Wednesday, July 27, 2005
Why hydrogen is no route to renewables
All the attention in the nation appears to be on hydrogen as the ideal medium for energy in a renewable economy. It has a lot going for it, in particular the fact that it can be produced from nothing more than water and energy. But this comes at a high (and hidden) price, especially for production from renewable energy; it is far from obvious that the use of hydrogen is worth the additional costs. The consequence is that we should downgrade hydrogen research, and cease deployment efforts immediately.
Hydrogen is certainly a wonderful molecule. It's the lightest element and has a very high energy/mass ratio. It's also the foundation of many chemical synthesis processes, both artificial and natural; when plants make sugar, they begin by splitting a water molecule to make hydrogen. There are even some ways to persuade plants to yield hydrogen directly. And when hydrogen is required, nothing else will do. You need hydrogen to make ammonia (for nitrogen fertilizer) or synthesize hydrocarbons.
We can learn a lot from plants (biomimicry has yielded a lot of good concepts), but there are limits to how far this can go and still be useful. It's one thing to borrow inventions and techniques from nature when they are well-suited to the task at hand, and quite another thing to cut the engineering problem to fit the Procrustean bed of a biological prototype. I intend to show that the "hydrogen economy", and particularly the hydrogen fuel-cell car, is a poor way to accomplish this.
Energy economy
The efficiency of any system has to be considered in context. Grass is perhaps 1% efficient converting sunlight to biomass? That's bad, isn't it? Not compared to the efficiency of forests. I understand that an acre of woodlot captures energy at an average rate of something like 500 watts. By way of contrast, you can average 500 watts by taking the rather small fraction of a 1/5 acre lot covered by the roof of the house standing on it and covering it with PV.
Relative efficiency is important for many things: what's better at getting energy from where it is to where you want it to go. This is where hydrogen falls down. Worse, it hurts exactly where most people would expect that a "clean" energy source would do the best: carrying renewable energy from source to end use. Hydrogen is far more efficient (and thus cheaper) at carrying energy from fossil fuels than renewable sources like wind and solar.
When comparing different approaches, there's nothing like an example. Suppose that we've got two sources of energy, coal and wind. The goal is to power a car. We have two options for using coal: gasify and convert to hydrogen, or burn and generate electricity to charge batteries. We have similar options for wind: generate electricity and either electrolyze water to hydrogen or charge batteries.
The theoretical efficiency of proton-exchange membrane (PEM) electrolyzers is quite high, about 85%. Unfortunately this efficiency is only achieved at low power levels and PEM systems cost too much to use them to make trivial amounts of product. Quoted efficiencies for real systems are in the range of 65% to 75%. Let's use 75% for now.
Fuel cells are the essential part of the hydrogen economy. According to the Rocky Mountain Institute, PEM fuel cells have efficiencies ranging from 35% to 60%. Let's use 60%.
Coal can be used to make either electricity or hydrogen; IGCC powerplants make large amounts of hydrogen as part of their syngas. The quoted efficiency of the gasifier at the Wabash River powerplant is 76%. The composition of the combustible (non-nitrogen, non-CO2) syngas is described as being 37% hydrogen, with most of the rest being carbon monoxide; unfortunately, I cannot unequivocally determine whether this is by volume (mol %) or by mass. The conversion of carbon monoxide to hydrogen via the water-gas shift loses energy, but without a clear distinction between the two cases it is impossible to calculate how much. If the product syngas is 37% hydrogen by mass, the losses in conversion to pure hydrogen will be relatively small; for the sake of argument, let us assume that they are zero. Let's also assume that the efficiency of electric generation from coal is 40%.
Last, let's assume that the efficiency of batteries is 90%.
