Sometimes when I talk to my kids about energy-related issues, they may propose a solution that seems quite simple and obvious to them. The problem is that the real issues may be more complex than they appear on the surface and may require some foundational knowledge to fully understand. One such potential solution to our energy needs is hydrogen-powered cars. Hydrogen is a clean burning fuel and is certainly plentiful given all the hydrogen that exists in Earth's oceans. Why do we not just use hydrogen to solve our energy problems?
To understand why we do not use hydrogen more as a fuel, we need some basic chemistry knowledge. Burning is a chemical reaction where energy is released. When hydrogen is burned, oxygen atoms from the atmosphere each combine with two hydrogen atoms to form water as a waste product while giving off heat in the process. Other chemical reactions consume energy rather than release energy. The problem with hydrogen is that it is very light and very reactive. All of the hydrogen on earth has either floated away into space because it is so light, or it has bonded with other atoms and requires at least as much energy to release as what we get from burning it.
Hydrogen then can be a convenient way to store energy, like a battery, but it is not a source of energy. Extracting hydrogen from water takes as much energy as we recover from burning it. It is like using boulders rolling down a hill as a source of energy. The problem is they are all currently lying at the bottom of the hill. We could push them to the top of the hill and then use them, but then we might as well just use the energy directly that we used to push them up the hill.
The only reason we might prefer the rolling boulders is that they give us a lot of energy fast while the process of pushing them up is longer and slower even though the total energy is equivalent (minus whatever is lost through inefficiency). This is why hydrogen is sometimes used as rocket fuel. The real source of energy was the coal that generated the electricity that was used to extract the hydrogen from water. But the hydrogen works much better as rocket fuel because it can release its energy much faster.
Backing up even further, the energy in the coal ultimately came from the sun. Prehistoric plants used photosynthesis to convert sunlight into chemical energy that was eventually buried, becoming the fossil fuels we use as our primary energy source today. The energy from the sun comes from hydrogen, so in essence we are already running everything on hydrogen. The difference is that the process that generates energy in the sun is nuclear rather then chemical. Chemical processes only rearrange atoms. Nuclear reactions change one kind of atom into another either by combining nuclei (fusion) or splitting nuclei (fission). For elements lighter than iron, fusion releases energy, while elements heavier than iron release energy with fission. The amounts of energy are several orders of magnitude greater than those involved with chemical reactions.
Unlike regular burning of hydrogen, nuclear fusion could provide us with all the energy we would ever need. The problem is that extremely high temperatures and close proximity are required to start and sustain a reaction. Stars do this with gravity, but it is not so easy on earth. So far the only way we have been able to use the energy of nuclear fusion is in thermonuclear (hydrogen) bombs. These blow themselves apart by design. To sustain the reaction and produce usable energy we would have to hold it together. This is a challenge we have yet to resolve.
Hey Tom! I pop over here and read your blog every once in a while; I really enjoy it! As far as this one goes, what about efficiency? Oil is very easy to get at and releases tons of energy. The problem is that most cars only use about 20% of that energy. If hydrogen powered cars are much more efficient than what we use currently, then wouldn't it be worth the effort to push the boulders up the hill?
ReplyDeleteThere are a couple of different ways to run a car on hydrogen. One is burning it, and the other is using it in a fuel cell where hydrogen is combined with oxygen to produce electricity with water as a byproduct which is used to run a car's electric motor. Either way, hydrogen functions basically the same as a battery since it does not occur naturally. I could not find any hard figures, but everything I read indicates that it is less efficient since you need to consider every step in the chain: 1)generating electricity, 2)extracting hydrogen from water with electricity, and 3)powering your car by burning or producing electricity to run your car's electric motor. There are energy costs to extracting and refining oil as well so an accurate comparison would need to consider this as well.
ReplyDeleteThe other disadvantage for hydrogen is that the infrastructure for oil already exists but would need to be developed for the large-scale production of hydrogen. Hydrogen's real competition is advances in battery technology. One advantage over batteries is that you do not have to wait for your car to charge. You could refuel very quickly. However, the technology is currently much more expensive than traditional batteries.
Hey dad I thought this post was interesting I have thought quite a bit about energy problems. What do you think about Al Gore's plan that he had to replace oil and coal energy with natural renewable energy and do you think this would work better in the long run?
ReplyDeleteI think we should do what we can to increase generation from wind, solar, and hydro-electric because they have no carbon footprint and are essentially unlimited. However, there are issues with each of them that make them poor candidates to become our primary base source of electricity. Wind and solar are sporadic and there are a limited number of suitable locations for hydro-electric. The best potential for solar is to meet marginal high demand needs that usually occur during the day when the sun is shining. Initial costs can be quite high for solar, but they could come down with technological advances larger-scale production of solar cells.
ReplyDeleteThe best potential for replacing coal and oil for the bulk of our electricity generation is nuclear. Nuclear has no carbon footprint, and while not technical renewable, know resources will last for thousands of years rather than hundreds as the case for fossil fuels. Breeder reactor technology can extend resources even further making them essentially unlimited. The main problem is public perception of safety and waste disposal. Real safety is not an issue since nuclear is statistically much safer than coal and new plants are even safer. Waste disposal could be solved with new technologies that are able to extract even more energy from spent fuel until radiation levels of the final waste products are nearly as low as ambient environmental radiation. Harnessing fusion could solve all of our energy needs as I mention in the post.
Bio-fuels such as ethanol have limited potential because so much fuel is needed in their production that there is very little net gain. Theoretically their carbon footprint is neutral because you first take carbon out of the atmosphere before putting it back in, but this is not entirely true because of the energy required in their production. It depends on what that energy's source is.