How many solar panels does it take to fill up a hydrogen car?

Toyota Mirai hydrogen fuel station
© Toyota

Stanford scientists figure out a way to get hydrogen out of seawater. Does this matter?

Every time the words "hydrogen fuel" come up, I want to yell in bold uppercase that if it is made through electrolysis, "HYDROGEN ISN'T A FUEL, IT'S A BATTERY!" And come up it has, in Fast Company, where Adele Peters writes Scientists just found a new way to make fuel from seawater.

She describes a new improvement where hydrogen can now be electrolysed from seawater without the anodes dissolving because of the salt. Stanford researchers figured out how to coat the anode to keep it from corroding, according to the press release:

The researchers discovered that if they coated the anode with layers that were rich in negative charges, the layers repelled chloride and slowed down the decay of the underlying metal....Without the negatively charged coating, the anode only works for around 12 hours in seawater, according to Michael Kenney, a graduate student in the Dai lab and co-lead author on the paper. “The whole electrode falls apart into a crumble,” Kenney said. “But with this layer, it is able to go more than a thousand hours.”

Peters at Fast Company writes:

The fuel could theoretically be widely used in transportation, from cars to planes... Hydrogen fuel cells could also store electricity from power plants or store energy in houses.

This is what makes me crazy. Ok, it is true that we have a lot of saltwater around. But it doesn't change the physics or chemistry of how much energy it takes to split water into hydrogen and oxygen. It's a lot of energy; let's pick an example and look at the thermodynamics of running a Toyota Mirai on saltwater hydrogen (and I welcome criticism of my math here).

electrolyzing water takes energyelectrolyzing water takes energy/ spreadsheet by Lloyd Alter/CC BY 2.0

To electrolyze one kilogram of water into hydrogen and oxygen, it takes 4.41 kWh of power and delivers 110 grams of hydrogen. That will push a Toyota Mirai about 110 meters.(this was off by a factor of 100, thanks Eric)

Running a Mirai takes a lot of hydrogenRunning a Mirai takes a lot of hydrogen/ Spreadsheet by Lloyd Alter/CC BY 2.0

To fill its tank, one would have to electrolyze 45kg of water and it would take close to 200kWh of power, to drive the Mirai 500 km, which is, by the way, twice as much electricity as would be needed to drive a Tesla the same distance.

Making that much electricity takes a lot of solar panels.Making that much electricity takes a lot of solar panels/ Spreadsheet by Lloyd Alter/CC BY 2.0

To generate the electricity needed to fill one Mirai every day would take 2,858 square feet of solar panels – in sunny Phoenix. In other parts of the country it could take twice as much.

And that is all running at 100 percent efficiency with no losses of hydrogen, even though the tiny molecule leaks through almost everything and reacts with almost everything else.

Over 95 percent of hydrogen is now made from natural gas, so it is basically a fossil fuel. To make it from electricity takes a huge amount of energy, and in the end it is half as efficient as a conventional battery. To power electric cars with renewable energy would take acres, hectares, square miles of solar panels – or a pile of nuclear reactors, which is why the nuclear industry were always such fans of the hydrogen economy.

But without those nukes or some magical catalyst that changes the numbers, the idea that we could run planes, trains and automobiles on hydrogen is just a fantasy. We don't have time and we don't have the renewables, and we have real alternatives, like bikes and electric trains. Or to paraphrase Mal in Serenity, "It's a long wait for a hydrogen train don't come."

One commenter actually summarized this all beautifully in an earlier post on hydrogen trains:

Physics, people, physics! Hydrogen atoms are super-small, so the atoms leak out of any container, just like helium leaks out of balloons for the same reason.
Chemistry, people, chemistry! Hydrogen is also super-reactive, so it's hard to keep pure and hard to keep your container/pipeline from reacting with it.
Economics, people, economics! Just because you made hydrogen through electrolysis in your school's science class doesn't mean it's cheap to do.

How many solar panels does it take to fill up a hydrogen car?
Stanford scientists figure out a way to get hydrogen out of seawater. Does this matter?

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