Computer Applications in Environmental Sciences and Renewable Energy

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1 Comparative study regarding the global influence of energy storage medium on autonomous hybrid systems for a building with economical energy consumption GHEORGHE BADEA, RALUCA - ANDREEA FELSEGHI, TEODORA M. ŞOIMOŞAN, DAN MUREŞAN, FLORIN BADEA, GEORGE NAGHIU Building Services Engineering Department Technical University of Cluj-Napoca Boulevard December 21, no , , Cluj-Napoca ROMÂNIA gheorghe.badea@insta.utcluj.ro; Abstract: - The efficient and rational use of produced energy with the help of unconventional sources is one of actual energetic problems, with stress upon the aspects regarding stocking the energy in excess and deficiencies caused by intermittencies in producing energy caused to weather conditions. The success of renewable energy depends greatly upon the optimization of storage methods of energy excess with its returning in the system whenever necessary, and also upon the technological solutions which will be adopted to cover the intermittencies in producing energy and satisfaction of energy necessities of peak load. The batteries could seem to be the right choice, also globally, the development of energetic systems based upon the use of hydrogen as a tampon medium of energy storage, is the central point of different demonstrative projects which will allow validation of these technologies for energy storage as an alternative to classic ones. In the present paper the global influences upon the systems are analyzed, in which the two energy storage methods are integrated batteries, respectively hydrogen produced from the excess of energy by electrolysis and reintroduced in the system by the fuel cell. The storage mediums serve an autonomous hybrid system, having an economical energy consumption and placement in Cluj - Napoca, Romania. Key - Words: autonomous hybrid system, energy storage medium, hydrogen, fuel cell, batteries, renewable sources of energy. 1 Introduction Hybrid systems of producing electrical energy can be defined as autonomous systems of producing electrical energy which comprise more than one source of energy, and which operates along with the auxiliary equipment, including storage, to supply electrical energy to network or place of interest. By this integration of different sources of energy in one supply system, the technology of hybridization offers the possibility of local usage of renewable sources of energy by supplying electrical energy, in places far from the network. The hybrid systems technology covers mainly autonomous systems, and also isolated networks with short coverage and medium voltage, energetic independent [10]. In all cases, the hybrid systems of producing electrical energy contain two or more sources of producing electrical energy to be able to balance the weak points and strong points of each [12]. The present article presents the results of a comparative study that was performed after the simulations using genetic algorithms [7]. Two scenarios have been simulated. In the first one, the hybrid system has as main elements of producing energy photovoltaic panels, wind turbines, and as main storage medium of excess energy it was considered hydrogen obtained by electrolysis, which will return as energy in the system by the fuel cell. The second hybrid system put to analysis has as main elements of producing energy identical with the first one (photovoltaic panels, wind turbines), and for storage medium batteries were used. Simulations on the above mentioned hybrid systems have as results the following aspects: a) technical and environment: the energetic balance of analyzed hybrid system, the excess of energy obtained by the system, the CO2 emissions resulted from the process; ISBN:

2 b) financially economical : the system s costs (the initial value of investment and the share of expenses regarding equipments in the total cost of investment). 2 Problem Formulation In the elaboration and foundation of comparative study, the following stages need to be covered: definition of general information regarding the placement and consumer, with setting out the necessary energy that needs to be assured by the hybrid system; characterization of renewable sources of energy used for energy production; the optimal choosing of components for the hybrid system set to analysis; establishing the objectives followed in the comparative study. Fig.1 Graphic of variation for the hourly energy outfit for 4 days 2.1 Defining consumer In the present paper it is treated the possibility to implement the autonomous hybrid systems to a domestic consumer, meaning a building for living, which has