(1) Institute of Solar Research, German Aerospace Center (DLR), Almería, Spain (Pascal.Kuhn@dlr.de, marco.wirtz@eonerc.rwth-aachen.de, Stefan.Wilbert@dlr.de, Natalie.Hanrieder@dlr.de, Bijan.Nouri@dlr.de), (2) Earth Observation Center, German Aerospace Center (DLR), Weßling Oberpfaffenhofen, Germany (niels.killius@dlr.de), (3) Departamento de Ingeniería Eléctrica y Térmica, Universidad de Huelva, Huelva, Spain (jlbosch@gmail.com), (4) Dept. of Mechanical and Aerospace Engineering, UCSD Center for Energy Research, University of California, USA (g3wang@eng.ucsd.edu, jkleissl@eng.ucsd.edu), (5) CIEMAT, Energy Department Renewable Energy Division, Madrid, Spain (Lourdes.ramirez@aei.gob.es, lf.zarzalejo@ciemat.es), (6) Institute of Networked Energy Systems, German Aerospace Center (DLR), Oldenburg, Germany (Marion.Schroedter-Homscheidt@dlr.de, Detlev.Heinemann@dlr.de), (7) Laboratory of Atmospheric Physics, Department of Physics, University of Patras, Patras, Greece (akaza@upatras.gr), (8) MINES ParisTech, PSL Research University, Sophia Antipolis CEDEX, France (philippe.blanc@mines-paristech.fr), (9) Institute of Solar Research, German Aerospace Center (DLR), Cologne, Germany (Robert.Pitz-Paal@dlr.de)

Within European Commission's FP7 DNICast project a nowcasting scheme based on Meteosat Second Generation cloud imagery and cloud movement tracking was further developed. It uses a sectoral approach and answers the question at which time any cloud structure will affect the power plant. It distinguishes between thin cirrus clouds and other clouds, which typically occur in different heights in the atmosphere and move in different directions. Also, their optical properties are very different - especially for the calculation of direct normal irradiance (DNI) as required by concentrating solar power plants. The method is also applied in ESA's CSP-FoSyS project developing a nowcasting and forecasting system. This paper shortly discusses the method and provides a comparison against an optical flow method. This comparison distinguishes between various cloud types. The study also provides an example how jumpiness and percentiles are part of the nowcasting 'message' and how they can be used quantitiatively in a first approach.

Cloud height information is crucial for various applications. This includes solar nowcasting systems. Multiple methods to obtain the altitudes of clouds are available. In this paper, cloud base heights derived from the European Centre for Medium-Range Weather Forecasts (ECMWF) and three low-cost and low-maintenance ground based systems are presented and compared against ceilometer measurements on 59 days with variable cloud conditions in southern Spain. All three ground based systems derive cloud speeds in absolute units of [m/s] from which cloud heights are determined using angular cloud speeds derived from an all-sky imager. The cloud speed in [m/s] is obtained from (1) a cloud shadow speed sensor (CSS), (2) a shadow camera (SC) or (3) derived from two all-sky imagers. Compared to 10-min median ceilometer measurements for cloud heights below 5000 m, the CSS-based system shows root-mean squared deviations (RMSD) of 996 m (45%), mean absolute deviations (MAD) of 626 m (29%) and a bias of-142 m (- 6%). The SC-based system has an RMSD of 1193 m (54%), a MAD of 593 m (27%) and a bias of 238 m (11%). The two all-sky imagers based system show deviations of RMSD 826 m (38%), MAD of 432 m (20%) and a bias of 202 m (9%). The ECMWF derived cloud heights deviate from the ceilometer measurements with an RMSD 1206 m (55%), MAD of 814 m (37%) and a bias of- 533 m (- 24%). Due to the multi-layer nature of clouds and systematic differences between the considered approaches, benchmarking cloud heights is an extremely difficult task. The limitations of such comparisons are discussed. This study aims at determining the best approach to derive cloud heights for camera based solar nowcasting systems. The approach based on two all-sky imagers is found to be the most promising, having the overall best accuracy and the most obtained measurements.

