A Comparison Between Experimental and Statistical Data of the Solar Potential at an Optimal Angle of an Inclined Surface for the City of Varna Irina P. Pavlova Department of Heat Engineering, Technical University - Varna, 1 Studentska str., 9010 Varna, BULGARIA Email: irinappavlova@yahoo.com Phone:+359/52/ 383 559 Abstract: A comparison is made of the experimental data for the solar potential the city of Varna gets at an optimal angle of an inclined surface in 2011 with the statistical data of the Photovoltaic geographic information system (PVGIS). The comparison shows the reliability of the gathered experimental data about the global solar radiation on an inclined surface in the specific geographical location the Technical University in the city of Varna. Keywords: solar radiation, optimal inclination of solar panels 1. Introduction The development of the project Development of a specialized scientific infrastructure for research of the solar and wind potential gave the opportunity for the realization of registering data for solar radiation for the city of Varna for a one-year period of time 1.01 31.12.2011. The experimental data is registered with a calibrated pyranometer LI-COR200, installed in the meteorological mast NRG Now System 34 m, produced by the NRG company. This mast is erected on the territory of the Technical University Varna in the beginning of May, 2010. The registered data is shaped in a form that is easy to be applied. The solar energy at an optimal angle of an inclined surface is calculated and the results are used for comparison with the respective data from PVGIS. The photovoltaic geographic information system (PVGIS) is provided by the European commission and its usage and free for all the countries, members of the European Union. It gives data for the solar radiation on horizontal as well as on an inclined surface. This data are a result of ten-year-long research and thus have enough precision and reliability [1]. The comparison of the experimental and statistical data shows the veracity of the experimental results and gives the opportunity to get preliminary information at the right selection of solar energy transformation system for specific geographical location the Technical University in the city of Varna. 2. Results 2.1. A comparison between the monthly optimal angle of an inclined surface On figure 1 the monthly diagrams for comparison between the experimental [2] and statistical data of the solar radiation of an inclined surface in the city of Varna are presented. The diagrams are constructed on the 10
Vol. 2 No. 6 July 2013 base of average daily value of the solar potential for each month. Summarized data are shown in Table 1. The comparison indicates that experimental data shows rather large deviation from statistical data in January, April, October and December from 20.7% (April) to 32.1% (October). This shows that the sky is Varna city was cloudy during these months оf the experimental 2011. During the other months, there is a comparability of data for the solar radiation on an inclined surface - the largest deviation was 7% in February. Fig.2. shows the change of the optimal angle of an inclined surface by month - according to the experimental (TU_VARNA) and statistical data PVGIS. The results show coincidence of the optimal angle of an inclined surface for the months: January (60 ), March (40 ), May (10 ), June (10 ), July (10 ), August (20 ), October (50 ), November (60 ) and December (60 ). Deviation from 17.5% to 33% is observed in February, April and September. 2.2. Comparison of the optimal annual angle of an inclined surface The optimal amount of solar radiation for the one-year study period, according to Fig.3. was obtained at the optimum angle of the inclined surface 30 and 1454.12 kwh/m². The optimal annual angle of an inclined surface as per statistical data PVGIS is 33 at which city of Varna receives solar energy 4190 Wh / (m². day). Figure 4. provides information for the solar energy, which the studied area receives during the summer and winter months as per experimental and statistical data. The comparison of data for the solar energy of Varna shows that there is a coincidence between experimental and statistical data for the summer period ( from April to September). During the winter period (from October to March) the statistical data are much higher than the experimental one. The variation in this period is in the range of 45% (at 10 angle of the inclined surface) to 22.7% (at 90 angle of inclined surface). 3. Conclusions Results serve as preliminary information for the design of solar energy transformation system. The right choice of solar system reduces the period for its design and construction in the studied area - Technical University Varna. 4. Acknowledgements The author express their gratitude to the Fund Science Researches of Ministry of Education, Youth and Science for the financial support in project D002-48/10.12.2008, Developing of Specialized Science Infrastructure for research of the wind and solar potential in Bulgaria. REFERENCES [1] Photovoltaic Geographical Information System - Interactive Maps. http://re.jrc.ec.europa.eu/pvgis/apps3/pvest.php [2] Pavlova, I. Dissertation (in Bulgarian) Павлова И. Дисертация на тема Теоретична и експериментална оценка на слънчевия потенциал за град Варна, 2012 г., Технически университет Варна. 11
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Vol. 2 No. 6 July 2013 Fig.1. Comparison of monthly optimum angle of an inclined surface for 2011 based on average daily value of the solar radiation for each month Fig 2. Change of the optimal angle of inclined surface by months 15
Fig.3. Comparison of the optimal annual angle of an inclined surface Fig 4. Solar energy at an inclined surface in summer and winter months Table 1. Monthly optimum angle of the inclined surface Varna Month Оpt.Angle I,kWh/(m 2.day) Оpt. Angle, I s kwh/(m 2.day) TU_Varna TU_Varna PVGIS PVGIS 1 2 3 4 5 I 60 о 1.93 60 о 2.56 II 60 о 3.25 50 о 3.02 III 40 о 3.73 40 о 3. 86 IV 20 о 3.78 30 о 4.77 V 10 о 5.84 10 о 5. 79 VI 10 о 6.39 10 о 6. 02 VII 10 о 6.55 10 о 6.20 VIII 20 о 5.77 20 о 5. 87 IX 33 о 5.34 40 о 4.99 X 50 о 2.85 50 о 4.2 XI 60 о 2.65 60 о 2. 76 XII 60 о 1.63 60 о 2.23 16