Wind Project Performance 1995 Summary

report cover page

Wind Project Performance 1995 Summary (PDF file, 100 pages, 510 kb)
Publication Number: 500-97-003. Release Date: October 2001

The data used to compiled the WPRS is also available to download as Microsoft Excel spreadsheet worksheets:
1995 Wind Reporting System Excel Worksheets (Excel file, 235 kb)


California has long been recognized as a world leader in the development of wind energy. Early wind industry growth in California was supported by the availability of federal and state tax credits and long-term interim standard offer (ISO4) contracts with electric utilities that offered favorable rates. These economic incentives provided the impetus for substantial growth from about 500 megawatts (MW) of installed capacity at the beginning of 1985 to a high of 1,679 MW at the end of 1991.

California dominated worldwide development of wind energy during the 1980s. In recent years, however, California's share of the world's installed capacity has decreased due to continued retirement of older turbines and low levels of industry growth in California compared to growth in the rest of the world. The 54 MW of new capacity added during 1994 and the 1.08 MW added in 1995 did not offset capacity losses from turbine retirements. Thus, installed capacity declined to 1,523 MW and California now accounts for 30 { 1 } percent of the world's installed capacity.

Presently, the California wind industry is facing a challenge as the long term power purchase contracts have stopped paying high avoided cost payments on each contract entering the eleventh year. Contracts based on forecasts made in 1983 began at about 5 cents/kilowatt-hour (kWh), ramping up to approximately 14 cents/kWh in 1997. Current forecasts of about 5 cents/kWh are less than one-third of the fixed payment. These revenue reductions are of particular concern to wind projects with outstanding loans extending beyond the 10th year.

Some California wind farm operators are responding to challenges facing the industry by planning for or initiating project redevelopment at existing wind sites with optimum wind resources. Repowering wind farms by upgrading existing equipment or replacing aging turbines with newer equipment offers benefits such as higher efficiency and generating capacity as well as lower operating and maintenance costs associated with maintaining older equipment.

Although the California wind industry's capacity factor, efficiency and output has steadily increased since 1985, statewide wind output for 1995 took a drop. The record 3.2 billion kWh of electricity generated in 1994, declined to 2.9 billion kWh in 1995. This figure, however, is higher than the 2.8 billion kWh produced in 1993, and represents enough output to meet the annual electricity needs of more than 500,000 typical California homes.

In previous years, it was assumed that the statewide capacity factor had leveled off at 20 percent; however, capacity factor performance continues to be higher at 21 percent in 1995. When turbines installed since 1985 were isolated, the capacity factor climbs to 26 percent. The statewide capacity factor would be even higher if turbines installed in the mid- to late-1980s were not considered.

Decreased electricity production in 1995 may have resulted from one or a combination of factors, including low availability of the wind resource and operators idling their turbines to lower costs. Other reasons may be due to the lack of market demand for wind generated electricity and the expiration of interim standard offer contracts.

WPRS Background

What Commission Efforts Led to the Wind Project Performance Reporting System?

The California Energy Commission (Commission) Wind Program was initiated in 1977 and later expanded in 1978 with the passage of California Assembly Bill 2976 authored by Assemblyman Henry Mello. The Mello bill required the Commission to implement a state wind energy program to expedite the commercialization of utility-scale wind turbines. The Commission was responsible for: assessing wind resources throughout California; operating a public wind information center; testing wind turbines; and conducting research to support development of large-scale prototype wind turbines.

When the industry began exponential growth in 1981, the Commission and the American Wind Energy Association (AWEA) recognized the need for performance and other technology-related information. Subsequent efforts by these two organizations led to adoption of Wind Project Performance Reporting System (WPRS) regulations in 1984.

What is the WPRS Program?

