Solar hydrogen

One of the biggest problems in moving to a renewable energy portfolio is the transportability question. In fixed plant, you can afford to have acres of solar capture material, for instance, but not in a car or plane (yes there are exceptions!) In addition, we need to store the energy for nighttime or cloudy day use. So batteries, ultracapacitors, underground pressurized caverns, water columns, etc. are all being explored for storage. One method getting some attention is cracking water to make hydrogen and oxygen, the hydrogen being a useful fuel, which burned makes pure (ish) water. It has a great mass energy density around 120MJ/kg and and marginal volumetric density of 8.5MJ/l in liquid form (gasoline by comparison is 45MJ/kg and 31MJ/l.) So we would need 4x the gas tank size, and at high pressure, to move us the same distance. Of course, engineering the car for better mileage could make up a lot of that difference. And for fixed installations, this doesn't necessarily present a problem.

So I was intrigued when this landed on my inbox. What IS good is they have apparently made cracking hydrogen a much less energy intensive process. This is important. But they have committed a foul in claiming the technology is inherently 'solar'. This is common now as solar energy is such a hot field that any way to connect ones work to that field is a way to raise its profile. However, any energy source will work fine as long as it produces electrons. Perhaps it is enabling for a home fuel cell driven by solar power, but it really is 'electron agnostic'. As opposed to this finding. Here, unlike the claims in the MIT finding, the technology is inherently solar. And it yields hydrogen. It may not be strictly photonic technology, but it is still quite interesting.

The hydrogen production question is being approached electrochemically as above, as well as biologically. But I wonder if this is fool's gold. The volumetric density is still low, much lower than hydrocarbons. Using this for a plane fuel for instance might be prohibitive. If we are doing something with water and CO2, maybe we should be making long-chain hydrocarbons [sub req]. They can be pumped straight into our existing energy infrastructure, refined like any oil, and transported without a massive investment in new handling and tranport mechanisms. Of course, if they are solar driven (e.g. algae), they will also have the scale problem