The project objectives

To achieve the goals of the EU energy policy and to accelerate the market penetration of solar energy technologies, improvements in both technological domains (e. g. to increase efficiency, to achieve mass production) and in the operation of solar energy systems are necessary. Detailed knowledge of the fluctuating energy source solar radiation is an issue of strategic importance for optimised system performance. Main limitations regarding the availability of highquality solar radiation data have been identified by customers from solar energy industries:

• Uncertainty of local solar energy potential estimates is too high
• Spatial and temporal resolution of available radiation data is too low
• Solar energy specific information (direct normal and spectral irradiance, angular distribution of diffuse irradiance, spatial structure) is commonly not available at all.

This lack of precise information frequently results in an incorrect system sizing, nonoptimum site selection, unreliable system performance, or unnecessary use of conventional energy sources. Consequently, the economic success of solar energy technologies are strongly influenced by these limitations.

HELIOSAT-3 will supply high-quality solar radiation data gained from the exploitation of existing Earth observation technologies. Because of the increasing capabilities of these technologies, the expected quality represents a substantial improvement with respect to the available methods and will better match the needs of customers of the resulting products.

The objectives of HELIOSAT-3 are:

• Provide a new surface solar irradiance calculation scheme according to customers requirements mentioned above. The forthcoming MSG satellite will be used to derive the actual atmospheric state. This information will be used in physically based parameterization schemes for the solar radiation parameters, which are derived from extensive radiative transfer calculations. The enhanced capabilities of MSG with 12 spectral channels from the visible to the infrared, and higher resolutions in space (1 km) and time (15 min) allow this new approach.
• Reduce overall errors for global irradiance on a horizontal surface to less than 5,10, and 20 % rmse on a monthly, daily, and hourly basis, respectively.
• Provide a set of up to now from satellite not available solar energy specific parameters: Direct normal and spectral irradiance, angular distribution of diffuse irradiance, spatial structure of irradiance.
• Implementation of an operational processing chain from MSG data to enduse products.
• Availability of retrieved data on clouds, water vapour, aerosols and ozone concentrations for other applications in global change and land use research, health monitoring, and weather forecasting.
• Provide an user interface based on WWW and GIS technology for easy access to HELIOSAT-3 results by the key customers, expert users and the public.
• Integration of results into existing efforts from EU and other projects and organization of a users workshop.

HELIOSAT-3 will significantly improve the planning and operating of solar energy technologies. This will be shown by example applications in cooperation with customers:

• Performance monitoring of grid-connected photovoltaic systems
• Planning and operation of concentrating solar thermal power plants
• Optimization of daylight usage in buildings.

For the first time an attempt will be made to provide high quality general and solar energy specific radiation data with high spatial and temporal resolution. This means a substantial improvement against news pyranometer networks or available satellite techniques, respectively and will better match the needs of companies and other customers of the resulting products.

Solar energy applications are supplied with radiation data mainly from ground based sensors, which show extraordinary high costs and maintenance efforts. In addition, these data have an unsufficient spatial density and are often restricted to global horizontal irradiance only.

Satellite-based techniques for surface solar radiation retrieval, which are in use on an experimental basis since more than ten years, suffer from their limited accuracy due to the absence of additional information on the atmospheric state (e.g., water vapor, aerosols, cloud properties). Only short-wave reflected radiances and IR radiances for cloud detection are available from the news Meteosat generation. To cope with these knowledge gaps all satellite methods rely strongly on empirical relationships for these parameters instead of using precise physical modeling. news techniques therefore only provide global horizontal irradiance with acceptable accuracy. Consequently, their value as reliable and cheap data source for the solar energy sector is limited.

Further improvements of algorithms would need a large amount of additional data about the atmospheric state which can be taken nowadays only from several different sources (ground-based, models, satellites) with various data characteristics and availability schemes. This makes that approach a very expensive and complicated task.

A central key to overcome this limitation is the use of the follow-on Meteosat satellite generation (MSG) which offers a greatly enhanced information source for radiation and the atmospheric state. With these advanced possibilities the application of sophisticated radiative transfer models instead of semiempirical relationships is reliable. This was previously not applicable due to the lack of suitable atmospheric input data. Additionally, MSG allows the retrieval of all necessary parameters from one single instrument. This avoids all difficulties that might occur otherwise due to complex data assimilation schemes or different input data characteristics (e.g. temporal, spatial, accuracy).

With HELIOSAT-3, solar energy applications will benefit from the huge potential of Earth observation technologies in an optimum manner: It is the first time that solar energy users will have access to satellite-based solar radiation data with a quality, that allows an optimised planning of solar energy systems and performance monitoring of these systems with respect to meteorological conditions. The harmonisation with the needs of the solar energy community will be secured through the close cooperation with users inside and outside the HELIOSAT-3 consortium.

The main advantages for solar energy users are:

• Energy specific parameters (direct and spectral irradiance, angular distribution of diffuse irradiance, spatial structure of irradiance) dedicated especially to planning, performance monitoring and potential estimation of solar energy systems will be provided.
• The produced information will be available with a temporal (15 min) and spatial (typ. 1-2 km depending on location) resolution not supplied to users before.
• The accuracy of the products is expected to increase significantly compared with newsly available satellite-based data (15-20 % rmse for hourly global irradiance vs. 25-30 % prior accuracy, similar improvements in accuracy are expected for the other parameters).
• An easy internet based access to these data sources will be provided by project partners EHF and ARMINES.
• HELIOSAT-3 products will serve as a high quality basis for future developments of solar radiation forecasting schemes.

Additionally, the determination of clouds, water vapour and aerosols from one satellite in such a high temporal and spatial resolution over Europe and Africa will be performed for the first time. Data comparisons from further studies let expect accuracies of 1/8 in cloud cover, 0.4 g/cm2 in water vapour column, 0.1 in aerosol optical depth and 18 Dobson units in ozone column. These atmospheric parameters are highly valuable for users working in the fields of global change and land use research, health monitoring, and weather forecasting as well and will be provided to them by partner DLR.

The main purpose of this proposal is to combine and to further develop well known approaches and methods with the final aim to provide customers with information that is not available so far. For each single step the consortium holds expertise and there are also some potential users acting as partners in the consortium. To enhance innovation, HELIOSAT-3 will also exploit the outcomes of previous and running projects funded by the European Commission.

The innovative character of HELIOSAT-3 with its enhanced capability for supplying radiation data has been recently acknowledged by ESA/EUMETSAT in its Research Announcement of Opportunity. This call of proposals has been released in order to promote the use of the new MSG satellites and to support new innovative investigations. The selection of HELIOSAT-3 will allow a close cooperation with EUMETSAT and preferred treatment in accessing all necessary MSG data and products. Neither ESA nor EUMETSAT will fund selected projects.

In benefiting from the new satellite technology HELIOSAT-3 will enhance the recent efforts made by the European Commission and its outcomes will be integrated into the follow-ups of the projects Satel-Light, PVSAT, SolarGIS, European Solar Radiation Atlas, SoDa.

These projects will directly benefit as customers from the outcomes of HELIOSAT-3. To give an example, in the remote performance control of photovoltaic systems the expected increase in accuracy due to better irradiance products will lead to an increase in the number of detected system failures by 10 % compared to the accuracies achieved presently. This directly results in an overall increase in system efficiencies.

As the partners of HELIOSAT-3 have links with the named projects they can adapt easily the new products supplied by HELIOSAT-3. The use of infrastructure built up in these projects is therefore guaranteed. Additionally, the connections to existing networks and communities will ensure an immediate transfer of the results into existing and new applications.

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