A Review of Clean Electricity Policies—From Countries to Utilities

: Due to the heavy stress on environmental deterioration and the excessive consumption of fossil resources, the transition of global energy from fossil fuel energy to clean energy has signiﬁcantly accelerated in recent years. The power industry and policymakers in almost all countries are focusing on clean energy development. Thanks to progressive clean energy policies, signiﬁcant progress in clean energy integration and greenhouse gas reduction has been achieved around the world. However, due to the di ﬀ erences in economic structures, clean energy distributions, and development models, clean energy policy scope, focus, and coverage vary between di ﬀ erent countries, states, and utilities. This paper aims at providing a policy review for readers to easily obtain clean energy policy information on various clean energies in the U.S. and some other countries. Firstly, this paper reviews and compares some countries’ clean energy policies on electricity. Then, taking the U.S. as an example, this paper introduces the clean energy policies of some representative states and utilities in the U.S in perspectives of renewable energies, electric vehicles, and energy storage. coherent national These results indicate that these clean energy policies are not guaranteed to be accomplished by the countries like most people thought, further suggesting that the practice and implementation of these clean energy policies need coordination from various levels of governments and electric power companies. In the next section, taking the U.S. as an example, the recent clean energy policies in representative states and utilities of the U.S are presented to show how to concretely implement nationwide clean energy policies to power providers and consumers.


Introduction
In the recent decade, various types of clean energy witness continuously growing shares in the electricity generation mix [1,2]. With the increase in clean energy penetration and the retirement of conventional fossil fuel plants, clean energies are expected to provide almost 50% of total electricity globally by 2050 [3].
To realize the ambitious objective of the energy shifting from fossil fuels towards clean energy technologies, nearly all utilities and countries worldwide have formulated renewable energy development goals and supporting policies [4][5][6][7]. Due to the trend of using electricity as the major form of energy delivery, the electric grid has been the focus of clean energy policies in recent years. With the decrease in power equipment investment costs, these renewable energy policies are helping to increase clean energy penetration in electric grids. In the Nationally Determined Contributions (NDCs), which was submitted by 181 countries under the United Nations Framework Convention on Climate Change, approximately 3/4 of NDCs particularly pointed out that renewables can be used for mitigating climate change, and more than 50% of them have set up clean energy goals. Some countries and many more utilities have also set aggressive targets at 100% electricity from clean energy [8].

Germany
Up to the end of the first half of 2020, the energy mix of Germany is shown in Figure 3 [22]. In 2016, the Climate Action Plan (CAP) 2050 was announced by the Germany government, in order to set a long-term pathway for reducing the greenhouse gas emission of utilities and emissions industries [23]. set a long-term pathway for reducing the greenhouse gas emission of utilities and emissions industries [23].
In the CAP 2050, the targets of greenhouse gas emission reduction are to achieve a 40% cut by 2020, 55% cut by 2030, 70% cut by 2040, and 80-95% cut by 2050. To reach the target for 2020, the federal government of Germany proposed a plan to realize 65% generation from clean energy sources by 2030 and requires an increase in the wind and solar capacity from 120 to 215-237GW. To achieve the CAP 2050, four sub-targets have been set as shown in Figure 4 [24][25][26][27][28].   In the CAP 2050, the targets of greenhouse gas emission reduction are to achieve a 40% cut by 2020, 55% cut by 2030, 70% cut by 2040, and 80-95% cut by 2050. To reach the target for 2020, the federal government of Germany proposed a plan to realize 65% generation from clean energy sources by 2030 and requires an increase in the wind and solar capacity from 120 to 215-237GW. To achieve the CAP 2050, four sub-targets have been set as shown in Figure 4 [24][25][26][27][28].
Up to the end of the first half of 2020, the energy mix of Germany is shown in Figure 3 [22]. In 2016, the Climate Action Plan (CAP) 2050 was announced by the Germany government, in order to set a long-term pathway for reducing the greenhouse gas emission of utilities and emissions industries [23].
In the CAP 2050, the targets of greenhouse gas emission reduction are to achieve a 40% cut by 2020, 55% cut by 2030, 70% cut by 2040, and 80-95% cut by 2050. To reach the target for 2020, the federal government of Germany proposed a plan to realize 65% generation from clean energy sources by 2030 and requires an increase in the wind and solar capacity from 120 to 215-237GW. To achieve the CAP 2050, four sub-targets have been set as shown in Figure 4 [24][25][26][27][28].

