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Conceived by Japanese scientists, the system consists of a xenon flash and a detector capacitor. It can apparently examine solar modules and detect any deterioration without disconnecting the electrical wiring in the chain.
Researchers at Japans Ibaraki University and Shiga Prefectural University have developed a novel photovoltaic module deterioration diagnostic device that can reportedly inspect a string of cells and detect deterioration in each individual module without disconnecting the strings electrical wiring.
“Detecting the deterioration of individual PV modules can minimise the number of PV modules that need to be replaced and enables economically beneficial long-term operation of commercial PV power generation plants,” the academics say. “Furthermore, it also contributes to the reduction of waste PV modules and the efficient use of resources.”
The novel solution uses a xenon flash illumination system to provide flash light irradiation onto a target module, which is connected to a detector capacitor. The measured value of the charge voltage of the detector capacitor is used as a decision index voltage to detect the presence of deterioration.
“When there are only two or three PV modules connected in series in a solar cell string, the decision index voltage is sufficiently high and almost the same as in the case of a single separate PV module,” the team explains. “However, unfortunately, it was revealed that the decision index voltage generally decreases as the number of series-connected PV modules increases. This voltage reduction makes it difficult to accurately diagnose the deterioration of individual PV modules, as it makes the difference between the decision index voltages in the cases of non-deteriorated and deteriorated PV modules minimal.”
To solve this problem, the academics added a unique auxiliary diode network to the device. This network is made up of many diodes and allows a single device to be isolated without disconnecting it, ensuring that the measured current comes only from the module in question. “This connection can be easily completed in the solar cell string junction box by preparing the preliminary electrical wiring from the output terminal of each photovoltaic module in the solar cell string to the junction box,” they noted.
Before building an experimental setup of the system, the team simulated it numerically using PSIM software. “It is clear from the simulation calculations with the inserted auxiliary diode network that high decision index voltages are generally obtained and that the voltages for different deterioration conditions can be clearly distinguished from each other,” they further explained. “In contrast, the decision index voltages obtained for the simulation model without the inserted auxiliary diode network are globally lower in comparison.”
Following the positive results of the simulation, the scientist created a prototype of the experimental setup. It included eight photovoltaic modules with a nominal output power of 30 W connected in a chain and a ceramic resistor set to 0.5 O attached to one of them to simulate a 5% degradation. In addition, the setup included a detector capacitor, a synchronous lighting period switch, a reset switch, a reset resistor, and an auxiliary diode network.
“The detection tests were conducted for the case where a 5% degraded PV module was mixed with the other non-degraded PV modules,” the scientists explained. “It was revealed that the voltage of the obtained decision index decreases only when the 5% degraded PV module is inspected by selecting it as the diagnostic target, and the 5% degraded PV module can be clearly distinguished from the other non-degraded PV modules by the significant voltage difference compared with the normal one.”
The new device was presented in “ Novel deterioration diagnosis device for individual photovoltaic modules usable without disconnecting electric wiring in solar cell string ,” published in Renewable Energy . |
