LIFE CYCLE ASSESSMENT OF SOLAR CHIMNEYS

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1 LIFE CYCLE ASSESSMENT OF SOLAR CHIMNEYS Marco Aurélio dos Santos Bernardes CEFET/MG - Av. Amazonas 7675, Belo Horizonte MG, CEP: , Brazil ABSTRACT The main goal of the study is a comprehensive evaluation of the impacts caused by mass and energy flows of solar chimneys systems from its design through to production and then final disposal using the method of Life Cycle Assessment. The conventional Life Cycle Assessment method has been improved by an additional sectoral analysis (input-output analysis), namely Hybrid Approach. With this approach, it is possible to establish an assessment covering all up-and downstream processes. The study is an important contribution for the integration of Life Cycle Assessment in the decision-making process in the renewable energy sector and for an integrated evaluation of processes. INTRODUCTION The solar chimney combines three techniques (Figure 1): 1. the glass roof hot air collector (a water-storage system can be used to improve the production at night (4)) 2. the chimney 3. wind turbines with generators Hot air is produced by the sun under a large glass roof. This flows to a chimney in the middle of the roof and is drawn upwards. This updraft drives turbines installed at the base of the chimney, and these produce electricity. The solar chimney was originally proposed by Professor J. Schlaich of Stuttgart in In 1981 began the construction on a pilot plant in Manzanares, Spain (Schlaich 1995). A 50 kw experimental plant was built which produced electricity for eight years, thus proving the feasibility and reliability of this novel technology. The chimney tower was m high and the collector had a radius of 122 m. It produced an upwind velocity of 15 m/s under no load conditions. The literature is extensive, and that referred to here is by no means exhaustive. (Bernardes et al. 2003) review some of the outstanding issues at that time. Life Cycle Assessment of Solar Chimneys Marco Aurélio dos Santos Bernardes CEFET/MG 1

2 Figure 1 Schematic drawing of a solar chimney A Life Cycle Assessment (LCA) accounts for all impacts that a particular product might have from the extraction and supply of the raw materials through production and usage to when it is finally disposed of as waste (ISO ). In general, it is performed by the use of Process Chain Analysis where the product system is divided into a set of well-defined process steps. In order to allow a quick and easy estimation of the elementary flows of up- and downstream processes, commodity flows which seen to be not relevant for the assessment are neglected and not included in the Process Chain Analysis. (Marheineke et al. 1999) introduced the Hybrid-Approach, which completes the generally used Process Chain Analysis by a model based on economic Input-Output-Tables. The results of the Input-Output-Tables can be used to estimate the elementary flows related to a product or service supply not included in the process chain. Then, the Input-Output-Analysis can be understood as a Life Cycle Inventory Analysis of average products of the economic sectors distinguished in the Input-Output-Tables. Figure 2 illustrates the combined use of Process Chain Analysis that describes the product system and Input-Output-Analysis that estimates the elementary flows of processes that are not included in the product system. Figure 2 Enlargement of a product system by an Input-Output-Model. APPLICATION OF THE LIFE CYCLE ASSESSMENT BY THE USE OF HYBRID-APPROACH Goal and Scope definition. In the following, the combined use of Process Chain Analysis and Input-Output-Analysis is demonstrated by applying in to the Life Cycle Inventory Analysis for three different solar chimneys power classes (s. Table 1), what Life Cycle Assessment of Solar Chimneys Marco Aurélio dos Santos Bernardes CEFET/MG 2

3 were calculated by means of a non-linear optimization procedure described by (Bernardes 2004). Algorithms for non-linear approximation were used for finding optimal values for the parameters in a mathematical model of an economic-physical problem. Table 1 Datasets for the calculated solar chimneys. Power Diameter Chimney Air upwind Temp. rise Unit inv. Chimney Collector height velocity in collector costs [MW el ] [m] [m] [m] [m/s] [K] [10³ /kwe] , , , Inventory Analysis. The product system includes unit processes for construction, operation, maintenance and dismantling of each plant. The supply of the energy carriers natural gas, coal products, light fuel oil and electricity is assessed using the Hybrid-Approach. Impact Assessment. The impact assessment is usually done by aggregating mass flows which have similar impacts with non-site specific and non-time specific weighting factors in order to estimate the impacts on human health and the environment material and energy flows. Results and Interpretation. As Table 2 shows, the ecological analysis results in approximately 170 (5 MW) and 70 gco 2 -equivalent/kwh (100 MW). Between approximately 570 (5 MW) and 240 mgso 2 -equivalent kwh (of 100 MW) SO 2 - equivalent is emitted. The consumption of not removable energetic and mineral resources as well as specific CO 2 and specific SO 2 -emissions decrease with larger plants. Table 2 CO 2 -, SO 2 -emissions and use of mineral resources for construction, operation, maintenance and dismantling of solar chimneys. Power CO 2 -eq. SO 2 -eq. Copper Bauxite Iron Chalk [MW el ] [g/kwh] [mg/kwh] [mg/kwh] [mg/kwh] [mg/kwh] [mg/kwh] ,168 53, ,594 31, ,040 20,636 A comparison with conventional and renewable energy resources in the state of Baden-Württemberg in Germany (Voß et al. 2002) was carried out. Table 3 presents the technical parameters of the compared technologies. Life Cycle Assessment of Solar Chimneys Marco Aurélio dos Santos Bernardes CEFET/MG 3

4 Table 3 Parameters of the selected power technologies. Energy source Power plant type Power Lifetime Full load hours Capacity factor [MW el ] [a] [h/a] [%] Mineral coal Condensation , IGCC , Natural gas Gas and steam plant , Biomass CHP , Co-firing , Solar radiation Multi-Si Solar chimney , Wind power 4.5 m/s ,680 n.a. 5.5 m/s ,450 n.a. Hydraulic power Small water fall ,100 n.a. Nuclear energy PWR , Figure 3 shows a comparison of the emissions of a solar chimney power plant of 100 MW with others technologies. The power generation based on coal produces the highest greenhouse potential. The CO 2 emissions by kw/h are more accentuated by coal with combined cycle plant than hydraulic and wind power systems with higher wind velocities. The calculated emissions of the photovoltaic energy production result completely from the PV-panel production process. The operation can be considered equal-zero-emission. The solar chimney presented a greenhouse potential smaller than for the natural gas power systems. Due to the relatively small efficiency of approximately 1 % of the solar chimneys, the calculated specific emissions by kw/h are higher than wind and hydraulic power systems. 1 Integrated gasification combined cycle 2 Combined heat and power 3 Pressurized-water reactor Life Cycle Assessment of Solar Chimneys Marco Aurélio dos Santos Bernardes CEFET/MG 4

5 Figure 3 Gas emission for several technologies of power generation. CONCLUSIONS In conclusion, a study for ecological evaluation of solar chimney has been developed. The Hybrid-Approach offers the possibility to complete the generally used Process Chain Analysis by adding a model based on economic Input-Output-Tables and corresponding data on sector specific elementary flows. The results show that large solar chimneys can help the relieving of the environment and the saving natural resources due its relative low CO 2 and SO 2 -emissions. REFERENCES Bernardes, M. A. d. S. (2004). "Technische, ökonomische und ökologische Analyse von Aufwindkraftwerken," Doktor, Universität Stuttgart, Stuttgart. Bernardes, M. A. d. S., Voß, A., and Weinrebe, G. (2003). "Thermal and Technical Analyses of Solar Chimneys." Solar Energy, 75, ISO (1998). Environmental management - Life cycle assessment - Goal and scope definition and inventory analysis. Marheineke, T., Friedrich, R., and Krewitt, W. "Application of Hybrid-Approach to the Life Cycle Inventory - Analysis of a Freight Transport Task." SAE 1998 Transactions Journal of Passenger Cars, Warrendale PA, USA. Schlaich, J. (1995). The Solar Chimney, Edition Axel Menges, Stuttgart. Voß, A., Bernardes, M. d. S., Briem, S., Krewitt, W., Nill, M., and Rath-Nagel, S. (2002). "Grundlagen zur Beurteilung der Nachhaltigkeit von Energiesystemen in Baden-Württemberg." BWR 99002, IER - Institut für Energiewirtschaft und Rationelle Energieanwendung, Stuttgart. Life Cycle Assessment of Solar Chimneys Marco Aurélio dos Santos Bernardes CEFET/MG 5