How much longer can fossil fuels be used? ( information from "Oil haves and Have-Nots"; Roger Doyle; Scientific America, 2004;

Oil: Geologists all agree that oil resources are limited. What they don't agree on is when oil will run out. THee US Dept of Energy has projected several scenarios, with the shortfall occuring at the earliest in 2021 and the latest at 2112. Othere geologists predict far shorter times- as early as next year while other economists predict supplies to hold for the next 25-50 years. In any case, we need to switch energy supplies before reserves go to keep the transition smooth.
Why such a variability in estimates?
One is official agencies worldwide are very cauctious about giving low predictions fearing economic markets will panic.
Second, availbale data for calculations is error prone. Various oil producers have over-estimated their reserves on purpose Companies have a stake in exaggeration, as for example, Royal/Dutch Shell which finally admitted it had boosted it estimates of reserve by 20%.
Global discovery of new oil fields peaked back in the 1960's. Inspite of new technologies, new oil mines are not being found.
Problems with declining reserves
Their are both economic and political ramifications of more competition for declining oil reserves:
China which is growing both in terms of numbers of individuals and economic demands, competes with Japan for Siberian oil
US, Russia and Iran are all in a diplomatic russle to control oil in Kazakhstan and Azerbaijan.
Instability in Saudia Arabia and surrounding regions has drawn US deeper into military conflict.
In spite of this many nations including the US have not put much effort into planning for a change to a new energy economy.

Gas: Natural gas is fairly abundant, but unlike oil,
It is located in out the way places and the system for transporting it is comparatively undeveloped.Unlike oil it can not be stored easily once it is tapped and must be transported immediately either by piplline or by ocean going vessels. To go by sea it must be first liquifies by colling to shrink it, loaded on a specially contructed vessel, regassified at the port of delivery and finally piped where needed. This process is expensive ( on regasification port = $4 billion dollars; pipline = $1 million per mile).
Currently in the US there is a shortage as the necessary infrastructure does not exist. Investors fear the volatilty of price and the possibility of explosions as occurred in Algeria.
The major change however will be GEOPOLITICS. No longer would OPEC dominate resouces.. Russia with it current weak economic structure would dominate world supplies.
The top sources of gas are

Solar: Basics of solar energy

How does it work?
The energy of the absorbed light is transferred to electrons in the atoms of the PV cell. With their newfound energy, these electrons escape from their normal positions in the atoms of the semiconductor PV material and become part of the electrical flow, or current, in an electrical circuit. A special electrical property of the PV cell—what we call a "built-in electric field"—provides the force, or voltage, needed to drive the current through an external "load," such as a light bulb.
To induce the built-in electric field within a PV cell, two layers of somewhat differing semiconductor materials are placed in contact with one another. One layer is an "n-type" semiconductor with an abundance of electrons, which have a negative electrical charge.

