Category Archives: EuroSun2008-2

Solar Heat for Industrial Processes. Operating Plants and Potential for Application

R. Battisti1*, S. Drigo2 and C. Vannoni2

1 Ambiente Italia, Via Vicenza, 5/a 00185 Roma, Italy

2 University of Rome “SAPIENZA”, Department of Mechanical and Aeronautical Engineering,

Via Eudossiana, 18 00184 Roma, Italy

* Corresponding Author, riccardo. battisti@ambienteitalia. it
Abstract

The majority of the solar thermal plants operating today provide hot water to households, for both sanitary purposes and space heating. Although the residential sector offers a huge potential for solar thermal applications, the industrial sector should not be ignored for two key reasons.

First, this sector shows a remarkable relevance, covering about 28% of the total primary energy consumption for final uses in EU25.

Second, a significant share of the heat consumed in the industrial sector is in the low and medium temperature range. About 30% of the total industrial heat demand is required at temperatures below 100 °C and 57% at temperatures below 400 °C. The areas of application with the most suitable industrial processes include cleaning, drying, evaporation and distillation, blanching, pasteurisation, sterilisation, cooking, degreasing and surface treatment.

These two issues make the industrial sector a promising and suitable application for solar thermal energy.

In the paper, both the results of the analysis of the existing solar thermal plants for process heat and the assessment of the application potential will be described. Both activities have been carried out in the framework of IEA SHC and SolarPaces Task 33/IV.

Keywords: Solar Thermal, Industrial, Potential, Process Heat

1. Introduction

Considering the new applications for solar thermal, the industrial process heat at low and medium temperature up to 250 °C is one of the most promising. Industrial sectors such as food, wine and beverage, textile, transport equipment (e. g. car washing), surface treatment (e. g. galvanic) and the chemical require process heat in this temperature range. The areas of application are numerous and include different processes such as cleaning, drying, evaporation and distillation, blanching, pasteurisation, sterilisation, cooking, degreasing and surface treatment. In addition, several built examples showed that space heating of factory buildings has to be considered one of the most promising applications of solar thermal in industry.

A survey on the existing solar thermal plants for industrial process heat (SHIP, Solar Thermal for Industrial Applications) and a review of the potential studies for future applications have been

performed in the framework of the IEA Solar Heating and Cooling Programme and SolarPaces Task 33/IV: the results are summarised in the present paper.

At the end of 2006, the installed solar thermal capacity worldwide [1] was about 118 GWth (168 million m2). Compared with 144 GWel for wind and 5,5 GWel for photovoltaic, solar thermal is helding a leading position among renewables. The majority of the solar thermal plants operating today provide hot water to households. Although the residential sector offers a huge potential for solar thermal applications, the industrial sector should not be ignored for two key reasons.

First, this sector shows a remarkable relevance, covering about 28% of the total primary energy consumption for final uses in EU25 [2]. Second, a significant share of the heat consumed in the industrial sector is in the low and medium temperature range. These two issues make the industrial sector a promising and suitable application for solar thermal energy.

Solar ORC with thermal energy storage and backup

As well as the energy storage, the use of conventional energy backup for a 24 hour demand of mechanical energy is also considered in this paper. In that case, the annual solar fraction, SF, (the ratio of solar heat to total heat delivered to the cycle) is the characteristic parameter of the performance of the system.

Together with the specific power production, SP, (the ratio of annual mechanical energy produced and solar field area), this analysis opens way for a future economical analysis of the system, after adequate cost information for solar field, storage system and backup energy. The results obtained for both cycles at the three tested locations are in figure 4.

The results presented in table 5 allow a comparison of the system, at the three tested locations, using a reference condition of (SC = 6 h, SP = 300 kWh. year/m2).

Fig.4 — Solar fraction (SF) and specific production (SP) results obtained for yearly simulations of cycle 2 and

3 at Almeria (SP), Cairo (EGY) and Moura (PT)

Table 5. Solar fraction and solar field dimensioning for reference conditions of (SC = 6 h, SP = 300 kWh. year/m2) for cycles 2 and 3 at tested locations

SC

SP

Almeria (SP)

Cairo (EGY)

Moura (PT)

[h]

[kWh. year/m2]

SF

Aa [m2]

SF

Aa [m2]

SF

Aa [m2]

C2

6

300

0.29

2940

0.37

2940

0.29

2940

C3

6

300

0.37

2940

0.47

2940

0.38

2940

5. Conclusions

Project POWERSOL [1] aims at the development of a small scale solar thermal based mechanical power/electricity generator, suitable for applications with lower requirements of maintenance and operation expertise, as those found in industry, desalination or small communities.

