Overview of the Decarbonization Options for the Electricity Sector: Opportunities and Challenges

The energy demand has grown alongside increasing population growth globally. Unfortunately, the utilization of fossil fuels, especially coal, has dominated the energy sectors, including power generation. Fossil fuels have no place in the sustainability future due to the limitation of these resources and the potential environmental impacts that may arise. Therefore, the decarbonization of the electricity sector has recently become the world’s attention, including in Indonesia. This study discusses opportunities and challenges of decarbonization initiatives in the electricity sector by conducting traditional reviews of various publications from direct science databases and publications from official websites of other organizations relevant to the research context. The results discuss decarbonization options by replacing coal with renewable energy. Other initiatives are also investigated in this paper to provide alternative possibilities. The study indicated that each option has challenges that can affect the success of each program.


Introduction
Nowadays, climate change takes the world's attention because of the consequences on social, environmental, and economic systems [1].In order to prevent the severe impacts of climate crisis, the world needs to decrease carbon emissions significantly.The biggest contributor to the generation of greenhouse gas (GHG) emissions globally is the dependency on the usage of fossil fuels, specifically coal, gas, and oil, in the energy sector [2].Compared to the previous year, carbon dioxide emissions from the worldwide energy sector increased by 0.9%, or 321 Mt, in 2022 [3].Various factors can influence carbon emissions growth.The amount of electricity used has a substantial negative impact on carbon emissions, when more electricity is generated using clean energy.Urbanization, industrialization, economic and population growth significantly impact carbon emissions production [4].In order to mitigate the impact of global warming on this planet, it is essential to adopt decarbonization options, specifically in the power sector [5].In FIGURE 1. Energy transformation process [6].
The reduction of carbon emissions in power systems tends to involve two approaches: 1) enhancing the energy effectiveness of the existing system, and 2) substituting a carbon-intensive source of electricity production with low-or carbon-free sources and with considering carbon capture and storage [2].Renewable energy sources do not run out over time.The main types of renewable energy include biomass, wind, solar energy, hydropower, and geothermal energ [7].Renewable energy sources aim not only to reduce GHG emissions but also to increase the diversity of the energy supply and reduce dependence on fossil fuels whose reserves are likely to run out, ultimately leading to sustainability [8].Sustainability is the ability of both the natural systems of the planet and the human cultural systems to survive, and adapt to changing environmental conditions over extremely long periods [9].
Indonesia has a vast potential for renewable energy sources; unfortunately the utilization is still low (0.3%) [10].The challenge of sustainability and the dominant role of fossil fuels in the electricity sector requires the right energy policy.A good understanding of decarbonization strategies will provide knowledge of appropriate actions in response to potential climate change impacts.This research contributes to reviewing the trend of applications for decarbonization strategies from various countries.Therefore, this study discussed the opportunities and challenges of decarbonization options in various countries and provided potential options for the Indonesian electricity sector.

Method
This study was conducted based on a qualitative approach.In this study, the research method focuses on finding relevant references with the context that will be discussed using a traditional review.The review is used to sort the literature based on the selected keyword and to highlight an issue in your field that your study aims to address.The review can be simplified into two phases: the initial step is concerned with the data that was gathered and includes the following activities: problem identification, selection of library sources based on inclusion and criteria, data collection, and sorting (screening).The collected references are sorted (screened) according to a variety of inclusion criteria (Table 1).The second step consists of data analysis, interpretation, and confirmation.

Results and Discussion
An overview of decarbonization options from various countries, a summary of decarbonization technological development, and the challenges for the decarbonization efforts are described in this section.

Decarbonization options of various countries
Some countries have committed to taking climate mitigation action by implementing the decarbonization initiative for various activities, including electricity, transport, agriculture, and other sectors, as shown in Table 2.

Mexico
-Replacing fossil fuels with renewable energy -Developing electric vehicles for private and public use -Reducing the use of fertilizer [11] Russia -Increasing the development of renewable energy usage for the power sector -Implementing renewable energy policy -Developing hydrogen production [12] China -Replacing fossil fuel power plants with solar, wind, hydro, biomass, and nuclear power plant -Developing electric vehicles for passenger and heavy-duty use -Implementing emissions trading system [13] Sweden -Increasing the investment in renewable energy sources -Implementing carbon capture and storage [14] Bolivia -Developing a carbon tax mechanism -Increasing the capacities of renewables -Preparing policy guidelines for greenhouse gas emissions mitigation [15] Based on Table 2, adopting renewable energy is a highly preferred technique for reducing greenhouse gas emissions.Several countries have increased the use of solar, wind, hydro, and biomass for the power sector.Only an extensive shift to the use of clean energy will enable a successful energy transition.Studies on implementing carbon capture, developing hydrogen production, and electric vehicle technology are also receiving greater attention than other alternative efforts.Policy attention was additionally given to carbon pricing mechanisms, a carbon tax, or an emissions trading system (ETS).Carbon prices have long favored promoting sustainable energy development [16].Japan was one of the first Asian countries to introduce carbon pricing, with a tax rate of $2.65 per JPY (t-CO2).Among developed countries, Japan has one of the lowest carbon tax rates.However, Japan's low carbon tax rate makes its carbon tax strategy ineffective [17].While China, the United States, and countries in Southeast Asia are increasingly adopting ETS as a policy tool to decarbonize and achieve their climate goals [13].
The realization of the energy mix for the power sector in Indonesia until December 2020 was still dominated by coal-fired power plants (CFPP) at 67%, followed by the consumption of gas (17%) and fuel oil (3%).Meanwhile, the energy mix from renewable energy was around 13% [18], as shown in Figure 2. [18] To be able to meet the renewable energy mix target of 23% in 2023 and in order to respond to climate change, future energy sources for Indonesia might include solar, hydropower, geothermal power, biomass, and nuclear energy.However, CFPP are necessary in the short to medium term before switching to a more sustainable low-carbon energy source.This transition phase must be carefully planned to meet energy demands while minimizing environmental effects.Therefore, considering carbon capture utilization in the future may be required [19].

