# Low-Cost Wireless Sensing System for Precision Agriculture Applications in Orchards
## 3 Results and Discussion
### Energy Consumption  
The nodes' lifetime is one of the most important factors in the networks' reliability. The ratio of energy harvesting to the consumption rate is a vital parameter [1]. Therefore, in our study, exhaustive tests on the energy consumption were performed. The tests included operation of the End-nodes at different sleep cycles and data acquisition intervals of 5, 10, and 20 min, while the Coordinator was in always-on mode. The main concern was to ensure that the charging/discharging ratio was adequate to assure continuous operation of both the Coordinator and the End-nodes of the network. According to literature, the majority of the nodes as parts of wireless system networks applied in agriculture are powered by battery alone, which in most cases lasts for few weeks [1]. In our study, the coordinator's battery reached the 20% of its capacity within seven days of operation relying solely on battery (Figure 3). This is considered as a satisfactory result since this node stayed always on, receiving all the data packets from the End-nodes, using the RF-868 MHz communication of the local wireless network and sending them to the cloud via 4G cellular grid using the 4G module. Thus, this node performed the most energy demanding operation. After depleting to 20% of the battery capacity, the solar panel was connected to study the charging rate under unfavorable weather conditions, to confirm continuous operation of the coordinator in real field conditions. The panel was positioned at a shaded location to simulate cloudy conditions in order to examine the worst-case scenario; operation under extended continuous of low solar radiation conditions. The initial setup was proved inadequate to charge the battery, thus, a second panel was set in parallel connection to increase the harvested energy. After these modifications, the system was proved to be energy efficient even at the most unfavorable conditions; cloudy weather during winter with limited daylight duration (580-630 min during January to mid-February when the tests were realized). These conditions were extremely unfavorable for the coordinator's energy balance, however, the energy harvested during the day was adequate to maintain the daily energy level accumulated in the battery which progressively increased with time (Figure 4). The Coordinator showed particularly satisfactory performance, handling 14 packets per hour (receiving packets from peripheral nodes, manipulating the content and sending them to the cloud). Therefore, such energy efficiency is expected with the coordinator connected to up to 14 peripheral nodes, programmed to send packets on hourly basis, or up to 7 End-nodes, sending packets every 30 min. As mentioned above, the End-nodes were examined at three sleep cycle scenarios. The results showed that even in the most demanding operation cycle (waking up every 5 min to take the measurements, send the data packet and set back to sleep mode), the node operated without any disruptions (Figure 3). The battery reached the 20% of its capacity within 22 days of operation. On the 24 th day of operation, the node was connected to the solar panel to evaluate the charging capacity in operation mode. In the first week the weather was considerably cloudy, thus the battery continued to discharge but with a slower rate. Once the solar radiation increased, the battery showed a rapid charging ratio, however, after that point, the battery level showed quite unstable behavior depending on the weather conditions. Concerning the node set to 10-min cycle, the discharge of the battery was slower than the 5-min cycle reaching the 20% of its capacity in 28 days. When the solar panel was connected to the node, the battery level had quite stable behavior, with an increasing trend depending on the solar radiation intensity. Finally, the node programmed to 20-min cycle lasted longer than the two other cycles, reaching 20% of the battery capacity in 41 days.