## 3 Materials and Methods  
### Design of an IoT-Based Solar PV Data Monitoring System  
In the designed system, real-time IoT-based condition monitoring of a solar PV panel and a battery charged by this panel is conducted. Issues occurring within the system are identified through the acquired data. Current, voltage, and temperature values of the panel and battery, along with environmental parameters such as humidity, temperature, and irradiance, are measured using relevant sensors. The obtained data are sent to SD cards and Firebase servers through the NodeMCU v2 Wi-Fi microcontroller board and stored. Firebase was chosen due to its ease of use and quick integration into the project. It provides real-time database connectivity, allowing multiple users to observe changes in data when they are created or edited. Despite not being open-source, Firebase offers open-source libraries and SDKs for developers. Data tracking can be carried out in real-time through Firebase, as well as via a mobile application. The mobile application has been developed in the Flutter environment using the Dart programming language. Moreover, various potential errors in the system can also be monitored in real-time through these systems. These errors encompass low panel voltage, low panel current, high panel temperature, low battery voltage, high battery temperature, and PV panel connection fault. The block diagram of the developed IoT-based PV data recording and monitoring system is provided in Figure 1.  
The NodeMCU v2 Wi-Fi microcontroller board, frequently favored in IoT applications, renders the system controllable and monitorable from any location worldwide. The development board possesses features such as a 10-bit ADC, USB-TTL converter, 17 GPIO pins, Wi-Fi module for wireless network connectivity, and ease of programming. In this study, various sensors are utilized to measure values requiring assessment, including PV panel voltage, PV panel current, PV panel temperature, battery voltage, battery current, and battery temperature, as well as humidity, temperature, and irradiance values of the ambient air. The ACS/12-30A current sensor is employed for measuring the current of both the PV panel and the battery. The LM35 temperature sensor is used for measuring the temperature of the PV panel and the battery. The Sparkfun weather shield is employed for reading temperature, humidity, pressure, and irradiance data from the air. Simultaneously, the GP-735 GPS (Global Positioning System) sensor on the board provides location information. The integration of the weather measurement and microcontroller Wi-Fi boards has resulted in the creation of an electronic board for the IoT-based data acquisition system. The measurement setup, situated within the premises of Karabuk University, is depicted in Figure 2.  
The NodeMCU v2 module within the solar PV data measurement, recording, and monitoring apparatus should initially establish a connection with a wireless network. Once connected, data from the sensors are sequentially measured, displayed on the built-in LCD display, saved to an SD card, and sent to the Firebase real-time database. The Firebase cloud  
Figure 1: Block diagram of the proposed monitoring and estimation system. system is a platform that enables the creation of mobile and web applications for monitoring real-time data, maintaining records and session information, making new announcements, and creating control units. It can be used freely for these purposes. The solar PV data sent to the cloud system can be tracked by end-users via smartphones through the developed mobile application. Additionally, the analysis and visualization of these data in a web-based manner are facilitated through the ThingSpeak IoT platform, where we direct the data flow in the cloud environment.