The SSIVT is an electrical current-voltage measurement system used to characterize photovoltaic cell performance. This current-voltage tester works by sampling various current versus voltage combinations of the photovoltaic cell with a variable impedance load. The performance of the photovoltaic cell is determined by measuring this output I-V relationship while it is being illuminated by light. This relationship is typically called an "I-V curve" and can be obtained by exposing the photovoltaic cell to a constant level of light while varying an external impedance load such that its current-voltage values change. Since multiple I-V data points are required to create an I-V curve, an external trigger function model is available for use with pulse solar simulators. This allows the tester to create multiple sequential pulses (typically 10-100 points selectable) to complete the IV curve measurements. Universal input 100-240VAC, 50/60Hz. Software is included. An external computer (sold separately) such as the PC computer controller is required to control this current-voltage measurement system.

 

 

Purpose of Current Vs Voltage Measurement Test

A solar cell may be operated over a wide range of voltage and current combinations, but there is generally an optimum combination for maximum energy collection efficiency. By varying an external load resistance from zero to infinity, the optimum I-V combination where the solar cell delivers the most power can be found.

 

Current and Voltage Measurement Range

The standard I-V Test system can measure electrical power from photovoltaic cells up to 20W. The voltage envelope is limited to 200V and the current is limited to 1A. A higher powered 60W version is available where the voltage is limited to 60V and the current is limited to 3A. For higher loads, shunts to measure a portion of the current can be used. In general, the limitation of the standard model is the 1A current limit. If your solar cell can generate more current than 1A, then we recommend upgrading to the 60W model.

 

Voltage Scaling Factor

Although the maximum voltage of the base unit is 200V, the software can rescale its scanning range to 2V, 10V, 20V or 200V. Once the scale is selected, the maximum number of I-V measurement points that can be taken in that selected range is 100 points.

 

Current Density

The software currently only measures I-V characteristics. The software outputs the I-V characteristics in an ASCII file which can then be read to derive current density values.

 

 

System Notes

The I-V Measurement System sweeps the IV curve with an automatically adjustable resistive load and records multiple I-V data points along the way. The voltage and current ranges are software selectable and so is the number of points taken, from 10-100 points depending on the time length of the test allowable. The I-V data point values are then recorded and plotted on a computer display and saved in an ASCII text file. The points are selected by voltage, hence the voltage readings are evenly spaced.

 

I-V Measurement Basics

Fill Factor:

Fill factor refers to the "squareness" of the I-V curve. It describes how closely matched the voltage is at its maximum power point and the current is also at its maximum power point. The higher the fill factor match, the more square the I-V curve.

 

Conversion Efficiency:

The conversion efficiency of a solar cell is the percentage of light energy that gets converted to electrical power.

 

References:

The U.S. Department of Energy maintains a good website on how to use I-V measurement systems in solar cell testing. Please see www.eere.energy.gov/solar/current_voltage.html

 

Technical Specifications

• Base unit 200V max. (scale to 2V or 10V, but 20V and 200V scales possible please ask)
• Dwell time (wait time between each I-V reading) - programable, but cannot be below 3ms
• Number of I-V scanned points - 10 to 100 programable
• Hardware Voltage Resolution: 50μv @ 2V scale, 500μV @ 20V scale (accuracy per reading)
• Hardware Current Resolution: 50μA @ 1A scale (accuracy per reading)
• I-V Measurement Sweep Resolution: (voltage scale selected / number of I-V scanned points)
• Software Display Resolution: typically mV and mA (but 3 decimals shown, so can be 3.456E-1 A for addition decimal)