There are four possible routes for energy depending on the source and the storage option:coal -> electricity -> batteries -> motorEach path has a different efficiency (ignoring losses in transmission, compression, etc):
coal -> hydrogen -> fuel cell -> motor
wind -> electricity -> electrolyzer -> hydrogen -> fuel cell -> motor
wind -> electricity -> batteries -> motor
| Path | Efficiency |
| coal -> electricity -> batteries -> motor | 40%*90% = 36% |
| coal -> hydrogen -> fuel cell -> motor | 76%*60% = 45.6% |
| wind -> electricity -> electrolyzer -> hydrogen -> fuel cell -> motor | 75%*60% = 45% |
| wind -> electricity -> batteries -> motor | 90% |
- When hydrogen is used as the medium, coal and wind have roughly the same end-to-end efficiency.
- If electricity is used as the medium, coal loses about 20% compared to hydrogen.
- If electricity is used as the medium, wind GAINS 100% compared to hydrogen!
Labels: hydrogen, renewable energy
¶ 7/27/2005 07:30:00 AM
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I wish people and our leaders would be responsible and immediately cut gas use by 50% to give us a decent amount of time for transition.
Back when CAFE was on the march, things got better fast.
Now we've got a majority of people driving 5,000lb pigs with one person going to get the groceries.
...and the whole safety issue is bogus also, since if a large majority were well designed small cars, we'd have fewer deaths than the present 6 foot tall, small car eating turnover specials.
Late here, but I'll be back to see what you've got in the way of photovoltaic research.
Back when CAFE was on the march, things got better fast.
Now we've got a majority of people driving 5,000lb pigs with one person going to get the groceries.
...and the whole safety issue is bogus also, since if a large majority were well designed small cars, we'd have fewer deaths than the present 6 foot tall, small car eating turnover specials.
Late here, but I'll be back to see what you've got in the way of photovoltaic research.
Always amusing to look at the CO2 production from a methane->H2 pathway compared to just burning the methane directly.
Your hydrogen analysis should probably include the refrigeration cost to liquify it at 20 K. At 40 kg/m^3, it's still not very dense but it's way better than a gas.
Just a couple asides:
One, transmission losses for DC electricity and hydrogen pipelines are about the exact same. Hydrogen's portability advantages are often less than one might think.
Two, you (very briefly) point out plants can be teased to produce hydrogen directly. Just to shoot this down right away, last time I checked it was more efficient to produce bio-methane and run it through a reformer to produce H2 than to get it direct from bacteria.
Your hydrogen analysis should probably include the refrigeration cost to liquify it at 20 K. At 40 kg/m^3, it's still not very dense but it's way better than a gas.
Just a couple asides:
One, transmission losses for DC electricity and hydrogen pipelines are about the exact same. Hydrogen's portability advantages are often less than one might think.
Two, you (very briefly) point out plants can be teased to produce hydrogen directly. Just to shoot this down right away, last time I checked it was more efficient to produce bio-methane and run it through a reformer to produce H2 than to get it direct from bacteria.
I just looked up the numbers for H2 versus DC transmission.
R. Hammerschlag, P. Mazza, "Questioning Hydrogen" Energy Policy 33 (2005), pp. 2039-2043.
Reports that H2 pipelines have approximately 0.77 % loss per 100 km versus 0.6 % loss per 100 km for DC.
Oh, Nick, by the way, he is being excessively generous for hydrogen with his numbers.
R. Hammerschlag, P. Mazza, "Questioning Hydrogen" Energy Policy 33 (2005), pp. 2039-2043.
Reports that H2 pipelines have approximately 0.77 % loss per 100 km versus 0.6 % loss per 100 km for DC.
Oh, Nick, by the way, he is being excessively generous for hydrogen with his numbers.
I wouldn't want the hydrogen advocates to say I was being unfair to them.
The real crime is when you take the advocates' numbers, show that their scheme is hopelessly expensive or wasteful or otherwise wrong, and they go right back to touting the awful scheme.
It makes one wonder if they aren't lying for profit or something.
The real crime is when you take the advocates' numbers, show that their scheme is hopelessly expensive or wasteful or otherwise wrong, and they go right back to touting the awful scheme.
