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 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 V 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.
One unique characteristic of this innovation is that it achieves the measurement of I-V curves without the use of large resistor arrays or active current sources that are 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, metal oxide semiconductor 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.
The system has numerous benefits. It is economical because it uses commercially available, high-temperature, radiation-tolerant electronic components. It uses time division multiplexed measurements, which allows multiple sensors to be sampled with only two A/D channels. In addition, compatibility is offered because it utilizes nearly universal spacecraft bus resources for ease of retrofitting or use in new systems without requiring new infrastructure.
The technology has potential applications in solar cell monitoring for manned and unmanned spacecraft, and in diagnostics for terrestrial solar power generation systems.