were organized by discipline, including several that bring measurement science to bear on the photovoltaic technologies area.
The Goal of Measurement Traceability
Why do measurements matter? They make possible the research collaboration and commercialization of products that underpin innovation and trade.
To illustrate his answer, Dr. Rochford described the recent international comparison of solar module ratings. Published three years earlier, these ratings were based on an experiment by NREL that sent solar modules to major laboratories around the world. These modules were of four kinds: monocrystalline silicon, thin-film silicon, cadmium telluride, and cadmium-indium-selenide (CIS). On the CIS system, a measurement spread of almost 9 percent was found about a mean. “The graph has taken eight participants’ measurements and assumed that the mean is the right value. That’s not necessarily true.” He also said that the accuracy was not sufficient. “Our role is to create measurement traceability,” he said. “As the National Metrology Institute for the U.S. our job is to be able to trace measurements to the international system of units. By providing measurement traceability, we can strengthen comparisons of measurements across companies, nations, and laboratories. To facilitate trade, the companies, vendors, and other participants have to agree on what a product is, and agreement is based on measurement. Also, if you want to innovate efficiently, you have to be able to accurately measure product characteristics throughout the R&D process so you can share results and perform reproducible engineering production and even reproducible research.” For these reasons, he said, NIST provides traceability to many places, for example NREL, which does PV measurements for a variety of vendors. At the top level, NIST ensures that all the units are traceable internationally by working with international partners and other national metrology institutes.
In addition to the high-level metrology, NIST also offers develops measurement science and services. For example, the Building and Fire Research Laboratory (BFRL) seeks to improve measurements needed to certify and model net zero buildings. Recently the Institute developed a new high-speed radiometer to measure the performance of PV panels, allowing the industry to move away from over-reliance on a single standard artifact. In some industries, he said, metrology is often limited to a single “golden sample,” in the assumption that a certain test piece is of adequate quality, stability, and suited to the measurement problem, but this makes broad applicability very difficult.
BFRL, he said, is building simulation tools to improve evaluation of energy usage in buildings. Because solar energy is just one aspect of this challenge, the lab has gathered data and modeled buildings in a variety of applications to bring a better understanding of how to perform simulations. This will enable better economic and energy budget analyses of buildings.