California law requires the California Energy Commission to serve as a central repository in state government for the collection and dissemination of information on energy supplies. Starting in January 1985, WPRS regulations required all California wind operators with projects rated at 100 kW or more to provide quarterly wind performance reports if they sold electricity to a power purchaser (utility). WPRS reports filed by operators include actual energy production and related project information. In addition, all California power purchasers are required to file quarterly reports documenting power purchases from wind operators. The Commission compiles and evaluates this data and documents findings in quarterly and annual reports on wind industry performance in California.

Why Were WPRS Regulations Developed?

WPRS regulations were instituted for several reasons. First, the industry, investors, financial community and government agencies needed actual performance data to better evaluate the status of wind technology. Second, information that would help minimize tax abuse would benefit everyone involved in wind development: the industry would generate less "bad press" and more favorable public opinion; investors would be better able to make informed investments; and government and public monies would be allocated to projects with optimal performance. WPRS regulations were intended to provide performance data useful for improved government tracking of energy supplies and better planning of the state's energy needs.

Before federal tax credits expired in 1985, project financing was primarily venture capital from private investors willing to take a substantial risk on the technology due to available tax benefits. Since the tax credits expired, wind projects have focused on revenues from power sales and placed greater reliance on conventional project financing from institutional lenders and foreign investors. WPRS data also were needed to establish performance credibility with these new sources of financing.

What Information Do WPRS Reports Provide?

The WPRS Annual Report includes the following information for all wind projects in California rated at 100 kilowatts (kW) or more that sell electricity to a power purchaser: turbine manufacturers, model numbers, rotor diameters and kW ratings; the number of cumulative and new turbines installed; the projected output per turbine; the output for each turbine model; and the output for the entire project. The WPRS Annual Report is compiled from quarterly reports submitted by project operators and public utilities. Commission staff use this WPRS data to analyze wind project performance and industry production and capacity trends. The Annual Report also contains data summary tables reflecting performance statewide and by resource area; turbine size, type and origin; manufacturer; and project operator. Note that totals expressed in tables and figures may not equal 100 percent due to rounding.

Since 1985, the Commission has documented and evaluated data submitted by operators and utilities in compliance with WPRS regulations. The extensive empirical data collected and disseminated by the Commission is used by industry, utility, investor, manufacturer, government, and research and development groups to measure the performance and relative benefits of wind technology.

What Information Is Not Found in WPRS Reports?

WPRS reports do not provide information on every wind energy project in California. Non-operating wind projects are not required to report to the Commission. The absence of a project from WPRS reports typically indicates that the project is not selling any power or is rated less than 100 kW. Other unreported capacity includes turbines that do not produce electricity for sale, such as turbines installed by utilities, government organizations and research facilities. Additional unreported capacity results when operators fail to file. Installed capacity for these operators cannot be confirmed and only kWh production verified from utility reports is included in WPRS reports.

WPRS reports cannot always account for the impact turbine age has on performance because turbines are often reported in groups combining old and new machines. To track improvements in technology, new turbine performance has been analyzed separately where possible.

The limited number of developers installing new capacity precluded adequate confidentiality of cost data. Therefore, aggregate cost data have not been included in the 1995 Annual Report.

What Limitations Should Be Considered Before Using WPRS Data?

although many valuable observations about California's wind industry can be drawn from WPRS data, it is important to recognize four major limitations:

WPRS Implementation Issues

Validating performance data.

It was originally intended that utility quarterly reports be used to validate operator output data; however, numerous problems occurred. Some utilities did not provide data according to calendar quarters or provided data for only those operators who filed a power sales agreement. In many cases, more than one project was reported under a single utility contract making it difficult to verify individual project output figures.

To establish a more reliable validation procedure, Commission staff allowed operators to voluntarily submit utility receipts with quarterly reports. When output figures provided by operators agree with either submitted utility receipts or utility reported data, output figures are recorded as "validated".

Operators who fail to file. Utility quarterly reports inform Commission staff of all wind farm operators with projects rated 100 kW or more who sell power. These operators are required to submit WPRS reports. Operators who sell power but do not submit reports are noted as "failed to file." During 1995, eight operators failed to file for one or more quarters. Depending on the circumstances, Commission staff consider various options for resolving filing issues.