It makes one wonder if they aren't lying for profit or something.
That's old news at The Ergosphere, Nick:
"Last, it made the oil, coal and gas interests snicker..."
You read it here first.
"Last, it made the oil, coal and gas interests snicker..."
You read it here first.
I'm not an expert on batteries, but several of these problems have been solved for quite some time.
1. Lead-acid cells can be fast-charged using pulses of discharge current to remove gas bubbles from the plates. I read about an electric pickup which charged in 15 minutes quite a few years ago.
2. The new nanoparticle Li-ion batteries charge fully in 5 minutes, and Toshiba claims 0 to 80% in 60 seconds (initial charge rate of 48C).
3. If that fails, the "proton polymer battery" has similarly spectacular performance, cycle lifetime in excess of 20,000, and a chemistry without heavy metals. Energy/mass is about the same as lead-acid, but the other properties are much better.
One thing that needs to be kept in mind: a car needs both a certain energy/mass ratio for range, and power/mass for acceleration. A small battery (say, for a Prius) needs very high power/mass, but if you have a bigger battery for substantial electric range you can trade off kW/kg against kWh/kg and cycle life.
If you surf over to commutercars.com and read the technical data on the Tango, one thing you'll find is a cycle-life vs. depth of discharge graph for certain PbSO4 batteries (you'll find it here). The implications of that are conclusive: even if nothing else comes along (fat chance!), we can do one heck of a lot with cheap Planté cells.
1. Lead-acid cells can be fast-charged using pulses of discharge current to remove gas bubbles from the plates. I read about an electric pickup which charged in 15 minutes quite a few years ago.
2. The new nanoparticle Li-ion batteries charge fully in 5 minutes, and Toshiba claims 0 to 80% in 60 seconds (initial charge rate of 48C).
3. If that fails, the "proton polymer battery" has similarly spectacular performance, cycle lifetime in excess of 20,000, and a chemistry without heavy metals. Energy/mass is about the same as lead-acid, but the other properties are much better.
One thing that needs to be kept in mind: a car needs both a certain energy/mass ratio for range, and power/mass for acceleration. A small battery (say, for a Prius) needs very high power/mass, but if you have a bigger battery for substantial electric range you can trade off kW/kg against kWh/kg and cycle life.
If you surf over to commutercars.com and read the technical data on the Tango, one thing you'll find is a cycle-life vs. depth of discharge graph for certain PbSO4 batteries (you'll find it here). The implications of that are conclusive: even if nothing else comes along (fat chance!), we can do one heck of a lot with cheap Planté cells.
Great post! One quick thing: The ratio of CO to H2 produced via coal gassification that you use is definitely not in mass. Methane has a hydrogen to carbon mass ratio of only 1:3, and that's before you oxidize part of it. For coal, it would be far less before you oxidize it, and far less still after you add an oxygen atom.
I can only assume that it's a molar ratio. What that means in terms of your calculations I don't know, but I think it's safe to assume that the hydrogen you end up with contains considerably less than 75% of the energy in the coal you started with.
I can only assume that it's a molar ratio. What that means in terms of your calculations I don't know, but I think it's safe to assume that the hydrogen you end up with contains considerably less than 75% of the energy in the coal you started with.
You clearly have an agenda regarding hydrogen and perhaps you have something to gain by doing so. Regardless, in you opinion, you leave out an incredibly important source of energy other than wind. Before I go on let me say that Iceland is one of he worlds largest producers of Aluminum. Why? Because aluminum requires an incredible amount of electricity to produce. The reason Iceland produces aluminum is because of Geothermal energy. The entire country gets 100% of it's electricity from it. There is not one coal or oil powerplant in the country.
I think when you consider this you may think that a country like Iceland may become the Saudi Arabia of this century and beyond.
Now if there is something I'm missing here I'd love to here it.
All the best,
Bill Schnell
I think when you consider this you may think that a country like Iceland may become the Saudi Arabia of this century and beyond.
Now if there is something I'm missing here I'd love to here it.
All the best,
Bill Schnell
"You clearly have an agenda regarding hydrogen and perhaps you have something to gain by doing so."
What factual basis do you have for these claims? Is it the same as the rest of your comment (none)?
"The reason Iceland produces aluminum is because of Geothermal energy. The entire country gets 100% of it's electricity from it."
Funny, the government of Iceland says about 1/6 of their electricity comes from geothermal; the other 5/6 is hydropower.
Your knowledge of easily-verifiable facts isn't looking too good.
"Now if there is something I'm missing here I'd love to here [sic] it."
You might start by reading the post and carefully following the facts and the math. You may also want to consider that Dr. Ulf Bossel of the European Fuel Cell Forum has come to the same conclusion quite independently (and, to give him credit, years before I wrote the above).
What factual basis do you have for these claims? Is it the same as the rest of your comment (none)?
"The reason Iceland produces aluminum is because of Geothermal energy. The entire country gets 100% of it's electricity from it."
Funny, the government of Iceland says about 1/6 of their electricity comes from geothermal; the other 5/6 is hydropower.
Your knowledge of easily-verifiable facts isn't looking too good.
"Now if there is something I'm missing here I'd love to here [sic] it."
You might start by reading the post and carefully following the facts and the math. You may also want to consider that Dr. Ulf Bossel of the European Fuel Cell Forum has come to the same conclusion quite independently (and, to give him credit, years before I wrote the above).
After reading your response to my comment I realize I wasted my time. You complain that I don't know my facts by saying hydro power is the main source of elec. in Iceland. My bad. They still create 100% of their energy without coal/oil. My bad. Anyhow, you didn't respond to my intended point. If the costs of elec generation are removed, does the creation of hydrogen still rediculous. (No question because I won't look for the answer.)
You lost all credibility when I read your response.
All the best,
You lost all credibility when I read your response.
All the best,
"After reading your response to my comment I realize I wasted my time."
You certainly did. You posted an incoherent comment with faulty claims, and expected to be taken as something other than a troll.
"They still create 100% of their energy without coal/oil. My bad."
Even in your correction, you border on incoherence. Iceland generates 100% of its electricity without fossil fuels. Iceland still uses oil for transportation, which is a problem they are trying to fix.
"Anyhow, you didn't respond to my intended point."
This should not have surprised you, since you didn't even hint at it the first time. Furthermore, had you actually written out your question clearly, you would probably have been able to answer it yourself.
"If the costs of elec generation are removed, does the creation of hydrogen still rediculous. (No question because I won't look for the answer.)"
I assume you mean "still LOOK ridiculous". That depends on the remaining costs, which are the electrolyzer, storage and fuel cells (which must be compared to batteries).
Again, had you actually tried to state the problem clearly you would
a. not have come across so badly, and
b. received a response in line with what you meant to say (instead of what you actually said).
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You certainly did. You posted an incoherent comment with faulty claims, and expected to be taken as something other than a troll.
"They still create 100% of their energy without coal/oil. My bad."
Even in your correction, you border on incoherence. Iceland generates 100% of its electricity without fossil fuels. Iceland still uses oil for transportation, which is a problem they are trying to fix.
"Anyhow, you didn't respond to my intended point."
This should not have surprised you, since you didn't even hint at it the first time. Furthermore, had you actually written out your question clearly, you would probably have been able to answer it yourself.
"If the costs of elec generation are removed, does the creation of hydrogen still rediculous. (No question because I won't look for the answer.)"
I assume you mean "still LOOK ridiculous". That depends on the remaining costs, which are the electrolyzer, storage and fuel cells (which must be compared to batteries).
Again, had you actually tried to state the problem clearly you would
a. not have come across so badly, and
b. received a response in line with what you meant to say (instead of what you actually said).
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