WEST Associates Online User's Manual

The WEST Associates Online User's Manual describes the Western Energy Supply and Transmission (WEST) Associates Solar Resource Evaluation Project and its resulting data.

Contained in this manual are general results from 52 solar monitoring stations in the Southwest that operated for various periods between mid-1976 and 1980. Also see the WEST Associates Solar Monitoring Network data files.

The annual reports from which this online manual is gleaned were prepared by the Southern California Edison Company (SCE) under contract with WEST Associates. These reports contain statistics and graphs for all stations active during the reporting year and maps of the WEST associates solar monitoring network. West Associates funded SCE for the project management, while station instrumentation, site, and maintenance costs for each station were borne by the representative utilities.


Roster of Members


Data Collection and Storage

General Observations and Summary

Data Format Description

Roster of Members of WEST Associates

Arizona Electric Power Cooperative Inc.

Arizona Power Authority

Arizona Public Service Co.*

Anaheim Utilities Department

Burbank Public Service Department

Colorado Springs Department of Public Utilities

Glendale Public Service Department

Los Angeles Department of Water & Power*

Pasadena Water & Power Department

Colorado-Ute Electric Association Inc.

El Paso Electric Company*

Nevada Power Company*

Pacific Power and Light

Public Service Co. of Colorado*

Public Service Co. of New Mexico*

Salt River Project*

San Diego Gas & Electric Co.*

Sierra Pacific Power Co.*

Southern California Edison*

Tucson Gas & Electric*

* Participant in the Solar Resource Evaluation Project


The Southwest has long been known as an area having an abundance of sunshine. This abundance has led to an increasing interest in supplementing fossil fuels with solar energy for use in space heating, water heating, industrial processes, and generation of electricity. This project was designed to provide data that could be used for solar equipment design and evaluation of various solar technologies.

In the course of initial technical assessments of solar energy applications in Southern California, SCE recognized the need to have accurate incident solar radiation (insolation) information. However, the existing data base was inadequate.

In mid-1975 SCE installed the first of its 21 solar monitoring stations at Barstow, California, in a program to establish an accurate solar data base. A proposal was submitted to WEST Associates to expand the solar monitoring effort outside of the SCE service territory. The project, as approved, created the WEST Solar Monitoring network, which included stations in six western states (Arizona, California, Colorado, Nevada, New Mexico, and Wyoming). The first station outside of SCE's service territory was installed in mid-1976 at Tucson, Arizona.

Thirteen stations reported data in the first West Associates Network publication in 1976. All told, during the approximately four and one-half years of networks operation, 52 stations gathered data on global horizontal insolation and ambient temperature. Twenty-six of these also reported direct normal insolation measurements.

Station instrumentation, site, and maintenance costs for each station were borne by the respective utilities. WEST Associates funded the project management portion of the program, which provided (through SCE) calibration of instruments, translation and storage of data, data reduction (summaries and graphs), and production of annual reports. The utility operating the station provided monitoring equipment, a site, station setup costs, maintenance, and data tape changeout.


A number of stations also measured direct insolation. This information shows the amount of energy available to concentrating collectors, such as the high-temperature collectors needed for electric power generation. Direct insolation was measured with the Eppley Normal Incidence Pyrheliometer (NIP).

The WEST procedures called for maintenance to be performed once per week at stations that monitored total insolation and dry bulb temperature. At this time the pyranometer dome was cleaned and the electronics package checked for correct operation. At stations that also monitored direct insolation, additional procedures called for maintenance to be performed three times per week. During this maintenance, the pyrheliometer was cleaned, and adjustments for declination and azimuth were made on the tracking mount.

All solar instruments on the network were calibrated to the Absolute Scale (SI units). This scale is about two percent higher than the Internal Pyrheliometric Scale of 1956 used in the 1976 data report.

SCE's goal was to calibrate all instruments on the network twice per year. To calibrate the pyrheliometers, SCE obtained a cavity radiometer. Pyrheliometers were calibrated side by side in sunlight, near noon, under clear sky conditions and only after waiting a suitable length of time for temperature stabilization. All solar instruments on the network were calibrated to the Absolute Scale (SI units).

Pyranometers underwent two different tests to assure a valid calibration: the Sun and Shade method and a side-by-side comparison with a reference pyranometer. The pyranometers are also checked for cosine and azimuth response calibrations.

Data Collection and Storage

Instrument outputs were converted by the electronics package to a series of pulses. These pulses were recorded on magnetic tape by equipment compatible with the SCE Data Acquisition System existing at the time the network was active. These tapes were changed once per month and sent to SCE's Data Acquisition Translator/Computer Facilities, where the data were read from the tapes and placed on the main data base as 15-minute average values. All data were recorded using local standard time as a time base.

