J. Basic. Appl. Sci. Res., (3)-3,, TextRoad Publication ISSN 9-44X Journal of Basic and Applied Scientific Research www.textroad.com Effect of Shadow and Dust on the Performance of Silicon Solar Cell A. Ibrahim Physics department, Faculty of Science, Tanta University, Egypt Present address: Physics department, Faculty of Science, Northern Border University, KSA ABSTRACT I-V characteristics of large area solar cells operated under simulated solar irradiation for the purpose of testing their quality and determining their optimal operational points for maximum electrical output is obtained. The paper included a solar-simulator (a Halogen lamp of W) and a large area silicon solar cell ( cm x 6 cm in dimensions) to be tested under solar simulator. Rather than simply looking at the short circuit current and the open circuit voltage of a solar cell, our system measures its full I-V characteristics while the cell is irradiated with an artificial light source which simulates the solar radiation. Measured I-V data and determines the maximum electrical power output of the cell as well as the series resistance, the parasitic effect most effective in lowering maximum power and efficiency. On the other hand, the relation between the I sc and V oc of the solar cell and both of shadow and dust effects on the solar cell are determined. Moreover, from 5 to 5% reduction in peak power has been obtained by varies climatic conditions, especially accumulated dust. Also, a reduction by.78% per day of Isc has been obtained. On the other hand, Voc has been decreased by.863 % per day time. KEY WORDS: silicon solar cells, indoor measurements, shadow effect, dust effect. INTRODUCTION Solar cell efficiency is an important input parameter in PV-powered product design. Often, only limited space is available for the solar cells to be integrated. Cell efficiency can even become a criterion of principal system feasibility. As a basic parameter, cell efficiency serves as an input in calculating the optimal system configuration, e.g., as a cost related trade-off between the storage unit and its lifetime, PV size and its efficiency, and finally the demand side (with correlated consumption profiles). Although these calculations are well known for autonomous PV systems, e.g. (Castaner and Silvestre, ), device integrated PV systems, especially when used indoors, become more complex to model. Different irradiation conditions compared to those outdoors require a more detailed knowledge of solar cell characteristics than is described with the current standard test condition (STC), wherein the efficiency definition is limited to an irradiation level of W/m at AM.5 spectrum. Whether the user of a solar powered device will be satisfied is supposed to be strongly related with the overall energy balance of demand and (solar) energy supply, which is the overall solar fraction of energy flow. Not surprisingly, one observes that the uncertainty in energy consumption data combined with the possible variations in intensity of use and irradiation results in large variations in the expected solar fraction. Therefore, this paper intends to determine indoor PV (ipv) energy yields linked to irradiation level classes, enabling product designers to reduce uncertainty of estimated light harvesting potentials of ipv, and resulting solar fractions in dedicated devices respectively. Calculating the energy yield of PV indoors require both indoor irradiation levels as well as spectral distributions. To get access to PV characteristics at indoor light levels as well as the specific spectral response (SR) characteristics, a cell survey *Corresponding author: Dr. Ali Ibrahim, Physics department, Faculty of Science, Tanta University, Egypt. E. mail: Ali_us@yahoo.com
A. Ibrahim, has been carried out (M.G. Guvench, C. Gurcan, K. Durgin and D. MacDonald. 4, Sze, S.M., 98& Green, M.A, 98). In this paper the measurement results of commercial available solar cells from different manufacturers and different cell technologies are presented. Cell samples have been investigated regarding their IV-characteristics down to light intensities in a range three orders of magnitude below STC. Also the SR of the test samples was investigated, using two different bias light intensities and spectra. The method of estimating ipv energy harvesting potentials is to link measured PV performances to different daylight factors of indoor irradiation conditions. Power measurements of PV modules in test laboratories and industry are usually performed with solar simulators as so-called indoor measurement. The advantages of indoor measurements are obvious: The measurement is not dependent on weather conditions A high reproducibility is achieved because test conditions