In the present article, a performance analysis of such a power system at three different locations and at two different working temperatures is presented, allowing a preliminary assessment of its design.

Simulation of the system working without backup energy allowed the determination of the critical storage system dimensioning, as well as a preliminary (and conservative, in view of the simplified simulation conditions) estimation of overall system efficiencies, which present values, at the best location tested, of 5.0% and 7.8% for the lower (C2) and higher (C3) temperature cycles, respectively.

Further development of the project, allowing a better cost/performance estimation for the different solar thermal collector technologies addressing the cycles operating temperatures, will enable a

final economical analysis of the system, following the approach of solar fraction and specific

power production estimation presented in this paper.

References

[1] — “POWERSOL — Mechanical Power Generation based on Solar Thermodynamic Engines”, co-funded by the EC [Contract No. 032344 (INCO)], https://www. psa. es/webeng/projects/joomla/powersol/index. php

[2] Larson, D. L. (1987). Performance of the Coolidge Solar Thermal Electric Power Plant. Journal of Solar Energy Engineering, vol. 109, p. 2-8.

[3] Stine, W. B.; M. Geyer. “Power Cycles for Electricity Generation”. In: Power from the Sun. 2001. <http://www. powerfromthesun. net/chapter12/Chapter12new. htm>. [Last checked: 19th February 2008].

[4] S. Canada, G. Cohen, R. Cable, D. Brosseau, and H. Price (2004). Parabolic Trough Organic Rankine Cycle Solar Power Plant. DOE Solar Energy Technologies. Program Review Meeting. October 25-28, 2004. Denver, Colorado.

[5] Angelino, G.; M. Gaia; E. Macchi (1984). A review of Italian activity in the field of Organic Rankine Cycles. 1984. Proceedings of the International VDI-Seminar. Zurich, 10th-12th September.

[6] Garcia-Rodriguez, L.; Blanco-Galvez, J (2007). Solar-heated Rankine cycles for water and electricity production: POWERSOL project. Desalination 212 311-318

[7] Blanco-Galvez, J., Garcia-Rodriguez, L. Delgado-Torres, A. M., Alarcon-Padilla, D. C., Vincent, M. Organic (2008). Rankine Cycle driven by parabolic trough solar collectors: pilot test facility at the Plataforma Solar de Almeria. Las vegas2008

[8] Delgado-Torres, A. M (2007). Definition of thermodynamic boundary conditions (cycle 3). Technical Report POWERSOL-T220-02(a).

[9] Price, H.; V. Hassani (2002). Modular Trough Power Plant. Cycle and Systems Analysis. Golden, Colorado: National Renewable Energy Laboratory, 2002. In < http://www. nrel. gov/docs/fy02osti/ 31240.pdf >. [Last checked 15 June 2005].

[10] Acharya, S. K.; W. Roetzel; J. Hussain (1993). Refrigerants as working fluid in a CPC collector system for electric power generation. Renewable Energy, vol. 3, p. 757-761.

[11] Maizza, V.; A. Maizza (2001). Unconventional working fluids in organic Rankine — cycles for waste energy recovery systems. Applied Thermal Engineering, vol. 21, p. 381-390.

[12] Barber, R. E (1978). Current costs of solar powered organic Rankine cycle engines. Solar Energy, vol.

20, p. 1-6.

[13] Stine, W. B.; M. Geyer (2001). “Power Cycles for Electricity Generation”. En: Power from the Sun. Disponible en <http://www. powerfromthesun. net/chapter12/Chapter12new. htm>. [Last checked: 24 January 2005].

[14] Horta, P., Carvalho, M. J., Collares-Pereira, M., Carbajal, W. Long term performance calculations based on steady state efficiency test results: analysis of optical effects affecting beam, diffuse and reflected radiation. Solar Energy, 2008, doi:10.1016/j. solener.2008.01.004. In Press.