Denmark
In 2018, the government of Denmark announced an energy agreement to fulfill the target set by the government that makes Denmark independent of coal fuels by 2050 and transformed into a low-carbon society. The funding has been allocated to achieve 55% of the total energy needs of Denmark from clean energy. Some highlights of the Denmark energy agreement are shown in Figure 5 [29].

Denmark
In 2018, the government of Denmark announced an energy agreement to fulfill the target set by the government that makes Denmark independent of coal fuels by 2050 and transformed into a lowcarbon society. The funding has been allocated to achieve 55% of the total energy needs of Denmark from clean energy. Some highlights of the Denmark energy agreement are shown in Figure 5 [29]. To achieve the energy agreement of Denmark, three sub-targets have been set as shown in Figure  6 [30][31][32].

Australia
The energy mix of Australia in 2020 is shown in Figure 7 [33]. The federal government of Australia announced a Mandatory Renewable Energy Target (MRET) in 2001, in order to increase the new 9500 GWh clean energy generation until 2020 [34]. In recent years, the federal government of Australia updated its MRET to make sure at least 33,000 GWh of electricity is from clean energy To achieve the energy agreement of Denmark, three sub-targets have been set as shown in Figure 6 [30][31][32].
In 2018, the government of Denmark announced an energy agreement to fulfill the target set by the government that makes Denmark independent of coal fuels by 2050 and transformed into a lowcarbon society. The funding has been allocated to achieve 55% of the total energy needs of Denmark from clean energy. Some highlights of the Denmark energy agreement are shown in Figure 5 [29]. To achieve the energy agreement of Denmark, three sub-targets have been set as shown in Figure  6 [30][31][32].

Australia
The energy mix of Australia in 2020 is shown in Figure 7 [33]. The federal government of Australia announced a Mandatory Renewable Energy Target (MRET) in 2001, in order to increase the new 9500 GWh clean energy generation until 2020 [34]. In recent years, the federal government of Australia updated its MRET to make sure at least 33,000 GWh of electricity is from clean energy

Australia
The energy mix of Australia in 2020 is shown in Figure 7 [33]. The federal government of Australia announced a Mandatory Renewable Energy Target (MRET) in 2001, in order to increase the new 9500 GWh clean energy generation until 2020 [34]. In recent years, the federal government of Australia updated its MRET to make sure at least 33,000 GWh of electricity is from clean energy generation at the end of 2020. In the updated MRET, about 50 percent clean energy by 2030 and 75 percent clean energy by 2040 must be ensured by utilities and electric providers [35,36]. To realize the MRET, some clean energy policies have been put forward as shown in Figure 8 [37][38][39][40]. generation at the end of 2020. In the updated MRET, about 50 percent clean energy by 2030 and 75 percent clean energy by 2040 must be ensured by utilities and electric providers [35,36]. To realize the MRET, some clean energy policies have been put forward as shown in Figure 8 [37][38][39][40].

China
The energy mix of China by the end of 2019 is shown in Figure 9  Law", some incentive policies, such as the subsidy to feed-in tariffs of renewable energies, the tax deduction for both renewable energies generators and consumers, and the priority natural resource supply for renewable energies infrastructure installation, have been structured to encourage clean

China
The energy mix of China by the end of 2019 is shown in Figure 9  Law", some incentive policies, such as the subsidy to feed-in tariffs of renewable energies, the tax deduction for both renewable energies generators and consumers, and the priority natural resource supply for renewable energies infrastructure installation, have been structured to encourage clean

China
The energy mix of China by the end of 2019 is shown in Figure 9  Promotion Law", some incentive policies, such as the subsidy to feed-in tariffs of renewable energies, the tax deduction for both renewable energies generators and consumers, and the priority natural resource supply for renewable energies infrastructure installation, have been structured to encourage clean energy development and stimulate the market for providing more opportunities to clean energy providers [42,43]. Under the booming of clean energy in China, in 2014, the International Renewable Energy Agency (IRENA) published a report called "Roadmap 2030-A Renewable Energy Roadmap for China" [44,45]. The report indicates that the proportion of clean energy could be up to 35 percent by 2030, which will make China become the largest clean energy user, about 20 percent of global clean energy. The planned development pathways of wind, solar, electric vehicles, and energy storage in China are summarized in Figure 10 [46][47][48][49].  45]. The report indicates that the proportion of clean energy could be up to 35 percent by 2030, which will make China become the largest clean energy user, about 20 percent of global clean energy. The planned development pathways of wind, solar, electric vehicles, and energy storage in China are summarized in Figure 10 [46][47][48][49].

