SOLAR THERMAL ELECTRICITY GENERATION. By Franz Trieb, Carsten Hoyer, Stefan Kronshage, Richard Meyer, Marion Schroedter-Homscheidt

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2 SOLAR THERMAL ELECTRICITY GENERATION By Franz Trieb, Carsten Hoyer, Stefan Kronshage, Richard Meyer, Marion Schroedter-Homscheidt 28

3 Solar Potentials and Markets Power Solar irradiance is the fuel for solar power plants. Its availability is crucial for the economy of a power plant project. Where, when and how much will the sun shine? This is the question to which everyone willing to make an investment and profit with solar energy will come across. Plants 29

4 SOLAR THERMAL ELECTRICITY GENERATION Jahr Fig. above: Fields of view of Meteosat Prime (red, left) and Meteosat East (orange, right). The colored area can be evaluated in high quality. For Meteosat Prime data will be available from 1983 to 2005 and for Meteosat East form 1998 to Fig. below: Average annual sum of direct normal irradiance for the years 2000 to 2002 for Morocco. 30

5 In the project planning phase, planners need precise information on the availability of the solar resource in order to find a good site, adjust components and to predict economic income. Near real time information on solar irradiance is needed in the surveillance of power systems. Since the incoming irradiance is varying also the output of electricity or heat is changing. To compare target and actual yields, the operator needs current information on his energy source. Assistance from satellite data Satellite remote sensing can offer important services. The main atmospheric components influencing the transmission of solar radiation through the atmosphere are clouds, aerosols and water vapor. All of these can be derived from measurements of meteorological satellites. The scientists at the DLR Institute for Atmospheric Physics and of the Institute of Technical Thermodynamics developed a method to derive the solar irradiance at ground from satellite measurements. Clouds have the strongest influence. They are determined from the half hourly images of the European meteorological satellite Meteosat, which is positioned 36,000 km above the Gulf of Guinea at the intersection of the zero meridian and the equator. The method uses the visible and the infrared measurements of Meteosat. The infrared channel enables a better determination of the cloud cover at sunrise and sunset and can also detect high altitude ice clouds. Dust and aerosols further reduce the incoming irradiance by absorption and scattering processes. Therefore, the method also uses data of water vapors and aerosols from remote sensing and atmospheric models. Precise long-term measurements One particular advantage of satellites is that they measure the components with constant quality over the whole area and that historic data is stored in archives. Therefore entire regions can be evaluated in retrospective. It is not necessary to travel into the target regions and long periods can be analyzed without the need for long and expensive measurements on the location first. Satellite based solar irradiance data has a higher significance than ground based data. Since the annual irradiance will vary from year to year, long-term time series are necessary to put design and economic calculations on a solid base. Longterm ground measurements are almost never available near a proposed site. The wide spatial coverage of the satellite enables the search for the best site and is therefore decisive for the market introduction of solar power plants, because they can be erected at sites with the lowest electricity generation costs. Service for the end-user Two services are currently being established at DLR together with its partners from industry and research: SOLEMI ( Solar Energy Mining, and ENVISOLAR ( Environmental Information Services for Solar Energy Industries, SOLEMI focuses on providing historical long-term data from Meteosat Prime for Europe and Africa with more than 20 years and from Meteosat East for Arabia and Asia with ten years time series length. ENVISOLAR will extend these archives into the future and offer near-real-time data. The end product is a powerful data set for the analysis of solar resources, which DLR will offer for planers, industry and researchers. The products will e.g. include maps of the annual sums or hourly time series of the direct normal irradiance i n kilowatt hours per square meter. The data will help investors to analyze how much energy can be gained at a certain site even before construction begins. ENVSISOLAR uses the new meteorological satellite Meteosat 8 (Meteosat Second Generation MSG), which is in operational use since January, 29 th It measures the atmosphere in 12 different spectral channels with 3 km resolution at the sub satellite point and a high resolution broadband visible channel with a resolution of 1 km. Its precursor Meteosat used only 3 channels and the spatial resolution was 2.5 or 5 km depending on the channel. The second generation satellites allow a more precise determination of clouds and water vapor in the atmosphere. This offers new opportunities for derivation of solar irradiances from satellites. The methods are currently under development in the European Commission founded project Heliosat-3 (ENK5-CT ). ENVISOLAR is in the process of being set up at DLR with financial support of the European Space Agency (ESA) under the lead of Deutsches Fernerkundungsdatenzentrum (DFD) of DLR. Earth observation data supplying partners are also the Ecole des Mines (F) and the University of Oldenburg (D). Like SOLEMI, ENVISOLAR s services will prove to be very valuable to the operators of solar thermal and photovoltaic power plants. The focus will be, besides the extension of the SOLEMI data base with Meteosat 8 (MSG) data, on the provision of near real time data for e.g. the surveillance of solar energy systems. The online received data can be used to calculate the target yield of a solar energy system with high precision. A larger deviation between actual and the ENVI- SOLAR derived value is a reliable sign for the operator, that something is out of order. A further focus of ENVISOLAR is the forecast of solar irradiance for up to 48 hours. This can be used for optimized operation of conventional and solar power plants. Cutting the investment costs The available solar resource is not the only criterion for the exploitation of solar energy. Electricity costs also depend on the necessary investment costs. Therefore, after the determination of solar irradiance, the second step is the determination of suitable sites and the necessary investment at each site. Geographical Information Systems (GIS) are suited for this purpose and they are increasingly used worldwide in infrastructure and project planning. First unsuitable sites are excluded, e.g. if the land slope is too high or the land is used as forests, agriculture, Settlements, or otherwise protected areas, etc. At suitable sites the electricity yield is calculated with the 31

