Blockchains become a suitable platform for peer to peer energy trade as it facilitates secure interactions among parties with trust or a mutual trusted 3rd party. However, the scalability issue of blockchains is a problem for real-time energy trade to be completed within a small time duration. In this paper, we use offline channels for blockchains to circumvent scalability problems of blockchains for peer to peer energy trade with small trade duration. We develop algorithms to find stable coalitions for energy trade using blockchain offline channels. We prove that our solution is secure against adversarial prosumer behaviors, it supports real-time trade as the algorithm is guaranteed to find and record stable coalitions before a fixed time, and the coalition structure generated by the algorithm is efficient.