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Best Practices Handbook Helps Industry Collect and Interpret Solar Resource Data

Read about this new comprehensive resource for the solar industry.

NREL's resource assessment and forecasting research staff provides expertise in renewable energy measurement and instrumentation. Major capabilities include solar resource measurement, instrument calibration, instrument characterization, solar monitoring training, and standards development and information dissemination.

Solar Resource Measurement

NREL's resource assessment and forecasting research staff collects high-quality solar resource and surface meteorological data. Since 1981, researchers have continuously gathered basic solar radiation information, and they now gather high-resolution data (in 1-minute intervals) from World Meteorological Organization first-class instruments, including high-resolution measured solar radiation data sets using photodiode instruments. In addition, 1-second data collection of solar irradiance in DeSoto, Florida, and Hawaii provides valuable information to study the effects of transient cloud fields on utility-scale PV systems.

Staff also perform regular cleaning and operational checks of the radiometers, data acquisition systems, and ancillary instruments, as well as annual calibrations to ensure data quality.

Measurement activities support a number of U.S. Department of Energy renewable energy programs as well as its Atmospheric Measurement Program, which applies radiometry to climate change research. Stakeholders include the DOE Solar Energy Technologies Office (SETO), solar designers/installers, policymakers, utility developers, project developers/investors/financiers, homeowners/customers/taxpayers, academia, and other national labs. To learn more about NREL's solar radiation measurement capabilities and results, see the related data and resources.

Instrument Calibration

NREL's resource assessment and forecasting researchers and metrology staff calibrate hundreds of instruments annually to ensure data quality. Calibration involves comparing an instrument output signal with a measurement standard traceable to a recognized standard to identify and eliminate deviations in accuracy. Calibration therefore allows researchers to compare data from different sources, be confident in those data, and produce better estimates of the uncertainty of a measuring instrument, system, or process.

Calibration traceability is the ability of a measurement to be related to national or international standards through an unbroken chain of comparisons with stated uncertainties. Traceability also ensures data quality and is an important part of NREL's calibration activities.

NREL's calibration facilities include the Solar Radiation Research Laboratory (SRRL), which provides ISO/IEC 17025 accredited calibration services and hosts a metrology laboratory and an optical metrology laboratory that offer well-maintained measurement references, optimum instrument mounting platforms, and automatic data acquisition systems for electrical, temperature, pressure, and optical properties. NREL provides reliable radiometric and spectral measurement and calibration services and performs annual comparisons of absolute cavity radiometers to transfer the World Radiometric Reference to researchers around the world. NREL also performs Broadband Outdoor Radiometer Calibration (BORCAL) to calibrate pyranometers and pyrheliometers using specialized software for process automation and quality assurance. Further, the staff maintains traceable references for spectral optical calibrations and measurements.

In addition, the NREL metrology team can provide:

  • Quick turnarounds (2–3 days) for calibrations
  • In-house technical assistance for measuring techniques and uncertainty evaluation
  • Special calibrations for limited instruments usage
  • Calibration data sheets with "before" and "after" data for corrective-action applications
  • A notification system to identify instruments due for calibration
  • Certificates and data for accreditation.

Because of their expertise and facilities, NREL's resource assessment and forecasting researchers and metrology staff can provide calibration services and work directly with outside metrologists to ensure calibration quality can be easily monitored.

Instrument Characterization

NREL also characterizes new instruments used to measure renewable energy resources. Researchers maintain procedures and calibration equipment traceable to national and international standards for electrical, pressure, temperature, and optical radiation measurements.

Solar Monitoring Training

Because NREL's resource assessment and forecasting research team is committed to open access to scientific data, it trains other researchers in solar monitoring network design, operation, and maintenance. Staff also provides training for meteorological measurements and experiment design. In addition, the team develops solar radiation research data-quality assessment procedures.

Standards Development and Information Dissemination

NREL's resource assessment and forecasting research team meets industry radiometric standards needs by leading the national and international consensus standards development on radiometry.

NREL's resource assessment and forecasting team also provides public access to measured and modeled solar resource data of known accuracy.