commercial wind power: recent experience in the united states
TRANSCRIPT
Annu. Rev. Energy Environ. 1992. 17:97-121 Copyright © 1992 by Annual Reviews Inc. All rights reserved
COMMERCIAL WIND POWER:
Recent Experience in the United States
Gerald W. Braun Pacific Gas and Electric Company, 3400 Crow Canyon Road, San Ramon, California 94583
Don R. Smith 466 49th Street, Oakland, California 94609
KEY WORDS: wind energy, renewable energy, California energy, electric utilities, Pacific Gas & Electric Company
CONTENTS
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
THE RECENT HISTORY OF WIND ENERGY DEVELOPMENT. . . . . . . . . . . . . . . 100
FUTURE ENERGY SUPPLIES . . .. .. . . . . 101
WIND ENERGY TECHNOLOGy ....................................... 104
RESEARCH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
WIND POWER PLANT PERFORMANCE . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . 108
THE WIND ENERGY RESOURCE . . . . . . . . . . . . . . . . . . . . . . . . . ......... .... 109
THE COST OF WIND ENERGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III THE VALUE OF WIND ENERGY ...................................... 114
ENVIRONMENTAL ASPECTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 PLANS FOR THE FUTURE . . . . . . . . . . . . . . . . . . . . . . . . ............. . ..... 116
CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
INTRODUCTION
In 1990 the 23,000 wind turbines in the world connected to utility grids were rated at a total of 2200 MW and produced 3,353,000,000 kWh of electricity (1). This represents the residential use of a city with a population of 1,000,000
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1056-3466/92/1022-0097$02.00
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at US energy use rates, or 2,000,000 at European rates. Denmark produced about 2% of its electricity from the wind, while California and Hawaii produced about 1% of theirs. Figure 1 shows the authors' estimates of utility-connected wind generation in several areas of the world in 1990. California wind farms produced 76% of the world total, and Pacific Gas and Electric Company (PG&E) received nearly half of this. In addition to these grid-connected turbines, more than 50,000 smaller turbines (averaging about 100 watts each) supplied electricity to remote areas, such as Mongolia. Such non-grid-connected turbines can be components of hybrid generation systems when combined with energy storage and/or complementary power sources. However, the emphasis of this paper is on utility-connected wind turbines. Wind also supplies mechanical energy, such as for water pumping.
The development of wind generation over the past 15 years was spawned by the world oil crises in the 1970s and growing concerns about energy security and the environment. In the United States, the Public Utility Regulatory Policy Act (PURPA) requires utilities to purchase power from qualifying non-utility independent power producers (IPPs) using "alternative" sources of energy including wind. The energy must be purchased at "avoided
"Altamont. Solano, Pacheco
Figure 1 World utility-connected wind electric production.
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cost," that is, the amount saved by the utility by not having to produce the energy itself. Thus the cost to the utility and its customers will not be increased by the purchase from the IPP. During the 1980s PURPA, coupled with various tax incentives, led to the development of many large wind farms in the United States (mostly in California), which generated power for sale to utilities.
PG&E, the major utility in northern California, purchases the electricity produced by the wind turbines in Altamont Pass, where more wind-generated electricity is produced than in any other area in the world. The case of PG&E shows how wind energy can penetrate a regional utility grid in a significant manner. PG&E is building its electric resource strategy on the foundation of customer, utility, and regional efficiencies, while working toward an efficiently structured competitive market for electric supply. PG&E's system can meet near-term needs without expansion. However, gradual retirement of existing units , combined with load growth pressures, are anticipated that efficiency will be unable to offset completely. After careful evaluation of available and potential options, PG&E concluded that future needs can be met in an environmentally and economically sound manner, provided certain emerging technologies, including wind energy, are commercially ready during the 1990s. This will require acceleration of research, development, and demonstration efforts for the targeted technologies.
Recent wind power projects had installed costs at or below $1100/kW, whereas advanced wind turbines that will soon go into production can result in total wind-plant costs under $900/kW. Wind generation in California and worldwide during the 1980s was characterized by a steadily increasing number of installed wind turbines and wind-generation capacity , decreasing cost of energy, increasing availabilityl and capacity factor, and decreasing operations and maintenance (O&M) costs. Wind turbines now becoming available can produce electric energy at the busbar for about $O.OS/kWh in constant 1990 dollars, or $0.08 in current dollars. This cost is roughly comparable to the costs associated with new power plants burning oil or natural gas, and with coal-burning plants having the best available emission controls.
The technical hurdles faced by the industry include issues of wind turbine integration with utility operation and commitment schedules. Wind turbines are usually operated in what can be described as uncontrolled generation, which means wind generation is accepted by the utility system whenever it is available, and the savings to the utility are achieved by reducing the load on the conventional units in the system. However, as wind turbines become a larger fraction of total capacity, the marginal value of the wind-generated electricity becomes less and integration presents operational challenges.
I Availability is defined as the percentage of time that a turbine is operational and available to produce energy if the wind speed is in the appropriate range.
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THE RECENT HISTORY OF WIND ENERGY
DEVELOPMENT
Recent wind-energy development has been concentrated in California with approximately three-fourths of the world's wind-generated electricity produced within the state. Yet California has a relatively small total wind resource potential compared to other US states and to other countries. The California development was a result of several factors. First, the state was found to have some areas with topographically concentrated wind, mainly in mountain passes. These areas have mean annual wind-power densities of 500 watts per square meter or better (as do huge areas in the central United States, northern Europe, and many other areas). Second, California had the most favorable power purchase rates and the most cooperative utilities, and strong regulatory support. Third, much of the windy land was available for low rental costs and with few land-use conflicts. Fourth, the investment climate was attractive because of state and federal tax credits along with ample supplies of investment capital within the state ready to take a risk on new ideas.
Wind-energy development in California has leveled off in the past few years. The major reason for this is the current lack of need for additional power, which, combined with low marginal production costs for the utilities dictates low payments for power purchases. This situation is expected to change in the late 1 990s.
