## 1 Introduction  
Wireless technology can be used in many fields, such as industry, transportation, agriculture, etc. Wireless sensor networks (WSN) have found wide applications in agriculture over the last few years, and research interest is constantly increasing. A WSN is a group of spatially distributed smart sensors for monitoring and recording data (such as air temperature, relative humidity, soil water content, etc. ), storing the collected data, and transmitting the gathered information to a central station [1]. [PERSON] et al. [2] developed a wireless sensor network for irrigation applications. This network was based on several solar-powered wireless acquisition stations suitable for soil moisture monitoring in greenhouses and open-field crops to save water and energy. [PERSON] et al. [3] deployed a smart irrigation control system based on a wireless soil moisture sensor network. The wireless sensor nodes were powered by three 1.5 V dry batteries. With this power supply, each sensor node could operate for a period of about 100 days. [PERSON] and [PERSON] [4] presented the architecture of the wireless sensor network for a smart irrigation system. The prototype of soil moisture wireless sensor node provided low power consumption and therefore it was appropriate for these uses. The main building block of the wireless sensor network is the sensor node. The system architecture of a sensor node includes the following components: a microcontroller for processing data, an LCD display to show data, wireless communication for transmitting and receiving data, and memory for data storage [5]. Each of these components works with different amounts of energy. Thus, the sensor node is powered by one or more batteries or a solar energy harvesting unit. Batteries have high energy density, are available in various sizes, and eliminate the need for power electronics. Batteries are classed into two main categories: primary and secondary. Primary batteries can only be used once, while secondary batteries, the so-called rechargeable batteries, can be discharged and recharged many times. When the battery voltage is below a threshold value, the node is out of service. Thus, it is necessary for batteries to be replaced or recharged. However, the replacement or recharging is costly and time-consuming work [6]. Various approaches have been adopted to slow down battery depletion. Among these approaches, the low power (sleep) mode of the wireless transceivers is one of the most used for energy saving. In any case, the batteries are soon discharged, and energy consumption therefore is a serious matter for sensor node designers. Hence, the designers have adopted a new technique that combines the use of rechargeable batteries with energy harvesting systems [7]. Energy harvesting systems can collect surrounding energy from various sources and convert it into usable electrical energy. It is a very important method to implement long-running systems in which there is no need to recharge in order remain active. Among all energy harvest systems, photovoltaic (PV) systems [8; 9] provide the best power outcome and can efficiently transform outdoor light so as to supply continuous and reliable power to the wireless sensor nodes. Some recent studies on PV harvesting systems are described in [10; 11; 12]. A solar energy harvesting system consists of a solar (PV) cell (harvester), an energy converter (DC-DC converter, maximum power point tracking (MPPT)), and energy storage (battery or super-capacitor) [13]. The PV cell is composed of a semiconductor material (wafer) that absorbs the sunlight's energy and converts it into electricity due to the photovoltaic effect. The efficiency of a PV cell is due to the maximum electrical power output provided by the cell as compared to the energy from the light absorbed by the cell. The amount of electrical power produced from PV cells depends on the characteristics (intensity and wavelengths) of the available light and the technical parameters of the PV cell [14].