[15] Zarza Moya, E (2003). “Generation Directa de Vapor con Colectores Solares Cilindro Parabolicos. Proyecto Direct Solar Steam (DISS)”. Tesis doctoral inedita. Departamento de Ingenieria Energetica y Mecanica de Fluidos. Universidad de Sevilla. 7 de noviembre de 2003.

[16] Ajona, J. I (2001). “Electricity generation with distributed collector system”. In Solar thermal electricity generation lectures from the Summer School at the Plataforma Solar de Almeria : Almeria, 13th-17th July, 1998. 2001. Madrid: CIEMAT. p. 7-77. Coleccion Documentos CIEMAT. ISBN 84-7834-398-9.

[17] Delgado-Torres. A. M (2006). Diseno preliminar de un sistema de desalacion por osmosis inversa mediante energia solar termica. Tesis doctoral inedita. Departamento de Fisica Fundamental y Experimental, Electronica y Sistemas. Universidad de La Laguna. 13 de diciembre de 2006.

Integration of Solar Heating System

Although breweries show a high heat demand at a low temperature level, it is relatively difficult to estimate in the first instance, if a solar heating system can be reasonable integrated into the existing processes. This is based on the diversity and complexity of the brewing process, as explained before. The basis for this decision is the detailed knowledge of the water — and energy balance of the overall production process. Some breweries don’t have any noteworthy hot water consumers beside the brewhouse, which can even lead to a surplus of hot water gained by heat recovery. In this case, the hot water is drained to the sewer and a non-concentrating solar heating system cannot be installed reasonably. Some breweries have several other hot water consumers beside the brewhouse, and need to produce the missing amount of hot water via conventional ways. And finally, hot water consumption and hot water generation can be balanced. If a change in the boiling system is planned, a new water — and energy balance has to be drawn, because of the interaction of boiling system and heat recovery. This might be difficult, since not all details are clarified before the new process is running. The link between boiling system, heat recovery and solar heating system and the associated changes in water — and energy balance shall be clarified in the following by the two considered boiling system at Hutt brewery.

image195The dynamic low-pressure boiling affects the water balance in a significant way.

The energy of evaporated water during boiling is directly used for the closed heat recovery cycle with a high temperature level and no longer to generate hot water. The only remaining source of hot water is wort cooling, which can supply the amount for mashing and lautering. In this case, the missing hot water demand can be suitable met with a solar heating system.

Together with the recovered heat from boiling that is used to heat the lauter wort,

high energy savings can be pig. 3. Possible integration of solar heating system in combination

achieved. with dynamic low-pressure boiling.

Подпись: The integration of the solar heating system into the brewing process after implementation of the vacuum boiling system is displayed in figure 4. In this case, the storage tank with higher temperature level would be fed by the heat recovery installation for wort cooling and the one with lower temperature level by the solar heating system. To ensure the required temperature for all process steps, the auxiliary heating system should be connected to both tanks. Additionally, the heat recovery during boiling can be used to increase the temperature level of both storage tanks. image197

image198The vacuum boiling system affects the heat recovery during wort boiling and wort cooling, but with lower effect. In case of wort boiling, the amount of recovered heat decreases by two reasons: the amount of evaporated water is reduced by at least 25% and approximately two third of overall evaporation is realised under vacuum. Beside the reduced amount of evaporated water, the boiling temperature during the vacuum evaporation phase is decreased successively from 100°C to 85°C. This leads to a reduced amount of energy that can be recovered. As a result of the lower temperature during vacuum boiling phase, the wort temperature prior to wort cooling is also lower compared to the old reference boiling system. However, a detailed knowledge of all process parameters in prior is not possible, since the brewer has to adjust the new boiling system to the specific requirements, which influence the final boiling temperature and ratio of atmospheric to vacuum boiling phase. Nevertheless, both heat recovery installations are here used to heat water, which leads to an amount that should be adequate to cover the overall hot water demand of the brewery. If the actual water balance in a brewery is already balanced, an implementation of a solar heating system is rather difficult after this retrofit. To find a suitable way for the implementation in combination with this vacuum boiling system, a change in the heat recovery during wort boiling is required. In this case the condensation enthalpy should not be used to generate hot water, but to increase the temperature of the already stored water. Likewise, the storage concept should consider the separation of high and low temperature level as shown in figure 3.