The experiences in California provided the rest of the world with a demonstration of a newly emerging electricity-generating technology available to provide an environmentally safe alternative to fossil fuels. Triggered by the Chernobyl disaster as well as European-unification movements, Europe is challenging the US role in wind energy development. The European Community (EC) has stated its objective to advance non-nuclear renewable energy sources in the next decades and has committed to funding of wind research and development activities throughout member states well into the 1990s. European wind-turbine manufacturers are emerging with mature designs based upon their California experience, and are now developing utility-class units. Furthermore, several European countries have made commitments to increase significantly their subsidies to their utilities for non-nuclear renewable energy implementation programs. Together, these are strong factors that will promote the development and improvement of wind technology in the near future.
Technology advancements and trends no doubt will reflect more utility perspectives and concerns than the California experience. Wind-power plants in Europe are generally to be operated by the utilities themselves, even though the privately owned turbines in Denmark formed the basis for the development of the present European wind-turbine industry. Currently, European electric
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utilities and development agencies are focusing on demonstration projects involving small numbers of large-size wind turbines. Consequently, additional increases in future subsidies will be used for continuing megawatt-scale strategic studies and encouraging European industrial joint ventures for megawatt-scale development. Presently 13 European manufacturers are involved in the production of wind turbines larger than 750 kW.
In the United States, a similar approach is being undertaken with PG&E, Niagara Mohawk, the Electric Power Research Institute (EPRI), and U. S. Windpower, the major US manufacturer of mid-size wind turbines.(2) They are in a five-year program to develop and test an economic, utility-class, variable-speed wind turbine that will meet all the utility requirements and can be readily integrated into utility power systems worldwide. Interestingly, no government funding is involved in this project. This cooperation of utility and industry is similar to recent European programs and will advance utility-grade technology and lead to greater acceptance of wind technology by other electric utilities.
Currently, the US federal wind-energy program is about one-fifth of the effort of 10 years ago, and state funding for wind technology is practically non-existent anywhere in the United States. Project development on local levels is highly dependent on favorable interconnection and power-purchasing agreements with the local utilities. In general, the policies of electric utilities and regulatory agencies outside of California have not supported wind development actively.
FUTURE ENERGY SUPPLIES
Many utilities face the same situation as PG&E, and will need to get the most out of energy efficiency and renewable energy resources in the future. California is fortunate in having varied sources of electric energy. At present, 42% of the electricity generated in California comes from renewable resources. Most of the renewable energy is hydroelectric (23% of California's electric energy), but substantial production also comes from geothermal ( 13%), biomass (4%), wind ( 1.3%), and solar (0.4%).
A technology acceleration initiative is being planned by PG&E that would address selected technologies in three categories: (a) renewables, (b) advanced natural gas conversion, and (c) distributed generation and storage. Its goal is to provide PG&E and the Pacific Coast region of the United States with a robust portfolio of options tailored to regional indigenous resources and existing electric supply infrastructure. The technologies targeted within these categories are at varying stages of technical, economic, and market readiness. However, in each case there is a substantial base of technology to
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build upon and a clear opportunity to design and demonstrate utility-grade systems over the next 10 years.
Long-Term Resource Planning
As illustrated in Figure 2, the following considerations frame PG&E's outlook toward future electric energy supply:
1. Based on critical-year energy analysis, PG&E will have to start adding new resources by the early 2000s, possibly earlier, if certain contingencies occur.
2. Customer Energy Efficiency (CEE) will be used to its maximum economic potential to meet these growing needs. However, because high-benefit/cost CEE will be captured first, long-term CEE additions will be more difficult to obtain than those in this decade and will have declining incremental benefits.
3. Current forecasts for load growth do not account for electric transportation market development, nor for dislocations in the supply of energy from non-utility-owned power plants [Qualifying Facilities (QFs) or Independent Power Producers (IPPs)].
4. To a limited extent in the 1990s, but to a large extent after 2000, PG&E's existing fossil plants will reach the point when retirement or repowering is economically justified. This will allow replacement of these plants.
5. As we approach the year 2000, PG&E will begin making investment decisions for large quantities of generation additions or purchases from QFs/IPPs. Once investment or purchase decisions are made, the new facilities will need to operate over their 30-40 year economic lives to recover investment. It will be advantageous to PG&E to have resource options with low environmental and fuel supply/price risks to install in that period.
By comparing two conceptual capacity expansion scenarios, the challenges ahead can be placed in perspective. In one scenario, decisions are driven by traditional criteria, i.e. present-value economic analysis. In the other, environmental concerns are also given weight.
The Economic Expansion Scenario
1. If PG&E were to call for bids today to meet its anticipated generation needs for the years 2000--2010, most of the winners would probably be current best available technology fossil-fired units (cogeneration and combined cycle/repowering). Wind would probably be the only renewable technology that might capture a share (even without consideration of social costs of fossil fuels).
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2. Concerns regarding the environmental performance could bring operating and/or economic problems during the lives of the traditional units.
3. Increased dependence on fossil fuel implies a risk of vulnerability to supply and price uncertainties.
4. Uncertainty about meeting future air-quality standards implies an environmental risk.
The Environmental Expansion Scenario
1. Renewable technology has already progressed to the point that PG&E could meet a significant amount of future energy addition requirements with renewables. Wind energy would be a major contributor to this. However, further technical advancements in solar electric energy are required to achieve cost reductions that increase the diversity of the renewable resource mix.
2. If regulators were to place significant weight on environmental attributes in resource selection today, ratepayers might incur a 20-25% premium on prices paid for renewable technology.
ENERGY (GWh) 200,000,----------------------,
150,000
100,000
50,000
° 1990
Renewables, Storage, and Advanced Fossil
Non Fossil & QFs
2000 2010
YEAR
Load
Customer Energy Efficiency
2020
'Includes 4000 GWh of Emergency Spot Purchases
Figure 2 PG&E's future energy supply.
2030
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3. For solar technologies, the premium could initially be even larger. 4. As technologies advance over the next 10--15 years, this premium will
decline. But without an accelerated effort by PG&E and others the premium will still be significant, probably more than 15%.
