Alternate Energy Source

[Kyobanim]

If this really works it will be great

http://www.metacafe.com/watch/128967/water_as_fuel/

[Alchemist]

Kyobanim:

Interesting find, sir, but there's a catch. I find it hard to imagine the inventor can be unaware of it, but I'll give him the benefit of the doubt and stipulate that he's naive rather than dishonest.

First off, my reaction to "HHO" is one of extreme skepticism. Molecular orbital theory (which describes how electrons around different atoms can interact with each other) strongly suggests that such a thing would be so unstable, you could never detect it, never build up any concentration of it. If you could make it, it should self-destruct as soon as a bond vibrates--few trillionths of a second. Now, some very strange and unstable species can exist fleetingly, during combustion processes, but they're still understandable. This one isn't.

But suppose I'm wrong, as I am often enough. Suppose HHO really can exist under just the right conditions, and if MO theory says it can't, then MO theory needs to be revised. (Unlikely, but not impossible.) There's still a fundamental problem, a deal-breaker.

He starts with water. He does his magic and makes HHO. The system burns it, and what happens? "Turns right back to water," he tells us.

It is not possible to start with ordinary water at room temperature, wind up with ordinary water at room temperature (once the exhaust cools), and get energy out in the bargain. Even if I stipulate that he's making HHO, whatever energy he gets out when it turns back into water, cannot be greater than the energy he put into the water to generate the stuff.

The key is the line, "take water and electricity...break it down." The feature mentions a unique electrolysis process. I'd guess that he's zapping the hell out of the water. This generates hydrogen and oxygen. With the right engineering, you could form these gases quickly enough to create an impressive torch-flame.

Or, in a car, you could feed the gases to a combustion engine, collect the exhaust (just steam), condense it and feed it back through. You wouldn't have to consume more than "four ounces of water"; on balance you're not consuming water at all, only electricity. You'd need one big battery, and you'd be better off running an electric motor off it, but it could work.

But someone had to generate that electricity for him, and that electricity probably came from fossil fuel combustion, because that's where we get most of ours.

Sorry if my post is pedantic, but I just couldn't pass this by.

[The Reaper]

Cold fusion in a test tube?

I had heard the same thing, that the electrolysis of the water to produce the hydrogen and oxygen took more power than was generated. Of course, if you were using nuclear, that might be a decent proposition. Straight electric motors from a battery would be more efficient?

TR

[Alchemist]

The Reaper:

Straight electric motors from a battery would be more efficient?

Just off the top of my head on that, sir. But generating hydrogen and oxygen from water wastes a lot of energy. With all this talk about moving toward a hydrogen economy, there are a lot of chemists trying to develop efficient electrocatalysts for water-splitting. It's so easy to split water with electrical current, but it's very hard to store as chemical energy even half of the electrical energy you spend in the process. Then once you have the hydrogen and oxygen you burn them. What's the efficiency of an internal combustion engine? Forty percent or so, from fuel to crankshaft?

I think you'd have to come out ahead just sending the current straight to an electric motor, instead of an electrolysis/combustion sequence. But I should have made clear that I'm guessing on that point for now. Actually, I should have figured it out for sure before posting; sorry for the speculation. Going now to try to see if I can disprove myself.

Edited to add: A statement above, that it is difficult to store half of the electrical energy used in water-splitting as chemical energy, is inaccurate. Overall energy-efficiency of hydrogen production by electrolysis is 20-25% efficient, but this takes into account the energy wasted in generating the electricity commercially in the first place. Once you have the electrical current, electrolysis can be 75-80% efficient:

Argonne

I regret the error, and will do my homework better in the future.

[Alchemist]

Straight electric motors from a battery would be more efficient?

More efficient than using a battery to generate chemical fuel, then burning the fuel? Yes, sir. Starting with a certain total of electrical energy stored on board the vehicle:

Hydrogen generation from electrical current and water is 75-80% efficient (Argonne). So if you could turn all the energy stored in hydrogen into mechanical energy, 80% would be the best you could do overall.

Diesel engines get somewhat over 40% thermal efficiency (MSN encyclopedia article), but some say that'll go up to 55% with technological improvements, so let's say 44% efficiency from electrical to chemical to mechanical energy. A hydrogen fuel cell can give 70% efficiency (EPA). Using one here would add up to turning electrical, to chemical, to electrical, to mechanical energy, so it's sort of circular reasoning, but I'm looking for the most efficient way to use the hydrogen. So, 56% overall.

A typical industrial motor, nothing fancy, can turn electrical to mechanical energy at 90% efficiency, according to an article in Mechanical Engineering Magazine. A high-efficiency motor would be one in the 93-94.5% range.

So, once you've decided the benefits of batteries are worth the drawbacks, and I think nuclear generation does make this a "decent proposition," then direct electrical-to-mechanical conversion looks like the way to go.

[The Reaper]

Good to know, thanks!

TR