How much power do you lose in hydrogen electrolosis?

[Try2B_Comprehensive]

The question is sparked by a Bloomberg article about Toyota’s prototype hydrogen fuel-cell vehicle, here :

Toyota’s 2015 model fuel cell car will have more than 500 kilometers (311 miles) of range per fueling

Toyota’s new model holds about 5 kilograms (11 pounds) of compressed hydrogen in tanks that can be fully refueled in three minutes, the company said. Fueling is about as easy as filling up with gasoline. A sensor in the hose ensures a proper attachment and fills until the tank is full to maximum recommended pressure. Total system power will be about 100 kilowatts

So far it looks pretty cool- 311 miles on 11 pounds of fuel? Are you kidding me?!

But I’m a skeptic of these things. We don’t have to hash it all out, but the relevant drawback here is that hydrogen for a fleet of fuel-cell vehicles would be produced with natural gas. That essentially amounts to an electric vehicle that runs on… fossil fuels. What’s the point?

Well, if fusion power ever became normal, we could use it to produce as much hydrogen as we wanted from water via electrolysis- it’d be like having unlimited electricity so why not?

All right. But here and now it doesn’t work that way. Green hydrogen power would have to come from renewables. If we were to produce hydrogen that way, how much electricity would it take to produce the 11 pounds (“100 kilowatts”- is that supposed to be kwh?) of hydrogen via electrolysis? How much energy is wasted? Is there a better way? And, if the oxygen also produced has a good use, let’s go ahead and factor that in as a supplemental question.

[Francis_Vaughan]

At low temperatures the conversion is not especially efficient, but as the temperature of the water is increased it gets a lot better. Paraphrased from the wikipedea page on high temperature electrolysis:

At 100°C, 41% efficient. At 850°C, 64% efficient.

[MrDibble]

@Try2B_Comprehensive

But I’m a skeptic of these things. We don’t have to hash it all out, but the relevant drawback here is that hydrogen for a fleet of fuel-cell vehicles would be produced with natural gas. That essentially amounts to an electric vehicle that runs on… fossil fuels. What’s the point?

Emissions control, I imagine. In H2 production from natural gas, the CO produced is used to produce other products, not just emitted, AIUI.

[septimus]

@Try2B_Comprehensive

… Total system power will be about 100 kilowatts

So far it looks pretty cool- 311 miles on 11 pounds of fuel? Are you kidding me?!
(“100 kilowatts”- is that supposed to be kwh?)

Hydrogen fuel provides almost three times the energy of gasoline fuel per unit of weight. Burning it in cars is very clean. Yes, carbon fuels may be burned to produce the hydrogen but large plants can have emission control much more easily than mass-produced vehicles can.

I’m not sure whether they intended “Net system work output from a full fuel tank will be about 100 kwh” or “Maximum delivered power will be about 100 kw.” Both figures seem to be in the plausible ballparks.

[Try2B_Comprehensive]

@septimus

Hydrogen fuel provides almost three times the energy of gasoline fuel per unit of weight. Burning it in cars is very clean. Yes, carbon fuels may be burned to produce the hydrogen but large plants can have emission control much more easily than mass-produced vehicles can.

I’m not sure whether they intended “Net system work output from a full fuel tank will be about 100 kwh” or “Maximum delivered power will be about 100 kw.” Both figures seem to be in the plausible ballparks.

Yeah- since the fuel and tanks are so light, 300+ miles on 100kwh sounds like it could happen, but it isn’t clear.

Anyway, if we’re doing the hydrolysis with 100C water, we need 243 kwh to produce 100 kwh worth of hydrogen fuel. Practically speaking I wonder if we’d have so much boiling water on hand. And then there is the leftover oxygen- what can be done with that on a large scale?

[ZenBeam]

@Try2B_Comprehensive

Anyway, if we’re doing the hydrolysis with 100C water, we need 243 kwh to produce 100 kwh worth of hydrogen fuel. Practically speaking I wonder if we’d have so much boiling water on hand.

Perhaps the hydrolysis could be done at an existing fossil fuel power station. Those tend to have lots of waste heat.

[dracoi]

@ZenBeam

Perhaps the hydrolysis could be done at an existing fossil fuel power station. Those tend to have lots of waste heat.

From a green perspective, it’d be even better to do it at a solar power plant. And here I’m thinking mostly about the types that use solar collectors to concentrate heat rather than the photovoltaic type of solar power… though I suppose either could have both electricity and waste heat to work with.

[Glazer]

O[sup]2[/sup] has many uses such as medical or welding just to name a couple.

[EdwardLost]

@Glazer

O[sup]2[/sup] has many uses such as medical or welding just to name a couple.

You have to be careful with it, though; people have been known to breath it and can become addicted.