Effect of shading photovoltaic panel interception rods in lightning protection

Transcription

1 Recent Researches in Electric Power and Energy Systems Effect of shading photovoltaic panel interception rods in lightning protection VILIAM MANDUCH OSMONT Elektromontaze s.r.o. Mladeznika 2172/ Povazska Bystrica Slovak Republic LUKAS RADIL, TOMAS BARTOSIK, PETR MASTNY Brno University of Technology Department. of Electrical Power Engineering Technicka 12, CZ616 Brno Czech Republic Abstract: The article deals with the protection of photovoltaic against lightning and consequences of incorrect design interception rods. The result may be a little protection, and especially poor performance and energy gain of the operating source. Key Words: Lightning rod, shadow on solar power, lighting protection, azimuth, declination 1 Introduction Effect of shading of the PV panel is in terms of production always undesirable. In the design, construction and operation of photovoltaic power plants must be preceded by the shadow. This is due to well-known fact - MPPT control and sorting of individual panels. The work is to show a significant impact minimal shadow that may affect the operation of photovoltaic power plants. This shadow can generate and inappropriately placed lightning rod lightning rod. Protection against lightning is resolved according to CLC / TS [4]. This standard addresses the installation of lightning and surge protection for household and outdoor installations. In general, based on the standard IEC , by Article 5 Prior standard CLS / TS is based on the German standard VDE , Bbl.5. Panels must be protected according to known methods - rolling sphere (fig.1) and the protective angle (fig. 2). Further text of the article does not deal with sublightning design, but the consequences of incorrect design of interception technology. 2 Figure 1: Method of rolling sphere Figure 2: Method of protective angle 2.1 If we take into account that can be used two types of solar radiation: direct radiation - Irradiance is reduced by passage through the atmosphere. The total value of 136 W m 2 can be efficiently get around 1 W m 2. The rest of the light is either reflected or it will be diffused. Effects of the shielding calculation diffuse radiation - There is a very direct light scattering. For Europe is about (5-7) % of the total indirect radiation. In winter this value rises to 9 %. The basis for the proper design of the measurement and the correct angle of panels is according to the azimuth and elevation of the sun. ISBN: Energy of the Sun and the Earth s motion 99

2 Earth s motion is governed by the trajectory, which has an elliptical shape. The country has because of its rotation inclined to the plane of the ellipse In the Czech Republic the Sun is up in 65. The lowest value is in the winter, and 17. This character is typical of the northern hemisphere. In fact height of the Sun above the horizon depends on the current stage of the day and year in a given location. The height of the Sun can be calculated as: h = arcsin (sin δ sin ϕ + cos δ cos ϕ cos τ) (1) h... he height of the Sun above the horizon [ ] δ... the solar declination [ ] ϕ... is the latitude [ ] τ... is the angle of the Sun[ ]. 2.2 Solar declination Is the angle, which is formed between the resulting line connecting the Sun and places the observer to the plane of the equator at noon. Instead observer corresponds to the latitude in which it is located. Solar declination is dependent on the season. Reaches its maximum value at the time of the summer solstice (23.5 ) and minimum ( ) at the time of the winter solstice. In the case of the equinox, its value is equal to zero. The value can be determined as follows during the year: δ = sin(.98 D M 19 ) (2) D... is the number of the month M... is the number of months in a year. 2.3 Azimuth Sun It represents the horizontal angle between geographic north and the position in which the Sun is located. The angle is measured clockwise. its value for example, corresponds to the south 18. The angle can be calculated using the following formula [3]: ( ) cos δ α s = arcsin cosh sin τ (3) α... the azimuth Sun [ ] δ... the solar declination[ ] h... the height of the sun above the horizon [ ] τ... the hour angle of the Sun [ ]. Because power panels are oriented to the south, have been calculated better illustrate the corrected 18. In the case of the south and azimuth equal to. westward bearing increases in negative and positive values comes in the direction of the east. The calculated corrected values are given in Table 1. It corresponds to the positions of the Sun located below the horizon. [3]. 2.4 The hour angle of the Sun It is a time expression shift Sun in degrees. One hour corresponds to an angle of 15, because 24 hours is 36. Its value is based on the true noon, when is. In the morning becomes negative and positive afternoon. On the basis of equations (1, 2) was calculated height of the Sun above the horizon for the 15th day of each month. 2.5 Analysis of the shadows Direct rays of sunlight falling on the panels just in time which is their greatest intensity during the day. This is related to the height of the sun. The actual shading panels by graph (fig. 6) should therefore be avoided during periods of high intensity daily radiation. This is already reflected in the design distance between each row of panels. It is proposed so that the winter solstice, when the sun is lowest, at noon to avoid self-shielding. This does not apply to capture systems against lightning. The shielding effect can be expected during a period when the panels are not blocking each other. About how large is shadow, and how long they will be thrown to the panels is dependent on their design. Because power panels are oriented to the south. The calculated values were adjusted for better clarity of 18. In the case of the South is both azimuth equal to. Westward bearing increases negative and positive values shall enter in the direction of the east. The calculated corrected values are given in Table 1. Correspond to the positions of the Sun located below the horizon. [3]. For a better representation of the movement of the sun directly over the area of photovoltaic panels and analysis of shadows, this situation was modeled in Rhinoceros. For analysis was used a sample of six bearing structures in three rows at the periphery of the photovoltaic field. All dimensions correspond to the above mentioned. The movement of sun was simulated for three days and for the winter solstice (21.12.), the vernal equinox (21.3.) and the summer solstice (21.6.). The situation in the case of the vernal equinox is the same day of the autumnal equinox (23.9). The trajectory of the sun across the sky each day is different, which correspond to different shades. The reason is that the movement of the sun was observed in multiple ISBN:

