Kelp plants grow on a 30-foot-long, white PVC pole suspended in the water. If this is successful, instead of just one row, there would be a whole platform, hundreds of meters across and hundreds of meters deep, full of kelp plants. Courtesy of David Ginsburg/Wrigley Institute hide caption

Solar Impulse 2, the solar powered plane, flies above Giza Pyramids as it finishes its penultimate flight, landing in Egypt on Wednesday. Anadolu Agency/Getty Images hide caption

U.S. Energy Secretary Ernest Moniz takes part in a press conference at the end of the 2015 meeting of the International Energy Agency Governing Board on Nov. 18, 2015 in Paris. ERIC PIERMONT/AFP/Getty Images hide caption

Vera Cole is president of the Mid-Atlantic Renewable Energy Association, a group arguing against proposed rules in Pennsylvania that would put stricter limits on how much grid-connected solar power homeowners can produce on their property. Jeff Brady /NPR hide caption

The new rules' would reduce harmful emissions, the EPA says. David Paul Morris/Getty Images hide caption

Greenpeace's annual report ranks Internet companies based on the efficiency of their cloud facilities. szaz/iStockphoto.com hide caption