Many automakers have chosen to promote battery-electric or hydrogen fuel-cell cars exclusively, but BMW is dabbling in both.

The German firm already sells its all-electric i3, along with a growing cadre of plug-in hybrid models.

But it's also developing hydrogen fuel-cell powertrains, with some help from Toyota.

DON'T MISS: BMW Hydrogen Fuel-Cell Prototypes Now Testing, Production "Sometime After 2020" (Jul 2015)

The company demonstrated prototypes based on the i8 and 5 Series Gran Turismo last year, and apparently has been busy since then.

It's aiming to have fuel-cell powertrain components that could be used in production cars ready by 2020, Merten Jung, BMW's head of fuel-cell development, said in a recent interview with Digital Trends.

BMW plans to have "second-generation" fuel-cell components ready by the end of the decade, Jung said.

BMW 5-Series Gran Turismo hydrogen fuel cell concept

BMW 5-Series Gran Turismo hydrogen fuel cell concept

Once that goal is reached, it will decide which vehicles they will be used in.

While no decisions have been made on that front yet, Jung said fuel cells make more sense in larger vehicles.

Batteries are adequate in smaller vehicles, because the weight of a battery pack is offset somewhat by the vehicle's tidier proportions, Jung explained.

ALSO SEE: Lexus Fuel Cell Car Likely To Be Based on New LS Luxury Sedan (Oct 2015)

But in larger vehicles that already have significant bulk to start with, relatively lighter fuel-cell powertrains are a better solution, he said.

BMW fuel-cell partner Toyota may already be going in this direction.

The company already offers the Mirai sedan in limited numbers, but it's widely rumored to be developing a fuel-cell version of the Lexus LS full-size luxury sedan, as part of an upcoming redesign for that model.

BMW 5-Series Gran Turismo hydrogen fuel cell concept

BMW 5-Series Gran Turismo hydrogen fuel cell concept

Whatever BMW's first production hydrogen fuel-cell car ends up being, it will likely launch in Japan and California first, Jung said.

The Japanese government is particularly aggressive about fuel cells, offering incentives to consumers, and encouraging the expansion of fueling infrastructure.

MORE: Japan's Ambitious Hydrogen-Vehicle Plans Stumble, With Bureaucracy To Blame (Dec 2015)

Japanese Prime Minister Shinzo Abe envisions a "hydrogen society," where fuel cells are widely used as an electricity source.

California remains the only U.S. state with significant hydrogen fueling infrastructure, and is the only state where fuel-cell cars are currently sold.

BMW i8 hydrogen fuel cell concept

BMW i8 hydrogen fuel cell concept

BMW also plans to focus on its home market of Germany, the Scandinavian countries, and the U.K., Jung said.

This strategy emphasizes countries that have already made commitments to supporting fuel-cell cars.

Lack of sufficient fueling infrastructure and hydrogen-production capacity remain major obstacles to fuel-cell adoption.

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