Energy

[muon2]

Electric power is needed, but the critical hurdle is energy density. This measures how much useable energy is stored in a given volume, like mass density measures the mass in a given volume. Conventional rechargeable batteries can't match gasoline and that limits batteries from competing with the internal combustion engine.

Work on the hydrogen fuel cell is much more promising. Hydrogen provides greater energy density then petroleum, and the fuel cell has been around for a long time now. It has been used in military and space applications. The biggest commercial hurdle is how to store roughly 10 kg of hydrogen in a car so that it has a range of 500 km, like a gas-powered vehicle. This is an active area of current research, and when solved can lead to a wholesale replacement of gas engines as we know them today.

[muon2]

Electric power is needed, but the critical hurdle is energy density. This measures how much useable energy is stored in a given volume, like mass density measures the mass in a given volume. Conventional rechargeable batteries can't match gasoline and that limits batteries from competing with the internal combustion engine.

Work on the hydrogen fuel cell is much more promising. Hydrogen provides greater energy density then petroleum, and the fuel cell has been around for a long time now. It has been used in military and space applications. The biggest commercial hurdle is how to store roughly 10 kg of hydrogen in a car so that it has a range of 500 km, like a gas-powered vehicle. This is an active area of current research, and when solved can lead to a wholesale replacement of gas engines as we know them today.

Muon I have a question that possibly you can answer. Where do you get the hydrogen from? I know of two ways, both of which have problems. You can get it from water through electroysis or extract it from hydrocarbon fuels like oil or methane.

To get it from water you must put in more energy that you will get out so that will  create a huge electricity demand. Most of our electricity comes from coal burning plants which produce mostly CO2 as a product of combustion. This could eliminate our need for foreign oil but would still leave us with the greenhouse gas problem (assumming it is a problem).

If we get it from oil we are still dependent on oil. Also oil contains much more carbon by weight than hydrogen, so what happens to the carbon?

You are correct that most hydrogen comes from hydrocarbons today. The most common technology converts methane in natural gas to hydrogen and carbon monoxide. Some hydrogen is produced through direct electrolysis of water with oxygen as a byproduct, but this can use electricity from any source, such as soloar or nuclear with no carbon emission.

In the near term, natural gas will still be the major source. However, biomass may be an important future source of hydrogen. Some current reserach involves engineered bacteria to generate hydrogen from biomass waste. The carbon byproducts can then be sequestered in the ground (think compost), instead of generating carbon dioxide.

[muon2]

You are correct that most hydrogen comes from hydrocarbons today. The most common technology converts methane in natural gas to hydrogen and carbon monoxide. 

That sounds worse than producing carbon dioxide, since carbon monoxide is a deadly poison.

Dont' worry, it's combusted before released.

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That would be slick if it can be made to work. But it still seems that there are some significant technical problems to be solved.

When I was in college over thirty years ago it seemed like fuel cells were likely to become viable for cars, but many of the  problems which existed then are still around today.

You are right, which is why the applications have been narrow so far. Until recently, there weren't a lot of dollars for research. After the 70's energy crisis, more went into direct sources like solar and wind, and on efficiency measures, but not on portable power.
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New production measures, like biomass, are relatively recent. The biggest hurdle will probably be finding the best way to store the hydrogen for a car - whether liquified or bound in a solid metal hydride.

[muon2]

The biggest hurdle will probably be finding the best way to store the hydrogen for a car - whether liquified or bound in a solid metal hydride.

The biggest hurdle is price.  The main advantage of the internal combustion engine is that it is a proven technology that is easy to build.  Biofuels can be used in internal combustion engines, solve the same greenhouse gas problem as more exptic technologies, and don't require new infrastructure for their distribution.  It is only the cost of biofuels compared to petrofuels that has kept them from being more widely used.  Until IC alternatives reach the point of being cheaper than biofueled IC engines, they will remain laboratory curiosities.

The actual fuel cell is also a proven technology and easy to build. It produces electricity that can run a conventional motor. Fuel storage and distribution drive the cost.

Some automotive technologies were around a long time before new technologies brought the price down for the mass market. For instance, fuel injectors were around since the early part of the 20th century, but were generally only found in racing and other performance cars until the 70's. Cheap microprocessor technology allowed fuel injectors to beat carburetors. Now they are standard, and the change over only took a few years.