Performance Simulation For Parabolic Trough Concentrating Solar Power Plants And Export Scenario Analysis For North Africa

Transcription

1 Performance Simulation For Parabolic Trough Concentrating Solar Power Plants And Export Scenario Analysis For North Africa By Daniel Horst A Thesis Submitted to the Faculty of Engineering at Cairo University in Partial Fulfillment of the Requirement for the Degree of MASTER OF SCIENCE In MECHANICAL POWER ENGINEERING FACULTY OF ENGINEERING, CAIRO UNIVERSITY GIZA, EGYPT 2012

2 Performance Simulation For Parabolic Trough Concentrating Solar Power Plants And Export Scenario Analysis For North Africa By Daniel Horst A Thesis Submitted to the Faculty of Engineering at Cairo University in Partial Fulfillment of the Requirement for the Degree of MASTER OF SCIENCE In MECHANICAL POWER ENGINEERING Under Supervision of Dr. Adel Kahlil Professor In Mechanical Power Engineering Department Faculty of Engineering Cairo University Dr.-Ing. Jürgen Schmid Professor In Electrical Engineering Department Faculty of Engineering Kassel University Dr. Carsten Pape Frauenhofer-Institute for Wind Energy and Energy System Technology FACULTY OF ENGINEERING, CAIRO UNIVERSITY GIZA, EGYPT 2012

3 Performance Simulation For Parabolic Trough Concentrating Solar Power Plants And Export Scenario Analysis For North Africa By Daniel Horst A Thesis Submitted to the Faculty of Engineering at Cairo University in Partial Fulfillment of the Requirement for the Degree of MASTER OF SCIENCE In MECHANICAL POWER ENGINEERING Approved by the Examining Committee: Prof. Dr. Adel Khalil Prof. Dr.-Ing. Jürgen Schmid Dr. Hany Nokrashy FACULTY OF ENGINEERING, CAIRO UNIVERSITY GIZA, EGYPT 2012

4 I Table of Contents List of Figures List of Tables List of Abbreviations List of Symbols Abstract 1. Introduction Renewable Energy and Climate Change Solar technology Parabolic trough technology Reflectors Absorber Tracking and controlling Heat transfer medium Thermal storage Thesis objectives and outlines Theoretical performance calculation CSPP Geometrical relations Sun earth geometry Sun collector geometry Solar filed Optical losses Heat losses Thermal storage Stratification Storage the Multi- Node- model The Plug- Flow model Power block Carnot Cycle Clausius- Rankine Cycle Steam Turbine Recourse assessment for CSPP Land Recourse assessment Slope... 30

5 II Land Cover Hydrology Geomorphologic features Protected areas Industry and Population Technical potential High voltage grid MED- CSP Scenario CG/HE Growth of population Growth of economy Electricity demand Scenario for energy security Weather data Irradiation data sets Ambient data sets Simulation Program Program overview GIS database and scenario processing Scenario processing Side evaluation Side depositing CSP performance simulation Solar field simulation Thermal storage simulation Power block simulation Curve fitting and ELCC calculation Least square optimization ELCC calculation Export scenario Scenario description Installed capacity and plant distribution Residual load curve Power plant park Simulation results Simulation for SM

6 III Simulation for SM Simulation for SM Simulation for SM Conclusion Simulation program Export Scenario References Appendix A (Validation table CSP performance calculation) Appendix B (Transmission grid maps North Africa)...105

7 IV List of Figures Figure 1: Functional principle of a parabolic trough [REB]..3 Figure 2: Absorber tube of a parabolic trough collector [REB]...4 Figure 3: Basic concept for the integration of thermal energy storage into a solar thermal parabolic through power plant [REB].6 Figure 4: Geometrical relation between sunbeam and tilted surface [EEG].8 Figure 5: Displacement of the sun image [SLP]...11 Figure 6: Three-node stratification liquid storage tank [SETP]..17 Figure 7: Plug and Flow model whit 4 layers [SLP].19 Figure 8: Carnot cycle p,v and T,s Diagram [TDK].20 Figure 9: Schematic drawing of a steam power plant and the T,s Diagram of a Clausius-Rankine cycle [TDK] 21 Figure 10: Real Clausius-Rankine Process T,s Diagram [KWT]..23 Figure 11: Increasing of the main steam parameters [KWT]...24 Figure 12: Water steam cycle with reheating [KWT].25 Figure 13: Regenerative feed water preheating [KWT] 26 Figure 14: Schematic drawing of a high-pressure turbine [KWT]...27 Figure 15: Areas whit a slope higher than 2.1% [SID]...30 Figure 16: The land cover in the Euro-Mediterranean Region [SID] 31 Figure 17: The Hydrology of the Euro-Mediterranean Region [SID] 31 Figure 18: Geomorphologic exclusion criteria in the Euro-Mediterranean region [SID].32 Figure 19: Protected areas of the Euro-Mediterranean Region [SID]..33 Figure 20: Industry and population of the Euro-Mediterranean region [SID]..34 Figure 21: Annual direct normal irradiation in kwh/m 2 /y on non-excluded areas in the areas in the Euro-Mediterranean Region [SID] 34 Figure 22: Annual direct normal irradiation on non-excluded areas in global scale [SID].35 Figure 23: Electrical Transmission System Network of North Africa [GENI] 36 Figure 24: Envisage Mediterranean interconnections with Europe [GENI]..37 Figure 25: Population growth in North Africa by countries [MCSP]..38 Figure 26: Average GDP growth rate between 2003 and 2050 for North African countries [MCSP].39 Figure 27: Energy consumption in North Africa until 2050 [MCSP]..40 Figure 28: Electricity production in the MENA region until 2050 [MCSP].41

