Key technologies research and application of green power traceability based on blockchain

Green power traceability is a crucial link to ensure the green power transactions’ authenticity, effectiveness and credibility. It’s an essential means to promote the large-scale development of green power. However, there are many links in the whole chain of green power. The data involves multiple departments and institutions. So it is not easy to trace the authenticity. This paper first introduces the entire chain of green power traceability and critical information. Secondly, it proposes the green power traceability scheme and key technologies. Then, it designs the system and functional architecture of green power traceability based on blockchain. Finally, it analyses the application effect of the system in green power trading and the Winter Olympics. This research provides the technical reference for the authenticity and traceability of green power. It helps the green-low-carbon transformation of energy consumption structure.


Introduction
With the deepening of energy green-low-carbon transformation, China has ushered in new opportunities for rapid renewable energy development.It is estimated that by 2060, the proportion of new energy installed capacity will reach 80%, and the ratio of power generation will reach 65% [1] .With the gradual development of new energy, market entities are increasingly demanding green power.In September 2021, the pilot project of green power trading was launched.A total of 259 market entities from 17 provinces across the country participated.On the first day, 7.935 billion kWh of power was traded.The users' type covered large state-owned enterprises, transnational corporations and export-oriented enterprises.On June 22, 2022, the European Parliament passed the "Carbon Border Adjustment Mechanism," which stipulates that tariffs should be imposed on the carbon emissions of imported products.
Under the dual pressure of carbon neutrality goal and carbon tariff, green power consumption has become a substantial market demand, popular with the low carbon market.So it's vital to guarantee the authenticity of green power consumption through green power tracing.The existing traceability methods have the following problems.
Firstly, the entire process of green power consumption involves generation, distribution, transmission, delivery, and use.So its authenticity is difficult to trace and easy to tamper.
Secondly, the circulation of green power trading contracts involves multiple business departments.The transparency of the trading links needs to be improved.
Finally, the existing traceability method is the management means of obtaining evidence after the event, which needs more effective technical certifications.
Blockchain is a new application mode of distributed data storage, point-to-point transmission, consensus mechanism, encryption algorithm and other information technologies [2][3][4] .It has such technical features as open mutual trust, multi-party consensus, tamper proof, and full traceability [5][6] , providing feasible solutions to the above business pain points.
Blockchain has been widely used in the field of energy trading.Reference [7] proposed a weakly centralized power trading mode based on the alliance blockchain and energy internet, solving the insufficient security problem caused by the decentralization of blockchain.Reference [8] proposed the architecture of a power market trading system based on blockchain.Reference [9] proposed a distributed energy transaction method based on a multi-chain collaborative blockchain.Reference [10] found that blockchain technology can realize decentralization of the energy trading system.Reference [11] proposed a renewable energy consumption certificate trading system based on the blockchain.Reference [12] proposed the incentive mechanism of energy carbon tokens for each market entity based on the blockchain.Reference [13] proposed a user-centered data model under the alliance blockchain.Reference [14] designed the overall architecture system based on blockchain and built a green power trading system.Reference [15] proposed a green certificate issuance and transaction mechanism based on the PBFT consensus algorithm.Reference [16] proposed a green certificate transaction matching model and architecture based on the blockchain.Reference [17] designed a green power tracking mechanism model based on graph calculation and blockchain technology.Reference [18] built a renewable energy power tracking simulation platform based on Ethereum and designed a smart contract covering renewable energy declaration and consumption.
Currently, the relevant blockchain research is mainly focused on innovative applications in various subdivisions such as power trading, distributed energy trading, green power trading, green certificate trading, etc.However, little literature has deeply studied the key information and technology of the whole green power traceability chain.This paper proposes a green power traceability scheme and designs a green power traceability system based on blockchain.It will realize the reliable traceability of the whole process data of green power, which is significant in promoting the orderly development of China's green power trading market.It will further guide society to form a consensus on green power consumption.

Whole chain construction of green power traceability
Reference [14] gives the connotation of green power traceability.It obtains green power production, transaction, and consumption information through the analysis of transaction contact and commitment, signed by users and renewable energy power generation enterprises.Blockchain technology is applied to link the key information of green power production, transaction, and consumption.It can guarantee tamper-proof and traceability.The green power traceability whole chain consists of market entities registration, transaction type confirmation, transaction contract management, transaction execution and transaction settlement, as shown in Fig. 1.

