Electricity market regulation: Global status, development trend, and prospect in China

With ever-growing electricity consumption, unwanted climate change, and evolving generation mix, some energy policies related to electricity markets are enforced in various countries to cope with emerging challenges in the energy sector. Electricity market regulation, which is required to keep pace with the continuous development of power industry restructuring and electricity market operation, is also evolving. To help researchers and policy makers have a better understanding of the state-of-the-art electricity market regulation, the aim is to survey the latest progress, as well as the development trends in this ﬁeld in the United States, Australia, United Kingdom, and France, which have mature and widely recognized electricity markets around the globe. Subsequently, the progress of the electricity market reform in China is described, and the status, drawbacks, and prospect of the electricity market regulation in China presented.


INTRODUCTION
The vertically integrated electrical power industry was broken up into discrete parts of the supply chain in 1980s in some countries, and electricity markets were then developed as the most significant milestone of power industry restructuring [1]. While the electricity network sector remains monopolized, generation and retail sectors have been open to market competition in many developed countries during the past 30 years. As a result of marketization, generation assets are better employed, electricity trading could be implemented in a large geographical area and even across various countries, and consumers are provided with more choices of power supply arrangements [2]. On the other hand, some problems associated with electricity markets, such as market power abuse, fairness and adequacy of market competition, market transparency, need to be well resolved. Therefore, market regulation is needed to protect the public interest against market failure, and to promote social welfare. Since electricity markets are evolving, market regulation, which is required to keep pace with the market mechanism and operation, is also facing new problems or even challenges. Some developing countries, including China, are still exploring their paths to electricity marketization, as well as the development of electricity market regulation systems [3]. International experience on electricity market regulation from mature electricity markets around the globe can be learned by those countries undergoing power industry restructuring, with the characteristics of each country taken into account.
Nevertheless, comparisons among existing designs of electricity market regulation are often hindered by new developments, as well as the practice in which details about electricity market regulation are often embedded in a multitude of documents on various websites of regulators. Given this background, it is the objective of this paper to systematically overview different electricity market regulation systems and present the development trends of electricity market regulation.
In this work, the prevailing regulation systems in four developed countries, including the United States, Australia, United Kingdom, and France, are first surveyed, covering the regulatory authority, legislative framework, wholesale market regulation, retail market regulation, and regulatory approach. Subsequently, the development trends of electricity market regulation are discussed with respect to several issues of extensive concerns around the globe. Then, the progress of electricity market reform in China is presented. Finally, the status and drawbacks of electricity market regulation in China are discussed, and prospect for the future development presented.

FIGURE 1 Regulatory authorities in the United States
A list of abbreviations used in this paper is presented in Table 1.

REGULATORY SYSTEM
The first and most fundamental part of electricity market regulation is the regulatory system. A well-designed regulatory system may take decades to develop and improve, and could greatly promote the efficiency and effectiveness of the regulation. Generally, an electricity market regulatory system is basically comprised of two parts: (i) one or multiple regulatory authorities responsible for carrying out regulation activities or enforcements to protect participants in the electricity market; (ii) legislations that grant specified power to the regulatory authority.

Regulatory authorities
The regulatory authorities can be either a part of, or independent from executive branches of the government; this would determine how decisions of the regulators are made and implemented.
The electricity market regulation in the United States is enforced by multiple federal and state governmental bodies with some degree of coordination. Federal and state regulatory authorities regulate certain aspects of the U.S. electric power industry, and a two-level regulatory framework is implemented [4,5,6], as shown in Figure 1.
Currently, there are seven regional electricity markets in the United States, with each of them having its own Independent System Operator (ISO) and Regional Transmission Organization (RTO). FERC authorizes ISOs/RTOs the power to operate and monitor their electricity markets and protects the independence of the decision process of ISOs/RTOs. In addition, ISOs/RTOs are required to have an internal or thirdparty organization as the Market Monitoring Unit (MMU). The MMU monitors the electricity market and reports directly to FERC and boards of the ISO. It is worth noting that, the power  Texas PUC ERCOT ERCOT / Potomac economics system in Texas is generally considered as an independent system, and the electricity market regulation in Texas is enforced by the Texas Public Utilities Commission and the Electric Reliability Council of Texas (ERCOT) [7], rather than FERC. Main regulatory authorities in the United States are listed in Table 2. Four governmental bodies are mainly responsible for regulating the electric power industry in Australia [8,9]: the Council of Australian Governments Energy Council (COAG Energy Council), Australian Energy Market Commission (AEMC), Australian Energy Market Operator (AEMO), and Australian Energy Regulator (AER), as shown in Figure 2.
The Gas and Electricity Markets Authority (GEMA) has the primary responsibility for regulation of the energy sector in United Kingdom. GEMA is constituted of a working group FIGURE 2 Regulatory authorities in Australia appointed by the Secretary of State at the Department for Business, which ensures its independence and limited stakeholder participation. GEMA operates through its office, the Office of Gas and Electricity Markets (OFGEM), to which it delegates its functions and provides with strategic directions and oversights [10]. OFGEM is therefore more commonly referred to as the energy regulator of United Kingdom. OFGEM is required to create a level playing field for the electricity wholesale and retail markets, and regulate transmission and distribution networks at the same time. In United Kingdom, industry licenses are required before companies conduct their generation, transmission, distribution, or sale of electricity. Such licenses are issued by OFGEM following the evaluation of the company's eligibility. OFGEM is also authorized the power to determine and modify the conditions in the license, monitor the license-holder's compliance with defined conditions, as well as various industry codes and standards. When necessary, OFGEM also takes enforcement actions to penalize market violations.
With the evolvement of the integrated European electricity market, the French electric power industry gradually moves towards marketization. In March 2000, in accordance with the European Union's requirements of the electricity market reform, the French Electricity Regulatory Commission was established to ensure that the electricity markets in France function smoothly. In 2003, the French Electricity Regulatory Commission was renamed the Commission of Regulation of Energy (CRE), with the function of natural gas market regulation added [11]. The Dispute Settlement and Sanctions Committee, known by its French acronym "CoRDiS" (Comité de règlement des différends et des sanctions), is an independent body of CRE, tasked with settling disputes concerning access to and use of the public electricity and gas networks, and imposing sanctions on violations of the Energy Code. In addition, the French Competition Authority (FCA) also has the power to prevent and sanction anticompetitive practices in any economic sector [12].
Since United Kingdom and France are members of the European Union, their electricity market regulations are also enforced by the Council of European Energy Regulators (CEER). In order to promote the establishment of the integrated European electricity market, the European Commission (EC) released the "Third Energy Package" and established the Agency for the Cooperation of Energy Regulators (ACER) [13]. ACER has the function of cross-border regulation and works in cooperation with the national regulatory authorities of EU member countries.