2. Conclusion

This paper showed the large diversity in the brewing sector, especially within the process steps of wort production. Although breweries generally show a high thermal energy demand at a relatively low temperature level, a reasonable integration of solar heating systems can be rather difficult. This is based on various technical installations that are available and a high rate of heat recovery, which can also vary a lot by means of temperature level and used installations. There is no general approach to implement a solar heating system in breweries so far. It will probably always be essential to draw a detailed water and energy balance of the overall production process for every single brewery. This balance should include all accumulating hot water streams with the respective temperature level. If there will be a change in the technical installations that influences the produced and/or consumed hot water, a new balance has to be drawn. Based on this balance it has to be proven, if a solar heating system can be integrated in the existing process or not. Furthermore, the integration can be difficult, if the complete heat recovery runs at lower temperature levels to produce hot water.

3. Acknowledgements

The authors gratefully acknowledge the financial support provided by the Reiner-Lemoine-Stiftung and the German Federal Ministry for Environment, Nature Conservation and Nuclear Safety, contract No. 0329601T. Additionally, we would like to thank the Hutt brewery (esp. K.-P. Reinl) and GEA Huppmann (esp. Dr. L. Scheller) for the close collaboration within this research project.

References

[1] W. Weiss, I. Bergmann, G. Faninger (2008). Solar Heat Worldwide — Markets and Contribution to the Energy Supply 2006, Edition 2008, International Energy Agency.

[2] C. Vannoni, R. Battisti, S. Drigo (2008). Potential for Solar Heat in Industrial Processes, Booklet IEA SHC Task 33/IV, CIEMAT, Madrid.

[3] ECOHEATCOOL (2007). The European Heat Market, Work package 1, Final Report, IEE ALTENER Project, www. ecoheatcool. org.

[4] C. Brunner, B. Slawitsch, K. Giannakopoulou (2008). Industrial Process Indicators and Heat Integration in Industries, Booklet IEA SHC Task 33/IV, Joanneum Research, Graz.

[5] Ernst & Young (2006). The Contribution made by Beer to the European Economy, Full report, Regioplan Policy Research, Amsterdam.

[6] DeStatis (2008). Survey of energy use of German industrial sectors in 2006.

[7] U. Jordan, K. Vajen, B. Schmitt, P. Bruchhauser (2006). Potential of Process Integration in four Industrial Companies in Germany, Proceedings EuroSun 2006, Glasgow, 27.06. — 29.06.2006.

[8] A. Aidonis, V. Drosou, T. Muller, L. Staudacher, F. Fernandez-Llebrez, A. Oikonomou, S. Spencer (2005). PROCESOL II — Solar thermal plants in industrial processes — Design and Maintenance Guidelines. Centre for Renewable Energy Sources, Greece.

[9] M. Jentsch (2005). Sudhaustechnologie Stand 2005, Brauindustrie (10) 2005, 10-16.

[10] M. Hertel, H. Dauth, H. Scheuren, K. Sommer (2008). Wort boiling: proper evaluation of boil-off processes — Part 3, Brauwelt International (I) 2008, 22-27.

[11] B. Kantelberg (2006). Modern wort production in brewhouse plants, Brauwelt International (I) 2006, 26-32.

[12] R. Mezger, (2006). Betrachtung moderner Wurzekochsysteme bezuglich ihres Einflusses auf technologisch und physiologisch bedeutende Wurzeinhaltsstoffe. Dissertation, TU Munchen.

PLANT GROWTH/PRODUCTION IN A CHAMBER WITH. BIOCLIMATIC CONDITIONING*

V. Garcia, A. Iriarte[12] [13], G. Lesino1, 2, S. Flores Larsen2,3, C. Matias

Grupo Energia Renovable Catamarca, INENCO — CONICET — Facultad de Ciencias Agrarias —

Universidad Nacional de Catamarca.