Green power traceability key information
The whole process of green power involves many links.Different links contain different information.It is necessary to sort out the vital on-chain data of each link to meet the traceability requirements.This paper sorts out the key information, and the details are as follows.
(1) The market subject information includes electric business license, financial report, generator sets' technical parameters, the sold scale, power supply scope, grid schematic diagram, registration information, etc.
(2) The transaction type confirmation information includes transaction type (such as annual transaction, monthly transaction, and intra-month transaction) and transaction announcement.
(3) The transaction contract information includes contract type, form, content, signing, adjustment, and cancellation information.The contract content includes market entities, transaction time, power quantity, transaction price, transmission channel, transmission cost, transaction measurement, electricity type, and other information.
(4) The green power transaction information includes security checks and transaction plan execution information.Security check includes channel transmission capacity limit, power balance, unit generation capacity limit, and unit auxiliary service limit.
(5) The green power settlement information includes metering point data, metering device information, metering data acquisition method, metering data confirmation, and settlement data information.

Green power traceability scheme
Based on green power traceability key information, the green power traceability scheme is constructed (as shown in Fig. 2).It can realize data collection, management, and inspection in the whole process of green power: First, the green power production, transaction, and consumption data are uniquely coded by the identification resolution system.It's formed a trusted data identification on the chain.Second, we use the identification addressing technology to carry out the coding association mapping.It achieves a multi-dimensional traceability query combined with encryption search technology.Third, we use the encryption commitment information generation method to build a green power traceability flexible verifiable mechanism in a distributed environment.
According to different market entities' needs for privacy security, we use the on-chain channel technology to protect users' data privacy security flexibly and controllably.Fig. 2 Green power traceability scheme based on blockchain and identity resolution

Blockchain-based identity authentication technology
This paper studies the cloud lightweight reliable identity authentication technology based on the blockchain (as shown in Fig. 3).The domestic cryptographic technology is used for identity authentication.We design a trusted distributed electronic certificate of the alliance, composed of a user ID and digital identity.It can realize the whole process management of signature behaviors.It also ensures the legitimacy and authenticity of users.Fig. 3 Blockchain-based identity authentication

Blockchain-based high-performance data storage and retrieval technology
It designs a real-time search method in the hybrid storage architecture of on-chain and off-chain to improve the system's scalability (as shown in Fig. 4).First, we extract the semantic information of offchain data.It can establish the collaborative mapping relationship between off-chain data and on-chain data.The accuracy of semantic feature extraction is improved by introducing a decentralized word frequency factor, part of speech factor, and location factor.We construct keywords' semantic inverted index.It is sent to the blockchain as transactions, which are stored in the MPT tree through consensus.Secondly, the inverted list is used to realize the fast real-time query of a single keyword.The index structure based on Merkle Semantic Trie (MST) is constructed to realize efficient multi-keyword searching.When querying, it needs to match the user's keyword combination with the index path and returns the matching results to the user.Fig. 4 Blockchain-based high-performance data storage and retrieval model

Joint trading technology based on smart contract
We study the power trading market theory ancillary service market model and proposed a joint trading model based on smart contracts.First, according to transaction type, we design the parameter template of the power trading market and ancillary service market.This paper took Frequency Modulation (FM) and Flexible Ramping Products (FRP) as examples.Then, we use smart contract logic to design the data storage form, numerical modification method, and modification permission.Finally, we specify the calling method, subject, and authority of the joint transaction smart contract.
Constraints of parametric template design shall include the followings.
(3) Capacity constraints are shown in Formula (4) and Formula (5).   ,  ,  ,   ,  , / , (4) Grade rate constraints are shown in Formula ( 6) and Formula (7). ,  , ,  , , ,  , are 0-1 variables, which are discharge and charge marks respectively. , ,  , are the discharge and charge power at t, respectively. , and  , are discharge and charge efficiency, respectively. , ,  , are the number of upward and downward FM participating in market transactions, respectively. , ,  , are the number of upward and downward FRP participating in the market. , ,  , are the maximum power of discharge and charge, respectively. ,  are the capacity state at time t and t-1, respectively. and  are the up and down power regulation rates, respectively.

System architecture
The system mainly serves four groups: clean energy power generation enterprises, power users, regulatory authorities, and trading institutions.The system's overall architecture provides resource support and business services for the whole process of green power traceability.It is composed of a resource layer, platform layer, data layer, contract layer, application layer, and cross-layer functional layer, which is shown in Fig. 5.

Fig.5 Blockchain-based green power traceability system architecture
The resource layer provides the operating environment and basic components, including computing resources, storage resources, network resources, etc.The platform layer defines the establishment method of the blockchain system node.It's an alliance blockchain system built by market entities, power-dispatching institutions, trading centers, and other relevant institutions in the whole chain.Appropriate consensus algorithms are selected to establish a consensus mechanism.Encryption algorithms ensure the security and reliability of the green power full chain data.The data layer includes identification information, user information, critical information of the whole chain, etc.The contract layer encapsulates the script code, trigger conditions and response operations of the smart contract deployed by the system.The application layer provides green power trading, green power traceability and green power whole chain management services.The cross-layer functional layer provides the system's basic services and security protection capabilities.

