Most of my reports from Physics@FOM have focused on physicists' physics—you know, the sort of thing people like me geek out on. But, there was also the odd talk that wasn't quite so fundamental in terms of physics. One example was the "Physics for energy storage" session, where I attended the final talk, entitled "The physics of energy storage and the role of hydrogen," given by Andreas Züttel

To be honest, I thought I was going to get something different from what was presented, but it was interesting nonetheless, mainly because of one idea: hydrogen's potential role in carbon sequestration.

Starting with the natural energy cycle of the planet, Züttel showed where and how current human fuel usage fit into the big picture. This was not illustrated to highlight environmental issues, but rather that we use something like 85 million barrels of oil per day, while nature makes eight barrels per day. Looking at production statistics and reports on oil finds, Züttel is pretty convinced that we are already at peak oil and even believes that the financial crisis may have been triggered, in part, by oil prices.

He pointed out that every product has a price point, beyond which no matter what you do, you cannot make money by using that product anymore—it simply becomes impossible to add sufficient value. He thinks oil reached that price just before the crisis, and, since oil underpins modern economies, they crashed. An idea that, given the direction oil prices are going, will be tested again in a rather short time.

Züttel then moved on to energy use, and accurate predictions of future energy demand. To illustrate this, he plotted energy use per capita against per capita income or GDP (I cannot remember which) and showed that nearly all societies fall on a single curve that saturates at about four kWhr per capita per day (this graph went by so fast that I have guessed the .hr per capita part of the unit). There were two outliers on the graph: Russia and the US, but even these show saturation, albeit at a higher rate.

Given this, it is pretty simple to show that we can't grow GDP indefinitely without drastically changing how we get energy. As Züttel puts it, we have to move from energy carriers, like petroleum, to energy fluxes, like sunlight. And that isn't easy. In fact, what we have to learn to do is to efficiently store energy fluxes in energy carriers, which brings us back to hydrogen.

Züttel then spent some time going over storage techniques for hydrogen, and they are all pretty bad. Liquid hydrogen is very difficult and dangerous, while gaseous hydrogen doesn't have enough energy per kilogram of gas to be worthwhile. Metal hydrides are better, and can achieve energy storage densities greater than liquid hydrogen. But their volumetric storage density is poor, with the exception of aluminum hydrides, which are often unstable and sometimes explode—exactly what I want in the back of my car.

An alternative is to store hydrogen as... wait for it... hydrocarbons. Simply put, electrolysis is a pretty efficient process, and hydrocarbons have great energy density and are quite safe. The problem is not getting the hydrogen, but rather sticking it on carbon chains. Plants do this, of course, but they are very inefficient at it.

However, this doesn't have to be so. One reason that photosynthesis is so inefficient is that supplying a hydrogen atom is a two-photon process—a process where two photons must be absorbed simultaneously by an atom or molecule to enter an excited state, which is then used to obtain the hydrogen. If we could alter photosynthesis so that the hydrogen was supplied externally, then there is a good chance that the efficiency could be improved substantially.

A nice side result of storage in hydrocarbons is that it involves reclaiming atmospheric carbon dioxide, resulting in an energy cycle that is, overall, carbon neutral. What's more, carbon sequestration then becomes a case of making more fuel than you actually need and storing it in empty oil-bearing rock—something that we know from nature works very well. In principle, you could offset other emissions, such as concrete production and metal refining, by the same simple process of making more oil than required.

Now don't get me wrong, I like the idea. But there is some significant new science required before these ideas come close to reality. In the meantime, I suspect Züttel is correct: we will burn every last drop of fossil fuel.