# Green IoT: A Review and Future Research Directions
## 8 Potential Future Directions  
We have identified several aspects for future research areas extracted from our study that are outlined in Figure 18. These research directions are further discussed and elaborated on in the following paragraphs. (i) _Zero energy_  
Designing IoT devices to be powered by self-sustaining power sources such as solar, wind, or kinetic energy is an important area of research, as it enables the deployment of autonomous and sustainable IoT networks. The use of self-sustaining power sources can alleviate the challenge of battery replacement or recharging, which is a significant concern in IoT systems. One important consideration in designing IoT devices that can leverage  
Figure 17: Comparison of the power efficiency of single-core vs. multi-core processors. Figure 18: Potential future directions for green IoT. self-sustaining power sources is the selection of appropriate energy-harvesting technologies. These technologies must be capable of harvesting energy from the surrounding environment and converting it into electrical energy that can be used to power the IoT device. Examples of such technologies include photovoltaic cells for solar energy harvesting, piezoelectric materials for kinetic energy harvesting, and small wind turbines for wind energy harvesting. In addition to energy harvesting technologies, the design of IoT devices that can leverage self-sustaining power sources must also take into account the power consumption of the device itself. IoT devices are typically designed to be energy-efficient to maximize battery life. However, when self-sustaining power sources are used, power consumption becomes less of a concern. As such, IoT devices designed for self-sustaining power sources may be designed to consume more power, enabling them to perform more computationally intensive tasks or transmit data more frequently. Another important consideration when designing IoT devices to be powered by self-sustaining power sources is the placement of the device in relation to the energy source. For example, solar-powered IoT devices must be placed in locations with sufficient exposure to sunlight to ensure adequate energy harvesting. Similarly, kinetic energy harvesting devices must be placed in locations where they can effectively capture kinetic energy. On the other hand, exploring the implications of energy storage solutions, such as batteries or supercapacitors, to enable IoT devices to operate without a constant power source is an important area of research, as it can help to address the challenges of limited battery life and the need for constant charging or replacement. Batteries and supercapacitors are two types of energy storage solutions that can be used to power IoT devices. Batteries store energy chemically and are a common choice for many IoT devices due to their availability, low cost, and high energy density. Supercapacitors, on the other hand, store energy electrostatically and have a lower energy density than batteries but are capable of providing higher power densities and faster charge and discharge rates. One important consideration when exploring the use of energy storage solutions for IoT devices is the selection of an appropriate energy storage technology. The choice of energy storage technology will depend on factors such as the power requirements of the device, the expected operating conditions, and the desired lifetime of the device. For example, a device that requires high power output for short periods may be better suited to a supercapacitor, while a device that requires a more steady power supply may be better suited to a battery. Another important consideration when exploring the implications of energy storage solutions for IoT devices is the impact on device design. Energy storage solutions may require additional space and may add weight to the device, which can be a concern for devices that need to be small and lightweight.