I've often wondered if the electricity generated from an internal combustion hydrogen engine could be used in an electrolosys system with the water generated as exhaust to produce more hydrogen for further fuel. I'm sure there's a reason it couldn't work or work that well, but i think it's an interesting concept.

Let me guess, you took music instead of physics/chemistry in high school, right?

(for a less snarky answer, every conversion loses you energy, so basically that would just be an interesting way to expend hydrogen. For it to work it would require that combining the hydrogen with the oxygen free more energy than was required to split them, which would violate one of the more fundamental laws of thermodynamics, or it would require that you have a frictionless internal combustion engine that operated at 100% efficiency, resistance free wires for transmitting energy, and an electrolosis setup that operated at 100% efficiency, all of which are impossible as far as I know. Even if you could accomplish it, it would be worthless as anything but a novelty, as 100% of the energy would have to remain in the system, so your engine couldn't do anything *but* produce hydrogen).

[Edited on Oct 08, 2004 by Helter]

i have a problem with running cars on water.....it has to be fresh water. not salt water. since when has fresh water been an infinite resource? I live in Australia and most of the country has been in drought for the last 8 years, where the driest non frozen continent in the world and can't see how water powered cars would be of any benifit to us. Shit we are on permanent water restrictions, some towns have to truck water in cause their water has dried up and they are only allowed to wash 4 times a week and the rest is only for drinking and other essentials.....water powered cars yeah right.

One interesting thing I heard (not researched) is that some guy in think in USA has figured out how the convert the energy produce by chloroplasts into electricity with reasonable efficiency...

Sorry, but I'm not going to drive around in a car full of gas that flammable, anyone remember the hindenberg?

Indeed, the claim that PVs do not reach payback during their useful life is widely debunked. This pdf from the National Renewable Energy Lab (US DoE), is but one. If you're really worried about it, use very little Si in high-temperature cells, and make most of the rest of the system mirrors. (The current plan of the group at the link below.)

Also, PV is not the only way to go. For instance, you could use mirrors and Stirling engines, like these people may yet do.

For an interesting look at the oil problem, I recommend the free pdf version of Winning the Oil Endgame, by the Rocky Mountain Institute. Available here.

[snark]

What are you driving now, an electric car?

[/snark]

As a propaganda/advertising ploy, the H was covered with a powdered aluminum paint. Powdered Aluminum is also used to fuel US ICBMs, and in some other rocket/pyrotechnic applications, such as thermite.

Seriously, though - those kids did very well for themselves and should be proud.

This really won't be revolutionary in mobile (car) applications for quite a while though.

Alt-fuel vehicles need to satisfy several needs before they can become widely accepted here. The requirements include:

Range - the vehicle must have a range comparable to conventional vehicles in its' class.

Cost - the vehicle must not carry a huge cost penalty over a conventionally fueled vehicle in its' class, either in upfront or operating costs.

Utility - the vehicle must be nearly as capable as a competing conventional vehicle.

Safety/convenience - the vehicle must meet all current Federal safety requirements, and must not require a huge sacrifice on the part of the owner (no hunting for sparse or nonexistent special fueling stations, vehicle must have A/C, heat and power steering, etc.).

So far, only hybrid vehicles qualify, and they are the only widespread success story in the US auto market to date. Pure electric cars have too short a range in the real world, especially in colder climates. Hydrogen is a net-loss energy carrier, not an energy source. CNG/propane cars are here now and use proven technology, but refueling stations are few and far between and range is limited.

Like it or not, our short-term path to energy self-sufficiency will revolve around some combination of coal fired power plants, higher CAFE ( mileage) standards for cars and trucks - this means lots more hybrids and lots more diesel engines - federally mandated efficiency standards on everything that uses electricity, and smaller, lighter vehicles. Probably a bump in the gas tax, too.
Longer term, look for more nuclear power plants in the US.

No, i took physics and chem....but that was nearly 7 years ago without a bit of science classes in between. I realize that energy is always lost in physical interactions of that type but really i was just wondering if some hydrogen could be produced to offset the environmental costs--if only by a bit--of the necessity of using fossil fuels to produce hydrogen.

Yeah, I was just being snarky for the sake of it (I don't get that many chances these days...) . Really, the answer is the same as for why they don't put a small windmill in front of fans to capture some of their power. It just doesn't make sense. The energy recaptured is less than was required to recapture it, so it makes more sense to just make smaller fans.

I'm not allowed to be pissed about two things at once? If that's the case I'm a little shocked I wasn't hauled away for thoughtcrime ages ago.

Framing this as a high school project, it's awesome. I would've given up a great deal to be enrolled in a high school that understood the value of practically applying science rather than just writing it on a chalkboard. And this is one of the better high school science projects I've heard about; potato guns don't usually get national media coverage. So, to the kids, the teachers, the school's administrators, and the media who thought this should merit some attention, I say bravo.

What bothers me is how investors and government funding trolls are going to react to this media coverage. "Wow! Hydrogen! Photovoltaics! High school kids! And there's more money at stake here than there is in Iraq!" The problem is, you can't take two immature technologies, smash them together, and expect them to magically break their theoretical barriers to suddenly become practical. People with the money to throw behind making the next generation of this type of vehicle need to realize there's far more money to be made coming up with new and better solar converters, or improving the manufacturing process that makes our current photovoltaics inefficient, or inventing the next big advance in energy storage that will render the problems of hydrogen moot. I'm not pissed at a bunch of high school kids for taking part in a kickass experiment, I'm pissed that focusing on these kinds of events diverts attention away from the things we should be focusing on to eventually end our dependence on fossil fuels.

Not really. Battery technology has been the limiting factor on many other technologies since.. well, since electrical engineering, really. The best batteries we can manufacture still store energy at orders of magnitude less efficiency by weight than chemical fuels. That's one of the reasons that keeping the energy in an intermediate hydrogen state between collection by the solar panels and burning by the engine is so appealing.

Some numbers:
NiMH batteries top out at about 130 Wh/kg (Watt-hours per kilogram) currently. Lithium ion batteries squeek out a little more energy density, but are significantly more expensive - enough so that laptop battery packs are the only common use for them.

Hydrogen, by comparison, has energy densities of 39,000 Wh/kg. Simply put, you can store 300 times as much power in an equal weight of hydrogen than you can in an NiMH battery. Not that NiMHs are useless for automotive purposes - My Honda Insight does just fine with a big pack of them to augment its conventional gas engine. But - hydrogen is promising.

References:
http://www.buchmann.ca/Article4-page2.asp
http://xtronics.com/reference/energy_density.htm

Great post, but doesn't this bit ignore the fact that hydrogen is a gas? It doesn't much matter if its energy storage potential is orders of magnitude higher if you need to carry a zeppelin full of it around just to equal the potential of a single NiMH battery, right?

Baudot's comparison was on a per kilogram basis, so not really. Being a gas, a kilogram of hydrogen can be packed into a variable volume; whether to put it into a Hindenberg volume or something small enough for the strong and weak nuclear forces to overcome the electromagnetic force (fusion) depends on the application. A zeppelin is so big because for that application, a large volume is appropriate. It lowers the density of the craft as a whole, allowing it to float in air like boats on water.

Being a gas, you can play with the physical density by changing the volume (lower the pressure). To a good approximation (very good for a small molecule like H_2) PV = RnT. (The product of pressure and volume is proportional to the product of the number of moles of the gas and the temperature.)