WIND ENERGY TECHNOLOGY
The technology for generating power from wind is relatively simple. A wind turbine consists of blades, gearbox, generator, tower, control equipment, and power conditioning equipment. Wind causes the blades to rotate, generating mechanical energy, which is converted to electrical energy by a generator. The blades of most wind turbines rotate in a vertical plane (horizontal axis). Some wind turbines rotate about a vertical axis. Most turbines have either two or three blades made of fiberglass, laminated wood, or aluminum. Towers are generally tubular or lattice structures. There are several ways to yaw, or aim the wind turbine into the wind. Small turbines often use tail vanes to yaw. Most utility-connected US turbines have free yaw; their blades operate downwind from the tower and yaw varies freely with the wind. Some employ damping to reduce oscillations that arise with change in orientation. Most European wind turbines use motors to aim into the wind. Most wind turbines that generate electricity rotate at the same rate regardless of the wind speed; some control their energy conversion rate by changing their blade pitch. Most of the medium-size wind turbines operating in the PG&E service area convert mechanical energy to electricity using induction generators.
Since the rediscovery of wind power in the 1970s, the wind turbines designed for utility-scale/bulk power production have progressed through firstand second-generation technology development. First-generation machines of the early 1980s designed in the United States included two size classes. The first class were small-scale, lightweight designs based upon helicopter blade technology. The typical turbine was rated at 50 kW and cost $2200/kW installed. Actual aerodynamic stresses imposed upon these wind turbines tended to be higher than expected, frequently resulting in poor reliability or catastrophic failure. Few of these turbines evolved into second-generation machines. However the US National Renewable Energy Laboratory (NREL, formerly the Solar Energy Research Institute) is presently funding the development of three of these earlier US lightweight turbines: the ESI 80, Enertech, and Northern Power Systems. PG&E, EPRI, and Niagara Mohawk are funding development of U. S. Windpower's advanced variable-speed wind turbine.
The second class of first-generation machines included large-scale wind turbines with multi-megawatt power ratings developed under grants from the US Department of Energy (DOE) by large aerospace and power systems
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companies. The most prominent design was the Boeing MOD-2, a 91-m (300-ft) rotor diameter, 2.5-megawatt wind turbine. Five MOD-2 turbines were designed and built by Boeing; three were installed in Goldendale, Washington, one in Medicine Bow, Wyoming, and one in Solano County, California (owned and operated by PG&E). PG&E's MOD-2 began operation in April 1982 and produced the most energy of the five (more than 15 million kWh). The Solano MOD-2 was installed and tested as a research project to determine the technical and economic viability of large wind turbines. If the turbine had operated reliably and cost effectively, PG&E planned to purchase other MOD-2 turbines and install them on PG&E property in Solano County. Major problems, such as cracks in the low-speed shaft and difficulties in lubricating the bearing supporting the pitchable blade tips, resulted in lowerthan-expected turbine reliability and availability and significantly higher-thanexpected O&M costs. These costs amounted to about $0.05/kWh in the last three years of operation. The MOD-2 was not reliable enough to meet PG&E's energy needs cost-effectively. Although an improved version of the MOD-2 wind turbine was placed in operation in Hawaii, commercialization of this design or its evolutionary successors appears unlikely given its costs.
Second-generation wind turbines, installed from the mid-1980s through the present, were mostly European machines, with improved reliability. These 65 to 300 kW "heavy-duty" machines are conservatively engineered for high structural and aerodynamic loads. Their turnkey cost in California is now about $1100/kW, with further reductions feasible. These turbines are designed to operate for 15 to 20 years, but further improvements in technology and turbine component modularity may extend the life of some turbine designs significantly.
As wind turbine technology has matured, a few types have gained prominence. Most utility-connected turbines are intermediate-sized and propeller-type (horizontal-axis). Most of the current designs (more than 90%) are horizontal-axis turbines. The balance are Darrieus (vertical-axis) types. Horizontal- and vertical-axis turbines have roughly equal conversion efficiencies. Of the horizontal-axis turbines, about one-fourth are downwind machines (i.e. the rotor spins downwind of the tower), most of which were built in the United States. About one-half of all machines installed in California were built in Denmark. Nearly three-fourths of all turbines use three blades; the remaining turbines have two blades.
About three-fourths of turbine blades are built from fiberglass; the balance are laminated wood and aluminum. Blades made of laminated wood are primarily used on turbines built by US companies such as ESI, Enertech, and Westinghouse. There have been no problems to date with the wooden blades. The only turbines with aluminum blades in PG&E' s service area are Flo Wind's vertical-axis turbines. Even though a vertical-axis turbine has longer blades
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than a propeller type with the same swept area, such blades could potentially be lower cost because they are made of extruded aluminum. Problems with blade joint fatigue are being addressed by FloWind. The turbines are installed on either a tubular steel tower or a lattice tower, with an equal number used on either type.
Pitch control has become the most common means of power limitation, but stall control is also used. Pitch control is done by rotating the blades in their long axis to obtain the desired aerodynamic force and thus rotor power. More than half of the Altamont turbines (by rotor area) use full-span pitch change to regulate output. The major users of this method are U. S. Windpower and WindMaster. Howden uses partial-span pitch control (the MOD-2 turbine also used it). The remaining turbines, including Fayette, ESI, Enertech, and the Danish turbines, use blade stall for power regulation. In blade stall regulation, the blade angle is constant, and is chosen so that the blade airfoils "stall" aerodynamically in high winds when the desired maximum power is reached.
Nearly all utility-scale wind power plants, including those in California, have induction generators, which require the presence of an energized utility line. Once an energized line is present, they generate at the same voltage and frequency as the utility. The MOD-5B is one of the few turbines with a synchronous generator.
About a dozen megawatt -scale turbines have been built and tested worldwide with varying results. Marginally successful performance of large machines, high cost, and high technical risk precluded their purchase by commercial wind farms. Experience gained by operating large wind turbines, as well as the demise of federal funding, prompted most of the US manufacturers to abandon the concept or to develop wind turbines having lower technical risk and capital cost; this usually meant smaller machines were developed. Further, small- to mid-sized wind turbines had the advantage of relatively short lead times, mostly attributable to modularity. In addition to lower financial risk, short lead times allow new innovations to be adopted quickly. The California Energy Commission (CEC) now classifies wind turbines in the lOO-kW range as commercialized units. These machines evolved to that category in just a few years.
