Energy storage and green technologies
A lot of people are trying to save the world with “green technologies.” Personally, I think the obsession the upper middle classes have with saving the world is misplaced, grandiose and often destructive. Such folks would be better off trying to make their little corner of the planet a nicer place for their fellow citizens. But it isn’t a bad idea trying to get some energy supplies from someplace besides dead dinosaur sauce.
The problem with getting rid of fossil fuels is these are tremendously dense and useful energy supplies. You need to store energy. Energy storage is a hard problem. Anyone who owns a portable computer knows this. Batteries run flat pretty quickly. Basically, batteries suck.
This is a universal technological problem. If you have a powerplant, it probably runs at close to its most efficient output rate at all times. Otherwise, you’re wasting a lot of fuel. If you have excess powerplant capacity, that is a waste of capacity. Power companies deal with this by building artificial hydroelectric installations: they build a big jar of water in a mountain, and use excess power to fill it up using pumps. Then when they need more electricity (when everyone turns on their air conditioners), they let the water fall and spin some extra turbines (which are cheaper than turbines + motors). You get something like 70% efficiency in this storage technique, even though it sounds really silly, but anything which allows a little more output during peak hours without building otherwise idle power plants is useful. This is also the idea behind “smartmeter” technologies, in that power companies think they can make consumers use less power during peak hours. I rather doubt that they can, but don’t blame them for trying, as peak generating plants are expensive infrastructure to have lying around idle most of the time.
The problem is compounded by “green” energy technologies presently under popular consideration. Anything solar, obviously, only works in the day time. Fortunately, peak power consumption also happens in the daytime, so cheap solar could help power companies deliver power more efficiently. Of course, it isn’t cheap; it’s outrageously expensive -so expensive, that nobody has installed large solar installations yet, despite all manner of tax credits and legal incentives to do so. Should solar ever become cheap enough to compete with fossil fuels, energy storage will become a problem. The other popular “renewable” is wind power, which is reasonably cheap and which isn’t strongly correlated with time of day. It is, however, highly intermittent, which makes power storage an important issue in building an electrical infrastructure which relies on “green” energy supplies.
In terms of small scale energy use, such as heating a house or powering a vehicle, chemicals is usually how things are stored on a small scale. Chemicals are a sort of real world crystalization of the electromagnetic force. All the little electron bonds in a chemical are potential energy which can be released by burning the stuff, or, if it is an explosive, letting it explode. Burning is most efficient, as you only have to carry around half of the chemicals. In principle, you could carry around electromagnetic energy in other forms. In practise, hydrocarbons (or some form of hydrogen) are a really dense and helpful way of doing this.
Capacitors store electric charge directly (batteries store electricity as chemical energy) by separating two conductors by a dielectric substance. If you make a big enough capacitor, it can store a lot of charge. Nobody knows how to build such a capacitor such that it beats batteries in energy storage per kilogram, though big capacitors are used to power systems in which the power output must be high and very temporary (like in a surface to air or air to air missile, or engine starter circuit). Something like the state of the art is represented here; as you can see it stores about 2kJ per pound. Lead acid bateries are more like 66kj/lb, and the energizer bunny about 180kj/lb. Nickel Metal Hydride batteries are about 150kj/lb. The most insane kind of battery, which is also explosive (and low in current capacity), is lithium chloride; it stores about 900kj/lb. You can’t generally buy those unless you are NASA or a large industrial firm. By contrast, gasoline stores about 20,000kj/lb. This is why we do not use electric cars on a wide scale; you can store a lot more energy per pound of fuel in a gasoline car. Each gallon is about 6lbs. So a 12 gallon capacity is equal to to 10,000lbs of advanced batteries in terms of energy storage. The next time a hippy tells you “clean electric cars” were destroyed via a conspiracy of oil barons and auto executives, remind him it is really the laws of physics.
For what it is worth, hydrocarbons are about as good as it gets; a factor of 10 better than TNT; and they don’t explode in inconvenient ways. The only simple thing I can think of which does substantially better in terms of energy storage is liquid hydrogen (about twice as good), and that poses difficult storage problems. Probably if we ever develop practical fuel cells, they will operate on gasoline or alcohol. Intelligent people have contemplated building small internal combustion engines with generators for powering laptops; that’s how bad batteries are at this sort of thing.
The other little-mentioned problem with alternative energy supplies taken from the ambient environment: they are sparse. So what, you say? Well, imagine we had a cheap way of harvesting, say, tidal energy. I’ve seen such projects proposed, and they even look fairly cost effective on paper, even if you overlook the potential maintenance costs and environmental damage caused by such gizmos. One of the obvious problems with this is getting the power to someplace useful. How do you do this? You can’t just stick a giant extension cord in the ocean; this is a vast engineering problem. The same problem manifests itself in collecting other kinds of diffuse energy, such as wind power. You need a lot of wires to hook up a wind farm to the grid. Solar is worse (excepting, perhaps, solar-thermal plants, whose major problem is getting enough windex to keep the heliostats clean). All such schemes require, at the very least, large amounts of expensive aluminum and copper. At the worst (the tidal energy idea), we don’t actually know how to move the energy from one place to the other efficiently.
When someone is talking about a new scheme for “green” energy generation, contemplate energy density considerations. Does the energy come from a small place like an electric generator, or is it dispersed over a wide region, like a solar panel the size of Delaware? If the latter, there are hidden infrastructure costs the inventor isn’t telling you about. Is the energy stored as efficiently as hydrocarbons? If yes, well, that is an important breakthrough which makes all kinds of things possible. Energy density is a simple idea which sorts out lots of bullshit.