Legislation
The establishment of an electricity market regulatory system covers much more issues than setting up a market regulator. Supports and restrictions from the legislation are demanded. A rule-based regulation, instead of administrative orders, is one of the main features of the electricity market regulation, making it different from the regulation of traditional vertically integrated utilities. It is demonstrated by international experience that legislation always plays an important role in the marketization process of the electricity sector. Over the last three decades, a number of laws and orders have significantly promoted the market competition in the U.S. electricity sector, and are therefore considered as milestones in the development of the U.S. electric power industry, as listed in Table 3. Apart from laws and acts, FERC has continuously issued more than 400 orders and regulations to address new challenges with the market evolvement since 1996, covering market access, transfer of control, license application, transmission planning, transmission and distribution cost allocation, reliability standards, and others [15].
The legislative framework of the Australian National Electricity Market (NEM) consists of four legislative schemes: the National Electricity (South Australia) Act 1996, the National Electricity Law (NEL), the National Energy Retail Law (NERL), and Competition and Consumer Act (CCA). Generally, NEL regulates the wholesale electricity market and electricity network, and determines the scope of function and authority of AEMC, AEMO, and AER. In accordance with NEL, the National Electricity Rules (NER) are formed and applied on the economic regulation of the wholesale electricity market, including market operation, power system security, transmission network planning, access, and cost allocation [16]. Correspondingly, issues related to retail electricity markets are regulated by NERL, under which the National Electricity Retail Rules (NERR) and the National Energy Customer Framework (NECF) are formed. NERR and NECF regulate the distribution and sale of electricity to end users. In jurisdictions that have not implemented NECF (Victoria, Western Australia, and the Northern Territory), the state and territory governments remain responsible for retail authorization, compliance monitoring and market performance reporting [9].
The regulatory framework in United Kingdom operates through a cooperation of legislation, licenses, and industry codes. The Electricity Act 1989 is the main legislation in the electricity sector, under which the licensing regime is established and statutory duties of GEMA and OFGEM set out. Other key legislations include the Utilities Act 2000, Competition Act 1998, Enterprise Act 2002, and Energy Acts 2011, providing OFGEM the power and responsibility to monitor the electricity market, setting policy priorities and making decisions on a wide range of regulatory matters. In addition, various industry codes (e.g. Balancing and Settlement Code, Distribution Code, Retail Energy Code [17]) establish rules that restrict electricity market operation, as well as terms of connection and access to electricity networks. These industry codes are executed by the licenses, which contain conditions that license holders must comply with, such as conditions on compliance with industry codes and standards. One of the main functions of OFGEM is to determine the conditions of electricity licenses, and to grant licenses to eligible applicants.
In France, many laws and regulations governing the electricity market are transposed from EU directives. For example, French Law No. 2000-108 on modernization and development of electricity public service is transposed from EU Directive 96/92/EC. According to Law No. 2000-108, industrials consuming more than 16 GWh per year were allowed to choose their electricity suppliers, the power grids were no longer directly operated by Electricité de France (EDF), and CRE was established as an independent regulator of the electricity market [18]. After the European Commission's release of the "Third Energy Package", which was transposed into French law in December 2010 by a new law commonly referred to as "Law Nouvelle Organisation du Marché de l'Electricité" (Law NOME) [19], to further open up the energy market, the obstacles to the development of the French electricity market was removed. In 2011, the French Energy Code was created by Ordinance No. 2011-504, finalizing the transposition of the EU electricity directives [20]. The French Energy Code covers many sectors related to energy, such as electricity, natural gas, renewable energy, hydropower, petroleum, heating and cooling networks [21]. In addition to national laws and regulations, the ruling of the electricity markets in United Kingdom and French also needs to stay in line with EU legislations. Until late 2011, the key piece of anti-market manipulation legislation in EU was the Market Abuse Directive (No. 2003/6/EC) (MAD), predated the creation of the EU's nascent wholesale energy markets [22]. Since MAD was designed to prohibit market abuse in EU's financial markets, in which commodity trading like electricity and gas trading is not covered, the EC presented the Regulation on Wholesale Energy Market Integrity and Transparency (REMIT) on December 8, 2010 [23]. From that day on, OFGEM and CRE have been required to implement market registration, promote information disclosure, prohibit insider trading and market manipulation in the wholesale electricity market.

Summary
Comparisons among electricity market regulatory systems in four developed countries are presented in Table 4. As detailed in this table, an independent regulatory body is established in countries with mature electricity markets to regulate their electricity sectors at the federal level. In vast countries like the United States, state level regulators and other regulatory bodies are created to jointly regulate specific issues of the electricity sectors concerned. Regulators sometimes participate in market rules making but typically do not involve in market operations, and are all given with legislative guarantees on their authority as well as the scope of functions. Therefore, the decision-making process of the regulator can be independent from stakeholders. Basically, power industry restructuring is usually driven by legislations rather than administrative orders, and hence is more capable of overcoming the obstacles in the implementation procedure.

