978-1-5386-5186-5/18/$31.00 ©2018 IEEE An Energy Blockchain, a use case on Tendermint M.L. Di Silvestre, P. Gallo, M.G. Ippolito, E. Riva Sanseverino, G. Sciumè and G. Zizzo DEIM – Dipartimento di Energia, ingegneria dell’Informazione e modelli Matematici Università di Palermo Palermo, Italy Abstract—The recent advances in distributed energy systems require new models for exchanging energy among prosumers in microgrids. The blockchain technology promises to solve the digital issues related to distributed systems without a trusted authority and to allow quick and secure energy transactions, which are verified and cryptographically protected. Transactions are approved and subsequently recorded on all the machines participating in the blockchain. This work demonstrates how users, which are nodes of the energy and digital networks, exchange energy supported by a customized blockchain based on Tendermint. We focus on the procedures for generating blocks and defining data structures for storing energy transactions. Keywords—blockchain; transactive energy; microgrids; energy market; peer to peer. I. INTRODUCTION The intermittent production of energy from renewable sources is still growing. If not managed optimally, it can compromise the stability of the electrical system. One solution could be the storage of this energy and the balanced peer-to-peer exchange between end users. This latter measure can be realized using a properly designed blockchain [1]. The blockchain is a distributed ledger of transactions, which is structured in blocks and stored in the network nodes. Blocks are connected to each other in a chain and are validated before being inserted in the distributed ledger. In a nutshell, the blockchain can be represented by a chain of blocks that contains and manages multiple transactions. Each node can see, control and approve all transactions and is part of a network that allows traceability of all transactions. Each node, in turn, is also an archive for all transactions and thus of the history of each transaction that, just to be approved by the network, is available on all the nodes of the network and is thus unmodifiable (unless the same modification is carried out in the whole network and only after the approval). In addition to immutability, the other important feature of the Blockchain Network is the use of cryptographic tools to ensure maximum security of each transaction [2]. By using a blockchain, it is possible to reduce transaction costs through, for example, a standardization via "smart contracts" and automatic order execution without the presence of a third party to act as guarantor, allowing direct exchange of energy between users of the network quickly and safely [3]. A Smart Contract is a contract, suitably coded, which automatically verifies the occurrence of certain pre-defined conditions and executes actions when the conditions between the parties are fulfilled and verified [4]. Each new transaction before being integrated into a block of the blockchain is validated by specific nodes, which are rewarded for their work [5]. The blockchain is a distributed ledger, namely a ledger that is not physically located only on one single server; it is located on multiple machines at the same time, all perfectly synchronized on the same information. The use of the blockchain technology in energy management introduces: 1. Transparency, because each block added to the blockchain is accessible by all participants. It becomes a permanent and unchangeable reference to that specific transaction; 2. Trust, based on cryptographic functions, the blockchain works in distributed and untrusted environments; 3. Efficiency, as it requires fewer intermediaries than the traditional energy trading system, thus simplifying processes, infrastructures and increasing operational efficiency; 4. Control and security, because, thanks to encryption, data protection is better and less risky (fraud). Furthermore, decentralization prevents market abuses through monopolies and requires lower costs and regulatory oversight. This document explains how to record energy transactions, occurred in a microgrid, using the Tendermint platform [6]. The use of Tendermint blockchain for the exchange of energy users allows transactions to be carried out quickly and securely, as the latter are made up of encrypted data and are verified, approved and subsequently recorded on all the machines participating in the blockchain. The same "information" is present on all nodes and therefore becomes unmodifiable unless through an operation that requires the approval of the majority of nodes of the network and that in any case will not change the history of that same