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The 2001 UNSW Solar Racing Team (SRT) is presently enroute to Darwin for the 2001 World Solar Challenge after a 6 am departure from the workshop. It was a busy weekend at "Camp Canberra" finishing up the list of 101 things to do and packing. Packing alone took the better part of the weekend - it's amazing the number of spare parts, tools, and equipment necessary to mount a WSC campaign. Last Friday afternoon, the University of New South Wales invited friends, family, and especially sponsors, of the Sunswift Project to say a great big "Thank You" and to unveil the new UNSW Sunswift II.
Mary Cowin was on hand to represent our newest sponsor, Hungry Jack's Resturants. We invited her to try out the new car.
Friends, family and UNSW staff were on hand for the ceremony, too.
We still getting used to the idea of waking up before sunrise. This morning, we had a 6:00am review, which meant a 4:30am wake up call for those team members who live as far away as Wollongong or Carlingford. Solar car drivers have the good fortune of being required to get a good night's sleep - so they get to sleep the latest!
Our first stop today was EM Signs in Newcastle. They make many of the large, illuminated polycarbonate signs you see on roadside restuarants, including, in fact, one of our sponsors, Hungry Jack's Resturants. We stopped in to see Andrew, Goran and Brad, who helped us mould the polycarbonate films we used for our solar array. The films had to be moulded to the exact shape of the car before the solar cells could be laminated into arrays. EM Signs have the largest polycarbonate moulding equipment in Australia, and the UNSW Sunswift II moulds barely fit inside.
Goran Feher, from EM Signs was curious about the UNSW Sunswift II. He spoke to Dave Snowdon, who pioneered the development of the new moulded, polycarbonate solar cell array.
Goran: "How long did it take you to develop the encapsulation technique?"
Dave: "We started working on our encapsulation technique as soon as we realised we would need to build a new array; about May, 2000. Sunswift II has been designed around the use of curved solar panels. Previous solar arrays had been built using flat panels, which were bent to the shape of the car, or with a conformal coating that covers and protects the solar cells. Bending flat panels over Sunswift very complex shape caused stress on the solar cells, and the eventual demise of the solar panel. Spraying conformal over the cells resulted in a rough surface, which is not ideal for the aerodynamic design of the car.
"From there, many months were spent investigating a huge variety of different techniques. Various experiments were conducted, with mixed success. We investigated a number of materials, such as Sylgard 184, Polycarbonate, various epoxies, Dow Corning Conformal, and other possible encapsulants.
"One of the biggest problems had with all of the techniques and materials was the formation of bubbles in the laminate. This is not only bad for the performance of the array, but it also looks terrible. This was resolved by removing all air from laminate before lamination -- essentially using a vacuum chamber.
"We decided to attempt the impossible and build a vacuum chamber capable of building what we believe to be the world's first pre-curved laminates. We performed a number of tests in the summer of 2000-2001 on Ethyl Vinyl Acetate (EVA) encapsulation.We were assisted greatly in this process by BP Solar, who also helped supply some of the vital materials and process tips. While the vacuum chamber was being built - which took over three months - the encapsulation technique was refined by building tens of prototypes - each taking over 30 hours to produce. In June of this year, we built our first large scale panel.
"The other key part of the process was the pre-moulded polycarbonate sheets that were made here at EM Signs. The pre-moulding minimises the wrinkling of the polycarb skin during the lamination process.
"Construction of the array proper was commenced in July and the encapsulation team worked non-stop for six weeks to produce the 9 panels that comprise the solar array -- positioning cells, soldering connections, and performing the laminations. Boeing Australia was inhabited by Sunswift 24/6 for those six weeks."
Goran: "How long does it take to build one panel of the solar array?"
Dave: "The final assembly of each panel took approximately four days (around the clock, working in shifts of five people). Prior to that each cell had to be carefully prepared. Each cell was characterised, and sorted such that the cells complemented one another. The electrical connections, the tabs, were soldered to the bus bars of the cells. Those cells were then soldered into short "strings" of cells, ready to be encapsulated. As you can imagine, any process that needs to occur on each of four thousand cells, consumes many many person hours. In total, the array took over 10,000 person-hours of work to take it from cells to panels."
Goran: "And why are two sheets of polycarbonate are needed, one on the front and one on the back?"
Dave: "The reason we use the two sheets is to get a symmetric layup. This means that when the solar array heats up during the encapsulation process, the solar array won't be placed under stress (and as a result, deform or bend)."
Goran: "How do you know when the batteries are full or flat?"
Dave:" The batteries are monitored constantly by the car's internal telemetry system. This system monitors a number of parameters related to the car, including the battery's voltage. This voltage is the main indication of the state of charge of the batteries. When the batteries reach 4.2 volts per cell, the batteries are full. When they are as low as 2.7 volts, they are flat. We also monitor the current going into, and out of, the batteries and work out how much energy has been stored or removed."
Willy The Whale
Willy!
Michael Kalegeropaulos, from Cypress, wrote us with the following question for the team: "How much power does the solar array produce in full sunlight?"
To which Adam Karkowski (Mech team) replies: "Typically, the solar array of a race car produces around 1000 watts of power in full sunlight. That's about the same power as a hair dryer. Of course, in cloudy weather or early/late in the day, the array power is less."
Mail Bag
If you have a question for the team, or would like to wish them well, write to our mail bag, care of Ask Willy. | | | |
