When my son was young, our family had a membership at our local hands-on science museum for kids. There he was exposed to a lot of cool scientific exhibits and displays, and I’m happy to say that at 20 years old he continues to have an interest in science and technology. Unfortunately, many kids don’t live near such a museum, but thanks to a handful of innovative science educators, one might be coming to them … on wheels. Introducing the Physics Bus:
The Physics Bus is a traveling science exhibit with dozens of hands-on activities that demonstrate a variety of fun scientific concepts. The idea originated at Cornell University, which seems appropriate considering that science popularizer Carl Sagan spent most of his career teaching at that institution. Since its inception, a number of Physics Buses have been rolled out across the country. Today I’ll look at one that works out of Tucson AZ. What’s special about this one? The bus runs entirely on renewable energy. The engine burns discarded vegetable oil, and once the bus is parked, its electrical exhibits are powered by sunlight.
A one kilowatt photovoltaic array, consisting of four Hyundai 250W monocrystalline PV modules wired in parallel, is mounted to the top of the bus. To ensure that the fun doesn’t end at sunset (or on excessively cloudy days), battery manufacturer US Battery donated a bank of eight deep cycle flooded lead acid batteries that provide up to 14 kWh of energy storage. It takes two to three days to fully charge the battery bank from solar power, depending on conditions. (Need it faster? Looks like there’s room for more solar panels!)
Since some of the exhibits use AC power, Magnum Dimensions was kind enough to donate a 4kW inverter/charge controller that’s capable of running in grid-tied or stand-alone mode. The inverter has a low startup voltage – only 18 to 34 volts – allowing it to produce electricity even on cloudy days. During a recent winter tour of Arizona, the PV array’s voltage dropped from 27.2 volts to 25.8 volts on a day of continuous cloudiness. Since this is well within the acceptable input range for the inverter, all systems were running on solar power, even with the Sun behind the clouds.
Dr. Sagan frequently pointed out that we’re all made of “star stuff.” I think he’d be happy to know that the Physics Bus continues his mission of bringing science to the people, and that its experiments are powered by our nearest star, Sol.