India
The energy mix of India by the end of 2019 is shown in Figure 11 [50]. As one of the biggest countries in the world, India has more than 1.3 billion people, and it also has a vast economy and a huge military. For maintaining the normal operation of this huge country, India's energy requirement is large and increasing rapidly. In 2018, the primary energy consumption of India reached 809.2 million tons of oil equivalent in 2018, which made it become the third-largest energy consumer

India
The energy mix of India by the end of 2019 is shown in Figure 11 [50]. As one of the biggest countries in the world, India has more than 1.3 billion people, and it also has a vast economy and a huge military. For maintaining the normal operation of this huge country, India's energy requirement is large and increasing rapidly. In 2018, the primary energy consumption of India reached 809.2 million tons of oil equivalent in 2018, which made it become the third-largest energy consumer

India
The energy mix of India by the end of 2019 is shown in Figure 11 [50]. As one of the biggest countries in the world, India has more than 1.3 billion people, and it also has a vast economy and a huge military. For maintaining the normal operation of this huge country, India's energy requirement is large and increasing rapidly. In 2018, the primary energy consumption of India reached 809.2 million tons of oil equivalent in 2018, which made it become the third-largest energy consumer country that is only behind China and the U.S. For keeping energy and sustainable development, India has set aggressive targets to realize an energy transition. The Indian government has set a target to realize 175GW of clean energy capacity by the end of 2022 [51][52][53]. The planned development pathways of wind, solar, and energy storage in India are summarized in Figure 12 [54][55][56].
Sustainability 2020, 12, x FOR PEER REVIEW 8 of 22 country that is only behind China and the U.S. For keeping energy and sustainable development, India has set aggressive targets to realize an energy transition. The Indian government has set a target to realize 175GW of clean energy capacity by the end of 2022 [51][52][53]. The planned development pathways of wind, solar, and energy storage in India are summarized in Figure 12 [54][55][56].    country that is only behind China and the U.S. For keeping energy and sustainable development, India has set aggressive targets to realize an energy transition. The Indian government has set a target to realize 175GW of clean energy capacity by the end of 2022 [51][52][53]. The planned development pathways of wind, solar, and energy storage in India are summarized in Figure 12 [54][55][56].     Figure 13 summarizes the clean energy policies in these countries. As given in Figure 13, the difference between the countries on their enacting clean energy policies is enormous due to the different existing constraints, the variety of clean energy types, and the diversity of economic and social development degrees, which further leads to a strategy difference for implementing planned scenarios, such as Denmark focusing on the development of the wind power to realize its clean energy target. The reason that Denmark adopts wind power as its mainstay of renewable energies is determined by its natural energy resource distribution as Denmark has abundant offshore wind energy. Similarly, the social recognition degree is also an important factor for specific clean energy development in one country. As shown in Figure 13, solar power developing in Germany is much more prompt than in other countries (98 GW by 2030, which is almost 30 times of Denmark), because the German public prefers distributed PV panels installed on their roof. The recognition of Sustainability 2020, 12, 7946 9 of 22 solar power by the public greatly facilitates the installation solar power in Germany and the maturity of solar energy-related industries also prompts the clean energy policies in Germany partially to solar power. In addition, from Figure 13, it could be seen that the policies for EV promotion in all countries mentioned in this paper are aggressive and ambitious, because of the stern requirement of carbon dioxide emissions reductions. In the meantime, these policies also indicate that the EV-related industries will meet great opportunities in the future. As given in Figure 13, the difference between the countries on their enacting clean energy policies is enormous due to the different existing constraints, the variety of clean energy types, and the diversity of economic and social development degrees, which further leads to a strategy difference for implementing planned scenarios, such as Denmark focusing on the development of the wind power to realize its clean energy target. The reason that Denmark adopts wind power as its mainstay of renewable energies is determined by its natural energy resource distribution as Denmark has abundant offshore wind energy. Similarly, the social recognition degree is also an important factor for specific clean energy development in one country. As shown in Figure 13, solar power developing in Germany is much more prompt than in other countries (98 GW by 2030, which is almost 30 times of Denmark), because the German public prefers distributed PV panels installed on their roof. The recognition of solar power by the public greatly facilitates the installation solar power in Germany and the maturity of solar energy-related industries also prompts the clean energy policies in Germany partially to solar power. In addition, from Figure 13, it could be seen that the policies for EV promotion in all countries mentioned in this paper are aggressive and ambitious, because of the stern requirement of carbon dioxide emissions reductions. In the meantime, these policies also indicate that the EV-related industries will meet great opportunities in the future.
In general, the clean energy policies of countries are more macroscopic and comprehensive, which involves the development of various clean energy technologies and future energy transition pathways. According to the recent reports or news, China and Denmark have already met their 2020 targets, but Australia may miss their 2020 emissions reduction target [57][58][59]. The main reason that Australia may miss its clean energy target is due to the lack of a coherent national energy policy. These results indicate that these clean energy policies are not guaranteed to be accomplished by the countries like most people thought, further suggesting that the practice and implementation of these clean energy policies need coordination from various levels of governments and electric power companies. In the next section, taking the U.S. as an example, the recent clean energy policies in representative states and utilities of the U.S are presented to show how to concretely implement nationwide clean energy policies to power providers and consumers.
3. The Clean Energy Policy of Progressive States in the U.S.