Wholesale electricity market regulation
The deregulation of the electric power industry does not mean the absence of regulation. Instead, the focus of the electric power industry regulation is shifted to address the emergent problems along with the marketization, such as market power control, market performance assessment, and generation capacity adequacy. International experience shows that the priority of the electricity market regulation can be different as the electricity market mechanism differs from country to country. The wholesale electricity market in Australia is typically a "gross pool" market, in which all electricity is traded in the pool, with financial instruments utilized to manage the risk [24]. Whereas, United Kingdom and France adopt the "net pool" market, also called the bilateral trading market, in which trading via the pool is optional and the majority of electricity is traded via bilateral contracts [25]. There are several electricity markets in the United States, and both pool-based and bilateral trading modes are employed. In some aspects of regulation, like market access and transfer of control, regulators in different countries adopt remarkably similar methods. However, in term of market monitoring and market power control, customized strategies are adopted in various electricity markets. Under the "gross pool" market structure, the key of market monitoring is the prevention and prohibition on market power abuse and market manipulation. In the United States, three bodies, FERC, ISO/RTO, and MMU, supervise the wholesale electricity market on different levels. The office of enforcement in FERC screens a large number of public and non-public data and uses market indicators to identify market anomalies [26]. Meanwhile, the ISO/RTO of each regional electricity market also sets up market monitoring department to internally monitor the market operation. Moreover, the MMU of each regional electricity market is granted by FERC the function and authority of market monitoring, information disclosure, and market design [27]. The MMU monitors, investigates, and assesses the operation of the wholesale electricity market externally, and then releases state-of-market reports on quarterly and yearly basis to disclose the performance of electric energy markets, capacity markets, ancillary service markets, grid congestion, and network losses, and others [28]. Based on the reports, recommendations for revising electricity market design are proposed to the regulatory authority as well by MMU. In CAISO and PJM electricity markets, the "Three Pivotal Supplier (TPS)" test is adopted to control the potential market power of generation companies. Besides, in the PJM market, generation units committed in the day-ahead market are only allowed to lower their offer price in the real-time market.
In Australia, AER monitors the wholesale electricity market and keeps a high frequency of reporting under the requirement of NER. AER reports on the status of the wholesale electricity market to market participants and the public on a weekly and quarterly basis, which covers the spot market clearing prices, biddings, ancillary services, and wholesale market violation with detailed investigation and analysis. The spot price in NEM is subject to a market price floor limit (−$1000/MWh), and a market price cap ($15,000/MWh), which are reviewed every 4 years to ensure they be in line with the NEM reliability standards and adjusted annually according to changes of the consumer price index. Every presence of extreme price (above $5000/MWh) would be reported, along with further analysis that identifies the factors contributing to the high price. However, there is almost nothing that effectively prevents generators to bid their generation outputs at high prices, as they can change their bids up until the start of the 5-min dispatch [29]. Therefore, the NEM has limited day-ahead visibility of the bids. Although lack of bidding restrictions, AER typically focuses on some form of withholding behaviours of generation companies (e.g. physical withholding or economic withholding) at times of high demand or curtailed supply, which may undermine the effectiveness of competition and market efficiency. A set of market monitor indices based on the "Structure-Conduct-Performance" (SCP) framework is designed to reflect on behaviours of the market participants, as well as the market operation performance [30].
The European Commission has been making significant efforts to develop an integrated European electricity market. After the electricity markets in South Western Europe and North Western Europe were coupled in May 2015, the crossborder electricity flows in EU are optimized and price differences across EU greatly smoothed out [31]. Both United Kingdom and France adopt a bilateral trading market structure. As there is only a small amount of electric power traded through the gross pool, the risk of market power abuse of participants is greatly reduced. Therefore, currently there is no ex-ante market power mitigation mechanism like TPS test in United Kingdom and France [28]. Instead, ex-post punishment for market manipulation by using system constraints or congestions would be imposed, such as financial penalty and license revoking. According to MAD, market manipulation, examples of which include "Fraud-based" behaviours, giving misleading signals, and market power abuse, is strictly prohibited. Another type of behaviour prohibited by MAD is trading on inside information that has not been made public [32]. REMIT has overcome the defects in MAD's inapplicability in electricity market regulation, and adopted a language more specific to the nature of electricity markets. Four key issues are included in REMIT: prohibition on insider trading and market manipulation, obligation on market registration, obligation on information disclosure, and establishment of ACER [23]. The definition of market manipulation within REMIT is essentially the same as that within MAD but more specific, including: (i) creating misleading information about supply, demand, or prices; (ii) intentionally spreading relevant false information; (iii) using misleading information to conduct fraud; (iv) manipulating the price of energy wholesale commodities.
Moreover, in order to promote the wholesale electricity market competition in France and weaken the monopoly position of EDF, Law NOME requires EDF to sell a great amount of nuclear power (25% of EDF's nuclear fleet or a maximum of 100 TWh) to its competitors at a CRE-regulated price every year, allowing French consumers to continue to benefit from the competitiveness of the French nuclear fleet [33].
Main aspects of wholesale electricity market regulation in the United States, Australia, United Kingdom, and France are presented in Table 5.

Retail electricity market regulation
Competition was first introduced into the electricity retail sector in 1990s, separating the supply business of electricity from transmission and distribution service. Since then, consumers have been provided with free choices of their electricity suppliers [40]. With the electricity retail sector open to competition, new requirements for retail electricity market regulation also emerge, including retail electricity market access, information disclosure, last resort supply, credit management, and others. In the United States, electricity retailing regulation is governed at the state level. The state-level PUCs set out policies and regulations of retail electricity markets, which are different among various states, and have jurisdiction over the supply of electricity. The scope of this jurisdiction depends on whether the state adopts retail competition. In states open to electricity retail competition, electricity consumers are able to purchase electricity at market-based prices from competitive suppliers other than a franchised public utility. The state-level PUCs generally do not regulate electricity prices set by competitive suppliers, but license the suppliers and impose other conditions on them instead [41]. The retailing price, terms, and conditions associated with franchised public utilities are still regulated by the state-level PUCs. However, most states in the United States have not yet opened to electricity retail competition. After the California electricity crisis, further efforts on electric power industry restructuring at the retail level in the United States came to a standstill and electricity retail • In the event of a no-deal Brexit, the additional OFGEM certification requirements for transmission and interconnectors will apply to participants who are not from the United Kingdom [38] • Transfers of control need to be notified to the EC before their implementation as the EC has jurisdiction over concentrations with a community dimension

