One portion of the ongoing debate over fuel cell vehicles questions how environmentally friendly the technology actually is; one new study said the answer depends on the source of the hydrogen fuel.

Dominic Notter, a researcher with Swiss Federal Laboratories for Materials Science and Technology (Empa) and his colleagues used a life cycle assessment approach to better understand this issue. Their methods tracked fuel cells for cars and home heating units, beginning with the hydrogen’s production, through the life of the fuel cell and its eventual disposal.

“The result was conclusive,” said Empa. “Fuel cells for cars are only ecologically sound if they are able to run on hydrogen from renewable energy sources.”

Notter and his associates compared fuel cell vehicles (FCVs) with battery electric vehicles (BEVs) and gasoline-powered cars. The calculations were based on standard refueling methods currently used for each type of technology in Europe.

“Today, a small fuel-cell car that uses [European Union] electricity to generate hydrogen would easily be the worst option,” Empa said. “The car would have the same environmental impact as a luxury sports car.”

Using electricity from the grid to produce hydrogen fuel is inefficient and creates a high amount of carbon emissions, said the study. And extracting hydrogen from natural gas didn’t improve the equation.

“At present, industrial hydrogen is predominantly obtained directly from natural gas. However, the fuel cell does not really have any environmental advantages with this kind of fuel, either,” Empa said. “A car with a combustion engine currently has the edge: The production of conventional cars is less harmful for the environment.”

When comparing fuel cells to BEVs, researchers found   the latter once again had the advantage.

“First of all, electricity is needed to generate hydrogen, which the car tanks up on,” explained Empa. “Electricity is then produced from hydrogen again in the car. This double conversion significantly reduces the efficiency level. People who use the same electricity to charge the battery in their electric cars directly travel more economically and thus in a more environmentally friendly way.”

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But that doesn’t mean that fuel cells can’t be an eco-friendly solution. The turning point, according to the study, will come when hydrogen fuel can be offered at mass-production levels from renewable sources.

“We found an environmental advantage” of an FCV over a gasoline-powered vehicle, “but only if hydrogen is produced with renewable electricity,” said Notter.

“A fuel cell car will become competitive as soon as a company chiefly produces its electricity from solar, wind and hydro power – because the vehicle will guzzle fewer resources during production than a battery-operated electric car, have a far greater range and can be refueled more rapidly,” Empa said.

Notter’s full study is available here through the Energy & Environmental Science journal.