Operators who file reports with missing data. Some operators filed WPRS reports with one or more data items missing. The predominant missing data item was projected quarterly output per turbine. Some wind projects reported only annual output estimates. In such cases, no value has been assigned. Commission staff continue to assist project operators with reporting so that data submitted will be complete.

California Wind Resource Areas

The wind resource map on this page includes the geographical location of, and quality associated with, major wind resource areas in California. During 1995, wind performance data was received from operators with projects located in the following five resource areas:

Wind Map


  • altamont Pass
  • Pacheco Pass
  • San Gorgonio Pass
  • Tehachapi Pass

Not Shown:

  • Solano (Solano County)

Areas designated "good" are roughly equivalent to an estimated mean annual power, at 10 meter height, of 200 to 300 Watts per square meter (W/m2), and "excellent" if more than 300 W/m2.

Source: A. Miller and R. Simon, Wind Power Potential in California, San Jose State University, prepared for the California Energy Commission, May 1978.

Staff Summary

Industry Performance

Total Capacity. A cumulative capacity of 1,523 megawatts (MW) was reported operational during the fourth quarter of 1995. The 1.08 MW of new capacity installed during 1995 was lower than previous years. Cumulative capacity also declined due to continued attrition of older turbines.

Electricity Output. In 1995, the California wind industry produced more than 2.9 billion kWh of electricity, enough power to meet the annual electricity needs of almost 500,000 typical California homes. The amount of electricity generated during 1995 declined from 1994, yet has exceeded all previous years including 1991 and 1992 when reported installed capacity was higher.

Electricity Production Percent of Projected. although California wind projects generate a substantial amount of electricity, the industry as a whole produced only 78 percent of the total output projected for 1995. This figure is a decline from the 79 percent of total projected output attained in 1994, yet is a significant improvement from the 45 percent of total projected output attained in 1985. Because many wind developers overstated output capabilities during the tax credit era, a number of older turbines with overstated projections lower the total average statewide percent of projected output. When turbines installed since 1985 are isolated, the percent of projected output for 1995 rises to 88 percent.

Capacity Factor. Capacity factor is defined as the ratio of actual energy output to the amount of energy a project would produce if it operated at full rated power for 24 hours per day within a given time period. As indicated previously, there should be standardized testing of all wind turbines for capacity factors to be truly comparable. With no such program, wind turbine ratings currently are based on widely varying test conditions and miles-per-hour specifications. Voluntary standards for testing wind turbines, however, have been developed by the American Wind Energy Association (AWEA).

Despite testing limitations, the capacity factor is still considered a strong indicator of wind project performance. The annual capacity factor is computed as the average of quarterly capacity factors calculated for each group of turbines reported. Only operating turbines are used to calculate capacity factors so that performance results are not skewed by non-operational capacity. For projects with new turbines, only one-half of new capacity is included in the capacity factor calculation during the quarter of installation because new turbines are not likely to operate for the entire quarter in which they are installed and new equipment typically needs a "debugging" period before operating at fully rated power.

The resulting statewide capacity factor for 1995 is 21 percent. although the capacity factor has decreased nine percent from 1994, current output represents almost a 62 percent increase from the 13 percent capacity factors for 1985 and 1986 (Figure 1). The upper limit capacity factor achieved by some California wind projects continues to exceed 30 percent. In particular, one project has consistently reached this upper limit, including an annual capacity factor of 35 percent in 1995.

Note that statewide average performance is still adversely affected by a number of older turbines that are less reliable and efficient than those currently being installed. When wind turbines installed since 1985 are isolated, the capacity factor rises to 26 percent (Figure 2).{ 2 }

kWh-per-square-meter results because data reported for some turbine models include new turbines that have not had the benefit of a full operational year. When any kWh-per-square-meter calculation does not include a full operational year for all turbines, an asterisk has been placed next to the value on all summary tables in Section 6 (not included in HTML / on-line version).

