Validation of three satellite-derived databases of surface solar radiation using measurements performed at 42 stations in Brazil

International audienceThe SoDa website (www.soda-pro.com) is populated with numerous solar-related Web services. Among them, three satellite-derived irradiation databases can be manually or automatically accessed to retrieve radiation values within the geographical coverage of the Meteosat Second Generation (MSG) satellite: the two most advanced versions of the HelioClim-3 database (versions 4 and 5, respectively HC3v4 and HC3v5), and the CAMS radiation service. So far, these databases have been validated against measurements of several stations in Europe and North Africa only. As the quality of such databases depends on the geographical regions and the climates, this paper extends this validation campaign and proposes an extensive comparison on Brazil and global irradiation received on a horizontal surface. Eleven stations from the Brazilian Institute of Space Research (INPE) network offer 1 min observations, and thirty-one stations from the Instituto Nacional de Meteorologia (INMET) network offer hourly observations. The satellite-derived estimates have been compared to the corresponding observations on hourly, daily and monthly basis. The bias relative to the mean of the measurements for HC3v5 is mostly comprised between 1 and 3 %, and that for HC3v4 between 2 and 5 %. These are very satisfactory results and they demonstrate that HC3v5, and to a lesser extent HC3v4, may be used in studies of long-term changes in SSI in Brazil. The situation is not so good with CAMS radiation service for which the relative bias is mostly comprised between 5 and 10 %. For hourly irradiation, the relative RMSE ranges from 15 to 33 %. The correlation coefficient is very large for all stations and the three databases, with an average of 0.96. The three databases reproduce well the hour from hour changes in SSI. The errors show a tendency to increase with the viewing angle of the MSG satellite. They are greater in tropical areas where the relative humidity in the atmosphere is important. It is concluded that except for the overestimation by CAMS radiation service, the three databases are suitable for studies of the solar resources in Brazil

Validation of HelioClim-3 version 4, HelioClim-3 version 5 and MACC-RAD using 14 BSRN stations

International audienceThis communication presents the results of a comparison of three satellite-derived databases covering Africa, Europe, Middle East and part of South America, against corresponding 15 min irradiations of very high quality measured by fourteen Baseline Surface Radiation Network (BSRN) stations. The three databases are accessible via the SoDa Service website, and are the two latest versions of HelioClim-3: versions 4 (HC3v4) and 5 (HC3v5), and the MACC-RAD database. The comparison was performed for durations of 15 min, 1 h, 1 day and 1 month for both the global irradiation received on a horizontal surface (GHI) and the direct irradiation received on a plane normal to sun rays (DNI). It is found that the three satellite-derived radiation databases exhibit satisfactory performances. For most of the fourteen locations, HC3v5 surpasses HC3v4 and MACC-RAD, with a bias ranging from-4 to 5% for the GHI and for all tested duration. The correlation coefficient is large for all databases and most often greater than 0.92 for 15 min and 0.98 for daily irradiation for GHI. The RMSE is fairly constant for all locations for 15 min and is approximately 20 kWh m-2 –slightly greater for MACC-RAD.-For daily irradiation, it ranges between 300 and 400 kWh m-2 for HC3v5, 300 and 500 kWh m-2 for HC3v4, and 400 and 550 kWh m-2 for MACC-RAD. Bias for the DNI is larger in absolute values than for GHI for all databases:-12 to 10% for HC3v5. The correlation coefficient is most often greater than 0.68 for 15 min and 0.84 for daily irradiation. The RMSE for 15 min ranges between 46 and 60 kWh m-2 for HC3v5, 46 and 63 kWh m-2 for HC3v4, and 48 and 66 kWh m-2 for MACC-RAD. For daily irradiation, it ranges between 1100 and 1600 kWh m-2 for HC3v5, between 1300 and 1700 kWh m-2 for HC3v4, and between 1000 and 1850 kWh m-2 for MACC-RAD. The MACC-RAD resource show promises provided the model for cloud properties is improved