Overview of the State Renewable Portfolio Standards and Goals
As one of the world's richest owners of wind, solar, hydro, and other renewable energy In general, the clean energy policies of countries are more macroscopic and comprehensive, which involves the development of various clean energy technologies and future energy transition pathways. According to the recent reports or news, China and Denmark have already met their 2020 targets, but Australia may miss their 2020 emissions reduction target [57][58][59]. The main reason that Australia may miss its clean energy target is due to the lack of a coherent national energy policy. These results indicate that these clean energy policies are not guaranteed to be accomplished by the countries like most people thought, further suggesting that the practice and implementation of these clean energy policies need coordination from various levels of governments and electric power companies. In the next section, taking the U.S. as an example, the recent clean energy policies in representative states and utilities of the U.S are presented to show how to concretely implement nationwide clean energy policies to power providers and consumers.

Overview of the State Renewable Portfolio Standards and Goals
As one of the world's richest owners of wind, solar, hydro, and other renewable energy resources, the U.S. state governments have actively revised their renewable portfolio standards (RPSs), which require their regional utilities to sell a specified percentage of clean energy electricity. Moreover, state governments have also announced these standards to make their energy resources more diverse. Furthermore, RPSs could also promote domestic energy production and boost economic development. However, state RPSs have significant diversities on RPS goals, evolved entities, eligible resources to meet requirements and cost caps, etc. Figure 14 lists the RPS/voluntary goals of different states/territories [60][61][62]. From Figure 14, it could be seen that the aggressiveness degree of a state government's clean energy policy depends on the economic level of the state. Most of the states in the west and on the East Coast have ambitious clean energy targets.
Moreover, state governments have also announced these standards to make their energy resources more diverse. Furthermore, RPSs could also promote domestic energy production and boost economic development. However, state RPSs have significant diversities on RPS goals, evolved entities, eligible resources to meet requirements and cost caps, etc. Figure 14 lists the RPS/voluntary goals of different states/territories [60][61][62]. From Figure 14, it could be seen that the aggressiveness degree of a state government's clean energy policy depends on the economic level of the state. Most of the states in the west and on the East Coast have ambitious clean energy targets.

Details for Some Progressive States
In this section, the clean energy policies of five progressive states in the U.S. are introduced.

California
As one of the most progressive states in the U.S., the Californian government signed the Senate Bill 100 (SB 100) in September 2018. The objective of SB 100 is to increase the overall requirement of clean energy from 50% to 60% by 2030 [63]. In addition, the legislation of California has also changed some rules of using large hydropower generation by publicly owned municipal utilities (POUs) and set a more aggressive target that realizes 100% electric retail sales from clean energy by 2045. The detailed procurement requirements based on the interim target from the governing board are listed in Figure 15 [64].

