The structure of a power energy system is becoming more distributed than before. It becomes challenging to manage such a system in a centralized way, because a central authority may not exist or may not be trusted by all parties. Blockchain is a promising tool to address this challenge, by enabling trusted collaboration in the absence of a trusted central authority. Its use in the energy sector has been pioneered by several pilot projects. However, to date the energy sector has not seen large-scale deployment of blockchain, partly because the founders of those pilot projects, the public, and utilities have not reached consensus on the values and limitations of blockchain in energy. This perspective aims to bridge this gap. First, the philosophy and unique values of blockchain are discussed. Second, some promising blockchain-based applications in energy systems are presented. Third, some common misunderstandings of blockchain in energy are discussed. Last, some frequently-asked questions from utilities are discussed. Hopefully this perspective can help advance large-scale deployment of blockchain in energy systems.