Hydrogen fuel cell vs. battery-electric cars: Which is greener?

For over a decade, there’s been talk of a “hydrogen economy.” Now, it may finally be arriving.

After taking a backseat to battery-electric cars, hydrogen fuel cell vehicles may be in driveways in significant numbers soon.

Toyota hopes to have a production fuel-cell car on sale in 2015, which will be based on the updated FCV concept displayed at the 2013 Tokyo Motor Show. Honda also hopes to have a fuel-cell car, previewed by the FCEV concept from the 2013 Los Angeles Auto Show, in production by 2015. It’s also working with General Motors on fuel cell technology.

And for those who don’t want to wait, the Hyundai Tucson Fuel Cell is already on sale in limited numbers in California.

In the early 2000s, battery-powered cars were largely viewed as impractical, while fuel cells were viewed as the technology of the future. Now it’s the other way around: fuel cells are the unknown quantity.

This is all about helping the environment and replacing fossil fuels, however, which begs the question: In an overall comparison, do batteries or fuel cells produce fewer emissions?

Two types of electric car

While people commonly refer to “electric cars” and “hydrogen fuel cell vehicles,” both types are powered by electricity. The former stores electricity in batteries, while the latter stores it as potential energy in gaseous hydrogen, much like a conventional car stores gasoline.

In both cases, however, electricity ultimately turns the wheels. In a fuel cell car, hydrogen gas is separated into protons and electrons, and the electrons are used to power a motor, just like in a Nissan LEAF.

In fact, at least one carmaker has pooled parts between the two types of vehicle: the Honda Fit EV uses the same electric motor as the FCX Clarity fuel cell car.

Where does it come from?

hydroelectric-dam

The Grand Coulee dam in Washington state is the largest electricity generator in the US

A battery discharging electricity produces no emissions, and the only byproduct of a hydrogen fuel cell reaction is water. However, the full picture is more complicated.

In both cases, one must consider the total environmental impact of energy production. This is known as “well-to-wheels” emissions. Electricity has to be generated, while hydrogen has to be separated from other elements and transported to filling stations.

The electricity used to power a Nissan LEAF or Tesla Model S comes from the same source as the electricity used to keep the lights on in your home: power plants.

According to the Energy Information Administration (EIA), the majority of electricity generated in the United States comes from burning coal, followed by natural gas, nuclear power, and other sources. This has led some electric car skeptics to believe that plug-in vehicles are actually worse for the environment.

However, a 2012 study by the Union of Concerned Scientists concluded that, even on the nation’s dirtiest grid, driving one mile on electricity is still roughly equivalent to 34 mpg. On cleaner grids, no internal-combustion car can match electricity’s low well-to-wheels emissions.

The vast majority of hydrogen available in the US is produced through a process called natural gas reforming. This involves mixing natural gas with high-pressure steam, which produces hydrogen, along with carbon monoxide and small amounts of carbon dioxide.

Most of the carbon monoxide produced by the reaction is exposed to water to produce additional hydrogen.

While this process is cheap and efficient, it is also very energy-intensive. That’s also the case with the numerous other hydrogen-production processes currently used.

In the end, the cleanliness of hydrogen production depends on where the electricity being used comes from. If that electricity is generated from renewable sources, the well-to-wheels emissions of a hydrogen fuel-cell car can be very low, but not if the fuel is produced with electricity from a dirty grid.

More than electricity

So if battery-electric and hydrogen fuel cell cars are only as clean as the electricity they use, why can the former draw power from burning coal and still be considered green?

It’s because the process of accumulating and using energy in a battery-electric car is inherently more efficient than it is in a fuel-cell one.

Remember that both cars run on electricity, but in a fuel-cell vehicle that electricity isn’t directly available. Like gasoline, hydrogen is a fuel – a medium for storing potential energy.

To power a fuel cell car, energy must be expended to make hydrogen. Then another reaction is required to convert that hydrogen into energy. At each step, there is potential for inefficiency and waste.

In contrast, a plug-in car simply stores the energy needed for movement in batteries, eliminating several steps from the process. Consequently, batteries and plugs are more efficient than compressed gas tanks and fuel cells.

In fact, a 2006 study by fuel-cell consultant Ulf Bossel concluded that, after the energy required to isolate hydrogen from the natural compounds it typically bonds to, package it, transport it, and energy lost in the fuel cell reaction, only 25 percent remains for “practical use.”

On the road

hydrogen-fueling-station

Hydrogen fueling stations are few and far between. They are also expensive.

Hydrogen was also found to be at a disadvantage in a study conducted by the state with the greenest fleet in the US.

California has one of the cleanest grids in the country, and the most electric cars. It also has nine of the 10 public hydrogen fueling stations currently operating. Right now, the Golden State is essentially a “best-case scenario” for electric cars, and an “only-case scenario” for fuel cells.

According to the 2010 California Low Carbon Fuel Standard Final Regulation Order, fuel-cell cars have an average lifetime greenhouse gas emissions rate of 61.83 grams of carbon dioxide per megajoule. This is for hydrogen produced through the popular natural gas reforming process.

Electricity, on the other hand, was determined to have average lifetime greenhouse gas emissions of 41.37g/mj.

There you have it, in a nutshell.

The future

New technologies and policies may lower the well-to-wheels emissions of both hydrogen and battery-electric cars even further.

As reported in The New York Times, the Environmental Protection Agency has proposed rules limiting greenhouse-gas emissions from power plants, which could force utilities to cleaner energy sources, and would further lower the guilt factor when electric-car drivers plug in.

Coal may already be on its way out as a power source. According to the EIA, none of the 136 new or expanded power plants scheduled to open in 2013 are coal fired; only two of the 127 plants expected to open next year will use coal.

At the same time, different methods for producing hydrogen are being developed. Among them is a process that involves mixing nanoparticles of haematite (iron oxide, or rust) with water and sunlight, according to Green Car Reports.

That would be both a cheap and green way to make hydrogen, but unlike the cleanup of America’s power plants, it’s less clear whether it will gain traction.

Electric cars rely on an existing infrastructure, making the switch from coal to a cleaner energy source like natural gas relatively straightforward. Hydrogen was no infrastructure, so for now the big battle is just making it available, not refining the production process.

Conclusion

hydrogen-tank-car

The hydrogen tank from a Hyundai ix35 Fuel Cell

Hydrogen cars seem like an environmental silver bullet. They emit nothing but water, while allowing drivers to avoid the relatively short ranges and long charging times of battery-electric cars.

That’s why, 10 years ago, fuel cells seemed poised to replace internal combustion. Yet in the interim, battery technology has matured and electric vehicles have proliferated.

All things considered, the inherently simpler process of storing energy in a battery and using it to power a car makes electricity greener than hydrogen.

The myriad variables of the isolation, packaging, transport, and consumption of hydrogen mean its well-to-wheels emissions can vary wildly, while those of battery-electric cars tend to remain consistently low regardless of where the electricity comes from.

That’s not to say that fuel-cell cars don’t have other advantages, but in the emissions battle, the batteries appear to be on top.

Posted by Stephen Edelstein

Stephen's obsession with cars is almost too hard to quantify. From the latest electric car to the classics, he's interested in anything with four wheels. When he's not writing, he can be found searching the Internet for a car he hasn't seen before, or reading a good book. He has a Master's Degree in History from Clark University. He currently lives in Connecticut.

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