Preliminary assessment of a new SoDa service for real-time estimates and short-term forecasts of the solar radiation

International audienceMeteosat images are routinely processed at Transvalor / MINES ParisTech for assessing the solar radiation at ground by the means of the Heliosat-2 method. So far, Heliosat-2 was launched every night to update the HelioClim-3 (HC3) database with the images collected during the day. HC3 data were thus available so far at d-1. Several requirements were made by customers of HC3 for a real-time and forecast capability for horizons up to 2 h. It would help in managing the PV plants or intelligent buildings, and eventually increasing the financial gains. The major challenges to develop such a capability were pertaining to the scientific domain in order to find an accurate method, and to operational constraints. The constraints are on both sides: provider and customer. The method should be fast enough to enable the processing of large areas such as Europe, and its outputs should be such as they can be directly ingested in the own processes of the customers. The selected model is based on a local persistence and has been validated against in situ measurements. A prototype has been set up and tested for several weeks by 15 customers. The customers used the outputs of this prototype as inputs to their own processes and made their own validation by comparing the results against measurements of, e.g. PV yield. The feedback gathered from testers was overall positive and a new operational service was set up based on the prototype (http://www.soda-pro.com/soda-products/real-time-and-forecast). Further validation campaigns are planned during the second semester of 2015, either by comparing to ground measurements or performed by users with their own criteria

The Solar Forecast Similarity Method: a new method to compute solar radiation forecasts for the next day

International audienceThe need for PV plant owners to plan what they are injecting in the electricity grid is more and more stringent to avoid endangering the whole supply in electricity. A new solar forecast algorithm, named Solar Forecast Similarity Method, has been developed to predict irradiance for the next day based on a statistical study of the long term HelioClim-3 irradiation database. This algorithm searches in the past for the most similar days compared to the day of interest and uses their following days to produce a forecast. The model has been optimized against the database itself to compute the most adequate set of parameters over France and for the month of January 2014. With this configuration, the results are a null bias and a root mean square error of 48%. The algorithm outperforms the persistence by 20% and the error is similar to existing methods. An objective validation has then been carried out to compare the irradiance forecasts to high quality measurements from several Baseline Surface Radiation Network (BSRN) ground stations. The method is very promising since the comparison results are in line or lower than the one obtained with the first validation analysis performed on the HelioClim-3 database. For high frequencies, however, predictions have a high error for rapidly varying weather. This demonstrates that the method provides information for the averaged production the following day but requires another input to reliably predict high frequency irradiance

Benefits and limits of OGC-Web Services to the new SoDa Service on Solar Energy

International audienceThe SoDa Service (website: www.soda-is.com) is providing an easy and standardized access to valuable information related to solar energy for professionals. Several providers offer via the SoDa Service an access to for-free and for-pay Web services and off-line services delivering data on solar radiation, atmospheric optics, position of the sun and many others. Since the launch of the Service in 2003, the SoDa team is making efforts to improve the quality of the service to customers. After the duplication of the whole system in 2010 for a better reliability, and the development of a more esthetic website in summer 2012, the team is now populating the new SoDa Service with new Web ser-vices. This is a perfect opportunity to explore different standards in order to increase the dissemination and accepta-tion of the existing and new services by the community of users. After several trials, the Open Geospatial Consorti-um (OGC) standards were selected. This communication discusses the OGC-compliant Web services and how the decision for developments within the new SoDa website was taken

A fusion method for creating sub-hourly DNI-based TMY from long-term satellite-based and short-term ground-based irradiation data

