Here’s an interesting piece on breakthroughs in artificial photosynthesis. My biggest problem with it is that it talks about hydrogen as being “easy to store,” but it doesn’t describe in any way how this is done. Clearly, if you don’t have to carry it in a vehicle (as would be required for transport fuel) the job is a lot easier, but it’s still non trivial. If it’s simply for load leveling, you have a lot more options, but they still come down to three: hydrides, high-pressure gas, or liquid. The latter uses a lot of energy to chill it, and loses it in rewarming.
There is a picture of a notional system in a garage, but it shows a water tank, hydrogen tank, and oxygen tank, and the separated gases (or liquids?). The water tank looks like about half the volume of the separated elements. How realistic is this? What is going on? I’d expect more from an article in Technology Review.
Well, you might be able to reduce CO2 to hydrocarbons, store the hydrocarbons, and then run a reforming fuel cell. Who knows? This is basic science, not engineering.
Even better would be to go to hydrocarbons in one step, like the plants do. No problem storing hydrocarbons, and we’ve already got the technology to distribute and use them set up.
But then, at that point, you might be better off giving your money to the biologists to re-engineer a living bug to do the trick, instead of too the inorganic chemists to re-invent the chloroplast.
The article doesn’t discuss reducing to hydrocarbons. It only talks about breaking it out into H2 and O2.
The article included some pretty skeptical observations. The bit about current density is particularly damning.
Bah. Think Popular Mechanix circa 1960. Ducted-fan aircars and atomic road vehicles.
I’ve lost the URLs, but this has been canvassed elsewhere. The efficiency is nil; you’d be better off building solar cells and using them for electrolysis. (That may improve, of course, but my money’s not on it.) And, as you point out, the hydrogen is stored in handwavium tanks. What I tell people is that the reason we use hydrocarbons as fuel is that the carbon serves as a ball and chain to keep the hydrogen from getting away.
The whole mess is an application for a Government research grant, playing off the carbon dioxide hysteria to keep anybody from looking too closely. Bugs that make Diesel fuel are a much better prospect.
Regards,
Ric
The bit about current density is particularly damning.
Yes, there was that, too.
Well, yeah, I know, Rand, but chemically speaking all you really give a damn about here is producing some reduced compound, so you can oxidize it with atmospheric O2 and get energy. H2 is rather the ultimate reduced compound, but as you’ve pointed out it’s a pain to handle. The obvious alternative is the one we’ve (and the plant world) have been using all along, which is CH compounds, i.e. hydrocarbons.
As Ric points out, the carbon more or less goes along for the ride. It’s very convenient because it forms large “backbone” chains easily, to which you can attach the H’s like grapes on a stem, and these compounds are dense, nonvolatile, easily handled, available in a variety of states (gas, liquid, solid) and viscosities. Really, if we had to make hydrocarbons from scratch, everyone would be all excited about this new clever method of energy storage.
en better would be to go to hydrocarbons in one step, like the plants do.
Plants don’t produce hydrocarbons (at least, not directly). They produce carbohydrates.
The hydrogen and oxygen are almost certainly gaseous. There’s no way that you could build a practical liquefaction plant in a garage. Liquid H2 isn’t especially practical, anyway – too much boil-off. Hydrides are a good option for stationary applications, but they’re ridiculously heavy and still very expensive. On the other hand, high pressure gas has made a lot of progress in the past few years. Automotive development has produced 5000 and 10,000 psi carbon fibre tank technology that you’ll find in use in many of the fuel cell vehicles on the road today. Compressing the gas to high pressure for storage isn’t that complex, either. The size of the tank is going to be sized to bridge the gap between demand and production, so probably doesn’t have to be huge. You need enough H2 to drive your car ~200 km every few days, or to keep your house running overnight and through a few cloudy days when sun output isn’t as high.
I have one word for you, young man. Butanol.
Butanol is okay, but methanol is easier to reform into hydrogen and you can make it in your own backyard. The effluent can be useful, too, once the methanol is removed…