6 SOLAR THERMAL ELECTRICITY GENERATION 4,000 3,500 3,000 2,500 2,000 1,500 kconventional old facilities CSP export CSP desalination CSP electricity year 1,000 1,500 1,500 conventional new facilities demand for electricity MENA Fig. above: Economic ranking of sites for 200 MW solar power plants in Morocco. (0: unsuitable, 1: best class). Fig. below: Potential for expanding concentrating solar power plants (CSP) for electricity generation, sea water desalination and export of solar power in the Middle East and North Africa (MENA) for a reference scenario with medium growth of the population and the per capita income. Further old and new capacities and the total electric power demand in MENA is shown. About 15 percent of the generated solar thermal energy is used for desalination in 2050, about 20 percent are exported. (Source: MED-CSP Study, 2005). 32

7 Period Phase Start-up with pilot plants and technology transfer Technology transfer Technology introduction Market Development Market extension Commercial phase Installed power for electricity and water 5 MW, 1.7 Mm 3 /a, 25% solar 355 MW, 118 Mm 3 /a 2,100 MW, 700 Mm 3 /a, 50% solar 6,600 MW, 2,200 Mm 3 /a, 75% solar 21 GW, 7,000 Mm 3 /a, >75% solar open Cum. capital MUS$ 20 1,300 7,400 21,900 80,000 open Requirements Public Private Partnership, political support, Subsidies, soft loans, feed in laws, long-term contracts on electricity and water purchase electricity, guarantees as above as above Public Private Partnership, long-term contracts on electricity and water purchase electricity, guarantees Public Private Partnership, long-term contracts on electricity and water purchase electricity none Cost level for electricity and water * ct/kwh ct/m ct/kwh ct/m ct/kwh ct/m ct/kwh ct/m ct/kwh ct/m ct/kwh 5-65 ct/m 3 The table shows the individual phases of the market introduction of solar thermal power, the extension of capacity, the connected investments and the achievable price levels for power and water. By 2015 at the latest a price level will be reached which corresponds to conventional installations. After that solar thermal power will increasingly dominate the international power plant market, since they are one of the most economic options. *Hybrid operation with full load hours per year. Range between a scenario with largely private funding (nine percent interest, 20 years dept service) and a scenario with public funding within a Framework of Public Private Partnership (four percent interest, 40 years dept service). irradiance data as input. Together with project costs (construction, connecting to infrastructure, insurance, capital cost) the electricity costs can be estimated. These results are used to set up a ranking of possible sites to estimate the potential of solar thermal power generation in an entire region. The estimations on the potential of solar thermal power technologies can be used in a third step to develop strategies for market introduction. Within the context of the project Concentrating Solar Power for the Mediterranean Region (MED-CSP), sponsored by the German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety, the resource and demand potential up to 2050 are evaluated on the basis of growth models for the Mediterranean countries. The study analyses the power, water and industrial sector in the Middle East and Northern Africa (MENA) and opportunities for export of solar power to Europe. It creates a data basis for the development of market introduction strategies within the context of the Global Market Initiative for Concentrating Solar Power (GMI-CSP) und the Trans-Mediterranean Renewable Energy Cooperation (TREC) and will give indications on implementation possibilities. Outlook to the future Extension of solar thermal power is limited up to 2025 by production capacities of the components. Therefore, the rapidly growing demand in MENA countries has to be served by conventional energy sources. After 2025 there will be enough capacities and the demand will be the limiting factor. Solar thermal power plants will then serve large shares of the energy supply. The available resources do not limit the potential within the considered timeframe. A climate protecting and sustainable extension of energy and water supply in the Mediterranean and Middle East poses a major challenge for this region because of the rapidly growing demand. At moderate growth the MENA countries will reach the current European level at 2050 and solar thermal power has the potential to play a key role in meeting this challenge. Franz Trieb, Carsten Hoyer and Stefan Kronshage are scientists at the DLR Institute of Technical Thermodynamics, Stuttgart. Richard Meyer is scientist at the Institute of Atmospheric Physics, Oberpfaffenhofen. Marion-Schroedter-Homscheidt is scientist at the German Remote Sensing Data Center (DFD), Oberpfaffenhofen. 33