Senior Neel Vakharia is a bio-electrical engineering major whose experience as a solar car driver and power-electrical engineer during the American Solar Challenge 2010 makes him the perfect team member to tell you all about the battery.

 We’ll start at the smallest level of the battery, the cell:

 So the battery pack is one of the three major high voltage systems on the car (the other two are the solar array and the motor). Before we can talk about the battery pack as a whole, it’s important to know a couple of key things about the individual battery cells. What is a battery? It’s a device that stores charge.  But what makes it different from a capacitor, which also stores charge? The big difference is that while a capacitor’s voltage scales linearly with the amount of charge (voltage = charge/capacitance), a battery will quickly reach some nominal voltage, hang-out there until it starts reaching its maximum capacity and then quickly start increasing again, like this graph shows:

Why does this matter?  Many electronic devices (like your phone or laptop) need a fairly constant voltage supply to work properly. But from the above graph you can see that batteries have a fairly constant voltage supply (unless they’re very low or very high on charge) while capacitors don’t. And the ability of the battery to produce a fairly constant voltage allows the car to run more efficiently.

 So then how do we pick the right batteries? Obviously the ones that can hold the most charge, right? Well, kind of. The key criteria in picking the best battery is something called energy density. It doesn’t really matter how much charge the battery can hold, the important thing is how much it can hold per unit weight. This is because for solar cars and electric vehicles, the less the car weighs, the less energy it burns trying to move all that weight. On top of that, because the World Solar Challenge has a limit on how much the solar car’s battery can weigh, the more energy we can get per unit weight, and the more energy we have in total.

A UMsolar Battery

Another big concern that can rule out many batteries for UMsolar is the battery’s relative capacity at high temperatures. Because batteries are chemical devices, the ability of the battery to release energy varies depending on temperature.  Since the World Solar Challenge is a race across the Australian outback, and since there are approximately 500 battery cells releasing heat within an enclosed box in our solar car, you can imagine how quickly the temperature inside the battery pack can escalate. Because of this, UMsolar has to pay attention to the smallest details on the battery’s spec sheet.  The spec sheet describes how the battery ideally should work, but it doesn’t always perform this way.  All batteries vary a little bit in their performance.  The team does a lot of testing to verify that the batteries we’ve ordered actually work like they’re supposed to. 

The last major concern is the maximum discharge rate and battery voltage. For any application, we must consider what our current and voltage demands are so that we pick the battery that can handle our application. If the battery voltage is too low, we would need to stack multiple batteries in series and if the maximum discharge rate is too low for our application, we would have to put batteries in parallel to split the current. This sets us up for the next level of the battery pack which is…

The Module:

 Now that we have discussed a little bit of the individual cells, we can move to the next level of organization — the module. A module of battery cells is simply a group of cells connected in the same way (series or parallel). Generally, solar car teams configure their modules in parallel because it is much easier to manufacture and manage. These modules can then be stacked in series. If you remember from your high school or college physics course, adding batteries in parallel will increase the module’s maximum discharge rate, but keep the voltage the same. We will then stack modules in series to increase the voltage. The combination of a series/parallel configuration is known as the battery pack configuration.  In a nutshell, a battery pack configuration is how all the cells are organized electrically in the battery pack.

For this week’s Trivia Tuesday, we want your opinion on solar energy.  Our favorite answer gets a free, official team t-shirt, delivered straight to your door (winner must email solarcar@umich.edu an address where we can send you your prize).

By most estimates, solar power provides less than 1% of total U.S. energy.  What solar technology do you think is most promising for increasing the popularity of solar energy (photovoltaic, thin film, monocrystalline silicon, polycrystalline silicon, ect)?  How do you think policy decisions could affect solar energy?

Tune in at our livestream tab on our website tonight at 6:45.

Ask questions in the chat window and the best will be answered during the Q & A session.

Santosh, President Mary Sue, and Rachel

On Friday, Project Manager Rachel Kramer and Engineering Division Director Santosh Kumar attended an event in Lansing.  The event was a celebration of the success over the past 5 years of a program called The Michigan Louis Stokes Alliance for Minority Participation (MI-LSAMP).  This event brought together presidents of universities and colleges from all over Michigan.  The program aims to increase the number of underrepresented minority students by getting minority students in high school excited about STEM subjects, (Science, Technology, Engineering, Math).  UMsolar was happy to go and spread enthusiasm about what we do.  Both University of Michigan President Mary Sue Coleman and Senior Vice Provost for Academic Affairs Lester Monts spoke at the event.

With a can-do attitude and a job all his own, Blaine makes it happen. 

Blaine Riley joined UMsolar as a freshman Chemical Engineer.  Now, 3 years later, he’s a Business Major who manages over a quarter of a million dollars in parts and oversees the production of the solar car.  Blaine sits down with blogger kanolan and explains his job. 

Blaine transcends being categorized as just one of any of the four traditional divisions, which makes it hard to pin down exactly what he does.  As a “Sourcerer”, he finds sources where UMsolar can get raw materials or where we can get the student-designed parts made. 

In a nutshell, you’re the guy who makes sure the car gets built, right?  

“Basically, I’m in charge of getting the car built safely, on time, and within budget.  It’s my job to procure all of the materials that will be needed, as well as all the services.  Procurement is pretty much wrapping up, so I spend most of my efforts working with machine shops and manufacturers around the area to produce all of the mechanical components of the car.” 

Blaine was a race crew member for both last year and this year, and when I ask Blaine how much time he spends on UMsolar, he claims he spends the same amount as the average Race Crew member (for those of you who don’t know, the race crew is the elite team of 16 extremely dedicated team members.  They’re chosen every year to compete in the national and international races). 