International audienceIn order to correctly perform Concentrated Solar Power (CSP) plant electric energy output estimation, a standard approach is to consider Typical Meteorological Year (TMY) as a reference input data in CSP simulation software such as System Advisor Model or Greenius. These TMYs may be built from satellite derived irradiation databases. In order to correctly estimate the CSP electricity production, it is highly recommended to use sub-hourly DNI information. Due to limitation in spatial and temporal resolution of geostationary satellite images, satellite-based irradiation data lack good representativity in term of any sub-hourly temporal variability. To overcome this limitation, we propose an innovative fusion method to combine a one year short time series of ground-based sub-hourly irradiation data and the long-term satellite-based one to create calibrated, sub-hourly and long-term based TMY irradiation data. This method has been successfully applied in the planning of the CSP plant project in Morocco: one year and a half of high quality 10-minute irradiation data from pyranometric ground stations belonging to the Moroccan Agency for Solar Energy (MASEN) has been used with long-term hourly satellite-based irradiation data to create calibrated 10-minute DNI based TMY. The ground-based irradiation data have passed the standard quality check procedure recommended by the Baseline Solar Radiation Network for the World Climate Research Program. The satellite hourly irradiation data has been calibrated on a one year learning period of ground station data and this calibration has been verified on a subsequent half year ground station data. This calibration has been applied to the hourly long-term satellite irradiation time series from which a TMY was computed. The final and innovative step consists in introducing the site specific sub-hourly variability into the whole set of hourly daily profiles of irradiation of the TMY time series, as needed to obtain a better estimation of the CSP producible. The method uses the whole 10-minute measured irradiation data as a store of available days, normalized in terms of time between sunrise and sunset

Assessment of five different methods for the estimation of surface photosynthetically active radiation from satellite imagery at three sites – application to the monitoring of indoor soft fruit crops in southern UK

International audienceThis paper assesses several methods for the retrieval of Photosynthetically Active Radiation (PAR) from satellite imagery. The results of five different methods are compared to coincident in-situ measurements collected at three sites in southern UK. PAR retrieval methods are separated into two distinct groups. The first group comprises three methods that compute PAR by multiplying the satellite-retrieved solar broadband irra-diance at the surface (SSI) by a constant coefficient. The two methods in the second group are based on more sophisticated modelling of the radiative transfer in the atmosphere involving advanced global aerosol property analyses and physically consistent total column water vapour and ozone produced by the Copernicus Atmosphere Monitoring Service (CAMS). Both methods compute a cloud modification factor from satellite-retrieved SSI. The five methods have been applied to two satellite-retrieved SSI datasets: HelioClim-3 version 5 (HC3v5) and CAMS Radiation Service (CAMS-Rad). Except at the seashore site, Group 2 methods combined with the cloud extinction from the HC3v5 dataset deliver the best results with small biases of − 5 to 0 µmol m−2 s−1 (−1 % to 0 % relative to the mean of the measurements), root mean square errors of 130 µmol m−2 s−1 (28 %) and correlation coefficients exceeding 0.945. For all methods, best results are attained with the HC3v5 data set. These results demonstrate that all methods capture the temporal and spatial variability of the PAR irradiation field well, although several methods require a posteriori bias adjustments for reliable results. Combined with such an adjustment, the Udo et Aro method is a good compromise for this geographical area in terms of reliability , tractability and its ability to run in real-time. Overall, the method performing a spectral discretization in cloud-free conditions, combined with the HC3v5 dataset, outperforms other methods and has great potential for supporting an operational system

HelioClim-3: a near-real time and long-term surface solar irradiance database

International audienceHelioClim-3 is a database containing surface solar irradiance assessed every 15 min from images taken by the Meteosat series of satellites since 2004. It covers Europe, Africa and Atlantic Ocean. In average, comparison with hourly measurements made in meteorological stations yields a correlation coefficient greater than 0.9, a relative root mean square error (rRMSE) around 20% of the mean measured irradiance and a relative mean bias error (rMBE) below 2%. HelioClim-3 can be accessed via the SoDa Service (www.soda- is.org). The availability and quality of HelioClim-3 data should help in performing steps towards a better knowledge of the surface solar irradiance and its variations over recent years

The Copernicus Atmosphere Monitoring Service (CAMS) Radiation Service in a nutshell