•
The incoming party has to meet the license obligations, and follows a similar vetting process as that for a new applicant [38] • ACER implements prohibition on insider trading and market manipulation, obligation on market registration, and obligation on information disclosure according to REMIT • Transactions do not meet the EC's merger regulation thresholds must be notified and supervised by the FCA [39] • The French Energy Code requires that the French state must hold at least 70% of the capital and voting rights of EDF [32] competition was suspended or rescinded in several states [42]. As of end of 2018, only 16 states and the District of Columbia allowed for electricity retail competition [35]. The retail electricity market in Texas is one of the most successful retail electricity markets in the United States. The Texas PUC approves the revenue requirements of electricity retailing companies, and appraises the electricity prices or rates of various consumers. Information disclosure is jointly enforced by the market operator and state-level regulator. The market operator dynamically updates and discloses market data to the public by employing information from relevant websites and data release platforms, such as market capacity and transaction results, while the statelevel regulator takes responsibility for the market performance analysis and reports. In Australia, the AER has assumed responsibility for regulating retail energy markets in jurisdictions with NECF adopted since July 2012. In terms of retail market access, AER assesses applications for national retailer authorizations from businesses that want to become energy retailers to ensure that the applicants have sufficient technical capacity and financial resources. As for retail price regulation, there are two classes of market customer contracts in Australia, the standing retail contracts and market retail contracts [36]. Standing retail contracts are basic contracts with a regulated contract price for residential and small business customers who do not negotiate a market retail contract. Market retail contracts are negotiated between customers and retailers, the price of which is deregulated and set by the retailer, rather than the regulator. Nevertheless, AER provides a price comparison guide on its website "Energy Made Easy", to provide customers with visibility of costs and charges across different suppliers [43]. By this way, AER aids competitive tension between suppliers to reduce prices in the retail market, instead of setting retail energy price limits. Besides, AER also monitors and enforces compliance with obligations in the retail law and rules, and administers a national retailer of the last resort scheme, which protects customers and the market if a retail business fails.
After four rounds of electricity market reform, full competition was introduced into the retail electricity market in United Kingdom, with domestic and non-domestic consumers able to shop around for their electricity suppliers [44]. However, more than 70% of the electricity supply is still concentrated in the hands of six largest suppliers, also referred to as "the big six" [45]. The role of OFGEM in the retail electricity market mainly includes four aspects: market monitoring, consumer protection, metering, and information disclosure. To promote market compliance, OFGEM monitors a wide range of information on the retail market, including market indices, customer research, supplier cost index, and typical domestic consumption values, and others. OFGEM also controls the retail market access restrictions by setting the conditions on the supplier licenses, ranging from consumer notification obligations to supplier switching processes, so as to protect the rights and interests of consumers. For example, it is clearly stated in a supplier's license that customers should be notified at least 30 days in advance of a supplier's implementation of a rise in price, ensuring that customers have enough time to switch suppliers without liability after receiving the notification [46]. In spite of this, more than half of U.K. households have never switched their suppliers, or only switched once, and are on a more expensive "default" tariff. In 2019, OFGEM introduced retail price caps to further protect those "less active" consumers from unfair price, and set the level of price caps twice a year [47]. Additionally, OFGEM also has regulatory functions in relation to metering, including regulating the rollouts of advanced and smart metering, and certain aspects concerning how network companies charge for metering services. Moreover, OFGEM annually updates a retail market report, detailing commentary on recent trends in the retail electricity markets to increase transparency.
The retail electricity market in France has been fully open to competition since July 2007. Similar to other countries, the sale of electricity is subject to governmental approval in France, and all transactions performed on the French electricity market must be monitored by CRE, regardless of ways of trading. According to the French Energy Code, there are currently two pricing mechanisms in France, the regulated tariff and nonregulated tariff. Consumers can choose to purchase electricity from EDF at government-regulated prices, or from retailers through bilateral negotiation. Since December 2015, the regulated tariff has been limited to small and mainly domestic consumers [32]. Additionally, in order to prevent ordinary users from the inconvenience caused by marketization, Law NOME requires that consumers with subscribed capacity less than 36 kVA be given an opportunity to sign a single contract dealing with both the distribution and supply of electricity, which should last at least for 1 year [39]. Since the electricity sector in France is still dominated by EDF, CRE monitors vertically integrated electricity companies (e.g. companies provide generation and retail service, or distribution and retail service at the same time) to strictly prohibit internal transactions.
Main aspects of retail electricity market regulation in the United States, Australia, United Kingdom, and France are presented in Table 6.

Regulatory approach
In regulation practice, regulatory authorities adopt a variety of policies and analytical tools to detect, deter, and deal with market violations and anti-competitive conducts, ensuring the compliance with the market laws and rules. When classifying various regulatory approaches, a useful distinction is between techniques that are applied ex-ante and those that are applied ex-post. Ex-ante regulatory approaches, such as market rule making, market access restriction, market price cap setting, structural market indices, and bid screening, mainly look for the potential of market violations. Market rule making and market access restriction are common practices around the globe. However, the market barrier is not easy to determine. On the one hand, the market barrier needs to be sufficient low, so that new participants could bring competitive tensions to the incumbents. On the other hand, the market barrier needs to make sure all market participants be well qualified so as to reduce the potential risk. International experience also shows that structural market indices, such as the Herfindahl-Hirschman Index (HHI), market share, pivotal supplier indicator, and residual supply index, perform well in pre-warning market risks. The PJM and CAISO electricity markets in the United States adopt the TPS test as an ex-ante screening approach to prevent the exercise of market power and ensure competitive pricing [28]. If a market participant fails in the TPS test, its offer would be set to the lower of its price-based or cost-based offer. Besides, the Australian NEM adopts a market price cap of AUS$15,000/MWh and a cumulative price threshold of AUS$221,100, which caps the total market price that can occur over seven consecutive days, to protect market from both extreme price fluctuations and sustained high prices [48]. Compared with the audit, investigation, and other ex-post regulatory approaches, ex-ante regulatory approaches have lower cost and higher transparency, and are therefore preferred by market participants. After the market operation day, more market data can be acquired and the market performance can be analysed, providing the regulatory body with more specific measures and evidences of market violations. Ex-post regulatory approaches include market data analysis, company self-report, audit, and investigation. Currently, the United States and Australia both adopt the "Structure-Conduct-Performance (SCP)" framework based on the industrial organization theory for electricity market monitoring and analysis, which analyses the market from three aspects: market structure, market conduct, and market performance. Based on the SCP framework, a series of practical market monitoring indices are developed, including ex-ante and expost indices, as shown in Table 7 [49][50][51].
When gathering information of possible market violations, self-reporting is encouraged by regulators to promote internal regulation. In many cases, self-reported market violations result in closure of the matter without sanctions, and in the cases that do not, the penalties would also reflect mitigation credit for the self-reporting that substantially lowered the amount [35]. In addition, audits are also widely used as a basic way to identify market violations and manipulations. Generally, an audit can be initiated without any information or allegation regarding any specific wrongdoing. The discovery techniques used in an audit typically consist of on-site interviews, conference calls, document reviews, transactional testing, and data requests. In contrast to audits, investigations are usually initiated only when there are reasons to suspect violations, or when the investigation staff received information from self-reporting, internal or external market monitors, or other sources. The necessity of the investigation needs to be evaluated by the investigation staff and officially notified to the investigated company, followed by a complex procedure. In the United States, the initiation of investigations and all related information in the process are nonpublic, unless there are orders of disclosure from FERC [52].
Once market violations are identified, regulatory authorities may take enforcement actions to penalize offending conducts and ensure future compliance with the law. Typical enforcement actions include disgorgement, imposition of compliance plans, license revoking, civil penalties, and criminal prosecution, and others. International experience shows that  Three pivotal suppliers test i -the TPS test score of supplier i; Plargest j -the supply from two largest suppliers.
Ex-ante/ex-post Pivotal supplier index (must-run ratio) i -the must-run ratio of company i; P in -the power import limit of the area. Market price analysis

Residual supply index
• Trend analysis of prices can reveal patterns which might be hidden by day-to-day volatility.
• Frequency of price hitting the market price cap is an indicator of how price might change if the cap is adjusted or removed.
Moving averages or other trend analysis; Volatility measures (average, variance, min-max prices); The identity of the price-setting unit.

Competitive benchmark analysis
• Taking account of the entire market in a refined version of price-cost margin analysis; • Capable of providing quantitative estimate of efficiency and welfare loss by market power abuse. Estimate the market price that would result if all suppliers behave as price-takers; Estimate the marginal cost of production of the marginal supplier by simulating a hypothetical competitive market.