Every manufacturer in the United States and abroad has now focused on the development of intermediate-sized 300-500-kW propeller-type designs. At the end of 1989, 35 Danish Wind Technology-Vestas 400-kW wind turbines were installed at San Gorgonio Pass, California. U.S. Windpower, the largest manufacturer of wind turbines in the United States, has plans for a machine of similar size, as does Mitsubishi Heavy Industries, Japan's leading wind turbine manufacturer. The main design concepts are largely extrapolated from their smaller machines.
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It is likely that this intermediate-sized wind turbine will remain the predominant size range in the early 1990s while wind power plants are still being installed by independent power producers (IPPs). Installation of these wind turbines is especially attractive at remaining permitted sites in California because they do not represent a significant change in project development lead time, costs, permitting, or commissioning from previous projects using smaller turbines. On flat land the total wind turbine rated capacity for a given area is almost independent of turbine diameter. At present turbine costs, the lowest cost of energy is from turbines of about 25 m (82 ft) diameter with a rating of about 300 kW. In Europe, however, the trend is for development of larger units approaching 600 kW to 1 MW. Europeans support this emphasis on larger machines because on linear sites, such as dikes, the potential capacity can be increased with larger turbines, and at off-shore sites, where foundation costs are high, larger turbines may be more economic.
The viability of wind generation for utility-scale power production could improve significantly with the following technological developments:
1. improved rotor material to better tolerate fatigue loads; 2. control technology to respond to changes in wind, electrical characteris
tics of the wind turbine generator, and connected loads; 3. combined wind turbine/energy storage systems to increase load carrying
capability significantly. Potential energy storage technologies include current and advanced batteries, compressed air energy storage (CAES), and modular pumped hydroelectric storage;
4. variable-speed, utility-optimized turbine designs with power electronics for high-quality, utility-grade power production.
RESEARCH
The US Department of Energy sponsors research and development for advanced wind turbines. For example, it sponsored the Solar Energy Research Institute (now National Renewable Energy Laboratory) development of airfoil profiles for use on wind turbines to maximize energy capture and reduce stresses.
Wind economics are driven in part by energy capture, and this can be improved by variable-speed operation, which allows the turbine speed to vary with wind speed. This means that the rotor operates at its optimum tip speed ratio in different wind speeds. Many early turbines used two-speed operation to approximate this. A more accurate, yet more complex, type of variablespeed operation can be achieved by decoupling generator and line frequencies electronically, thus allowing me rotor speed to be tuned to wind speed. Modem power electronics devices now have the current and voltage capabilities to
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meet the requirements of the necessary power conversion systems. Figure 3 shows how the variation in speed and generator output frequency of the variable-speed turbine results in a nearly constant output torque; variable-speed operation buffers the turbine drive train from the variations in torque that accompany operation in gusty or turbulent wind conditions. The resulting reductions in fatigue loadings permit use of structural and rotating components that are lighter, cost less, and have longer lives and lower maintenance requirements.
Significantly to utilities, the electronic conversion component can, as an artifact of its function, also permit real-time adjustment in power factor, such that a wind power plant can have the same reactive power supply capability that conventional utility power plants traditionally provide. Likewise the quality of power from the generation source is high, in terms of harmonic content, frequency operating band, and other important factors.
WIND POWER PLANT PERFORMANCE
The performance of the first wind power plants in California in the early 1980s was somewhat disappointing. The federal and state tax credits designed to promote investment in renewable energy sources were based only on the amount of money invested, and not energy produced. The winds at many sites were not adequately monitored before the installation of turbines, and also
Rotor Speed
Drivetrain Torque
Generator Electrical
Output Frequency
Effect of Power Electronic Converter
1 �-�--� - Constant1peed turbine
��:�
1· e .S- A e «, as 0
Time
Figure 3 Variable-speed turbine operation characteristics.
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many inadequately tested turbine designs were used. A third major reason that early results fell short of projections is that array effects, resulting in lower winds downwind from operating turbines, were not accounted for.
An unfortunate misconception arose in the mid-1980s that wind power plants in the United States were primarily "tax" farms. However, taking the case of Altamont Pass, only about one in a thousand of the turbines installed have never produced energy. Many turbines did operate at only a small fraction of their projected output owing to mechanical problems, most of which were with blades, gearboxes, yaw drives, and towers. About one-fifth of the Altamont turbines have had operating lives of about five years. Although information for the early years is not available, in recent years the county government has required that all catastrophic turbine failures (throwing a blade or a tower collapse, for example) be reported. Less than one-percent of turbines have had such failures each year.
California wind turbines operated at an annual average production of only 20 kWh per installed kilowatt in the early 1980s. Production rose to 1300 kWh per installed kilowatt in 1987 through 1990. High availability and rapidly improving productivity of the wind turbines in the 100-250-kW range installed since 1988 demonstrate that wind technology is approaching levels of reliability and performance required by utilities.
THE WIND ENERGY RESOURCE
Theoretically the capturable wind energy resource in the world could supply all the energy needs of human society . The same is true of the United States (3).
Proper and accurate estimates of resource potential are difficult. It has been 15 years since utilities in California began to develop and analyze wind resource information, and there is still a factor of two or three uncertainty in estimates of ultimate development potential. For the PG&E service territory the developable wind resource is between 2000 and 5000 MW. The sources of uncertainty are technological, legal, and economic.
The California Energy Commission (CEC) began an extensive resource assessment program in 1977. The CEC report identified several areas of the state with promising wind energy resources. Five areas-Altamont Pass, the Tehachapi Mountains, San Gorgonio Pass, the Montezuma Hills, and Pacheco Pass-have since seen extensive wind development largely_ as a result of the CEC's pioneering effort. In 1985, the CEC published the California Wind Atlas (4), which was the culmination of its effort in wind resource assessment.