The other layer is a "p-type" semiconductor with an abundance of "holes," which have a positive electrical charge.
Although both materials are electrically neutral, n-type silicon has excess electrons and p-type silicon has excess holes. Sandwiching these together creates a p/n junction at their interface, thereby creating an electric field.
When n- and p-type silicon come into contact, excess electrons move from the n-type side to the p-type side. The result is a buildup of positive charge along the n-type side of the interface and a buildup of negative charge along the p-type side.
Because of the flow of electrons and holes, the two semiconductors behave like a battery, creating an electric field at the surface where they meet—what we call the p/n junction. The electrical field causes the electrons to move from the semiconductor toward the negative surface, where they become available to the electrical circuit. At the same time, the holes move in the opposite direction, toward the positive surface, where they await incoming electrons.
How do we make the p-type ("positive") and n-type ("negative") silicon materials that will eventually become the photovoltaic (PV) cells that produce solar electricity? Most commonly, we add an element to the silicon that either has an extra electron or lacks an electron. This process of adding another element is called doping. Benefits of Solar:
High Reliability.
PV cells were originally developed for use in space, where repair is extremely expensive, if not impossible. PV still powers nearly every satellite circling the earth because it operates reliably for long periods of time with virtually no maintenance.
This PV-powered water-level monitor on the Laramie River in Wyoming will operate reliably for several years with little or no maintenance. (Photo: W. Gretz, NREL)
Low Operating Costs.
PV cells use the energy from sunlight to produce electricity—the fuel is free. With no moving parts, the cells require little upkeep. These low-maintenance, cost-effective PV systems are ideal for supplying power to communications stations on mountain tops, navigational buoys at sea, or homes far from utility power lines.
Once installed, PV power systems can operate continuously with little upkeep and minimal operating costs—a great benefit for this telecommunications station in a remote area of California's Inyo National Forest.
Environmental Benefits.
Because they burn no fuel and have no moving parts, PV systems are clean and silent. This is especially important where the main alternatives for obtaining power and light are from diesel genertors and kerosene lanterns. As we become more aware of "greenhouse gases" and their detrimental effects on our planet, clean energy alternatives like PV become more important than ever.
As we begin to realize and respect the fragility of our planet's ecosystem, clean power choices like PV become extremely important. (Photo: NASA)
Modularity.
A PV system can be constructed to any size based on energy requirements. Furthermore, the owner of a PV system can enlarge or move it if his or her energy needs change. For instance, homeowners can add modules every few years as their energy usage and financial resources grow. Ranchers can use mobile trailer-mounted pumping systems to water cattle as the cattle are rotated to different fields.
The Florida Solar Energy Center (FSEC) demonstrated the modular benefits of PV after Hurricane Andrew in 1993. FSEC employees deployed this PV emergency power system right at the point where it was needed after the hurricane. (Photo: FSEC)
Low Construction Costs.
PV systems are usually placed close to where the electricity is used, requiring much shorter power lines than if power is brought in from the utility grid. In addition, using PV eliminates the need for a step-down transformer from the utility line. Less wiring means lower costs, shorter construction time, and reduced permitting paperwork, particularly in urban areas.

Wind turbines are economical in wind power class 4–7.

Aerial view of a wind power plant shows how a group of wind turbines can make electricity for the utility grid. The electricity is sent through transmission and distribution lines to homes, businesses, schools, and so on. These three-bladed wind turbines are operated "upwind," with the blades facing into the wind. The other common wind turbine type is the two-bladed, downwind turbine. So how do wind turbines make electricity? Simply stated, a wind turbine works the opposite of a fan. Instead of using electricity to make wind, like a fan, wind turbines use wind to make electricity. The wind turns the blades, which spin a shaft, which connects to a generator and makes electricity. Utility-scale turbines range in size from 50 to 750 kilowatts. Single small turbines, below 50 kilowatts, are used for homes, telecommunications dishes, or water pumping.

From:http://www.eren.doe.gov/wind/feature.html

Water Power

In the news today...Big Chill
The city of Toronto recently unveiled a novel way to use Lake Ontario to cool some of its citizens. An elaborate set of pipes dredges cold water from the bottom of the lake to cool downtown buildings. According to Enwave, the company responsible for
the $170-million project, it will reduce overall annual power usage by more than 40 megawatts and greenhouse gas emissions by nearly 40,000 metric tons--the equivalent of taking 8,000 cars off the road--once it is fully operational.

What is OTEC?
OTEC, or ocean thermal energy conversion, is an energy technology that converts solar radiation to electric power. OTEC systems use the ocean's natural thermal gradient—the fact that the ocean's layers of water have different temperatures—to drive a power-producing cycle. As long as the temperature between the warm surface water and the cold deep water differs by about 20°C (36°F), an OTEC system can produce a significant amount of power. The oceans are thus a vast renewable resource, with the potential to help us produce billions of watts of electric power. This potential is estimated to be about 1013 watts of baseload power generation, according to some experts. The cold, deep seawater used in the OTEC process is also rich in nutrients, and it can be used to culture both marine organisms and plant life near the shore or on land.