Congestion analysis (transmission congestion index)
• Taking transmission capacity constraints into account, which represent an important issue in market power monitoring and are often overlooked. TCI = C congestion ∕Q system TCI -the transmission congestion index in a given period; C congestion -the total transmission congestion cost in a given period; Q system -the total system electricity energy in a given period.
voluntary future compliance is preferred to resolve minor infractions, rather than penalties. For example, as noted in the staff report of FERC, between 2005 and 2007, enforcement staff closed approximately 75% of FERC's investigations without any sanctions being imposed, even though violations are found in about half of those closed investigations [53]. Additionally, more than half of self-reports submitted to staff were closed with no action. In United Kingdom, OFGEM may take alternative actions to bring a company into compliance when potential breaches are not serious [54]. The alternative actions, such as agreements on a period of reporting, non-statutory undertakings or assurances, independent audit, can be used in lieu of opening an investigation into a potential breach, or as part of closing an investigation. Besides, information disclosure is one of the key points of electricity market regulation in international practices. Regulatory authorities publish market reports and enforcement matters reports on a regular basis, together with the media broadcast; this would directly impact the stock prices and public images of generation companies, which are crucial to their operation [55]. Therefore, information disclosure performs well in enforcing compliance with rules in regulation practices of electricity markets around the globe.

Summary
The contents of electricity market regulations in four developed countries are detailed in Section 3, and are summarized as follows. First, while being similar in some common initiatives, like market access barriers, market monitoring and reporting, regulations of wholesale electricity markets in four developed countries are marked by a series of deep disparities due to differences among various wholesale electricity market mechanisms. Essentially, the wholesale electricity market regulation is highly connected with the market mechanism concerned, which greatly lies on the generation mix of the region. Therefore, it is hard to develop a generally applicable regulation system for various wholesale electricity markets. Certainly, the degree of market competition can be adjusted through a regulatory method, to better fit the innate generation resource of the region. Secondly, the evolvements of retail electricity market liberalization are at different levels in different countries and states, and the variations of regulation priorities and pricing schemes are then manifested. In those regions with fully opened retail competition, the qualification of electricity retailers is under strict review to make sure that they meet specified technical and financial requirements. Credit assessment and deposit are also required to control the risk of retailer failure. During the market operation, information disclosure has become an effective way to promote competition among electricity retailers so as to benefit consumers. For those consumers who do not want to engage in a market competition, the regulations on electricity retailers concerning the last resort scheme and selectable regulated price schemes are taken seriously to protect their interests from unreasonable prices.
Thirdly, with the development of the theoretical basis of electricity market regulation, many regulatory approaches and market indices are proposed, and more market conditions are taken into account in regulation practices. Besides, the way of information gathering has been greatly widened but selfreporting and voluntary compliance are still most encouraged to reduce the cost of regulation. When taking enforcements to penalize market violations, the self-reporting and voluntary alternative actions would reflect in a reduction of penalty.

DEVELOPMENT TRENDS IN ELECTRICITY MARKET REGULATION
Generally, electricity market regulation needs to keep pace with the evolvement of the market mechanism, which is ultimately reflected by energy transition and the change of generation mix in the country concerned. Market regulation can be used, to some extent, to guide the direction of market development. In recent years, climate change, emission reduction, renewable energy generation development, and power supply reliability have become common concerns in developed countries with mature electricity markets, and a number of energy policies have been proposed to cope with the global energy shortage and ever-increasing emission of greenhouse gases.

Climate change and emission reduction targets
The global energy consumption in 2018 increased at nearly twice the average rate of growth since 2010, and thereby an annual average rise of CO 2 emission of 1.7% was observed [56]. As global concerns for climate change increase, governments in some countries have set up emission reduction targets for their energy industries in order to limit rising global temperature and reduce man-made CO 2 emission. However, since the United States announced its withdrawal from the Paris Agreement in 2017, further efforts on emission reduction at the federal level came to a standstill, and states in the United States are expected to lead the way on renewable energy use and emission reduction by responding with their own policies. Many states have implemented legally binding carbon pricing mechanisms, and are pursuing decarbonisation targets for 2030 and beyond by supporting zero-carbon technologies through a wide range of regulatory and market-based instruments. In Australia, the government aims for 23.5% (equivalent to 33,000 GWh) of electricity to be generated by renewable sources by 2020. Meanwhile, a number of large coal-fired power stations have been closed or announced to be closed in Australia, including the closure of the 546 MW Northern power station in 2016, and the closure of the 1760 MW Hazelwood power station in early 2017; the 2000 MW Liddell power station is expected to be closed in 2022 [43]. In European Union, Directive 2009/28/EC on the promotion of renewable energy and biofuel generation sets out EU-wide targets that at least 20% of the EU's overall energy consumption (electricity, heat, and transport fuels) come from renewable sources by 2020. The EU target for renewables is broken down into individual national targets. Accordingly, United Kingdom is Emission reduction targets and renewable energy accommodation targets of the developed countries mentioned above are shown in Table 8.
To counter the problems above, some recommendations are proposed: (i) accelerating efforts to develop and deploy carbon capture and storage (CCS) technologies; (ii) promoting the use of electric vehicles and development of an accessible national/regional charging network; (iii) guiding energy transition with an emission reduction target and related mechanisms to provide a market signal for older and less efficient power plants to retire and a stable outlook for long-term investment in efficient energy technologies.

