POWER GENERATION Popular Energy is supposed to be about things that the homeowner or builder can do to save energy and money at home. So, a chapter about power companies might seem out of place here. However, you are paying too much for their product, and a little information about power plant efficiency and fuel selection might help you to press the Congress, or your local representatives, to Think Renewable. Power Generation Today: When any conductor, such as a copper wire, is moved thru’ a magnetic field, an electric current will be generated in that conductor. So, to generate electricity for public use, power companies spin a rotor, wound with many copper wires, through the force field of fixed magnets. The energy that spins that rotor for the power companies comes, in the main, from the fossil fuels, including plutonium, with hydropower and “other” totaling less than ten percent. About 55% of our electricity is generated by burning soft coal. Nuclear provides about 21%, Gas 10%, and Oil 3%. To spin the rotor, the fossil fuel is burned to make steam, which drives itself explosively against the blades of a turbine. That turbine is mounted on the same shaft as the wire-wound rotor. Nuclear power plants work this way, too, except that they don’t spew combustion products into the air. The mechanical action of driving the turbine, and generating our electricity, uses about thirty percent of the energy that was put into the steam by the fuel. The rest of the heat energy that created the steam is still stored in the steam, and it must be removed so that the steam will “come back down” to water to be sent back to the boiler. Tremendous amounts of air or water have to be moved over the outside of heat exchangers to cool the steam until it changes back into water. In fact, when these steam turbines are used, two-thirds of the
energy provided by the fossil fuel is carried off by the coolant. In
the end, about 30% of the fossil energy comes out as electricity. In recent years, a system for electrical generation has been introduced to the US market that has proven successful in parts of Europe. This system uses two turbine engines, fired by natural gas, driving electric generators. The electrical output from the two turbines is combined with the electrical output from a steam-driven generator. That steam-driven generator uses the exhaust heat from the turbines to create the steam. The net result is that about 60% of the energy in the fossil fuel is converted to electrical energy, a doubling of the electrical output per ton of fossil fuel. In the northeastern United States, some large buildings are considering the installation of these gas-turbine generating plants. In that relatively small arena, the gas-turbine method shows promise, although there are some nimby problems, as with any new power-plant proposal. For most of the country, where coal is cheap, and environmental laws are not implemented, this newer technology may not do as well. Another application of cogeneration, promising a good ROI for large buildings, uses a reciprocating engine, driven by street gas, to spin an electric generator, and uses the engine’s hot exhaust to heat the building. In the more southerly climes, where cooling requirements far outweigh the need for heat, that waste heat may drive an absorption air-conditioning system, a much larger version of the old Servel gas-fired refrigerators with the big coils on top. In those semi-independent applications, the generator is connected to the public grid, buying from, or selling to, the grid when the generator produces less, or more, electricity than the building needs. For the home, it is technically feasible to use a small gas engine to generate electricity, with its hot exhaust used for space or water heating, or space cooling with absorption A/C. However, it seems as though a satisfactory ROI for cogeneration in a house or other small building would be possible only where year-round heating, or year-round cooling, is needed. RENEWABLES: The cogeneration options described above are, at best, interim methods for extending the life of the world’s fossil reserves. In the meantime, with the renewables gaining daily, parts of the country may one day be relieved of the need to build new fossil-fired generating plants. See, for example, the chapter on Windmills. Photovoltaic: The process by which the sun’s rays are converted directly into electrical current is called Photovoltaic, which the expert (turning indulgently toward the listener) refers to as “PV Technology”. There is already a limited market for PV products, particularly in situations where it would be too expensive to bring electricity from the grid to the point of need. For the homeowner, there is promise in the concept of making roof shingles that will produce electricity at the same time that they weatherproof the roof. However, after thirty years of intensive, subsidized research, the industry seems to be hung up on a conversion efficiency of 15% or less. This is not very high, and that limitation translates into a relatively low Return on Investment. Further, the collectors will be in sunlight less than 30% of the time, which means that the homeowner must invest additional $ in batteries to bridge the gap, or in a tricky and expensive interconnect to the grid. Until we see a breakthrough in product efficiency, or storage technology, we will not be urging the installation of home photovoltaic. If/when we see improvement, we will so report in our News section. Wind: In the 1970s, a great many small companies brought out windmills designed to generate electricity for the home, with output ratings of 5 to 10 kilowatts per hour. Marketing results were not good, mostly because people could not go where the wind was, and the wind rarely came to them. Today, a new business with plenty of money, none of it invested in land, is free to go where the wind goes. And they are doing it! Also, the well-financed company can design for optimum efficiency, which has led to generators that are much too big for a single household. And, with power from many locations going into the grid, with some parts of the grid always in the wind, the limited need for back-up will come from otherwise-idle fossil-fuel plants. Windmills get their own, well-deserved chapter later in the book. Tidal, etc: The rise and fall of the tides and the rush of tidal waters through restricted openings in coastal sites, present many opportunities to lessen our dependence on the fossils. As the costs, and risks, of fossils increase, research into tidal energy and thermal gradients, already underway, will undoubtedly accelerate. Such projects will require very large investments. With the rapid rise in the cost of petroleum, Financial Markets are getting interested. In the meantime, there are some waste-to-energy plants already operating, and some small projects that hold promise, like converting slaughter-house waste to clean, combustible oil. As new projects show promise of significant non-fossil electrical generation, they will be covered under Energy News. |