California
As one of the most progressive states in the U.S., the Californian government signed the Senate Bill 100 (SB 100) in September 2018. The objective of SB 100 is to increase the overall requirement of clean energy from 50% to 60% by 2030 [63]. In addition, the legislation of California has also changed some rules of using large hydropower generation by publicly owned municipal utilities (POUs) and set a more aggressive target that realizes 100% electric retail sales from clean energy by 2045. The detailed procurement requirements based on the interim target from the governing board are listed in Figure 15 [64]. In addition, 1325MW of energy storage is required for utility collective procurement by 2020 and needs to be installed and delivered to the grid no later than 1 January 2025. The phase of procurement for each utility starts in 2014, and the share of each utility has to include a certain amount of energy storage at both the transmission and the distribution levels. Meanwhile, a certain amount of energy storage has to be deployed at the customer side.

New York State
As a pioneer in clean energy popularization, New York has been building momentum for many years through a strong and consistent climate and clean energy actions. The government of New York State aims at realizing a carbon-free electricity system and a carbon-neutral economy by 2040 [65]. The clean energy roadmap of New York State is shown in Figure 16. This plan includes all areas including electricity delivery, transportation, building, and industrial production. The New York Climate Leadership and Community Protection Act (CLCPA) has also set a new standard, which codifies the clean energy goal of New York to 70% by 2030 while cutting down the greenhouse gas emissions to 15% by 2050. The standard aims to scale up grid modernization, energy storage, and solar power to improve system flexibility, reliability, and resilience. The necessary foundation mentioned in this work is to support the expansion of 3000 MW of energy storage and 6000 MW of distributed solar power [66]. The detailed procurement requirements based on the interim target from the government board.
In addition, 1325MW of energy storage is required for utility collective procurement by 2020 and needs to be installed and delivered to the grid no later than 1 January 2025. The phase of procurement for each utility starts in 2014, and the share of each utility has to include a certain amount of energy storage at both the transmission and the distribution levels. Meanwhile, a certain amount of energy storage has to be deployed at the customer side.

New York State
As a pioneer in clean energy popularization, New York has been building momentum for many years through a strong and consistent climate and clean energy actions. The government of New York State aims at realizing a carbon-free electricity system and a carbon-neutral economy by 2040 [65]. The clean energy roadmap of New York State is shown in Figure 16. This plan includes all areas including electricity delivery, transportation, building, and industrial production. The New York Climate Leadership and Community Protection Act (CLCPA) has also set a new standard, which codifies the clean energy goal of New York to 70% by 2030 while cutting down the greenhouse gas emissions to 15% by 2050. The standard aims to scale up grid modernization, energy storage, and solar power to improve system flexibility, reliability, and resilience. The necessary foundation mentioned in this work is to support the expansion of 3000 MW of energy storage and 6000 MW of distributed solar power [66].

Washington State
Washington State has also proposed an aggressive target on the clean energy transition. The Clean Energy Transformation Act (S.B. 5116 of 2019) proposes to realize 100% clean electricity by 2045. This Act requires that all utilities must eliminate coal from their state portfolios by 2025. Besides, the utilities should be greenhouse gas-neutral from 2030. By 2045, all electricity in Washington State must come from clean energy without emission [67,68]. The target of Washington State on clean energy is shown in Figure 17.

Washington State
Washington State has also proposed an aggressive target on the clean energy transition. The Clean Energy Transformation Act (S.B. 5116 of 2019) proposes to realize 100% clean electricity by 2045. This Act requires that all utilities must eliminate coal from their state portfolios by 2025. Besides, the utilities should be greenhouse gas-neutral from 2030. By 2045, all electricity in Washington State must come from clean energy without emission [67,68]. The target of Washington State on clean energy is shown in Figure 17.

Virginia
In 2020, Virginia State set a clean energy target for realizing mandatory 100 percent clean energy for Phase I utilities (Appalachian Power Company, etc.) and Phase II utilities (Dominion Energy Virginia, etc.). In the previous plan, Virginia State enacted a voluntary target for utilities in order to achieve 15% clean energy by 2025 [69]. After the revision, according to the new requirement, the targets of Phase I utilities and Phase II utilities are shown in Figure 18 [69][70][71].

