ClearEdge Power, a manufacturer of fuel cells that run on natural gas, announced today that it has raised $73.5 million in its fifth round of funding.

The company manufactures fuel cells that run on natural gas, which is broken down into a hydrogen-rich gas. The natural gas mixes with oxygen in the fuel cell, inducing a chemical reaction and generating electricity within the cell. The reaction also produces heat, which can be used in commercial heating applications — such as keeping a hotel hot during the winter or heating water for a home instead of requiring a separate water heating source.

The funding was led by Artis Capital Management.

ClearEdge Power’s funding is one of the largest investments in clean technology this year outside of electric vehicle manufacturers. The other largest investments this year have come in the form of a $60 million investment in efficient light-emitting diode (LED) manufacturer Bridgelux and trash-to-fuel company Enerkem’s $60 million investment. The funding is mainly geared toward marketing and expanding the company’s sales team, ClearEdge power vice president of marketing Mike Upp told VentureBeat.

“We’re still doing research and development, but we’re no longer a laboratory,” he said. “We’ve been shipping product for a while, so the funding is more on the marketing and sales side to expand beyond California to the East Coast, as well as Korea.”

The cells capture energy in the form of both electricity and heat, so they capture about 90 percent of the available energy from the reaction. The fuel cells plug into a typical power grid, but there are plans to make them independent of a power grid, the company said in its announcement. The fuel cell is about the size of a refrigerator, costs around $56,000 and generates 5 kilowatts of power and 5.8 kilowatts of energy in the form of heat — so it’s a little impractical for typical residential owners.

“We’re still interested in residential, high-end residential cells — a 5,000 square foot house or larger,” Upp said. “Those are our early customers, that’s a market focus for us, but the main focus is light commercial or institutional customers, like schools or businesses.”

The company recently secured a $2.8 million grant from the U.S. Department of Energy that gave the company capital to install 10 fuel cells at businesses in Oregon. The funding came from the Department of Energy’s Pacific Northwest National Laboratory (PNNL), which will monitor the fuel cells to see if they are producing the kind of energy savings expected for the businesses that purchase them.