3 Recent Researches in Electric Power and Energy Systems times each day and the larger number of images present the only state to noon on [3]. As shown the Figure 5: Shadow of the day in 12.hours Figure 3: Shadow of the day in 12.hours Figure 4: Shadow of the day in 15.hours Figure 6: Azimuth Sun for the 15th day of each month figure (4), the mutual shielding panels occurs in the afternoon. This means that the distance between the rows are designed properly. For the summer months there is no shade at all, which shows the correctness of the proposed protection (figure 5). The shading of photovoltaic panels is only interception rods from external lightning protection. Thickness rises above the panels is 1 mm from the top first meter and 16 mm remaining.5 m to the edge of the panel. The distance between the rods and the subsequent series is 8.25 meters. It should be noted that the purpose of modeling program to illustrate motion magnitude and direction of the shade for a better idea of the problem. This was also adapted for color representation, to submit maximum effect traces of the shadow. Therefore the applications must be regarded as only tentative. Not reveal the to us fact a real proportion of diffuse radiation components. [3]. 3 panel shading by steel rod. During the second measurement were measured value of the intensity of radiation and the shielding panel. This averaged to obtain the initial and final values for more accurate results transients. Each measured and calculated results are listed in the tables 2, 4: The results show that the performance degradation due to the shadow is 2 %, which is neglected in practice. However, this value is reflected in the total energy produced when the system is poorly designed for the summer time. When measuring the following conditions: For a better comparison would be better measured on two panels in the summer, one of them was without a shadow of a second overshadowed by. Subsequently will be compared energy gain of the two panels. But even so it confirms that the correct design of lightning protection is very important. Experimental measurements In this day there were two subsequent measurements. Values were recorded every 2.5 minutes for equilibration. It measured the optimal performance of MPP (maximum power point). The procedure was to measure the voltage and current values before and during ISBN: Causes of inequality of output power from photocells in photovoltaic power plant unequal output power caused by microstructure 11

