Current Situation of Solar Power String Monitoring
The “Matsusaka Yamamuro Mega Solar Power Plant,” a mega (large-scale) solar power plant with a total output of about 15MW, is located on land adjacent to an industrial park in Matsusaka City, Mie Prefecture, Japan.
The power plant was developed and is operated by Sanko Real Estate of Tsu City, Mie Prefecture, which belongs to Mie Kotsu Group Holdings Inc. The power generation was started in December 2015.
The mega solar power plant incorporates a string monitoring system (Fig. 2), which utilizes power line communication (PLC).
In the string monitoring system, the power generation amount of each string (a unit of solar panels connected in series/parallel) is monitored. Unlike monitoring by the PV inverter unit, where tens of thousands of panels are connected, the state of power generation by ten to several tens of panels can be checked by this system.
Therefore, it is easier to discover problems in the power generation equipment including solar panels when this system is incorporated, and the power sales loss can be minimized if appropriate action is taken responding to the problems.
The data of the power generation amount per string is collected in both general string monitoring systems and the systems that use PLC. The data is collected by attaching a current sensor to the terminal for input from the string circuit in the combiner box or by installing an external box in case the space inside the combiner box is limited.
The method of data transmission from this point is different. In general string monitoring systems, exclusive communication lines are needed, as well as exclusive power supplies depending on the case.
Meanwhile, string monitoring systems that use PLC do not require exclusive communication lines or power supplies. A cable that transmits DC power is used for communication between the combiner box and the PV inverter, and the power generated by the solar power plant is used to operate the terminal installed in the combiner box.
According to Sanko Real Estate, compared with conventional string monitoring systems that were introduced to mega solar power plants in the past, the introduction cost is lower by several tens of percent when the string monitoring systems that use PLC are incorporated, and the advantages in maintenance operations also attracted their attention.
The company incorporated a string monitoring system utilizing PLC developed by Sumitomo Electric Industries Ltd.