Blaine, overprepared for any solar car task.

So you say you spend the same amount of time on solar car as the average race crew member.  How much time is that? 

That’s a pretty large chunk of your life.  Do you ever get overwhelmed with getting through the business school AND playing a huge part in getting the car built?

 

“You’ve got to keep things in perspective, the highs and the lows, and just remember to never let off the gas until we’re at the finish line in Adelaide.  Everything that happens between now and the finished car impacts our overall finish, so it’s important to take things seriously.” 

 

 But UMsolar won first in June.  That must mean you’ve earned a little time off, right?  

“It’s important to stay humble as well, and realize that while we’ve had success in the US, the same can’t be assumed for the World Solar Challenge.  Furthermore, on an individual level, looking at who’s come before me in my role, and knowing the standards that have been set by guys over the last decade, it’s important to keep whatever mild taste of success I’ve had in perspective and just realize that things could always have been done better, smoother, lower cost…”  

Ever the enthusiastic team member, Blaine jumps at the American Solar Car Challenge first place finish.

What’s the weirdest part of your job/ what did you not anticipate having to deal with or do when you took on your role? 

“Taking a shower at the workspace. It’s a long story, but I was up late one night working on the car, getting ready for the American Solar Challenge 2010, and I got hardly any sleep.  We were preparing the car to switch to a NGM Motor, instead of the CSIRO motor, which we typically use (as John talked about in his blog post last week).  I woke up at 6 AM when Dave Hunter called me from Leonard Machine and said the parts for the new motor were ready.  We had to get the parts in the car as soon as possible because we were leaving for Texas 48 hours later as a team to race.  I didn’t have time to take a shower- I drove right out to get the parts.   

By the time I got back to the workspace to drop off the parts, it was 8:30.  And after the parts were installed, we still had to immediately test the car to make sure the new parts worked properly. So I took a shower in the warehouse where we build the car, which is just sort of thrown in the corner and is full of spiderwebs and kind of grimy.  In the meantime, a few people on the team installed the motor. And then we immediately left at 9 for the track to test it.” 

Wait, so no one uses that shower? 

“Let’s put it this way, we’ve owned the workspace for 10 years and I’d be surprised if it’s been cleaned once.”  

The solar cars we design are built to race.  Driver comfort is ignored.  This leads to the question, what about driver safety?

Technical Thursdays are back, this time with mechanical engineer Troy Halm. He was a valuable member of race crew for the American Solar Challenge when UMsolar took first place, and now he’s here to fill you in.

Troy builds the car. The very safe car.

Solar cars lack many safety devices that are standard in normal cars such as airbags and ABS brakes.  As a result driver safety is one of the main focuses during all phases of designing and racing our solar cars.  The baseline of safety is set down in the race regulations.  If a car doesn’t meet these regulations, it can’t race.

Regulations vary only slightly between the World and American Solar Challenges.  One of the first requirements is a 5-point harness which is similar to those used in traditional racecars.  This harness is much better at restraining a driver than any normal seatbelt which only has 3-points.  The driver wears a helmet, too, just for good measure.

The next required item is a roll cage.  The roll cage is designed to protect the driver in the case of a collision or rollover and to deflect debris away from the driver in the event of an accident.  Regulations for roll cages have varied widely in the past, but Michigan traditionally designs a two bar steel or titanium roll cage, with one bar in front of the driver’s head and one behind.   This is heavier than a single bar or carbon fiber roll cage, but it satisfies the regulations for both races.  Horizontal crush space is also required by regulations in order to further protect the driver.

The driver in his helmet, harness, and roll cage.

In last week’s post, “Do Solar Cars Flip?” Karl explained how crucial it is to the overall safety of the vehicle to factor in stability during the mechanical design phase. The next step in designing a safe vehicle is to design all of the mechanical parts so that they can withstand extreme situations without failing during the race. This involves calculating the forces on the car and then using these calculations to model stresses on the car parts. These calculated stresses are then used make sure the part is both safe and light. Engineers also design parts such as collapsible steering columns to further reduce the risk of injury in case of collision.

Once the car is fully designed and built, the team takes further steps to ensure the safety of the driver. During testing and racing mechanical engineers are always there to perform checks and make sure that all of the parts on the car are performing as they should be. On the road, the caravan vehicles also keep the solar car safe (see this week’s Trivia Tuesday Post). The lead and chase vehicles act as a barrier between much larger cars and the solar car by “blocking” for the solar car during turns through intersections (preventing normal cars from getting too close), and being constantly aware of other drivers around the car. Our tireless attention to driver safety will hopefully not be needed, but if by some freak accident it is needed, we’ll be ready.

There are 4 cars that must ride with the solar car during races.  These 4 cars are called Chase, Lead, Scout, and Weather.

1) The “Chase” vehicle rides behind the solar car, and in addition to keeping the car safe, Chase is where the team monitors telemetry data and makes strategy  decisions.

2) “Lead” rides in front of the solar car and contains parts and tools for roadside repair of the solar car.  This is also where the electrical engineers closely monitor electrical readings from the car.

3) The “Scout” rides a few miles in front of the solar car and clears the road of debris (in Australia, this means kangaroo roadkill) and looks for a new campsite around dusk each day.

4) ”Weather” rides way in front of every UMsolar car and carries a meteorologist who makes weather predictions.

Thanks to everyone who answered, and congrats to our winner, Matt from California.  Check back next Tuesday for another Trivia Question.

A few members of the caravan