CHAPTER VI. 6. Angle Dependence on Performance of Dye Sensitized and V-Grooved Silicon Solar Cells

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1 CHAPTER VI 6. Angle Dependence on Performance of Dye Sensitized and V-Grooved Silicon Solar Cells Abstract An investigation of the angular dependence for 3 DSSC modules (Cocinia Indica, Eclipta Alba and Solanum Melongena Dye) & 3 commercial microcrystalline Flat type silicon solar cell, V-grooved Si-cell without Microlens and V-grooved Si-cell with Microlens have been carried out under controlled airmass conditions. The incidence angle has been varied with very good accuracy due to the mechanisms of the test setup. It is desired to carry out outdoor measurements of solar cells in order to determine the performance dependency with respect to the Angle of Incidence, AOI. These measurements are best carried out outdoor, as the sun provide parallel beams and has the desired spectral distribution of light. 163

2 6. 1. Introduction The optimum angle show some variations when compared with values reported in the literature. The amount of solar radiation incident on a tilted module surface is the component of the incident solar radiation which is perpendicular to the module surface. The array s tilt is the angle in degrees from horizontal. A flat roof has 0 degree tilt and a vertical wall mount has a 90 degrees tilt angle. Whether you are installing solar panel on a flat roof or a pitched roof, the output of the solar PV system would be increased by optimizing the tilt angle. This information gives about the theoretical aspects of choosing a tilt angle for the solar flatplate collectors used at different locations in India. So the calculations are based upon the measured values of monthly mean daily global and diffuse solar radiation on a horizontal surface. It is shown that nearly optimal energy can be collected if the angle of tilt is varied seasonally, four times a year. Annual optimum tilt angle is found to be approximately equal to latitude of the location. This study determined that PV module oriented towards the South India (TN-Salem) gives the greatest value of electrical energy for the angle of 30. Almost all the renewable energy sources originate entirely from the sun. Photovoltaic solar energy conversion is the direct conversion of sunlight into electricity. This can be done by flat plate and concentrator systems. An essential component of these 164

3 systems is the solar cell, in which the photovoltaic effect the generation of free electrons using the energy of light particles takes place. These electrons are used to generate electricity. Solar power is energy from the sun and without its presence all life on earth would end. Solar energy has been looked upon as a serious source of energy for many years because of the vast amounts of energy that are made freely available, if harnessed by modern technology. The tilt angle has a major impact on the solar radiation incident on a surface. For a fixed tilt angle, the maximum power over the course of a year is obtained when the tilt angle is equal to the latitude of the location. However, steeper tilt angles are optimized for large winter loads, while lower title angles use a greater fraction of light in the summer. The sun, at noon time, is not always directly on top of us. The sun will be slightly to your south throughout the year, if your location is in the north of 30th latitude in the Northern Hemisphere. The array output is highest, if the array faces directly to the sun at all times. Since the location of the sun moves throughout the day, it is not possible to face directly to the sun unless we use 2-axis solar tracker. But solar tracking is expensive and it is possible to optimize the output by tilting the array at a correct angle. It is simplest to mount your solar panels at a fixed tilt and just leave them there. But because the sun is higher in the summer and lower in the winter, you can capture more energy during the 165

4 whole year by adjusting the tilt of the panels according to the season. The amount of radiation flux incident upon a solar collector is mainly affected by the installation angle. Proper design of a collector can increase the irradiation received [1] Tilt Measurement Solar radiation data is usually measured in the form of global radiation on a horizontal surface at the concerned latitude. Flatplate collectors are tilted so that they capture maximum radiation. Since the flat-plate solar collectors are positioned at an angle to the horizontal, it is necessary to calculate the optimum tilt angle which maximizes the amount of collected energy. It is generally known that in the northern hemisphere, the optimum collector orientation is South facing and that the optimum tilts depend on the latitude and the day of the year. In winter months, the optimum tilt is greater (usually latitude +15 ), whilst in summer months the optimum tilt is lower (usually latitude -15 ) [2]. For building-integrated applications, the system orientation is also dictated by the nature of the roof or façade in which it is to be incorporated. It may be necessary to trade off the additional output from the optimum orientation against any additional costs that may be incurred to accomplish this. The aesthetic issues must also be considered [3, 4]. 166