Over the first three years, data losses ranged from 3 to 6 percent on the complete network. In 1979 when 3.9 million data points were collected at 50 solar monitoring by stations, 7.6 percent were lost. It should be noted that most of the data losses occurred at a few stations that experienced instrument or maintenance problems. Most stations had very small amounts of lost data. It should also be noted that direct insolation measurements require much more attention to produce good data.

General Observations and Summary

While compiling the data for its annual reports on the WEST Associates network, Southern California Edison made certain observations regarding the solar energy level and its distribution in the Southwest. To aid in explaining these observations, 10 tables have been included to show the total horizontal and direct normal insolation for the last five years. It should be noted that all solar instruments are calibrated to the Absolute Scale (SI units). All values shown in the tables are in kWh/sq m-day.

Table 1: Average Daily Total Insolation, 1980

Table 2: Average Daily Direct Insolation, 1980

Table 3: Average Daily Total Insolation, 1979

Table 4: Average Daily Direct Insolation, 1979

Table 5: Average Daily Total Insolation, 1978

Table 6: Average Daily Direct Insolation, 1978

Table 7: Average Daily Total Insolation, 1977

Table 8: Average Daily Direct Insolation, 1977

Table 9: Average Daily Total Insolation, 1976

Table 10: Average Daily Direct Insolation, 1976

General Observations

Not all stations were in operation for the entire year for each of the years they were members of the solar monitoring network. Annual averages were computed only for stations having 12 months of data out of the year for which the average is computed.

On the average, solar data collected during 1980 were very similar to 1979, with 1976 data values still the highest measured (see Table 1). The year 1976 was characterized by drought conditions in the southwest United States. This condition led to what now appears to have been a higher than average insolation year. Solar data collected during 1979 were, on average, mostly higher than 1978. The years 1979 and 1980 had substantial rainfall during the first three months of the year while the rest of the year was fairly clear with no major storm activity.

Long-Term Observations

Over the five years that data were collected by the WEST network, some long-term averages have been established. For those stations that had operated for several years, Lancaster, California, and Yucca Valley, California, had the highest annual averages (5.90 and 5.88 kwh/sq m-day, respectively). These averages also show that 1976 was a very good year for solar radiation, exceeding all following years in most cases. The stations with the lowest total insolation averages have not been in operation for as long a period. From the data gathered, the Denver #2, Colorado, station had the lowest annual average. The two-year average for this station is 4.46 kwh/sq m-day. This station is closely followed by Cheyenne, Wyoming, and Saguaro, Arizona.

The long-term direct insolation annual averages show that Ridgecrest, California, and Yucca Valley, California, had the highest annual averages (7.85 and 7.83 kwh/sq m-day respectively). The lowest average comes from the downtown Los Angeles, California, monitoring station (5.11 kwh/sq m-day). The other Los Angeles Basin stations are also low due to the presence of fog and air pollution.


At the end of 1980, several of the WEST monitoring stations had been in operation for five years. The five-year averages from these stations approach what could be called the station long-term average.

Information on the WEST network, its organization, and maintenance was shared with the Department of Energy, National Oceanic and Atmospheric Administration, the National Weather Service, and their contractors who worked with the national solar data network.

This online manual was drawn from the annual reports prepared for the WEST Associates Solar Resource Evaluation Project by Southern California Edison.

Data Format Description

The data are presented in 52 files, one for each station. All of the data for a single station, up to six years, are in the file for that station. At the top of each file is a single header line containing the name of the station site, the site latitude and longitude, and the site elevation.

The files are divided into blocks of 100 lines, each block representing one day. The first two lines of each block except the first are column headings; the first line of the first block is the file header. The first line of the column headings indicates what is represented in each column. From left to right these are the year, month, day, and ending minute of the measurement, global horizontal radiation, direct normal radiation, and temperature. The second line of the column headings lists, in parentheses, the units used for the measured quantities. The next 96 lines of each block are data lines followed by two blank lines, except in the first block of each file. In the first block only one blank line follows the data. The block structure is indicated in Table 11.

The data are fifteen-minute averages of global horizontal and direct normal radiation, and ambient temperature. The first quarter-hour's data of any day represents the period from midnight (00:00) to fifteen minutes after midnight (00:15). The last fifteen minutes of the day represent the period 23:45 to 24:00. Missing data are represented by 9999.00, while data not recorded (e.g., direct normal radiation at El Cajon) is represented by -999.99. The data format is (5I3, F9.2, 2 (2x, F9.2)).