Category Archives: EuroSun2008-2

Optimizing the Tracking System

The main task in optimizing the active component (the tracked solar collector) is to maximize the energetic gain by increasing the solar input and minimizing the energy consumption for tracking. The solar collector can be rotated without brakes during the day-light, or can be discontinuously driven (step-by-step motion), usually by rotating the collector with equal steps at every hour. Obviously, the maximum incident solar radiation is obtained for the continuous motion, but in this case the operating time of the motor is high. In order to accomplish the paper goal, we used an optimization strategy comprising two steps: designing the optimal motion law — the key idea is to maximize the incident radiation gained through step-by-step orientation, for absorbing a quantity of solar energy closed to the ideal case (continuous orientation); designing the optimal tracking mechanism — this design intends to minimize the actuating force that is needed for realizing the motion law; the optimization problem uses the dynamic model of the mechanical structure, and computes the geometrical parameters.

The step-by-step tracking strategies were formulated using optimal algorithms based on the number of steps necessary for orientation [12]. These algorithms were developed considering the correlation between the maximum amplitudes of the motion and the number of the tracking steps, aiming to the minimization of the steps number. In fact, the optimization is made by reducing the angular field of the daily motion and the number of actuating operations without significantly affecting the incoming energy. It has been demonstrated that for every month there is one day whose irradiation is equal to the monthly average: it is the day in which the declination equals the mean declination of the month [13]. Due to this consideration, a noticeable facilitation is introduced in the computing calculation, considering just the mean days of each month instead of the 365 days of the year.

The paper presents the exemplification for the spring equinox day, the numeric simulations being performed for the Bra§ov geographic area, with the following data: the location latitude, 45.6333 N; the longitude, 25.5833 E; the day number during the year, 81; the local time for sunshine, 6.316; the local time for sunset, 18.533; the seasonal position, 42.5°. According with the orientation program developed in [12], the angular field for the daily motion in the spring equinox day is P* є [+64°, -64°] (P*=0 in the solar noon position, positive values in the morning, negative values in the afternoon). The orientation is made in 6 motion steps, as follows (local time): 8.967 (AP*=23°), 10.467 (Ap*=22°), 11.817 (Др*=19°), 13.017 (Д3*=19°), 14.367 (Др*=22°), 15.867 (ДР*=23°); the operating time for each step is 0.1 h. The system is fixed maintained in the intervals after sunshine, P* = +64°, T = (6.316 — 8.967), and before sunset, P* = -64°, T = (15.967 — 18.533). The return of the system in the initial position is made after sunset, with continuous motion in 0.2 hours. With these data, the time-history of the daily angle of the solar collector (i. e. the motion law

Подпись: Fig. 3. The motion law of the tracking system. Подпись: Fig. 4. The incident radiation curves.

of the tracking system) is shown in figure 3. At the same time, in figure 4 there are presented the incident radiation curves for the following situations: a — the proposed motion law (according with figure 3), b — the maximum incident radiation that can be obtained for the continuous orientation of the panel in the maximum angular field p* є [+90°, -90°], and c — the fixed panel case. As we can see, the energy obtained by tracking the Sun with the proposed motion law is close-by the ideal case, with a minimum operating time of the motor (this is very important for the reliability & durability of the system, including the motor’s wearing).

The next step in optimizing the tracked solar collector is the geometric optimization of the tracking mechanism. The optimization is approached as a problem to minimize the objective function over a selection of design variables, while satisfying various constraints on the design. The objective function is a numerical representation of the tracking system efficiency, the optimum values of this function corresponding to the best possible design. In our case, the minimization of the energy consumption for realizing the motion law is the design objective. The energy consumption (in fact, the mechanical work consumption) is obtained by integrating the power consumption curve in absolute value.