In May 1993, an open-cycle OTEC plant at Keahole Point, Hawaii, produced 50,000 watts of electricity during a net power-producing experiment. This broke the record of 40,000 watts set by a Japanese system in 1982. Today, scientists are developing new, cost-effective, state-of-the-art turbines for open-cycle OTEC systems.

The economics of energy production today have delayed the financing of a permanent, continuously operating OTEC plant. However, OTEC is very promising as an alternative energy resource for tropical island communities that rely heavily on imported fuel. OTEC plants in these markets could provide islanders with much-needed power, as well as desalinated water and a variety of mariculture products.

Less-Developed Countries with Adequate Ocean-Thermal Resources 25 Kilometers or Less from Shore
Country/Area
Temperature Difference (°C) of Water Between 0 and 1,000 m Distance from Resource to Shore (km)
Africa
Benin 22-24 25
Gabon 20-22 15
Ghana 22-24 25
Kenya 20-21 25
Mozambique 18-21 25
São Tomé and Príncipe 22 1-10
Somalia 18-20 25
Tanzania 20-22 25

Tidal Power:

From: http://www.iclei.org/efacts/tidal.htm
Certain coastal regions experience higher tides than others. This is a result of the amplification of tides caused by local geographical features such as bays and inlets. In order to produce practical amounts of power (electricity), a difference between high and low tides of at least five metres is required. There are about 40 sites around the world with this magnitude of tidal range. In Canada, the only practical site for exploiting tidal energy is the Bay of Fundy between New Brunswick and Nova Scotia ). The higher the tides, the more electricity can be generated from a given site, and the lower the cost of electricity produced. Worldwide, approximately 3000 gigawatts (1 gigawatt = 1 GW = 1 billion watts) of energy is continuously available from the action of tides. Due to the constraints outlined above, it has been estimated that only 2% or 60 GW can potentially be recovered for electricity generation.

Geothermal (From: http://geothermal.marin.org/pwrheat.html#Q2)

WHAT IS GEOTHERMAL ENERGY? Our earth's interior - like the sun - provides heat energy from nature. This heat - geothermal energy - yields warmth and power that we can use without polluting the environment. Geothermal heat originates from Earth's fiery consolidation of dust and gas over 4 billion years ago. At earth's core - 4,000 miles deep - temperatures may reach over 9,000 degrees F. HOW DOES GEOTHERMAL HEAT GET UP TO EARTH'S SURFACE?The heat from the earth's core continuously flows outward. It transfers (conducts) to the surrounding layer of rock, the mantle. When temperatures and pressures become high enough, some mantle rock melts, becoming magma. Then, because it is lighter (less dense) than the surrounding rock, the magma rises (convects), moving slowly up toward the earth's crust, carrying the heat from below. Sometimes the hot magma reaches all the way to the surface, where we know it as lava. But most often the magma remains below earth's crust, heating nearby rock and water (rainwater that has seeped deep into the earth) - sometimes as hot as 700 degrees F. Some of this hot geothermal water travels back up through faults and cracks and reaches the earth's surface as hot springs or geysers, but most of it stays deep underground, trapped in cracks and porous rock. This natural collection of hot water is called a geothermal reservoir.

HOW HAVE PEOPLE USED GEOTHERMAL ENERGY IN THE PAST?
From earliest times, people have used geothermal water that flowed freely from the earth's surface as hot springs. The oldest and most common use was, of course, just relaxing in the comforting warm waters. But eventually, this "magic water" was used (and still is) in other creative ways. The Romans, for example, used geothermal water to treat eye and skin disease and, at Pompeii, to heat buildings. As early as 10,000 years ago, Native Americans used hot springs water for cooking and medicine. For centuries the Maoris of New Zealand have cooked "geothermally," and, since the 1960s, France has been heating up to 200,000 homes using geothermal water.
HOW DO WE USE GEOTHERMAL ENERGY TODAY?
Today we drill wells into the geothermal reservoirs to bring the hot water to the surface. Geologists, geochemists, drillers and engineers do a lot of exploring and testing to locate underground areas that contain this geothermal water, so we'll know where to drill geothermal production wells. Then, once the hot water and/or steam travels up the wells to the surface, they can be used to generate electricity in geothermal power plants or for energy saving non-electrical purposes.


