SPLTRAK Abstract Submission
Effective Irradiance Monitoring Using Reference Modules
Jennifer L. Braid1, Joshua S. Stein1, Bruce H. King1, Christopher Raupp2, Jaya Mallineni2, Justin Robinson3, Steve Knapp3
1Sandia National Laboratories, Albuquerque, NM, United States
/2SOLV Energy, San Diego, CO, United States
/3GroundWork Renewables, Holladay, UT, United States

We evaluate the use of reference modules for monitoring effective irradiance in PV power plants, as compared with traditional plane-of-array (POA) irradiance sensors, for PV monitoring and capacity tests. Common POA sensors such as pyranometers and reference cells are unable to capture module-level irradiance nonuniformity and require several correction factors to accurately represent the conditions for fielded modules. These problems are compounded for bifacial systems, where the power loss due to rear side shading and rear-side plane-of-array (RPOA) irradiance gradients are greater and more difficult to quantify. The resulting inaccuracy can have costly real-world consequences, particularly when the data are used to perform power ratings and capacity tests. Here we analyze data from 2 bifacial single-axis tracking PV power plants, (175.6 MWdc and 135.5 MWdc, respectively) consisting of a total of 8 meteorological (MET) stations, located on corresponding inverter blocks with capacities over 4 MWdc. Each MET station consists of bifacial reference modules as well pyranometers mounted in traditional POA and RPOA installations across the PV power plants. Short circuit current measurements of the reference modules are converted to effective irradiance with temperature correction and scaling based on flash test or nameplate short circuit values. Our work shows that bifacial effective irradiance measured by pyranometers averages 3.5% higher than the effective irradiance measured by bifacial reference modules, even when accounting for spectral, angle of incidence, and irradiance nonuniformity. We also performed capacity tests using effective irradiance measured by pyranometers and reference modules for each of the 8 bifacial single-axis tracking inverter blocks mentioned above. These capacity tests evaluated bifacial plant performance at ~3.2% lower when using bifacial effective irradiance from pyranometers as compared to the same calculation performed with reference modules.