## 3 Motivation and Challenges  
Motivation: It is noticed through the review literature that in most of the proposed P2P energy platforms, the trading takes part between the prosumers and consumers. Prosumers' energy is injected into the power grid, which is metered and tokenized. Tokens are created using an asset-based token protocol such as the ERC20 protocol in Ethereum. A token smart contract is created with a certain amount of total supplied tokens, which are set to have an abstracted value in terms of energy. Energy aggregated to the utility power grid (by the prosumers) is redeemed in the form of tokens, which are transferred to them. Tokens can then be traded according to their value in the market [26; 27; 28]. Accordingly, the initial smart contract defining the energy token is set with a total supply of tokens, which means, if new tokens need to be created, then, a new smart contract needs to be deployed with additional supply, which is very costly. The gas cost to deploy the EWT energy token is 1,274,198 with a cost of $171.62 [29]. Moreover, transferring tokens is costly as well. In addressing such gaps, we wish to consider in our paper that prosumers cooperate as a single provider and the energy they aggregate to the utility grid is tracked in a smart contract deployed by the DSO. This amount of energy is mapped to the issuer prosumer's account as its energy balance. Instead of a token transfer, prosumers' energy balance is updated by a mere contract call that updates a mapping, rather than a costlier financial token transfer. The energy balance of the prosumers represents the amount of energy the DSO owes them. Then, consumers can buy energy from prosumers. If the prosumer (seller) has enough energy balance to supply the demand, the payment is made from the consumer (buyer) to the seller set of prosumers. Consequently, the energy being sold is transferred from the DSO to the consumer as a debt that is paid back to the respective prosumer. His energy balance is then updated accordingly [30; 31]. Mainstream token-based P2P energy trading platform bears another main drawback. In fact, in such a situation, the client does not pay per use for the energy he purchased. After the energy token is bought, it can be then redeemed as energy. However, the respective corresponding energy amount is transferred to the client and he is charged accordingly, regardless of to which extent the purchased energy is consumed. Additionally, most of the time, purchased energy is not consumed to the fullest [23]. It is as worth mentioning that some substantial research papers have been also conducted using smart contract-based electricity consumption billing system, outside the context of P2P energy trading, where household electricity bills' computation and payment are monitored by a smart contract in a traditional centralized DSO-client architecture [32; 33; 34]. In this perspective, we proposed in our research paper, a platform where consumers are billed per consumption in the same fashion the DSO bills its consumers. Challenges: One can identify a few challenges in developing such a platform. The first challenge is to be able to accurately bill the consumers for the energy they consumed. To achieve this, prosumers need to be the only supplier from the start to the end of the trading round. Trading rounds have a certain duration, each one is administrated by a smart contract that sets the electricity tariffs. For this purpose, prosumers and microgrids' owners collaborate to form a single provider, which would be a full-time supplier to the subscribed customers for an entire trading period. The second challenge is concerned with the prosumer's power generation, which is based on renewable energy and low voltage energy sources. It is a concern that it can be not sufficient to supply for consumers on a continuous period. Yet, this could be seen as a fake problem.