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The Solar Cells

Characterization Experiment Goals

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.

Characterization Experiment Procedures

Two similar micro solar cells were tested. To create a constant light we used an adjustable illuminator to test at 1000 lux, 10,000 lux, and 30,000 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.

Characterization Results

Below are the characterization graphs of the voltage and output power plotted across the current. These values were collected at three different illuminations: 1000 lux, 10,000 lux, 30,000 lux.


Graph 1: Voltage vs. Current for Cell 1 for Three Light Levels



Graph 2: Output Power vs. Current for Cell 1 for Three Light Levels

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 500 mV. The maximum power maximum power point ratio should be around 0.7 to 0.8 as described in literature.

Cell Configuration LUX Open Circuit Voltage (mV) Short Circuit Current (uA) Max Power (nW) Max Power Point Ratio
Cell #1 1,000 358.1 17.67 4352.7 0.78
Cell #1 10,000 447.1 141.3 42318.1 0.729
Cell #1 30,000 487 403.3 129116.5 0.776
Cell #2 1,000 352.4 16.65 4087.9 0.769
Cell #2 10,000 439 129.5 38061.2 0.779
Cell #2 30,000 491 415.5 133926.1 0.784
Parallel 10,000 440 280.62 82864.9 0.745
Series 10,000 887 134.16 78868.6 0.72

Solar Cell Models

It is extremely important to be able to model OSRAM SCPD micro solar cell devices for simulation purposes. For our project, we need an accurate representation on how our micro solar cell will behave in different illuminations and for different loads. There are many different models, but we chose to use a simple single-diode model, as seen in Figure 1.




Figure 1: The Single Diode Model



Below are the values we found for each solar cell at each illumination used for creating simulation models.

Illumination (lux) 1,000 10,000 30,000
Voltage at Max Power (V) 0.2795 0.342 0.378
Current at Max Power (A) 1.5573E-5 1.11E-4 3.42E-4
Short Circuit Current (A) 1.766-5 1.29-4 4.03E-4
Open Circuit Voltage (V) 0.3581 0.439 0.487
Rso (Ohms) 2540.8 408.58 186.359
Rsho=Rsh (Ohms) 932000 555082 22145
n 1.103 1.767 1.402
Is (A) 6.215-11 8.78E-9 5.73E-10
Rs (Ohms) 887.4 52.98 91.11
Iph (A) 1.77E-5 1.29E-4 4.05E-4


Solar Cell Reports