8 V Figure 29: Area for the CSOMO-EU model displaying topographic height in meter [COE]...43 Figure 30: Global horizontal irradiation calculated out of the COSMO-EU data compared whit global horizontal irradiation data from HC3 database..44 Figure 31: I, b and DNI for 31 N 29 E and year 2007 simulated out of COSMO-EU data..45 Figure 32: Monthly average ambient data for Egypt June 2007 provided by the COSMO-EU database..46 Figure 33: General overview of the Matlab program for CSPP calculation.47 Figure 34: Basic program structure 48 Figure 35: Basic program structure scenario analyzes...50 Figure 36: Number of CSPP according to MED CSP Scenario.51 Figure 37: Black-white map for evaluating available areas 52 Figure 38: Schematic drawing of high voltage grid in North Africa...53 Figure 39: Possible installed gross capacity per country per country. Simulated with a grid distance of 25km and 200 MW el installed gross capacity per pixel.53 Figure 40: Irradiation map of North Africa, CSPP distribution for scenario Figure 41: Irradiation map of North Egypt, CSPP distribution for scenario 2030 Cairo area..55 Figure 42: Irradiation map of North Africa, CSPP whit cooling system distribution for the scenario Figure 43: Basic Program structure performance calculation 56 Figure 44: Incidence angle, tilt angle and solar height at 31 N 20 E for the 21 st of March Figure 45: Geometrical Collector losses in a location of 31 N 29 E at 21 st March 2007 one axis tracking system, collector orientation north south..59 Figure 46: Efficiency and thermal energy harvest by the solar field with a size of 188,000m 2 and a direct normal irradiation of 800 W/m 2 at 31 N 20 E for 21 st of March 2007 one axis tracking, collector orientation north south 60 Figure 47: Schematic drawing of storage arrangement in the simulation program 61 Figure 48: Schematic drawing of SM arrangement, storage unit is 6h 62 Figure 49: Full load operating hours /Simulation operating hours for solar-multiple 1-4 simulated for a CSP plant equipped with wet cooling system and back cooling system located at 31 N 29 E metrological year Figure 50: Schematic drawing of water steam cycle with basic design parameters..65 Figure 51: Schematic drawing of the arrangement for a wet cooling system equipped whit back cooling system and water turbine....67

9 VI Figure 52: Schematic drawing of evaporation cooling system with air-cooling tower 69 Figure 53: Schematic drawing of condenser connected to a dry cooling system...71 Figure 54: Plant performance calculation for SM1 equipped with dry cooling system at a location of 31 N 29 E for the meteorological year Collector orientation is north south..73 Figure 55: Plant performance calculation for SM4 equipped with evaporation cooling system at a location of 31 N 29 E for the year Collector orientation is north south...74 Figure 56: Feed in series direct calculated and optimised and for CSPP SM 4 with wet cooling and back cooling system located at 31 N 29 E. CSOMO-EU ambient data for Figure 57: Schemata for the ELLC calculation [UVE].77 Figure 58: Method of recursive convolution, example for 3 power plants [DENA1]..78 Figure 59: Distribution of exporting CSP plants for Germany, with installed gross capacity of 200 MW el for each plant, in North Africa for Figure 60: SIM-EE model IWES for simulation of the residual load curve [UBA]...82 Figure 61: Annual load duration curve for Germany in 2050 with an energy supply by 100% renewable energy sources [UBA] 84 Figure 62: Residual load curve from the UBA study 100% renewable electricity supply by 2050 [UBA]..84 Figure 63: SIM-EE model IWES for simulation of the residual load curve. Changes are under taken in the position of importing energy according to the simulation in this thesis. [UBA]...85 Figure 64: Weekly average energy production from CSP plants SM1 based on the weather data COSMO-EU Figure 65:Residual load curve without import energy and residual load curve including import energy form CSP with SM2. Irradiation and ambient data from COSMO-EU model Figure 66: Partial view of figure XX residual load curve without imported energy and residual load curve including imported energy from CSP with SM2. Irradiation and ambient data from COSMO-EU model for Figure 67: Annual load duration curve for the residual load with and whiteout CSP import SM2 89 Figure 69: Residual load curve without imported energy and residual load curve including imported energy from CSP with SM3. Irradiation and ambient data from COSMO-EU model

10 VII Figure 69. Partial view part of figure XX residual load curve without import energy and residual load curve including import energy form CSP SM3 as well as energy production CSP. Irradiation and ambient data from COSMO-EU model for Figure 70: Annual load duration curve for the residual load with and whiteout CSP import SM3.91 Figure 71. Residual load curve without imported energy and residual load curve including imported energy form CSP SM4. Irradiation and ambient data from CSOMO-EU model Figure 72. Partial view part of figure XX residual load curve without imported energy and residual load curve including imported energy from CSP with SM4. Irradiation and ambient data from COSMO-EU model for Figure 73: Annual load duration curve for residual load with and without CSP import. Ambient data COSMO-EU