The geometric optimization of the tracking mechanism was made by using the MBS environment ADAMS, considering the following steps: parameterizing the virtual model, defining the design variables, defining the design objective, and optimizing the model. The parameterization of the tracking mechanism was made using the points that define the structural model, in fact the location of the revolute joint between collector and support. The revolute axis, which is parallel with the polar axis, is defined by the points pair A-A’ (from kinematic point of view, in A’ there is a redundant joint). For the optimization process, there was taken into consideration the global vertical coordinate of the points A-A’ (see figure 1), which has been modelled as design variable (ZA = ZA’ ^ DV_1). In fact, this coordinate (variable) defines the relative distance between the mass centre of the collector and the revolution axis.

The sensibility of the objective function on the modification of the design variable is shown in figure 5 (the value range for the design variable is ±10% relative to the initial value). The solution for minimizing the consumption (the objective of the geometric optimization) is to dispose the revolute axis as close as possible to the mass centre of the collector, respecting the constructive constraints induced by the mounting of the motor.

Подпись: Fig. 5. The influence of the design variable on the objective function.

image132 image133

In these conditions, the results obtained after the optimization process of the tracking systems are shown in the diagrams from figure 6, as follows: the control torque, the power & energy (mechanical work) consumption, and the resistant torque in the irreversible transmission when the system is in the stationary positions, for blocking the system between the motion steps (the measure units: newton, meter, hour, joule). These results are very useful for evaluating the behaviour of the solar tracking system. The energy balance can be performed considering the energy gain obtained by orientation, and the energy consumption for realizing the motion law.

Fig. 6. The results of the simulation for the mechatronic tracking system.

2. Final Conclusions

The application is a relevant example regarding the implementation of the virtual prototyping tools in the design process of the tracking systems used for the solar collectors. One of the most

important advantages of this kind of simulation is the possibility to perform virtual measurements in any point or area, and for any parameter (motion, force, energy). At the same time, integrating the electronic control system in the mechanical structure of the solar tracker at the virtual prototype level (i. e. the modelling in the mechatronic concept), the physical testing process is greatly simplified, and the risk of the control law being poorly matched to the real system is eliminated.

The optimization strategy based-on two operational steps (the optimization of the motion law, and the geometric optimization of the mechanical structure) leads to an efficient tracking system, without developing expensive hardware prototypes. In this way, the behavioural performance predictions are obtained much earlier in the design cycle of the tracking system, thereby allowing more effective and cost efficient design changes and reducing overall risk substantially.

The tracking system will be manufactured and tested in the Centre Product Design for Sustainable Development from Transilvania University, creating a real perspective for the research in the field. This allows a relevant comparison between the virtual prototype analysis and the data achieved by measurements.

References

[1] G. N. Tiwari, Solar Energy, (2002). Alpha Science Int. Ltd., Pangbourne.

[2] J. Garcia de Jalon, E. Bayo, (1994). Kinematic and Dynamic Simulation of Multibody Systems, Springer — Verlag, New York.

[3] W. Schiehlen, Multibody Systems — Roots & Perspectives, Multibody Systems Dynamics, 2 (1997) 149­188.

[4] R. Ryan, (2001). Functional Virtual Prototyping, MSC Software Publisher, Santa Anna.

[5] C. Alexandra, M. Commit, (2007). Virtual Prototyping of the Solar Tracking Systems, Proceedings of the International Conference on Renewable Energy and Power Quality — ICREPQ, Seville.

[6] S. Abdallah, S. Nijmeh, Two-Axes Sun Tracking with PLC Control, Energy Conversion and Management, 45 (2004) 1931-1939.

[7] M. Alata, M. A. Al-Nimr, Y. Qaroush, Developing a Multipurpose Sun Tracking System using Fuzzy Control, Energy Conversion and Management, 46 (2005) 1229-1245.

[8] K. Karimov, M. Saqib, P. Akhter, A Simple Tracking System, Solar Energy, 87 (2005) 49-59.

[9] S. Odeh, (2004). Design of a Single-Axis Tracking Collector, Proceedings of the 14th EuroSun Conference, Freiburg.

