Science Interviews

Interview

Tue, 17th Nov 2015

Solar Powered Car Race

Graeham Douglas, Simon Schofield, University of Cambridge

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Cambridge University’s Eco Car team have just landed back in the UK after takingFinnish Line Eco Car part in the World Solar Challenge. This is a gruelling 3,000 kilometer race across the Australian outback. Graihagh Jackson found out that interviewing a solar car racing team doesn’t guarantee you a suntan...

Graeham - The race is the world’s solar challenge, so every two years, teams from all over the world go to Australia and do a race 3,000 kilometres from the north in Darwin to the south in Adelaide.  There’s about 40 teams that start at the beginning, usually between a quarter and  a third finish at the end, and that takes about four days.

Graihagh -   Entirely on solar power, so surely that give you a number of obstacles to overcome from the get go?

Graeham -   Yes, absolutely.  Our  solar array gives you less power than you get in a hairdryer and we use it to propel car with a driver in it, at highway speeds, so there’s a lot of challenges on the engineering side.

Graihagh -   Powering an electric car on the same electrical output as a hairdryer.  How on Earth does this work?  Back on the racecourse I caught up with Technical Manager, Simon Schofield.

Simon - One of the things that Cambridge University is very good at is being very innovative in the way that we design our cars.  Most of the other teams have a very different design.  It looks more like what we call a table top design, which means it’s a large, flat set of panels which face the sky and then there’s a pod that the driver sits in in the middle of the car.  So our decision to go for something that’s much more aerodynamic but has a smaller solar array is something that no other team has tried up to this point.  

Graihagh - The solar panels to me aren’t very big.  I’m thinking about the solar panels you get next to swimming pool.  There’s loads of them and, even then. You’ve got maybe two metres by half a metres of solar panel there.  How are they so efficient?

Graeham -   So the solar cells are gallium arsenide cells.  Gallium arsenide is a very good semi-conductor to use for solar cells because it’s a direct bandgap semiconductor.  That means that rather than needing phonons as well as photons to absorb light, you only need the photons and that means that more of the photons that hit the solar cells will actually be converted into electrons, that turns into energy, which allows you to power a battery.

Graihagh -   And I notice you’ve got a covering. Does that not block some of the photons getting through?

Graeham - So the canopy is about 95% transmitted, which does mean we lose about 5% but, the benefit of having it there is that it actually keeps the aerodynamics of the car extremely good.

Graihagh -   I was amazed to see that, despite the rain, Amy managed to take off around the track for a testing.  Although, only at about 20 kilometres per hour.  But come race day the team had hoped Evolution to be racing at speeds of 110 kilometres per hour. Three months after their little demo around the running track, the team set off for Australia ready for race day but, it was a bit of bumpy ride as Graeham Douglas told me on his return to the U.K. this week.

Graeham -   While we were testing about four days before the race we had a really big problem with our motor.  The inside of it melted while the car was going about 95 kilometres on the testing track. The car swerved a bit, the driver managed to hold it together but, it was quite a scary moment and it ended up that one of the teams had a motor, from a few years ago, that had the exact spare part that we needed to fix our motor.  We put it together overnight in really an epic effort of so many of the team coming together and making it work.

Graihagh -   It sounds like nail biting stuff.

Graihagh -   How was the race because it took six days, didn’t it?  How was that?

Graeham - There was ups and downs definitely.  The biggest problem we had was our battery coming close to overheating.  So we use lithium based batteries which, as many people know, there have been some famous fires with lithium batteries, so we keep ours well within its operating limits of 55 degrees Celsius, and we got up to about fifty three and a half, and when we got that high, our electrical guys notified the rest of the team and decided we had to stop and cool the battery down.

Graihagh -   I mean the battery is one thing but what about the poor person driving it.  That fifty three and a half degrees is boiling.

Graeham -   Yes, we have some really tough drivers on our team and all our solar car drives do.  Our cars are built for speed and comfort comes into play but it’s a bit down the line.

Graihagh - Wow.  Scintillating stuff. That was the lowlights but, I know, day six you had a triumph.

Graeham - Yes, day six was the last day of the race and we were coming in the last 250 kilometres into Adelaide, to the finish line.  We ended up travelling in at quite a faster speed than we were hoping to.  We projected driving in at about 50 kilometers an hour and the power we had in our battery from that extra charge in the morning, we were getting up to about 65.

Graihagh - And where did you come?

Graham -   We came about twentieth out of the challenger class.  We were only allowed to drive between about 9am and 5pm, but our end time was just over 53 hours.

Graihagh - And how did that compare with the winning team?

Graeham - The winning team was a fair bit quicker.  They finished in 37 hours and 56 minutes.  So, we’ve got our work cut out for us for next time.

Graihagh - Something Simon talked about previously was the table top design is what most other cars go for, you went for something a bit different.  So was there something fundamental about the other cars designs?

Graeham - As Simon said, the Cambridge philosophy is building a smaller car that’s based on aerodynamics.  Nuon, the team that won takes the classic design, they’re a table top design.  So the flat top with four wheels coming out the sides.  They’ve just done a very execution.  They’ve got very good aerodynamics, they clearly do a lot of time in the wind tunnel and doing computer simulations of their design.

Graihagh -   Either way, it’s a spectacular achievement and you must be so proud of you and all your team’s efforts.

Graeham -   Yes, it was really great.  I mean, there was a moment just walking across the finish line with the team and the car.  They have a moment for all the teams.  The car stops just before the finish line, all the team comes up, and they all walk across the line together, which is really a powerful moment and very emotional for everyone because you know how much work you’ve put into it, and how much work everyone on the team in the past have put into the project  and that builds every year and gets us where we are now.

 

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