Energy Resources

Steven Dutch, Natural and Applied Sciences, University of Wisconsin - Green Bay
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Geothermal Energy: A Free Lunch?

Environmental Problems of Geothermal Energy

Technical Problems of Geothermal Energy

Thermodynamic Efficiency

Thermodynamic Efficiency is defined by the Second Law of Thermodynamics. It is the maximum possible efficiency any heat-driven process could produce, before any practical considerations like friction, heat losses, etc. The formula for thermodynamic efficiency is:

Eff. = (Ti - Tf)/Ti
(T = Degrees Kelvin = Degrees C + 273)
(Ti = initial temperature, Tf = final temperature)

Automobile Engine

One of the fondest popular fantasies is that there is a device being kept secret by the oil companies and car manufacturers that would allow cars to get hundreds of miles per gallon. As this calculation shows, no amount of tinkering with the engine will do much better than double gas mileage (actually much less). Most of our improvements in gas mileage have come from reducing weight, air resistance and friction. This is one reason why most new cars have spare tires about the size of bagels, for example.

Typical Steam Power Plant

Critics of current energy practices point out that most energy is used to produce temperatures below the boiling point of water, and ask if it makes sense to have power plants generating extremely high temperatures. The answer is yes; it results in high thermodynamic efficiency. Attempting to supply hot water or hot air directly would lose far more energy in transmission losses than it would save in heating bills.

Geothermal Power Plant

This Is Before Any Engineering and Operating Losses. The situation above is actually a very favorable one as geothermal power sources go. Actual achieved efficiencies:

Who's Got the Oil?

According to one comprehensive listing of the world's great oil fields, the total known oil reserves (including amounts already extracted) total 2100 billion barrels. These are concentrated in:

The pattern is clear: oil is overwhelmingly concentrated in a small number of giant and supergiant fields. There are not many places left to hide something that big. The discovery rate of giant fields has been falling for decades.

Giant Oil Fields

oil field statistics

The figure above shows the proportion of the world's oil reserves in fields of various sizes.

oil field statistics

The figure above shows the regional location of oil fields larger than one billion barrels. Note the overwhelming importance of the Middle East. The two largest fields are Gharwar in Saudi Arabia and Burgan in Kuwait. Still wonder why we fought the Gulf War?

Is There a Lot More Undiscovered Oil?

Gas Hydrates

Natural gas hydrates are a curious kind of chemical compound where two dissimilar molecules are mechanically intermingled but not truly chemically bonded. Instead one molecule forms a framework that traps the other molecule. Natural gas hydrates can be considered modified ice structures enclosing methane and other hydrocarbons, but they can melt at temperatures well above normal ice.

At 30 atmospheres pressure, methane hydrate begins to be stable at temperatures above 0 C and at 100 atmospheres it is stable at 15 C. This behavior has two important practical implications. First, it's a nuisance to the gas company. They have to dehydrate natural gas thoroughly to prevent methane hydrates from forming in high pressure gas lines. Second, methane hydrates will be stable on the sea floor at depths below a few hundred meters and will be solid within sea floor sediments. Masses of methane hydrate "yellow ice" have been photographed on the sea floor. Chunks occasionally break loose and float to the surface, where they are unstable and effervesce as they decompose.

The stability of methane hydrates on the sea floor has a whole raft of implications. First, they may constitute a huge energy resource. Second, natural disturbances (and man-made ones, if we exploit gas hydrates and aren't careful) might suddenly destabilize sea floor methane hydrates, triggering submarine landslides and huge releases of methane. Finally, methane is a ferociously effective greenhouse gas, and large methane releases may explain sudden episodes of climatic warming in the geologic past. The methane would oxidize fairly quickly in the atmosphere, but could cause enough warming that other mechanisms (for example, release of carbon dioxide from carbonate rocks and decaying biomass) could keep the temperatures elevated.

In the diagram at left, each vertex is occupied by an oxygen atom and the midpoint of each edge is a hydrogen atom. This atom is attached to one oxygen as part of a water molecule and hydrogen bonded to the other. In the diagram at left one cage is shown with oxygen atoms in blue and hydrogen in red. A methane molecule is shown inside one of the cage skeletons.

Is the Energy Crisis a Myth?

One of the clearest analyses of the energy crisis is Energy Sources -- The Wealth of the World, by Eugene Ayres and Charles A Scarlott, two industrial scientists. This work is worth quoting in some detail.

The internal-combustion engine used for automobiles is a fragile device compared with other prime movers -- even compared with the internal combustion engines used for diesel- electric locomotives that have been known to go over a million miles without mechanical overhauling.

Something about the possession and operation of a motor car provides effective anesthesia for any awareness of economy ... A few people for technical reasons keep an account of miles per gallon of fuel, depreciation per mile, and other costs of motoring, but the result is usually so appalling that the accounts are hurriedly discontinued and forgotten.

