Solar Cell Characterization

Transcription

1 UNIVERSITY OF IDAHO ELECTRICAL AND COMPUTER ENGINEERING Solar Cell Characterization PIV Curves and Analysis for SCPD Device Valerie Barry, Anthony Kanago, Benjamin Sprague 9/1/211 VLSI Sensors Research Group This report shows the characterization and analysis for OSRAM SCPD micro solar cell devices under a variety of illumination conditions and device configurations. Based on current literature, the hypothesized ratio of the voltage of maximum power (Vmpp) to the open circuit voltage (Voc) for a large solar cell ranges from approximately.7 to.82. We seek to characterize the given device and determine if this ratio is accurate for micro solar cells. This characterization also determines the required number of solar cells for powering our circuits and an application system and contrasts the performance of series and parallel micro solar cells. Illumination levels between 1, and 3, lux demonstrate the maximum power point under realistic and changing operating conditions similar to the target application.

2 VLSI Sensors Research Group Page 2

3 Table of Contents A. Abstract... 4 B. Introduction... 4 C. Results... Error! Bookmark not defined. D. Conclusion and Discussions... 5 VLSI Sensors Research Group Page 3

4 A. Abstract The goal of this procedure was to characterize the micro solar cell that we are using. We needed to get power ranges for different light inputs, as well as the maximum output power, output voltage, and output current. We expected the current and power curves to have a specific shape, but wanted to determine the scale of the curve. The curves had the expected shape and this experiment was used to discover the scale. We did tests with two different solar cells at 1 lux, 1, lux, and 3, lux. We also did tests with the two cells in parallel and series at 1, lux. The two cells behaved about the same and the maximum power was μw at 3, lux. As expected when the cells were placed in parallel or series the output power was approximately doubled. Additionally the maximum power point ratio was in the.7 to.8 range for all values, which was expected. B. Introduction The goal of this experiment was to characterize the micro solar cell that we will be using with our senior design project. It is necessary to create the Output Power vs. Voltage and Current vs. Voltage graphs by measuring the output voltage and current for difference resistances. We tested two different cells by themselves, in parallel, and in series. Additionally we wanted to discover max power point (mpp) ratio which is defined by dividing the voltage at the maximum power point by the open circuit voltage. C. Experiment Two similar micro solar cells were tested. To create a constant light we used an adjustable illuminator to test at 1 lux, 1, lux, and 3, lux. A lux meter was used to measure the light intensity. The solar cell was placed on a bread board and stabilized by attaching it to a white box. The illuminator and box were cut off from the room s light source by a black covering. The solar cell was placed in series with various resistances and multimeters were used to measure output voltages and currents. The setup is shown in Figure 1 below. Figure 1: On the left shows the solar cell and lux meter, the middle shows the setup while taking measurements and the far right shows the setup open to show how the illuminator was setup. VLSI Sensors Research Group Page 4

5 Current (ua) First, to measure the intensity of the light, we rotated the illuminator to shine the light directly onto the sensor for the lux meter. There the illuminator was adjusted to the correct illumination, either 1, 1, or 3, lux. Then we rotated the illuminator back to point the light directly onto the micro solar cell. For each illumination recorded the open circuit voltage and the short circuit current. Additionally we measured output currents and voltages for a range of resistors placed in series with the solar cell. The resistors ranged from 9 ohms to 15 kili-ohms and were chosen to give an accurate view of the I-V and the power curves. Using this data we graphed the results and calculated the max power point. After testing both solar cells individually, we then put the solar cells in parallel and series and developed the I-V and power curves for only the 1, lux light level. D. Conclusion and Discussions Figures 2 and 3 below show the curves for the three illuminations for the first solar cell. Figure 2 is the Current vs. Voltage curve. Figure 3 is the Power vs. Voltage curve. Each curve followed the general pattern that we expected. Additionally, as expected when the lux was increased the current output and the output power also increased. This was also an expected result Solar Cell 1 Current (ua) R² =.9998 R² =.9998 R² = Lux 1, Lux 3, Lux Poly. (1 Lux) Poly. (1, Lux) Poly. (3, Lux) Figure 2: The current versus voltage curve for Solar Cell 1. VLSI Sensors Research Group Page 5