M. Quiroga 93 — 4700 Catamarca, Argentina. vga rcia @ plab. unca. edu. a r

Abstract

One of the difficulties in walnut and carob trees propagation is the genetic variability and insufficient offer of grafted plants. In walnut trees, it is necessary to graft high quality buds in a walnut stem; whereas in carob trees, one of the techniques used is the stem cutting propagation. Both techniques require different temperature, light and humidity conditions. With the purpose of producing both species simultaneously, an existing chamber was set up to control the hygrothermal conditions inside it. In order to obtain the best rooting conditions, the proposal is to heat beds using a mixed sun-gas system by means of solar collectors and a gas water tank to heat the water circulating in pipes. In this work, the aim is to analyze the hygrothermal behavior of the chamber, the whole system operation, and the agronomic results obtained with the simultaneous walnut grafting and the carob rooting. Results show the advisibility of using solar collectors to heat the beds in production systems with the purpose of saving energy, stressing the high percentage of plants obtained.

Keywords: Growth/Production, chamber, bioclimatic

1. Introduction

Due to the agronomic enterprises great demand for fruit plants, and the possibility to provide plants for the reforestation of degraded areas in the province of Catamarca — Argentina (28.38° South, 66° West, 600m above sea level), the need emerges to produce an important amount of young plants, specially walnut trees (Juglares regia L.) and carob trees (Prosopis Sp.). The technique most nurserymen use is the agamic propagation by means of micro grafts in walnuts, and rooting in carob plants. This latter technique consists of separating one stem from the mother plant and putting it in a mist system for root and stem growth. To obtain good results with these techniques, well controlled hygrothermal and light conditions are required so as to maintain all the qualities of the mother plant.

The walnut grafting technique used in nurseries is not completely defined and the steps to reach success in the operation are not implemented in the right way. Reproduction in our region shows some problems caused mainly by the great room temperature amplitude and the strong North wind by the time of grafting, which results in an important reduction of the stem taking percentage. To this respect, [1] emphasize the significance of controlling temperature and moisture levels in the

cicatrization area in order to promote cell activity; they state that callus exposure to certain temperatures promotes the disorderly and variable cell multiplication in the grafting union and the root and stem growing zone.

The walnut of the Prosopis genus multiplies itself naturally through dormant seeds in the soil. For this reason, the trees populations are heterogeneous, and inter specific hybridization is common. One way to obtain uniformity and superiority of the clones is by the vegetative propagation method, which eliminates the growing phase and shortens the time to reach reproductive maturity. To this end, stems of vigorous, healthy and identifiable plants should be selected.

For the rooting process, beds are used which are heated with electric elements colocated under the cabinet containing the substrate where the stems are placed. Another alternative is the circulation of a hot fluid through pipes or tubes suitably placed. When the fluid is air, the infrastructure required is not expensive, but distant points piping becomes more expensive due to its low density and thermal capacity. This problem can be avoided by using water, but the investment is higher.

[2]

For the walnut propagation, temperature and humidity ranges must be within certain limits. The temperatures ranges required are: from 18°C to 21°C for rooting, and from 21°C to 25°C in the apex and middle part of the plant. In order to avoid dehydration due to leaf water loss, room humidity must be about 80% for walnuts. For carob trees, optimum temperature in the rooting area is between 32°C and 35°C and a photoperiod of 12 to 18 hours [3].

To carry out the simultaneous production of both species, a chamber was bioclimatically conditioned in already existing premises (like a greenhouse), located in the Experimental Station of the National Institute of Agricultural Technology (Instituto Nacional de Tecnologia Agropecuaria, INTA — Catamarca). The chamber was monitored in the initial stage [4], and modifications arising from the results obtained were implemented in the new period. For carob rooting, a bed was prepared by heating the place with water circulating through pipes placed under the substrate in order to maintain the optimum temperature. The water is heated by a mixed sun-gas system with the aid of a solar collector and a liquid gas container.

In this work, the thermal behavior of the modified chamber is assessed analyzing the possibility of using it for simultaneous micro grafting and rooting, and the behavior of the rooting bed with the combined sun-gas system is also assessed. The hygrothermal and agronomic results of the trials are also presented here.

Validation of the library components

The validation of the models is necessary to ensure that the calculated results are valid. Furthermore it is to proof what differences consist due to the assumptions made in the models.

The different components were validated mainly with calculation results of other software. The comparisons showed good agreement of the new models with the references for steady state simulation. The validation of the receiver model has been done with calculation results for one day from the DLR TRNSYS simulation model. The comparison (see Fig. 3) showed a difference in the absolute values but it could be shown that the model has the same behaviour as can be seen by the calculation of the power that reaches the boiler.

image174

Fig. 3: Comparison results for the power Prec leaving the receiver

After the construction of the STJ is finished, the software will be compared with measured data of the operation. Through this validation, models can be verified with real values and it can be checked if they have to be adjusted to achieve better results.