HOW IS ELECTRICITY GENERATED USING GEOTHERMAL ENERGY?
In geothermal power plants steam, heat or hot water from geothermal reservoirs provides the force that spins the turbine generators and produces electricity. The used geothermal water is then returned down an injection well into the reservoir to be reheated, to maintain pressure, and to sustain the reservoir.

WHAT ARE SOME OF THE ADVANTAGES OF USING GEOTHERMAL ENERGY TO GENERATE ELECTRICITY?
* Clean. Geothermal power plants, like wind and solar power plants, do not have to burn fuels to manufacture steam to turn the turbines. Generating electricity with geothermal energy helps to conserve nonrenewable fossil fuels, and by decreasing the use of these fuels, we reduce emissions that harm our atmosphere. There is no smoky air around geothermal power plants -- in fact some are built in the middle of farm crops and forests, and share land with cattle and local wildlife.
For ten years, Lake County California, home to five geothermal electric power plants, has been the first and only county to meet the most stringent governmental air quality standards in the U.S.
* Easy on the land. The land area required for geothermal power plants is smaller per megawatt than for almost every other type of power plant. Geothermal installations don't require damming of rivers or harvesting of forests -- and there are no mine shafts, tunnels, open pits, waste heaps or oil spills.
* Reliable. Geothermal power plants are designed to run 24 hours a day, all year. A geothermal power plant sits right on top of its fuel source. It is resistant to interruptions of power generation due to weather, natural disasters or political rifts that can interrupt transportation of fuels.
* Flexible. Geothermal power plants can have modular designs, with additional units installed in increments when needed to fit growing demand for electricity.
* Keeps Dollars at Home. Money does not have to be exported to import fuel for geothermal power plants. Geothermal "fuel'" - like the sun and the wind - is always where the power plant is; economic benefits remain in the region and there are no fuel price shocks.
* Helps Developing Countries Grow. Geothermal projects can offer all of the above benefits to help developing countries grow without pollution. And installations in remote locations can raise the standard of living and quality of life by bringing electricity to people far from "electrified" population centers.

HOW MUCH ELECTRICITY IS FROM GEOTHERMAL ENERGY?
Since the first geothermally-generated electricity in the world was produced at Larderello, Italy, in 1904 the use of geothermal energy for electricity has grown worldwide to about 7,000 megawatts in twenty-one countries around the world. The United States alone produces 2700 megawatts of electricity from geothermal energy, electricity comparable to burning sixty million barrels of oil each year.

Geothermal power use (Top 14 Countries)
1. China 8,724
2. United States 5,640
3. Iceland 5,603
4. Turkey 4,377
5. New Zealand 1,967
6. Georgia 1,752
7. Russia 1,703
8. Japan 1,621
9. France 1,360
10. Sweden 1,147
11. Mexico 1,089
12. Italy 1,048
13. Romania 797
14. Hungary 785

FUEL CELLS
HOW A FUEL CELL OPERATES ( Franklin H. Holcomb: Construction Engineering Research Laboratories)

In simplest terms, a fuel cell is similar to a battery. Both operate by electro-chemically converting a fuel to usable energy (electricity and heat) without the use of combustion.
The main difference is that a battery has a finite supply of reactants, while in the ideal sense, fuel cells can run indefinitely as long as their reactants are replenished. By feeding a fuel such as hydrogen through one porous electrode (the anode) in the presence of a catalyst, electrons are stripped from the fuel and make their way through the external circuit. The remaining positive ions travel through the electrolyte to the other porous electrode (the cathode), where they combine with oxygen ions, formed when the free electrons combine with oxygen fed in at the cathode. The by- products of the reaction are heat, water in the form of steam, and the electricity produced from the flow of electrons from the anode to the cathode. Figures 1 through 4 illustrate this process for an acid electrolyte fuel cell.