Integration of renewable energy generation in the electricity market
Driven by reduced costs and policy supports, renewable energy generation technology has advanced significantly over the last decade. Integrating a high share of intermittent renewable energy generation, such as wind and solar power generation, in an electric power system and an electricity market is essential for transition to a less carbon-intensive and more sustainable energy system. However, the variability, uncertainty, intermittency, and location-dependence of renewable energy generation often cause extra operational costs in the concerned power system to accommodate renewable generation, and hence it is difficult for renewable energy generators to directly participate in electricity market competition. Ideally, a well-designed electricity market can help integrate renewables and drive technological innovation, but the existing electricity market rules are largely tailored to traditional power plants. The prevailing supporting schemes, such as the dispatch priority and feed-intariff (FiT), typically create market distortions and ignore the negative impacts on system operation. Therefore, market-based supporting policies and financial mechanisms that expose renewables to market price signals are adopted by regulatory bodies to comprehensively correct systemic lag between electricity market operation and ever-increasing penetration of renewable generation.
In the United States, the prevailing policy tool at the federal level for incentivizing the accommodation of renewable energy generation is the so-called federal tax credits, including production tax credit and investment tax credit [41], which can be used to offset income tax obligations for households and companies. At the state level, the renewable portfolio standards (RPS) are widely adopted, requiring retail electricity providers to source a certain share of supply from qualified renewable sources [57]. Though the RPS policy is not in place at the federal level, but is adopted by 29 states and the District of Columbia (voluntary targets are employed in eight states), and acts as an important driver of renewable energy technology deployment in the United States. In addition to RPS, many U.S. states have adopted the net metering mechanism, which permits residential and commercial end users with their own renewable power generation to sell surplus electricity back to the power grid.
In Australia, renewable energy generation in the electricity sector is supported by policies at both commonwealth and state levels. The quota system, similar as the RPS in the United States, serves as the incentive for renewable energy generation at the commonwealth level, sets a minimum medium-term target for renewable energy generation; this target is expected to attain via the established tradable certificates. The certificates are issued for each eligible MWh of electricity produced by an accredited renewable power generator, and can be sold to obligated entities who have to surrender their certificates annually to the Clean Energy Regulator so as to demonstrate their compliance with the annual renewable energy targets. State and territory policies aim to reach targets which may or may not be aligned with the commonwealth targets and policies. Most Australian states have FiT schemes, which provide owners of small renewable energy systems with guaranteed fixed rates for the sale of electricity fed into the power grid. However, a nationally mandated FiT mechanism is not available.
Similar financial mechanisms supporting renewable energy generation are adopted in United Kingdom as well, known as the renewable obligation (RO), introduced in 2002, placing an obligation on electricity suppliers to source an increasing proportion of electricity from renewables. However, the RO scheme is recently being replaced by the contract for difference (CfD) scheme, which is now the main mechanism of supporting new large-scale renewable energy generation projects. CfDs are long-term contracts which could be used between a government-owned counterparty and low carbon generators such as renewables, nuclear, and carbon capture and storage (CCS) equipped plants. Generation companies holding CfDs are guaranteed a certain selling price throughout the contract mechanism, hence the income predictability can be improved, and the capital cost of a new renewable energy project reduced. CfD payments are raised through a levy on all electricity suppliers in United Kingdom, who pass these costs on to consumers. In this way, the additional cost of renewable electricity is spread over the entire electricity market. The French government encourages the development of renewable energy generation through two schemes: the FiT and the market premium. Under the FiT scheme, all electricity generated by renewable energy is bought by EDF, who is compelled to do so due to a public service obligation, at a price over the market price. The price premium will further be passed to final electricity consumers. Since the enforcement of the Energy Transition Act from 17 August 2015, FiT contracts have become exceptional, and the present main support mechanism is the market premium [58]. The monthly or annual market premium, depending on technology, is calculated as the difference between the reference value of technology and average revenues of all installations of the same technology from the French energy and capacity markets, augmented by a management premium covering the cost of market access. As a result, the market premium allows generators to receive market signals, and generators who meet the market needs better earn higher revenues.
Traditional supporting schemes for renewable energy generation are gradually replaced by more market-compatible ones, in order to minimize market distortions. Supporting policies of renewable energy generation in the four developed countries are summarized in Table 9.
To counter the problems above, some recommendations are proposed: (i) refining ancillary service markets and extending the scope of ancillary services to ensure system security, especially during periods of high wind and photovoltaic generation; (ii) ensuring timely decisions on renewable energy generation support schemes to address the need for transparency, longterm predictability, and certainty to gain investors' confidence; (iii) expanding opportunities for renewable energy in heating and cooling, industry, and transportation.

Security and adequacy of power supply
Facing with rising extreme weather events, a growing share of renewable energy generation, and retirements of old coalfired and nuclear power plants, many countries are seeking their ways to ensure the security and adequacy of power supply.
In the United States, the growth of natural gas and renewables at the expense of coal and nuclear generation is raising new concerns about potential impacts on power system reliability and resilience. A federal proposal was submitted by DOE in September 2017, urging FERC to develop cost recovery mechanisms for baseload power plants, such as coal-fired and nuclear power plants. The proposal also called for compensation mechanisms for baseload power plants that have 90 days of fuel supply on-site. However, in January 2018, an order issued by FERC terminated the proceeding to address the proposed rule and initiated a new proceeding to evaluate the resilience of a bulk power system in the footprints of the RTOs and ISOs, which remains pending. At the state level, capacity markets are adopted in electricity markets where the RTO/ISO is responsible for resource adequacy (i.e. ISO-NE, PJM, and NYISO), to ensure adequate supply reserves. Capacity markets seek to ensure adequate generation capacity reserves in the near future, from 1 month (MISO) to 3 years (PJM and ISO-NE), in a marketbased way. In electricity markets that do not operate a capacity market, like ERCOT, a scarcity pricing mechanism is adopted, which permits extreme high price during periods of tight supply and hence significantly increases payments to generators, providing incentives for both generation investment and active participation by demand bidding [59]. Scarcity price can be adjusted either by bids and offers of market participants, or by the operating reserve demand curve set by market operators or regulators [15]. Besides, in 2018, NERC, who is responsible for conducting assessments and reporting on the overall reliability and adequacy of the power system, started a 2-year special reliability assessment of risks facing the electric power system due to a changing generation mix.
In Australia, electric power system security and reliability have received considerable public and political attention since a state-wide blackout in South Australia in 2016 and the load disconnections during a country-wide heat wave in 2017 happened. Government and regulatory authorities are currently focusing on ensuring continued energy security and reliability in light of refurbishment of ageing infrastructure, rising peak demand and stronger participation of renewable energy resources. For instance, to avoid electricity price increase following unexpected generator closures, AEMC implemented a rule change requiring large generators to notice the market operator at least 3 years before closing [9]. However, the electricity market is still facing considerable uncertainty about future policy, particularly around emissions reduction from the power sector after 2020, which has increased risk premiums for investments of new generating facilities and made capital-intensive projects less attractive. To attract new investments for ensuring the implementation of the emissions reduction target and power system reliability, a scarcity pricing mechanism is also adopted in Australia. Meanwhile, in order to prevent generators from gaining extra revenue, their bids are capped at $300/MWh when the frequency of scarcity price exceeds a certain threshold. Additionally, the retailer reliability obligation (RRO), commenced on 1 July 2019, supports power system reliability in the NEM by incentivizing retailers and large energy users to contract or invest in dispatchable and "on demand" resources. The RRO will be triggered when AEMO identifies a potential reliability gap in NEM regions 3 years and 3 months out of 5 years, then liable entities are on notice to enter into sufficient qualifying contracts to cover their shares of a peak demand [60].
In United Kingdom, about 21% of the existing generation capacity is due to close in the next decade as a result of the scheduled decommissioning and European environmental regulations [61]. Since the electricity capacity margin is tightening, power system security has been a priority for the government. To manage the low margin, OFGEM approved the supplemental balancing reserve (SBR) and demand side balancing reserve (DSBR) in 2013 as extra tools for the National Grid company to help balance the supply and demand in the power system in case of need. SBR and DSBR allow the National Grid company to contract with generators and other balancing service providers to provide additional balancing services outside the normal operation of the market, which could effectively reduce risks to the security of electricity supply. Moreover, United Kingdom's first capacity market auction was held in December 2014, with all types of capacity able to participate (except for capacity providers already in receipt of support from other policy measures, such as renewable energy generation). The main objective of the capacity market is to ensure adequacy of electricity supply and close the anticipated supply gap resulted from large-scale retirements of old coal-fired and nuclear power plants.
On 31 January 2020, United Kingdom formally left the European Union (a process known as "Brexit"), and started an 11month transition period. During the period, the electricity market in United Kingdom remains coupled with those of the EU, with relevant EU legislations governing their operation. The U.K. government is working to reach a free trade agreement with the EU, which will come into effect following the transition period. If the free trade agreement negotiation fails, energy suppliers in United Kingdom may have to pay huge taxes for the cross-border electricity transmission. Besides, the impacts of Brexit on the energy market and the rules applicable in United Kingdom may undermine investments on cross-border transmission networks and open trades.
The French electricity generation mix has a low diversity and high baseload thanks to the dominance of nuclear power (78%) and hydropower (10%) in the mix [32]. Despite having a largely decarbonized power generation, there are a number of worries related to power system adequacy, such as ageing nuclear power plants with requirements for shut-downs, lower water availability in dry years, reduced flexibility from thermal power plants following the closure of oil-and coal-fired power plants, and decreasing peak-demand response capacity in recent years. These impacts are only partially offset by increasing shares of variable renewable generation. To address this situation, a capacity obligation mechanism is proposed, requiring suppliers to obtain sufficient capacity guarantees to cover the consumption of all of their customers during peak demand periods. Subsequently, a capacity guarantees market is established and started in December 2016, to provide market participants incentives of developing demand side management capacity [62], which is helpful to reverse the decline in demand response capacity. Capacity guarantees can be obtained by investing in generating facilities or demand side response capacities, or by acquiring them from other generation companies or demand side response providers.
To counter the problems above, some recommendations are proposed: (i) requiring power plants to provide required advance notice of their intention to close; (ii) developing workable generation capacity adequacy mechanisms to address the need of stranded cost recovery for new generation entries; (iii) providing market operators with more power to intervene in the market more timely so as to ensure system security in case of need.