[10] P. Roth, A. Georgiev, H. Boudinov, Design and Construction of a System for Sun-Tracking, Renewable Energy, 29 (2004) 393-402.

[11] M. Commit, I. Vi§a, (2007). Design of the Linkages-type Tracking Mechanisms by using MBS Method, Proceedings of the 12th IFToMM World Congress, Besangon.

[12] I. Vi§a, D. Diaconescu, (2007). On the Incidence Angle Optimization of the Dual-Axis Solar Trackers, Proceedings of the 11th International Research Expert Conference — TMT, Hammamet.

[13] R. Sorichetti, O. Perpinan, (2007). Solar Tracking Systems Analysis, Proceedings of the 22nd European Photovoltaic Solar Energy Conference — EUPVSEC, Milano.

. Parabolic trough collector

Solar concentrators have been optically designed, analysed and experimented in our laboratory since 1997 [1-8]. The possible applications relate to Photo Voltaic sector, thermal field and internal
illumination. The paper examines one-axis tracking collectors with parabolic profile by means of ray tracing simulations. The configuration includes a linear parabolic mirror concentrating the light on an absorber represented by a metal pipe, surrounded by a glass tube. Figure 1 presents an overview of the parabolic trough collector. Figure 2 shows parabolic mirror profile and circular absorber section, whose centre is located in the parabola focus.

The paper summarises the results of several studies analysing the interactions between collector axis placement, sun’s altitude and collected light. The complete series of ray tracing simulations examines the solar parabolic trough and its possible geometrical modifications. Different versions of solar trough are combined to various sun’s altitudes and errors in collector axis placement, estimating the amount of energetic losses.

The reference configuration includes a linear parabolic mirror with focal length f=800mm. The dimensions of collector aperture are: width W=1.8m and length L=5m. The metal pipe has external diameter d=50mm and length L=5m. The glass tube has external diameter D=60mm and thickness T=3mm. In all simulations the absorber centre is located in the focal position.

Outlook / Operation

It is planned to start installation of the receiver-reactor at the SSPS tower of Plataforma Solar de Almeria in 2008. Initial solar testing is scheduled to the end of 2008 and will last for 3 months. The test program includes the following:

1. Startup and shut down procedures including transition air to steam and steam to steam/coke, and vice versa.

2. Steady state test for evaluation of performance (variation of solar flux conditions, mass flow and feed gas composition).

3. Transient tests (controlled defocus of heliostats). Thermal inertia, response to operating conditions, etc

4. Long term testing to obtain information about lifetime aspects

5. Control tools for normal operation. Start-up procedure vs mass flow, steady-state conditions, shut-down parameters, etc

6. Chemical campaign. Chemical and receiver efficiencies, gas composition, maximum hydrogen conversion, etc

The objective of this initial campaign (points 1 to 4) will be to obtain operating experience with the system at power levels approaching the maximum load. Another test series (5 to 6) will be carried out to investigate the chemical behaviour of the whole installation.

A conceptual layout of a commercial 50 MWth gasification plant in Venezuela will complete this project. Results of the testing campaign will provide input to the pre-design of the gasification plant in Venezuela. The test data will be evaluated and compared with simulation tools in order to verify the calculations and to identify potential problems. The major components of a solar petcoke reforming plant will be analysed to assess their impact on the conceptual layout of the plant. For the upstream part of the gasification loop, the operation with different gaseous feedstocks (natural gas, weak gas, bio-gas, landfill gas), and concepts for gas cleaning and gas treatment will all be assessed.

2. References

[1] Z’Graggen A., Haueter P., Trommer D., Romero M., de Jesus J. C., Steinfeld A. (2005) Hydrogen production by steam-gasification of petroleum coke using concentrated solar power — II. Reactor design, testing, and modeling, Int. J. Hydrogen Energy, Vol. 31, pp 797-811, 2006.

[2] Minchener, A. “Coal gasification for advanced power generation” Fuel, 84 (2005), 2222-2235.