FIGURE 1: Statewide Capacity Factors 1985-1995

Figure 01

FIGURE 2: Capacity Factors for Turbine Stock

Average kWh-per-square-meter annual production for 1995 was 732, an eight percent decrease from the 798 kWh per square meter recorded for 1994. When turbines installed since 1985 are isolated, however, the resulting kWh-per-square-meter annual production figure increases to 853 (Figure 3).

Figure 02

FIGURE 3: kWh-Per-Square-Meter Production of Turbine Stock

Figure 03



During 1995, 1.08 MW of new capacity was installed in California (Figure 4). This new capacity was significantly lower than the 54 MW installed in 1994 and 9 MW installed in 1993. Total installed capacity decreased due to continued attrition of older turbines.

Figure 04

FIGURE 4: Statewide Wind Capacity

Wind output during 1995 was consistent with the typical California wind resource profile: low winds at the beginning and end of the year and high winds during spring and summer when the warmer seasons create a natural draw of cool coastal air into hot inland valleys and deserts. WPRS data indicates that 74 percent of all annual output was produced in the second and third quarters of 1995 (Figure 5). This is a good seasonal match to California's peak demand for electricity during summer months. Quarterly capacity factors were consistent with the California wind resource profile previously discussed. The statewide capacity factors for 1995 were 10, 34, 29 and 12 percent respectively for the first, second, third and fourth quarters.

Figure 05

FIGURE 5: Statewide Wind Output (Millions of kWh)

The 2.9 billion kilowatt hours of electricity produced by California wind project operators during 1995 decreased from 1994, yet exceeded production for all previous years including 1991 and 1992 when reported installed capacity was higher. (Figure 6). Decreased production during 1995 may result from low availability of the wind resource. Other reasons may be due to the lack of market demand for wind generated electricity and the expiration of interim standard offer contracts.

Figure 06

FIGURE 6: Statewide Wind Output 1985-1995

Resource Areas

although wind project operators from five different resource areas in California reported to WPRS, about 95 percent of all California capacity and output is generated in only three resource areas: altamont, San Gorgonio and Tehachapi. All three of these areas are narrow mountain passes leading into hot valley or desert regions. Among these three resource areas, 41 percent of all capacity is found in Tehachapi, more than 36 percent in altamont, and about 18 percent in San Gorgonio resource areas (Figure 7).

Figure 07

FIGURE 7: Resource Area Capacity

When resource area capacity (Figure 7) and percent of total statewide output (Figure 8) for the three primary resource areas are compared, Tehachapi (41 percent output at 41 percent capacity) produced output equal to the percentage of capacity, and San Gorgonio (23 percent output at 18 percent capacity) produced more than its share, and altamont (32 percent output at 36 percent capacity) produced less than its share.

Figure 08

FIGURE 8: Resource Area Output (Millions of kWh)

Of the three largest resource areas, San Gorgonio had the highest capacity factor (29 percent), followed by Tehachapi (22 percent) and altamont (18 percent). Solano and Pacheco, two smaller resource areas, had capacity factors of 18 percent and 15 percent respectively (Figure 9).

When comparing resource area performance, many factors should be considered. For example, age of equipment appears to be a significant factor affecting the performance difference between San Gorgonio and altamont. The altamont resource area includes two large developers with very old capacity, significantly lowering altamont's overall performance. San Gorgonio wind developers met substantial delays getting local government approval for their projects, thus their equipment is newer.

Figure 09

FIGURE 9: Capacity Factor by Resource Area

Turbine Size

About 46 percent of all new capacity installed in 1995 was in the 201+ kW size category (Figure 10). although the 51-100 kW turbine size still accounts for slightly less than one-half of all cumulative capacity, this percentage share may decrease over time as smaller, older turbines are permanently retired from service.