The Atlas indicates there is a theoretical wind power potential of about 30,000 MW in PG&E's service territory; however, this· overstates the development potential because land-use restrictions, terrain, and elevation limit
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the useful portion of the resource. Some of these areas are unlikely to be developed because they are heavily populated, or within National Forests, scenic areas, or state parks. Subtracting these reduces the potential developable resource to approximately 4000 MW, of which about 1000 MW are already developed or in the planning stages.
The four stages of resource assessment are: (a) to acquire a general understanding of the regional meteorology to identify wind "hot spots," (b) to pass these areas through successive screens to eliminate areas where development is precluded by environmental, land-use, or transmission considerations, (c) to conduct properly designed long-term measurement campaigns to characterize the resource in each promising area, and (d) to use this data to develop models of the siting areas to support micro-siting decisions. Needless to say, this is expensive, and even in California wind resource assessment is incomplete, according to this protocol.
Lessons learned in this process include:
1. Accurate, properly designed measurements are extremely valuable, if they are available in time to support decisions. A lot of money is wasted when decisions have to be made without the information.
2. A proper understanding of technological capabilities and micro-siting considerations, e.g. array effects, is necessary to estimate the potential of specific sites. For example, the energy productivity of the Altamont resource could probably be doubled or possibly even tripled, through optimal deployment of emerging machine designs and development of presently undeveloped areas. Siting areas that are not economically developable with current technology may be economic with future technology.
The Pacific Northwest Laboratory produced a Wind Atlas for the United States (5). Information from this Atlas indicates that the Great Plains in the central United States have a wind energy resource hundreds of times greater than that of California. They have the theoretical potential to produce more wind energy than the electric energy used in the entire country. The emphasis of Department of Energy wind programs is on developing wind turbines that can harness this resource to produce electricity at $0.03/kWh.
A European Wind Atlas has also been produced (6), showing huge potentials in northwestern Europe and certain areas in the rest of the continent. Wind surveys are also being done in numerous other countries.
Wind Resource Location and Transmission
The cost of interconnection of a wind power plant with the utility grid can be a major economic driver, and, in some cases it may require transmission routings that are aesthetically or environmentally unacceptable. Wind devel-
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opment in northern California has been facilitated by the fortuitous proximity of the Altamont Pass area to a particularly strong area of the PG&E transmission system. The Tehachapi area in Southern California represents a much less fortuitous match.
The Tehachapi case is instructive, because it motivated the use of a relatively new technology that permits dynamic rating of transmission lines. Current carrying capabilities of transmission lines are conventionally determined by the need to limit conductor temperature and thus avoid accelerated damage to the line. Conservative assumptions regarding ambient conditions are used. Traditional design criteria do not account for the fact that when the wind power plant is generating, the wind speed is also increasing the rate of convective heat transfer from the line to the ambient air. Using "power donuts" and other sensors, line temperature can be measured, and more wind power can be transmitted than the static ratings would allow. This technique can avoid costly line upgrades, which might otherwise economically limit the extent of resource development in utility line areas with limited capacity.
Relationship of Wind Energy Resource to Cost of Energy
It is impossible to specify the wind energy resource in a given area without knowing how much the user is willing to pay for energy. Logically, the areas producing the lowest-cost wind energy, i.e. the areas with the most energy in the wind, the topography easiest to build on, and locations nearest to the utility grid or user, will be developed first. As more wind energy is desired, the areas producing higher-cost energy will be used. This situation is shown for the PG&E service territory in Figure 4.
THE COST OF WIND ENERGY
The cost of wind-generated electricity has declined significantly over the past decade. Capital costs have dropped significantly since 1981. The first wind turbines were installed for about $3000IkW; the installed cost now approaches $1l 00/kW. Capital costs could eventually drop to below $500/kW with new, advanced, lightweight turbine designs in mass production.
Recent studies indicate that O&M costs for wind power plants have dropped to about $O.OllkWh for the best plants, which is below levels achieved by competing technologies (if fuel costs are considered).
Wind energy costs presently range from $0.07-0.1O/kWh. Existing wind-farm layouts were done largely with limited understanding of critical machine-siting parameters, using economic criteria driven by now-expired tax considerations.
The best wind sites in northern California (those with average annual energy densities of 500 W/m2 or higher) can produce wind energy at costs of about
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$0.05/kWh, based on a real interest rate of 5%, a life of 25 years, and recent reductions in the cost of wind power plants to $863/kW (7, 8).
The cost of energy from new wind plants at good sites using emerging turbine designs is competitive with the cost of energy from new fossil fuel plants. In fact, as PG&E indicated in a filing with the California Public Utilities Commission in August 1991, a new 150 MW wind plant is among the resource additions proposed over the next decade (8). Other California utilities have also included wind power plants in their future plans.
As a result of product development programs such as the PG&E/EPRI/U. S. Windpower Advanced Wind Turbine Project, and follow-on demonstration efforts, a more robust portfolio of high-quality wind machines will become available. Work in progress to scale-up wind machine size and optimize designs will result in 30% reduction in turbine costs to less than $750/kW. This is a critical need, considering the capital-intensive nature of wind power plants. Improved machines, coupled with better understanding of machine
15000�--------------------------------------------� Resource Adjusted for Terrain and Altitude
10000
5000
Including Transmission Line COsts
National I"Dr' •• l[_ A State 'arkl
Scarcely A Modera
Populated. Bureau of Land Management
OL-_....d���� .04 .06 .08
LEVELIZED COST OF ENERGY ($/KWH)
Figure 4 Wind resource and cost of energy in PG&E area.
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siting parameters, will reduce wind energy costs to $0.05-O.07/kWh (with at least 2000 MW potential in Northern California).
The California Energy Commission (CEC) evaluates 200 energy supply technologies every two years. The resulting Energy Technology Status Report (ETSR) reviews the commercial and economic feasibility of each technology and provides critical input into the CEC's energy policy recommendations. Although wind technology shows the potential for producing the lowest-cost electric energy, estimates range widely owing to uncertainty about the long-term performance of current wind turbine technologies.
