# Blockchain Solution for Buildings' Multi-Energy Flexibility Trading Using Multi-Token Standards
###### Abstract  
Buildings can become a significant contributor to an energy system's resilience if they are operated in a coordinated manner to exploit their flexibility in multi-carrier energy networks. However, research and innovation activities are focused on single-carrier optimization (i.e., electricity), aiming to achieve Zero Energy Buildings, and miss the significant flexibility that buildings may offer through multi-energy coupling. In this paper, we propose to use blockchain technology and ERC-1155 tokens to digitize the heat and electrical energy flexibility of buildings, transforming them into active flexibility assets within integrated multi-energy grids, allowing them to trade both heat and electricity within community-level marketplaces. The solution increases the level of interoperability and integration of the buildings with community multi-energy grids and brings advantages from a transactive perspective. It permits digitizing multi-carrier energy using the same token and a single transaction to transfer both types of energy, processing transaction batches between the sender and receiver addresses, and holding both fungible and non-fungible tokens in smart contracts to support energy markets' financial payments and energy transactions' settlement. The results show the potential of our solution to support buildings in trading heat and electricity flexibility in the same market session, increasing their interoperability with energy markets while decreasing the transactional overhead and gas consumption. buildings; multi-energy tokens; heat trading; electricity trading; blockchain; ERC-1155; peer to peer energy markets; integrated energy system +
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services to the electrical and thermal grids [8]. On one side, the buildings can use their electrical flexible loads (e.g., consumer devices, batteries, heating and cooking loads, and renewable generation) for electricity trading and demand response services, creating a positive environmental impact as well as commercial value and, at the same time, they can trade and provide their residual heat to the thermal grids, leveraging the heat pumps to increase its quality. In this direction, the smart building concept has been introduced to ensure technological approaches for closer to real-time control and interaction with end users, converging towards decentralized building level coordination with distributed multi-carrier energy networks [9; 10]. In parallel, the advent of blockchain technology is changing the energy sector, from the integration of renewable energy sources to smart energy grids and smart-ready buildings and peer-to-peer energy trading [11; 12]. It offers opportunities to digitize the energy of different carriers using tokenization and paving the way to decentralized control of electricity grids in synergy with other energy carriers and the delivery of cross-sectorial integrated services. In our vision, the energy flexibility of non-grid-owned assets should be digitized and made tractable on different energy markets. Blockchain offers integration opportunities for multi-carrier energy buildings to digitize their flexibility using tokenization and decentralized coordinated control via smart contracts, which may transform them into active flexibility assets at the interplay of multi-energy networks able to trade energy on both heat and electrical markets [13]. In this paper, we consider a trading mechanism designed to work in an integrated multi-energy system, where electricity and heat are traded within an energy community [14]. Most of the existing literature on P2P energy trading addresses electricity and the lack of cross-energy carrier integration relevant to the buildings sector. The heat trading is focused on buildings that may generate heat using their heat pumps to create hot water, which is then fed into a shared heat grid within the community.