[3] Z’Graggen A., Haueter P., Maag G., Vidal A., Romero M., Steinfeld A., “Hydrogen Production by Steam-Gasification of Petroleum Coke using Concentrated Solar Power — III. Reactor experimentation with slurry feeding”, International Journal of Hydrogen Energy, Vol. 32, pp. 992-996, 2007.

[4] Thorsten Denk, Philipp Haueter, Alfonso Vidal, Luis Zacarias and Antonio Valverde. Upscaling of a solar powered reactor for CO2-free syngas and hydrogen production by steam gasification of petroleum coke. 13th International Symposium on Concentrating Solar Power and Chemical Energy Technologies. June 20, 2006. Seville. Spain.

Experimental Investigation

The preliminary experimental evaluation involved building and instrumenting an ISAHP system in a laboratory setting, based on the recommendations of component sizing given by Freeman [4].

The solar collector in Figure 1 was replaced with an auxiliary heater in order to perform controlled experiments. Quasi steady-state tests were run at range of constant input temperatures with all variables constant except for the natural convection flow rate. The natural convection flow rate varied throughout the duration of the test while the tank temperature increased. The preliminary results indicated that the original computer model over-predicted the actual COP of the system.

This discrepancy was determined to be due to an over-prediction of the heat exchanger effectiveness values for both the condenser and evaporator. After correcting the heat exchanger effectiveness values in the simulation, the results for power consumption and COP matched to within 3.0 % of each other for the 10oC test.

Steam Rankine cycle — Reverse Osmosis plant

image047

To construct the model, all the components of the system are interconnected of appropriate manner in the Trnsys program, as shows in the Fig.2. Table 1 shows the main parameters used in each Trnsys component. The working pressure required in the RO system is calculated for seawater with a salinity of 36000 ppm. The meteorological data corresponds to the city of Almeria in the south of the Mediterranean coast of Spain. The solar plant uses a trough collector SEGS LS-2 modelled as implemented in the Trnsys program. The plant has an area of 1000 m2 of solar collectors with the tracking axis oriented in the North-South direction. In [19] the results for the steam Rankine cycle using a different orientation can be found for comparison.

The Trnsys unit Type 66, allows the user to call an EES file, receive data from Trnsys component: Flow Rate Solar Field (Fs) and Outlet temperature Solar Field (To) and pass its output data to other

image048
image049

Tmsys component: Inlet Temperature Solar Field (Ti), turbine power (Wt) and exchanged heat in the evaporator and condenser, (Qv, Qpre), as represented by Fig. 3(b). The model developed in EES program, consists basically in material and energy balance equations as well as thermodynamic properties, using n-pentane as working fluid. Fig 3(c) shows the main components of the ORC: preheater, evaporator, recuperator, turbine, pump and condenser.

Fig. 3. (a) Main components of Trnsys used in the Solar ORC simulation. (b) Component Type 66. (c)

ORC cycle diagram.

Table 1. Main parameters used in Trnsys

Steam Rankine cycle — RO System

Organic Rankine cycle — RO system

Components

Parameters

Value (Trnsys)

Value (Trnsys and EES)

Solar System

Total field area

1000 [m2]

1000[m2]

Pump max flow rate

10000 (January), 40000 (June) [kg/h]__________

10000 (January), 40000 (June) [kg/h]

Pump max power

20000[kJ/hr]

20000[kJ/hr]

Demanded outlet temperature

190[°C]

300[°C]

Sun Zenith

Turbine

Inlet flow rate

18000 [kg/hr]

18000 [kg/hr]

Efficiency isentropic

0.7

0.7

Condenser

Temperature

5 [°C]

5 [°C]

Superheat

Heat transfer coef. of exchanger

2300 [kJ/kgK]

Evaporator

Efficiency

0.7

Heat transfer coef. of exchanger

18000 [kJ/kgK]

Preheat

Heat transfer coef. of exchanger

3500 [kJ/kgK]

Efficiency

0.7

Pump (Rankine cycle)