Wind power generation has significantly lower social, or external, costs than most conventional power generation sources. External costs are those that are not paid directly by users of the energy, but are borne by society at large (for example, health costs associated with air pollution from coal-fired power plants). Although no consensus has been reached about the magnitude of external costs associated with particular power production technologies, some estimate that external costs of fossil-fueled power production could be quite significant. A recent PG&E study surveyed the literature on external costs. Renewable and conservation technologies typically have the lowest external costs, while fossil fuel technologies have significant to very high external costs. In particular, many fossil fuel technologies have significant unrecognized costs, such as health and safety, research and development support, tax incentives, and military support (e.g. to maintain US dominance of oil-producing areas). Next to conservation, wind technology has the least environmental effect costs. Hohmeyer's study of Germany found external costs of fossil fuels to be $0.02 to 0.06/kWh and those of nuclear to be $0.06 to O.13/kWh (9).
Technology issues are difficult to separate from cost issues. Perhaps the important distinction is that cost trends discussed above are driven by scaling-up and otherwise reducing the installed costs of the wind turbines, while at the same time improving energy capture. By contrast, most technology deficiencies and problems manifest themselves in low availabilities, expensive corrective maintenance, and high operating and maintenance costs overall.
One must look beyond the average technical performance of the more than 15,000 turbines operating in California. The most reliable, highest availability, and best performing machines have operation and maintenance costs in the range $0.0I-O. 015/kWh, even though they are not expensive machines on the basis of installed cost. Installed costs of wind power plants using these machines are now about $1100/kW. Good technical characteristics can be achieved through costly overdesign, or through incremental improvement of less material-intensive designs based on accumulated field experience.
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Cost Issues and Utility Perceptions
It makes a world of difference to a utility whether it perceives a particular opt!pJl--as economically preferred, economically marginal, or uneconomic. Note the emphasis on the word "perceives." Most utilities in the United States and probably also Europe perceive wind power as uneconomic and likely to remain so, at least in the context of their own wind resource. These perceptions are largely based on 5-1O-year-old information, and in that framework, they are entirely correct. Some utilities are beginning to realize that current wind technology applied to high-quality resources brings the wind option into the "economically marginal" range. Few utilities are yet aware that technology could be available within five years or so that will make wind an "economically preferred" option, even without significant internalization of the environmental and social costs of nonrenewable options. Thanks to the active market for wind power in California, the major California utilities are now convinced of wind's economic superiority. Accordingly, they are now proposing wind as their first choice, along with natural gas power plant repowering, for future system expansion to meet load growth.
THE VALUE OF WIND ENERGY
Wind energy is an intermittent source of energy, and the times of its production are determined by somewhat predictable, albeit uncontrollable, natural weather conditions. Wind energy's value to a utility is partially determined by how well the wind energy fits the times of high utility loads.
The value is based on two factors: energy saved and capacity deferred. The energy savings come from having to produce less energy from existing plants (or purchase less energy from outside sources) when the intermittent source is producing. At present, in the PG&E area these avoided energy costs are reflected in the short-term contract energy prices paid by PG&E to independent power producers. These prices vary from just below $O.03/kWh to just over $O.04IkWh depending on the season and the time of day that the energy is delivered. These energy costs are primarily based on the fuel and operation and maintenance savings from having to produce less energy in PG&E's natural gas-fired steam generation plants. (Note: most of the wind power plants operate under long-term contracts at higher rates set in the early 1980s of about $0.08/kWh.)
A second element of the value of intermittent sources is t�e capacity cost. During hours of high electric load, which in California come on weekday afternoons during the summer, the utility must have sufficient generating capacity available to meet the maximum loads with enough reserve to ensure system reliability. This value is reflected by a capacity payment (in addition to the energy payment) to independent power producers of $O.064IkWh for
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energy delivered from noon to 6:00 p.m. Pacific Daylight Time on regular working days from May I to October 31. These "peak load hours" amount to about 9% of the time in the year, yet they determine how much capacity must be built. During the past few years the Altamont wind power plants have produced about 11 % of their annual output during this 9% of the year, indicating a slightly better than random fit to PG&E electric loads. In 1990, the new wind power plant in Solano County produced 15% of its energy during peak hours, indicating a better fit than Altamont Pass energy to PG&E electric loads.
The daily pattern of wind energy from wind power plants determines the fit of wind energy to load. The Solano County plant had a much higher average specific output during the "peak load hours" of the afternoon. During the hour that PG&E usually has its highest loads (4:00 p.m. P.D.T.) the Solano plant had an average capacity factor of 0.50, and two Altamont plants had 0.41 and 0.26 (10). The Solano plant output indicates that its mid-day reduction of wind is less severe than that in Altamont Pass. The difference in the two Altamont wind power plants' daily output patterns is due to their different locations and elevations in the Pass. The high-elevation southwestern wind plant is on land with an elevation above 300 m (1000 ft) above sea level, while the northern plant is below 300 m in elevation. The output of the high-elevation plant shows less of a mid-day decrease than that of the northern plant, although both plants show more decrease than the Solano plant.
A more accurate way of judging the capacity credit of the northern California wind power plants is to calculate the loss of load probability for every hour of a year with and without the output of the plants (7). This has been done for several years for the Altamont Pass wind farms. As a result, a capacity credit value of 0.15 times the rating has been used by PG&E for wind power plants, although this measure varies significantly within Altamont Pass, and from year to year.
ENVIRONMENTAL ASPECTS
Wind energy is a renewable resource, which has significantly less harmful impact on the environment than most other energy sources. Negative environmental impacts associated with wind generation are attendant land-use restrictions, visual and noise impact, erosion, impact on flora and fauna and their habitat (which is site-specific), bird mortality, possible negative effects on endangered species (which is site-specific), and electromagnetic interference with radio and television signals. However, wind generation causes no pollution except that associated with manufacturing and uses no fuel. The primary concerns related to land use are for the aesthetic impact and the impact on nature in the form of local flora and fauna. Some object to the
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appearance and noise. Some measures that are used to address these concerns are setbacks from project boundaries, visual impact and noise impact studies, and restriction of turbine types or sizes and colors.
