Of Hydrogen Economies and Thermodynamics (Draft 3.3)

There is a misconception that hydrogen may someday solve our energy woes. This is unfortunately impossible, not from the standpoint of feasibility, practicality, or economics, but from that of basic physics. The laws of thermodynamics do not allow for a complete "hydrogen economy" (wherein hydrogen is the primary source of our energy). The following explains why.

The laws of thermodynamics are essentially as follows:

1) Energy cannot be created or destroyed. In other words, if you want energy, you have to get it from somewhere.
2) No use of energy is 100% efficient. If a given amount of energy is used to do work (or anything else productive), some of the energy is always ‘lost’ (typically in the form of heat energy radiating away).

Of greatest significance is the first law. When we burn oil or coal, where does the energy we gain come from? It cannot simply ‘materialize.’ Instead, the energy comes from the chemical bonds in the coal or oil molecules which are broken apart. To make the idea clearer, imagine a box of springs. If the springs are outside of the box (perhaps scattered across the floor), it takes a considerable amount of effort (or energy) to get all of the springs inside the box and close the lid. The energy you exert is stored in the compressed springs. When you later open the box, the springs explode all over the place, releasing this energy. The burning of fossil fuels is similar to the box of springs in many ways. Natural processes transform (over the course of a very long time) simple organic compounds into complex molecules with many chemical bonds, and each bond contains the energy imparted upon it by the natural process. In this way, the chemical bonds are like the compressed springs. When these complex molecules (of coal or oil) are burned, the burning process pulls violently at the chemical bonds until they cannot hold together and ‘spring apart,’ releasing their energy in the form of heat. This is similar to the box of springs exploding, releasing its energy in the form of flying springs. Of course, this ‘explosion’ of energy is not in itself of practical value. The explosion must be put to work, and the example of a car engine or a steam turbine are perfect examples. The key realization is where the energy comes from when we burn fossil fuels: the energy comes from the release of chemical bonds. Coal and oil literally have energy in them, and the process of burning serves to release this energy.

This kind of stored energy is called potential energy. Any form of energy which seems ‘hidden’ and can be carried from place to place before it is used is called potential energy. Coal, oil, and natural gas all carry potential energy, and we release this energy when we burn these complex substances and tear apart the chemical bonds within which the energy is stored. Hydrogen gas carries potential energy in a similar way. Hydrogen is famously explosive (as was showcased by the Hindenburg airship), and exploding hydrogen can be made useful in the same way that burning gasoline or coal can be made useful; it can be put to work in an engine.

Of the many potential problems of a so-called “hydrogen economy,” rarely does this one ever come up: to actually gain energy from the use of hydrogen as a fuel, we have to find the hydrogen somewhere. Coal and oil are like finding a box of springs already loaded up and ready to go. We find these substances buried deep in mines and in wells underground, but in practice it ends up being worthwhile because the energy contained in the coal and oil we find is much greater than the energy expended to extract it from the ground. If we were to produce any of these substances ourselves by extracting them from other substances, we would have to expend as much energy creating our fuel as we would eventually get out of it by burning it. This is because, metaphorically speaking, we would essentially have to cram the springs into the box ourselves. This is critical: we cannot extract hydrogen from other substances if we hope to gain energy by burning it later. For example, the process of burning hydrogen causes it to release energy as it combines with oxygen, forming water. To extract hydrogen from water (the most realistic option) would reverse this process, which would require us to contribute energy, resulting in zero net gain in energy over the entire process (and, according to the second law, a slight loss).

So where do we “find” hydrogen then? The good news is, hydrogen is the most abundant element in the universe. In fact, it makes up 98% of it! The bad news is, on the planet Earth it has a way of either combining with other elements to form compounds from which we would have to extract it, or of escaping the atmosphere altogether. Hydrogen is extremely reactive; this is why it burns so well. However, this also causes it to engage readily in chemical reactions, preventing it from maintaining its pure, useful form. Nowhere has pure, naturally existing hydrogen ever been found on our planet, and because of its highly reactive nature, it is extremely unlikely that it ever will. In the atmosphere it exists in trace amounts, but only on the order 0.5 parts per million.

So where does the hydrogen used in prototype hydrogen vehicles and other emerging technologies come from? It is currently extracted from other substances. But remember what the laws of thermodynamics tell us: the potential energy in our 'manufactured' hydrogen gas has to come from somewhere. Since we have to create the hydrogen gas ourselves, this means we first have to come up with the energy needed to create it. We must get this energy from other sources of potential energy which already exist, such as fossil fuels. Because it doesn't exist on our planet in a pure form, hydrogen cannot provide us with any new energy; it can only serve as a means of storing energy from other sources. Assuming this energy comes mostly from fossil fuels, hydrogen accomplishes nothing it claims to in terms of reducing pollution caused by the generation of energy. True, burning hydrogen creates no extra pollution, but obtaining the energy to create the hydrogen still does.

Now, hydrogen is not a realistic source of energy, but perhaps it will prove an effective way to store and transport energy? Well, the issues of storing and transporting hydrogen are the main problems facing the long-pending hydrogen economy. What’s worse, we still haven’t considered the second law of thermodynamics. It turns out, using hydrogen to store and transport energy is less efficient than simply using the original sources of energy to do the work. By using hydrogen, we end up wasting energy, all while offsetting zero pollution (because of the production of hydrogen).

It is possible, if we find a different source of clean energy, to produce hydrogen as a transportable fuel (at some loss of energy content). Hydrogen wouldn't be the source of the energy, but it would serve to replace gasoline. This, of course, assumes that the logistics of storing and transporting hydrogen are ironed out. Remember, though, that this still requires that we find a clean source of energy independent of hydrogen. Hydrogen does not solve the original problem of coming up with a clean, abundant source of new energy.

The only way that a complete "hydrogen economy" will prove effective is if we find our hydrogen somewhere instead of producing it ourselves. The only place within our solar system known to have excess pure hydrogen is the sun, and short of developing a supply chain that obtains hydrogen from the sun in much the same way as we mine our coal here on earth, a hydrogen economy is out of reach.

It’s not economics. It's not politics. It’s physics.