Search results for " irradiance"
showing 10 items of 64 documents
Identification and Handling of Critical Irradiance Forecast Errors Using a Random Forest Scheme – A Case Study for Southern Brazil
2015
Abstract Large forecast errors of solar power prediction cause challenges for the management of electric grids. Here, the classification technique Random Forests is applied to analyze the possible linkage of hourly or daily forecast errors to the actual situation given by a set of meteorological variables. This form a prediction of the forecast error and is thus usable to update the forecast. The performance of this scheme is assessed for the example of irradiance forecasts in Brazil. While limited to none improvements are obtained for next-hour forecasts, significant improvements are obtained for the next-day forecasts.
A multi-instrument approach for characterizing the atmospheric aerosol optical thickness during the STAAARTE/DAISEX-99 campaign
2002
This work deals with the retrieval of the aerosol optical thickness (AOT) needed to carry out the atmospheric correction of remote sensing data measured in Barrax (Spain) on 4 June 1999 in the framework of 1999 Digital Airbone Imaging Spectrometer Experiment (DAISEX'99). The AOT was estimated through three approaches based on: spectral extinction of direct solar irradiance at ground level, airborne nephelometer measurements at different altitudes, and backscatter lidar in the lower troposphere. We found extremely low AOT values due to a cold Atlantic front that swept across the Iberian Peninsula from west to east producing light rain over the test area on 2 June 1999. The results were solar…
Design of a sun tracker for the automatic measurement of spectral irradiance and construction of an irradiance database in the 330-1100 nm range
2007
Abstract An automatic global and direct solar spectral irradiance system has been designed based on two LICOR spectroradiometers equipped with fibre optics and remote cosine sensors. To measure direct irradiance a sun tracker based on step motors has been developed. The whole system is autonomous and works continuously. From the measurements provided by this system a spectral irradiance database in the 330–1100 nm range has been created. This database contains normal direct and global horizontal irradiances as well as diffuse irradiance on a horizontal plane, together with total atmospheric optical thickness and aerosol optical depth.
A hierarchical architecture for increasing efficiency of large photovoltaic plants under non-homogeneous solar irradiation
2019
Abstract Under non-homogeneous solar irradiation, photovoltaic (PV) panels receive different solar irradiance, resulting in a decrease in efficiency of the PV generation system. There are a few technical options to fix this issue that goes under the name of mismatch. One of these is the reconfiguration of the PV generation system, namely changing the connections of the PV panels from the initial configuration to the optimal one. Such technique has been widely considered for small systems, due to the excessive number of required switches. In this paper, the authors propose a new method for increasing the efficiency of large PV systems under non-homogeneous solar irradiation using Series-Para…
Emulation of Leaf, Canopy and Atmosphere Radiative Transfer Models for Fast Global Sensitivity Analysis
2016
Physically-based radiative transfer models (RTMs) help understand the interactions of radiation with vegetation and atmosphere. However, advanced RTMs can be computationally burdensome, which makes them impractical in many real applications, especially when many state conditions and model couplings need to be studied. To overcome this problem, it is proposed to substitute RTMs through surrogate meta-models also named emulators. Emulators approximate the functioning of RTMs through statistical learning regression methods, and can open many new applications because of their computational efficiency and outstanding accuracy. Emulators allow fast global sensitivity analysis (GSA) studies on adv…
Centre-to-limb variation of photospheric facular radiance and image resolution
2005
Abstract We study the effect of the angular resolution on the determination of the angular properties of the facular radiance. We analyze photospheric intensity in the continuum, around the Ni 676.8 nm line, and longitudinal magnetic field along the line of sight, measured by the MDI instrument aboard SOHO with two spatial resolutions, 4″ and 1.2″ (2″ and 0.6″ pixels, respectively). The effect of the limited photometric sensitivity of the instrument and the limited information on the angular structure of the magnetic field tubes are considered. Our study of the high-resolution data shows that intensity contrast of magnetic features between 80 and 600 Gauss increases from centre to limb up t…
A study of extreme overirradiance events for solar energy applications using NASA’s I3RC Monte Carlo radiative transfer model
2015
Abstract Near the Equator, some cloud types can boost the terrestrial solar irradiance to above 1.8 kW/m2. Even at high latitude close to 60°N, we have measured bursts up to 1.6 kW/m2, almost at sea level. For comparison, the extraterrestrial irradiance peaks at about 1.4 kW/m2 in early January. The global upper limit for extreme overirradiance is still unknown. The enhancement is strongest within about 3° from the unobstructed solar disk. We use the NASA’s I3RC Monte Carlo model to simulate the radiative transfer of solar photons in a cloudy atmosphere. The geometry includes an overhead sun and an infinite plane parallel water cloud with a ‘circular’ gap of the same angular diameter as tha…
Thermal–infrared emissivities of natural surfaces: improvements on the experimental set-up and new measurements
2003
Ground measurements of thermal infrared emissivities of terrestrial surfaces are required to derive accurate temperatures from radiometric measurements, and also to apply and validate emissivity models using satellite sensor observations. This paper focuses on the demanding aspects that are involved in the field measurement of emissivity using the box method and a hand-held radiometer. Measuring emissivities in field conditions can be hampered by external factors such as wind and solar irradiance. This can increase the time spent on the field campaign but, most importantly, it can cause no-sense fluctuations between consecutive observations. Here we propose original developments for the exp…
Indoor lighting quality: Effects of different wall colours
2016
This paper reports the results of measurements performed in a test room to investigate the impact of using different wall colours and light scenes on indoor lighting quality. Eye level spectral irradiances were measured for a user located inside the room and seated at a desk. These measurements allow the use of the Irradiance Toolbox, which makes it possible to calculate equivalent illuminances for the photopigments in the human eye. Moreover, the CIECAM02 colour appearance model was used to investigate the variations in hue and chroma values of the different wall colours when changing the light scene. The results demonstrate that there are significant variations in eye level spectral irra…
Apparato di commutazione
2012
La presente invenzione si riferisce ad un apparato di commutazione per il controllo e l'impostazione della configurazione circuitale dei pannelli di un modulo fotovoltaico.