# IoT Middleware Platforms for Smart Energy Systems: An Empirical Expert Survey
## 6 Discussion  
Monitoring and operation through IoT solutions is seen as a key interest for energy technology companies, building managers and end users. This highlights that scalability and modularity are key requirements for IoT solutions. IoT platforms have to support a wide range of functionalities, as the use cases for energy technology companies are fundamentally different from the use cases of the other end users. Based on the expert survey, around 70% of the respondents found that visualization of energy production and consumption remains the central use for IoT infrastructure, and the potential of data analysis services and control automation are not yet exploited. However, there seems to be rising interest in energy optimization, including benchmarking, automation and control, and demand side management. Many commercial platforms provide services, service templates and SDKs for seamless integration with their platforms. Regarding the IoT architecture model, in our research, we found that a five-layer approach offers the most practical solution by distinguishing layers based on their functionalities, while keeping it as simple as possible. The most relevant application layer protocols used by most of the middleware platforms in research are HTTP, CoAP, MQTT, OPC UA, XMPP, AMPQ and DDS. On a network communication level, IPv6, ZigBee, Z-Wave, Bluetooth, 4G/LTE, 5G, LoRAWAN, 6 LoWPAN, LTE-M and NB-IoT are the predominant technologies. The survey results highlight that MQTT is considered to be even more important than HTTP by the respondents of the survey; however, especially in the matter of scalability and real-time control, CoAP, XMPP or DDS might find more relevance in future applications. Regarding the communication technology, LoRaWAN got the spot of the most relevant technology in the survey at roughly 65%, followed by WiFi, at slightly more than 55%. Offering more technologies could also help in drawing the attention to some alternatives that solve the drawbacks of the used technologies, such as using HTTP instead of MQTT to improve the scalability. To improve the portability of energy services between different platforms and to avoid vendor locks, it will be necessary to be able to  
Figure 9: Responses to a survey question about the communication technologies that need to be supported by the IoT middleware platforms. use uniform semantic data models and data point labels in the future (see Figure 3). In addition, to allow the integration of a wide variety of third-party services, devices and (legacy) systems, it is critical to standardize APIs. Extending the scales in which the IoT middleware platforms are used imposes the need of sharing and handling large amounts of real-time data in a scalable, controlled and secured way. Indeed, at least 64% of the participants claimed to use IoT middleware for multiple buildings. Security is particularly important considering the severity of security breaches in the context of privacy and confidentiality and the risks for the operation of buildings, districts and grids. Figure 6 demonstrates how important security is for the users, by being considered as the most important non-functional requirement with approximately 90% of the votes. With more services and functionalities being automated, it is imperative to ensure the reliability of the middleware platform. Although openness is seen as the least important property provided by middleware platforms among the NFRs, Figure 3 shows that while there is a general willingness to participate in the development of open-source IoT platforms by practitioners in energy technology companies, building operators and municipality officials, many users would still prefer to outsource operation and maintenance of platforms to third-parties. The same opinion applies for the management of these platforms: the majority of users would prefer to pay for the administration of the middleware platforms, rather than administrating their own. At the same time, some users are still undecided and have a wait-and-see attitude.