# Democratization of PV Micro-Generation System Monitoring Based on Narrowband-IoT
###### Abstract
Different approaches can be found in recent literature. [PERSON] et al. [11] provided a comprehensive review of PV monitoring systems, comparing most of PV monitoring evaluation techniques in terms of their relative performances. This contribution also examined sensors, controllers in data acquisition systems, data transmission methods and data storage and analysis. In [17], [PERSON] et al. proposed a low-cost PV monitoring system based on an open-source Arduino platform and demonstrated its use for the assessment of PV monitoring and supervision potential. The system developed by [PERSON] et al. can monitor solar irradiance, electric outputs and temperature of multiple solar panels. A similar approach can be found in [18], where the authors described a prototype for a portable data logger that integrates standalone instruments with open-source hardware technologies for monitoring PV systems. The proposed datalogger accomplished the accuracy requirements of the IEC standards for PV systems. In 2019, [PERSON] et al. [19] improved the design with a new version of this low-cost datalogger to overcome the shortcomings related to power consumption, the limited voltage range and the user interface for stand-alone PV systems located in remote areas deprived of telecommunications networks. Data were stored on an SD card to work autonomously. This work continued with a new design that included allowing 3G technology to monitor the PV systems remotely via web or via mobile application [20]. Regarding communications, [PERSON] et al. [14] reviewed various monitoring technologies for PV power plants focused on data processing modules and data transmission protocols. They showed key issues and limitations of this technology. In terms of transmission protocol, this work selected LoRa as a relevant data transmission solution, but it was not suitable for large payloads. Moreover, a continuous data packet sending process should be avoided due to some rules and constraints regarding the frequency band, which is in line with other recent contributions [21]. From the limitations of the techniques found in the specific literature, and considering the requirements of the application at hand, the authors previously proposed a solution using a Raspberry Pi that served as a comprehensive solar PV monitoring following the IEC-61724 requirements. The solution was used at the module level [22]. It was tested and assessed at real PV solar installations with remarkable results. The tests took some months in CETENMA SOLAR installations facilities. A 250 Wp module connected to the grid with a Soltec Solarfighter microinverter was monitored, as well as a 5 kWp ver-roof installation connected to the grid and located in the Universidad Polit'cnica de Cartagena (Spain) during some weeks. All variables were collected with standard equipment at both facilities. The results showed that the estimated error rate was lower than 2%. From this preliminary design, a low-cost LoRa-based solar PV monitoring system to communicate solar PV power plants located in remote locations was subsequently proposed in [23]. This topology used an Arduino Board with an RFM95W transceiver fabricated by HOPE RF configured as a LoRa TM modem available for the EU-868 MHz band [24]. The solution stored data in a packet size of 38 bytes with a transmission power of 14 dBm and spreading factor (SF) metric ranging from 10 to 12. An alternative system to be implemented in remote PV power plants for monitoring and dispatching electrical and meteorological data was then proposed and evaluated. This study demonstrated that the line of sight between source and destination and propagation issues had a clear influence on the suitable data reception process. As a main drawback, this solution only allowed a limited number of transmissions, due to the over-air time of works with high spreading factor value (SF11 and SF12) to ensure an accurate reception of data packets with a restricted duty cycle (1%).