can be adjusted for certain ranges of module temperature and irradiance The nominal power of PV modules is related to the maximum output power under standard test conditions (STC). According to IEC 694-3 Photovoltaic devices Measurement principles for terrestrial photovoltaic (PV) solar devices with reference spectral irradiance data, these conditions are: irradiation = W/m², module temperature = 5 C, spectral irradiance = AM.5. Measuring techniques for solar simulators are, therefore, aiming to measure as close as possible to these conditions. However, solar simulators are no perfect light sources, and the quality of emitted light can strongly influence the result of a power measurement. In particular, the following quality parameters must be considered: i. Effective irradiance ii. iii. iv. Pulse length for flash type solar simulators Spectral irradiance distribution of lamp Uniformity of irradiance in the test area v. Temporal instability of irradiance vi. This paper aims to characterize the effect of dust on photovoltaic cell performance by determining the rate that dust deposits on solar panel glass and how much sunlight is absorbed and reflected by dust. EXPERIMENTAL SET UP In this work, the system of measurements is consists of a silicon solar cell of area cm, a digital multimeters (PeakTech 3596), a halogen lamp of W, and also a suitable load resistance. RESULTS AND DISCUSSIONS The data obtained for I-V characteristics and P-V curve for the silicon solar cell under investigation shown in Figs. &. Since, the short circuit current Isc and the open circuit voltage Voc was ma and. V respectively. Also, the maximum power point MPP is.33 W. 3
J. Basic. Appl. Sci. Res., (3)-3, I-V characteristics for silicon solar cell 5 Current (ma) 5 Series 5.5.5.5 Voltage (V) Fig.: I-V characteristics for silicon solar cell under sun simulator. P-V Curve for silicon solar cell.35.3.5 Power W..5 Series..5 5 5 5 Voltage (V) Fig.: P-V characteristics for silicon solar cell under sun simulator. Shadow effect on both Isc and Voc for the solar cell Environmental effects on the performance of PV are caused by many factors either natural like clouds, dust and temperature, or artificial like evaporation of pollution from different factories. These effects may cause variation on the PV electrical output due to spectrum, intensity, local shadowing or reflection and variations of solar radiation distribution falling on it. The effect of an inhomogeneous irradiation distribution on the energy output of buildingintegrated PV arrays is investigated through either simulations or measurements in many publications (Mooney, 99; Guvench, 993; Kovach et al., 996). Shadow parts of the module causing what is so-called hot spot which causes a general reduction of the PV output. Another type of shadowing is the edge shadowing which may happen in PV field due to dust accumulated on the tilted PV array. This happens intensively in the bottom edges of the panels causing another type of reduction. Gradual reduction of energy yield up to -% of PV cell was observed as a result 4
A. Ibrahim, of accumulation of a permanent pollution strip at the edge of the framed cell. Edge shading is also possible to happen in field due to the shadows cast by other PV cells and the tilt, the orientation and the surface temperature variation of the PV panel. To study the influence of the partial shadowing on the solar cell performance, an experiment is performed to investigate that phenomenon under a solar simulation by using a halogen lamp of 5 W. The experimental work described below was held on a rectangular- shaped of cm monocrystalline Si solar cell. The measuring device is a Class A spectrum output solar cell tester that uses spectrally corrected continuous halogen light source with 85% uniform collimated light. Shadowing on the solar cell is done using a certain percentage of a completely obscure film fixed on the cell front surface to prevent exposing that part to incident radiation, and the remaining portion of the solar cell was illuminated. In the experimental procedure, shadowing was first done for the upper sections one by one of the surface of the solar cell, with several strip areas. After that, edge shadowing was replaced by / shadowing (left or right sides) for the same cell. Fig. 3 shows a schematic diagram of the solar cell under illumination with the shadowing in many cases, the edges, and the corners. Fig. 3: Schematic diagram of the movable shadowing sections from the silicon solar cell under illumination. A comparison is done between the cell parameters and performance of the solar cell in case of section by section shadowing, with different shading area relative to the solar cell. All the experimental procedures were done at constant temperature. Figs. 4&5 show the dependence of both Isc and Voc on the shadowing sector from the solar cell under test. A linear decrease of the short circuit current (Isc) with minimizing cell area in case of sections (&4 - &3-5&7- &&3&4 &4&6&8) shadowing was measured, which is normal due to minimizing the area exposed to illumination, and accordingly electron hole generation is decreased. In comparison, a non-linear decrease of the Isc is observed with decreasing the active cell area in case of edge shadowing (- - 8-7 sections). The cell opens circuit voltage (Voc) versus active cell area for the many types of cell shadowing. A noticeable decrease in the Voc with decreasing the active cell area is recorded with halfshaded solar cell. This behavior was completely reversed with edge-shaded solar cell 5
J. Basic. Appl. Sci. Res., (3)-3, effect of shadow on Isc for a silicon solar cell 5 Isc (ma) 5 5 & &4 &3 &&3&4 8 7 7&8 6&8 5&7 5&6&7&8 &4&6&8 &3&5&7 & &4 &3 &&3&4 8 7 7&8 6&8 5&7 5&6&7&8 &4&6&8 &3&5&7 solar cell sector Fig.4: Variation of Isc of the solar cell versus shadowing sectors. effect of shadow on Voc for a silicon solar cell.5 Voc (V).5.5 & &4 &3 &&3&4 8 7 7&8 6&8 5&7 5&6&7&8 &4&6&8 &3&5&7 & &4 &3 &&3&4 8 7 7&8 6&8 5&7 5&6&7&8 &4&6&8 &3&5&7 solar cell sectors Fig.5: Variation of Voc of the solar cell versus shadowing sectors. Effect of dust on solar cell performance Dust has been attributed by Nimmo and Seid to as much as 4% degradation in peak power of photovoltaics, there is surprisingly little scientific work done on the subject. Since no information about the type of dust, density of dust, or rate of accumulation of dust was noted, no general understanding of the underlying physical principles could be deduced. Therefore, their test is specific only to the time and location of their test. Dust accumulation on the glazing of solar thermal collectors associated with distillation plants for seawater desalination is one of the main natural causes for performance degradation. This is particularly so for plants in operation in remote desert locations subject to sand storms where the air is laden with fine sand particles. Dust deposition on flat plate collectors has been studied by several authors (e.g. El-Shobokshy and Hussein, 993; 6
A. Ibrahim, Sayigh et al., 985; Hegazy, ; Nimmo and Seid, 979; Garg, 974). El-Nashar (994) studied the influence of dust deposition on the performance of evacuated tube collectors on a large field of collectors and found that accumulated dust on this type of collectors can result in a substantial reduction in collector efficiency. The airborn particles in the atmosphere affect the amount and properties of the radiation finally reaching the collectors (Mastekbayeva and Kumar, ; Al-Hassan, 998). Outdoor measurements on glazing transparency have been performed by Nahar and Gupta (99) and Bonvin (995). Hegazy () studies dust accumulation on glass plates with different tilt angles and measured the transmittance of the plates under different climatic conditions in Minia, Egypt over a period of one month. The degradation in solar transmittance during this period was found to depend on the tilt angle of the glass plates with a maximum value when the plate is in a horizontal position and minimum value when it is vertical. Measurements made by Sayigh et al. (985) and Hasan and Sayigh (99) of dust accumulation on tilted glass plate located in Kuwait was found to reduce the transmittance of the plate by an amount ranging from 64% to 7% for tilt angles ranging from to 6, respectively after 38 days of exposure to the environment. In this part, the short circuit current Isc and the open circuit Voc for a silicon solar cell through a period of exposure of days to the environment (dust ) was measured. Figs. 6 &7 explain the correlation between the deposited accumulated dust on the surface of the solar cell and both Isc and Voc. Where Isc was decreased as the time of exposure increased, according to the following fitting equation:- I sc 5.56t.85 The minus sign means Isc decreased as time of exposure increased. Also, the value.85 ma is the initial Isc of the solar cell before field exposure, and 5.56 ma losses of Isc per daytime,.78% losses from Isc per daytime. Effect of dust on Isc for solar cell 5 y = -5.56x +.85 R =.9635 Isc (ma) 5 Series Linear (Series) 5 4 6 8 days Fig. 6: The variation of Isc with the time of field exposure for a silicon solar cell of area cm during December, Arar KSA. While, for Voc the data show that Voc is slightly decreasing with field exposure, according to the equation:- V oc.9t. 7
J. Basic. Appl. Sci. Res., (3)-3, effect of dust on Voc of a solar cell 5 4.5 4 3.5 y = -.9x +. R = -.4 Voc (V) 3.5.5.5 Series 4 6 8 days Fig. 7:- The variation of Voc with the time of field exposure for a silicon solar cell of area cm during December, Arar KSA. From the equation it is clear that Voc is slightly decreasing with the time of field exposure. The value. V is the initial open circuit voltage of the solar cell while.9 V is the losses of Voc per daytime of field exposure, i.e., decreased by.863 %. On the other hand, the correlation between the tilt angle and its affects on dust accumulation on the glass cover a photovoltaic solar cell is shown in Fig. 8. The numbers for this graph were obtained by first averaging the % current reduction caused by dirty glass. Then from this value the % current reduction of clean glass was subtracted. The % current reduction of clean glass was obtained by averaging the % current reduction of clean glass on the same day as the test with the overall average % current reduction, 3.63%. This method was designed to correct for some of the unwanted variation of clean glass current reduction..5%.% Dec. 8 % Current Reduction.5%.% Nov. 6 Nov. 7 Degree Degrees 3 Degrees.5%.% Nov. 8 Nov. 6 Nov. 3 Dec. 6 Dec. 8 Dec. Date of Test Fig.8:- The relation between the % current reduction of a solar cell and the tilt angle. 8
A. Ibrahim, Conclusions The performance of a solar cell under a sun simulator is necessary to describe the electrical parameters of the cell. The Isc, Voc, MPP, can be estimated. Also, effect of shadowing location from the area of the silicon solar cell has been tested experimentally by preventing light to reach certain location on the solar cell with certain shadowing area. Comparison has been done between shadowing the cell sectors and cell edges at a constant incident illumination (i.e., halogen lamp). It was found that there is an unexpected difference in the solar cell behavior in the above-mentioned cases. Isc is more decreased in a high percent than Voc for the solar cell under shadow, so the other solar cell parameters will be decreased. On the other hand, both Isc and Voc of the solar cell were decreased under deposited dust through field exposure. Since, Isc is more decreased then Voc (.78% and.863% respectively). As a future work, the behavior of a solar cell/module under shadowing effect could not be explained by the diode model, as the exposed cell area is indistinguishably stated in the model. A better and more realistic model of solar cells in non-uniform illumination and a computer simulation for the process are needed. REFERENCES Al-Hassan, A.Y. (998). A new correlation for direct beam solar radiation received by photovoltaic panel with sand dust accumulated on its surface. Solar Energy 63, 33. Bonvin, J. (995). Dirt deposit level measurements on different glass type in various surroundings. In: Freiesleben, W., Paltz, W., Ossenbrink, H.A., Helm, P. (Eds.), Proceedings of the 3th European Photovoltaic Solar Energy Conference, Nice, France, pp. 74 74. El-Nashar, A.M., (994). The effect of dust accumulation on the performance of evacuated tube collectors. Solar Energy 53, 5 5. El-Shobokshy, M.S., Hussein, F.M., (993). Effect of the dust with different physical properties on the performance of photovoltaic cells. Solar Energy 5, 55. Garg, H.P. (974). Effect of dirt on transparent covers in flat- plate solar energy collectors. Solar Energy 5, 99 3. Green, M.A. (98) "Solar Cells," Prentice-Hall. Guvench, M.G. (993) "Automated Measurement of Semiconductor Device Characteristics For Computer Assisted Electronic Design" Proc. of ASEE, pp. 67-675, vol.. Haeberlin H, Graf JD. (998), "Gradual reduction of PV generator yield due to pollution", In: Second World conference and exhibition on photo- voltaic solar energy conversion, 6 July 998, Austria. pp. 764 67. Hasan, A., Sayigh, A.A.M., (99), "The effect of sand dust accumulation on the light transmittance, reflection, and absorbance of the PV glazing", In: Sayigh, A.A.M (Ed.), Renewable Energy, Technology and Environment. Pergamon Press, Oxford, pp. 46 466. Hegazy, A.A. (), "Effect of dust accumulation on solar transmittance through glass covers of plate type collectors", Renewable Energy, pp. 55 54. Kovach A, Schmd J., Sol. Energy (996), 57(), pp. 7 4. L.Castaner & S.Silvestre, (), "Modelling PV systems using PSPICE", Wiley & Sons. M.G. Guvench, C. Gurcan, K. Durgin and D. MacDonald (4), "Solar Simulator and I-V Measurement System for Large Area Solar Cell Testing ", Proceedings of the 4 American Society for Engineering Education Annual Conference & Exposition. Mastekbayeva, G.A., Kumar, S., (), "Effect of dust on the transmittance of low density polyethylene glazing in tropical climate", Solar Energy 68, pp. 35 4. 9
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