Our Photovoltaic (PV) Device Performance group is accredited by the American Association for Laboratory Accreditation (A2LA) to ISO-17025 standards for primary reference cell, secondary reference cell, and secondary module calibrations for samples that meet the requirements.
This accreditation gives our results the same stature as those performed by a national metrology laboratory such as the National Institute of Standards and Technology (NIST). See the 17025 certificate of accreditation.
All numerical values reported by our group outside the scope of the ISO 17025 accreditation are accredited to ISO 9001 standards by Orion Registrar. The ISO 9001 quality system follows the group's ISO 17025 quality systems with the notable exception of a formal calibration certificate, and uncertainty analysis has not been reviewed by the auditor. There are other minor deviations such as the lack of a check list for ISO 9001 calibrations. See the 9001 certificate of accreditation.
We provide certified efficiency and other performance parameters to validate the entire range of PV technologies. Our facility for calibrating primary reference cells, located at the National Renewable Energy Laboratory, is one of four facilities certified in accordance with the World Photovoltaic Scale (WPVS).
We cooperate internationally through intercomparisons and technical interactions to provide the PV community with a path of traceability to standards.
We help to develop consensus in U.S. and international PV standards by participating in American Society for Testing and Materials (ASTM) and International Electrotechnical Commission (IEC) standards groups.
As part of the reference cell certification process, it is necessary to determine that the reference detector responds linearly with total irradiance. We determine the linearity of the short-circuit current (Isc) vs the total irradiance (Etot) by illuminating a prospective reference cell with two lamps. The irradiance range is about 0.01-sun to several suns. A device is linear if the current measured with both lamps illuminating the cell is the same as the sum of the currents with each lamp illuminating the cell. The two-lamp method is insensitive to the light spectra or spatial nonuniformity changing with irradiance.
To calibrate the cells, we concurrently measure Isc, Etot, and spectral irradiance outdoors with the same field of view (5.0). Total irradiance is measured with an Eppley HF primary absolute-cavity radiometer. Spectral irradiance is measured with an ASD Spectro-Pro spectroradiometer and is extended using a comprehensive spectral model derived from Modtran. From these measurements, we calculate an average corrected calibration value, which relates the cell's Isc to Etot. The atmospheric parameters and cell temperature are also measured. Once a valid calibration value is obtained, the Isc is corrected for temperature and spectrum to the standard conditions.
C.R. Osterwald, K.A. Emery, D.R. Myers, and C.J. Riordan, "Extending the Spectral Range of Silicon-Based Direct-Beam Solar Spectral Radiometric Measurements," Proc. 20th IEEE Photovoltaic Specialists Conf., Las Vegas, NV, September 2630, 1988, pp. 12461250, IEEE, New York, 1989.
C.R. Osterwald, K.A. Emery, D.R. Myers, and R.E. Hart, "Primary Reference Cell Calibrations at SERI: History and Methods," Proc. 21st IEEE Photovoltaic Specialists Conf., Orlando, FL, May 2125, 1990, pp. 10621067, IEEE, New York, 1990.
C. Osterwald and K. Emery, "Spectroradiometric Sun Photometry," Journal of Atmospheric and Oceanic Technology 17, 11711188 (2000).