Created to promote highly efficient, solar powered houses, the Solar Decathlon is a competition that challenges university students to design and build single family homes that promote a sustainable future. This year, teams from 15 schools have brought their creations to Irvine, California, where judges determine which is the most efficient and the most affordable to build.
While rooftop solar systems have figured prominently in the designs for the past 13 years, the contest rules for 2015 require the concept homes to not only create all the electricity they need for domestic purposes but also to recharge an electric car that will drive two people 25 miles a day, simulating a typical commute.
“If you live in a solar-powered house, you reduce your carbon footprint for the house down to zero,” said Richard King, founder and director of the Solar Decathlon. “But if you live in a zero emissions house with two cars in the driveway, you’ve only reduced your carbon footprint by half.” That’s because the emissions from those two cars can equal or exceed those created to power an energy efficient residence.
The teams are only allowed to use a total of 175 kilowatt-hours of electricity for the entire 9 day competition, and that includes recharging the electric car. That works out to about 19.5 kilowatt-hours a day. The average American home uses about 30 kilowatt-hours of electricity, and that doesn’t include recharging an electric car. King estimates homes would need an additional 2 to 4 kilowatt hours of photovoltaic panels to generate enough electricity to fuel an electric vehicle that’s driven 50 miles a day.
Most Solar Decathlon teams are using their smallest and lightest team members to maximize the range of the car they are using. Even at that, they often drive at speeds as low as 13 mph to use as little electricity as possible.
Team Orange is from Orange County, California and consists of 20 students from UC Irvine, Chapman University, Saddleback College and Irvine Valley College. With the help of another 100 students, they have created a Solar Decathlon entry they call Casa Del Sol, or House of the Sun. It features something no other team has — a sophisticated inverter that operates in both AC and DC modes.
Rooftop solar systems need an inverter to convert the DC electricity made by the solar panels to the AC electricity needed to run the household. An inverter can eat up as much as 10% of the available electricity during the conversion process.
Team Orange is the only group using a DC inverter made by Princeton Power Systems. It is six feet tall, weighs 800 pounds and comes with a built-in EV charging cord. If an electric car is capable of being charged with DC current, it passes the electricity made by the rooftop solar panels directly to the car’s charging system without converting it to AC first. This eliminates most conversion losses, leaving more electricity available to charge the car.
“I certainly hope this house has outreach potential for inspiring our students to pursue this technology in the future and those in the general public to realize that, first, it can be beautiful; second, it can be energy efficient; and third, it can be sustainable for them to use for centuries to come,” says Jack Brouwer, associate professor of mechanical and aerospace engineering at UCI and faculty adviser for Team Orange’s mechanical, electrical and plumbing systems.
“We’re going to run out of oil. We’re going to run out of natural gas. We’ll have problems with greenhouse gases from all these other technologies. This one, we could be using it centuries from now.”
This year’s competition was won by the team from Stevens Institute of Technology, which also entered the competition in 2011 and 2013. Although it took home the top prize, all those who participated were winners who contributed valuable insights and innovative thinking to the challenge of sustainable living.