Because I have to say it somewhere

[redbird]

A battery is not an energy source.

Batteries are storage devices, and the energy has to come from somewhere. A fuel cell is a kind of battery.

[Also, mushrooms are not squash, but I'm not actually annoyed at having been given a different kind of soup than I ordered.]

Comments

[brooksmoses]

Normally I'd agree with this, what with it being one of my pet peeves.

A fuel cell isn't a storage device, though, any more than it's an energy source -- it doesn't store energy. It transforms energy in the form of fuel (which is stored in an external tank) to energy in the form of electricity. Just like an internal-combustion engine transforms energy in the form of fuel into energy in the form of mechanical motion.

[avram]

And that desk's not made of oak, it's made of the wood from an oak tree!

[brooksmoses]

I regret that I do not understand the point that you are making, beyond that you think I'm making silly distinctions. Why do you think my distinction is silly? I'm not even clear on which of the distinctions I'm making you're complaining about!

A fuel cell car needs some sort of energy storage. This energy storage can be refilled, in timescales that are very different from the timescales that batteries can be recharged. More significantly, the range of a fuel-cell-powered car is independent of the size of the fuel cells, which is entirely different from the situation with a car powered by a storage battery. Thus, in a lot of practical ways a fuel cell is much closer to an engine than it is to a standard battery. I find these things to be of very substantial practical consideration in considering whether the technology is useful, not to mention being a matter of terminology.

[avram]

The distinction between "storing energy" and "transforming energy into a different form" seems silly to me, since in my experience, when people talk about energy being stored it's often a case where the energy is being transformed into another form.

Your point about timescales seems sensible, though.

[xiphias.livejournal.com]

Well, what IS an energy source, then, except maybe nuclear reactions in which matter is converted into energy? Everything else is merely using energy which already exists in some other form.

I see a battery as an energy source -- a LOCAL energy source, true, but within a system of, say, a toy car and a battery, the toy car gets its energy from the source of the battery. Certainly, the battery had to get its energy from somewhere else, and that had to get its energy from somewhere, and so forth.

Is wood an energy source? It doesn't create energy -- it simply stores it in its tissues. How about protein, or carbohydrates? They store energy gotten from somwhere else.

How are you defining "energy source"?

[brooksmoses]

I would define "energy source" as a means by which I get energy into a system (where system is something like, say, a car).

This makes it dependent on what I call the system, which I think is the appropriate thermodynamic answer.

For a toy car that runs on disposable AA's, I think the most likely system to be reasonable is the car, for what the AA's are the energy source.

For a full-size car that has batteries permanently mounted in it, I don't think there's any reasonable system for which the battery is the energy source, unless you're defining your boundaries in the time dimension over a period of a few hours (which, okay, in some cases makes sense).

For the whole transportation and technological system that is "human civilization", the oil pumped out of the ground that fueled the generator that charged the battery is an energy source. That's generally the reasonable system to talk about when thinking about global technological energy issues, I think.

A key pet peeve is that, in that global system, hydrogen is not an energy source. A lot of the discussion of the "hydrogen economy" treated it as if it was.

[redbird]

This is more or less what I was getting at. Thank you.

And yes, it was prompted by another manuscript in which someone was talking about developing hydrogen fuel cells to deal with the U.S.'s dependence on oil, with no mention of where the hydrogen is going to come from. That theory might make sense if the electrical grid wasn't using significant amounts of oil, and powered more by coal than any other source.

[brooksmoses]

Ooh, that was one of my Ph.D. advisor's significant pet peeves, yes.

These days, hydrogen is mainly produced from natural gas, basically by splitting the carbon atoms off the natural gas molecules and releasing them as CO2. (I think some processes may get some of the oxygen for the CO2 from water, so you get some more hydrogen out than came in with the natural gas, but it's still mostly just splitting the natural gas.)

Using coal does, at least, reduce dependence on foreign oil.

French trains!

[the-magician.livejournal.com]

Recently someone pointed out a prediction of the future that had nuclear-powered railway trains ...

... in France around 80% of their electricity is produced from nuclear power stations ... they have electrically powered trains ... therefore they are already running nuclear-powered trains!

I think the distinction between batteries as energy storage and some of the other points made by commenters in this entry, is that people keep going on about how electric cars produce no greenhouse gases etc. etc. and don't think about either the power stations required to fill the batteries, or the battery full-lifecycle (the metals involved, the material-miles to assemble it all, the cost of decommissioning etc.)

Fuel cells are not energy storage. They are part of the engine. The hydrogen (or whatever) fuel tank is the battery.

[avram]

If you follow that logic to its ultimate conclusion, the only energy source was the Big Bang, and even that could get demoted to mere "storage device" if we ever figure out where its energy came from.

It's perfectly reasonable to regard a battery as an energy source within a specific system.

[brooksmoses]

See my definition above.

In the discussion of transportation infrastructure and environmentally-motivated policy related to it -- which is what I suspect this peeve is coming from (because a lot of people discussing such things get it painfully incorrect), though I could be entirely wrong about that -- there are very few cases in which it's reasonable to define the system in such a way that the battery is an energy source.

[webbob.livejournal.com]

I agree that a fuel cell, comprising the electrochemical reactor in which oxygen reacts with hydrogen, the oxygen storage tank, and the hydrogen storage tank, is an energy storage device. Energy is used to separate reactants chemically, the reactant chemicals are stored in the fuel cell device (given that it's comprised as above), and energy can be extracted from the fuel cell only to the extent that reactants were produced for and stored in it.

In the sense of a fuel cell operating on natural gas, propane, or some other hydrocarbon (via a regenerator) and atmospheric oxygen, I disagree. The fuel and oxidant are more or less available in the ambient environment (or at least made available for multiple energy-transforming purposes) and the electrochemical fuel cell (which does not comprise the fuel store or an oxidant store) transforms chemical potential energy to heat and electrical energy. It's an energy source to the same extent that a gas-fueled motor-generator pair is an energy source.

Artillery batteries are energy storage and release devices. Battery chickens, on the other hand, don't fall into either of the "energy storage" and "energy source" categories.

[the-magician.livejournal.com]

Battered chickens on the other hand *are* an energy source, one I very efficiently convert into energy storage around my waist!

[webbob.livejournal.com]

Correction: reformer, not regenerator. The unit in which natural gas is broken down into carbon oxides and hydrogen.

[minnehaha.livejournal.com]

If a storage device is something inside that system that stores energy, and an energy source is something from outside the system that brings energy in, isn't this a function of where you bound the system? If the system is my camera's flash, then new batteries are a source of energy. If the system is my computer, then the battery is storing energy and the AC adapter is bringing energy into the system. If the system is Earth, then fossel fuels are just another storage device and the sun is the only energy source.

B

[sraun]

Re: Earth as the system - wouldn't the energy source be The sun and one or more dead stars? Didn't the heavy metals in Earth come from supernovas?

[redbird]

Yes, defining the system is key.

A lot of the discussion of hydrogen fuel cells is more reminiscent of "I don't need to buy oil for my house, I have a generator in the back yard" than of "internal combustion engines are inefficient and we can do better."