Wind Power - A Clean Supportive Source

Wind is actually a form of solar energy. The uneven heating of the atmosphere by the sun combined with the irregularities of the earth's surface and the rotation of the planet creates wind. The terrain, bodies of water and vegetation modify wind flow patterns, making a small percentage of the earth surface suitable for wind power development. In spite of the fact that only 6% of the contiguous United States land mass can be considered "good wind areas" the Department of Energy estimates that this area could conceivably produce 150% of our current electricity needs. Wind is also the only low-priced renewable energy technology; the projected cost is between $.04 and $.06 per kilowatt-hour making it competitive with natural gas and coal-fired power plants.

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Physicists tell us that energy can neither be created nor consumed or destroyed - they call it the First Law of Thermodynamics. Energy, however may be converted or transferred to different forms: The kinetic energy of moving air may be converted to rotational energy by the rotor of a wind turbine, which in turn may be converted to electrical energy by a wind turbine generator. With each conversion, part of the energy from the source is "lost" to heat energy. Since the vast majority of wind turbines produce electricity, we usually measure their performance in terms of the amount of electrical energy they are able to convert from the kinetic energy of the wind. We usually measure that energy in terms of kilowatt hours (kWh) or megawatt hours (mWh) during a defined period of time, e.g. an hour or a year (Kilowatt = 1,000 watts - Megawatt = one million watts - kilowatt hour kWh, the unit that appears on the electricity bill = the energy equivalent of one kilowatt (kW) of power expended for one hour).

Wind turbines are commonly classified by their rated power. If a wind turbine has a rated power of 1,000 kilowatts (kW), that tells us that the wind turbine will produce 1,000 kilowatt hours (kWh) of energy per hour of operation, when running at it's maximum performance. If a wind farm has 1,000 Mega Watts (mW) of wind power installed that does not tell you how much energy the turbines produce. Wind turbines will typically run at rate of 75% of annual hours, but they will only be running at rated power during a limited number of those hours each year. Energy output is also influenced the inherent features of a wind turbine's design, including:

    • Cut-in speed, defined as the wind speed at which the wind turbine begins to produce power.
      • The power output actually produced at moderate wind speeds; which is primarily determined by blade airfoil shape and geometry. In recent years, the U.S. wind industry has begun using seemingly small refinements in blade airfoil shapes to increase annual energy output from 10 to well over 25 percent.
        • Cut-out speed, defined as the wind speed at which the turbine may be shut down to protect the rotor and drive train from damage.
          • Operating characteristics such as low speed on-off cycling, shutdown behavior, and overall reliability, which together determine the turbine's availability to produce power when the wind speeds are in it's operating range.

          Annual energy output however, is actually a more important measure of evaluating a wind turbine's value than rated power. Wind is clearly limited by the "capacity factor". The capacity factor is simply the wind turbine's actual energy output for the year divided by the energy output if the machine operated at it's rated power output for the entire year. A reasonable capacity factor would be 25% to 30%. A very good capacity factor would be 40%.

          Thus, if we truly wished to generate 20% of our power from wind we would have to build wind turbines with 60% to 80% rated capacity for all our energy needs. Unfortunately, even if we built all that capacity, power could be intermittent because when we need it most, such as on a hot still summer day, the wind may not blow at all. As a consequence, traditional coal and natural gas power plants must be kept fired up and ready to take over in the event of an unexpected interruption. This creates a complex problem. If a metro area requires 500 megawatts of power and it's wind turbines produce 200 megawatts (40%) conventional wisdom would suggest that traditional power generation and the concurrent fossil fuel utilization could also be cut by 40%. The actual saving in fossil fuel consumption may be considerably less because of the inherent unpredictability of wind power. Thus, traditional power plants must be run at what the electrical industry calls "spinning reserve". In other words, they are obliged to produce excess energy to keep the power grid from flagging when wind generation declines without warning. In the perverse logic of ensuring that electricity is always available the more we depend on wind, the more backup natural gas plants will have to be built.

          What can we realistically expect from wind power? As Mr. Pete du Pont, the former governor of Delaware, and chairman of the Dallas-based National Center for Policy Analysis pointed out in his April 2007 Wall Street Journal editorial in support of the increased use of wind power: "Wind velocity is highly variable, and so the electricity generated by the turbines is highly variable too. As the Tennessee Valley Association pointed out in 2002, wind-speed variations can be extreme, from less than 10 mph to more than 35 mph within a single second, and bursts of up to 70 to 100 miles per hour. Such wind fluctuations will cause equally unpredictable levels of electricity generation, from surges of 160 megawatts in high winds to no juice at all when the air is calm. Offshore wind turbines in Europe illustrate the problem. They start generating electricity when the wind speed reaches nine miles per hour, and have to shut down if it exceeds 55 mph. They generate electricity somewhere between 70% and 90% of the time, but in lower wind speeds much less than their capacity. According to an analysis by Denmark's Incoteco energy consulting firm, in 2002 there we're 54 days in western Denmark on which the wind power systems "supplied less than 1% of demand." For the whole week of Feb.13 through 20, 2003, there was no offshore breeze so "virtually no wind power was generated in West Denmark." And for two days in March wind power electrical output exceeded power consumption for only two hours, between 2 and 4 a.m. one of those days.

          Wind power systems are also less efficient than other power sources. Because of wind speed changes, turbines cannot generate over time more than about 30% of their capacity."

          Wind power, which has grown rapidly, still only, provides about two-thirds of 1% of all U.S. electricity. The Energy Department calculates that ramping up to 20% of U.S. energy needs by 2030 would require more than $2 trillion investment to install turbines across the Midwest "wind corridor," along with multiple offshore installations. And we'll need a new "transmission superhighway system" of more than 12,000 miles of electric lines to connect the wind system to population centers, at a yet to be determined price. Unlike conventional power plants that can be located near the end user, wind and for that matter solar must be generated in special locations and then transported sometimes a 1,000 miles or more to where it is needed.

          What the above illustrates is that even ardent supports of wind energy must recognize it's inherent limitations and a realistic view must be factored into an overall plan. Wind can at best play an important clean supportive role. Can wind produce 20% of our energy needs over the next two decades? Yes, but only if we build at least three times that capacity, at a very high cost and make provision for it's quirky nature. It should also be noted that if we devote such a significant portion of our limited financial resources to use wind to supplement our electricity needs, it would not save us $1.00 in oil imports. We would be replacing either domestic coal or natural gas. Clearly, one could make a rationale argument for replacing carbon dioxide intensive coal but why would we spend $2 trillion, plus build a massive transmission system to replace the cleanest fossil fuel, natural gas? On the other hand if wind we're added to the energy supply rather than substituted for older carbon dioxide intensive power sources i.e. coal, then the excess electricity generated could be used to power hybrid plug-in vehicles cleanly and reduce our dependency on foreign oil.

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          Posted in Software Post Date 08/11/2016






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