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Cloud enhancement events at a Romanian BSRN site and their impact on photovoltaic energy yield.

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Title: Cloud enhancement events at a Romanian BSRN site and their impact on photovoltaic energy yield.
Authors: Fragkos, Konstantinos1 (AUTHOR), Adam, Mariana1,2 (AUTHOR) mariana.adam@inoe.ro, Carstea, Emil2 (AUTHOR), Papadimitriou, Nikolaos3,4 (AUTHOR), Fountoulakis, Ilias4 (AUTHOR)
Source: Solar Energy. Sep2026, Vol. 315, pN.PAG-N.PAG. 1p.
Subjects: Photovoltaic power generation, Solar radiation, Energy industries, Photovoltaic power systems, Global radiation
Geographic Terms: Romania
Abstract: Cloud enhancement events (CEEs) are intervals when global horizontal irradiance exceeds clear-sky values due to cloud-radiation interactions that redistribute the solar beam. This study examines two aspects of CEEs for photovoltaic (PV) energy production: how their radiative properties depend on the cloud regime that produces them, and how the resulting irradiance excursions translate into PV energy gains over operational timescales. The analysis is based on an event-level characterisation of CEEs stratified by cloud regime, including phase, vertical position, and multi-layer geometry, using two years (2021–2022) of high-resolution radiometric measurements from the Măgurele BSRN station in Romania combined with collocated Cloudnet cloud profiling, with PV capturable-energy modelling for fixed-tilt and tracking configurations. CEEs are detected using a solar zenith angle-dependent threshold derived from the 99.7th percentile of clear-sky residuals. 5050 events are identified, with maxima occurring in spring and summer and minima during winter. Most events are short-lived, while extreme cases exceed top-of-atmosphere projections and some persist for more than 2 h. Multi-layer and single-layer liquid clouds produce the strongest enhancements. 17–20% of the CEE-affected hours produce a net positive capturable-energy gain relative to the clear-sky reference, totalling 7.7–9.2 kWh kWp−1 over the two-year period. Success rates rise sharply with the temporal coverage of CEE activity within an hour, from 13.6% when CEEs occupy less than 10% of an hour to 65.2% when they occupy at least 60%, showing that temporal persistence is more important than peak intensity for net energy benefit. • Two-year event-level analysis of cloud enhancement at a BSRN station in Romania. • CEEs are stratified by cloud phase, vertical position, and multi-layer geometry. • GHI during CEEs frequently exceeds the clear-sky reference and occasionally TOA. • Long-duration CEEs raise daily capturable PV energy across all configurations. • Fixed-tilt systems gain most; tracking systems are less responsive to CEEs. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
Description
Abstract:Cloud enhancement events (CEEs) are intervals when global horizontal irradiance exceeds clear-sky values due to cloud-radiation interactions that redistribute the solar beam. This study examines two aspects of CEEs for photovoltaic (PV) energy production: how their radiative properties depend on the cloud regime that produces them, and how the resulting irradiance excursions translate into PV energy gains over operational timescales. The analysis is based on an event-level characterisation of CEEs stratified by cloud regime, including phase, vertical position, and multi-layer geometry, using two years (2021–2022) of high-resolution radiometric measurements from the Măgurele BSRN station in Romania combined with collocated Cloudnet cloud profiling, with PV capturable-energy modelling for fixed-tilt and tracking configurations. CEEs are detected using a solar zenith angle-dependent threshold derived from the 99.7th percentile of clear-sky residuals. 5050 events are identified, with maxima occurring in spring and summer and minima during winter. Most events are short-lived, while extreme cases exceed top-of-atmosphere projections and some persist for more than 2 h. Multi-layer and single-layer liquid clouds produce the strongest enhancements. 17–20% of the CEE-affected hours produce a net positive capturable-energy gain relative to the clear-sky reference, totalling 7.7–9.2 kWh kWp−1 over the two-year period. Success rates rise sharply with the temporal coverage of CEE activity within an hour, from 13.6% when CEEs occupy less than 10% of an hour to 65.2% when they occupy at least 60%, showing that temporal persistence is more important than peak intensity for net energy benefit. • Two-year event-level analysis of cloud enhancement at a BSRN station in Romania. • CEEs are stratified by cloud phase, vertical position, and multi-layer geometry. • GHI during CEEs frequently exceeds the clear-sky reference and occasionally TOA. • Long-duration CEEs raise daily capturable PV energy across all configurations. • Fixed-tilt systems gain most; tracking systems are less responsive to CEEs. [ABSTRACT FROM AUTHOR]
ISSN:0038092X
DOI:10.1016/j.solener.2026.114824