The Blogging of the President site has a somewhat arcane, but useful piece on how energy density will affect our future energy choices. Density refers to the amount of energy per unit of volume of an energy source. Oil is a very, very dense energy source. Coal is quite dense per unit of energy, but much more bulky than oil. Unfortunately, solar power has very low relative energy density. Density, is often, but not always, associated with the energy profit ratio, the ratio between how much energy you get for how much you expend to get it. Generally, speaking, the higher the density, the higher the energy profit ratio. Oil energy profit ratios were well over a 100 to 1 in the early days of the oil age, that is 100 units of energy gained for every unit expended to get it. Oil has slipped to about 20 to 1 for most old discoveries now and to around 8 to 1 for new discoveries which are getting harder and harder to extract and are of lower quality (i.e., lower energy density). Compare this to 4 for nuclear power, 2.5 for biodiesel, 2 or more for wind, and slightly more than 1 for solar. Oil and coal (about 10 to 1) continue to be favored because of this ratio.
Since the energy density is expected to fall further as we extract oil and coal of lesser and lesser energy content, we can either move to other sources of energy and accept lower energy outputs (and thus a lower standard of living, essentially) or try to enhance the density of the fossil fuel sources. Lower quality oils are currently being enhanced with the addition of hydrogen. But, hydrogen has be gotten from somewhere. For advocates of this approach the source will be nuclear plants which produce hydrogen, probably from water.
Another way to upgrade energy to meet our needs is to add electrical energy to traditional fossil fuels. This is already being done with hybrid cars. If the source of the electricity is renewable, then we have a better chance of a long-lived sustainable energy system. If the source is say, coal-fired power plants, then we will simply continue down the path of unsustainability. This is the choice that the piece mentioned above outlines.
(Via Energy Bulletin.)
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