## 1 Introduction
Recent works have shown the capability of 5G for several smart grids' applications, such as for (1) fault management [21] in power distribution networks, including centralized and distributed network management; (2) state estimation monitoring applications [22]; (3) line differential protection in MV substations [23]. A recent survey investigating possible applications of 5G for smart grids is provided in [24]. Despite their very interesting insights, the existing studies mainly focus on the 5G radio access network (RAN), while important aspects, such as the 5G service-based architecture (SBA), which could leverage advanced techniques for the support of smart grid applications (e.g., slicing), have not been studied. In this regard, _Smart5 Grid_[25], an EU-funded project started in January 2021, aims to support the energy sector evolution by providing the required digital layer to leverage the availability of new communication technologies and infrastructure, accelerating the transition towards 5G and adopting the edge computing and cloud-native paradigms by means of chained virtual network functions, defined as network applications (NetApps). In this paper, we introduce the Smart5 Grid concept and architecture and highlight the NetApp concept, which, together with the Smart5 Grid platform design that facilitates its deployment, accelerates digitalization and innovative services for smart grids. Unlike the existing literature, our work takes into account the end-to-end 5G SBA and the interplay between the service and the network towards the formation of service function chains that can be hosted in 5G networks and which meet their strict application requirements. To this end, the main contributions of this work are as follows:  
1. The introduction of the NetApp concept to enhance the capabilities of domain-specific applications for one of the most important 5G vertical industries, that is, the power and energy grid. This concept takes into account the 5G SBA and provides a joint framework for application and network management, among others. 2. The definition of an open cross-domain platform, which includes the energy and the telecommunication domain and the Smart5 Grid open-experimentation platform, along with open interfaces for third parties to assess their custom energy-related NetApps. 3. The presentation of a set of different use cases with different communication requirements and their impact on the definition and interplay between the Smart5 Grid components. The paper is organized as follows: Section 1.1 exemplifies several smart grid functionalities that could most benefit from the 5G technology and the NetApps concept. Section 1.2 introduces the demonstrators for 5G technology as proposed by the Smart5 Grid project. Section 2 details the innovative concept of NetApps from the point of view of conceptual representation, development, and deployment in the 5G telco infrastructure. Section 3 presents the Smart5 Grid platform as an open experimentation environment for third-party NetApps. Section 4 showcases the application of the NetApp concept to realistic, ready-to-be-implemented applications for smart grids. Specifically, this section details the NetApp functionalities specific to the four real use cases of the Smart5 Grid project. Section 5 provides the conclusions and information about future work.