Wind energy: Current status and future prospects

Notes and references

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• This includes sites where the windpower density is greater than 300 watts m‐2 at 50 meters elevation. Lands excluded from wind farm development include 100 percent of environmentally sensitive and urban lands, 50 percent of forest lands, 30 percent of agricultural lands, and 10 percent of rangelands.
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• The first research machine was the MOD‐0 (100 kilowatts); this was followed by the MOD‐0A (200 kilowatts), the MOD‐1 (2 megawatts), the MOD‐2 (2.5 megawatts), and culminated with the MOD‐5B, a 3.2 megawatt wind turbine (originally designed as a 7.2 megawatt machine). The last machine, which was built by the Boeing Aerospace Company on Oahu, Hawaii, was sold to Hawaiian Electric Renewable Systems in 1988 and shut down in 1992 due to excessive maintenance requirements. Because the cost of electricity from these large experimental machines (see reference 76) was significantly higher than from smaller systems, utilities and small power producers have not shown commercial interest in such multimegawatt wind turbines.
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• For resistive loads in AC circuits, the voltage and current flowing in the circuit are in phase, and the power consumed is the product of the voltage and the current. For circuits with inductive or capacitive elements, the voltage and current are not in phase and the power consumed is the product of the voltage and the current and the cosine of the difference in phase between them (cos 9). The latter is referred to as the power factor; utilities need to have this as close to one as possible. A power factor different from one indicates that currents are flowing simply to charge and discharge capacitive or inductive components. Because transmission losses are proportional to the current squared, this results in higher transmission losses. Wind turbine generators have large inductive elements (the coils in the generator) and may produce power with a power factor far from one.
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• These assumptions are based on the accounting rules recommended by the Electric Power Research Institute for evaluating alternative power technologies (see reference 77). With these accounting rules the assumed real discount rate is about 6 percent and both corporate and property taxes are taken into account. The resulting annual capital charge rate (10.2 percent) is about midway between the two values (8.3 percent and 13.3 percent) obtained here for the accounting rules here: 6 and 12 percent real discount rates with all taxes neglected.
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• The capital recovery factor (CRF) is calculated as:
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• where r is the interest rate and n the assumed life of the installation. For a 25‐year lifetime, if r = 6 percent, CRF = 0.0782; for r = 12 percent, CRF = 0.1275. If the assumed lifetime is 15 years instead of 25 years, the CRF increases by 32 percent (r = 6 percent) and 15 percent (r = 12 percent).
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• Indirect costs are calculated using the following assumptions: 1) 100 megawatt station rating, 110 kilowatt machines 2) 4,500 operation hours, zero wind shear, 3) capacity factor of 0.29 at 97 percent availability, 4) capital recovery factor of 15 percent 5) burdened labor rate (includes all overhead etc.) $25 per hour.
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• Lynette also indicates that turbines of higher output rating should have lower O&M costs, although in 1987 there was no evidence that this was true, perhaps because the larger turbines had less time in the field.
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• The Lynette report discusses the actual operational problems and maintenance costs, as well as actual versus projected power production, availability, capacity factor, and reliability and increase in reliability for a large number of wind farms in California. There was a significant decrease in O&M costs and an increase in reliability of the wind turbines during the period covered by the report (1981–1987), indicating a rapidly maturing industry.
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• Lynette's estimate of the average O&M cost is close to that for a recently installed wind farm of twenty‐nine 225 kWe machines in an area with a wind speed of 7.4 m sec‐1 at hub height (31.5 meters) in western Jutland, Denmark (see reference 67). The estimated O&M costs were 1.75 percent of the installed cost of the turbine, or about 0.008 European Currency Unit (ECU) ($0.01) per kWh (based on the extensive experience of the wind turbine manufacturer). (One ECU = $1.27, December 1991).
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