Pressure

64.8 [bar]

64.8 [bar]

Efficiency

0.7

0.7

RO Membrane

Recovery ratio (RR)

0.5

0.5

Feed Seawater

Pressure

1 [bar]

1 [bar]

Temperature

20 [oC]

20 [oC]

Scope of the work

The Solar Turbine Group (STG) was founded for the purpose of developing and implementing a small scale solar thermal technology utilizing medium temperature collectors and an ORC to achieve economics analogous to large-scale solar thermal installations. This configuration aims at replacing or supplementing Diesel generators in off grid areas of developing countries, by generating clean power at a lower levelized cost (~$0.12/kWh compared to ~$0.30/kWh for Diesel [9, 11]). At the core of this

Подпись: Figure 1 Solar ORC platform for off grid micro utility power generation Подпись: Figure 2 Solar ORC in field trials in Lesotho, southern Africa 2007 (Solar Turbine Group)

technology is a solar thermal power plant consisting in a field of parabolic solar concentrating collectors and a vapor expansion power block for generating electricity (figure 1). An electronic control unit is added for autonomous operation as sub-megawatt scale plants cannot justify the staffing of operating personnel. The design tradeoffs for maintaining low costs at small scales, include operating at a lower cycle temperatures (<200 DC) and using an ORC: lower temperatures enable cost savings in the materials and manufacture of the absorber units, heat exchangers, fluid manifolds and parabolic troughs.

Because no thermal power blocks are currently manufactured in the kilowatt range a small-scale ORC has been designed for this application (Figure 2). The design is based on off-the-shelf components with little modification, such as HVAC scroll compressors (for the expander), and car power steering pumps.

A novel control strategy and electronic control system is required for the components discussed above to work in concert and in a maximally efficient manner. Among the functions to be managed is the control of individual components, such as Solar ORC fluid machinery, as well as directing the energy flows between these components, battery storage and AC loads. Optimization of the control strategy, a major objective of ongoing research, will be based on theoretical and experimental characterization of all system components, and will, in practice, rely on developing a control system with feedback from diverse parameters ranging from ambient temperature to the particular load profile to be matched.

The work presented in this paper focuses on the characterization of the ORC system by developing and validating a model, which will be used to select the best components, working fluid and control strategies for the solar Rankine engine.

2. Modeling

The ORC model is built by connecting the models of its different main components. A volumetric pump and a scroll expander models are considered since they are the technologies selected for the ORC prototype presented in this paper. All models are developed under EES [5] using semi-empirical parameters that are identified with experimental data.

REDUCTION OF CO-EMISSIONS BY COMBINING PELLET. AND SOLAR HEATING SYSTEMS

F. Fiedler1*, T. Persson1 and C. Bales1

1 Solar Energy Research Center SERC, Hogskolan Dalama, S-78188 Borlange, Sweden
* Corresponding Author, ffi@du. se

Abstract

Emissions are an important aspect of a pellet heating system. High carbon monoxide emissions are often caused by unnecessary cycling of the burner when the burner is operated below the lowest combustion power. Combining pellet heating systems with a solar heating system can significantly reduce cycling of the pellet heater and avoid the inefficient summer operation of the pellet heater. The aim of this paper was to study CO-emissions of the different types of systems and to compare the yearly CO-emissions obtained from simulations with the yearly CO-emissions calculated based on the values that are obtained by the standard test methods. The results showed that the yearly CO-emissions obtained from the simulations are significant higher than the yearly CO-emissions calculated based on the standard test methods. It is also shown that for the studied systems the average emissions under these realistic annual conditions were greater than the limit values of two Eco-labels. Furthermore it could be seen that is possible to almost halve the CO-emission if the pellet heater is combined with a solar heating system.