1. 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 successful electricity grid integration of solar energy into day-ahead markets requires at least hourly resolved 48 h forecasts. Technologies as photovoltaics and non-concentrating solar thermal technologies make use of global horizontal irradiance (GHI) forecasts, while all concentrating technologies both from the photovoltaic and the thermal sector require direct normal irradiances (DNI). The European Centre for Medium-Range Weather Forecasts (ECMWF) has recently changed towards providing direct as well as global irradiances. Additionally, theMACC (Monitoring Atmospheric Composition & Climate) near-real time services provide daily analysis and forecasts of aerosol properties in preparation of the upcoming European Copernicus programme. The operational ECMWF/IFS (Integrated Forecast System) forecast system will in the medium term profit from the Copernicus service aerosol forecasts. Therefore, within the MACC-II project specific experiment runs were performed allowing for the assessment of the performance gain of these potential future capabilities. Also the potential impact of providing forecasts with hourly output resolution compared to three-hourly resolved forecasts is investigated. The inclusion of the new aerosol climatology in October 2003 improved both the GHI and DNI forecasts remarkably, while the change towards a new radiation scheme in 2007 only had minor and partly even unfavourable impacts on the performance indicators. For GHI, larger RMSE (root mean square error) values are found for broken/overcast conditions than for scattered cloud fields. For DNI, the findings are opposite with larger RMSE values for scattered clouds compared to overcast/broken cloud situations. The introduction of direct irradiances as an output parameter in the operational IFS version has not resulted in a general performance improvement with respect to biases and RMSE compared to the widely used Skartveit et al. (1998) global to direct irradiance conversion scheme. Cloudy situations and especially thin ice cloud cases are forecasted much better with respect to biases and RMSE, but large biases are introduced in clear sky cases. When applying the MACC aerosol scheme to include aerosol direct effects, an improvement especially in DNI biases is found for cloud free cases as expected. However, a performance decrease is found for water cloud cases. It is assumed that this is caused by the lack of an explicit modelling of cloud-aerosol interactions, while other meteorological forcings for cloud processes like the temperature field are modified by the aerosols.

The OrPHEuS project elaborates hybrid energy network control strategies for smart cities implementing novel cooperative approach for the optimal interactions between multiple energy grids. The OrPHEuS project aims at optimising the synergies between multiple energy grids by enabling simultaneous optimization for individual response requirements, energy efficiencies and energy savings as well as coupled operational, economic and social impacts. The project will investigate the implementation of the control strategies on specific use cases scenario in two demonstration sites located in the City of Skelleftea in Sweden and in the City of Ulm in Germany. The operational focus of the project is the cross-domain coupling of energy infrastructures in order to increase energy efficiency through energy transformation and grid coupling. In particular, the project researches scenarios for transition between energy resources and flexible infrastructures e.g. along Power-to-Heat processes. It investigates the balancing of fluctuating renewable energy generation against the flexibility in supply, demand and storage capacities within the power grid and via process coupling across energy networks. The project will look on technical as well as socio-economical aspects considered as multi-dimensional strategy framework. With respect to the hybrid energy characteristics, both demonstration sites are quite distinct. At the demonstration site in Sweden, the reduction of vertical production (driven unsustainable with fossil fuel) is in the centre of the targeted control strategies. Looking on the specifics of the Ulm testing site, the major issue is the balancing of the high penetration of solar generation under today’s operation with a pre-dominant operational challenge for PV control. The key focus is to define control strategies to increase the intake of the energy supply from PV on the roof generation into the grid while maximizing the benefits for the low voltage power grid. The 29th European Photovoltaic Solar Energy Conference and Exhibition (EU PVSEC) in Amsterdam represented a unique opportunity to present information on the methodology adopted by the OrPHEuS Consortium to optimise the synergies between multiple energy grids. On the occasion of the EU PVSEC the OrPHEuS Consortium focused the project presentation on how to optimise the PV electricity production with the implementation of Information and Communication (ICT) devices at the Ulm demonstration site, the Test area in Einsingen, which presents an over production of the PV electricity of 230 MWh annually. The average annual electrical consumption is around 1000 MWh.

For the nowcasting of solar irradiance in solar power plants and for electricity grid control, sky cameras detecting cloud and cloud-free sky conditions are widely in use. Cloud base height (cbh) information is essential for the geolocation of any cloud feature detected and to determine the cloud speed relative to the ground. One quite precise source of cbh are ceilometers. Ceilometer cbh is delivered as a single point measurement, but its value is often taken as “truth” for all clouds viewed by the camera – a procedure that may result in cbh errors for parts of the camera field of view. Cbh as a numerical weather prediction (NWP) output parameter surely is less accurate than a single point ceilometer measurement at the location of the instrument because of its spatial grid resolution. However, as NWP output is required anyhow for solar forecasting on the longer time horizon, the question arises if cbh from NWP can be used as an alternative to a ceilometer. Conclusions and outlook