International audience1. The Copernicus Programme and its Atmosphere Monitoring Service (CAMS) Copernicus, previously known as GMES (Global Monitoring for Environment and Security), is the European Programme for the establishment of a European capacity for Earth Observation [1] with respect to land, marine, and atmosphere monitoring, emergency management, security, and climate change. The atmosphere service of Copernicus combines state-of-the-art atmospheric modeling on aerosols with Earth observation data to provide information services covering European air quality, global atmospheric composition, climate, and UV and solar energy [2]. Besides the radiation service, it provides information on – among others – ultra-violet radiation and aerosol concentration on a global scale. 2. The CAMS Radiation Service Within the radiation service, existing historical databases HelioClim-3 and SOLEMI for monitoring incoming surface solar irradiance have been further developed. The new service is jointly provided by DLR, Armines, and Transvalor. The Monitoring Atmospheric Composition and Climate (MACC) project series has been preparing for the service provision, which is now operational as part of the Copernicus programme. Data are made available both via the Copernicus portal and the SODA portal [3]. A User’s Guide [4] has been created during the MACC project and will be updated on a yearly basis. The scientific algorithm is described in [5] and [6]. The radiation service consists of an all-sky radiation time series service taking satellite-based cloud parameters into account and a clear-sky radiation time series service for cloud-free skies. Quality of the service is ensured by regular input quality control, regular quarterly benchmarking against ground stations, and regular monitoring of the consistency in order to detect possible trends. Following the Copernicus data policy, all data is provided free for any use after a registration giving a name and email address. It is not allowed to sell the data directly without modification, but data may be used for any purpose and value-added data may be part of any commercial usage. Details of the all-sky radiation service are: • Period of record: Feb 2004–present, updates are made continuously, data is provided with up to 2 days delay • Temporal resolution: 1-minute, 15-minute, hour, day, month • Spatial coverage: Europe/Africa/Middle East/Eastern part of South America/Atlantic Ocean. • Spatial resolution: Spatial resolution is the original pixel of the Meteosat Second Generation image (approx. 3 km at satellite nadir and 5 km at mid-latitude). • Data elements and sources: Global, direct, diffuse, and direct at normal incidence irradiances; global, direct, diffuse and direct normal irradiances in cloud free conditions; verbose mode with all atmospheric input parameters used for clouds, aerosols, ozone, water vapor and the surface reflective properties. The fast clear-sky model called Copernicus McClear implements a fully physical modeling replacing empirical relations or simpler models used before. It exploits the recent results on aerosol properties and total column content in water vapor and ozone produced by the Copernicus service. Details of the clear-sky radiation service are the same as the all-sky service, but the spatial coverage is global and any point of interest can be interpolated. Data elements provided are clear sky (i.e. cloud free) global, direct, diffuse and direct at normal incidence irradiances, and a verbose mode with all atmospheric input parameters used for clouds, aerosols, ozone, water vapor and the surface reflective properties. The paper will summarize the new service capabilities and illustrate quality control and validation results

The HelioClim-1 database of daily solar radiation at Earth surface: an example of the benefits of GEOSS Data-CORE

International audienceThe HelioClim-1 database contains daily values of the solar radiation reaching the ground. This GEOSS (Global Earth Observation System of Systems) Data Collection of Open Resources for Everyone (Data-CORE) covers Europe, Africa and the Atlantic Ocean, from 1985 to 2005. It is freely accessible at no cost through the SoDa Service (www.soda-is.com). Several assessments of the HelioClim-1 data against measurements made in meteorological networks reveal that the HelioClim-1 database offers a reliable and accurate knowledge of the solar radiation and its daily, seasonal and annual variations over recent years. The HelioClim-1 data may help in qualifying in situ measurements and may supplement them, thus offering 21 years of accurate daily means of surface solar irradiance. Several published works benefited from openness, availability and accuracy of the HelioClim-1 database in various domains: oceanography, climate, energy production, life cycle analysis, agriculture, forestry, architecture, health and air quality. This demonstration of the benefit of the HelioClim-1 database draws attention to resources open to everyone such as those labeled GEOSS Data-CORE