11 VIII List of Tables Table 1: Compulsive and optional criteria for the exclusion of land used for CSP plants [SID].29 Table 2: Areas for CSP in km 2 available in the MENA countries for different DNI Classes [SID]..35 Table 3: Concentrated solar thermal potential in North Africa [MCSP]...42 Table 4: Basic input parameters for individual simulation of CSPP..49 Table 5: Input parameter for scenario analyze..50 Table 6: Design parameters for simulation of the solar field for CSP plant with gross capacity of 200 MW el [DLS].57 Table 7: Design parameter for storage simulation [DLS] 60 Table 8: Design parameters for simulation of the power block whit gross capacity of 200 MW el [DLS].64 Table 9: Design parameters for water steam calculation with a wet cooling system [DLS] 67 Table 10: Design parameters for water steam calculation evaporation cooling system [DLS 69 Table 11: Design parameters for water steam calculation dry cooling system [DLS] 71 Table 12: Installed exporting CSP plants and gross capacity separated by countries for North Africa Table 13: Unplanned outage probability [DENA1]...85 Table 14: PPN for ELCC simulation...86 Table 15: Summery of the results from export scenario analyze..97

12 IX List of Symbols A = Area C = Concentration ratio (chapter 2) / ventilator constant (chapter 4) c = specific heat capacity D = distance collector row F = area angle (chapter 2.2) / control function (chapter2.3) f = focal length (chapter 2.) / solar field coefficient (chapter 4) G = irradiation at absorber pipe (chapeter2.2) / Gibbs free energy (chapter2.3) H = height of collector h = specific enthalpy / probability density function (chapter 4.4) I = global horizontal irradiation I b = global horizontal beam radiation I d = global horizontal diffuse radiation L = length of the collector l = length of the not irradiated absorber part m = mass flow N = number of nodes n = number of the day P = power / black out probability (chapter 4.4) p = pressure Q = thermal energy q = specific thermal energy S = entropy s = specific entropy T = temperature in Kelvin t = time U = heat transfer coefficient (chapter2.2) / internal energy (chapter 2.3) V = volume (chapter 2) / availability collector field (chapter 4) v = specific volume (chapter 2) /wind speed at ground height (chapter 4) W = work w = specific work (chapter 2)/ speed (chapter 4) x = distance (chapter 2) /water contend (chapter 4.3) z = distance for water transportation

13 X Greek letters α s = surface azimuth α r = surface azimuth relative β = tilt angle β s = solar elevation χ= storage capacity δ = angle of declination ε = emissivity φ = latitude η= efficiency ϕ = relative humidity ρ= density θ= incidance angle θ Z = zenith angle ψ = solar field reduction factor

14 XI List of Abbreviations ALB_RAD: ASOB_S: CC: CSP: CSPP: DLR: DNI: DSMW: ELCC: GDP: GHG: GIS: GLCC: GNI: HC3: IDR: IEA: IWES: IPCC: LOLE: LOLP: MENA: NDVI: PPA: PPN: RE: SM: SEGS: UBA: WBGU: WCU: ground albedo short wave radiation at ground high capacity credit concentrated solar power concentrated solar power plant German aerospace center direct normal irradiation digital soil map of the world effective load carrying capacity gross domestic product green house gasses global information system global land cover characterization gross national income HelioClime3 Incidence direct radiation international energy agency Frauenhofer-institute for wind energy and energy system technology Intergovernmental Panel on Climate Change loss of load probability loss of load probability Middle East and North Africa normalized difference vegetation index purchasing power parity power plant network renewable energies solar multiple solar energy generation system German Federal Environmental Agency German Advisory Council on Global Change World conservation Union

15 XII Abstract Since the Intergovernmental Panel on Climate Change (IPCC) report 2007 established: it is very likely that global warming nowadays is man made [IPCC2007a], it becomes obviously that the emission of CO 2 have to be reduced drastically. The green house gas (GHG) concentration for 2010 was 39% above the preindustrial level. Therefore the warming trend has increased significantly over the last 50 years [IPCC2007a]. Still GHG emissions associated with the provision of energy services are the major cause of climate change. Nevertheless, cold-fired power plants are still the basis of electricity production all over the world. In order to work against this trend research and political influence is necessary to avoid the negative impact of the global warming. Based on the history of industrial development the industrialized countries have the duty to reduce their own emissions, as well as supporting developing countries by doing so. In this context, options like exporting solar energy form the deserts of North Africa to Europe would offer great possibilities and both sides might have a benefit. Because of the high solar irradiation form 2500kw/m 2 /y in some parts of North Africa and the high share of direct radiation concentrated solar power plants (CSP) are an excellent option for a sustainable electricity production in this region. The thesis is providing a model witch can calculate the electrical output of CSP parabolic trough plants for several locations in North Africa. Furthermore it is analyzed how these CSP plants can contribute to a 100% renewable energy supply in Germany for the year Therefore the first part of this thesis presents a model estimating suitable locations for CSP plants in North Africa and calculating the electrical output of CSP plants. Several criteria s for land use, annual irradiation and infrastructure, are processed, and rules for depositing CSP plants were specified. In alliance with weather prediction models an energy-balanced CSP model simulates the electrical output of exclusive solar driven CSP parabolic trough plants. By using different configurations the simulation can display various forms of storage sizes and different cooling system. The second part of the thesis is focused on how the CSP plants can support a 100% renewable energy system in Germany in the year Therefore, the effective load carrying capacity (ELCC) and the capacity credit (CC) for a number of CSP plants in relation to the residual load in Germany is evaluated. The focus is on the influence different storage sizes have on the possibility to supply energy on demand for Germany.