6 Current (ua) Power (nw) Solar Cell 1 Power (nw) R² =.9994 R² =.9995 R² = Lux 1, Lux 3, Lux Poly. (1 Lux) Poly. (1, Lux) Poly. (3, Lux) Figure 3: The power versus voltage curve for Solar Cell 1 Figures 4 and 5 below show the curves for the three illuminations for the second solar cell. Figure 4 is the Current vs. Voltage curve. Figure 5 is the Power vs. Voltage curve. Each curve followed the general pattern that we expected and that we saw from the first solar cell. Additionally, as expected when the lux was increased the current output and the output power also increased. This was also an expected result and seen with the first solar cell. Current (ua) R² =.9998 R² =.9999 R² = Lux 1, Lux 3, Lux Poly. (1 Lux) Poly. (1, Lux) Poly. (3, Lux) Figure 4: The current versus voltage curve for Solar Cell 2 VLSI Sensors Research Group Page 6

7 Current (ua) Power (nw) Power (nw) R² =.9995 R² =.9997 R² = Lux 1, Lux 3, Lux Poly. (1 Lux) Poly. (1, Lux) Poly. (3, Lux) Figure 5: The power versus voltage curve for Solar Cell 2 Below, Figures 6 and 7, compare the two solar cells at 3, lux. Figure 6 shows the I-V curve for each cell. Figure 7 displays the output power versus voltage curve for each cell. These graphs demonstrate how close in values the two solar cells were, which indicates consistency between the two cells Cell 1 vs. Cell 2 Current (ua) Cell #1 Cell #2 Poly. (Cell #1) Poly. (Cell #2) Figure 6: IV curve at 3, Lux for cells 1 and 2 VLSI Sensors Research Group Page 7

8 Current (ua) Power (nw) Cell 1 vs. Cell 2 Power (nw) Cell #1 Cell #2 Poly. (Cell #1) Poly. (Cell #2) Figure 7: PV curves at 3, Lux for cells 1 and 2 Both series and parallel combinations of the devices were tested with illumination levels of approximately 1, lux. Figures 8 demonstrates the IV curves for these configurations, and figure 9 demonstrates the PV curve for the same devices. As expected, both series and parallel device combinations approximately double the output power. A series configuration doubles the voltage while maintaining approximately constant current (minus losses from bond wires), and a parallel configuration roughly doubles the current Series Vs. Parallel Current (ua) Cells #1,2 - Parallel Cells #1,2 - Series Poly. (Cells #1,2 - Parallel) Poly. (Cells #1,2 - Series) R² =.9999 R² = Figure 8: IV curve for the cells in series and parallel VLSI Sensors Research Group Page 8

9 Power (nw) Series Vs. Parallel Power (nw) Cells #1,2 - Parallel Cells #1,2 - Series Poly. (Cells #1,2 - Parallel) Poly. (Cells #1,2 - Series) R² =.9998 R² = Figure 9: PV curve for the cells in series and parallel In addition to visually seeing the differences in the graphs, there are a few important values that we are interested in to characterize the cells. These include maximum power, open circuit voltage, short-circuit current, and the maximum power point ratio. We expect maximum voltage to occur at open circuit voltage and the maximum current to be the short-circuit current. The maximum voltages should be around 5 mv. The maximum power maximum power point ratio should be around.7 to.8 as described in literature. Cell Open Circuit Short Circuit Max Power Max Power Point Lux Configuration Voltage [mv] Current [ua] [nw] Ratio Cell #1 1, Cell #1 1, Cell #1 3, Cell #2 1, Cell #2 1, Cell #2 3, Parallel 1, Series 1, Table I: Measurement results As shown in Table I, maximum power point ratios remain between.7 and.8, with lower ratios seen by the series and parallel device combinations. The open circuit voltages range, but the maximum single cell voltage is just under.5 Volts, which was as expected. The maximum single cell power is also an important value to know, as well as the range of power output so we can insure our design works for the entire range. The range of output power for a single cell is 4.87 μw to μw with light inputs from 1, to 3, lux. VLSI Sensors Research Group Page 9