According to a study published in Earth's Future, covering the world's highways with solar panel roofs could significantly reduce carbon dioxide emissions and traffic accidents. (Image courtesy of Alex Kalinin, Unsplash) By Kayt Sukel While taking the bus home from work one day, Hou Jiang, Ph., was trying to figure out how to overcome. Placement of photovoltaic roofs on the main highways worldwide has the potential to utilise existing land and produce 17,578 terawatt-hours annually, which is over four times the yearly energy output of the United States. Solar roadways have integrated solar cells generating power from the sun. The problem is, there's nowhere to put them.