Method and apparatus for I-V data acquisition from solar cells
First Claim
1. A method for logging current-voltage data characteristics of the operation of an array of solar cells between open-circuit and short-circuit load conditions comprising the steps ofcontrolling load current in one mode while voltage is measured from open circuit to at least halfway into the knee of the curve where the percentage change in voltage is equal to or greater than the percentage change in current, andcontrolling the load voltage in a second mode while current is measured from the lowest load voltage possible to at least halfway into the knee of the curve where the percentage change in current is equal to or greater than the percentage change in voltage.
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Abstract
A method and apparatus for logging current-voltage (I-V) characteristic d of a solar cell module (10) in two modes using a portable instrument. One mode controls the load current through a circuit (36) in 256 equal intervals while voltage is measured from open circuit to at least halfway into the knee of the curve and the other mode controls the load voltage through a circuit (34) in 256 equal intervals from the lowest voltage measurement possible (short circuit) to at least halfway into the knee of the curve, under control of a microcomputer (12). All measurements are packed by discarding each measurement that is within 0.5% of the value predicted from two previous measurements, except every ninth (9th) measurement which is retained. The remaining data is further packed into a memory block of a detachable storage medium (14) by recording the data points in sequence following a header containing data common to all points, with each point having the value of the controlled parameter recorded as the number of increments from the previous point recorded followed by the measured value. The detachable storage medium is preferably a solid state device for reliability, and is transferable to a playback terminal which unpacks the data for analysis and display.
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Citations
10 Claims
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1. A method for logging current-voltage data characteristics of the operation of an array of solar cells between open-circuit and short-circuit load conditions comprising the steps of
controlling load current in one mode while voltage is measured from open circuit to at least halfway into the knee of the curve where the percentage change in voltage is equal to or greater than the percentage change in current, and controlling the load voltage in a second mode while current is measured from the lowest load voltage possible to at least halfway into the knee of the curve where the percentage change in current is equal to or greater than the percentage change in voltage.
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6. Apparatus for logging current-voltage data characteristics of the operation of an array of solar cells between open-circuit and short-circuit load conditions comprising
means for controlling the load voltage of said array points between and including open circuit and short circuit, means for selectively controlling the load current of said array at points between and including open circuit and short circuit, means for sensing the voltage output of said array under varying load conditions, means for sensing the current output of array under varying load conditions, means for operating said current load control means for selectively controlling at intervals the current load of said array while said voltage output is sensed from open circuit to at least the point where the percentage change of voltage is equal to or greater than the percentage change of controlled current, means for operating said voltage load control means for selectively controlling at intervals the voltage of said array while said current output is sensed from short circuit to at least the point where the percentage change of current is equal to or greater than the percentage change of controlled voltage, and means for storing each value of sensed current and voltage output in digital form.
Specification