16 XIII The work shows that even a high capacity credit of around 53% for solar multiple four CSP plants is not necessarily helpful to reduce significant the high demand in Germany during winter times. This can be mainly related to the seasonality noticed in the CSP output even whit high storage capacities. The thesis is outlined by the MED-CSP study [MCSP] and the study 100% renewable electricity supply by 2050 [UBA2050] of the German federal environmental agency.

17 ! 1 1. Introduction 1.1 Renewable energy and climate change The 2007 IPCC report states that Most of the observed increases in global average temperature since the mid-20 th century is very likely due to the observed increase in anthropogenic greenhouse gas concentration. [IPCC, 2007a] The concentration of CO 2 has been increased to about 390 ppm CO 2 at the end of 2010, 39% above the pre-industrial level. This lends to an average global temperature increase of 0.76 C. In order not to exceed a global temperature increase of 2 C with a probability of 67% the CO 2 concentration has to be limited at 450 ppm by This means that only 750 billion tons of GHG can be emitted until For that reason the 2050 GHG emissions must be bisecting in relation to the emissions of Taking into consideration historical reasonability as well as their economic strength, developed countries must reduce their emissions by about 80% to 95% by Countries in transition and developing countries have more time to reduce their emissions. However, taking into consideration the growth of population and the ongoing development in countries of transition and developing countries, a significant increase in energy consumption along with GHG emissions will be noticed. In 2011 the global energy consumption was around 510 EJ/year compared to 340 EJ/year in In parallel to this trend, the yearly amount of GHG emissions is increasing, reaching 30 Gt CO 2 in If this trend is ongoing the limit of 750 Gt GHG emissions will be reached before 2035 and it would cause the 2 C goal to not be met. Nevertheless all societies require energy services to meet basic human needs like lighting, cooking, mobility, communication, and to serve productive processes, but GHG emissions associated with the provision of energy services can be seen as the major cause of climate change [IPCC, 2007a]. Consequently, other ways of energy production have to be found Solar technology The use of renewable energies (RE) offers a great chance to reduce the GHG emissions in an economical way. The costs and the challenges for the integration of RE into an existing energy supply system is mainly dependent on the actual system characteristic, the current share of RE and the availability of RE resources. Based on these circumstances the WBGU recommends establishing representative projects for introducing RE on a large scale. In this way, incentives on a strategic level for a

18 ! 2 global change in energy policies can be set. A strategic partnership between the European Union (EU) and the MENA region can be seen as a key element of such a policy. In such cooperation the EU can offer technologies and finances in order to address their national and international responsibility for climate protection. The MENA region can benefit from transferring their renewable resources as an export product along with benefiting from the accompanying economic growth. [DLR, MED- CSP] The MENA countries have the greatest potential for using direct solar energy on a global scale, with a minimum of 412 EJ/year and a maximum of 11,060 EJ/year. Solar energy especially offers a significant potential for the near-term (until 2020) and the long-term (until 2050) climate change mitigation. The wide range of technologies for harvesting the energy provided by the sun can be excellently implemented in North African countries and the Middle East. The costs of these technologies have considerably reduced over the last 30 years and political conditions as well as technical development will offer additional cost reduction in the future. Besides thermal energy for heating and cooling, PV systems and concentrating solar power electricity generation can play an important roll in the MENA countries. The majority of the world s electricity production nowadays derives from nuclear, coal, gas, oil, and biomass driven power plants. The CSP plants work on the same concept while simply providing an alternative heat source. Therefore CSP can benefit from not only the improvements made in the solar concentrator technologies but also from the ongoing advantages in steam and gas turbine cycles. Further advantages of this technology are that it does not need exotic materials and adding a thermal storage for operations on grid stability is possible. Also the CSP technologies that can be used are cheap. It can be installed in small-scaled applications with a few kwinstalled-capacities (dish/stirling systems) up to multiple MW s (tower and trough systems). [IPCC, SREEN] Parabolic trough plants can be operated as hybrid plants, together with gas turbines, that can be used as desalination plants or operating as pure solar plants with different storage sizes. Actualization of this technology already exists in the MENA region like the Kuraymat power station. The focus in this work is with parabolic trough technology installed in North African regions. The next part will give a rough overview about the parabolic trough technology.

19 ! Parabolic trough technology The solar field produces thermal energy by using direct normal irradiation (DNI), and delivers this energy to a steam power plant. The solar field can be considered in a first approach as a solar steam generator. The glass mirror of the solar field has a parabolic shape and is reflecting the incoming direct radiation with a concentration value of around 80 to the absorber tube. One of the most modern Collectors nowadays is the type LS-3. One LS-3 collector consists of 224 mirror segments, where each segment has an area of 2.68 m 2. Taking into consideration the bending of the mirrors, an area of 545 m 2 is reached with one LS-3 collector. In addition the collector contains 24 absorber tubes. The complete construction is a lightweight metal structure, which normally is equipped with a single axis tracking system. Figure 1: Functional principle of a parabolic trough [REB] A complete solar field contains several parallel rows of solar collectors, which get connected in loops of normally 6 LS-3 collectors. The power block is located in the center of the solar field. The distance between the collector rows is planned according to minimizing the piping costs on the one hand and having a minimal shading effect between the rows on the other. In general the design of the solar field depends on plant and collector size, the temperature and pressure losses in the piping system and the specific ambient conditions. Parabolic trough fields can be erected in any direction, but erected in a north-south direction leads to the highest

