Those in the know tout fuel cell technology as a coming revolution in energy production, saying that it will power automobiles, homes, small businesses, and more.
My question is: can major power plants (those producing thousand of megawatts) be made to run on fuel cells? Or, am I missing the point and the real idea that energy production in the near future will be decentralized and almost every home and business will have their own fuel cell energy centers?
Fuel cells do not generate energy, they store energy that’s dumped into them from some other energy source (in other words, they’re like a big battery).
Thus, there’s no way to have a major power plant be powered from fuel cells- it would take more energy to produce the fuel for the cell than you’d get out of it, unlike coal, for example, where you get much more energy by burning it than you used to mine and transport it.
Fuel cells are touted as a way to store energy for use in cars, etc., because they are much cleaner when used, compared to something like burning gasoline.
A fuel cell generates energy just as surely as an oil-fired, er, I mean coal-fired power plant [sub]SHHH! Anthracite bait…[/sub] does. You put fuel (coal) into the power plant, and energy comes out. You put fuel (hydrogen) into the fuel cell, and energy comes out.
How do you get hydrogen? Well, you can get it by busting up water, but that’s silly because water is what you make when you burn hydrogen in the fuel cell. You can also get hydrogen from other sources, I think there are fuel cell designs that work on natural gas or gasoline or other hydrocarbons. I recall some process whereby sodium hydroxide is generated as a waste product, but I really am just too lazy this evening to look it up.
The good things about fuel cells are
[ul][li]higher efficiency - Turning heat into mechanical motion is inefficient. Turning mechanical motion into electricity and vice-versa is fairly efficient, but getting the mechanical motion is the inefficient part. Most power plants (coal, nuclear) use heat->mechanical motion->electricity, which results in relatively low efficiency. A fuel cell relies on a chemical process to generate electricity, so there is no heat->mechanical motion phase to waste energy. So, for the same amount of fuel, you can get more electricity from a fuel cell than from an internal combustion engine. I don’t have exact figures, I’m hoping someone a bit less lazy than me will show up.[/li][li]cogeneration - not only do you get electricity, but the byproduct (in addition to sodium hydroxide or whatever fuel residues you get) is hot water. You can thus heat your house and take a shower for free.[/li][li]Easy recharge compared to batteries. Just refill the tank, no need to plug into the power grid for hours at a time.[/li][/ul]
Please note that efficiency is not everything - nuclear plants are horribly inefficient. But, because the fuel is so gosh darn cheap, who cares? The key here is that fuel cells can burn similar fuels to internal combustion engines, but more efficiently.
I hope someone comes along soon to fill in the sizeable gaps in my knowledge, and hopefully I’m not spectacularly wrong.
I had forgotten about the these- I think there’s a methane fuel cell in the works.
I guess it’s somewhat a matter of semantics- I’m calling it a battery (or since a battery is actually a collection of cells, I could call it, um, a “cell” that requires “fuel” ;)) if we have to supply energy to charge it (i.e. busting up the water to get hydrogen), and an energy source if we don’t (i.e. putting methane into a methane fuel cell).
This is the Powerball approach. The hydroxide (lye) is recyclable to produce more fuel pellets. It seems reasonable to me, but it’s still just a fuel storage approach. The essential problem with most mobile fuel cells is “Where do we get the hydrogen?” (there are fuel cells that use other fuels, but there are problems with them as well). There’s no practical way to directly reform water on-board to provide the hydrogen; it has to be stored somehow–high-pressure tanks, metal hydrides, Powerballs, gasoline, and carbon nanotubes are storage approaches currently being studied. The advantage to using the fuel cells is that you can use any kind of energy to produce the fuel, including sources (solar, hydro, thermoelectric, etc) that aren’t very portable. Also, stationary plants that use polluting sources can be built to scrub their emissions much more thoroughly than a car.
Fuel cells offer a lot of promise, but they don’t constitute a magic bullet for our energy and pollution problems.
