UM Solar - ASC - Day 6

Thanks for the kind words. I would really hope everyone could get a chance to see Quantum up close. It really is an amazing machine.

The car constantly receives significant powere from the array while driving (assuming it's sunny). However, it usually burns more energy than it brings in while driving at highway speeds. So the morning and evening charges are essential for maintaing speed during the day.

The battery packs have enough juice to go a couple hundred miles. The packs can be charged in full sun in about 3 hours, depending on solar cell efficiency.

Let me see if I can address a couple of your questions but I'll pose them all to some former Team members.

A charging session usually begins in the afternoon after the car stops for the day. Usually the Team will stop racing mid-afternoon and charge for a few hours. The race won't resume until 9 AM the following morning, so they get up and chage for a few hours first thing in the morning. The solar array provides electricity to the motor as does the battery. So, on a sunny day, you're pulling electricity from the array as well as the battery but the array is doing most of the work. On cloudy days, the battery does most of the work and the car must run at a reduced rate to ensure the charge lasts.

I would guess a full charge can take four hours or so (??). I'll find out.

I do not know how far the car can go on just one battery recharge alone.

I'll return with more info, provided I get it. Stay tuned.

EDIT: former Team member 'gbdub' replied with answers ^^. Here's some replies I gathered from other former members (this is several people responding):

All teams will try to get as much energy out of morning and evening charges as possible. Whether those charges can replenish the battery pack depends on how drained the pack was at the end of the day.
Cars continue to receive energy from the solar panels as they drive. Each car has a "break even" speed based on how much sunlight there is - driving below this speed means that some of the solar energy will be put into the battery pack as a charge, driving above this speed means that all solar energy plus some battery energy is required.

Charging a car depends on how sunny it is, how big your pack is, and how good your solar array is. An example using Minnesota's old published numbers: For Centaurus II, they listed a peak array output of 1.2kW and a battery capacity of 2.8kWh. That gives a charge time of 2.3 hours. However, that 1.2kW output on the array had to have been from strong sunlight (intensity of ~1000W/m^2)

Alright, let's do math for the charging time. Battery regs may have changed, but I seem to recall 5 kWh being a reasonable battery pack size. Let's say the silicon array is 20% efficient at 6 m2 and solar radiation is 1000 W/m2. That's about 1200 W array output, so 4-ish hours to refill the pack.
Sounds like batteries are smaller now than they were in the past. But yeah, 1000 W/m2 is only plausible around noon. So if you're looking at morning or evening charging multiply the time by like 2.

If you were to drive at night, you could drive 4 hours perhaps. If you wanted to go highway speeds, perhaps only 2 hours.

It depends a lot on speed and terrain. If it's perfectly flat and you're going slow, (you can go) a long way.

You will also sometimes hear teams talk about a "break-even speed" at which they are neither discharging nor charging their pack while driving. Of course, this break-even speed is dependent on how much solar radiation you are getting. On a sunny day in Australia, you might be looking at a 55 mph break even speed.

Anyways, assume a constant solar radiation: Go your break-even speed, and you can travel forever, even without a battery. Go faster than this, and you discharge your pack. Go slower and you charge your pack, even while driving.

Here is a better summary of your battery only driving question: Cruising around the suburbs/town on surface streets - 4 hours perhaps (with not a lot of stop/go)

Cruising on a US route (maybe 55mph) - 2 hours.

We can probably run about 250 miles on just the battery at a decent pace (45-55 or so).

 

Current silicon cells are more like 20-25% efficient. Gallium arsenide triple junction cells are over 30% effiicient, but have been more or less banned from the major solar car races to make the competition tighter (those cells are incredibly expensive and shut out the less wealthy teams).

The size of the packs is set by regulations to a certain weight, depending on battery chemistry (e.g. you can carry more lead-acid cells by weight than lithium ion, but lithium ion cells are more power dense). The net result is that a good pack holds about 5 kilowatt-hours of energy (i.e. you can use 1000 watts, basically a microwave, for 5 hours).

Awesome, thanks for the pictures. Former Team member, Ethan Lardner, posted images from the same parking lot. There was talk of penalities for carrying the car over the gravel. Since it was after the control stop, there should be no penalty. Chuck is very cool.

I think the car (without driver) might be lighter than Will Campbell. 

Thaks for the update. Goldy isn't having the best ASC, this year.

We truly do exist and refuse to allow our allegiances to be swayed by that hideous (but apparently adorable if you're a youngster) mascot employed by the local university in Madison. 

It was great fun to watch the UM Solar Car team operate in Badger Country yesterday.   They represented UM very well.

Fantastic shots, thanks for sharing. Was that Rachel Kramer chatting with current Team member Caitlin Sadler?

It now appears to be about 10 hours and 54 minutes. But, yeah, I'm so disappointed in you.......=D