1. INTRODUCTION
Global warming, fuel shortages, pollution, problems with nuclear power, and the deregulation of electric power may dramatically change energy using technologies in North America as well as other parts of the world. Looming on the horizon for stationary power is the dream of hot and perhaps even cold fusion powerplants.
Our modern world consumes vast amounts of energy. Electricity is the favored form of energy because it can be used in so many different ways. One of the main reasons why electricity is so valuable is that it is a form of external energy [1]. This means that it can theoretically be converted into any other form of energy and can be done so at a high efficiency. It is a very clean power and can be easily controlled. Industrialized countries rely on their electric grid in which most of the country is interconnected to different power generating facilities. Common methods of generating the electricity are by using hydro dams, steam power plants burning coal, gas turbines burning natural gas, and nuclear fission power plants. Presently these generating facilities are generally very large. There is however a big shift away from centralized powerplants to smaller distributed powerplants.
Solid Oxide fuel cells presently look the most promising for electricity production but also for larger transportation vehicles such as buses, trucks, trains, and ships. If solar cells become even more efficient and inexpensive they could really gain in popularity for grid connected systems.
It is not likely that we will have a hydrogen supply system any time soon. Hydrogen is too hard to store and transport. Liquid fuel is more convenient for mobile applications and so alcohol will be popular. Direct alcohol fuel cells may be widely used for powering portable equipment such as power tools, laptop computers, portable phones, and emergency generators, but may also be used for automobiles.
It is likely that natural gas will continue to be popular for stationary applications as it will be made synthetically in the future from biomass, coal, and solar energy.
The most common method for producing mechanical power for transportation applications presently is with internal combustion engines that burn fossil fuels. While renewable sources of energy such as wind power can be easily converted to electricity and connected to the electric grid, developing new ways of powering transportation devices will prove to be difficult in the future.
Much of the energy we use in society is for heating buildings and for industrial processes. Because much of this thermal energy is only required at low temperatures, burning fuels represents a waste of high grade energy. Theoretically much of this thermal energy could come from solar energy but this is considered too intermittent a source. Waste thermal energy from distributed fuel cells would be a more ideal source of this heat.
2. KNOWN PRESENT AND PROPOSED SOURCES OF ENERGY
There are many sources of energy on earth. The original source of all this energy is nuclear energy in the universe. All other forms of energy are the result of nuclear energy trickling down into lower forms. The following are common sources of energy on earth:
Geothermal ..taking thermal energy from the earth's core
Falling water ..rivers, ocean tides
Wave motion ..in ocean
Thermal cycles ..in water and air
Wind motion ..of air
Pressure changes ..in atmosphere
Solar radiation ..from the sun
Fossil fuels ..coal, oil, natural gas
Biomass ..trees, plants
Fission nuclear energy ..splitting atoms
Fusion nuclear energy ..combining atoms
3. MAJOR TECHNOLOGIES FOR PRODUCING POWER
Electricity and mechanical power are largely used for powering our modern industrialized society. These are not stored in some natural form on earth in any great quantity. Other forms of energy must be converted. Different conversion technologies must be used. With some methods the electricity or mechanical power is produced directly in a single process. In others there are multiple steps involved.
Hydro turbines ..convert moving water from river and ocean dams into electricity
Wave generators ..use floats that move up and down with waves and produce electricity
Solar cells ..solid state materials that produce electricity directly from solar radiation impact
Thermocouples ..also called thermoelectric devices that produce electricity by heating dissimilar metals
Thermionic devices ..turn thermal energy into electricity by solid state means
Vapor turbines ..convert steam pressure into rotary motion then electricity
Piston vapor engines ..convert vapor pressure into rotary motion then electricity
Piston gas engines ..turn expanding gases to motion then electricity, Diesel, Otto, Brayton, Atkinson etc.