an economical energy consumption, type passive house, placed in Cluj - Napoca, Romania General information. Placement. For Cluj - Napoca City climate data location are: latitude = 46,76 N, longitude = 23,60 E, elevation = 523 m, heating design temperature = - 9,52 C, cooling design temperature = 24,26 C, earth temperature amplitude = 19,79 C according to NASA Surface meteorology and Solar Energy: RETScreen Data [11] Setting the energetic necessary consumption The necessary electrical energy is preset, standardized depending on different consumers. To perform the present study, I have chosen the hourly outfit of energy standardized for calculation of energetic performance which applies to all categories of buildings for living and with economical energy consumption [13], being illustrated in figure 1 and by the graphic representation of variation for the hourly energy outfit for the period of and in figure 2 by the graphic representation of hourly energy outfit for the entire November month. Fig.2 Graphic of variation for the hourly energy outfit for November 2.2 Renewable energy sources Renewable energy sources used in the present study and available for the town of Cluj Napoca, which the hybrid system is using for producing electrical energy are two types, solar and wind, as follows Solar source For calculation of energy produced by the photovoltaic panels, the solar component which interests is solar irradiation. Depending on the weather information and placement, the optimal slope is calculated for the photovoltaic panels and then the hourly irradiation of panels is calculated in relation to the solar irradiation values [2]. Calculated values are shown in figure 3, with reference to the variation of annual medium level of solar irradiation. ISBN:

3 2.3 Components of hybrid system For configuration of hybrid system and optimal choosing of component equipments it have been performed simulations with HOGA Software (Hybrid Optimization by Genetic Algorithms) and with HOMER Renewable Energy Software, presently available programs, having the basis the genetic algorithms for simulation and measuring the energy producing systems [4]. The general component elements of autonomous hybrid system have the main characteristics stated as follows. Fig.3 Graphic of variation of medium level of solar irradiation On the horizontal surface of soil, in Cluj - Napoca the daily average irradiation is 3,3 kwh/m² and the total annual irradiation is 1204,65 kwh/m², and on the photovoltaic panels surface the daily average irradiation is 4,0 kwh/m² and the total annual irradiation is 1464,41 kwh/m². For the stated location the azimuth of photovoltaic panels is 0, the soil s reflection is 0,2, and the photovoltaic panels from the hybrid system are not set with Sun observation systems [14] Wind source Information regarding the wind component of renewable sources available for Cluj Napoca, which presents interest are related to the wind speed from the area of system s placement. The values that will be taken into consideration represents the monthly average of wind speed registered at a distance of 10 m above soil. The wind speed for Cluj - Napoca can be observed in Graphic of variation of annual average wind speed from figure 4 [11] Photovoltaic panels These are of type SiP12 Suntech ST130 and have the following characteristics: nominal voltage is 12(V), shortcut current is 8,33 (A), nominal power is 130 (Wp), lifetime is 25 (years), CO2 emissions manufacturing is 800 (kgco2 equiv./kwp), TONC 45 C, coef.t is -0,47(%/ C), acquisition cost is 335( ) [4]. In measuring them, the compensation factor for loss of power due to shadows and cover with dust is considered to be 1, Wind Turbine These are of type Southwest Whisper DC, which have the following characterostics: mounting height is of 11(m), lifetime is 15 (years), CO2 emissions manufacturing is 650(kgCO2), acquisition cost is 2865( ) [4]. The nominal power depends on the wind speed and has the values according to table 1 and diagram from figure 5. 6 Table 1 Output Power vs. Wind Speed Fig.4 Graphic of variation of annual average wind speed Fig.5 Diagram of Output Power vs. Wind Speed ISBN:

