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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 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 Δk*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 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.
Highlights
Both the installed capacity and the number of photovoltaic (PV) power systems are increasing in many regions of the world (Solar Power Europe, SPE)
As changes in PV power are primarily determined by cloud-induced changes in solar irradiance, a comprehensive data-driven characterization of irradiance variability can help mitigate the risks associated with the above-mentioned problems
When considering smaller rooftop PV systems and/or partial shading, previous research has shown that the temporal resolution needed to capture irradiance variability on all time scales may be as small as 0.1 s (Torres Lobera et al, 2013; Yordanov et al, 2013b) or 0.4 s (Gagné et al, 2016)
Summary
Both the installed capacity and the number of photovoltaic (PV) power systems are increasing in many regions of the world (Solar Power Europe, SPE). When considering smaller rooftop PV systems and/or partial shading (which can strongly reduce an inverter’s power output as soon as a few connected modules are shaded; Belhaouas et al, 2017), previous research has shown that the temporal resolution needed to capture irradiance variability on all time scales may be as small as 0.1 s (Torres Lobera et al, 2013; Yordanov et al, 2013b) or 0.4 s (Gagné et al, 2016) Those studies that argued the need for sub-second resolutions made this determination based on various different lines of reasoning: 1.
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