Solar Radiation, Plane-of-Array, Uncertainty, Pyranometer, Reference Cell
Summary / Abstract:
Irradiance is one of the most important parameters for the solar industry. However, it is very challenging to measure accurately, therefore it is all the more important to quantify the uncertainty of irradiance measurements. Current best practices tend to use worst-case assumptions and apply them more-or-less uniformly, possibly leading to overly pessimistic uncertainty evaluations. In this work we evaluate the uncertainty of individual tilted irradiance measurements of time series data using two different approaches: first, we compare the measurements from five different devices of each type operating in parallel for a GUM type A evaluation; and second, we calculate the uncertainty associated with several key properties of the instruments (spectral response, directional response, temperature response) and combine them in a GUM type B evaluation for comparison. Correlations seen between the A and B results in one year of data at two very different sites indicate that the second method should be suitable for uncertainty evaluations in other locations.