Electricity generation using hydrogen

[QwertyXP]

In fuel cells hydrogen combines with oxygen (due to a catalyst) resulting in a potential difference. Is it not possible to burn the hydrogen and use the energy from this exothermic reaction to produce electricity? Since the rate of reaction of hydrogen combustion is quite high we could keep the flow of hydrogen low so that we get a steady supply of energy.

 

[Ygggdrasil]

It is possible to burn hydrogen and use the energy from the combustion to generate electricity, but combustion is an inherently inefficient method of generating electricity. The efficiencies of internal combustion engines are generally ~20% (and are limited by thermodynamics to ~40-50%).

In contrast, fuel cells use electrochemical processes that do not have the same thermodynamic limitations as internal combustion engines. Furthermore, because fuel cells react hydrogen and oxygen in a much slower, more controlled fashion, they extract energy from the reaction much more efficiently. I think fuel cell efficiencies run around 50%. So, let's say you burn some amount of hydrogen and produce 100 J of electrical energy. If you were to take the same amount of hydrogen and put it into a fuel cell, you would end up with 250 J of energy.

 

[QwertyXP]

Thanks for replying.

Fuel cells are certainly more efficient, but are they really more practical if you consider their cost? I mean obviously I would have to store a much larger volume of hydrogen to generate the same amount of energy but if you don't take the cost of storage into account, isn't hydrogen combustion more feasible?

Actually my aim is to look for cost effective solutions to provide electricity to rural areas.

 

[Borek]

Cost effective solution is based on hydrocarbons - they much cheaper than hydrogen, both in terms of production and storage.

 

[Topher925]

You may want to look into solid oxide or phosphoric acid fuel cells that run on natural gas for cheap power that produces less CO2. Using PEMs that run on H2 isn't going to be cheap for a long time.

 

[russ_watters]

Fuel cells are certainly more efficient, but are they really more practical if you consider their cost? I mean obviously I would have to store a much larger volume of hydrogen to generate the same amount of energy but if you don't take the cost of storage into account, isn't hydrogen combustion more feasible?

A hydrogen powered combustion engine may be more feasible based on first-cost. That's why gas turbines still dominate over fuel cells for applications where the commercial products overlap (powered by methane). It also helps a lot if you need heat, as you can recover most of the waste heat from both a gas turbine and fuel cell, ultimately making their efficiencies near identical.

Since this discussion is somewhat hypothetical, though, it allows some speculation as to the possibility that fuel cells may get cheaper in the future.

Also, there is the issue that hydrogen isn't really a fuel source but is actually just an energy storage medium. In order to make it you need a conventional power plant of another kind or another energy source such as methane. However, as said above, fuel cells can run directly on methane.

 

[QwertyXP]

Also, there is the issue that hydrogen isn't really a fuel source but is actually just an energy storage medium. In order to make it you need a conventional power plant of another kind or another energy source such as methane. However, as said above, fuel cells can run directly on methane.

The idea in my mind is a solar system which stores energy in the form of Hydrogen, instead of relying on traditional storage mediums like car batteries. Now I wouldn't even need hydrocarbons to produce H2. So in the case of a solar system, do you think this is the best solution?

 

[Borek]

Hard to answer. I don't live on the solar system scale, so my experience is limited.

 

[russ_watters]

The idea in my mind is a solar system which stores energy in the form of Hydrogen, instead of relying on traditional storage mediums like car batteries. Now I wouldn't even need hydrocarbons to produce H2. So in the case of a solar system, do you think this is the best solution?

Probably not, due to the inefficiencies you introduce: a car battery is a much more efficient way to store energy than hydrogen is.

 

[Borek]

Important thing to remember is that hydrogen is not worth anything without an oxidizer, unless we are talking about using it as a fusion fuel. On the Earth we take oxidizer for granted, that's not the case on other planets.

 

[Ygggdrasil]

The idea in my mind is a solar system which stores energy in the form of Hydrogen, instead of relying on traditional storage mediums like car batteries. Now I wouldn't even need hydrocarbons to produce H2. So in the case of a solar system, do you think this is the best solution?

I agree with russ. While batteries are not known for being able to store large amounts of energy, newer technologies are being developed to store large quantities for just such applications (the following article talks about using them for wind power, but the principle would be the same for solar).

http://www.scientificamerican.com/a...ze-new-battery-might-make-wind-power-reliable

 

[alxm]

Important thing to remember is that hydrogen is not worth anything without an oxidizer, unless we are talking about using it as a fusion fuel. On the Earth we take oxidizer for granted, that's not the case on other planets.

Yup, once you factor in oxidizers, the energy/weight ratio of hydrogen isn't as fantastic anymore.

As a theoretician, I'm partial to tetrahedral N₄. Very high energy compound, requires no oxidizer for its decomposition to N₂, is relatively stable, produces environmentally friendly products.
"But alxm", you say, "isn't it so that that compound has never been observed or synthesized?" This is true. But as I said, I'm a theoretician and do not concern myself with such practical trivialities!

 

[QwertyXP]

I checked out the link provided by Ygggdrasil. It does mention the possibility of such a system (the type i have mentioned).

Anyway, I think I get what u ppl are saying. I would be using solar cells, but hydrogen combustion's inefficiency means that although I might not have to spend much on maintenace (ie no battery replacements), I would be getting only a few hours worth of electricity. Therefore if I want to supply electricity for an extended time, I would need to make a huge investment on solar panels so that they are able to produce sufficient hydrogen. But then the payback time would be too long and would prob exceed the lifetime of the solar panels.

Have I got it right?

 

[Ygggdrasil]

but hydrogen combustion's inefficiency means that although I might not have to spend much on maintenace (ie no battery replacements), I would be getting only a few hours worth of electricity.

There would also be inefficiencies involved in converting the electricity into hydrogen (not a very efficient process compared to charging a battery) and storing the hydrogen.