Keywords: Carbon monoxide emissions, Pellet and solar heating systems

1. Introduction

The dramatically increased prices for oil and electricity over the last few years encourage many house owners with electric heating or and oil heating systems to convert their heating systems. Today in Sweden mainly heat pumps are installed but also pellet heating systems become more and more popular. Studies have shown that the combination of conventional boiler heating systems with solar heating is beneficial in terms of fuel savings and lower emissions since the boiler usually in the summer can be turned off when it’s efficiency is low [11; 14].

Emissions of harmful gases are important parameters in addition to the efficiency and the thermal performance of pellet heating units. The national building codes and emission regulations include limits of allowable emissions of noxious gases for wood pellet boilers. More stringent limit values are applied by the Swedish Testing Institute (SP) and eco-labels such as the Svanmark [7; 13]. The limit values can be expected to further sharpened when comparing the limit values from other European regulations and eco-labels [1; 12]. More stringent limit values have also been proposed by the Nordic eco-label Svanmark [6]. In Table 1 the official limit values for emissions and efficiencies for pellet boilers and pellet stoves are compared with the current limit

Regulation

Limit value for emission

NOx

CO

OGC

Particles

mg/m3 dry flue gas with 10 vol-% O2, 0°C, 1013 mbar

EN 303-5 (class 3)

3000

100

150

SP-Swedish testing institute,

2000

75

P-mark

Svan-mark

1000

70

70

Svan-mark, proposed 2006

340

400

25

40

Blauer Engd Pellet stoves [To be measured with 13vol-%

150

200 — 400

10-15

35

O2] Pellet boiler

150

100-300

5

30

Table 1. Limit values for emissions from automatic fed pellet heating units with a nominal combustion power smaller than 50 kW, CO-carbon monoxide, OGC-organic gaseous carbon.

In this study the emphasis has been on CO-emissions released from different pellet heating systems with different operating strategies combined or not combined with a solar heating system. CO­emissions from pellet stoves/boilers are highest during the start and stop phase. By operating the burner with modulating combustion power the number of starts and stops and consequently the start/stop CO-emissions can be reduced. On the other hand, the longer operation time leads to higher total CO-emissions during normal combustion. Both these effects are simulated in this study, and results are given for complete annual simulations with sub-hourly time step.

2. Method

This work compares and analyses the simulation results of six combined solar and pellet heating systems that have been chosen from a variety of design variants. Four of them were chosen to represent the range of commercially available solutions found in Sweden. The systems contain: a water mantled stove; an air cooled pellet stove; a store integrated pellet burner; and a standalone pellet boiler. The fifth system is similar to the system with the standalone boiler but uses a boiler with an adequate size of 12 kW. The sixth system is based on a completely new system concept using a very efficient Austrian pellet boiler. The pellet heating units in these systems had been previously tested at the Solar Energy Research Center, Borlange [10]. A detailed description of the systems can be found in [3] and [11].

The systems were modelled in the simulation environment IISiBat/TRNSYS [5]. The systems have been simulated for one year for the same boundary conditions. Particularly design parameters such as the boiler combustion control have been varied to study the effect on the CO-emissions of the systems. For comparison one system has also been simulated with only the boiler as main heat source and without solar heating system.

MEDESOL project

Owing to its features, membrane distillation process is believed to have a great potential to be employed for the production of high-purity water from seawater, brackish water and industrial wastewater [7]. Membrane distillation systems have the ability to work with low operating temperatures and high concentration brines, which reduces both the specific energy required per cubic meter and the impacts of large amounts of brine disposal. Membrane distillation, unlike other membrane technologies can be easily coupled with solar energy due to its compatibility with the transient nature of the energy. Despite the advantages of solar membrane distillation, few experimental systems have been developed compared with the mature technologies: solar PV-driven reverse osmosis and solar distillation. The comparison of PV systems and thermal driven ones, with respect to long­time performance and reliability needs further research and therefore, more data is needed in order to compare both technologies [1].