Gas turbines ..turn hot expanding gases to rotary motion then electricity
Stirling piston engines ..closed cycle engines turn thermal energy into motion then electricity
MHD ..turn moving charged fluids directly to electricity
Fuel cells ..turn chemical energy directly to electricity by the action of moving ions
Wind turbines ..turn moving air into rotary motion then electricity
Nuclear radiation cells ..solid state materials that produce electricity directly from nuclear radiation impact
Nuclear "ion" cells ..solid state materials that produce electricity directly from nuclear "ions"
Fig 1 Chart showing projected efficiencies of different future electricity generating powerplants
4. ELECTRICITY DEREGULATION AND COGENERATION
There is a rapid trend in North America to deregulate the production of electric power. One of the benefits of deregulation is that it will promote smaller scale electric power production technologies. Many of these technologies are only viable on a deregulated basis. Large utilities do not like to maintain thousands of small sites.
North America may likely generate much of its electricity from fossil fuels at least for the next several decades. Small powerplants distributed around the country can be CHP ..combined heat and electricity powerplants.. This will conserve fuel reserves by utilizing the waste thermal energy that is produced as a result of generating electricity. Because thermal energy can not be piped efficiently for long distances, these CHP powerplants will need to be much smaller than the present ones which are often around 200,000 kw.
Some of the more common sources of energy and conversion technologies that will likely be used in the next 50 years will be investigated in the next chapters.
5. HYDRO ELECTRIC POWER
Ecologically acceptable places to put new hydro dams are rapidly diminishing around the world. While there are no emissions produced with hydro electric power, there is generally a deterioration of fish spawning in the areas when dams are used. One advantage with this type of hydro electric power is that there is little loss of efficiency by varying the amount of power produced between peak and low periods of electricity demand.
Dams can also be put in ocean inlets to generate electricity from the tidal action. These are also not so ecologically friendly. Also dams disrupt the passage of ships. The height of the tide is not generally enough to be profitable.
Hydroelectric power can also be generated without dams. In rivers, part of the flow can be diverted to pipes leading down to a water turbine. Water turbines can also be placed directly in the flow of the river or moving ocean tides. While these methods are often considered to be more environmentally friendly, they result in only a fraction of the power produced by a system using a dam.
6. COAL FIRED STEAM POWER PLANTS
A considerable amount of electricity in the world is produced by burning coal in steam powerplants. These powerplants must be large to be efficient. Presently the best steam powerplants have up to 50% fuel to electricity efficiency (50% A-X eff or chemical lower heating value to electricity). As these powerplants in their simplest form produce unwanted gases and particulates, different technologies must be used to clean up the exhaust gases.
7. GAS TURBINES
Presently many new large electric powerplants use gas turbines and burn natural gas. Contrary to popular opinion, these gas turbines (with addition of heat exchanging or steam turbines) can be highly efficient in the large sizes. The latest are 57% efficient in converting fuel to electricity . In the future, ceramic gas turbines may even reach 70% efficiency. Unfortunately very small gas turbines are not nearly as efficient. Present microturbines in the 30 kw range are only about 25% efficient even when heat exchanging is employed though future ceramic microturbines may achieve 35% efficiency. While fuel cells are largely in the process of being developed, reliable gas turbines are available now. Gas turbines are considered superior to diesel engines because of their lower maintenance, vibration and emissions. For more information on gas turbine efficiency read the online paper "Simple Second law Analysis of Gas Turbines"
8. DIESEL PISTON ENGINES
Diesel piston engines are presently seeing somewhat of a revival. This is because of deregulation. They are presently the most efficient small powerplant available for CHP. Small diesel powerplants are about 30% fuel to electricity efficient, medium diesel powerplants are 40% efficient, and large one's are up to 50% efficient. Their efficiency is good from about 30%-100% power and they can be running at peak efficiency in a short period of time after startup.
9. FUEL CELLS
Fuel cells, which can convert chemical energy directly into electricity, have been proposed as a replacement for other methods of generating power from fossil fuels for 100 years. Till recently there have been numerous difficulties in commercializing them however. Will these problems be overcome in the new century? If the problems can be overcome, fuel cells will likely be the favored technology of the future for all CHP as well as large centralized powerplants. Not only do fuel cells produce reasonable efficiencies at the smaller sizes, they will likely be able to run quietly, need infrequent maintenance and emit little pollution.
A fuel cell works similar to a battery. In a battery, electricity is generated as a result of a fixed amount of substance undergoing a chemical change inside the cell. In a fuel cell, a continuous flow of chemical substance flows through the cell and is made into electricity. While a battery has a limited amount of electricity it can produce per cycle, a fuel cell can produce electricity as long as more fuel is pumped through it.
Solid oxide fuel cells will likely be the favored fuel cell for CHP [2]. Small solid oxide fuel cells will be about 50% fuel to electricity efficient, medium powerplants 60% efficient, and large one's up to 70% efficient. Their efficiency is good from about 15%-100% power. Most solid oxide fuel cells utilize both hydrogen and carbon monoxide fuel inside the cell. This means that they can readily operate on hydrocarbon fuels such as coal gas, gasoline, diesel fuel, jet fuel, alcohol, and natural gas. The efficiency of the solid oxide fuel cell used in CHP applications will be higher than the polymer electrolyte fuel cells for two major reasons. The first reason is that the hydrocarbon fuel is reformed into hydrogen and carbon monoxide fuel largely inside the solid oxide fuel cell. This results in some of the high temperature waste thermal energy being recycled back into the fuel. The second reason is that air compression is not required. Especially on smaller systems, this results in a higher amount of net electricity being produced and quieter operation.
Most polymer electrolyte fuel cells that are being developed for automobiles and CHP use hydrogen gas as a fuel. It is not likely that we will have hydrogen pipelines supplying homes and businesses in the near future. This means that hydrogen will often be extracted from hydrocarbon fuels in CHP systems. Because the polymer electrolyte fuel cell operates at a low temperature, there is no waste thermal energy recycling in the reformer. Air compression to about 3 atmospheres or higher must be used to have a reasonable power density [3]. On small systems this results in a substantial loss of efficiency. Small polymer electrolyte fuel cells will be about 35% fuel to electricity efficient, medium powerplants 40% efficient, and large one's up to 45% efficient.
Because of the high temperatures that the solid oxide fuel cell must run , they may not be practical for sizes much below 1,000 watts or when portable applications are involved. Several companies in the world are presently working on direct alcohol fuel cells. In this type of fuel cell, the alcohol is not reformed but used directly in a very simple type of fuel cell. This fuel cell is ideal for portable equipment such as power tools, laptop computers, portable phones, and emergency generators. For more information on fuel cells read the web-booklet "The Future of Fuel Cells"
10. WIND POWER
There is enough energy in the blowing winds to generate a substantial proportion of the electrical energy requirements in the world. In windy areas, the cost to produce electricity is already less than using fossil fueled combined cycle powerplants. One of the major problems with wind turbines in the past has been durability. Often serious wind storms would damage many units. Newer units appear to be built stronger. Another large problem is the extremely variable speed of the wind. Wind turbines may provide peak power in times when the electricity is not required. Storage of the electricity is expensive. If wind turbines are linked into a large grid system, such fluctuations are not as much of a disadvantage. Of course if a major proportion of our electricity would be generated this way, that would create major problems. Wind turbines in the past resulted in bird kills however it appears that with newer one’s this may not be a problem. Wind turbines are also noisy and can be unsightly. Still there are major advantages in tapping into a source of inexpensive power that can be converted into electricity in such a simple device as a wind turbine.
11. SOLAR POWER
During the day, there is a constant supply of radiation coming from the sun. The amount of radiation is considerable, but presently low cost commercial solid state solar cells only convert about 11% of the solar radiation into electricity. There are already laboratory solar cells that are 40% efficient, and in the future even higher efficiencies may be possible. Solid state solar cells are very attractive because they have no moving parts and are very simple. Because sunlight is free, this makes the technology very attractive especially in countries that have difficulty buying fuel. The downside of solid state solar cells is that when the sun goes down, there is no electricity being produced. Batteries can be used, but present batteries are only about 60-80% efficient in storing the electricity. Just as with wind turbines, if solar panels are linked into a large grid system, such fluctuations are not as much of a disadvantage.
A second method of using the sun's radiation is to convert it into high temperature thermal energy and then use conventional steam turbines, gas turbines or Stirling engines to generate electricity. Such methods are already 30-50% efficient in converting the sun's radiation into electricity. There are also efficient solid state thermoelectric converters being researched. If a fluid is heated, a large amount can be stored for operation of the plant during the night or cloudy days. As well, a backup fuel fired heater can be used, but this is only economical when the power plant is highly efficient.
A third desirable method is to use the sun's rays produce a fuel. This fuel could then be used at a later date. Hydrogen could be produced but it is difficult to store. An ideal fuel to produce would be ethanol or natural gas which could be used in a fuel cell at a later date to generate electricity or be used in other applications that require fuel. The solar cell would recycle the carbon dioxide from the atmosphere back into the ethanol or natural gas fuel. Such a solar cell might use genetically engineered bacteria to do the job.
Theoretically much of the thermal energy required in society could come from solar energy. Practically so far it has been considered too intermittent a source. Solar collectors for this purpose can be quite simple, but storage of the thermal energy during periods when the sun isn’t shining has so far been considered expensive compared to cheap fossil fuel. This situation could dramatically change when fuel prices go up in the future.
12. FISSION POWERPLANTS
In nuclear fission, large atoms are split apart to form new smaller atoms. Because the new atoms have a slightly smaller amount of matter than the old atoms, a large amount of energy is emitted. After the 2nd World War some prominent people predicted that fission nuclear powerplants would be able to create electricity so cheaply that the power companies would not bother installing electric meters. This prediction did not come true. Nuclear powerplants are unpopular today not only because of the possible threat of radiation leaks, but because they are expensive to operate. The safety precautions are very costly and the life span of the equipment is rather short. Scientists also have not come up with satisfactory ways of storing the waste products.
Present nuclear powerplants generally use the thermal energy produced by the nuclear reaction to produce steam and turn a steam turbine. Some designs use a gas turbine instead. In outer space the thermal energy is turned to electricity with thermoelectric devices which are very reliable and have no moving parts but are presently inefficient. Theoretically other solid-state conversion methods could be used.
13. HOT FUSION POWERPLANTS
In nuclear fusion, atoms are fused together to form new atoms. Because the new atoms have a slightly smaller amount of matter than the old atoms, a large amount of energy is emitted. In a hot fusion power plant the extra energy is released in the form of thermal energy. Presently scientists have not been able to maintain a fusion reaction for long enough to be practical, but many hope that sustained reactions may be possible within the next 2 decades. The thermal energy produced could be used in the same way as in the fission powerplant. Though there is radiation during the fusion reaction, there would not be the problem of having to dispose of spent fuel. If a problem would occur, the reaction could be shut down immediately and the radiation stops almost instantly.
If hot fusion power becomes practical, it could completely reverse the trend towards distributed power. Fusion powerplants would likely be even larger than the present centralized powerplants.
14. COLD FUSION POWERPLANTS
There is some controversy as to whether cold fusion is even possible as far as producing excess external energy. In a most basic theoretical sense, cold fusion is possible. If cold fusion ever proves to work, then both large central powerplants as well as smaller distributed powerplants would likely be practical.
15. GEOTHERMAL
There appears to be incredible amounts of thermal energy just below the crust of the earth. It is likely that the earth is gradually cooling down, but the center of the earth hasn't cooled off nearly as fast as the surface. In places near volcanoes there is hot molten rock very close to the surface of the earth. In other places underground water streams run into the hot molten rock and produce steam or hot water. There are already geothermal steam powerplants operating. Surely more of this hot lava could be tapped to produce electric power. It appears that there is a fear among scientists that cooling off the lava too much would produce earthquakes.
16. CONCLUSIONS
It is very difficult to tell which form of energy and which technologies will be predominant for providing energy for society in the future.
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