20 ! 4 possible energy yield over the year while an east-west orientation smoothes down the seasonal fluctuations. Some of the components like the metal structure, the tracking system, the controllers and other subsystems, which make up around 60% of the direct solar field costs, are standard components and can be ordered from several countries and in different forms. The reflectors and the absorber tube, however, are special components and have to be produced specifically for the parabolic trough solar field Reflectors The concentrators (see figure 1) consist of a heat-formed glass cake. It is carried by the metal structure of the collector. By using special production techniques, like the float-glass method, absolute evenness of the cake is guaranteed. Glass, which is used in solar applications, must have very low iron content for getting a transmissivity in the solar spectrum of around 91%. The iron content of a so-called White Glass is around 0.015% compared to normal glass with an iron content of around 0.13%. The binding of the reflectors is done under heat conditions. Several safety layer coatings are added, giving additional protection for the mirror. Finally the contour accuracy is tested using a laser beam Absorber For the LS-3 collectors the absorber pipe consists of a stainless steel tube with a length of 4 meters and a thickness of 70mm. A glass pipe surrounds the tube (see figure 2). The glass tube allows evacuating of the area between the absorber tube and the glass pipe in order to minimize convection and conduction heat losses. Figure 2: Absorber tube of a parabolic trough collector [REB] The vacuum also serves to protect the highly sensitive coating. Nowadays, such selective coatings remain stable in temperatures of 450 C upwards to 500 C. On average the solar absorption is currently above 95% and at an operational

21 ! 5 temperature of around 400 C the emissivity is below 14%. This leads to an optical efficiency of around 80% for upcoming perpendicular radiation. Furthermore the hydrogen getter (see figure 2) absorbs the hydrogen, which is getting through the glass pipe and the stainless steel pipe by diffusion. A membrane finally pumps the hydrogen out of the vacuum. As a final point, glass/metal joints realize extension bellows compensating the thermal expansion of the pipe, and the connection between the glass pipe and the metal structure Tracking and controlling Solar fields in a CSP plant use single axel tracking systems. The tracking is according to the position of the sun and/or the requirement of the power block. Therefore a solar sensor is used to evaluate the sun position. Sensors consisting of a convex lens focus the sun light to a small photovoltaic cell, reaching a resolution of around 0.05%. These kinds of sensors are used in the so-called SEGS plants, where they prove most effective. The tracking system must have sufficient torque to operate the collectors even at higher wind speeds. For LS-3 collector s normally electrohydraulic drives are used. In the design specs the movement can take place with a speed of 9 m/s. For emergency reasons or for operation conditions, which are not requiring a high optical efficiency, the speed can be increased up to 20 m/s. In existing plants the controlling of the field takes place in two separate stages. The overall control is located in the central control room and the second stage is placed on each collector unit. The local units take care of the incoming irradiation; wind speed and mass flow of heat transport medium. In case of emergency the local units can shut down parts of the solar field. The overall unit operates the solar field according to the overall plant requirements, mainly the electrical output in relation to the actual solar radiation Heat transfer medium At the moment high-boiling synthetic thermal oil has been applied as the heat transfer medium in the absorber tubes. According to the thermal stability of this oil the actual operation temperature of the solar field is approximately 400 C. When operating at this temperature, the oil has to be pressurized at around 12 to 16 bar. The thermal oil is circulating in the collector tubes, where the driving forces are speed adjustable pumps. For the purpose of thermal expansion during its heat up an expansion vessel is installed.

22 ! Thermal storage The availability of thermal storages currently plays an important role for the economic success of solar thermal power plants. In parabolic trough plants sensible heat storages, operating with temperatures between 300 C and 400 C, are in use. The storage has a significant influence on the operating conditions of the solar thermal plant. Changes in the solar radiation availability lead, without proper storage, to a change in the electrical output. This not only leads to the plant having a reduced supply security, but also to a reduced lifetime of the steam turbine itself. Frequent changes to the load of the turbine lead to more thermal stresses, thus reducing the lifetime of the turbine. Larger storages are able to support load shift to non-day times, for example the evening hours when peak load demand is needed. In combination with an over dimension of the solar field the yearly operational hours can be extended significantly. Therefore the operation time of around 2,000 hours per year can be increased to 4,000 hours per year by doubling the solar field and storing the produced energy over the day. The solar multiple can extend up to 8,000 operating hours per year. This allows solar multiple (SM) plants to operate as base load plants. SM is used as an indicator of how much the solar field is oversized. SM 2 means an additional energy for around 2,000 operating hours per year, SM 3 for a sum of 6,000 operating hours per year and so on. The figure 3 displays one possible arrangement of a CSPP with thermal storage. Figure 3: Basic concept for the integration of thermal energy storage into a solar thermal parabolic trough power plant [REB]

23 ! Thesis objectives and outlines The objective of the thesis is to develop a physical model; witch can predict the electrical output of CSP parabolic thought plants in North Africa. Furthermore it have to be analyzed how these CSP plants can contribute to a 100% renewable energy supply in Germany for the year Consequently the model must be able to deal with data sets out of the SIM-EE model [UBA2050]. Using Matlab as programming software it is possibility to fulfill this requirement. So far no exclusive solar driven CSP plants installed in North Africa. Realistic predictions for the future have to be developed, and ways of distributing the CSP plants in North Africa must be evaluated. Therefore, the first work for the thesis is to find a way to estimating suitable locations for CSP plants in North Africa. Criteria s for land use, annual irradiation and infrastructure, can be used to do so. Furthermore weather prediction model must be added to the simulation for getting exact results. Also different configurations for the plant like various forms of storage sizes and different cooling must be considered. The second part of the thesis is implementing process criteria s from the SIM-EE model in order to compare the results from part one, with results from the SIM-EE simulation for The focus should be on the effective load carrying capacity witch will allow to make statement related to the influence import energy from North Africa has on the 100% renewable energy system in Germany for the year The thesis starts with a theoretical description of the physical processes, occurring in a parabolic trough CSPP. In the next chapter the recourses and the potential for CSP plants in North Africa, related to several criteria s are analyzed. The program development is described in the 4 th chapter. This chapter contains also the results of the simulation program and the added program parts from the SIM-EE model. The 5 th chapter finally, presents the outlines and the results for the export scenario analyze. Chapter six summarizes the results and is giving an outlook for possible further investigations.

24 ! 8 2. Theoretical performance calculation CSPP 2.1 Geometrical relations The energy contained in the direct normal radiation is harvest by the concentration collectors of a solar field. By reflecting the received normal direct radiation to the absorber, thermal energy is produced and transported to the power block. Conventional technology is used to convert this energy into electrical energy. Therefore the incoming radiation can be seen as the fuel of a CSP plant. For a precise calculation of the CSPP performance it is essential to understand the geometrical relations between the sun and earth at any time of the day. In this chapter these theoretical relations are described Sun earth geometry The geometrical relationship between the incoming direct radiation and a plane of any orientation at every hour can be described in terms of several angles. The following schematic drawing gives an overview of these geometrical relations. Figure 4: Geometrical relation between sunbeam and tilted surface [REG]. The most important angel, in this arrangement is the so-called incidence angle! it can be calculated out of [SETP; S.14]: (2.1) Here " is the tilt angle of the plane, and # the surface azimuth angle, with 0 in the southern direction, then becoming negative when moving towards an eastern direction or positive in a western direction. Both angles can be either fixed or adjusted according to sun position by using a tracking system. The angle of

25 ! 9 declination $ can be found by the approximate equation of Cooper (1969) [SETP; S.16]: # " = 23.45sin n & % ( (2.2) $ 365 ' This angle represents the angular position of the sun at solar noon in relation to the plane of the equator. The number of days in a year is represented by n. The hour angle % sets the angular displacement of the sun east or west of the local meridian. This is done due to rotation of the earth with a value of around 15 per hour. The angle will be negative in the morning and positive in the afternoon. The latitude in equation (2.1) is mentioned with & and reveres to a certain location. The zenith angle can be understood as the incidence angle of beam radiation on a horizontal surface. Therefore equation (2.1) can be simplified to [SETP; S.16]: cos" z = (cos# cos$ cos% + sin# sin$) (2.3) The sun height " s shown in figure 4 is the complementary angle of! z. Due to this reason it can simply be stated as: " s = 90 #$ z (2.4) Tracking systems for the collector are important in terms of harvesting the maximum amount of energy out of the sunlight. The standard tracking system for a parabolic trough collector is a single axis tracking system. The collector orientation is normally either in a north-south or east-west direction. For a fixed east-west direction the surface azimuth is defined as [SETP; S.21]: $ " = 0 if " s < 90 % & 180 if " s # 90 (2.5) Therefore the tilt angel of the surface can be calculated by [SETP; S.21]: tan" = tan# z cos$ s (2.6) The aim of the one axis tracking system is to minimize the angle of incidence. For tracking in north south direction the angle can be evaluated according to [SETP; S.21]: cos" = (1 # cos 2 $ sin 2 %) (2.7) The same calculations can be undertaken for a fixed north-south orientation of the collector surface. Here the surface azimuth is defined by [SETP; S.22]:

26 ! 10 % " = 90 if " s > 0 & '#90 if " s $ 0 (2.8) Consequently, the collector tilt angle is evaluated according to the following equation [SETP; S.21]: tan" = tan# z cos($ % $ s ) (2.9) According to equation (2.8) the surface azimuth angle will be 90 or -90 depending on the sign of the solar azimuth angle. The incidence angle for a plane rotating about a horizontal north-south axis, with continuous tracking, is [SETP; S.21]: cos" = (cos 2 " z + cos 2 # sin 2 $ ) (2.10) Based on the angles described in this chapter it is possible to calculate the incoming beam radiation on a collector field, with one axis tracking system for a certain location and time Sun collector geometry For the operation of a CSPP temperatures of around 400 C are necessary. These high temperatures cannot be reached with a flat plate collector. Therefore concentrating collectors are used. One type of these concentrating collectors is the parabolic trough collector. The direct normal radiation reaching the collector is concentrated on the absorber tube located in the focal point of the parabolic collector. The most important characteristic factor therefore, is the concentration ratio. It is defined as the aperture area in relation to the absorber area [SETP; S.327]: C = A a A abs (2.11) Here A a is the aperture area and A abs the area of the absorber. For a three dimensional system like a parabolic dish system with a two axis tracking system, which is focusing on one point, the maximum concentration ratio is around 45,000. However, the parabolic trough is a two dimensional system, where a maximum concentration ratio of 200 can be reached. The most significant losses under some circumstances occurring in a solar field are the shading losses. This reduction is happening when one collector row reflects their shadow onto the next row. In well-designed CSP plants this effect only shows up in the morning or evening hours with shadowing due to low tilt angle. However at these times shading losses can reach a maximum of up to 100%, where the rest of the day