..........
 
Figure 1. Hydrogen gas flows over the anode.
Figure 2. Electrons are stripped from the hydrogen and flow through the anode to the external circuit.

....
Figure 3. Hydrogen ions move through electrolyte to cathode. Electrons move into cathode from load.
Oxygen is introduced to the cathode.
Figure 4. Hydrogen ions, electrons, and oxygen combine to form water (steam).

The general design of most fuel cells is similar except for the electrolyte. Several different substances have been used as the electrolyte in fuel cells, each with their own advantages and disadvantages. The main types of fuel cells as defined by their electrolyte are:
* Alkaline fuel cells (AFCs); These are the original fuel cells that were developed by NASA for use with the space program. They have a very high efficiency, but are also very expensive to use on a large scale. They use potassium hydroxide as the electrolyte.
*Solid polymer fuel cells (also known as proton exchange membrane fuel cells or PEMs);These fuel cells are designed to function at fairly low temperatures (200 Fahrenheit). These are the most promising fuel cells for use in automobiles due to their ability to shift their power output on demand. Also, they can also start-up very quickly, making them ideal for use in small devices and electronic applications.
* Phosphoric acid fuel cells (PAFCs);This is the most commercially researched and developed type of fuel cell. These types of cells utilize phosphoric acid as an electrolyte. They tend to be heavy, and this makes them less than ideal for use in small automobiles. However, using this cell in busses, other fleet vehicles, and trains, is a possibility.
*Direct Methanol Fuel Cells: These are a a relatively new invention in the world of fuel cells. In this method, the hydrogen is derived directly from the methanol by the anode of the fuel cell. This eliminates the need for the carrying of hydrogen fuel, while instead using liquid methanol. An operating range of roughly 200 Fahrenheit is needed for this process.
*Molten carbonate fuel cells; This is a promising type of fuel cell since it offers a very high fuel to electricity efficiency and can also consume fossil fuel based fuels. The cells, however operate at very high temperatures (1200 Fahrenheit) and therefore cannot be used in small scale applications.

* Regenerative Fuel Cells:   These fuel cells utilize water as a fuel! The water is split using solar energy to produce hydrogen and oxygen. These two items are then utilized to create a current which thereby can be utilized to provide power to an automobile or other object. As by-products, water and heat are generated. This water, however, can be recycled and reused in the fuel cell to generate more electricity. The presence of a cheap fuel source and the reusability of the fuel, makes Regenerative Fuel Cell technology a very heavily researched subject.

Alkaline and solid polymer fuel cells operate at lower temperatures (50-260°C) and are mainly designed for transportation applications. The other three operate at higher temperatures (up to 1000°C for solid oxide fuel cells) and are being developed for use in co-generation and large central power plants.

A fuel cell power plant uses several of the individual "cells" described in the preceding text. Most individual fuel cells are small in size and produce between 0.5 and 0.9 volts of DC electricity. The individual cells are often combined together in a "stack" configuration to produce the higher voltages more commonly found in low and medium voltage distribution systems. The stack is the main component of the power section in a fuel cell power plant.

The other two components are the fuel processor and the power conditioner. Figure 5 shows these components.

Figure 5. Block diagram of fuel cell power plant.
The fuel processor or reformer extracts hydrogen-rich gas from natural gas or other fuel, emitting carbon dioxide and trace amounts of carbon monoxide.
Finally, the power conditioner section of a fuel cell power plant most often consists of an invertor, which converts the DC electricity to AC electricity. The power conditioner can also regulate the voltage and current output from the fuel cells to accommodate variations in load requirements.