Solar Radiation Data Manual
Flat-Plate and Concentrating Collectors

Table of Contents

Technical Background

Interpreting the Data Tables

For each of the 239 stations, a data page describes the station location, presents average solar radiation values for flat-plate and concentrating collectors, and gives average climatic conditions. Except for mean atmospheric pressure, given in millibars, Standard International (SI) units are used. To convert to other units, use the conversion factor table.

Station Description

Information at the top of each page describes the station.

Solar Radiation Data for Flat-Plate and Concentrating Collectors

For the period of 1961-1990, tables provide solar radiation data for flat-plate and concentrating collectors.

Minimum and maximum monthly and yearly averages are included to show the variability of a station's solar resource. The uncertainty of the data is presented in the table headings.

The manual includes data for the flat-plate and concentrating collectors described in the next few paragraphs.

Flat-plate collectors facing south at fixed tilt. Data are presented for five tilt angles from the horizontal: 0 ° , latitude minus 15 ° , latitude, latitude plus 15 ° , and 90 ° . Data for a tilt of 0 ° , referred to as global horizontal solar radiation, show how much solar radiation is received by a horizontal surface such as a solar pond.

Maximum yearly solar radiation can be achieved using a tilt angle approximately equal to a site's latitude. To optimize performance in the winter, the collector can be tilted 15 ° greater than the latitude; to optimize performance in the summer, the collector can be tilted 15 ° less than the latitude. Data for a tilt of 90 ° apply to collectors mounted vertically on south-facing walls and apply to south-facing windows for passive solar designs.

(Click figure to enlarge.)

One-axis tracking flat-plate collectors with axis oriented north-south. Data are presented for four different axis tilt angles from the horizontal: 0 ° , latitude minus 15 ° , latitude, and latitude plus 15 ° . These trackers pivot on their single axis to track the sun, facing east in the morning and west in the afternoon. Large collectors can use an axis tilt angle of 0 ° to minimize collector height and wind force. Small collectors can have their axis tilted up to increase the solar radiation on the collector. Just as for the flat-plate fixed tilt collector, the yearly and seasonal solar radiation can be optimized by the choice of tilt angle. The data presented assume continuous tracking of the sun throughout the day.

(Click figure to enlarge.)

Two-axis tracking flat-plate collectors Data for two-axis trackers represent the maximum solar radiation at a site available to a collector. Tracking the sun in both azimuth and elevation, these collectors keep the sun's rays normal to the collector surface.

(Click figure to enlarge.)

Concentrating collectors Direct beam solar radiation data are presented for four concentrators: one-axis tracking parabolic troughs with a horizontal east-west axis, one-axis tracking parabolic troughs with a horizontal north-south axis, one-axis concentrators with the axis oriented north-south and tilted from the horizontal at an angle equal to the latitude, and two-axis tracking concentrator systems. Direct beam radiation comes in a direct line from the sun and is measured with instruments having a field-of-view of 5.7 ° . These instruments see only the sun's disk and a small portion of the sky surrounding the sun.

(Click figure to enlarge.)

(Click figure to enlarge.)

Climatic Conditions

A table shows average climatic conditions by listing monthly and yearly values for various parameters.

Degree days indicate heating and cooling requirements of buildings. They are defined as the difference between the average temperature for the day and a base temperature. If the average for the day (calculated by averaging the maximum and minimum temperature for the day) is less than the base value, then the difference is designated as heating degree days. If the average for the day is greater than the base value, the difference is designated as cooling degree days.

Other Data Formats

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