System function module
The system function module is shown in Fig. 6.It mainly consists of user identity management, contract management, green power transaction, transaction settlement, green power whole chain traceability, and system management.The details are as follows.
(1) The user identity management module provides market entities with such functions as account registration, query, change, cancellation, and daily maintenance.It includes user registration, user information update, user login, user information confirmation, identity authentication, etc.
(2) The contract management module provides contract management capability in the transaction process.It realizes the management of contract type, contract form, contract content, contract signing, contract adjustment and contract dissolution.
(3) The green power trading module provides such functions as transaction announcement release, data declaration acceptance, transaction execution, transaction clearing, and transaction results release.
(4) The transaction settlement module provides power settlement and green environmental value settlement functions.
(5) The green power whole chain traceability module provides the traceability capabilities of the user, contact, transaction, settlement information, etc.
(6) The system management module provides access management, log management, classification scheme management, interface management, security management, and other primary functions.Fig. 6 Blockchain-based green power traceability system function module

System test results
The system is tested in the standard production test environment (16 core 32G, dominant frequency 3.6 Ghz).The transaction throughput is more than 30000 TPS.The response time reaches the milliseconds level.It supports a dedicated data storage engine (FileLog) and multi-level cache (MultiCache) state data storage mode.The system supports solidity, Java, and other programming languages.It provides complete contract lifecycle management.It has the characteristics of friendly programming, contract security, and efficient execution.So it can adapt to changing and complex business scenarios.It has a standard HTTP RESTful interface to facilitate fast application access.It provides multi-chain parallel load, data cache, and reliability verification services, improving overall reliability and performance.It supports SM2, SM3, SM4, SM9, and other domestic password algorithms.It also supports domestic mainstream hardware password equipment.In short, the system is safer and more controllable.It can fully support the development of green power traceability business.

Green power transaction
The system is applied in green power trading pilot work to record the whole chain key information.The two-dimensional code of the green power traceability query service was launched.It provides reliable digital services for various market entities, trading institutions, and regulators.Currently, 24 provincial grid companies are in the state grid business zone, and more than 12,000 market entities have participated in green power transactions.The trading volume reached 38.281 billion kWh.Blockchain technology generated 3111 wholesale contracts and 10708 retail contracts on the chain.More than 12000 green power consumption certificates were issued based on blockchain.Through the blockchain traceability code on the green power consumption certificate, the green power traceability process can be visible, observable and traceable.

Green power traceability in Winter Olympics
In June 2019, the Beijing Organizing Committee for the Winter Olympic Games released the "Low Carbon Management Work Plan for the 2022 Beijing Winter Olympic Games and the Winter Paralympic Games".It proposed comprehensively realizing a 100% green power supply to meet the regular needs of the Winter Olympic venues and supporting facilities.This work plan puts forward new technical requirements for reliable recording, accurate traceability, and transparent supervision of the whole process of green power trading.Using the green power traceability system based on blockchain, it realized the multi-dimensional traceability query of green power.During the 2022 Beijing Winter Olympics, 28 new energy power generation enterprises and 25 Winter Olympic venues realize data access.It helps carry out eight batches of green power transactions for the Winter Olympics.The green power trading volume was 780 million kWh.It can help reduce 620,000 tons of carbon dioxide emissions.The application realized reliable traceability of green power generation, transmission, trading, and consumption, effectively assisting all venues' 100% green power supply.

Conclusion
Aiming at the difficulty of tracing green power authenticity, this paper proposes a green power traceability solution based on blockchain.It researches the whole green power traceability chain and gives key information about each link.Based on blockchain and identification resolution technology, the green power traceability scheme is constructed.Considering market entities' requirements, it designs a green power traceability system based on blockchain and tests the system.The test results show that the system has significant advantages in core performance, security signature, data sharing, and other aspects.It can meet the green power traceability business requirements.In addition, the paper analyzes the application effect of the system in green power trading and the Winter Olympics.This research provides authoritative and credible green power traceability technology for market entities.It will help create a fair green power trading environment.It also fully stimulates the green power consumption potential on both supply and demand sides.Next, we will conduct microservice transformation based on business application needs and application feedback.We will continuously optimize the service capability of the system and expand the application scale.

Fig. 1
Fig.1 Green power traceability whole chain