Effects of temporal averaging on short-term irradiance variability under mixed sky conditions

Abstract

Abstract. Characterizations of short-term variability in solar radiation are required to successfully integrate large numbers of photovoltaic power systems into the electrical grid. Previous studies have used ground-based irradiance observations with a range of different temporal resolutions, and a systematic analysis of the effects of temporal averaging on the representation of variability is lacking. Using high-resolution surface irradiance data with original temporal resolutions between 0.01 s 5 and 1 s from six different locations in the Northern Hemisphere, we characterize the changes in representation of temporal variability resulting from time averaging. In this analysis, we condition all data to states of mixed skies, which are the most potentially problematic in terms of local PV power volatility. Statistics of clear-sky index k * and its increments ∆k * τ (i.e., normalized surface irradiance and changes therein over specified intervals of time) are considered separately. Our results indicate that a temporal averaging time scale of around 1 s marks a transition in representing single-point irradiance variability, such 10 that longer averages result in substantial underestimates of variability. Higher-resolution data increase the complexity of data management and quality control without appreciably improving the representation of variability. The results do not show any substantial discrepancies between locations or seasons.

Spatial and Temporal Non-Linear Dynamics Analysis and Predictability of Solar Radiation Time Series for La Reunion Island (France)

“…The nature of complexity in time series is related to the way in which fluctuations change with time through broadband time scale [ 23 , 24 , 25 ]. Basically, the daily solar irradiation fluctuations for each station at La Réunion could be adequately characterized by descriptive statistics to assess a potential complexity footprint in the corresponding time series.…”

Comment on the clear-sky index and on the variogram

“…Printer-friendly version Discussion paper by a factor 2 (see e.g. Wald, 1989). The difference with Eq.…”

Analysis of high frequency photovoltaic solar energy fluctuations

“…At present, operational calculations used for grid design are limited to a temporal resolution in the order of 5 to 15 min (Sande et al, 2017). However, variability of solar energy due to cloud shading occurs at very short timescales, in the order of 1 s (Lohmann and Monahan 2018). Considering the typically used, coarser timescales the frequency and amplitude of high-frequency power fluctuations is flattened due to time averaging.…”