Virginia
In 2020, Virginia State set a clean energy target for realizing mandatory 100 percent clean energy for Phase I utilities (Appalachian Power Company, etc.) and Phase II utilities (Dominion Energy Virginia, etc.). In the previous plan, Virginia State enacted a voluntary target for utilities in order to achieve 15% clean energy by 2025 [69]. After the revision, according to the new requirement, the targets of Phase I utilities and Phase II utilities are shown in Figure 18 [69][70][71]. In order to realize this mandatory 100% clean energy target, some targets and policies on solar and onshore wind farms, offshore wind farms, and energy storage have been announced by Virginia. Some highlights of the clean energy plan are shown in Figure 19. In order to realize this mandatory 100% clean energy target, some targets and policies on solar and onshore wind farms, offshore wind farms, and energy storage have been announced by Virginia. Some highlights of the clean energy plan are shown in Figure 19. In order to realize this mandatory 100% clean energy target, some targets and policies on solar and onshore wind farms, offshore wind farms, and energy storage have been announced by Virginia. Some highlights of the clean energy plan are shown in Figure 19.

Hawaii
Hawaii set a renewable portfolio standard in 2015. In this standard, each utility that sells electricity in Hawaii must set the mandatory target to realize the following percentages of "renewable electrical energy" sales [72]. The clean energy roadmap of Hawaii is shown in Figure 20.

Hawaii
Hawaii set a renewable portfolio standard in 2015. In this standard, each utility that sells electricity in Hawaii must set the mandatory target to realize the following percentages of "renewable electrical energy" sales [72]. The clean energy roadmap of Hawaii is shown in Figure 20. As shown from the five representative states in the U.S., the focused types of clean energy policies follow the national clean energy policies. However, compared to the national clean energy policies, the targets determined by states are more specific and accurate (such as the energy storage requirement of California by 2020), which demonstrates that the enforceability of clean energy policies in states may be better than the federal government. In addition, the difference between the states on their enacting clean energy policies still exists due to the variety of clean energy types and the diversity of economic development degrees. For example, the clean energy policies that New York State focuses on increase the clean energies share in its generation mix. However, the clean energy policies of Washington State aim at forcing the utilities to eliminate coal from their state portfolios. The different focus of the clean energy policies will lead to the utilities or power providers adopting different schemes that affect the power consumption habit of the public and the related industries' development. In the next section, the clean energy policies of representative utilities of the As shown from the five representative states in the U.S., the focused types of clean energy policies follow the national clean energy policies. However, compared to the national clean energy policies, the targets determined by states are more specific and accurate (such as the energy storage requirement of California by 2020), which demonstrates that the enforceability of clean energy policies in states may be better than the federal government. In addition, the difference between the states on their enacting clean energy policies still exists due to the variety of clean energy types and the diversity of economic development degrees. For example, the clean energy policies that New York State focuses on increase the clean energies share in its generation mix. However, the clean energy policies of Washington State aim at forcing the utilities to eliminate coal from their state portfolios. The different focus of the clean energy policies will lead to the utilities or power providers adopting different schemes that affect the power consumption habit of the public and the related industries' development. In the next section, the clean energy policies of representative utilities of the U.S are introduced to show their policy changes.

The Clean Energy Policy of U.S. Utilities
The implementation of state clean energy policies needs the cooperation of the utilities. This section discusses the clean energy policies of five representative utility companies that are leaders in clean energy development in the U.S.

Pacific Gas and Electric (PG&E)
As the largest electric power provider in California (and one of the largest combined natural gas and electric companies in the U.S.), the Pacific Gas and Electric Company (PG&E) has issued a comprehensive reorganization plan in order to strengthen the commitment of clean energy and the climate. Although PG&E is under bankruptcy protection and meets serious financial challenges, it is still ready to take leadership in guaranteeing a clean future for California and the U.S. [73].
In the reorganization plan, PG&E intends to support the state's goals of 5,000,000 zero-emission vehicles (ZEV) on the road by 2030. It will need PG&E to provide about 250,000 charging stations, which will include more than ten thousand fast chargers, and two hundred hydrogen fueling stations by 2025. In addition, the utility plans to realize 60% clean energy of the total energy procurement by 2030. It is envisioned that the clean energy-related reorganization plan and investments of PG&E will play an important role in California's clean energy future.