The created channel burner, which considers a complete combustion process, enables the calculation of the necessary mass flow of fuel which is needed for a certain required temperature. Furthermore the model calculates the resulting composition with certain species in molar fraction of the exhaust gas.

Fig. 4 shows the attached burner model in Simulink.

image175

Fig. 4: Validation of the burner model

To validate the burner model different static states were calculated and the results were compared to calculation results of another software called Cycle-Tempo, developed by the Delft University of Technology (TU Delft). This Software allows to model, design and calculate thermodynamic cycles and its components at different states. The results for a calculation with both models in MATLAB and Cycle-Tempo are shown in Table 1. They show that the model calculates the same values with slight

differences due to rounding errors. Other comparisons come to the same results though the model is valid for using it in the simulation.

Results

MATLAB

Model

Cycle-Tempo

Difference

(%)

Pressure (Pa)

1.01325e5

1.01325e5

0 %

Temperature (K)

948.15

948.15

0 %

Mass Flow (kg/s)

11.688

11.688

0 %

Composition:

Molar Fraction CO2 (Vol%)

2.24

2.24

0 %

Molar Fraction H2O (Vol%)

5.33

5.33

0 %

Molar Fraction O2 (Vol%)

15.81

15.82

0.06 %

Molar Fraction Ar (Vol%)

0.91

0.91

0 %

Molar Fraction N2 (Vol%)

75.70

75.71

0.01 %

Mass Flow Fuel (kg/s)

0.188

0.188

0.6 %

Table 1: Validation results for the burner

Preheating circuits decrease the efficiency factor of the system

Every kind of preheating has a negative effect on the total efficiency factor of the boiler or the power plant respectively. This is especially evident with condensing boiler technology because return-flow temperatures increased by solar energy reduce or block condensing boiler technology. However, also with every other back-up heating the total efficiency factor is decreased by preheating processes. The causes are e. g. higher standstill and operating losses as well as higher demand for pump energy and storage tanks.

4. Summarization, Conclusions

Tube collectors in general and especially CPC vacuum tube collectors with water as heat transfer medium have proved to have potential to simplify and improve solar-thermal systems so that flat plate collectors can be called outdated. In the following examples there is no reasonable alternative to this technology at the moment:

— all-year production of process temperatures over 60 °C beyond the tropics and subtropics

— avoidance of heat losses with oversized storage tanks without stagnation

— avoidance of installation damage due to unintended thermal stagnation

— hot start of the installation from stagnation for (the purpose of) permanent usability and so that the collector can be used as an additional storage tank

— operation without antifreeze

— in case the collector orientation differs essentially from the optimal cardinal point In general solar energy can be used the better the higher the temperature level is.

Solar collector performance

3.1. System design and operation

The solar thermal system considered consisted of a fan connected to a PV panel unit and the solar

collector that warmed up the air flow. Small increments of temperature were expected from the

thermal performance so this fact implied simplicity of the prototype. The solar collector was based

* Parcially financed by ANPCyT, UNCa. INTA

[13] CONICET researcher

2 INENCO — UNSa.

3 CONICET Post doctoral Scholarship holder

Solar industrial process heat plants in operation

Data gathered in the framework of the IEA Task 33/IV include comprehensive information about the geographical distribution of the solar thermal plants, the industrial sectors addressed, the specific processes, the process temperatures, the solar thermal collectors technologies, the capacity installed, the type of back-up systems and some economics. This survey include the majority of the worldwide built examples with few exceptions such as China and Japan. At the present time data collection comprises 19 countries. Plants in operation in Austria, Greece, Spain, Germany, Italy and the USA represent about 75% of the total installed capacity reported.

image185

Currently about 90 operating solar thermal plants for process heat are reported worldwide, with a total capacity of about 25 MWth (35,000 m2). The size of SHIP plants varies from small (around 10 kWth) to large scale installations over 800 kWth.