27 ! 11 these losses are close to zero. The part of the collector area that is not in the shaded region, can be approximately calculated according to [DLS; S.10]: & )& ( + H sin$ sin% ) ( D + D " SL =1# ( 1# + ( tan$ ( & H cos$ + cos% 1# s + ) + ( & r ( ( sin$ + + H cos$ + cos% ) + r ( ( sin$ + L+ ' ' cos$ s **' ' cos$ s * * (2.12) If the result of the equation above is smaller or equal to zero the collector is completely in the shadow. If the result is greater or equal to one, no shading losses are occurring on the collector. It is obvious that the shading effect is dependent on the collector size and the distance between the collector rows. In equation (2.12) D represents the distance between the collector rows in meters, H the height of the collector in meters and L the length of a collector row also in meters. The relative azimuth angle # r can be calculated as the absolute value of the different between the solar and the surface azimuth angel. Another loss factor occurs because, the incoming radiation to the collector is not exact perpendicular and the absorber tube has a finite length. At the end of each collector a certain part of the absorber tube will be not be irradiated. This displacement of the sun image is shown in the following figure Figure 5: Displacement of the sun image [SLP]. In the northern hemisphere these effects can be noticed especially during wintertime. Normally these losses are under two percent in feasible areas for CSP plants. Nevertheless, the reduction factor can be calculated according to [SLP; S.22]: l = f tan" sin (# $ # s ) (2.13) In formula (2.13) l represents the length of the not irradiated part, displayed in figure 5. The focal length f depends on the collector design. Consequently, the losses in percentage can be calculated as:

28 ! 12 " EV =1# l L (2.14) Further losses that occur depend on the finite earth sun distance where the beams reaching the collectors are also not exactly parallel. As a result the sun image on the absorbers is not precisely circular. The image can be seen in the form of an ellipse, which changes the frame, depending on the angle of incidence. Only for! is zero the image will be circular. By increasing the incidence angle the performance characteristic of the sun image becomes worse. This happens because the absorber is designed for a perfect circular sun image. This effect is called incidence angle modifier and can be predicted according to Marco (1995) as follows [SLP; S.23]: " IAM = cos#(1+ sin 3 #) (2.15) From formula (2.15) we can observe that the losses occurring are negligible. Nevertheless, they do increase with distance from the equator. Finally the irradiation reaching the collector can be separated in two parts. One is exactly perpendicular the other one is horizontal to the collector. The collector however only can reflect the perpendicular part of the radiation. This leads to the socalled cosin-effect. Here the amount of useful irradiation can be calculated by [DLS; S.9]: " COS = cos# (2.16) Finally the amount of energy, which can be reflected per square meter of collector area to the absorber, can be calculated [DLS; S.10]: IDR = " COS " IAM " SL " EV (2.17) IDR stand for Incident Direct Radiation and represents the useful part of energy provided under ideal conditions to the absorber tube. 2.2 Solar field Inside of the absorber tube a heat transport medium, mainly synthetic oil, is used to collect the thermal energy and transport it to heat exchangers for producing steam in order to operate a steam turbine. During the transportion of the oil thermal losses can be recognized, and also further losses during the concentration process have to be taken into account Optical losses Energy losses not only occur because of geometrical reasons like shading or unirradiated absorber parts, but also from the material properties of the mirror, the

29 ! 13 hull pipe, and the absorber. Therefore, some operating figures will be defined. They are all dependent on the design quality of the collector elements being used [DLS; S.12]: Reflectivity of the mirror: A small part of the incidence radiation is not reflected to the absorber, because the reflectivity of the mirror being finite. The mirror absorbs a part of the incoming radiation. As an average the reflection coefficient of a mirror used in solar thermal abdications can be set to '=0.93 [DLS; S.12]. Contamination of the mirror: The part of irradiation, which is absorbed by the mirror, is increasing with ongoing contamination of the mirror surface. Taking into consideration frequently washing procedure the contamination factor can be estimated with $=0.98 [DLS; S.12]. Transmission factor of the mirror: The glass on the top of the mirror also partly absorbs the irradiation. The irradiation has to pass the glass cover two times, which leads to a transmission coefficient of around ( s =0.99 [DLS; S.12]. Quality factor of the mirror: The quality factors depending on the production processes as well as the erection on site. For example the absorber tube is not exactly mounted in the focal point of the mirror additional losses will occur. Also different focal length of the mirror plats will lead to additional losses. Nowadays a quality factor of )=0.90 is assumed. [DLS; S.12]. Transmission factor of the hull pipe: A small part of the reflected irradiation is again reflected by the glass pipe, which surrounds the absorber tube. This transmission coefficient can be set here to ( H =0.95 [DLS; S.12]. Absorption factor of the absorber pipe: At the absorber tube not all of the reflected radiation will be absorbed. Due to physical conditions a part of the radiation will always be reflected. The absorption factor can be estimated with #=0.95 [DLS; S.12]. All the quality and material factors mentioned above are factored for an LS-3 collector type. Taking into consideration all the additional factors above it is finally possible to calculate the amount of energy received per square meter absorber pipe:

