Natural Gas

How does the power density of Natural Gas compare to other fuels?

Fuel	Carbon-to-Hydrogen Ratio	When was this fuel the dominant source of energy?	Primary use	Description
Fuelwood	10-to-1	Fuelwood and biomass were the dominant sources of energy for human civilization through the 18th century.	Space heat.
Coal	2-to-1	Coal came to dominance in the 19th century with the introduction of the steam engine.	Space heat and industrial heat.	Coal is a first generation hydrocarbon.
Oil	1-to-2	20th century.	Space heat, industrial heat, and motive power.	Oil is a second generation hydrocarbon
Natural Gas	1-to-4	21st century.	Electical power, space heat, industrial heat, and motive power.	Natural Gas is a third generation hydrocarbon
?	?	22nd century	?	?

Microturbines for generating electricity from unprocessed wellhead natural gas.

Natural gas is a gas consisting primarily of methane. Before natural gas can be used as a fuel, it must undergo extensive processing to remove almost all materials other than methane.
However, recently developed microturbine devices can generate electricity by directly burning unprocessed wellhead gas.
In the combustion of methane, several steps are involved:
Methane is believed to form a formaldehyde (HCHO or H₂CO). The formaldehyde gives a formyl radical (HCO), which then forms carbon monoxide (CO). The process is called oxidative pyrolysis:

CH₄ + O₂ → CO + H₂ + H₂O

Following oxidative pyrolysis, the H₂ oxidizes, forming H₂O, replenishing the active species, and releasing heat. This occurs very quickly, usually in significantly less than a millisecond.

2H₂ + O₂ →2H₂O

Finally, the CO oxidizes, forming CO₂ and releasing more heat. This process is generally slower than the other chemical steps, and typically requires a few to several milliseconds to occur.

2CO + O₂ →2CO₂

CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(l) + 890 kJ/mol

where bracketed "g" stands for gaseous form and bracketed "l" stands for liquid form.

By burning methane in a turbine, the heat that is released can be used to generate electricity, which can then be sold at wholesale rates onto the grid.
Natural Gas electricity generating turbines cost about $500 per kilowatt of generating capacity -- including installation costs. This fixed captial cost is substantially lower than that of coal plants, nuclear plants, hydroelectric plants, solar plants, wind plants, and geothermal plants.
- The cost of using Natural Gas to generate electrical power is dominanted by the variable cost of the fuel.

The standard model by which economists explain growth is the Solow-Swan neoclassical growth model, which is described in Robert Solow's 1956 paper, A Contribution to the Theory of Economic Growth. This paper looks at the contribution of labor and capital to the growth of the US economy, using a model that assumes that the contributions of labor and capital are proportional to their respective costs. The paper finds that labor and capital in fact explain less than 25% of the actual growth of the US economy. The assumption is then made that "technology" must explain the huge residual.

With a model that explains so little (less than 25% of actual growth), it is not clear that the model is very helpful. The residual comprising over 75% of growth could just as well be energy as technology.

One economic growth model that explains growth quite well is Accounting for Growth, the Role of Physical Work by Robert U. Ayres and Benjamin Warr. This model looks at the amount of work (in a physics sense) that is done by energy. Thus, it considers both the amount of energy used and how productive that energy is. For example, power stations in 1900 converted only 4% of the potential energy in coal to electricity, but by 2000, the conversion efficiency was raised to 35%. This model explains the vast majority of US real economic growth between 1900 and 2000, except for a residual of about 12% after 1975.

Results of model by Ayres and Warr. The selected model is the dotted red line, which includes biomass and animal labor, as well as other types of fuels (fossil and nuclear):

A closely related result from the Ayres and Warr paper is that declining real cost of energy, particularly electricity, and the rising use of the much cheaper electricity, fed economic growth in the 1900 to 1998 period.