4 Month January February March April May June July August September October November December Hour α s[ ] α s[ ] α s[ ] α s[ ] α s[ ] α s[ ] α s[ ] α s[ ] α s[ ] α s[ ] α s[ ] α s[ ] -18, -18, -18, -18, -18, -18, -18, -18, -18, -18, -18, -18, 1-151,8-155, ,9-165,7-165,4-163,9-161,4-157,7-153,4-15, ,1-135,2-141, , ,3-148,6-144, ,4-127, , ,5-137,1-139,1-138,3-134,7-128,9-121,6-114,3-11,1 4-98,4-14,6-112,4-119,6-124,9-127,3-126,3-122,1-115,5-17,7-1,6-96,7 5-86,8-92,5-1,1-17,7-113,5-116,3-115,1-11,4-13,4-95,5-88,7-85,2 6-75,9-81,2-88,6-96,3-12,6-15,6-14,3-99,2-91,9-84,1-77,7-74,4 7-65, ,1-84,9-91,6-94,9-93,5-87,9-8,3-72,7-66,7-63,8 8-53,9-58, ,7-79,8-83,4-81,8-75,9-68,1-6,8-55,4-52,7 9-41,9-45,6-51,5-58,9-66, , ,4-47,8-43,1-4,9 1-28,8-31,6-36,2-42, ,9-51,1-45,2-38,6-33,3-29,7-28, ,7-16,2-18,8-22,5-26,9-29,6-28,4-24,3-2,2-17,2-15,2-14,3 12,,,,,,,,,,,, 13 14,7 16,2 18,8 22,5 26,9 29,6 28,4 24,3 2,2 17,2 15,2 14, ,8 31,6 36,2 42, ,9 51,1 45,2 38,6 33,3 29,7 28, ,9 45,6 51,5 58,9 66,1 7 68, ,4 47,8 43,1 4, ,9 58, ,7 79,8 83,4 81,8 75,9 68,1 6,8 55,4 52, ,1 7 77,1 84,9 91,6 94,9 93,5 87,9 8,3 72,7 66,7 63, ,9 81,2 88,6 96,3 12,6 15,6 14,3 99,2 91,9 84,1 77,7 74, ,8 92,5 1,1 17,7 113,5 116,3 115,1 11,4 13,4 95,5 88,7 85,2 2 98,4 14,6 112,4 119,6 124,9 127,3 126,3 122,1 115,5 17,7 1,6 96, , ,5 137,1 139,1 138,3 134,7 128,9 121,6 114,3 11, ,1 135,2 141, , ,3 148,6 144, ,4 127, ,8 155, ,9 165,7 165,4 163,9 161,4 157,7 153,4 15, , 18, 18, 18, 18, 18, 18, 18, 18, 18, 18, 18, Table 1: Azimuth Sun for every 15th day of the month [3] The values of measurement Average Irradiance [W m 2 ] Temperature of panels [ C] Table 2: Measurement from 5/9/212 U (V) P (W) The values of measurement Average Irradiance [W m 2 ] Temperature of panels [ C] Table 3: Measurement from 7/3/213 The difference of volt-ampere of every semiconductor is well know. This is reason, why also photovoltaic panels have different nominal current and voltage. Photovoltaic panel become degraded after few years, this results in further output power unbalance between photocells in photovoltaic panel. It is advisable to connect panels in a way that each string has similar nominal voltage. deviation in setup angle When photovoltaic power plant is not installed properly, angle difference between panels in string can also occur. This result only in slight difference of voltage and current because of Lambert s cosine law. partial shading of panel shading from surrounding construction and I (A) 8 V-A without shading V-A with shading P-A without shading P-A with shading Figure 7: Result of measurement sharp shading inappropriate placement trees and buildings nearby line of photovoltaic panels (dawn, dusk) lightning protection rods shading from dirt on surface dust, sand, pollen and leaves bird excrement, insect snow, ice and frost deposit Partial shading of panel is caused by construction, location and environment. While selecting a location, it ISBN:

5 Before shading After shading Difference Note Measurement U [V] I [A] P [W] U [V] I [A] P [W] P[%] Sharp shading Full shading disperse Part. shading disperse Table 4: The measured values in the implementation of an attempt - values labeled by were modified due to irradiance change U (V) I (A) V-A without shading V-A with full shading V-A with part. shading P-A without shading P-A with full shading P-A with part. shading Figure 8: Result of measurement disperse irradiance should be taken in account possible sources of shading. Construction of lightning protection rods should be omitted possibility of damage caused by lightning is very low. Environment is another very significant factor that can be handled by proper maintenance. 3.2 Impact of partly shadowed photocells on voltage and current According to own measured V-A characteristic and characteristic from [1] partly shaded panel brings much lower output power. Impact of shadowing moves second derivation of this curve from negative values to positive values, which means, that characteristic changes from concave curve to convex curve. In serial - parallel connection, is shaded only one module, can be also partly convex and partly concave curves (multiple inflection points) [2]. 4 Conclusion It is very important for design solutions not only provide lightning protection equipment itself, but also optimize the deployment of interception rods. Should an P (W) improper rod deployment can reduce the long term performance of the panels, which is very undesirable and may lead to damage to the panels. Loss of power in our case made up 1.6%. When measured at better conditions in the Czech Republic, the number could be around 2% (maximum value for limit condition was 3.4 %). Therefore, the proposal must devote sufficient attention. Suitable as the use of modeling software, which shows the shadows. Acknowledgements: This paper contains the results of research works funded from project of specific research program of Brno University of Technology No. FEKT- S The research was performed in Center for Research and Utilization of Renewable Energy Sources (CRURES). Authors gratefully acknowledge financial support from European Regional Development Fund under project No. CZ.1.5/2.1./1.14. References: [1] Mohandes B. M. A., El-Chaar L., Lamont L. A. Application Study of 5 W Photovoltaic (PV) System in the UAE. Applied Solar Energy, 29, pp Allerton Press, Inc., 29, ISSN 3-71X [2] Martinez-Moreno F., Muoz J., Lorenzo E. Experimental model to estimate shading losses on PV arrays Instituto de Energa SolarUniversidad Politcnica de Madrid (IES-UPM), 6p. [3] Manduch, V., Navrh ochrany FVE pri uderech blesku a jisteni datovych rozvodu. Diploma Thesis. Brno: Brno University of Technology, s. [4] CLC / TS Low-voltage surge protective devices - Surge protective devices for specific application including d.c. - Part 12: Selection and application principles - SPDs connected to photovoltaic installations ISBN: