# Efficient Wireless Monitoring and Control of a Grid-Connected Photovoltaic System
## 4 Communication Module
### Hardware of the Network Nodes  
Two sensor nodes send their data to the coordinator through wireless links. The coordinator uses the data locally. It is responsible for processing the data from the sensors and responding to every DC/DC converter and every inverter. As such, the coordinator manages the WSPS and the WCU as two relatively independent networks. Despite their aforementioned advantages, proper attention must be paid when selecting the components of the WSNs because failure to do so could compromise the reliability of the monitoring system. The implementation of the network nodes is compact and features a versatile design, with a highly integrated and cost-effective solution. The proposed solution is power-aware, with care to the selection of the microprocessor, and power management is addressed in both the hardware and the software design. Figure 8: Wireless signal flow of the wireless centralized control (WCC) system. Figure 9: Wireless signal flow for the sensor nodes of the DC/DC converters and the inverters. The hardware has been designed so that the network node can be configured as both a sensor node for the DC/DC converter and the inverter and a coordinator node. The SJ1 jumper allows this change of role of the node. Figure 10 shows the board of the wireless network node. It comprises a wireless module, sensors, a microcontroller, a differential analog to digital converter (ADC), and a power source. Several nodes have been deployed to configure the sensor network for the grid-connected PV system. Each unit is governed by an ATmega328 microcontroller from Atmel (San Jose, CA, USA) that processes information from the sensors. The set of sensors measure the required parameters, i.e., voltages, currents, temperature, and irradiance, and have analog outputs that are sampled by the external ADC. A second microcontroller ATmega128 RFA1 (Atmel), which includes the wireless transceiver, controls the transmission stack of the IEEE 802.15.4 standard. These components are powered by a rechargeable 3.3 V/2600 mAh battery. The charge is maintained by the photovoltaic panel to achieve full energy autonomy when the network node performs as a sensor node. If it acts as a coordinator, it is powered from the base station. All components were selected to minimize the power consumption for the target application. The proposed dual-processor architecture allows balancing cost, power consumption, and performance. If a single microcontroller were used, it would be more difficult to achieve real-time monitoring and control of the PV system because the number of samples required for accurate tracking would be more limited. 1. ATmega328 processor: An 8-bit microcontroller with 32 pins and Automatic Voltage Regulator (AVR) enhanced Reduced Instruction Set Computer (RISC) architecture, with an input voltage range from 1.8 V to 5.5 V, and a 20 MHz internal oscillator. It has up to 23 digital input/output pins, 8-channel 10-bit Analogue to Digital Converter (ADC), two Serial Peripheral Interface (SPI), one I2C and one Universal Synchronous/asynchronous Receiver Transmitter (USART) module, two 8-bit timers and one 16-bit timer, 32 KB of program memory, 1 KB of Electrically Erasable Programmable Read-Only Memory(EEPROM), 2 KB of Statis Random Access Memory (SRAM), and a real-time counter (RTC). The microcontroller is well suited for this application, given its low-power operating current, which is 200 \(\upmu\)A at 1.8 V and 1 MHz, and 0.75 \(\upmu\)A for standby current in power-save mode with 32 kHz RTC. 2. Single-chip wireless module: The short-range radio module is an ATmega128 RFA1, which exchanges data via wireless communication at 2.4 GHz following the IEEE  
Figure 10: PCB of the network node. 802.15.4 standard. The ATmega128 RFA1 is a low-power 8-bit microcontroller based on the AVR-enhanced RISC architecture combined with a high data rate transceiver. It handles the physical layer of the wireless communication, enables very robust transmission, and only uses a minimum number of external components.