The main objective of the MEDESOL project is to develop an environmentally friendly cost-effective of minimum maintenance and easy to handle desalination technology based in SMD, for a capacity range between 0.5 to 50 m3/day, to supply rural areas with water difficulties. The design involves the innovative concept of multistage MD in order to minimize the energy requirements. The system is developed to be supplied by compound parabolic solar concentrators (CPC), specifically designed to be energy-efficient at working temperatures. The project is divided into the following phases:

1. Design and construction of three MD prototypes for multistage concept, and an optimised solar static collector.

2. First tests at PSA facilities with saline solutions connecting the modules to a existing solar collector field and evaluation of the collector prototype.

3. Assessment of two different scenarios in applying MD, in EU and developing countries respectively.

4. Techno-economical and environmental assessment of pre-commercial systems to both scenarios.

To date, stage 1 has been completed and stage 2 is being carried out at PSA facilities. This communication will focus on phase 2 results.

Pilot Plant for Solar Process Steam Supply

K. Hennecke,1* T. Hirsch2, D. Krtiger1, A. Lokurlu3 and M. Walder4

1 DLR — German Aerospace Center, Linder Hohe, 51147 Koln, Germany
2 DLR — German Aerospace Center, Pfaffenwaldring 38-40, 70569 Stuttgart, Germany

3 Solitem, Susterfeldstr. 83, 52072 Aachen, Germany

4 Alanod, EgerstraBe 12, 58256 Ennepetal, Germany * Corresponding Author, klaus. hennecke@dlr. de

Abstract

An aluminium upgrading process will be supplied by steam directly generated in parabolic trough collectors. In this first of it’s kind installation in an industrial environment, steam at 4 bar will be fed into the existing distribution lines of the production to heat anodizing baths and storage tanks. The integration of the solar steam through separate heat exchangers in parallel to the existing system was also considered. In principle, due to the low temperatures of the baths, solar hot water systems could be integrated in the same way. However, the additional heat exchangers and pipelines between the solar system and the consuming process generate significant investment cost on top of the solar system. The selected integration of the solar steam generator in parallel to the existing boiler reduces the complexity of the system, saves cost by avoiding duplication of piping and heat exchangers, and provides flexibility in the operation to ensure security of supply and maximum use of available solar energy.

Keywords: Renewable energy, solar process heat, process steam, direct steam generation

1. Introduction

Industrial process heat accounts for about 28% of the total primary energy consumption for final uses in EU25. More than half of that demand is required at temperatures below 400°, making it a promising and suitable application for solar thermal energy. Nevertheless, only an almost negligible fraction of the total solar thermal capacity presently installed is dedicated to this application [1]. The collaborative Task 33/IV of the Solar Heating and Cooling program and the SolarPACES program of the International Energy Agency (IEA) aimed to support a more wide spread application of solar heat for industrial processes by

• Assessing the potential and identifying most promising applications for solar technologies in industry

• Developing methods for the design and integration of solar systems for industrial applications

• Developing and testing of collectors for medium temperatures up to 250°C, and

• Initiating and monitoring of pilot plants.

In support of these efforts, the P3 project (Pilot plant for solar Process heat generation in Parabolic trough collectors) was started in February 2007 with the goal to demonstrate the direct steam generation in small parabolic trough collectors for industrial applications. The pilot plant will be installed at the production facilities of ALANOD in Ennepetal, Germany. One of the products of this aluminium anodizing plant is MiroSun™, an aluminium based mirror also used as reflector

material in the SOLITEM PTC 1800 parabolic trough collector. Scientific support for the development of the solar system design, integration, operation and control concepts is provided by DLR. The future operation will be closely monitored and evaluated by Solar Institute Julich and ZfS Rationelle Energietechnik GmbH. Although the site provides less than ideal solar radiation conditions, precedence was given to the relatively close neighbourhood of the project partners supporting the successful realization of this innovative application. To limit technical and financial risks, the solar field is restricted to a moderate size of 108 m2 aperture area. An economic operation is not expected under these conditions. However, ALANOD regards the opportunity to demonstrate on site the utilization of their product in innovative applications as an additional benefit.

2. Background