While wind energy does not have pollutants and harmful emissions, aspects of the technology can be harmful to wildlife. One obvious danger is to birds that may come in contact with rotating blades and transmission lines. A study is present! y being done on the deaths of raptors in Altamont Pass. Other dangers include the effects on wildlife and its environment caused by construction and presence of turbines, their foundations, and the support structures and transmission lines.
Concern about emissions into the air is not significant. There is some concern about fugitive dust, which is carried by the high winds usually associated with wind projects. Mitigation methods for this problem include surfacing roads, wetting unpaved roads, and restricting access to sensitive areas. Wind energy's impact on water supplies is also minimal in comparison to that associated with other energy sources. Perhaps the largest problem has been the impact of the detergent used in the water used to wash the blades periodically. This problem has been eliminated by banning the harmful detergents from the washing process.
During a wind turbine's normal phase of operation, solid and hazardous waste dangers are negligible. When accidents occur, there is some spillage of oil and hydraulic fluid, which must be cleaned up; when wind turbines are no longer needed, they can be considered a solid waste if they are abandoned. There are essentially no solid and hazardous waste problems, however, that cannot be cleaned up as they occur, and at modest expense.
The first California wind power plants were built in areas with very low popUlation density, and there was little land-use conflict. However, some recently proposed wind power plants have met opposition from residents near the areas. This has been especially true in Europe, with its relatively high population density. Consultation with nearby residents and integration of their desires into planning early in the project is important. Also because of population density, turbine noise has been a greater concern in Europe than California. Much research has been devoted to reducing turbine noise, and the latest models meet stringent noise-level rules.
PLANS FOR THE FUTURE
As mentioned above, the wind resource in the PG&E area is related to cost of energy. At a penetration of wind power giving about 10% of the annual electric energy, the cost of wind energy becomes approximately equal to solar thermal electricity costs (10). Even if, as in some of the central United States, the economic wind potential could theoretically produce all of the electric
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energy used, this would require massive amounts of energy storage. The optimum sustainable energy system for PG&E would include solar energy and storage as well as wind. For these reasons, PG&E conducts research into all of these areas.
The energy demands of Northern and Central California are growing at more than 2% per year. Unmanaged, this growth would require PG&E to deliver 25% more energy to its customers in the year 2000 than it did in 1990. PG&E's electric energy growth needs through the 1990s can be met through the aggressive pursuit of efficiencies-improvements in customer energy efficiency, existing generating system efficiency, and regional operations efficiency. Through this approach, PG&E intends to cut its energy growth by half and its peak demand growth by 75% (2500 megawatts) at a cost significantly less than the levelized cost of building new fossil generation. Nevertheless, like many other utilities, PG&E will need significant new supply-side resource additions early in the next century. Although aggressive customer energy-efficiency programs will continue to be the mainstay of PG&E's strategy for the foreseeable future, electric loads will continue to grow beyond the company's ability to offset them through efficiency measures, and portions of the existing system will need replacement because of service life considerations.
While PG&E's existing system and efficiency plans provide a solid bridge to the future, what awaits on the other side of the bridge is a need to expand and rebuild utility infrastructure. If, as is hoped and expected, society chooses the course of environmental stewardship, an economic premium will have to be paid to implement an environmentally preferred resource mix. PG&E has been exploring steps that can be taken to reduce this premium significantly. The key strategies PG&E has identified are discrete but also synergistic. Specifically:
1. Given the objective of having generation options that the are both economically and environmentally preferred, governments and utilities must take action in the 1990s to advance targeted technologies.
2. To bring about competitive options, both technology push and market pull strategies will need to be employed.
3. The distinction between technology push and market pull lies in the type of learning required.
4. Technology push includes laboratory development, scale-ups with substantial risk, and early demonstrations.
5. Market pull focuses on cost reduction through incremental "marketdriven" innovation.
6. The targeted technologies are modular and based on economies of mass production, not economies of scale. Experience in use is rapidly translated
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into product improvements that lead to additional cost reduction (organizational learning).
7. The third strategy involves competition. Though PG&E may invest in new generating facilities of its own in the future, the company expects to be a major purchaser of power from the independent energy community. PG&E's customers will benefit if power comes from diverse suppliers who sell power at fully competitive prices, with timing and controllability that result in traditional levels of service reliability. Legislative and regulatory changes will be needed to foster this true competition.
Technology Acceleration
Significant progress has been made in identifying what can be done to implement the technology push strategy. Clean renewable energy and highefficiency natural gas conversion technologies are expected to reach the point of readiness for cost-effective deployment in PG&E's service territory after the year 2000. PG&E's initiative involves phased implementation of cooperative demonstrations of emerging technologies between now and the year 2000.
PG&E's goal is to acquire a robust portfolio of viable clean electric supply options by the end of the l O-year initiative. Robustness is ensured by addressing multiple technology opportunities applicable to three key market trends:
1. Renewables. There are downward trends in the cost of intermittent renewable supply technologies. The need to broaden generation options, combined with environmental preferences, will lead to a competitive advantage for renewables in the future.
2. Advanced Gas Conversion. The aging of PG&E's fleet of fossil plants, combined with expected increases in natural gas prices, tighter emissions limits, and the anticipated availability of highly efficient conversion systems, may compel economic retrofitting of our existing sites with such systems.
3. Distributed Generation and Storage. The continued improvement of modular generation and storage technologies, combined with increasing power distribution costs and advances in information, control, and demand-side technologies, may economically motivate development of distributed generation and storage markets.
In this context, the viability of a particular technology will depend on whether:
1. The primary resources it captures or converts are abundant. 2. Its current technical risks and uncertainties can be resolved over roughly
a la-year development period.
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3 . The potential for cost-effectiveness over the early decades of the next century is well established.
4. A competitive technology delivery infrastructure can be put in place. 5. The overall market for the technology is sufficient to support the necessary
infrastructure. 6. The technology fits in with long-term PG&E system needs and planning
scenarios that reflect substantial uncertainty.
Technologies are re-emerging that will meet these tests of viability. They differ significantly in the steps required to achieve viability in the desired time frame. Thus, PG&E's plan requires a separate strategy in each case.