30 ! 14 G A = IDR"#$% H % 2 S = IDR& opt (2.18) As displayed in equation (2.18) the combination of all quality factors can be summarized as the optical efficiency of the mirror * opt. In the formula above G A represents the irradiation reaching the absorber pipe per square meter. Now the part of how the transformation into thermal energy and consequently, the losses occurring during transportation in the absorber pipe is described Heat losses Until now it has been described how the energy of the direct solar radiation reaches the surface of the absorber. Here the form of energy is now changed into thermal energy. This can be described by constructing an energy balance equation like [SLP; S.23]: G A A" = Q n+ Q (2.19) losses Here A is the absorber area and + is the absorbance of the absorber. Q n identifies the useful thermal energy collected in the thermal oil and the thermal losses are combined in Q Losses. Physically there are three different types of heat transportation, occurring naturally. These are heat transport according to convention, conduction and radiation. However these phenomena are the reason for the thermal losses in the solar field. The losses depending on conduction and convection can be set in a first approach in a linear relation with the difference between the average absorber temperature and the ambient temperature [SLP; S.24]: Q CC = U CC A(T a " T U ) (2.20) U CC is the heat transfer coefficient, which is adjusted by measurement results. The average absorber temperature is labeled T a, and T u is the ambient temperature. In addition to the convection and conduction losses, the thermal radiation losses must be taken into consideration. Therefore the heat flux between two surfaces by thermal radiation is described as [VDW; S.255]: Q "(T 4 rad = 2 # T 4 1 ) 1 #$ #$ 2 $ 1 A 1 A 1 F 1,2 $ 2 A 2 (2.21) T represents the temperature for each of the two surfaces, F is the area angle between the surfaces, A is the area of the surfaces, + is the Stefan Boltzmann constant, and, is the emission coefficient for each surfaces. In case of a solar field it

31 ! 15 can be assumed that the absorber area is relatively small compared to the ambient area. These allows to simplify equation (2.21) to [SLP; S.24]: Q rad = " 1 A 1 #(T 2 4 $ T 1 4 ) (2.22) In the formula above the emissivity of the environment is considered with one. A 1 displays the area of the absorber. Now the energy used for heating up of the collector, for example in the morning hours can be calculated by [SLP; S.25]: Q C = AU C (T c " T a ) (2.23) U C shows the heat transfer coefficient of the collector and Tc is the collector temperature. Putting all these thermal losses together and combining it with formula (2.19) the amount of thermal energy produced by the solar field can be calculated out of : Q n = G"A # AU CC (T c # T a ) #$% c A(T 4 c # T 4 a ) # AU c (T c # T a ) (2.24) Consequently, the amount of energy collected in the absorber must be transported either into storage or to the power block. Here additional losses in the absorber pipe will be occurring. Finally these piping losses can be calculated according to [SLP; S.33]: Q P = U P (T F " T a ) (2.25) Now all necessary relations for the description of how the energy provided by the sun is harvested and distributed either into storage or to the power block are described. The point of interest is now the storage and power block arrangements. 2.3 Thermal Storage There are two general types of thermal storage mechanisms. The first one is based upon the use of sensible heat in various forms of solid and/or liquid materials. The other storage type involves the latent heat of phase change reactions. Sensible heat is added to a material simply by heating it up. Generally all energy that is involved in changing the temperature of a medium is called sensible heat, and it amounts simply to the product of the specific heat and the temperature change. [ES; S.22]: q = "c p V#T (2.26) In equation (2.26) ' is the density of the storage material, c p the specific heat capacity at constant pressure of the storage material and V the volume of the

32 ! 16 storage. A different mechanism for storing thermal energy involves a phase transition with no change in the chemical composition of the storage material. A simple example therefore is water. At low temperatures under 0 C it is solid, at temperatures between 1 C and 99 C it becomes liquid and at temperatures above 100 C it converts into gas. Thus, it can undergo two transition phases, with associated changes in entropy and enthalpy. The Gibbs free energy, or chemical potential, for the two phases are in equilibrium with each other at the transition temperature. Therefore it can be evaluated according to [ES; S.23]"! "G = "H # T"S = 0 (2.27) At the temperature, the change in heat content -H at the transition temperature is equal to T-S. The slope of the temperature dependence of the Gibbs free energy and is proportional to the negative value of the entropy, which is different in diverse phases and materials. Considering that state-of-the-art sensible heat storages are used in CSP plants, here two different ways of calculating this kind of thermal storage will be described Stratification Storage the Multi-node-model Liquid storage tanks are operated at a significant degree of stratification. The degree of stratification in real operation is strongly dependent on the design of the tank and its location. In the multi-node model heat storage is modeled and divided into N nodes in order to display the stratification layers. In order to formulate the necessary equations, it will be appropriate to set some assumptions about how the liquid will be entering the tank and how the distribution to the several nodes takes place. The density of the liquid is dependent on the temperature. Therefore we can assume that the storage material will find its way to the node with the same temperature as the liquid. As it is displayed in figure 6 the mass flow coming from the collector field m c finds its way to a node according to its temperature between T s,1 and T s,3. The same physical effect can be discovered when the liquid enters the tank upstream.