Future powers system is considering huge flux of information flow due to increase in Renewable Energy Sources. Due to the limited monitoring and management of SCADA systems, inclusion of DER at local distribution level is a challenging task for the Smart Grid. We discuss the non-functional requirement aspects and their implication in trustworthy systems. The paper also illustrates an engineering approach towards trustworthy ICT systems. We present a use case about Injection/Curtailment of DER in distributed network. Further, we argue the importance of Service Level Agreements as coordination tool for information exchange between DSO and DER for the provisioning of trustworthy services. Finally conclude that modeling of SLA using Multi Agent Systems is a viable approach towards Trustworthy future Smart Grid applications.