Except for wind energy, none of the targeted technologies or systems can be characterized as viable today. They are not technically ready for significant levels of cost-effective application. At the current pace of development, their full viability by the end of the decade is problematic. There is well-documented progress, but prevailing market uncertainty, combined with the current weakness of embryonic vendor infrastructures and supporting R&D programs, is likely to impede further progress and, in some cases, may even place key technology supplier organizational capabilities at risk. PG&E, as a financially and technically strong utility, is in a position to leverage its position and accelerate technology readiness in selected cases through carefully designed projects and complementary business and regulatory initiatives.
Technology Strategy-Renewables
PG&E's service territory includes high-quality wind and solar siting areas, and as an outcome of standard offer contracts and subsidies, both wind and solar thermal trough technologies are approaching the economic range. There is a synergy between the two technologies that needs to be better understood. Both resources are intermittent, though solar thermal (in natural gas hybrid or thermal storage configurations) is dispatchable. Even without this feature, wind and solar thermal match PG&E's system needs well, as both are stronger in the summer, when loads are highest, and the solar insolation peaks a few hours before the load peak on summer days, while the wind resource peaks a few hours later (10) . The match is not perfect, however, nor are future system load shapes entirely predictable, which suggests that when penetration of these resources into PG&E's mix has reached significant levels, additional system storage beyond the 1000 megawatts currently installed at the Helms pumped storage plant will probably be needed for optimum economic operation of PG&E's system. The PG&E service area has abundant sites for a technology that involves using off-peak electricity to compress air for storage underground and later use in avoiding compression losses in a conventional combustion turbine. Compressed air energy storage (CAES) may provide PG&E with a strategic tool to optimize purchases of power and overall system operation
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long term, while providing a service of significant value to wind and other nondispatching QFs. Implementation of these technologies will also be aided by the development of automated control strategies for more efficient operation of resource mixes.
Wind Energy and Electric Utilities
Having provided a general sense of how wind energy fits into one electric utility's resource strategy, it is appropriate to identify the issues electric utilities will be facing as they make decisions regarding wind.
The issues will initially be addressed in the following order, and then with increasing sophistication over time, if the initial answers are positive.
1. Is there a developable resource within the service area and how large is it?
2. Given the quality of the indigenous resource and its match to system load, is there hope for economical production?
3. Is viable technology available, and are existing wind equipment vendors financially stable and technically capable?
4. To what extent are improvements in current technology possible and likely?
5. What is the capability of transmission links between prime resource areas and load centers?
6. How does wind fit strategically into the utility's generation mix and business environment?
7. How will the the national and worldwide wind industry and market evolve and what impact will this have on wind cost?
Utility Acceptance
PG&E is not the only US utility interested in wind energy. The Utility Wind Interest Group , associated with EPR!, supports the appropriate integration of wind technology for utility applications. Members include the Bonneville Power Administration, Green Mountain Power Corp . , Hawaiian Electric Industries Inc., Niagara Mohawk Power Corp . , Northern States Power Co . , PG&E, Southwestern Public Service Co., and the Western Area Power Administration .
CONCLUSIONS
Since wind will be a least-cost energy supply option for PG&E, the company wants to accelerate the introduction of advanced wind technology, because this will maximize the percentage of system energy needs that are supplied by wind. In 1990 the percentage was 1.3%, or 1 , 165 ,000,000 kWh .
The wind energy industry must continue growing to better manage the
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RECENT US COMMERCIAL WIND POWER 121
financial risks that now face the field in the aftermath of government subsidy and lucrative power-purchase contracts. The relative lack of experience with the resource makes financial planning of a project more speculative than in the case of a better-known resource.
A strategy designed to promote renewable energy, tailored to address local opportunities and constraints, is widely applicable in developed and developing parts of the world. Moreover, PG&E is convinced that wind power will comprise a major portion of the expanded renewable energy use that will be required. Finally, PG&E is hopeful that its corporate experience may encourage other utilities to examine seriously and thoughtfully their wind resources and opportunities.
ACKNOWLEDGMENTS
Material was supplied by Ray Dracker , Mary Ilyin, and Bill Steeley of PG&E. Much of the technical information was collected by Aerovironment under contract from PG&E.
Literature Cited
1. Smith, D . R . , Dracker, R. J. 199 1 . Wind and solar energy potential in Northern California. Proc. Eur. Wind Energy Conf. , Oct. 1991 . Amsterdam: Elsevier.
2. Steeley, W. J . , Lucas, E. J . , McNerney, G. M . , DeMeo, E. A. 1989. The EPRI· utility-U.S .W. Advanced Wind Turbine Program-Status and plans. Proc. Am. Wind Energy Assoc. Conf. : Windpower' 89, Sept. 1989, San Francisco
3. Weinberg, C. J . , Williams, R. H. 1990. Energy from the sun. Sci. Am. Sept.
4. Calif. Energy Comm. 1985. California Wind Atlas. Sacramento, Calif.
5. Elliot, D. L. , Holladay, C. G . , Barchet, W. R . , Foote, H. P . , Sandusky, W. F. 1987. Wind Energy Resource Atlas of the United States. Golden Colo: Natl. Renewable Energy Lab.
6. Troen, I., Petersen, L. 1989. European Wind Atlas. Published for the EC-Di-
rectorate-General for Science, Research and Development, Brussels, Belgium . Roskilde, Denmark: Risoe Natl. Labs.
7 . Smith, D. R. 1987. The wind farms of the Altamont Pass area. Annu. Rev. Energy 12:145-83
8. Pacific Gas and Electric Company's ER-90 Phase Resource Plan Report for the Biennial Resource Plan Update in Compliance with Ordering Paragraph No. 3 of D. 91-06-022. Submitted to the Calif. Publ . Util . Comm . , Aug. 199 1 , p. 19.
9. Hohmeyer, O. 1988. Social Costs of Energy Consumption. Berlin: SpringerVerlag
10. Smith, D. R., Ilyin, M. A. 1 990. Eval· uation of wind energy in Northern California including its fit to utility hourly loads. Proc. Eur. Community Wind Energy Conf. , Sept. 10-14, 1990, Madrid. Spain.
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