Southern California Edison (SCE)
Southern California Edison (SCE) is the primary electric utility for most of Southern California, which provides more than 14 million people with electricity across approximately 50,000 square miles. SCE also presented a clean energy policy named the Clean Power and Electrification Pathway in order to reduce carbon dioxide emissions and air pollutants in California [74]. The objective of this plan is to reduce pollution and improve air quality for the future. The highlights of the Clean Power and Electrification Pathway until 2030 are summarized in Figure 21 [74].

Southern California Edison (SCE)
Southern California Edison (SCE) is the primary electric utility for most of Southern California, which provides more than 14 million people with electricity across approximately 50,000 square miles. SCE also presented a clean energy policy named the Clean Power and Electrification Pathway in order to reduce carbon dioxide emissions and air pollutants in California [74]. The objective of this plan is to reduce pollution and improve air quality for the future. The highlights of the Clean Power and Electrification Pathway until 2030 are summarized in Figure 21 [74].

Dominion Energy
As one of the largest utilities in Virginia and North Carolina, Dominion Energy has committed to meeting clean energy targets and standards set by the government of Virginia and North Carolina. The Dominion Energy clean energy plan proposed two realizable and measurable targets [69]:

Dominion Energy
As one of the largest utilities in Virginia and North Carolina, Dominion Energy has committed to meeting clean energy targets and standards set by the government of Virginia and North Carolina. The Dominion Energy clean energy plan proposed two realizable and measurable targets [69]: • Achieving 15% renewable power by 2025 (Virginia); • Achieving 12.5% renewable power by 2021 (North Carolina).
For supporting these standards through existing clean energy resources, Dominion Energy plans to develop new clean energy besides purchasing clean energy certificates.

Duke Energy Carolinas
Duke Energy Carolinas has announced a new clean energy policy, whose goal is to realize zero-carbon emissions from electricity generation by 2050. Duke Energy Carolinas plans to accelerate the recent goal by cutting greenhouse gas emissions by 50% or more from 2005 to 2030.
The highlights of Duke Energy's proposed clean energy plan are summarized in Figure 22 [75].

DTE Energy
DTE Energy has announced a clean energy plan to realize a 32 percent cut in carbon emissions by 2023. The first phase is to shut off three of five remaining fuel generation plants. The carbon emission cut plan aims at reducing carbon emission by 50 percent by the end of 2030 and 80 percent or more by the end of 2040. They also pledge to adopt 25 percent clean energy for production by 2025 and at least 30 percent by 2030.
The highlights of DTE's proposed clean energy plan include traditional coal-fired plants shutdowns, carbon emission reduction, and clean energy development, which are summarized in Figure  23.

DTE Energy
DTE Energy has announced a clean energy plan to realize a 32 percent cut in carbon emissions by 2023. The first phase is to shut off three of five remaining fuel generation plants. The carbon emission cut plan aims at reducing carbon emission by 50 percent by the end of 2030 and 80 percent or more by the end of 2040. They also pledge to adopt 25 percent clean energy for production by 2025 and at least 30 percent by 2030.
The highlights of DTE's proposed clean energy plan include traditional coal-fired plants shut-downs, carbon emission reduction, and clean energy development, which are summarized in Figure 23. Figure 19 lists some clean energy policies of the main utilities [76][77][78][79][80]. From the mentioned five representative utilities and Figure 24, it could be found that the clean energy policy focus of utilities is highly related to the available clean energy resources in each state. The clean energy policy formulation for most utilities is based on the Bills enacted by the state government, such as Dominion Energy. They set two different clean energy consumption goals for Virginia and North Carolina in order to meet different requirements determined by their own clean energy policies. These clean energy policies will be a guideline for their inner energy companies for determining future, mainly energy, technology. In addition, the developing focus of renewable energies of different utilities is related to the natural clean energy source in the states, thus from Figure 24, it could be seen that some states aim at using clean energy generation to replace conventional fossil fuel generation, while some states focus on energy saving and emission reduction. However, the clean policy pathways of most utilities are the same, which are planned to support clean energy capacities and generation increases in the state, boost the domestic job creation, and reduce the carbon emission. The achievement of these clean policy pathways will mainly be through market rules adjustment and tax deductions.