The advertising specialists, conscious of the public pulse, do not waste much space and money talking about economy. They talk instead, of performance, comfort, style and reliability. Nearly everything said about a new car means lower fuel efficiency ...

... the energy-system efficiency of the motor car with petroleum motor fuel is, thus, 5 percent ... no one is proud of this accomplishment -- least of all the automotive-design engineers ... The trouble is, every time the design engineer manages to save a few BTU it is more than spent answering the clamor for softer tires, for radio, for better heaters, more lights, cigarette lighters and possibly even air conditioning.

Histories written a few centuries hence may describe the United States as a nation of such extraordinary technologic virility that we succeeded in finding ways of dissipating our natural wealth far more rapidly than any other nation. At any rate, we are having a wonderful time doing it. From the discussions in the earlier chapters of this book it is clear that the problem of energy for the United States is not one of the dim future. It is upon us now.

You may wonder why this book was quoted at such length; after all, it is little different from what energy analysts say all the time, although some of the remarks are clearly dated. These quotes are pretty much the same as any contemporary energy study, with one very important difference. They were written in 1952! Here's how Ayres and Scarlott viewed our future oil supplies.

Our imports of petroleum are small but each year they become larger. By 1960 they are likely to be quite substantial. By 1970 they will almost certainly be huge -- if foreign oil is still available then in sufficient quantity (emphasis mine) ... This tiny period of earth's life, when we are consuming its stored riches, is nearly over ... Fortunately for us there is still time for fundamental research [on alternative energy sources]. But not too much time.

There it is, all laid out with clockwork precision almost fifty years ago. We cannot say we weren't warned or that we were taken by surprise.

The unmistakable signs to those who were willing to see go back even further in time. As noted earlier, even before World War II the number of discoveries of new large oil fields was declining.

The person who has done the most to develop resource prediction strategies is M. King Hubbert. Hubbert is no neglected prophet but a long-respected petroleum geologist. Hubbert noted that the production history of an oil field follows a bell-shaped curve; increasing development, a production peak, then decline as the field is depleted. The cumulative production curve, which is actually a graph of the area under the bell curve with time, is a gentle S called the sigmoid curve. Oil fields often consist of a number of disconnected reservoirs, so if the curve applies to a single field it might also apply to a region, a state, a nation, or even the entire world. Hubbert also noted that production from new oil fields typically lags behind discovery by about ten years. In 1958, Hubbert noted that new discoveries in the U.S. had already peaked and were declining, and he predicted that U.S. oil production would peak in the late 1960's; it peaked in 1967. There was a later surge after the North Slope oil fields were discovered, but based on what was known in 1958, Hubbert was right on target.

Hubbert's curve has an interesting property. The sides of the bell-shaped curve rise steeply, and most of the area, or total production, is in a narrow band under the peak. Because of this geometric property, even a huge increase in the total production has little effect on the date the peak is reached and decline begins, If we were suddenly to double or triple our energy reserves, we would find plenty of ways to use it: bigger and more comfortable cars, cheaper jet fares and more flights, more electrical appliances, less insulation, throwaway containers, and so on (have doubts? I have three words for you: Sport Utility Vehicle). The sobering reality is that no oil discovery, however large , can forestall the energy crunch very long. Hubbert published a prediction of global oil production in 1969, based on energy use to that time. If the total recoverable oil on earth amounted to 1.35 trillion barrels (a generous estimate in 1969 and 50% more than the total reserves known in 1981), petroleum production would peak and begin to decline about 1990. If the total is half again larger yet, 2.1 trillion barrels (the figure used in the diagrams above), the time of peak production shifts only by ten years, to 2000. We can (and have) flatten out the peak artificially by regulating energy use or raising prices, but the days of unlimited cheap energy are gone with the dinosaurs. Frankly I think the mobile lifestyle we enjoy has a lot of good features; I'd like to see some way to guarantee cheap energy, but fantasy and denial won't bring it about.

We will not run out of oil anytime soon. Oil will be available through the 21st century and probably well after. What will happen is that sometime in the next couple of decades, world demand will exceed production. Oil can only be made to flow through the rocks just so fast, and extracting it too fast can actually shorten the life of an oil field; there may be lots of oil left but so finely dispersed that wells go almost dry. When demand exceeds production the price will go up and stay up.

Some Final Blunt Comments

Americans complain bitterly whenever they have to pay more for something than they think they should (translation, any price that interferes with their buying something else they want). A sense of entitlement pervades American society. Only someone who believes in the Easter Bunny could doubt that oil companies and oil-producing nations try to keep prices up. But consider the following:


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Created 21 May 1997, Last Update 14 April 1999

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