## 7 Challenges and Future Research Directions  
To achieve technical goals in applying IoT in SG, there are many challenges which must be addressed in future research directions. Since IoT devices must work in different environments that may have harsh conditions (e.g., high or low temperatures, high voltages, exposure to electromagnetic waves, working in water, etc.), therefore, they must satisfy requirements at those conditions such as reliability or compatibility.  
In many applications, IoT devices and sensors operate on batteries (e.g., different types of sensors which are used to monitor transmission lines), so suitable energy harvesting techniques should be used or designed. We have several communication networks in different parts of the SG, so, IoT devices should support necessary communication protocols so that transferring data from smart meters to the central system is possible and guaranteed.  
Since IoT devices in SG have limited resources and capabilities such as batteries, processing power, storage, or bandwidth, so data fusion processes should be used to compress and aggregate useful data so that we have more efficient energy and bandwidth usage and data collection.  
Delay and packet loss are important parameters that determine the performance of smart gird. Since congestion causes delay and packet loss, it degrades system performance (because IoT devices and/or gateways IoT devices must resend data which causes more delay and increases the probability of congestion again) and SG cannot satisfy predetermined requirements, e.g., maximum tolerable delay. Therefore, it is necessary to minimize delay, optimize network design by finding an optimum number of gateways and IoT devices, and minimize the number of connections to each gateway.  
Since the smart grid contains many different gateways and IoT devices with different specifications and resources, interoperability between these devices to exchange information is very critical. One solution to achieve interoperability is to use IP-based networks. Another solution is that IoT devices should support different communication protocols and architectures.  
Sensors, smart meters, and other similar devices that measure and collect information in a smart grid create big data that can consume a lot of energy and other resources and create a bottleneck. We should design the smart grid in such a way that can efficiently store and process this huge amount of collected data.  
There are many separate standards for IoT devices, but there is no unified standard for IoT devices in the smart grid. This may cause security, reliability, and interoperability issues for IoT devices in SG. Therefore, standardization efforts should be unified.  
To monitor and control IoT devices in SG, we should use the Internet which is very vulnerable, and attackers can manipulate measured data by sensors and smart meters and cause a lot of financial losses. Therefore, we should develop secure communications for IoT devices in the smart grid by considering resource limitations of IoT devices and determine some security measures for these devices. For example, IoT devices have limitations in computation and storage. Thus, we should design or use security solutions so that IoT devices are able to run them. From the collected data by smart meters, it is possible to extract some information about consumers' habits (e.g., wake up times, etc.), therefore it must be guaranteed that this private information will not be used without consumers' permission. Also, suitable mechanisms for security measures such as trust management (between IoT devices which are owned by different parties, e.g., customers and utilities), authentication, authorization, data integrity, maintaining confidentiality, and detecting identity spoofing should be devised.