Capacity factor performance in 1995 is highest for turbines in the 201+ kW size range (Figure 11). Further, a comparison of cumulative capacity and percent share of kWh output reveals that larger turbines in the 201+ kW range produced more than their share at 35 percent output and 30 percent capacity (Table 1).

1995 Capacity & Output by Turbine Size
Size Cum. Capacity
(% of Total)
New Capacity
(% of Total)
kWh Output
(% of Total)
1-50 2 0 2
51-100 48 11 42
101-150 15 0 14
151-200 4 25 4
201+ 30 64 35
Failed to File --- --- 3

[ FIGURE 10: 
		Capacity by Turbine Size] [Capacity
		Factor by Turbine Size]

Turbine Type

FIGURE 12: Capacity Factors by Turbine Axis

WPRS performance results also have been categorized by horizontal or vertical axis machines. When comparing performance of horizontal and vertical turbines, it should be recognized that vertical axis turbines used in California at the present time represent relatively old technology. No new capacity has been added since 1986.

The California wind industry continues to be dominated by horizontal axis machines accounting for 95 percent of all capacity and 100 percent of new capacity. Comparison of performance indicates a 22 percent capacity factor for horizontal axis turbines compared to a 9 percent capacity factor for vertical axis turbines (Figure 12).

Figure 12

FIGURE 13: kWh Per Square Meter Production by Turbine Axis

Performance by kWh per square meter was 741 for horizontal axis turbines compared to 487 for vertical axis turbines (Figure 13). WPRS data does not explain why the variation in kWh per square meter performance between horizontal and vertical axis turbines is so much less than the difference in capacity factor performance.

Note that other important turbine characteristics such as downwind and upwind configurations, number of blades, fixed or variable pitch blades, and braking devices are not tracked in WPRS reports.

Figure 13

Domestic and Foreign Turbines

By the end of 1995, capacity from foreign made turbines was 869 MW, compared to 654 MW from domestic turbines. During 1995, .18 MW of domestic and .9 MW of foreign turbine capacity was installed (Figure 14).

A comparison of capacity distribution for domestic and foreign turbines in 1985 and 1995 is shown in Figure 15. For a more complete historical perspective, cumulative and new capacity for domestic and foreign turbines is shown in Table 2.

Figure 14 Figure 15
1985-1995 Capacity Distribution by Turbine Origin
Year Domestic (%) Foreign (%)
Cum. New Cum. New
1985 67 55 33 45
1986 55 25 45 75
1987 56 49 44 51
1988 58 87 42 13
1989 52 17 48 83
1990 53 45 47 55
1991 46 4 54 96
1992 47 39 53 61
1993 45 58 55 42
1994 46 74 54 26
1995 43 17 57 83

The overall capacity factor results of foreign turbines (23 percent) exceeds that of domestic turbines (19 percent). Both foreign and domestic turbine stock benefit from the inclusion of newer, more efficient machines. Historically, the performance of the domestic turbine stock has been more adversely affected by older, less efficient turbines. When turbines installed since 1985 are isolated, the performance gap narrows. The capacity factor of domestic turbines increases from 19 percent to 28 percent, while that of foreign turbines increases from 23 percent to 25 percent (Figure 16). The improvement in capacity factor for domestic turbines may result from the retirement of old turbines with poor performance and the addition of newer, more efficient turbine stock.

The impact of other variables on domestic turbine performance is demonstrated by two large projects in the altamont resource area with more than 139 MW of turbine capacity and an average capacity factor of only 13 percent. Domestic turbines account for 110 MW of the 139 MW capacity with only a 9 percent capacity factor. When these two projects are eliminated from the domestic turbine base, the adjusted capacity factor increases to 21 percent (Figure 17).

Figure 16 Figure 17

Analysis of kWh-per-square-meter performance data indicates that foreign turbine performance (774) is about 13 percent higher than domestic turbines (671) without any adjustments (Figure 18). It should be noted that when newer turbines installed since 1985 are isolated, kWh-per-square-meter production for both domestic and foreign turbines normally increases.

