Michigan started Day 6 with a full battery pack, but despite its sunny conditions, the sixth day was taxing; it took Aurum along hilly roads and the cracked rims put stress on the car’s efficiency. To top it all off, Day 6’s End of Day charge was weak. Last night’s charge was not enough to replace a significant portion of the power that Aurum had depleted during the day. The team is concerned. The University of Michigan sets up for Day 7’s Start of Day charge, hoping to gain back some of the charge that was lost on Day 6. But it is a cloudy morning, and the team does not get much charge, leaving Aurum to run on a relatively low battery pack.
Driving at 35 miles per hour, Aurum pulls in first to the Stage Three Finish at Scott’s Bluff National Monument in Gering, Nebraska at around noon. The battery pack situation has worsened. “I am not in a happy place,” 2016 Head Strategist Alan Li says. He thinks he’s messed up, that he had Aurum run too fast on Day 6, using up too much energy. “It was my biggest mistake of the race.”
It is still cloudy at Scott’s Bluff, and the team’s IBM weather model shows 200 W/m^2 of radiation. This is a discouraging, low number; a typical sunny day would mean 1000 W/m^2 of radiation.
As the day goes on and other teams pull into the End of Stage location, the cloudiness persists. Most of the other teams also didn’t seen much sun the night before. 2016 Business Director Sarah Zoellick describes how the same conversation seemed to repeat itself as the different teams interacted: “Everyone was saying, ‘We’re really low on charge, this has got to be the most sun-less ASC ever.’” Everyone is looking to that End of Day charge at 6:00 PM.
Although it isn’t sunny, all the teams ready for the End of Day charge, setting up their solar cars in the same place. An expanse of tall grass lies between the two gigantic cliffs of Scott’s Bluff, and in this sea of grass is a single grass-less patch of ground. Come 6:00 PM, this patch is covered with solar cars, their arrays all pointing in the same direction and from the same location.
And then, with 30 minutes left to go before the end of charge time, the sun bursts out from behind the clouds and the patch of ground erupts with cheers from every team. But the tall blades of grass shade the solar arrays slightly, casting shadows onto them and disrupting their access to the elusive sun. So, members from several teams lay their tents out on top of the grass, trying to flatten the blades and minimize shading. Some people even throw themselves onto the grass. The fit on the grass-less patch of ground is so tight that no one can walk without shading a team’s array, so people get around by crawling instead. “Everyone was fighting for that last charge,” 2016 Operations Director Jonathan Cha explains.
UM Solar has won all the stages so far and has not yet trailered. Michigan hears that Appalachian State University and École Polytechnique de Montréal both stopped to charge a few miles before the Stage Three finish line and then trailered to Scott’s Bluff, getting their solar cars to the finish line by placing them in their trailers and towing their solar cars to Scott’s Bluff. The ASC gives out trophies to the overall winner and to individual stage winners, and these teams have their eye on a Stage Four win. They chose to get terrible Stage Three times and to take the time penalty of trailering—three minutes per mile trailered—in order to set themselves up for a better chance at a stage victory. Knowing that these two teams trailered, Michigan estimates that they must have close to full battery packs. By contrast, Michigan’s state of charge numbers are not strong, and will limit Aurum’s ability to drive at high speeds on Day 8. “I know we’re not going to win Stage Four,” Alan elaborates. “But we are going to win the race.”
That night, Michigan assesses what weather Aurum could possibly face tomorrow, and how its state of charge numbers could dictate strategy.
At 153 miles, Stage Four is the shortest stage, but Aurum does not have much power and the weather models project a cloudy Day 8. The team is concerned, unsure of whether Aurum can finish the race tomorrow on solar power alone or whether the team will have to trailer, as well.
Michigan isn’t alone in this regard. “All the teams were worried. ‘Are we going to make it? Are we going to have enough power?’” Sarah describes. “Including us. There’s a ‘what if,’ ‘what do we do’ feeling in the air for all the teams.”
UM Solar begins weighing its options. What happens if Michigan has to trailer? The cost of trailering, an addition of 3 minutes per every mile trailered, is steep. What distance should Michigan drive and what distance should it trailer in order to keep its lead? Overall, Michigan had a 10-hour lead on the second place team, Dunwoody, and UM Solar does the math: if Michigan trailers the entire way, how great a penalty will it incur? Can the team still win? No.
The Strategy division runs simulations and calls team alumni. The WRF weather model says the team may see some sun at around noon on Day 8, but the team’s meteorologists and the alumni on the call don’t believe that’s a possibility. Strategy runs a simulation with very low radiation numbers, which is more realistic, and puts Aurum at a low set speed of 25 miles per hour. The car would finish in seven hours, but it would finish.
By the end of the call, Michigan has resolved not to worry about what other teams are doing. The other teams will run more aggressive races tomorrow, eager for a stage victory and really gunning for it, because Stage Four is their last chance. But Michigan has resolved to run its own race, to drive at the speed that will get Aurum to the finish line on its own power.