RReDC: an on-line resource

by M Rymes NREL, USA

The Renewable Resource Data Center, or RReDC (pronounced "Red Sea"), is an Internet site at http://rredc.nrel.gov that provides renewable energy resource information for the United States. In addition, the RReDC site provides links to relevant sources of renewable resource information throughout the World. The site includes publications, data, summaries, tutorials, and maps.


ENTECH, Inc. uses RReDC data to develop PV systems like this 100 kW plant in Texas.

Solar origins
The RReDC was initiated in 1993 as part of NREL's Solar Radiation Resource Assessment Project, in response to the growing number of requests for solar resource data. Since then, about 14 gigabytes of solar radiation data for hundreds of sites across the United States have been incorporated into the RReDC and are made available at no cost to the user. Researchers may obtain one year of data taken at one-minute intervals from the Solar Energy Measurement Research & Training Sites or 30 years of data and estimates taken at hourly intervals from the 239 stations of the National Solar Radiation Data Base. Available solar irradiance data types include measurements of the total energy that strikes a horizontal surface or concentrating collector, as well as the more exotic solar and sky energy spectrum and detailed mapping of the circumsolar region (the bright region near the solar disk).

Although the RReDC was originally designed to facilitate the transfer of high-quality solar energy data to researchers, the scope of its products was expanded to include monthly and annual summaries and maps of interest to a more general audience including community planners, architects, and designers of solar energy conversion systems. As the user community expanded, a glossary of solar resource terms and the overview publication Shining On were added. This has resulted in the transition of the RReDC from an exclusive, research-oriented facility to a fully-documented, educational gateway to the largest free collection of reliable renewable resource information in the USA.

Data from current solar energy measurement networks are of considerable interest to a wide range of agencies and companies that have a stake in monitoring the current solar climate. One such network is the 13-station Cooperative Network for Renewable Resource Measurements (CONFRRM)­a cooperative effort between NREL and other agencies to conduct long-term solar radiation and wind measurements at selected locations in the United States. Other data sources include a 12-station network in Saudi Arabia, and NREL's Solar Radiation Research Laboratory, which provides outdoor facilities for radiometer calibration and characterisation.

One company that has made extensive use of RReDC's solar data is ENTECH, Inc, a US firm whose 100 kW concentrator PV system at the Texas Utilities Energy Park near Dallas is shown in the photograph on the previous page.The direct normal radiation data that ENTECH obtains from RReDC have critical applications for its concentrator technology and are used to target markets and to predict how much electricity its customers could expect to get from their solar equipment.

A RReDC data field for Solar Radiation Research Laboratory solar and weather conditions.

Other resources
The RReDC's offerings have been expanded beyond solar to include biomass, wind, and geothermal energy resources data. The Biomass Resource Information Clearinghouse (BRIC) coordinates on-line biomass information sources provided by DOE, the Departments of Agriculture and Commerce, Oak Ridge National Laboratory, the US Forest Service, and others. In addition to this coordinating function, the BRIC provides a tutorial, numerous on-line documents and analyses, and an extensive portfolio of maps. Wind resource information can be found in the Wind Energy Resource Atlas of the United States and through a link to NREL's National Wind Technology Center. The Geothermal Resource Information Clearinghouse provides an annotated list of links to Internet sites with useful information about geothermal resources throughout the world.

Simple design
The RReDC design philosophy-simplicity of presentation­is clearly reflected in each of its thousands of Web pages. All data have accompanying documentation, and the sizes of large data sets are given. The pages are designed to save time and frustration, especially for users with slow computers or telecommunication lines.

Wind data are also available from RReDC.

The future
The RReDC has introduced a Codes and Algorithms section, which provides the codes (written in "C" language) for the common algorithms that NREL's solar resource researchers use. One code, for example, calculates solar position and maximum intensity for any time and place on Earth. This section will be expanded as algorithms are documented and published. In response to recent interest in the solar spectrum and ultraviolet energy, the RReDC will continue to compile all available information on these topics. The embryonic Geothermal Resource Information Clearinghouse will expand as information becomes available. The 11-station Wind Resource CONFRRM network will provide wind profiles obtained from 40 m towers, so that information on wind resources at the hub height of typical large commercial wind turbines operating today can be reviewed.

NREL's Geographic Information System (GIS) team is developing an on-line map server. Using the RReDC's underlying databases, users will be able to create customised maps to fit their needs. Initially, the data will include solar energy resources, political boundaries, roads, and cities. This combination of GIS mapping and resource data will allow users to target the regions with the best potential for renewable energy applications.

The RReDC site is maintained by the Center for Renewable Energy Resources at the National Renewable Energy Laboratory (NREL) near Denver, Colorado, USA, through funding from the US Department of Energy's (DOE's) Office of Energy Efficiency and Renewable Energy.

For more information contact the RReDC Webmaster via e-mail at: rredc@nrel.gov

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