Progress of electricity market reform in China
As one of the largest economies in the world, China is deeply embedded in the global energy value chain. Consequently, the electricity market reform in China has received considerable global attentions. In 2015, the State Council of China issued "The Opinions regarding Further Reform of the Electric Power Regime (The Opinion)" and related supporting documents, covering almost every detail of the electricity sector, and initiated a new round of electricity market reform in China [63]. Up to 2017, a great progress had been made with transmission tariffs of all provinces examined, the medium and long-term electricity market liberalized, and electricity prices reduced. However, without the spot market and real-time pricing mechanism, the real-time value of the electricity is not properly revealed, and demand response not well motivated. Besides, the reduction of electricity price was largely owing to excess generating capacity and administrative intervention. Generally, the electricity market in China is far from competitive and efficient, which has already been noticed by the Chinese government. In 2017, eight provinces in China, including Guangdong and Zhejiang, pioneered the establishment of electricity spot markets. With eight electricity spot markets entering into trial operations in 2019, China is undergoing a critical period of electricity market reform.
During the electricity market reform, electricity market regulation needs to keep pace with the market evolvement. New requirements have been put forward in The Opinion and its supporting documents, such as improving electric power industry regulatory framework, innovating regulatory strategy, promoting electricity market competition. Compared with developed countries, electricity market regulation in China is also facing a number of peculiar Chinese challenges. First, China is a developing country with a steady economic growth. Stable and adequate energy supply is the foundation of economic development, hence the security and adequacy of the electric power system are the top priorities that the regulatory body needs to address, and radical market reform strategies would not be adopted for the sake of economic stability. Secondly, during the transition period to marketization, both market competition and national monopoly exist in the electric power industry at the same time, bringing more restrictions on the market mechanism design and market regulation. Thirdly, since the electricity supply and electricity market establishment are mainly administered at the province level, electricity market designs can be different among various provinces, and hence electricity market regulation needs to be customized as well. Finally, the electric power industry in China involves a great number of stakeholders, including governmental authorities that used to heavily regulate the energy sector, dominant state-owned enterprises, and private companies that are trying to catch up the market opportunities, presenting additional obstacles to the electricity market regulation in China.

5.2
Status and drawbacks of electricity market regulation in China

Regulatory authority
The Opinion and its supporting documents detailed the functions of regulatory authorities in China. The National Development and Reform Commission (NDRC) and the National Energy Administration (NEA) are in charge of the electricity market reform in China. The NEA, along with provincial governments, take the responsibility of electricity market regulation in provinces, including market power control, anti-market manipulation, promoting market efficiency, and ensuring a nondiscriminatory access to electricity transmission networks. Since both NDRC and NEA are governmental bodies, the electric power industry regulatory functions in China are fully integrated into the government. In the short term, such a regulatory framework can streamline the regulatory institutions; this is in line with the features of the power industry restructuring in China and is helpful for achieving the consistency among various energy policies. However, the electricity market regulation heavily relies on the government under such a regulatory framework, which not only increases the workload of the government, but also leads to the absence of social supervision over the electric power industry. The absence of a third-party • Quality control and technical standards setting in electric power industry regulation may result in the excessive reliance on administrative orders or approvals in the regulation practices, and rulebased regulation is hard to implement; this is likely to reduce the transparency of regulation, and undermines restrictions on regulatory power, which would make the regulatory system outgrown and outmanoeuvred by the institutions and markets it was responsible for regulating and constraining in the long run.

Allocation of regulatory functions
The electric power industry regulatory framework in China is based on the collaboration among various governmental bodies, including NDRC and NEA, as detailed in Table 10. Inappropriate allocations of regulatory functions are likely to cause conflicts among regulatory bodies. As detailed in Table 10, the regulatory functions of the electric power industry are allocated among a number of governmental bodies, and quite complex issues can be involved. When facing with complicated tasks that call for cooperation among regulatory bodies, the process of enforcement would be problematic and may bring considerable coordination costs. Moreover, the involvement of too many regulatory bodies is likely to cause duplication or absence in some aspects of the regulation. For instance, the economic regulation conducted by NEA may be overlapped or conflicting with the state-owned assets regulation enforced by State-owned Assets Supervision and Administration Commission. The overlap or absence of regulatory functions may result in buck-passing or low efficiency in regulation practices. In addition, the vested interest of various regulatory authorities is also one of the obstacles to the market competition and market reform.

