Energy flux density
What is Energy Density and Power Density?
That civilizations progress and population growth mirror the expansion curve of energy consumption, bot in total and per capita, is a correlation well documented and widely recognized, but what is less understood, if at all, is the generative cause of this historic truth.
It is the role of the creative discovery in the scientific mind, over the course of history, which has brought to light the hierarchical sequence of principled discoveries about the underlying chemical structure and energetic-radiative properties of our material world. The consequent ability to harness the energy liberated from manipulation of material processes and to apply that energy in novel ways through the creation of new technologies is what has enabled the long arc of growth for civilization. What is fundamental to understand if that trend of growth is to continue is that the general characteristic of this sequence of progressive steps is an increase in the energy density of fuel sources and power density of applied technology.
Energy density is often measured in terms of the amount of energy that can be liberated from a fuel source per unit mass or volume of that source. Compare the energy density of oil at 46 mega-joules/kilogram to uranium in a nuclear power plant with an energy density of 80 million MJ/Kg. Power density measures the amount of energy flow per unit of time(power) that can be concentrated per unit of area or volume. (See figure 1) For example, a petawatt laser concentrates the power equivalent of 1000X the entire U.S. energy grid onto an area the size of a dime. In terms of energy density of different energy sources in terms of energy per cubic meter, compare for example solar power to natural gas to nuclear power. The difference is exponential. (See energy density chart)
Figure 1. Figure above shows the amount of energy produced ( in kiliwatt per hour, or units of 1000 watts per hour) for 1 pound of source material
To clarify the fundamental point here, the growth of the energy curve is not simply a function of a liner expansion of consumption. The inherent limits of growth that bound the rate of expansion for any phase of civilization is only overtaken by a move to an energy platform with higher energy density and power density potentials, which result from discovery of new principles and development of higher order technology.
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