The majority of the SHIP plants operate in the sectors of food, wine and beverages, car washing facilities, metal treatments, textile and the chemical industries. Examples in food processing sectors (especially dairies) are particularly numerous: i. e. 20 plants corresponding to 23% of the sample. Wineries account for 4 of the 8 examples reported within the beverages sector, showing a large potential for future applications especially bottle washing and cooling of wine cellars.

image186

Figure 2. Solar industrial process heat plant for a brewery in Austria (Source: AEE Intec)

Solar car washing facilities are concentrated in Germany and Austria (8 examples), while dairies in Greece and in Italy (6 examples). 10 solar facade integrated systems are in operation in Austria for space heating of factory buildings, while in Spain the most recent solar thermal applications are mainly in the food (e. g. olives, meat and fish processing) and transport equipment sectors (e. g. washing facilities for lorries and containers).

Solar heat is mainly used at 20-90 °C for process hot water, preheating of boiler feed-water and space heating (and cooling). Therefore standard selective flat plate collectors (FPC), working in the temperature range of 30-90 °С, result to be the most installed.

Cost figures, available for about 50% of the plants analysed, range from 450 to 1,100 €/kWth with few exceptions and some differences at national level. These costs refer to plants built before 2006, while cost figures for more recent plants are not available. In Austria and Spain, the investment cost (plant size < 350 kWth) is in the range between 470 and 700 €/kWth, while costs collected for Germany and Italy in average are higher. Costs for Greek plants are lower because of some targeted marketing strategies adopted in the 90ies by the solar thermal companies. Most of the reported plants benefited of public contributions between 30% and 50% of the total cost.

Solar application for drying woodchip in Scotland

A. Clemente, T. Grassie, D. Henderson and J. Kubie

Napier University, 190 Colinton Road, Edinburgh, EH10 5DT Scotland, UK

Abstract

A novel solar dryer for drying woodchip has been developed in Scotland. In this paper, designs and performance of both solar collector and dryer have been presented separately. Woodchip drying performance has been analysed for a range of temperatures (10°C to 51°C) and flow rates (70m3/h to 280m3/h). Page model has been used for modelling the drying curves as a function of temperatures and drying velocities.

The thermal solar system considered consisted of a solar collector based on the transpired plate type and a small 10We PV panel unit employed to run a 5We fan. The performance of the system is presented in terms of air flow rate and temperature increments as a function of irradiance levels.

Keywords: Solar air heating, solar dryer, woodchip

1. Introduction

Woodfuel is a clean energy resource that reduces the dependency on imports of fossil fuels and contributes to the reduction of CO2 emissions that cause climate change. The main production of woodfuel in Scotland comes from forestry and timber industries. Changes in the energy policy and high production of forestry mass give a significant role to the wood fuels in the Scottish heat power market. [1]. Researchers have predicted that wood fuel production will be equivalent to 4.5 TWh or 11 % of the heat demand in Scotland [2].

Woodchip for burning is a bulky fuel characterized by the size and the shape of the chip and its heating value, highly dependant on the moisture content, MC. The percentage of water in a fresh cut Sitka Spruce wood sample can be up to 65 % MC on wet basis. Thus removing water from the woodchip is a necessary step in the wood fuel chain supply in order to improve the quality of the product: reduce storage and haulage costs and enhance the burning performance [3]. Drying wood requires time and energy. As an alternative to natural drying or fuel heated dryers, solar thermal systems can be used as a cheap and sustainable method to reduce the drying times, suitable for small scale producers [4].

Scotland is located at high latitudes (between 50°N and 60°N) and it has a moderate maritime climate. Despite the low average temperatures, there is a long period of daylight during the spring and summer time that makes solar energy an important power resource for preheating air applications. Previous works on solar ventilation have been accomplished in Scotland as a solar slate system by Odeh [5] and solar heater for pebble bed stores by Grassie [6].

A novel solar dryer has been designed in order to assess the capacity of drying woodchip using exclusively solar energy. The solar thermal system consists of a solar collector that increases the

temperature of air that has been delivered by a fan connected to a PV-panel. This warm air passes through the wet wood chip located on a tray.

The design and operation of the present system is considered in respect of drying woodchip in a small scale. Although woodchip is commonly dried in high volume rates in forestry factories, the decentralization of wood fuel production in Scotland leads to its use in medium and small size installations where users look for minimizing production costs [2] Woodchip usually is stored outdoors drying in natural air ventilation. So a solar thermal system can be used as a backup to reduce the drying times for a small woodchip production.

