Overirradiance (Cloud Enhancement) Events at High Latitudes

Yordanov, Georgi Hristov; Midtgård, Ole-Morten; Sætre, Tor Oskar; Nielsen, Henrik Kofoed; Norum, Lars

doi:10.1109/jphotov.2012.2213581

Cited by 59 publications

(26 citation statements)

References 24 publications

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“…Additionally, the upper limit can exceed 1, primarily due to short-term reflections from the sides of clouds (and also to a secondary degree due to the limitations of the clear-sky model). Under broken cloud conditions this phenomenon, known as cloud enhancement, can cause single-point GHI to exceed its corresponding clear-sky irradiance value by more than 50 % on short timescales (Luoma et al, 2012;Piacentini et al, 2011;Yordanov et al, 2013a).…”

Section: Clear-sky Indexmentioning

confidence: 99%

Local short-term variability in solar irradiance

2016

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Abstract. Characterizing spatiotemporal irradiance variability is important for the successful grid integration of increasing numbers of photovoltaic (PV) power systems. Using 1 Hz data recorded by as many as 99 pyranometers during the HD(CP) 2 Observational Prototype Experiment (HOPE), we analyze field variability of clear-sky index k * (i.e., irradiance normalized to clear-sky conditions) and sub-minute k * increments (i.e., changes over specified intervals of time) for distances between tens of meters and about 10 km. By means of a simple classification scheme based on k * statistics, we identify overcast, clear, and mixed sky conditions, and demonstrate that the last of these is the most potentially problematic in terms of short-term PV power fluctuations. Under mixed conditions, the probability of relatively strong k * increments of ±0.5 is approximately twice as high compared to increment statistics computed without conditioning by sky type. Additionally, spatial autocorrelation structures of k * increment fields differ considerably between sky types. While the profiles for overcast and clear skies mostly resemble the predictions of a simple model published by Hoff and Perez (2012), this is not the case for mixed conditions. As a proxy for the smoothing effects of distributed PV, we finally show that spatial averaging mitigates variability in k * less effectively than variability in k * increments, for a spatial sensor density of 2 km −2 .

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Section: Clear-sky Indexmentioning

confidence: 99%

Local short-term variability in solar irradiance

2016

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“…Cloud enhancement has been traditionally related to reflection of sun radiation on the borders of Cumulus clouds around the sun disc, with the sun unobstructed. Recently, another explanation has been proposed: strong forward Mie scattering of sun light inside the clouds within a narrow angle around the solar disc (Yordanov et al, 2013a). A discussion about the real foundation of cloud enhancement is beyond the scope of this note.…”

Section: Introductionmentioning

confidence: 99%

Extreme overirradiance events in São Paulo, Brazil

2014

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“…Daily maximum total irradiance exceeded extraterrestrial irradiance for 3.4% of the days of the measurement period [3]. Still higher enhancements of total solar irradiance by 12% over extraterrestrial irradiance were reported by [4] for high latitudes in Southern Norway.…”

Section: Introductionmentioning

confidence: 82%

“…(3) and (1) by assuming a constant CMF = 1.4, and alternatively by assuming a constant ratio DIFCL/DIR according to Equation (4), which results in a variable CMF. Results of DIF/DIR ratios and CMF according to Equation (4). Irradiance curves at the right-hand side; ratio curves at the left-hand side; SZA = 0°.…”

Section: Cmfuvb Uvbcs Uvbcs/uvacs Cmfuvb/cmfery Uvbcs/erycs Uvimentioning

confidence: 99%

UV Irradiance Enhancements by Scattering of Solar Radiation from Clouds

2015

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Scattering of solar radiation by clouds can reduce or enhance solar global irradiance compared to cloudless-sky irradiance at the Earth's surface. Cloud effects to global irradiance can be described by Cloud Modification Factors (CMF). Depending on strength and duration, irradiance enhancements affect the energy balance of the surface and gain of solar power for electric energy generation. In the ultraviolet region, they increase the risk for damage to living organisms. Wavelength-dependent CMFs have been shown to reach 1.5 even in the UV-B region at low altitudes. Ground-based solar radiation measurements in the high Andes region at altitudes up to 5917 m a.s.l showed cloud-induced irradiance enhancements. While UV-A enhancements were explained by cloud scattering, both radiation scattering from clouds and Negative Ozone Anomalies (NOA) have been discussed to have caused short-time enhancement of UV-B irradiance. Based on scenarios using published CMF and additional spectroradiometric measurements at a low-altitude site, the contribution of cloud scattering to the UV-B irradiance enhancement in the Andes region has been estimated. The range of UV index estimates converted from measured UV-B and UV-A irradiance and modeled cloudless-sky ratios UV-B/erythemal UV is compatible with an earlier estimate of an extreme UV index value of 43 derived for the high Andes. OPEN ACCESSAtmosphere 2015, 6 1212

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Overirradiance (Cloud Enhancement) Events at High Latitudes

Cited by 59 publications

References 24 publications

Local short-term variability in solar irradiance

Local short-term variability in solar irradiance

Extreme overirradiance events in São Paulo, Brazil

UV Irradiance Enhancements by Scattering of Solar Radiation from Clouds

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