DTE Energy
DTE Energy has announced a clean energy plan to realize a 32 percent cut in carbon emissions by 2023. The first phase is to shut off three of five remaining fuel generation plants. The carbon emission cut plan aims at reducing carbon emission by 50 percent by the end of 2030 and 80 percent or more by the end of 2040. They also pledge to adopt 25 percent clean energy for production by 2025 and at least 30 percent by 2030.
The highlights of DTE's proposed clean energy plan include traditional coal-fired plants shutdowns, carbon emission reduction, and clean energy development, which are summarized in Figure  23.  Figure 19 lists some clean energy policies of the main utilities [76][77][78][79][80]. From the mentioned five representative utilities and Figure 24, it could be found that the clean energy policy focus of utilities is highly related to the available clean energy resources in each state. The clean energy policy formulation for most utilities is based on the Bills enacted by the state government, such as Dominion Energy. They set two different clean energy consumption goals for Virginia and North Carolina in order to meet different requirements determined by their own clean energy policies. These clean energy policies will be a guideline for their inner energy companies for determining future, mainly energy, technology. In addition, the developing focus of renewable energies of different utilities is related to the natural clean energy source in the states, thus from Figure 24, it could be seen that some states aim at using clean energy generation to replace conventional fossil fuel generation, while some states focus on energy saving and emission reduction. However, the clean policy pathways of most utilities are the same, which are planned to support clean energy capacities and generation increases in the state, boost the domestic job creation, and reduce the carbon emission. The achievement of these clean policy pathways will mainly be through market rules adjustment and tax deductions.

Gaps and Future Directions on Clean Energy Policies Review
In the process of reviewing the clean electricity policies from countries to utilities, this paper shows the values of the clean policy review. Firstly, it provides a reference for readers to easily obtain clean energy information. Secondly, the intuitive comparison in this paper indicates the difference of

Gaps and Future Directions on Clean Energy Policies Review
In the process of reviewing the clean electricity policies from countries to utilities, this paper shows the values of the clean policy review. Firstly, it provides a reference for readers to easily obtain clean energy information. Secondly, the intuitive comparison in this paper indicates the difference of the clean energy policies between various countries, states in the U.S., and utilities. However, a number of gaps in this clean energy policies review were identified with many unanswered questions that need to be further addressed. Firstly, this paper indicates that the clean energy policies of the utilities are followed by the clean energy targets of states or countries. In fact, the electric market also plays an important role in policies promotion. However, the operation of the electric market is complex due to various types of generators, loads, and response resources participation. Thus, it is hard to clearly describe the stake between the clean energy policies implementation and electric market, which is valuable to be investigated in the future. In addition, public recognition has become a very critical factor to clean energy policies implementation. From reviewing, it could be seen that the optimum clean energy for a specific area may not be the final decision by the government. The acceptable level of the public becomes more and more important in clean energy policies determination. However, the quantitative analysis for the public recognition of clean energy policies has not received too much attention. This topic may be very interesting and significative for future research.

Conclusions
Clean energy policy influences the development of clean energy technologies and markets. The diversity of the scope, intensity, and comprehensiveness of clean energy policies in different utilities, states, and countries leads to the different development degrees of clean energy. This paper firstly introduced the clean energy policies on electricity of some countries who are positive on clean energy promotion. Then, taking the U.S. as an example, this paper presented the recent clean energy policies in representative states and utilities of the U.S. It can be seen from the results of the review and comparison that, firstly, due to the variety of clean energy types and the diversity of economic and social development degrees, the clean energy policies enacted by different countries have many differences. In addition, the clean energy policies of countries are more macroscopic and comprehensive, which involve the development of various clean energy technologies and future energy transition pathways. However, the practice and implementation of these clean energy policies need coordination from the various levels of governments and electric power companies. From comparing the results, it could be seen that, in the U.S., the clean energy policies determined by states are more specific and accurate compared to the national policies, which demonstrates that the enforceability of these clean energy policies may be better than the federal government. Besides, the aggressiveness degree of a state government's clean energy policy depends on the economic level of the state. The clean energy policy focus is related to the available clean energy resources in each state. The implementation of states' clean energy policies relies on utilities and power companies. The clean energy policy formulation for most utilities is based on the Bills enacted by the state government. Thus, the clean policy pathways of most utilities aim at supporting clean energy capacities and generation increases in the state, boosting domestic job creation, and reducing carbon emissions. These observations indicate that a comprehensive review and comparison are necessary and may help clean energy researchers and practitioners to understand clean energy policy determination, promotion, and implementation.