5 6.3 Solar Thermal Collector Overview The average power density of solar radiation is watts a square meter. The net conversion efficiency of solar electric power systems (sunlight to electricity) is typically percent. So substantial areas are required to capture and convert significant amounts of solar energy to fulfill energy needs (especially in industrialized countries, relative to today s energy consumption). For instance, at a plant efficiency of 10 percent, an area of 3-10 square kilometers is required to generate an average of 100 megawatts of electricity-0.9 terawatt-hours of electricity or 3.2 pet joules of electricity a year using a photovoltaic system. 6.4 Solar Radiation Solar radiation describes the visible and near-visible (ultraviolet and near-infrared) radiation emitted from the sun. The different regions are described by their wavelength range within the broad band range of 0.20 to 4.0 µm (microns). Monthly average daily global radiation on a horizontal surface is defined as H = Hdir + Hdiff (6.1) Where Hdir is Monthly average daily direct radiation on a horizontal surface and Hdiff is Monthly average daily diffuse radiation on a horizontal surface. Terrestrial radiation is a term used to describe infrared radiation emitted from the atmosphere. The following is a list of the components of solar and terrestrial radiation and their approximate wavelength ranges: Ultraviolet: µm, 167

6 Visible: µm, Near-Infrared: µm & Infrared: µm. Approximately 99% of solar, or short-wave, radiation at the earth's surface is contained in the region from 0.3 to 3.0 µm while most of terrestrial, or long-wave, radiation is contained in the region from 3.5 to 50 µm. Outside the earth's atmosphere, solar radiation has an intensity of approximately 1370 watts/meter 2. On the surface of the earth on a clear day, at noon, the direct beam radiation will be approximately 1000 watts/meter 2 for many locations. Beam Radiation (Rb): The solar radiation received from the sun without having been scattered by the atmosphere. Diffuse Radiation (Rd): The solar radiation received from the sun after its direction has been changed by scattering by the atmosphere. Total Solar Radiation (Rt): The sum of the beam and diffuse solar radiation on a surface. Irradiance: The rate at which radiant energy is incident on a surface, per unit area of surface. The symbol G is used for solar irradiance. Insolation-The incident energy per unit area on a surface, found by integration of irradiance over a specified time, usually an hour or a day. Insolation is a term applying specifically to solar energy irradiation. The symbol H is used for insolation for a day. The 168

7 symbol I is used for insolation for an hour (or other period if specified). The extraterrestrial radiation on a horizontal surface at any time is given by Ho = Hon cosθ (6.2) Where Ho is Extraterrestrial radiation on horizontal surface, Hon is Extraterrestrial radiation at normal surface and θ is Angle of Incidence Modelling Based on the literature survey it is seen that the incident solar radiations on a collector surface are greatest for an optimal tilt angle of the collector at a particular region which is also not constant throughout the year. To obtain maximum power output from the solar collector system it is desirable to tilt the collector to that tilt angle at which the incident solar radiations are maxima. To optimize capture of solar panels a tilt angle of is recommended. However, tilt angles between are possible without great yield losses. Increasing the tilt angle favors energy production in the winter, while decreasing the tilt angle favours energy production in the summer. As most published meteorological data give the total radiation on horizontal surfaces, correlation procedures are required to obtain insolation values on tilted surfaces from horizontal radiation. Monthly average daily total radiation on a tilted surface (Ht) is normally estimated by 169

8 individually considering the direct beam (Hb), diffuse (Hd) and reflected components (Hr) of the radiation on a tilted surface. Ahmad M. Jamil and Tiwari G.N. [5] analyzed the theoretical aspects of choosing a tilt angle for the solar flat-plate collectors used at ten different stations in the world and makes recommendations on how the collected energy can be increased by varying the tilt angle. For Indian stations, the calculations are based upon the measured values of monthly mean daily global and diffuse solar radiation on a horizontal surface. For other stations, the calculations are based upon the data of monthly mean daily global solar radiation and monthly average clearness index on a horizontal surface. It was shown that nearly optimal energy can be collected if the angle of tilt is varied seasonally, four times a year. The dependence of extraterrestrial radiation on time of year is indicated by Duffie J.A. and Beckman W. A. [6]: Extraterrestrial radiation on the plane normal G is defined as G G sc cos 360n 365 (6.3) Where Gsc is Solar Constant, approximately KW/m 2. The constant is fairly constant, increasing by only 0.2 percent at the peak of each 11-year solar cycle. Sunspots block out the light and reduce the emission by a few tenths of a percent, but bright spots, called plages, that are associated with solar activity are more extensive and longer lived, so their brightness compensates for the 170

9 darkness of the sunspots. Moreover, as the Sun burns up its hydrogen, the solar constant increases by about 10 percent every billion years. Mubiru J. and Banda E.J.K.B. [6] explored the possibility of developing a prediction model using Artificial Neural Networks (ANN) A mathematical model is used to estimate the total (global) solar radiation on a tilted surface and to determine the optimum tilt angle for a solar collector in Izmir, Turkey. Total solar radiation on the solar collector surface with an optimum tilt angle is computed for specific periods. Joakim Widén [7] mentioned the models of solar radiation, daylight and solar cells as a chapter in his thesis. He described the models implemented for calculating the daylight level and the power output from PV system, to be used in further simulations of domestic (Sweden) electricity demand, he gave a brief overview of models, then he described in his chapter how to determine incident radiation on a tilted plane from radiation components measured on a horizontal plane. 6.6 Intension One of the objectives of this research is to provide technical information about tilt angle and orientation of PV Panels for both Architectures who interests in Building-Integrated Photovoltaic applications and Practitioner Engineers who interests in the utilization of renewable energy in India to improve and enhance the 171

10 efficiency of PV System used in their designs with reduced cost. Daily and monthly Optimum slope angles. The sunset hour angle (ω) for any day (n) of the year can be obtained as follows. The total daily irradiation on a horizontal plane, H, is the combination of two Components- the direct (beam) irradiation and the diffuse irradiation from the sky. Orientation of solar collector in space is the main factor influencing the quantity of absorbed solar radiation energy. In the case with optimal angles of a solar collector, we will have the maximum of solar radiant energy. The optimal angles depend on the geographical position and on the investigation period (day, week, month, etc.) when the position of a solar collector will be stationary. It is very important, because the trajectory of the sun changes. The intensity of solar radiation energy, sunlight duration per day and per year change as well. Emanuele [8] found in his paper a relationship between the optimum tilt angle and the geographic latitude. Furthermore, he found that the optimum tilt angle values for winter months were very different than those relative to summer months, so he suggested the idea of planning semi fixed solar panels. 172

11 Total radiation on a tilted surface, can thus be expressed as Where 1 cos H t H H diff R b H 2 H R d d (6.4) R H b R 1 H 1 cos b H b sin 3 d b H H 2 H o o 2 (6.5) Here β is Tilt of the surface from horizontal and ρ is Ground reflectance ( 0.2). 6.7 Site Analysis and Results Understanding solar radiation data and the amount of solar energy intercepts specific area are essential for modeling solar energy system and covering the demand. Therefore, precise knowledge of historical global solar radiation at a location of study is required. The following is data retrieved from Meteorological Station Data as given the table 6.1. Table 6.1: Horizontal Irradiation data for South India/Salem Sl. No. Month KWh/m 2 /day 13. January February March April May June July August September October November December 4.27 Annual

12 Sl. No. Cell Type Irradiance (W/m 2 ) Intensity (Lux) In order to create a base for comparison of the results achieved from the tests at an irradiance of 100 W/m 2 and 1000 W/m 2, linear regression on the results have been performed with respect to cell temperature for all cells, with the slopes given in Table 6.2. Table 6.2: I-V Charactristics results of various Irradiance with Intensity for different types of cells Isc Voc (mv) (ma) ff (%) η (%) 1. DSSC-1 (Cocinia Indica) 2. DSSC-2 (Eclipta Alba) 3. DSSC-3 (Solanu m Melonge na Dye) 4. Flat type silicon solar cell 5. V-grooved Si-cell without Microlens 6. V-grooved Si-cell with Microlens

13 The data provides a temperature coefficient which describes the temperature dependence with respect to the investigated electrical parameter. For different silicon solar cells, the average of the tests carried out for each cell is given in the table 6.2 Tasi et.al [9] implemented a generalized photovoltaic model using Matlab software package which can be representative of PV cell, module, and array for easy use on simulation platform. Their proposed model is designed with a user-friendly icon and a dialog box like Simulink block libraries. His model will be helpful to develop similar model taking into account the variation of irradiation and temperature, also to be used in several power systems. In rainy season the beam radiation decreases whereas the diffuse radiation increases still the beam radiation South India/Salem shows similar trends as that of North India/Delhi is much higher than the diffuse radiations in Delhi. The average daily total solar radiation at Delhi on a south facing surface as the angle of tilt is varied from 0 to 90 in steps of 0.5. It is clear that a unique optimum tilt angle exists for each month of the year for which the solar radiation is at a peak for the given month. The optimum angle of tilt of a flat plate collector in January is 52 and the total monthly solar radiation falling on the surface at this tilt is W/m 2 day. The optimum tilt angle in June goes to a minimum of zero degree and the total monthly 175

14 solar radiation at this angle is W/m 2 day. The optimum tilt angle then increases during the winter months and reaches a maximum of 53.5 in December which collects W/m 2 day of solar energy monthly. The average daily total solar radiation at South India/Salem on a south facing surface as the angle of tilt is varied from 0 to 90 in steps of 0.5. It is clear that a unique optimum tilt angle exists for each month of the year for which the solar radiation is at a peak for the given month. The optimum angle of tilt of a flat-plate collector in January is 44.5 and the total monthly solar radiation falling on the surface at this tilt is W/m 2 day. Table 6.3: Optimum tilt angle for each Month of the year at South India/Salem Sl. No. Month Optimum Tilt Total Irradiance Angle ( ) (10 7 W/m 2 day) 1. January February March April May June July August September October November December Average

15 WRDC (World Radiation Data Center) provides monthly irradiance for 1195 sites in the world, this data is available free of cost. Based on the data table 6.4 is shown below: The optimum tilt angle in May goes to a minimum of zero degree and the total monthly solar radiation at this angle is W/m 2 day. The optimum tilt angle then increases during the winter months and reaches a maximum of 46 in December which collects W/m 2 day of solar energy monthly. Table 6.4: Horizontal Radiation and Optimum tilt Radiation in major cities in India Sl. Major City in Horizontal Optimum No. India Radiation tilt Radiation 1 Salem Delhi Nagpur Kolkata Average (India) The fixed tilt angle for each season was evaluated as an average of monthly optimum tilt angles for a period of three months. The seasonal variation of optimum angles for different location consider in the study. The seasonal optimum tilt angle for South India/Salem is minimum as compared to other locations in 177

16 winter, spring and autumn. The seasonal optimum tilt angle for Delhi goes to 0 for the summer. Therefore comparison of monthly optimum tilt angle for Delhi using different models which also indicate that the model is appropriate for Delhi to find the optimum tilt angle, it also indicate that the monthly optimum tilt angle goes to zero for the month of May June and July for Delhi consider in the studies. And comparison of monthly optimum tilt angle for Salem using different models which also indicate that the model is appropriate for Salem to find the optimum tilt angle, it also indicate that the monthly optimum tilt angle goes to zero for the month of May June and July for all the Salem in the studies. The seasonal optimum tilt angles for Salem is minimum as compared to other locations in winter, spring and autumn but in summer Delhi goes to minimum seasonal optimum tilt angle. The optimum tilt angle in June goes to a minimum zero degree as indicated by all the models. On the basis of the above mentioned one can say that: 1. Solar module oriented towards the South gives the greatest values of electrical energy for all the chosen angles. 2. Solar module oriented towards the South for the angle of 30 generates the greatest registered value for electrical energy. This is an optimal tilt angle in the summer 178

17 3. Parametric study for evaluating the sensitivity of optimum tilt angle to radiation rate, solar declination, effect of wind etc. can be carried out. 4. Pecuniary assessment can be carried out using a variety of techniques such as net present value, unit cost of electricity and internal rate of return for a power plant. 5. When the sun s rays fall normally on the module s surface, the incident sunlight power is maximum. The energy from the sun in the form of photon energy is used by solar cells to generate electricity. The solar irradiation has a broad energy spectrum which is distributed into wavelengths. The irradiance as well as spectral distribution of the light depends on the distance the light has to travel through the atmosphere. The amount of solar irradiance available as well as the intensity depends on the position of the sun. The irradiance in a plane therefore depends on orientation, tilt and location. This is illustrated for Asian showing the averaged daily sum of irradiation on a global horizontal faced plane [10]. Three components define the total amount of solar irradiance G, measured in W/m 2 : Direct irradiation - amount of irradiance which has not been scattered in the atmosphere. On clear days, this component can be up to W/m 2 depending on the relative air mass the irradiance has to pass. Diffuse irradiation is defined as irradiance which is scattered in the atmosphere. It has 179

18 the amount for approx W/m 2 [11-13] on clear days. Reflected irradiation is defined as irradiance which has been reflected by the ground or the surroundings. Figure 6.1. Horizontal Solar Radiation of Selected Asian Countries. The incidence angle of the incoming irradiance on a solar cell determines influence the power output. When regarding the maximum power output can be at its maximum when the irradiation is perpendicular to the plane as the illuminated area of the solar cell is proportional to cosine to incidence angle. 6.8 Angle of Incidence (AOI) Dependence Experiments with the objective to investigate the angular dependence of the DSSC and V-grooved Microcrystalline Silicon Solar Cells have been carried out at Department of Physics, Periyar University, Salem, respectively: Since the results are obtained with both different DSSC- and V-grooved Microcrystalline Silicon Solar 180

19 Cells, a direct comparison of results for these two tests were performed. The tests and results from the two experiments described in the following ways. The influence of incidence angle on cell performance has been investigated both simultaneous side-by-side tests setup. Since the structure of the DSSC-and silicon cells differ, an advantage for the DSSC at high incidence angles was expected due to a volumeabsorption of incident light instead of restricted to the surface like the silicon. A beneficial Isc contribution for increasing incidence angles has been identified for the DSSCs, whereas the silicon cells are seen to react according to the cosine relation until incidence angles exceeding approx. 55. This critical angle could be identified as Brewster s Angle for where reflectance from the p-polarized component is zero. All cells are affected by the increased surface reflectance at increasing incidence angles. As increased incidence angle is connected with a lowering of irradiance with cosine to incidence angle and a logarithmic Voc decay has been revealed for both DSSC and silicon cells under low light levels the benefit that the DSSC might have due to angular dependence is not markedly in the final output. The angular effect of increased relative Isc as function of incidence angle is not seen in the long-term measurements, which can be interpreted as the influence of surface reflectance. 181

20 Figure 6.2: Definition of Incidence Angle The angle between a ray incident on a surface and the line perpendicular to the surface at the point of incidence, called the normal. The incidence angle for a south-oriented plane will be at its minimum when the sun is directly faced south, without regards to plane tilt. This time is defined as solar noon, when Ts, true solar time is 12: Experimental Set up & Testing for Tilt Angle The test was performed in the Laser Optics and Solar Cells Laboratory at Department of Physics, Periyar University, Salem, Tamilnadu, India, and as shown in figure 6.3. The set up consist of a Xenon lamp as light source, a water filter to imitate the atmosphere, a mirror to bend the beam, a diffusing plate to distribute the illumination to the test area and fans to avoid heating cells. The panel is fixed on a wood frame with 45 tilt angle so that the panel surface is normal to the irradiation. In order to determine the temperature of cell, three thermo couples were used 182

21 in the set up, placed: One in level with the backside of the cell, one on the front side of the cell. The irradiation intensity at the test area is measured by a standard pyranometer. The spectral distribution of Xenon lamp compared to solar irradiance at 1000 W/m 2, A.M1.5 [14]. The peak of intensity for the Xenon Lamp is found around 550 nm, whereas the solar energy spectral distribution peaks at 450 nm. The intensity is changed by varying the distance between the light source and front glass of the cell and therefore it can be estimated that the spectral distribution of the light is comparable for each distance. The test set up has been created with the focus to develop a set up, where all other parameters that can influence the cell performance other than irradiance intensity is kept constant such as humidity and ambient temperature. The ambient and the temperature on the backside of the cells during testing are monitored. The typical variation in cell temperature was below 5 C, so it is assumed reasonable to estimate constant cell temperature. In this representation, it is necessary to separate how the light ray will act in each direction in order to determine the total path length in the solar cell. The advantage of this design is the light trapping capability that is made possible by covering most of the cell surfaces with aluminum except in optical coupling areas. 183

22 Figure 6.3. Experimental Set Up & Testing for Tilt Angle A photon enters the cell obliquely and can be absorbed on first transit or during subsequent passes as it bounces off the internal walls. By comparison in a plain surface solar cell the photons that are reflected from the back surface may be coupled out without contributing to photocurrent generation. Cell series contact makes minimized power loss in the cell. The effect of oblique incidence was determined using the V groove profile with unit aspect ratio. This is assuming that oblique incidence will have the same effect on the total light path regardless of the surface texture. First, the source was shifted to the rear of the cell, so that light would strike at the rear and continue to the front of the cell. The source was then tilted by 10 degrees so that rays strike the top surface of the glass at an angle of 10 degrees with respect to the normal. At this angle, a number of rays were sent into the cell and finally the total number of rays hit was recorded. The same procedure was repeated for incident angles up to 90, at an internal 184

23 of 10. Ethylene Vinyl Acetate (also known as EVA) is used as an encapsulation material for micromachined V-Grooved Silicon Solar Cell in the device geometry and its refractive index is assumed to be same as that of quartz. A study on the influence of irradiance intensity for the DSSC cell shows a direct proportionality of Isc with G as well as the logarithmic decay of Voc when light intensity is lowered. Further it is possible to identify a strong dependence of the FF, which is seen to decrease for increasing G at very low light levels, the FF drops markedly. The DSSC suffers from Ohmic losses, which are increased by 2 nd order for increasing light intensity, due to the relation, P = I 2 R. This Ohmic loss is more pronounced for DSSCs than for silicon cells, since the distance to the conductor lines and therefore the resistance is greater. The loss is a measure for limitation of charger transfer from the TCO to the external circuit. A decrease in efficiency is seen for increasing light intensities, due to the direct proportionality of irradiance and Isc. The reflectivity was obtained by multiplying with the fraction of light, cos α and by integrating over the angle of incidence Variation of Reflectivity with Angle of Incidence α (deg) for Reported, DSSC and V-Grooved Silicon Solar Cell is shown in figure

24 Figure 6.4 Variation of Reflectivity with Angle of Incidence α (deg) for Reported, DSSC and V-Grooved Silicon Solar Cell Figure 6.5 Variation of Normalised Reflectivity with tilt angle α (deg) for DSSC, V-Grooved Silicon Solar cells with and without Microlens 186

25 The direct sun power incident on a solar cell depends not only on the power contained in the sunlight, but also on the angle between the solar panel and the sun. When the absorbing surface and the sunlight are perpendicular to each other, the power density on the surface is equal to that of the sunlight (in other words, the power density will always be at its maximum when the solar cell is perpendicular to the sun). As the angle between the sun and a fixed surface is continually changing, the power density on a fixed solar cell is less than that of the incident sunlight. The tilt angle has a major impact on the solar radiation incident on a surface. For a fixed tilt angle, the maximum power over the course of a year is obtained when the tilt angle is equal to the latitude of the location. However, steeper tilt angles are optimized for large winter loads, while lower title angles use a greater fraction of light in the summer. Figure 6.5 shows the variation of normalised reflectivity with tilt angle α (deg) for DSSC, V-Grooved Silicon Solar cells with and without Microlens. Graphical representations in variation of reflectivity with change in angle of incidence θ (deg) for tilt angle of α = 0, 30, 60, 75 degrees (Theoretical and experimental variations for Flat Type Silicon Solar Cell, DSSC, V-Grooved with and without microlens) are shown in Figure

26 Figure 6.6 Variation of reflectivity with change in angle of incidence θ (deg) for tilt angle of α = 0, 30, 60, 75 degrees 6.10 Results and Discussion Two experiments with the objective to investigate the performance dependency of incidence angle for DSSC and silicon cells have been carried out. This would be a collective conclusion for the two experiments where only the overall tendencies could be compared for the two experiments. As the cells tested are not similar, a direct comparison of absolute values is not thought to be relevant. Further the irradiance level and conditions were very different. One experiment was performed in a controlled laboratory environment and the DSSC modules available showed good reproducible results. Three DSSC modules and commercial microcrystalline silicon module was tested. The overall tendency 188

27 seen for DSSC behaviour with respect to Isc indicate that this technology benefit from the oblique incidence angles, as the path for light penetrating the active layer of the solar cell is elongated. Therefore the relative Isc is above one until high incidence angles occur. For the silicon a decrease in relative Isc is seen for increasing incidence angles mainly affected by the enhanced reflection of the top glass at high incidence angles. This result for Isc is in good correspondence with experimental results posed in the literature, where the same beneficial effect of Isc for increasing incidence angles was seen for a tested DSSC. For both experiments a reduction in Voc for enhanced incidence angles is seen for DSSC and silicon cells with the strongest dependence seen for the silicon cells. The overall performance seen in the results for the experiment gives the DSSC an advantage in relative generated power Pmax as well as conversion efficiency when scaled to the expected cosine dependence. The influence of the reflection from the top glass is evident at high incidence angle which results in a lowering of expected power output, due to the enhanced reflection. This also results in minimizing the effect of longer path for the photon in the DSSC at oblique incidence angles so the beneficial results in reality are not very dominant. 189

28 6.11 Conclusion The results obtained indicate the performance dependency of Isc, Voc, FF and Pmax with respect to incidence angle for the two types of solar cell technologies. The test has been carried out under a very low illumination. The result for Isc as function of incidence angle is seen to decrease for the silicon cell due to enhanced reflection of the top glass for increasing Angle of Incidence (AOI). The DSSCs show a beneficial behavior under oblique incidence angles, where the relative Isc scaled to the cosine relation is seen to be above 1 for incidence angles up to 70. As the relative Voc and FF is seen to decrease for increasing AOIs for both the silicon and DSSC cells, the difference in relative Pmax for the two types of modules is due to the different dependence of Isc. The relative Pmax is seen to differ up to 28% for the DSSCs and silicon module at the highest measured AOI (75 ), with the advantage to the DSSC. The reflectance of glass is seen to hold a prominent influence at high incidence angles, reducing the expected power output up to 20 % for the DSSC and 40% for the other module. 190

29 6.12 Reference 1. Tian Pau Chang, Study on the Optimal Tilt Angle of Solar Collector according to Different Radiation Types, International Journal of Applied Science and Engineering , 2: D. Ibrahim, Optimum tilt angle for solar collectors used in Cyprus, Renewable Energy 6, 7 (1995) N. M. Pearsall and R. Hill, Photovoltaic modules, systems and applications, Ch 15 edma3.doc (2001). 4. Chen, Y. M., Lee, C. H., and Wu, H. C Calculation of the optimum installation angle for fixed solar-cell panels based on the genetic algorithm and the Simulated-annealing method. IEEE Transactions on Energy Conversion, 20, 2: Ahmad M. Jamil and Tiwari G.N., Optimization of Tilt Angle for Solar Collector to Receive Maximum Radiation, The Open Renewable Energy Journal, 2009; 2: Duffie J. A. and Beckman W. A., Solar Engineering of Thermal Processes, John Wiley & Sons Inc, Widén, Joakim. Distributed Photovoltaic in the swedich energy systems. The Faculty of Science and Technology, Uppsala University, Uppsala, Sweden, Calabrò, Emanuele. Determining optimum tilt angles of photovoltaic panels at typical north-tropical latitude, Journal of Renewable and Sustainable Energy Messina, Italy, /6. 9. Huan-Liang Tsai, Ci-Siang Tu, and YiJie Su. Development of Generalized Photovoltaic Model Using MATLAB/SIMUL INK,Proceeding of the World Congress on Engineering and Computer Science, San Frasesco, USA, Jensen, J. M., Eksamensprojekt: Notat om Solstråling, Laboratoriet for varmeisolering, Danmarks Tekniske Højskole, forår

30 12. Svendsen, S., Solstråling, Lecture note, Bygningsenergi & Bygningsinstallationer, BYG.DTU, Aug MG173.html 14. M. Geetha, P. Senthil kumar, R. Govindan, P. Ramu, L. Arivuselvam and P. M. Anbarasan, Design of Microlens Focused V-Groove Textured Silicon Solar Cell with Different Aspect Ratio using ZEMAX Recent Research in Science and Technology 2(6): (2010) pg , ISSN: