Hydrogen Cars?

Question

I was thinking about alternative fuels and engines that would be cheaper and/or cleaner.

I started to think about a car that runs off hydrogen and oxygen, so I did some research and I've been informed that: although a hydrogen fueled car has no pollution, it is very expensive to separate the hydrogen and oxygen, resulting in it costing more [to fuel] then a regular petroleum [fueled] car.

Is this true? If so why? Will the cost ever go down?

Answer 1

Several patents have been issued that claim to have reduced the energy input to separate hydrogen from oxygen.

If  the energy being used to do the splitting were coming from large nuclear electric plants running at constant high output, so that the power must be used or discarded, or the power is from wind machines that have no market for current right now, we might get hydrogen at a reasonable cost.

The problem here is that we do not have a reliable supply, so we have to be prepared to store it. Storing hydrogen is another problem.

Answer 2

The energy used to isolate the hydrogen can be produced from clean, renewable sources, making hydrogen an energy storage medium.

The issues are:

1)how to get the energy to the cars

2)how to store the energy in the cars

There are a lot of things that would work.  it's really not a complicated problem as far as that is concerned. it just happens that we have a nice infrastructure already set up for gas.

Answer 3

Their already are several companies in the U.S. that separate hydrogen, bottle, and distribute it. We have it delivered to the plant by the semi load on a regular basis. The problem with the general public filling their own bottles could be solved by bottle exchange stations, just like lots of people do with their BBQ grill LP bottles

Answer 4

Absolutely true, when you split water, you have to expel a certain amount of energy.  When you burn hydrogen again you reform the chemical bond of hydrogen and oxygen.  The theoretical best outcome for net energy gain from reaction is ZERO.  So instead of wasting time and money trying to split water, just use that same energy directly in an application such as a motor.

This paragraph sums up the article linked below:  Notice that you need to input 237 kJ of energy to start the reaction and you gain 237 kJ of energy from the fuel cell.  237-237=0.  And that is the best outcome possible, you also have to compress the hydrogen and of course there is mechanical loss to factor in.  In a real world application the net energy gain is negative.  

"So in the electrolysis/fuel cell pair where the enthalpy change is 285.8 kJ, you have to put in 237 kJ of energy to drive electrolysis and the heat from the environment will contribute TΔS=48.7 kJ to help you. Going the other way in the fuel cell, you can get out the 237 kJ as electric energy, but have to dump TΔS = 48.7 kJ to the environment."

Answer 5

You just described a fuel cell, which electrochemically combines H2 and O2 according to the following half cell reactions:

H2 --> 2H+ + 2e-

2H+ + 2e- + 1/2 O^2 --> H2O + heat + work

This concept works. Look up fuel cells and you'll see. The question is where does the hydrogen come from. If it comes from electrolysis of water, then yes it costs more energy than it produces. BUT if the electrolysis is powered by a renewable source like solar, then it costs nothing. It's free. The problem is to develop the technologies to do that. That's a major research field right now.

*EDIT*

Richard: Of course I was being very loose with my terminology. What I meant is that from a thermodynamic point of view, YOU don't have to put any energy in. That energy is free. With renewable energy, thermodynamic efficiency is meaningless. From an engineering point of view, cost effectiveness is more meaningful.

You will have to pay for the technology, but that is always the case. In the case of using solar energy to electrolyse water for fuel cells, there may be a net cost effectiveness. There will never be a positive net first law efficiency.

Furthermore, the idea of using solar cells to produce hydrogen for cars is not that the solar cells will physically be in the car. The hydrogen is produced and stored externally. Then the car goes to a fueling station where hydrogen is pumped in (whether as a compressed gas or a reversible hydride).

*EDIT*

Richard: What do you mean by charging batteries? Do you have a specific kind of batteries in mind. Producing hydrogen is essentially the same thing, since hydrogen is the fuel used in fuel cells (which are sort of like batteries). Fuel cells do use the energy in an efficient manner. Why do you say in the real world it's only 40%. That is not true. Do you have a source for that? Real life efficiencies of the fuel cell are close to 90%. System efficiencies (which include auxilliary equipment) are around 60%.

Besides, however you feel about it, fuel cells is the direction the world is headed. Fuel cell cars are already here. I drove one in  Irvine, Ca 2 years ago. Over time they will be more commercially available.

*EDIT*

Richard: First of all, you talked about SOFC and PAFC. Neither of those are proposed for use in vehicles. It's PEMFCs, polymer electrolyte memrbane fuel cells. These operate at much lower temperatures.

Secondly, what is your practical suggestion for lead acid batteries? Do you replace the battery every 400 miles? A battery to power a car is not like the regular 12V battery cars presently have. They are much larger and bulkier. The very first line in this wikipedia article talks about the low energy-weight and energy-volume ratios of lead acid batteries.

http://en.wikipedia.org/wiki/Lead-acid_b...

You would think that there must be a good reason why fuel cells are considered the future power devices for vehicles and not lead acid batteries. Hydrogen can actually be pumped into a car. I'm not sure how refilling works with lead acid batteries. This is a perfect example where engineering practicality beats thermodynamic efficiency.

And I don't think Dana1981's article really addresses anything. It's merely a statement of personal opinion. I don't see where he/she discusses the problems with hydrogen cars. Having said that, there are issues with hydrogen cars that need to be resolved. But that's no reason why the technology should be dismissed. That's what research and development is all about.

For those interested, check out these books on electric and fuel cell vehicles, which should be available in your local university library.

http://www.amazon.com/Hybrid-Electric-Fu...

http://www.amazon.com/Modern-Electric-Hy...

*EDIT*

Richard: You made some very compelling arguments I myself would have been proud of. I haven't studied Li-ion or Ni batteries, but I have studied fuel cells. I insist that your 40% efficiency is an understatement. That includes the electrolysis process, and as I've stated before, you don't pay per kWh of solar irradiation.

Anyway, based on my experience, I can tell you that there is much funding (globally not just in the US) for fuel cell automotive research, considerably more than Li-ion batteries. Why do you suppose that is the case? The physical changing of battery packs is a 1970s concept that in my humble opinion is a great inconvenience. Albeit you make a compelling case for battery electric vehicles, but why don't funding agencies share your enthusiasm?

If anyone's interested in a good review of various automotive propulsion systems, try getting your hands on this article:

Evaluating automobile fuel/propulsion system technologies,

by Heather L. MacLeana and Lester B. Lave,

Progress in Energy and Combustion Science vol 29 (2003) pp. 1–69

Answer 6

Yes I think it may require nearly 3 times the energy  to produce the hydrogen.

Answer 7

Yes it’s true, mostly because you’re adding steps. You’re taking energy electricity and using it to convert water into hydrogen and oxygen that costs you energy, then you use the hydrogen to fuel a car. With each step you lose energy. Yes the cost will go down, but there are more efficient ways to use the electricity.

To (Ω) Dr D

“BUT if the electrolysis is powered by a renewable source like solar, then it costs nothing. It's free.”

No it’s not “free” solar cells cost money, solar boiler’s cost money, etc, nothing is “free”. Besides you’d be better off energy wise using the electricity to charge batteries and use the batteries to power the car.

It you look at solar cells on a roof of a house, they could not produce enough hydrogen to power a car through a average person’s daily needs, but if you use the same electricity you could power a electric car

EDIT

Even from the thermodynamic point of view it’s not free. As I pointed out a roof full of solar cells couldn’t power a car for a person’s daily needs, but if you used the energy to charge a set of batteries you could satisfy a person average daily transportation needs.

Even with renewable energy, thermodynamic efficiency has meaning. How you use the “free” power makes a difference. You could use the energy in a efficient manner or you could waste it doing some inefficient, like producing hydrogen instead of charging batteries for example. Also cost effectiveness is only one factor; there are times where cost effectiveness takes a backseat, say to the environment or any other number of factors.

I meant on the roof of a HOUSE, sorry if I wasn’t clear. I was assuming you would store the hydrogen and pump it into a car.

I hate to say hydrogen power cars are a pipe dream, but they are IMHO. Why? Even you got back 90% of the energy from cracking water, you’re using in a engine that at best is 30% efficient, a fuel cell has a maximum theoretical efficiently of 83% in the real world efficiency they are about 40% efficient and  they are horribly expensive. You are still far better off charging batteries.

