Solar Cell Health Monitoring

One unique characteristic of this innovation is that it effects the measurement of I-V curves without the use of large resistor arrays or active current sources normally used to characterize cells. A single transistor is used as a variable resistive load across the cell. This multi-measurement instrument was constructed using operational amplifiers, analog switches, voltage regulators, metaloxidesemiconductor field-effect transistors (MOSFETs), resistors, and capacitors. The operational amplifiers, analog switches, and voltage regulators are silicon-on-insulator (SOI) technology known for its hardness to the effects of ionizing radiation. The SOI components used can tolerate temperatures up to 225°C, which gives plenty of thermal headroom allowing this circuit to perhaps reside in the solar cell panel itself where temperatures can reach over 100°C. NASA's Glenn Research Center has developed a method and apparatus for in situ health monitoring of solar cells. The innovation is a novel approach to solar cell monitoring, as it is radiation-hard, consumes few system resources, and uses commercially available components. The system operates at temperatures from -55°C to 225°C, allowing it to reside close to the array in direct sunlight. The circuitry measures solar cell current versus voltage (I-V) curves using relatively inexpensive electronics, a single switchable +28 volt power bus, and two analog-to-digital (A/D) converter channels. A single transistor is used as a variable resistive load across the cell, rather than the large resistor arrays or active current sources normally used to characterize cells. Originally developed for space, the technology can be adapted for use in terrestrial solar power generation systems and other applications.