Slashdot Mirror
World Solar Challenge Beginning
Stuart Bowden writes: "Today (Sunday at 8:00am Central Australian time) is the start of the 2001 World solar Challenge, a sort of alternative Cannonball Run in which the solar cars cost up to $10 million. Over the next five days or so thirty three solar powered cars will race 3000km across the Australia desert powered only by sunlight. The official site is at WSC and there is extra gossip, pictures and information at our site at the University of NSW. We'll be doing the web upgrades on the road by begging connections at roadside diners and the occasional satellite phone. The big problem is keeping up with solar cars that don't stop for fuel." Our previous story had more links.
Solar cells have a theoretical maximum efficency of not more than 50%. Currently, triple junction GaAs cells will get you about 35% (pretty close to the limit). Such an array for a solar car (5m by 1.8 m) can cost in the neighborhood of 500,000 USD. Meanwhile, a 19% Si array can be had for 70,000, and a 13 - 14% array for 10,000. As you can see, the price of an array has something of an exponential relationship to the efficency. To inprove the maximum efficency, you have to have the money to play with some very expensive toys. Only a few companies can afford such equipment (such as Honda and Aurora) and no school that I know of has a suffcient budget. We can (and do) play with making cells, but to commit to designing them and trying various chemistries and encapsulations requires more money than we have. Our object is to make cells that at a given efficency are cheaper than the ones on the market.
Meanwhile, the only things that slow you down are rolling resistance and aerodynamic drag. Cutting weight usually requires nothing more than a lot of thought into material selection and structural design (not hundreds of thousands of dollars).
Aero is a little more interesting, as there are tradeoffs betweeen the effective efficency of your array and your aerdynamic drag (for example, a taller car can catch more sun in the mornings and evenings, but will have more drag). These tradeoffs are related to how fast you want to go, and the conditions of the specific race you are designing for (whether it is primarily from north to south or east to west effects how you handle these tradeoffs; a car sloped to a particular side doesn't help if that side never faces the sun).
Also worth mentioning is that all the American college teams that I know are in the WSC just came off competing in the American Solar Challenge. Teams that did not have large budgets in that race competed in stock class, where they were only allowed to spend $10 per watt that they expected out of their array (limiting them to silicon cells) and lead acid batteries. I do not know if any of those teams went to WSC, but that would explain their use of lower power cells.
Photovoltaic cell research is one of the mose exciting fields of renewable energy, but when it comes to racing cars, you're more likly to win by buying the best array you can afford, and improving the other aspects of your car.
My roommate is President of the Solar Car team at Kansas State University. His team recently finished 5th overall at the 2k1 American Solar Challenge. Since he's president I get to hear all about these things. Very few actual solar panel manufacturers enter, but rather sponsor universities. Sponsorship is why the University of Michigan, near the auto industry capital of the USA, is taking their car, and why we cant afford to ship ours over there.
.1~1 percent. In contrast, redesigning the body of the car gave us about 35 percent less drag. In addition, the concept of "regenerative braking," using the kinetic energy of the car to run the engine in reverse and charge the batteries, greatly increases overall effiency. Essentially, research into solar panel mechanisms requires extensive knowledge in both electrical engineering and mechanical engineering, which few people have, and of those who DO have that exp, few of them would put up with a university salary.
As far as the actual electricity generation goes, I'd think its a bit beyond the capabilities of a group of freshman and sophmore (my roommate is a sophmore) undergrads to not only design a better grade solar array, but then manufacture it. Even if some kid did manage it, they couldn't afford the costs. I believe the cost of the current solar array is some 25k, which generates about 14 hp. That gets them up to about 75 mph max, but that eats of the batteries pretty fast.
Most solar cars don't use the latest and most efficient solar array. If I recall correctly, the latest car from KSU, CATalyst, uses 14 percent efficienct solar panels. The most efficient are gallium-cyanide (or something like that) that are extremely expensive (like 500k or so). Of course there are a few things that can be done besides simply upgrading the solar array. I've heard of shaping the solar cells in inverted pyramids at the near molecular level will increase absorbtion, but the return is expected to be on the order of
Yea, I can't spell efficiency, but who cares, I'm only a Computer Science major.
I Browse at +4 Flamebait
Open Source Sysadmin
Race speeds of the top cars are above 50 MPH. At speeds up to 45 MPH air drag increases on a linear scale. Above 45 MPH air drag increases geometrically and quickly becomes the main factor in car performance. Teams rebuild their car body if they find a way to shave a few tenths off the drag coefficient.
The new body on University of Missouri - Rolla's Solar Miner III (rebuilt after the sunRayce last summer) has a drag coefficient of about .09 compared to the previous body's stat of .12. As such, we should get an average speed of several miles per hour faster.
Other major factors are vehicle weight (obviously), battery type, and solar array type. Lithium ion batteries have much higher retention than older lead-acid batteries that some teams still use and are lighter as well.
The solar array varies from car to car depending on team budget. Teams with huge budgets have higher efficiency arrays and much more available power. More power does not translate into better performance, though, because over the long haul a more efficient body design with less parasitic power loss will perform much better even with less power.
KingPrad
Stop the Slashdot Effect! Don't read the articles!
first, a shameful, kowtowing plug: http://solar42.umr.edu
;) ), but when we design a car, we know that there are teams out there that have 3 times the funding that we do. So, rather than sacrifice our budget for the nifty "one-item" improvements, we spread costs out to balance improvements. I would say that batteries, solar cells, and the motor are the three big ticket items in a solar car. sacrificing the quality of the motor and battieries that you can purchase for a really high efficiency solar array is bad engineering. in this way, solar raycing is kind of like taoism, everything must be in balance
solar car design and raycing is (for us uni and high-school persons)is primarily an endevor of engineering. you can't always splurge on the 34% efficient space-grade cells. sometimes you have to determine that you don't have the money, and you'd rather have a decent car overall than a boffo solar array on a wooden crate. if an engineer works hard enough at it, and has the right insight at the right time, many good things can happen...independent of the almighty buck. at UMR we have pretty good funding (how much is for me to know, not you all
The team of my university (Delft, Netherlands) does use the triple junction solar cels. That should be the best there is, its still untested in space! Thanx to the European Space Agency and a very generous sponsor [~1M$] they finally could afford this. They even have a few square centimeters of cells that actually flew on Hubble! In addition to this they use Maximum Power Trackers that always load the cells and the battery at the optimum settings.
It seams to pay off: they currently lead the race!
Check it out at here [www.alpha-centauri.nl]