As a general rule, the kWh-per-square-meter measure is comparatively better than the capacity factor measure when evaluating domestic turbine performance. This is because overstated capacity ratings for older domestic turbines appear to significantly reduce capacity factor performance.

Figure 18

The 10 Largest Wind Turbine Manufacturers

The 10 largest wind turbine manufacturers represent about 93 percent of California's wind generating capacity. The five largest manufacturers alone (Kenetech, Vestas, MWT, Micon and FloWind) account for more than 76 percent of all capacity. The 10 largest manufacturers and their individual generating capacities are shown in Figure 19. A wide range of capacity factors exist among these manufacturers (Figure 20). Manufacturers with the highest capacity factors are Danwin (27 percent); MWT (24 percent); Vestas (24 percent); Bonus (23 percent); Micon (23 percent); and Kenetech (22 percent). It should be noted that capacity factor performance for all but one of the 10 largest manufacturers, (FloWind), decreased from the previous year. Also, note that Fayette is no longer reporting, and has been substituted by Howden as one of the largest manufacturers.

Both equipment and siting variables should be considered when evaluating turbine manufacturer data. Manufacturers with older turbine stock are more adversely affected relative to their total performance. The overall quality of a particular resource area also has considerable impact on reported performance of turbines sited in that area. Higher capacity factors for some specific turbine types may result from their concentration at particularly good sites within high quality resource areas.

Figure 19 Figure 20

Annual kWh-per-square-meter results are shown for the ten largest manufacturers in Figure 21. Manufacturers with the highest kWh-per-square-meter production are Danwin (893), MWT (883), Vestas (796), Kenetech (744) and Bonus (729). KWh-per-square-meter performance for all of the 10 largest manufacturers decreased from the previous year.

Figure 21

The Five Largest Wind Project Operators

The 1995 Annual Report continues to focus on the five largest wind project operators due to industry consolidation and growth primarily limited to major developers. The five largest wind project operators include Kenetech, SeaWest, Zond, FloWind and Cannon. These five operators alone account for 1,276 MW, representing almost 84 percent of total California wind generating capacity (Figure 22). Note that Arcadian is no longer reporting and has been substituted by Cannon as one of the five largest wind project operators.

Capacity factors for the largest wind project operators are quite varied (Figure 23). Operators with the highest capacity factors are Cannon (26 percent); SeaWest and Zond (23 percent); Kenetech (22 percent); and FloWind (13 percent). It should be noted that one smaller operator, San Gorgonio Farms (not shown in Figures 22 and 23), has consistently produced the highest capacity factors for every year WPRS data has been compiled and published, including a 35 percent capacity factor for 1995. This project is significant because it consistently demonstrates the impressive potential for wind technology performance when developers combine quality machines and maintenance programs with a good wind resource site.

Annual kWh-per-square-meter results for the five largest operators are shown in Figure 24. Among the five largest operators, Cannon (831), Zond (764), SeaWest (761), and Kenetech (738) had the best performance. It should also be noted that two smaller wind project operators (not included in Figure 24) also had impressive kWh-per-square-meter production during 1995. These operators are San Gorgonio Farms (1,153), and AB Energy (1,100).

FIGURE 22: Cumulative Capacity for 5 Largest Operators

Figure 22

FIGURE 23: Capacity Factors for 5 Largest Operators

Figure 23

FIGURE 24: kWh-Per-Square-Meter for 5 Largest Operators

Figure 24


  1. Calculated from "Windpower: Clean Energy for the 21st Century", AWEA, 1996.
    Return to Text.
  2. All calculations of the turbine base "Since 1985" in this report exclude 3,430 100kW turbines in altamont because the project operator is reporting kWh production in the aggregate. Some of these turbines were installed prior to 1985 and some were not. Since the operator is reporting a single electricity-produced figure for this mixed turbine base, performance calculations in the category "Since 1985" cannot be made.
    Return to Text.


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