EDIT

Nicad, lead acid, it really doesn’t matter in this, lead acid is about 75-85% efficiency, that is you’re going to get back about 75% of the energy you put in back, with Ni-cad you get back between 70 to 90%. With a fuel cell the research I’ve read shows a maximum theoretical efficiency of 83%, at 25C. Here’s one link,

http://www.fossil.energy.gov/programs/po...

They state an electricity-generating efficiency of 37 to 42%

http://fuelcellsworks.com/Typesoffuelcel...

They also state 37 – 42% efficiency for Phosphoric acid fuel cells.

Molten carbonate fuel cells are approaching 60% and as high as 85% if you capture waste heat. Molten carbonate fuel cells operate at around 650ºC.

Solid oxide fuel cells 50-60% and up to 85% if you capture waste heat.  Solid oxide fuel cells operate at around 1,000ºC.

But let’s assume your number is right and they are getting 90% back, I searched but could find NO-ONE who even claimed they were getting that, a few people state the maximum theoretical for some fuel cells could reach 90% but nobody is claiming they reached that yet.

Let’s say our solar cells put out 100 units of energy to make it easy. By charging the batteries and driving the car I get 70% back on the low end.

The efficiency of electrolysis is about 66% with a maximum theoretical being between 80% and 94%.

Now you start with 100 units and crack water leaving you with 66 then you make electricity with a fuel cell and I’ll use your number of 90% which leaves you with 59.4% (27.72% if you use the governments number), NOT counting the energy to compress the hydrogen.

Even if you look at the theoretical max you’re down to 84.6% (using your 90%) or 74.7% using my 83% not counting the energy to compress the hydrogen, where on the battery side I can get up to 90% in real life.

In order for fuel cells to even have a chance they first have to get the cost down (to less than the cost of a battery) and the efficiency up, they will have to come very close to the maximum theoretical efficiency for both fuel cells and electrolysis and even then it won’t be as efficient as a battery. There are much better and more efficient ways to use electricity then to make hydrogen, that’s why I said IMHO hydrogen power cars are a pipe dream.

You should read Dana1981, Master of Science article it’s very good, I don’t always agree with him but the article is very good.

EDIT

PEMFC have an efficiency rating of 40% it’s projected to go up to 50% nowhere close to the 90% that you stated in your post although you didn’t state what fuel cell you were talking about, but I think I could have found which one it was as it would have made headlines in every journal.

“A battery to power a car is not like the regular 12V battery cars presently have. “

The first batteries used to power an electric car were nothing more the deep cycle batteries used in cars, truck, golf carts, etc we now have improved batteries. But some electric cars still use older type batteries. Some of the newer batteries have very good energy-weight and energy-volume ratios and they are expected to get better and cheaper.  I never said we had to use lead acid but I used lead acid batteries to point out the even one of the oldest batteries we use beats out hydrogen.

“I'm not sure how refilling works with lead acid batteries. This is a perfect example,,,”

Again we’re not locked into lead acid, but “refilling” problem was worked out way back in the 1970’s and even a few real world tests were done. What was proposed that all electric car battery packs be the same size (dimensions) and use a standard connection. You simply pull up to a “gas” station they swap one battery pack for another, pay for the service and go on your way. In the tests it took less the five minutes.

Battery powered car have very few and very small problems to work out, the manufactures would have to agree on a standard size (dimensions) for the battery pack and a standard connector. The equipment needed would be minimal. Most of the equipment is already available and would only need slight modification (to accept the connector) and moving racks for the battery transfer.

Also by using batteries I can take advantage of the newest batteries that come along. If for example someone invented a new battery that held twice the power, I would simply upgrade the next time I did a battery swap, but if someone builds a better fuel cell you can’t easily upgrade.

We could easily put a fully electric car on the road NOW, if the manufactures would standardize the dimensions and connectors. Once everyone knows what the dimensions are and what connector to use, then anyone could manufacture batteries packs. I don’t have to wait for sometime in the future for the cost to come down or for a breakthrough.

Can you say that about fuel cells?