I attended a seminar on this a few weeks back–I should have paid more attention. In their most basic form fuel cells combine hydrogen and oxygen together to form water and electrical power. You may remember an old chemistry experiment where a current is passes through water hydrogen forms on the anode and oxygen forms on the cathode–this is that process in reverse.
Hydrogen fuel is ideal since the only by products are electricity, water and heat (BTW the space shuttle uses a hydrogen fuel cell for its power supply). Hydrogen is rare as a independant element in nature and isolating it is relatively costly. Storage is another problem but I won’t cover it here.
Other fuel cell designs can make use of a fuel reformer to utilize the hydrogen in any hydrocarbon fuel - from natural gas to methanol, and even gasoline. The lact of a combustion process (it’s all chemical) eliminates the formation of nitrous oxides. Greenhouse gas emissions still exist (unless you are using pure hydrogen) but they are lower than combustion engines due to the better efficiency.
The main problem with fuel cells is the cost. It’s still a whole lot cheaper to burn fossil fuel. There are a few applications like the space shuttle where they make a lot of sense but by and large it is still a developing technology.
Since I just heard this lecture in Chem this morning, I thought I should add what I know (Don’t worry, I stayed awake almost through the whole thing:)).
A fuel cell allows oxidation(loss of electrons) of hydrogen (or, hopefully, hydrocarbons) and reduction(gain of electrons) of Oxygen. The electron transfer is accomplished through a wire. This electric current through the wire can be used to do work (like any electric current).
In some ways a fuel cell is much like a battery: it converts chemical potential energy into electrical energy through redox reactions. It produces DC current.
However, fuel cells do not get “recharged” by plugging them into the power grid. That is ludicrous. As energy storage, they are relatively bulky and inefficient. You “recharge” them like you would your car engine, by putting in more fuel.
I think that most fuel cells work the best with pure hydrogen, but soon (hopefully) there will be some that use methane or other more easily attainable common hydrocarbons.
Theoretically, feul cells could reach efficiencies of 90+ percent, because the most energy loss is in the resistance of the wire. Of course, there are always other things that reduce the actual efficiency. Still, that’s a darn sight better than the very best (in terms of efficiency) coal-fired plants, which are about 55% IIRC.
I’m sure Anthracite will be along to correct my misconceptions about coal-plant efficiencies, but I believe that 55% is what SHE said in another discussion as the current best efficiency of coal-fired plants.
Funny thing this… My roommate is an engineer currently working on the fuel cell bus project. He was previously working on a machine that creates the oxygen used in the hydrogen cell. That’s one thing no one has mentioned - oxygen is needed in its pure form.
If I understood him correctly, the current fuel cell busses that we have running up here in Vancouver are basically designed thus:
On the roof there are two long tanks which contain hydrogen and oxygen (one element in each tank). This is passed on to the cells which are under the floor of the bus. They combine the H and the O2, releasing energy which is then stored temporarily in batteries. These batteries then drive electric motors. The only by-product of the process is water (pure, pure water - better than that crappy tap stuff).
The problem is, where do you get the oxygen and hydrogen? The oxygen is created by these (currently) huge machines which suck air in one end, and spit oxygen out the other. Don’t ask me what goes on in between. Currently these machines are large and fairly inefficient, however there is a new machine in the works that is smaller and something like 10x more efficient. That’s the machine my roommate worked on. During the next few generations of this machine they hope to get it small enough to easilly fit in a vehicle, eliminating the need for an oxygen tank.
The hydrogen is another matter. Currently I belive they’re getting it from fossel fuels. I’m not sure about the exact mechanism though, so you’ll all have to go do some research.
Here’s the thing though. If it becomes possible in the future to make a machine similar to the one that extracts oxygen, but instead extracts hydrogen from, say, water, you’ll have something close to a free ride. I’m thinking that something other than water will have to be used though, as it need more hydrogen that is available in a molecule of water.
This can’t possibly work. Any scheme along the lines of “take some substance, split it up, and then burn the products” will fail because you will need to input energy to split up the substance in the first place. Even with perfect efficiency, you would do no better than to break even. In real life, the “power source” would actually consume energy instead of generating it because perfect efficiency is not possible.