For effective woodchip drying it is necessary to supply the maximum flow rate at higher temperatures. The solar thermal system when run at high flow rates yields lower flow temperatures and vice-verse. The optimum system design and operation are a compromise between the performance of the woodchip dryer and the solar collector.

The solar dryer tests were taken in the workshops of Napier University in Edinburgh. The project consisted of two independents parts that were studied separately: the dryer and solar collector. The dryer was designed and built on basis of the outlet flow from a solar collector described in the paper. After the study of the woodchip drying performance, the dryer was connected to the solar collector for the study of the solar collector and solar dryer.

Experimental Investigations On Solar Driven Desalination Systems Using Membrane Distillation

J. Koschikowski*, M. Wieghaus*, M. Rommel*,

Vicente Subiela Ortin**, Baltasar Penate Suarez**, Juana Rosa Betancort Rodriguez**

* Fraunhofer Institute for Solar Energy Systems ISE
Heidenhofstr.2,79110 Freiburg, Germany
Tel +49-761-4588-5294
Fax +49-761-4588-9000
email ioako@ise. fhg. de

** INSTITUTO TECNOLOGICO DE CANARIAS, S. A.

Playa de Pozo Izquierdo, s/n
35119 — Santa Lucia, Las Palmas
Tel: +34 928 727511 Fax: +34 928 727517
email: baltasarp@itccanarias. org

Abstract

In many places world wide drinkable water is already a scarce good and its lack will rise dramatically in the future. Missing energy sources and no grid connections complicates the use of standard desalination techniques in these places. Fraunhofer ISE develops solar thermally driven compact desalination systems based on membrane distillation (MD) for capacity range between 100 and 500 l/day and larger systems for the capacity range up to 10m3/day. All systems can be operated energy self sufficient and almost maintenance free. Membrane distillation is a technique which is operated with thermal energy but also uses a membrane for the separation of pure water from the concentrated solution. The physical basics of transport processes in MD are described. Experimental investigations demonstrate that MD keeps important advantages for the operation in solar driven stand alone desalination systems. Altogether eight fully solar driven pilot plants were installed in 5 different countries. Measurements and experimental investigations of these demonstration units are provided.

Keywords: stand alone, desalination, solar thermal, membrane distillation

1. Introduction

In many places world wide drinkable water is already a scarce good and its lack will rise dramatically in the future. Today, sea and brackish water desalination plants are well developed in industrial scales to provide big cities with fresh water. Small villages or settlements in rural remote areas without infrastructure do not profit from these techniques. The technical complexity of the large plants is very high and can not easily be scaled down to very small systems and water demands. Furthermore, the lack of energy sources as well as a missing connection to the grid complicates the use of standard desalination techniques in these places. In arid and semi arid regions the lack of drinkable water often corresponds with a high solar insulation. This speaks for the use of solar energy as the driving force for water treatment systems. Especially in remote rural areas with low infrastructure and no grid connection, stand alone operating systems for the desalination of brackish or sea water are suitable to provide small settlements with clean potable water.

Within the scope of two projects subsidised by the European Union Fraunhofer ISE developed solar driven compact desalination systems for capacity range between 100 and 500 l/day and Two-

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Loop-Systems for capacities up to 10m3/day. All systems are supplied by solar energy only. The energy for the desalination process is provided by solar thermal collectors and the auxiliary equipment as pumps and valves are powered by PV. The main advantage of the compact system is on the very low technical complexity enabling long term maintenance free operation periods. The Two-Loop-System is constructed for low maintenance operation as well, but has a higher technical complexity. A modular design of all systems is important in order to adapt them to a wide range of user profiles.

Membrane distillation is a technology which is operated with thermal energy but also uses a membrane for the separation of pure water from salty water. Apart from some experimental systems the MD-technology is currently not used for desalination, but with respect to the implementation in solar driven stand alone desalination systems it holds important advantages.

Eight fully solar driven pilot plants (2 Two-Loop-Systems and 6 Compact Systems) were installed in 5 different countries. Comprehensive measurements and experimental investigations were carried out on these pilot units for more than 3 years demonstrating on the one hand that membrane distillation is a very suitable technology but discovered on the other hand also significant potentials for improvements.