 2e is still 2-3 times more efficient than a Prius, but it's nothing like the extreme demonstration vehicles out there such as Pac Car II.

Could you do better than the Aptera? Probably. You could go for tandem seating to reduce cross sectional area, at the expense of cargo space and some consumer acceptability. You could build out of honeycomb foam core carbon fiber rather than the equivalent using fiberglass (which is 50% denser), but that'd raise your sale price by a lot. You could skip the electric drivetrain and save a hundred pounds or two, but then you're worsening your environmental impact in other ways. So, I'm not really sure you'd want to take the concept any further than Aptera has. A lot of people already think they've gone too far... ... I should add, myself definitely *not* included; I'm on their waiting list!

Re:Which means for the greenies...

[jellomizer]

I doubt we will see a sell-able fully solar powered car in our lifetime. As there are many concepts that make it impractical
Night Driving
Garages
Extended periods of poor weather.
Tree Coverage
Building coverage in Cities

However out of these competitions we come with a lot of good technology more then just solar power. The fact that you car powered off the energy of a hair dryer. Could be used in many mechanical devices longer lasting battery powered devices. Heck they could use the technology and make a more efficient hair dryer.

Let's do the math

[Ancient_Hacker]

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:Let's do the math

[Rei]

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.

EV's could do 375 miles per charge in 1997

[Colin Smith]

Using NiMH batteries.

http://en.wikipedia.org/wiki/Solectria_Sunrise

http://www.sunrise-ev.com/

Everyone else is just re-inventing the wheel.

The best place of solar panels is on the roof of your house, charging up a battery bank you can use to charge the car when you park it.