Laws and regulations
The laws and regulations for electricity market regulation in China are imperfect. In international practices, the establishment and functions of an electric power industry regulatory authority are granted by the laws promulgated by national legislative bodies, such as the Federal Power Act of America and the Electricity Act of United Kingdom. However, the prevailing Electric Power Law in China does not clarify the scope of functions of regulatory authorities, making the law less applicable. The Electric Power Regulations, as the top administrative electricity market regulations in China, were released in 2005, and only issues related to the unilateral electricity market in the previous round of electricity market reform are covered [64]. Facing with new market participants (e.g. power exchanges, electricity retailers), the scope of the regulations needs to be revised to meet the need of the electricity spot market regulation. Without legislative authorizations on the regulatory power, it is difficult to guarantee the independence and authority of the regulators. Improvements have been made since 2015, with NEA's release of "Letter on Soliciting Opinions on the Implementation of Electricity Market Regulations (Trial)", which covers issues related to electricity spot market competition, so as to enhance the independence of the market regulator. Moreover, the abuse of market power is not covered in the existing legislative framework in China, making it almost impossible to hinder dominant generation companies from executing market power.

Regulatory approaches
The electric power industry in China is undergoing a transition to the marketization, but most of regulations and regulatory approaches remain only suitable for the traditional vertical integrated electric power industry, with the priority on medium and long-term electricity transactions. However, after the introduction of spot market competition, more electric power will be traded by market competition either through centralized auctions or bilateral trading. Compared with conventional regulatory approaches, such as on-site inspection, document review, or administrative order, the marketization requires a change of the regulatory approach from the administrative management to a rule-based regulation, making regulating activities supplementary to the market rules. The market independence and market transparency should be protected and regulatory approaches need to be more advanced, preventive, and off-site.

Revising the allocation of regulatory functions
During the new round of the electric power regime reform in China, it is vital to learn from international experience in the allocation of regulatory functions, remove the overlap and/or identify the absence of regulation, and achieve the consistency of economic regulation and social responsibility regulation in the electric power industry. After the electricity market is fully developed in the future, an independent third-party regulator should be introduced into the regulatory system as a supplementary to the government regulation. Meanwhile, there is an urgent need to revise the Electric Power Law or release new laws related to electricity market regulation, so as to establish a comprehensive legislative framework covering market participants, market operators, power exchanges and regulators, so as to provide legal guarantees on the authority and function of regulators.

Setting regulations suitable for the electricity spot market competition in China
The ever-increasing demand for electric power, coupled with the coexistence of market competition and national monopoly, makes the electricity market regulation in China quite different from that in developed countries. In the long term, incentives on investments and generation efficiency should be considered to ensure a sustainable development of the electric power industry. In the short term, regulations need to be compatible with the process of economic and social development in China, as well as the process of electricity market evolvement, so as to achieve a smooth transition to the electricity spot market. Compared with the traditional electric power industry regulation, market regulation needs to minimize the intervention of administrative orders and address issues in a market-based way as much as possible. The focus of the regulation should be shifted on areas prone to market failures, such as market power abuse, antimarket manipulation, and excessive emission. Due to the dominance of the five generation group companies in China, market rules for mitigating potential market power abuse need to be developed before corresponding laws and regulations come into being. Additionally, targeted market regulation needs to be carried out according to the market designs in different provinces of China, with customized market rules and standards set to improve the effectiveness of electricity market regulation.

Credit management
The ever-increasing number of market participants, increasing frequency of electricity transactions, as well as imperfect market rules, have exposed market operators and participants to a high level of financial risks, making the credit management even more urgent in the market environment. An effective credit management mechanism can promote market rule compliance, reduce the cost of regulation, and contribute to successful electricity market reform. As required by The Opinion, a credit rating mechanism will be established to assess and record the credit of each market participant regarding the participation in the market and compliance with market rules. A unified national credit management system should be built to log market violations and related individuals, so as to provide evidences for credit rating and market access restrictions.

Developing practical regulatory instruments
With the evolution of electricity market reform in China, the scope of market regulation has been gradually expanded, and the difficulty associated increased as well. Since the commonly used on-site investigation in the regulation practice cannot meet the requirement of real-time regulation in the electricity spot market, the lack of regulatory technology and regulatory instruments has become a critical issue for regulators to address. It is necessary to develop practical regulatory instruments that cover the entire cycle of market operation. Ex-ante tools, like market indices setting, structural market power detection, and market access restriction, can prevent the potential market violation to some extent. Real-time market monitoring can identify market anomalies, and proper actions can be taken to remedy the market violations. Ex-post tools, such as information disclosure and net revenue benchmark analysis, look for the actual exercise of market violations, provide regulators with specific evidences to take enforcement actions, and hence promote future compliance with market rules. Moreover, the rapid development of information technology has greatly changed the way of information exchange, making off-site regulation much more practical than ever. For example, an online market information platform connecting market participants, market operator, and power exchange can integrate market operation data into a single system, and in this way the timeliness, integrity, and authenticity of the information can be significantly improved. Advanced technologies, such as big data, artificial intelligence, and emerging cloud/edge computing, can also be applied in electricity market regulation in the future.

CONCLUDING REMARKS
To help researchers have an overall understanding of existing policies of electricity market regulation, detailed comparisons of state-of-the-art electricity market regulations in four developed countries with widely recognized electricity markets are presented and discussed here. Some key elements of electricity market regulation, including the regulatory authority, legislative framework, wholesale market regulation, retail market regulation, and regulatory approaches, are systematically addressed and compared.
The comparisons show that the marketization process of the electricity sector is usually driven by legislations rather than administrative orders, and regulatory bodies of mature electricity markets are all given with legislative guarantees on their authority and scope of functions. Therefore, their decisionmaking process can be independent from stakeholders, and their regulatory power is granted and also restricted. Among the developed countries concerned, the contents of wholesale electricity market regulation are marked by a series of deep disparities due to differences among market mechanisms. Although it is hard to find a universal regulatory method for wholesale market regulation, the developed countries concerned have found their own ways in enforcing wholesale market compliance. Regarding electricity retailing, the evolvements of retail electricity market liberalization are at different levels in different countries and states, and the variations of regulation priorities and pricing schemes are then manifested. In those regions with retail electricity competition, retail market access, credit management, last resort supply scheme, and the regulated default price scheme, are the focuses of regulation. To enforce regulations, multiple regulatory approaches are developed, with the entire cycle of market operation covered. Compared with audit, investigation and other ex-post regulatory approaches, ex-ante regulatory approaches have lower cost and higher transparency, and are therefore preferred by market participants.
Nevertheless, the evolving generation mix and electricity market mechanism have imposed new requirements for market regulation. Certain aspects of up-to-date energy policies are surveyed to reveal the latest concerns regarding electricity market regulation, including emission reduction, renewable energy generation integration, security and adequacy of electricity supply, and recommendations on counter measures provided.
Finally, the status of the electric power regime reform and electricity market regulation in China is presented, with existing drawbacks stated, typically on regulatory function allocations, legislative guarantee, and regulatory approaches. Based on comparisons and analysis, the future electricity market regulation in China is prospected.