4 2.3.3 Storage medium of excess of energy and technologies of returning it into the system The methods of stocking the energy excess and returning it into the system when necessary, also the technological solutions that will be adopted for covering the intermittencies in producing energy of peak load are represented in the present case by electrolysis device and fuel cells based on hydrogen, respectively batteries Hydrogen The fuel cells that are part in the analyzed hybrid system s configuration are the presented characteristics in table 2. The hydrogen consumption of fuel cell depends on the nominal power of fuel cell and the real power delivered into the system. Pmax_ef represents the delivered power into the system by the fuel cell at its maximum efficiency, and A and B represents the coefficients of consumption curve [8]. Table 2 Characteristics of fuel cell Power A B Pmax_ef Acquisition cost Lifetime [kw] [kg/kwh] [kg/kwh] [% Pn] [euro] [ore] 1 0,05 0, The efficiency of fuel cell is determined as being the proportion between the delivered power into the system by the fuel cell and the product between the hydrogen consumption for the fuel cell and the calorific power of hydrogen [8] illustrated in figure 6. consumption of electrical energy of electrolysis device depends on the nominal flow and the real flow by the hydrogen produced by it [6]. The characteristic elements are presented in table 3. Power Table 3 Characteristics electrolysis device A B Pmin Acquisition cost Lifetime [kw] [kg/kwh] [kg/kwh] [% Pn] [euro] [ani] The efficiency of electrolysis device is determined as being the proportion between the real flow of hydrogen produced multiplied with the calorific power of hydrogen and the consumption of electrical energy of electrolysis device, identical with the case of fuel cells [6], and has the curve illustrated in figure 7. It is imposed the system s control on two conditions: a) if the produced power by the renewable sources is bigger than the request of energy then the electrolysis device produces hydrogen, which will be deposited in H2 tank; b) if the produced power by the renewable sources is lower than the request of energy then the fuel cells generate electrical energy based upon hydrogen. Fig.7 Diagram of Consumption vs. Efficiency Fig.6 Diagram of Consumption vs. Efficiency The system of producing hydrogen is represented by the electrolysis device, which enters in the configuration of hybrid system. The Battery The accumulator (battery) chosen for storage the energy in excess is of type OPzV Hoppecke 2900, with C.nom is 2525(Ah), Vn is 2(V), SOC min is 10(%), self discharge is 3(% mon.), Imax is 505(A), ISBN:

5 global efficiency is 85(%), float life at 20 C is 18 (years), CO2 emissions manufacturing is 55 (kgco2 equiv./kwh capacity) and acquisition cost is 1176( ). Cycles to failure vs. depth of discharge is presented in diagram illustrated in figure 8, and number of full equivalent cycles is 1174,4 [4]. Fig.8 Diagram of efficiency Other necessary auxiliary components for the hybrid system to function are: batteries charging regulator, rectifier 230V-CA, 48V-CC). Fig.8 Diagram of Cycles to failure vs. depth of discharge Considering a minimum rate of battery charge of 40(%) it is imposed the system s control on two conditions: a) if the power produced by the renewable sources is bigger than the request of energy then the batteries are charging; b) if the power produced by the renewable sources is lower than the request of energy then the batteries are discharging Auxiliary components The invertors are important components with a high influence upon function and total cost of system. These ones transform the continuous current produced by the hybrid system in alternative current necessary to consumers. The performance of an invertor is strongly dependent to the apparent power in any moment. For the hybrid system configured in the present case study, the used invertor has the characteristics presented in table 4, and the efficiency diagram of the invertor in proportion to the produced power [4] is illustrated in figure 8. Table 4 Invertor s characteristics Rated Efficiency Acquisition power cost Lifetime [VA] [%] [euro] [ani] General presentation of hybrid system Taking into consideration the analysis and the performed simulation based upon the above mentioned components, to ensure the necessary energy and the optimal function of systems, the following appear the equipment components [3] The hybrid system with hydrogen storage medium It has the following structure: photovoltaic panels SiP12-Suntech:ST-130(130 Wp) 3 serial x 6 paralel, with Ptotal is 2,34(kWp); 1 wind turbines DC Southwest:Whisper100 (925 W at 14 ) cu Ptotal is 0,925(kW), fuel cell rated power 1(kW), electrolyzer cu rater power is 1(kW), H2 tank (27,3 d.aut) and 1 inverter Steca: Solarix PI1200 cu rated power is 900(VA). The power chart/system s components are illustrated in figure The hybrid system with battery storage medium It has the following structure: photovoltaic panels SiP12-Suntech:ST-130(130 Wp) 3 serial x 6 paralel, cu Ptotal is 2,34(kWp); 1 wind turbines DC Southwest:Whisper100 (925 W at 14 ) cu Ptotal is 0,925(kW), batteries OPzV-Hoppecke:2900 (Cn is 2525Ah) 24 serial x 1 paralel, cu Etotal is 121,2(kWh - 49,1 d.aut), PV battery charge controller of 149(A) and 1 inverter Steca:Solarix PI1200 cu rated power is 900(VA). The power chart/system s components are illustrated in figure 9. ISBN:

