Solar Radiation Data Manual
Flat-Plate and Concentrating Collectors

Table of Contents


Technical Background

The solar radiation data in this manual are based on the National Solar Radiation Data Base (NSRDB),Version 1.1, which was completed in March 1994 by the National Renewable Energy Laboratory. Version 1.1 supersedes Version 1.0, which was completed in August 1992. Differences between the two versions are described briefly in the Appendix. The NSRDB contains hourly values of measured or modeled solar radiation and meteorological data for 239 stations for the 30-year period from 1961-1990. A complete description of the NSRDB and how it was produced is presented in its user's manual (NSRDB-Vol. 1, 1992).

There are two types of stations in the NSRDB: primary (denoted by asterisks on the station map) and secondary (denoted by dots on the station map). Primary stations, of which there are 56, measured solar radiation for a part (from 1 to 27 years) of the 30-year period. The remaining 183 stations made no solar radiation measurements and have modeled solar radiation data that are derived from meteorological data such as cloud cover. They are designated secondary stations. Both primary and secondary stations are National Weather Service stations that collected meteorological data for the period of 1961-1990.

Succeeding the older 1952-1975 SOLMET/ERSATZ data base, the NSRDB accounts for any recent climate changes and provides more accurate values of solar radiation for several reasons:

A comparison of the old and new data bases provides the incentive for developing new solar radiation resource products such as this data manual. On an annual basis, 40% of the NSRDB and SOLMET/ERSATZ stations are in disagreement for global horizontal radiation by more than 5%, with some stations showing disagreement of up to 18% (Marion and Myers 1992). For direct beam radiation, 60% of the NSRDB and SOLMET/ERSATZ stations are in disagreement by more than 5%; some stations show disagreement of up to 33%. Disagreement between the two data bases is even greater when compared on a monthly basis. Most of the disagreement is attributed to differences in the instruments' calibration procedures and models.

This manual presents monthly and yearly average solar radiation values for various flat-plate and concentrating collectors to enable quick estimates of the incident solar energy for common collectors. The solar radiation values were computed using a model and NSRDB hourly values of direct beam and diffuse horizontal solar radiation. Climatic data were obtained from the NSRDB and from climatic data sets provided by the National Climatic Data Center, Asheville, North Carolina. The Appendix describes in more detail how this manual was produced.

NSRDB-Vol. 1 (1992). User's Manual-National Solar RadiationData Base (1961-1990). Version 1.0. Asheville, NC: National Climatic Data Center.

Marion, W.; Myers, D. (1992). A Comparison of Data from SOLMET/ERSATZ and the National Solar Radiation Data Base, NREL/TP-463-5118, Golden, CO: National Renewable Energy Laboratory.

Interpreting the Data Tables

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