An overview of decarbonization technological development
Several decarbonization technologies can be required to reduce carbon emissions from the electricity sector.The implementation of biomass cofiring, and carbon capture technologies, are selected to be more discussed in this section.

Biomass cofiring
In order to achieve sustainable energy goals, implementation of biomass cofiring, which might reduce the potential adverse environmental effects of burning fossil fuels, can be crucial.Cofiring biomass and coal can reduce greenhouse gas emissions and provide a short-term decarbonization alternative [20].The primary benefit of biomass is that it releases carbon dioxide into the atmosphere after combustion, which plants may even reabsorb through photosynthesis, effectively addressing the need for minimizing carbon emissions in the environment to mitigate the climate's warming impact [8].Due to environmental factors, cofiring different forms of biomass with coal has attracted much attention and is seen as a low-cost option [21].Biomass includes a wide range of products, by-products, residues from agriculture and forestry (including animal husbandry), municipal and industrial waste [22].According to Jaiswal et al. ( 2022), depending on the source, biomass can be divided into four categories, namely those derived from wood by-products, agricultural waste, solid waste, and other wastes, as shown in Table 3. [7].

Biomass Resources
Feedstocks Wood processing residues Agricultural residues Firewood, wood chips, wood pellets, timber, bark, sawdust from furniture factories, and by-products of wood processing Agricultural crop residues, straw, corn cobs, leaves, branches, forestry residues, algae Solid waste Residential and commercial waste, vegetable/fruit peels, waste food Manure, municipal wastewater, industrial wastewater, and leachate

Biogas
Despite not being implemented constantly and with a small cofiring ratio (5%), Indonesia's biomass cofiring program has been running for more than a year in more than thirty locations of CFPP with direct methods.Biomass cofiring is applied on various boilers, namely pulverized combustion (PC), circulation fluidized bed (CFB), and stoker.Woodchips, waste pellets, sawdust, palm kernel shells (PKS), and corn cobs are among the biomass types used.Compared with other types of biomass, sawdust consumption is currently the most widely used for cofiring biomass applications in Indonesia, as shown in Figure 3.

Carbon capture
Carbon capture and storage technology is one of the mitigating strategies to reach net zero emissions by 2050, with absorbs carbon dioxide emitted from thermal power plants [23].The method of carbon capture can be categorized into pre-combustion, post-combustion, and oxy-fuel capture.Pre-combustion separates carbon dioxide before the combustion process begins, enabling the product to meet carbon emission requirements.Post-combustion separates carbon dioxide from exhaust gas after the combustion process occurs.Oxy-fuel differs from both methods mentioned earlier because fuel combustion uses high-purity oxygen to separate carbon dioxide [24].Two large-scale CCUS retrofit projects have been installed at the existing CFPP, namely The Petra Nova and The Boundary Dam.The Petra Nova project is the largest CCUS which has been operating since 2017 using the post-combustion method [25].A comparison between different carbon capture methods is shown in Table 4. [26].The efficiency of carbon dioxide removal, the technological readiness level (TRL), the capital and operating expenses, and the capacity to store or utilize carbon dioxide are the main factors to be considered while adopting CCUS technology [27].Developing large-scale carbon capture is not possible because the investment cost remains very high.Companies may be encouraged to invest in these technologies by adopting carbon pricing mechanisms via carbon taxes or cap and trade schemes [28].CCUS have the important role to support energy transition due to the emissions level from existing fossil fuel power plants can be reduced by additional the carbon capture technologies into the power plants.

Challenges to the electricity sector's decarbonization
The barriers faced in decarbonizing the global power generation sector are currently listed in Table 5.

Barriers
Reference High investment cost [29], [30] Technological barriers [30] Public perception [26] Regulation and implementation uncertainties Skilled worker Land issues [12] [19] [19] Based on Table 5, for the development of the energy transition to be successful, problems like expensive investment costs, technological barriers, public perception, ineffective regulations, land issues, and lack of skilled workers should be solved as soon as possible.Increasing renewable energy demand (including nuclear energy) contributes to reaching a carbon-neutral goal.However, unfortunately, inadequate investment in renewable energy generates more significant carbon emissions since fossil fuels are extensively utilized in the power sector [31].Decarbonization policy is essential to support the development of renewable energy and sustainable management of natural resources in a country [32].The decarbonization policy through renewable energy investment can enhance energy security by reducing our reliance on expensive fossil fuel imports and creating a wide range of new opportunities in the form of new markets for low-emissions products and support services.Consumer perception also contributes to the development of clean technologies.Consumers' product knowledge positively influences user perception of the product value.However, consumer preferences for innovative low-carbon products vary widely, and not all consumers can afford "decarbonized" products [33].

Conclusion
In order to reduce the growing negative impacts of climate change, various countries are currently prioritizing expanding the use of renewable and sustainable energy for various sectors, including the power sector.Several countries have significantly increased the application of renewable sources, such as solar, wind, hydropower, and biomass.Research on carbon capture, hydrogen production, the development of electric vehicles, and carbon pricing mechanism have also become considerations.Among the various renewable energy sources available, cofiring biomass has emerged as one of the most attractive decarbonization strategies, including in Indonesia.Unfortunately, the current capacity for developing biomass is constrained due to limited continuous supply.Factors that can contribute to the success of a decarbonization program are the maturity and cost-effectiveness of the technology and the development of supporting policies at the national or regional level.Further research could be focused on evaluating the role of social and economic factors in developing renewable energy.