6 power (kw) 2,5 2 1,5 1 0,5 0 2,34 2,34 System H2 0,925 0,925 1 System B 1 0,9 0 0 PV WT FC ELYZ INV 0,9 Fig.9 Comparative chart regarding power/hybrid system s components 3 Problem Solution The present paper presents the research results regarding dimensioning the main components of autonomous hybrid systems and also the impact of use of certain storage medium of energy [5] upon these systems. In this matter, for presenting the solutions, the results will be presented as a comparative study. The aspects resulted after the simulations, which will be compared, are energetic and environment type (energetic balance of systems, energy excess from the system, CO2), but also financial economical type (initial investment cost and the share of expenses with the main components acquisition in the system s total cost). Fig.10 Comparative chart regarding the energetic balance during one year of operation From the presented chart it can be observed that batteries discharge an energy of 277(kWH), while the fuel cell generates an energy of 415(kWh), which is preferably Energy excess During one year of operation, an excess of energy of 287(kWh) has been performed by the hybrid system with batteries as an storage medium component, illustrated in figure 11. It is to be mentioned that in case of batteries it was taken into consideration an optimal number (24 serial x 1 parallel), because in order to stock the entire quantity of energy it would take a large number of batteries (24 serial x 1147 parallel), and this would be a total inefficient solution. 3.1 Energetic and environment aspects In the analysis were taken into account component both in terms of energy and environment Energetic balance The energetic balance of hybrid systems was simulated for a period of one year operation and they have been compared in figure 10 the following aspects: total load, the energy delivered by the analyzed system s components (photovoltaic panels, wind turbines, fuel cell), the energy stocked by storage medium (electrolysis device hydrogen, batteries). From the presented results and previously analyzed it can be seen that for an optimal configuration of an autonomous hybrid system is very useful to use hydrogen as a storage medium of energy and returning it into the system by the fuel cell, and also for the intermittence periods, and to cover the periods with peak load [1]. Fig.11 Comparative chart regarding the excess of energy during 1 year of operation From the excess energy point of view, the hybrid system with hydrogen as a storage medium component has an advantage towards the batteries one, as it results from the above chart. ISBN:

7 3.1.3 CO2 emissions Emissions of CO2 resulted from the system, during one year of operation are of 218(kgCO2/year) the hybrid system with hydrogen as component of stocking and of 488(kgCO2/year) for the hybrid system with batteries as component of stocking illustrated in figure 12. than the batteries one, as it results from the above chart, with cca. 30% Share of expenses with equipment in the total cost of system The share of expenses with the acquisition of main components elements in the total cost of system with hydrogen as stocking component is illustrated in the chart from figure 14. 1,91% 37,07% 7,24% 42,55% Fig.12 Comparative chart regarding CO2 emissions Analyzing the above chart it can be concluded that the hybrid system with hydrgen as stocking component presents values much diminished regarding emissions of CO2, with cca. 55% towards the hybrid system with batteries. 3.2 Financial economical aspects Initial cost of investment The initial cost of investment comprises the acquisition costs for component elements included in the system. For the hybrid system with hydrogen stocking component the initial investment is 29226( ), and for the hybrid system with batteries the initial investment cost is 42011( ), illustrated comparative in figure 13. PV WT FC ELYZ.+ H2 tank alte Fig.14 Chart regarding expenses with component equipments of hybrid system with hydrogen as storage medium The photovoltaic panels represent 11,23%, the wind turbine represents 7,24%, fuel cell is 42,55%, electrolysis device and H2 tank are 37,07%, other components represent 1,91%. Noticeable is the fact that the finacial effort for acquisition the excess energy stocking component, meaning the electrolysy device, is of 37,07% the total cost. The share of expenses with the main components acquisition in the total cost of hybrid system with batteries is as follows: photovoltaic panels represent14,76%, wind turbine represent 9,52%, batteries are 62,08%, other components are 13,64%, as it it is shown in figure ,76% 62,08% 9,52% Fig.13 Comparative chart regarding initial cost of investment From the initial costs of investment point of view, the hybrid system with hydrogen is cheaper PV WT BATTERIES alte Fig.15 Chart regarding expenses with component equipments of hybrid system with batteries ISBN:

8 The financial effort of acquisition the stocking component of excess energy, meaning batteries, is of 62,08% from the total cost. From this point of view it can be concluded that the technology based upon producing hydrogen in order to use it as a storage medium of excess energy is preferable against the batteries. 4 Conclusion The energetic efficiency by saving the primary energy, reducing the loss from the networks, reducing the price and the electricity cost for consumers, reducing the impact on environment, especially gases with green house effect, all together contribute to the security of supplying consumers with energy. After the analyzed case study, it can be concluded that the technology of fuel cell, integrated in an autonomous hybrid system, can act an important role in producing electrical energy for supplying different consumers, the optimal solution of system s configuration depending on the availability of renewable sources. The technology of fuel cells based on hydrogen has a real potential to become a solution in providing access for each citizen of this planet to a clean, non polluted energy, at a reasonable price. Including this technology in the hybrid systems performs a streamlining of the entire system, by using hydrogen as storage medium of energy to cover the peak load and for periods of intermittencies in producing energy, having as result reducing the energy produced by the system in excess and emissions of gases [9]. The universality of hydrogen makes it possible to approach as being the synthetic fuel carrying secondary energy, energetic vehicle, and storage medium for the energy produced from renewable sources. References: [1] Badea G., ş.a., The role of hydrogen in the context of current economic and technical divisions, Volumul Conferinţei Ştiinţa Modernă şi Energia ediţia XXXI, Ed.Risoprint, Cluj-Napoca, 2012, pp [2] Badea G., Şoimoşan T., Giurca I., Safirescu C., Aşchilean I., Felseghi R-A., Aspects regarding using solar energy in heating systems and sanitary hot water, in the Book Recent Advances in Urban Planning and Construction - Energy, Environmental and Structural Engineering Series 20, Proceedings of the 4 th WSEAS International Conference on Urban Sustainability, Cultural Sustainability, Green Development, Green Structures an Clean Cars (USCUDAR 13) and Proceedings of the 1 st WSEAS International Conference on High - Performance Concrete Structures and Materials (COSTMA 13), Budapest, Hungary, December 10-12, 2013, pp [3] Bernal-Agustín J.L., Dufo-López.R., Efficient design of hybrid renewable energy systems using evolutionary algorithms, Energy Conversion and Management, Volume 50, Issue 2, 2009, pp ; [4] Dufo - López.R, Bernal - Agustín J.L., HOGA Software Version 2.2, Electrical Engineering Department, University of Zaragoza, Spain; [5] Ibrahim H., Ilinca A., Perron J., Energy storage systems - Characteristics and comparisons, Renewable and Sustainable Energy Reviews, Volume 12, Issue 5, June 2008, pp [6] Iordache I., Ştefănescu I., Hydrogen production - Methods and processes, Editura AGIR, Bucureşti, [7] Mitchell M., An introduction to Genetic Algorithms, Cambridge, MA, MIT Press, [8] Ştefănescu I., Fuel cells - between theory and practice, Editura CONPHYS, Râmnicu Vâlcea, [9] Smith W., The role of fuel cells in energy storage, Journal of Power Sources, Volume 86, Issues 1 2, March 2000, pp [10] Wang C., Power Management of a Stand- Alone Wind/Photovoltaic/Fuel Cell Energy System, Energy Conversion, IEEE Transactions on, Volume 23, Issue 3, Sept. 2008, pp [11] *** Climate data location NASA Surface meteorology and Solar Energy: RETScreen Data, Document generated on Tue Dec 3 06:19:28 EST 2013 disponibil la p=1&lat=46.76&lon=23.60&submit=submit [12] *** LdV Project HYPOS-DILETR, WP3 Summary Introduction to HPS disponibil la /flags/pdf/ro/introducere.pdf [13] *** Romanian Ministry of Transport, Construction and Tourism, Methodology for calculating the energy performance of buildings Part II - Energy performance of buildings installations - Indicative Mc 001/2-2006, Published Official Monitor, Part I no. 126bis of 21/02/2007. [14] *** Solargis, Global horizontal irradiation, Romania IMap. ISBN: