1 Heat Transfer F11-ENG-135 - Lab #5 Photovoltaic Solar Cell School of Engineering, UC Merced. October 23, 2012 1 General purpose of the Lab. The purpose of this experiment is to provide information about photovoltaic solar cells and measure the efficiency of a photovoltaic solar collector under various operating conditions. 2 Lab. Theory Photovoltaic solar cells are devices that transform solar radiant energy into electricity. The electricity is produced when the sun excites electrons in the photovoltaic cell, causing the electrons to concentrate on one side of the cells electrodes. When a sufficient amount of electrons have concentrated in a certain electrode, a potential difference is created between the electrodes. This potential difference creates electricity, as seen in Figure 1 below. To make the results of the experiment valid the incident angle (between the normal vector outward from the solar cell and the direction of solar radiation) must be known. The proper incidence angle is determined by two angles - the altitude/polar angle and the azimuthal angle. Collector Altitude (θ): An altitude of 0 degrees corresponds to a horizontal array, while an altitude of 90 degrees corresponds to a vertical array (see Figure 2). Collector Azimuth (φ): An azimuthal of 0 degrees corresponds to a south- facing array; 90 degrees to an east-facing array; 180 degrees to a north-facing array; and 270 degrees to a west- facing array. Therefore, the azimuthal of an array facing 20 degrees east of south will be 20, while the azimuth of a photovoltaic array facing 20 west of south will be 340 (see Figure 3). In this experiment, only the altitude/polar angle will be varied to take various measurements. The solar power output (P out ) of the panel can be calculated from the voltage (V) and current (I) that is measured using joules s and Ohm s Laws. P out = V I (1) The efficiency (η) of a panel is the ratio of the power output to the power received by the solar panel from the solar radiation (P in ) i.e. the amount of incident solar flux (power/unit area), called illuminance E, times the area of the collector (A) and P in = E A (2) η = P out P in. (3)
Figure 1: The Photovoltaic Effect When the incident solar radiation is perpendicular to the collector surface, the power input or the illuminance is maximum (E max ). If the azimuthal angle is kept at this condition and only the altitude/polar angle is varied, the illuminance will be lower (E). The altitude/polar angle can be found by ( ) E θ = cos 1 E max (4) Figure 2: Altitude/polar angle diagram 3 Lab. equipments - Apparatus Photovoltaic solar module (Area A = 0.4m 2 ) Measuring unit with digital displays (current I = 0 20 A DC, voltage V = 0 20 Volt DC) Variable resistor with slider (resistance R = 10Ω, peak current 8 A)
Figure 3: Azimuthal angle diagram Temperature sensor (0 100 C) Illuminance sensor (0 2000W/m 2 )
4 Figure 4: General setup of the apparatus 1. Tilting Support on Castors 2. Measuring Unit with Digital Displays 3. Variable Resistor with Slider 4. Solar Module 5. Temperature Sensor 6. Illuminance Sensor 4 Lab. procedure The sensors (temperature and illuminance) are connected to the measuring unit using a 5-core cable. The measuring unit requires a mains supply (230V, 50Hz) The solar modules, resistor, ammeter and voltmeter are connected as follows for the series connection of the modules (see Figure 5) Find the maximum illuminance by adjusting the altitude and azimuthal angle and fix the wheels of the solar module so that the azimuthal angle do not change. Measure illuminance (E), output voltage (V) and output current (I) at this condition (θ = 0), first by keeping the variable resistor at middle and then using the maximum resistance. Find efficiency using Eq. (3) Change altitude angle and repeat the above steps; for this case also find out the altitude angle (θ) Repeat the measurements for three different angles; for each angle using two different resistances
5 After the series connection repeat the experiments for parallel connection (see Figure 6) similarly as done in the series connection measurements. Figure 5: Series connection
5 Data and calculations table Figure 6: Parallel connection Connection Type E [W/m 2 ] V [Volt] I [A] P out P out θ η 6 Lab report The report should include the following: Brief introduction Description of the problem. Experimental methodology including list of measurements taken. Results and physical interpretation of results. Conclusions Any references used
7 References [1] Frank P. Incropera and David P. DeWitt, Fundamentals of Heat and Mass Transfer, Wiley (2007). [2] Anthony F. Mills, Basic Heat and Mass Transfer, IRWIN (1995). [3] GUNT Geratebau GmbH, Barsbuttel, Instruction Manual ET 250 Photovoltaic Trainer, Publication-No.: 916.000 00 B 250 13 (Germany 11/1999).