EVALUATION THE PROPRETIES OF A PV-WIND HYBRID SYSTEMS

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1 EVALUATION THE PROPRETIES OF A PV-WIND HYBRID SYSTEMS Istvan Farkas, Imre Kalmar, Attila Lagymanyosi Department of Physics and Process Control, Szent István University, H-13 Gödöllõ, Hungary, Tel.: , Fax: , ifarkas@fft.gau.hu Sandor Bartha and Mihail Predescu I.C.P.E.-New Energy Sources Laboratory (NESL), Bucharest, Calea Vitan 313, Romania, Tel/Fax , sbartha@planet.ro Abstract In this paper the properties of a small scale PV-wind hybrid system were evaluated. Two regions were selected as an application site, one is at Budapest in Hungary and the second one at the Black Sea coast in Romania. The relevant data concerning to the energy consumption of a typical family were gathered and classified. Radiation and wind data for the selected regions were also gathered. Based on the data analysis a suggestion was made for the system set-up. In Hungarian case an autonomous grid connected PV system, in Romanian case a stand-alone PV-wind system was advised. Remarks on the finances were also given. 1. INTRODUCTION It is no doubt that application of the hybrid renewable systems has a great importance. Due to the high investment costs, however, the dissemination of PV, wind and other hybrid systems is still limited (Farkas, 1998). To reach a broader market penetration level financial incentives are considered. Such economic incentives are: enhanced payback tariffs, rebates, full cost rates, solar stock exchange (Haas et al, 1999). As a result of national programs in Germany, Austria, Japan the investment costs on the PV market dropped. It is shown in all of the mentioned countries that informed persons have a rather higher willingness to invest in PV. Yet, they claim rebates to put the willingness-to-pay into practice. That is why marketing and promotion of PV systems is important in developed countries and more important in developing countries. The key factors for a further dispersion of a PV system are: - the presence of financial incentives, - reduction of the investment cost, - standardisation of systems, - increase in reliability, - distribution of information, - enhancement of environmental awareness. (Haas, 1999) One of the largest dissemination programs has been launched in Japan in 1994, in which more than 1, small grid-connected systems have been installed (Ikki, 1998). The 1, Rooftop Program initiated in January 1999 in Germany is running till 4. Nowadays almost in every country in Europe and all around the world programs are launched or planing to launch national renewable energy programs mostly solar (PV) program. The Hungarian dissemination program plans to install, PV and solar thermal systems on roof until the year 1. Under the Hungarian meteorological and geographical conditions it is advisable to install hybrid systems as Wind-PV or Biomass-PV for more effectiveness. Grid connected PV rooftop systems are generally privately owned in a power range of up to 1 kw. The main aim of a private operator is to maximise its energy yield (Calais et al, 1999). Stand-alone PV or hybrid systems are more reasonable in rural and developing areas. Hybrid systems are an important source of electricity not only for schools, clinics and village communities but also for farms and tourist facilities in areas remote from the grid (Seeling-Hochmuth, 1997). Marrison and Seeling-Hochmuth (1997) describes the interdependence between system sizing and system operational strategy. It has been formulated the appropriate cost/benefit function for the optimisation of hybrid systems. Stand-alone systems on the basis of solar and wind energy are just one option supplying small electrical loads at remote locations. The applicable configuration depends on the climatic conditions at the considered site. The seasonal pattern of wind and solar energy flows are mutual supplements, the combination of wind and solar sources may have advantages (Beyer and Langer, 1996). This paper is going to describe the evaluation of the properties of a small renewable energy systems made up of a wind generator and a PV unit used in energy supplying of the household and tourist units laying in a remote area. The off-grid application requires relatively small amount of power, typically less than 1 kwp. Both of the hybrid components used in the charging of batteries that store the energy captured by the modules. The study shows estimations of the energy usage in the household and the tourist units and the load profile together with the meteorological data of the selected

2 regions. There are two remote areas where the data are collected, i.e. the Black Sea coast for the Romanian site and a North-Hungarian region for the Hungarian site. The result of the physical and economical simulations is used in the evaluations of the performance of the hybrid systems. Based on the results achieved it is possible to design and build a systems for a small-scale remote area applications.. ENERGY ANALISYS FOR THE REGIONS STUDIED In this paragraph the monthly energy demand of different consumption groups and the possible energy gain from solar radiation and wind are analysed..1. Electrical energy demand Concerning to the electrical energy demand in a typical household in Hungary, eight consumer categories have been established. The Table 1 shows the values of the relevant estimated energy consumption. It can be seen from the table that the kitchen equipment and the household appliances are the greatest portion of energy consumption at almost a constant level. In this study the energy storage problem is not taken into account. For security reason however, it is supposed a three-day storage capacity. So it means, that the energy demand is expected to cover directly by the PV or by the hybrid system. For the Romanian site the energy consumption in a typical household is less, about by %, especially in autumn than it is at the Hungarian case. This difference can be caused by the diversification of the equipment applied. The monthly estimated values of consumption types in Table 1 meets the measured demand of electrical energy which can be seen in Fig. 1. The measured values were taken from typical representative consumers. Table 1 Monthly energy demand of different consumption groups Total Type of consumption Kitchen equipment 1 Household appliances TV, Hi-Fi, Computer Water pumping Working tools 3 Type of consumption Kitchen equipment 1 Household appliances TV, Hi-Fi, Computer Water pumping Working tools 3 Total Energy demand, kwh/month Jan. Febr. March April May June Energy demand, kwh/month July Aug. Sept. Oct. Nov. Dec. Energy kwh/year refrigerator, deep freezer, microwave, toaster, coffee machine, mixer, etc. washing machine, iron, vacuum cleaner, hair drier, etc. 3 boring machine, sawing machine, lawn mower, etc.

3 % Fig. 1 Cumulated demand of electric energy December was taken as a basis, where the average use of energy was the highest (7 kwh/month). From the Figure above it can be see that the energy consumption in April is significantly decreasing as the heating period ends. It is interesting to see the increase of energy usage in May. Cooling devices, watering and working tools can explain the relative big amount of energy in May and also during the summer. In September we are facing to a lot of work to do around a house... Solar energy availability Having knowledge on the energy demand let us see now the available energy sources. The Fig. shows the average daily radiation for horizontal and the two typically tilted surfaces for Budapest region. Radiation energy kwh/m day Horizontal 3 degree 6 degree Fig. Average daily solar energy yield in Budapest (H) For the Romanian case the typical Black Sea coast (Agigea) radiation data for horizontal surface in 1997 is shown in Fig. 3. Radiation energy, kwh/m day Fig. 3 Average daily solar energy yield at Agigea (Ro) 1997 Based on the energy demand it is no worth to install the PV modules horizontally in the region, because of the radiation energy yield is high in summer, but relatively low in winter, so there is a great difference between the two values. In order to obtain reasonable energy income it would be optimal to install two types of tilted PV modules. In Fig. 4 and Fig. 5 (Pálfy) the actual energy gain of 3 o and 6 o tilted PV panels for region in Kecskemét (H) are presented. Energy gain, kwh m day Fig. 4 Average daily PV energy gain in Kecskemét at 3 o Energy gain, kwh/ m day,7,6,5,4,3,,1,7,6,5,4,3,,1 Fig. 5 Average daily PV energy gain in Kecskemét at 6 o It is very clearly to see that the 3 o tilted PV panels produce the highest energy output in midsummer against the 6 o tilted PV panels where the energy output spreads almost evenly in the whole year except the winter months.

4 The consequence would be that it is advisable to install more panels at 6 o angle because of its more effectiveness. The Fig. 6 shows the efficiency of the PV modules during the year round operation. As known, the efficiency of the PV module decreases at higher temperature, so the efficiency can fall even by 1% in summer months in both installation positions at 3 o and 6 o, respectively. Fig. 6 Efficiency curve of the PV modules.3. Wind energy availability In order to take into consideration a hybrid system, beside the PV solar, the wind energy combination seems to be more realistic in many reasons in order to get additional energy gain. For this purpose an area is required with proper wind potential and at least 4-6 m/s wind speed. Under the Hungarian geographical and climatic condition for the region studied it has been observed that there is a minimal significance of such wind-potential. Wind direction is very variable because of the basin character of the land. On the other hand to the Romanian coastal site it has a permanent wind direction so there is better chance to plan and build a PV-wind hybrid system there. It does not mean that it is not possible to realise such hybrid systems in Hungary at all, but there are more parameters to be analysed for the economical and environmental success. From the Romanian site the typical wind data are available for the year 1997 at the Black Sea coast (Agigea) as presented in Fig. 7. Wind energy kwh/m day % 3 degree 6 degree,5 1,5 1,5 Fig. 7 Average daily wind energy yield at Agigea (Ro) 1997 Comparing the Fig. 3 and Fig. 7 it can be stated that the solar energy yield from May to October compensate the less wind energy yield, so we can get a more equalized total energy income of the hybrid system. At the same time, mearly the wind energy would not cover efficiently the energy need for a family in a weekend house if they have an average consumption of about 18 kwh in the summer months and the grid connection is not available. With help of PV modules along with proper size of batteries could provide energy for cloudy and/or not windy days, as well. 3. SYSTEM SET-UP In the recent study two different kinds of set-up were evaluated according to the gathered radiation and wind data. Based on the statements in the previous paragraph the Hungarian site application would not include the wind turbine, but for the Romanian site on the Black Sea coast a real PV-wind hybrid system is suggested. The planned autonomous grid (diesel, gas, etc.) supporting PV system is taking into account the actual Hungarian energy consumption levels and solar energy availability as well, as it can be seen in Fig. 8. Kitchen equipment Inverter Household appliances Battery TV, Hi-Fi Computer Charge controller Water pumping PV modules Working tools Autonomus grid connection Fig. 8 Scheme of a PV system for Budapest region (H) In the scheme all the consumers listed in Table 1 are presented. In order to supply the average energy demand (36 kwh/year) it is recommended to install PV modules in both tilted positions (3 o and 6 o ). Supposing 5-5% of both positions of the PV panels the total average energy income can be estimated for 16 kwh/m year. In case of installing 8 m of PV module there is more than one third of total energy demand can be covered in such a way. Concerning to the Romanian case, based on the energy analysis carried out a real stand-alone PV-wind system can be advised to install. Calculated with 17 kwh/m year of solar energy output and 14 kwh/year wind energy output from a 5 kw wind generator, based on measured data, the average energy demand (41 kwh/year) totally can be covered. The yearly demand is proportionately divided between

5 the PV panels and the wind turbine. Already 6 m of PV module covers about 4% of the energy consumption and the other 58% covered by the wind generator. Apart from the wind turbine and the grid connection the scheme of the applied system (Fig. 9) is similar to the Hungarian one. Kitchen equipment Inverter Household appliances Wind turbine Battery TV, Hi-Fi Computer Charge controller Water pumping PV modules Working tools Fig. 9 Scheme of a PV-Wind hybrid system for Black- Sea coast (RO) 4. FINANCIAL ASSESSMENT Concerning to the Hungarian case study the payback time of the planned PV system is about 5-6 years in comparing on the base of,8 EURO/kWh electric energy price. As far as it is concerned in the Romanian case the energy consumption is less than the Hungarian one, but the payback time can be longer because of higher investment cost especially for the wind generator. In the case, the payback time of the entire system was estimated about 7-8 years. The main problem of the renewable energy technology application is, that without any subsidy from government it is rather high the investment. The maintenance cost is relatively low but especially owing to the long-term use a detailed life cycle analysis is necessary to perform which calculates with inflation, debt rate, maintenance costs, etc. 5. CONCLUSION The use of renewable energy sources to develop rural tourism have significant advantages: as reducing the pollution of environment, making possible to include isolated areas in the tourist circuits, creating new jobs, possibility in the isolated area. Based on the literature overview it has been concluded that the application of a small-scale PV-wind hybrid system is realistic. Concerning to the potential application sites two regions were analysed: one is in the Budapest region in Hungary, and the other one at the Black Sea coast in Romania. Supposing a small-scale application a typical family size of energy consumption data were gathered and analysed. Concerning to the hybrid system a solar radiation and the wind data for the selected regions were analysed. Based on the energy consumption and the solar, wind potential suggestion was made for the system set-up. In Hungarian case, due to the low wind potential, a single PV system was suggested along with the autonomous grid availability. In Romanian case a stand-alone PV-wind system is applicable. The sizing of this set-up was also performed. Finally, some financial analysis was carried out concerning to the economics of the system suggested. It can be concluded that the calculated payback time is about 5-6 years for the Hungarian and 7-8 years for the Romanian case. Acknowledgement This paper was carried out within the framework of the project MTA-TKI F-6/1998 and FKFP-459/. References Bagul, A.D. and Borowy, B. (1996) Sizing of a standalone hybrid wind-photovoltaic system using a three event probability density approximation, Solar Energy, Vol. 56, No.4., p Beyer, H.G. and Lange, C. (1996) A method for the identification of configurations of PV-wind hybrid systems for the reliable supply of small loads, Solar Energy, Vol. 57, No.5., p Calais, M., Agelidis, V.G. and Meinhardt, M. (1999) Multilevel converters for single-phase grid connected photovoltaic system: an overview, Solar Energy, Vol. 66, No.5., p. 35. Farkas, I. and Rendik, Z. (1993) Handling of solar climatic data, The International Journal of Ambient Energy, Vol. 14, No., p Farkas,I., Buzás, J., Hegyi, K., Fekete, M. and Bartha, S. (1998) Application of renewable energy sources to develop rural tourism, EuroSun'98, Book of Proceedings, Vol. 1, Portoroz, Slovenia, p. I.3.8. Farkas, I., Buzás, J., Hegyi, K., Fekete, M., Predescu, M. and Bartha, S. (1999) Use of PV-hydro-wind hybrid system in rural tourism, Proceedings of the Conference on Energy and Agriculture towards the Third Millenium, AgEnergy'99, Athens, Greece, June -5, Vol. II, p

6 Haas, R., Ornetzeder, M., Hametner, K., Wroblewski, A. and Hübner, M. (1999) Socio-economic aspects of the Austrian kwp - PHOTOVOLTAIC-ROOFTOP programme, SolarEnergy, Vol. 66, No.3., p Ikki, O. (1994) PV activities in Japan, Vol. 4. Lysen, E.H. (198) Introduction to wind energy, Publication SWD 8-1. Pálfy, M. (to be published) PV systems, Chapter No. 5. of the book on Solar Energy in Agriculture /ed. By Farkas, I./, Mezogazda Publisher, Budapest, Hungary Seeling-Hochmuth, G.C. (1997) A combined optimisation concept for the design and operation strategy of hybrid-pv energy systems, Solar Energy, Vol. 61, No.., p. 77. Marrison, C.I. and Seeling-Hochmuth, G.C. (1997) A design tool using genetic algorithms to size hybrid systems for power supply at remote sites, Part One: Analytic Framework, Proceedings of CASE conference on Village Electrification, New Delhi, India