Evaluation of Decarbonization Technologies for ASEAN Countries via an Integrated Assessment Tool

Abstract

A new assessment tool for evaluating decarbonization technologies that considers each technology’s sustainability, security, affordability, readiness, and impact for a specific country is proposed. This tool is applied to a set of decarbonization technologies for the power, transport, and industry sectors for the ten Southeast Asian countries that constitute ASEAN. This results in a list of the most promising decarbonization technologies, as well as the remaining issues that need more research and development. This study reveals several common themes for ASEAN’s decarbonization. First, carbon capture and storage (CCS) is a key technology for large-scale CO₂ emission. Second, for countries that rely heavily on coal for power generation, switching to gas can halve their CO₂ emission in the power sector and should be given high priority. Third, hydropower and bioenergy both have high potential for the majority of ASEAN countries if their sustainability issues can be resolved satisfactorily. Fourth, replacing conventional vehicles by electric vehicles is the overarching theme in the road transport sector, but will result in increased demand for electricity. In the medium to long term, the use of hydrogen for marine fuel and biofuels for aviation fuel are preferred solutions for the marine and aviation transport sectors. Fifth, for the industry sector, installing CCS in industrial plants should be given priority, but replacing fossil fuels by blue hydrogen for high-temperature heating is the preferred long-term solution.

1. Introduction

Power, transport, and industry are the three largest energy consumption and CO₂-emitting sectors in the world [1]. In 2019, they contributed 38%, 24%, and 21%, respectively, of Southeast Asia’s total energy-related CO₂ emissions [2]. Figure 1 shows the author’s depiction of how fossil fuels (coal, oil, and gas) and uranium are used in these sectors. The relative contribution of these fuels for each sector is country-specific. In the power (electricity) sector, coal, natural gas, and uranium are used as fuel in coal-fired, gas-fired, and nuclear power plants, respectively. Oil-fired power plants are less common, although still used in some countries. In the transport sector, crude oil is refined to liquid fuels used for cars, ships, and planes. In the industry sector, naphtha, a refined oil product, is used as a raw material for petrochemical plants to produce products such as plastics and chemicals; coal and gas are also used for high-temperature (exceeding 1000 °C) heating in iron and steel mills, cement factories, and other industrial plants. In all three of these sectors, CO₂ is produced when fossil fuels are combusted. In nuclear power plants, nuclear waste is produced, which needs to be transported and permanently stored in suitable locations. Decarbonizing these three energy consumption sectors is the key objective of the ongoing energy transition [1,2,3,4,5,6,7].

Many ways have been proposed to decarbonize these three sectors. In two recent articles, Lau et al. reviewed and summarized them [2,7]. The decarbonization technologies are summarized in Figure 2.

In the power sector, the main focus has been on the use of renewable energies for electricity generation (Figure 2a) [2,8]. Commonly used renewable energies are hydropower, wind, solar, bioenergy, and geothermal. Another method is to replace coal-fired power plants by gas-fired power plants (coal→gas), as the combustion of gas produces about half the CO₂ compared to coal [2,7]. A third method is to install CCS to mitigate the CO₂ emitted from coal or gas-fired power plants (CP-CCS or GP-CCS) [2,7]. In CCS, CO₂ captured from emitting sources is compressed and transported via pipelines or ships to a suitable location for permanent storage in the subsurface. In general, there are three types of subsurface reservoirs suitable for CO₂ storage: gas reservoirs, oil reservoirs, and saline aquifers [1]. Under the right reservoir temperature and pressure, and hydrocarbon composition, CO₂ injection into an oil or gas reservoir may lead to incremental oil recovery by enhanced oil recovery (EOR) or incremental gas condensate recovery by enhanced gas recovery (EGR) [1]. In addition, the injected CO₂ can be designed to stay permanently in the reservoirs. Therefore, in this paper, both CO₂-EOR and CO₂-EGR are classified as CCS technologies, instead of carbon capture and utilization (CCU) technologies. CO₂ storage in saline aquifers is also known as CO₂ geological sequestration. CO₂ storage in these three types of subsurface reservoirs is commonly regarded as a form of CCS. At present, CCS is the only method capable of storing CO₂ on the scale of a million tons per year [1].

In the transport sector, the focus has been on replacing internal combustion engine (ICE) vehicles by electric vehicles (EVs) or hydrogen fuel cell vehicles (HFCVs), using hydrogen for marine fuels and biofuels for aviation fuels (Figure 2b) [1]. This focus moves mobile CO₂ emission to stationary emission in power or hydrogen plants, which still needs to be removed by CCS if fossil fuels are used.

In the industry sector, the focus has been on installing CCS in existing plants to capture and store the emitted CO₂ in subsurface reservoirs (Figure 2c) [1,3,4,5,6,7]. This technology is called Ind-CCS. Another CO₂ reduction method is to convert captured CO₂ into useful products, such as chemicals, polymers, or building materials [9]. This conversion is commonly known as CCU. Another area of research is focused on using blue hydrogen generated from coal via coal gasification or by gas via steam methane reforming (SMR), instead of using fossil fuels for high-temperature heating [2,7]. We call these processes coal→H₂-CCS and gas→H₂-CCS, respectively [2,7].

A summary of recent research on decarbonization in Asia is provided in

Table 1. Summary of recent studies on decarbonization in Asian countries.

Previous Study	Country Studied	Conclusions	Research Gap
Lau et al. (2021) [1]	Not applicable	CCS plays key role in decarbonizing the power sector and producing blue hydrogen.	Results applicable but not specific to ASEAN.
Lau et al. (2022) [2]	ASEAN	Fossil energy will continue to play a key role in ASEAN’s energy mix. A sustainability rating for decarbonization technology is proposed. Six large-scale CCS projects are proposed for ASEAN.	No ranking of technology based on readiness and impact for specific country.
Zhang and Lau (2022) [3];	Singapore, Indonesia, Malaysia	Minas and Arun are the largest oil and gas reservoirs, respectively, within 1000 km from Singapore, suitable for CO2 storage.	No ranking of decarbonization technologies by country.
Zhang et al. (2022) [4]; Bokka et al. (2022) [5]	India	Identified CCS opportunities in India.	No ranking of decarbonization technologies.
Zhang et al. (2022) [6]	Thailand	Identified CCS opportunities in Thailand.	No ranking of decarbonization technologies.
Lau (2022) [7]	ASEAN	Technology mapping exercise for ASEAN countries.	Energy trilemma (sustainability, affordability, security) not included in study
Oh (2012) [10]	Malaysia	CCS is needed to decarbonize Malaysia’s coal-fired power plants	Study specific to CCS.
Lai et al. (2012) [11]	Malaysia	CCS for the power sector is needed, but there is a lack of assessment of CO2 storage capacity.	Study specific to CCS
Ibrahim et al. (2015) [12]	Malaysia	CCU and CCS are must-have technologies for decarbonization. Government incentives are needed.	Study specific to CCU and CCS.
Sukor et al. (2020) [13]	Malaysia	CCS to remove CO2 from produced gas from offshore field.	Study specific to CCS
Adisaputro and Saputra (2017) [14]	Indonesia	Both CCS and CCU are needed for decarbonization.	Study specific to CCS and CCU.
Lau et al. (2022) [15]	Singapore	A roadmap for Singapore decarbonization is proposed.	No ranking of decarbonization technologies.

. It can be seen that most studies were either country- or technology-specific (e.g., CCS). One key research gap not addressed in previous studies is the screening of various decarbonization technologies for specific countries. This paper proposes an integrated assessment tool to screen various decarbonization technologies according to their sustainability, security, affordability, readiness, and impact. This paper then applies this tool to Southeast Asian countries to arrive at pathways for decarbonization in those countries.

ASEAN consists of ten Southeast Asian countries: Indonesia, Vietnam, Thailand, Malaysia, Philippines, Singapore, Myanmar, Cambodia, Laos, and Brunei. It was formed to promote economic peace and stability among its member countries. ASEAN countries had a combined population of 661 million and a combined GDP of USD 3.08 trillion in 2020. Since the 1990s, ASEAN’s CO₂ emissions have been rapidly rising due to increased population, urbanization, and economic prosperity. In 2020, ASEAN countries emitted 1.65 Gt of energy-related CO₂ [16]. All ASEAN countries are signatories to the Paris Agreement and have pledged to reduce their CO₂ emissions to limit the rise in atmospheric temperature to less than 2 °C above that in pre-industrial times [17].

2. Objective and Methodology

The objective of this study is to derive a technology pathway for each ASEAN country for rapid decarbonization that takes into account its unique energy landscape. This objective is highly relevant and timely for ASEAN countries in achieving the goal of net-zero in the second half of the century.

The methodology of this study is illustrated in Figure 3. Each sector-specific decarbonization technology was given a sustainability ranking based on its CO₂ emissions, material footprint, and impact on people, the environment, and animals [2]. Next, each technology was assessed on the two remaining issues of the energy trilemma, i.e., energy security and affordability. Third, each technology was assessed on its readiness and impact for a specific country, resulting in a set of country-specific decarbonization technologies. Prioritizing these technologies results in country-specific decarbonization pathways. The criteria for these screening exercises are provided below.

2.1. Sustainability Assessment

Recently, Lau et al. [2] proposed a sustainability ranking of technologies based on their CO₂ emissions, material footprints, and impact on people, animals, and the environment [2]. The criterion for ranking technology sustainability is provided in

Table 2. Ranking criterion for technology sustainability.

Sustainability Category	Sustainability Ranking
	Low	Medium	High
CO2 emission	Minimum to low CO2 emission	Some CO2 emission	Large amount of CO2 emission
Material footprint	Minimum to low amount of material needed	Moderate amount of material needed typical of light industry	Large amount of material needed typeof heavy industry
Impact on people	Mininum to low impact on human health and safety	Moderate impact on human health and safety	Potential large adverse impact on human health and safety
Impact on animals	Mininum to low impact on wildlife health and safety	Moderate impact on wildlife health and safety	Potential large adverse impact on wildlife health and safety
Impact on environment	Mininum to low impact on environ.	Moderate impact on environ.	Potential large adverse impact on environ.

. In

Table 3. Sustainability ranking for decarbonization technologies for Southeast Asian countries.

Sector	Technology	CO2 Emission	Material Footprint	Impact on People	Impact on Animals	Impact on Environ.
All	Grey H2	H	M	H	H	H
	Green H2	L	M	L	L	L
	CCU	L	M	L	L	L
Power	Nuclear	L	H	H	H	H
	Hydropower	L	H	H	H	H
	Solar	L	M	L	L	L
	Wind	L	L	L	M	L
	Bioenergy	L	M	H	H	H
	Geothermal	L	M	L	L	L
	Coal→gas	M	L	L	L	M
	CP-CCS	L	M	L	L	L
	GP-CCS	L	M	L	L	L
Transport	EV	L	M	L	L	L
	HFCV	L	M	L	L	L
	H2-marine	L	M	L	L	L
	Bio-aviation	L	M	H	H	H
Industry	Coal→H2-CCS	M	M	L	L	L
	Gas→H2-CCS	M	M	L	L	L
	Ind-CCS	L	M	L	L	L

L = low (green), M = medium (yellow), H = high (red).

, this sustainability ranking is applied to the various decarbonization technologies described in Figure 2.

In Table 3, there are three technologies that can be used to decarbonize the power, transport, and industry sectors: grey hydrogen, CCU, and green hydrogen. Grey hydrogen is produced from either coal or natural gas by coal gasification or steam methane reforming (SMR), respectively, where the produced CO₂ is emitted to the atmosphere. Consequently, grey hydrogen is ranked high in CO₂ emission and in its impact on people, animals, and the environment. Its material footprint is ranked medium because of the need to construct a coal gasification or SMR plant. Green hydrogen is produced by water electrolysis using renewable electricity. It is ranked low in CO₂ emission and in its impact on people, animals, and the environment, but medium in its material footprint because of the need for renewable electricity and the construction of an electrolysis plant. CCU is ranked low in CO₂ emission and in its impact on people, animals, and the environment. However, it is ranked medium in its material footprint because of the need for energy and a catalyst.

All other technologies listed in Table 3 are sector-specific. In the power sector, nuclear energy is ranked high in its material footprint and its impact on people, animals, and the environment because of its need for radioactive uranium and its adverse impact on health, safety, and the environment if an unsafe incident occurred. In an effort to remain nuclear free, ASEAN countries have traditionally avoided using nuclear energy. Although there has been recent interest in installing nuclear power in some ASEAN countries, at present public awareness and acceptance of nuclear power in ASEAN countries is limited [18]. It is doubtful that nuclear power will be installed in any ASEAN country in the foreseeable future.

In Southeast Asia, most hydroelectricity comes from the damming of major rivers such as the Mekong. Currently, over-damming of the Mekong has caused substantial sustainability issues, such as soil degradation, disturbance of fish migration, negative impact on biodiversity, and the resettlement of riparian communities in Laos, Cambodia, Thailand, and Vietnam [19,20]. Therefore, hydroelectricity is ranked high in its impact on people, animals, and the environment. It is also ranked high in its material footprint, due to the demand for concrete needed to build big dams.

Bioenergy is ranked high in its impact on people, animals, and the environment in Southeast Asia because practically all bioenergy comes from first generation biocrops, such as palm oil, sugarcane, cassava, or coconut, which compete with other needs for land and water resources. In Indonesia, Thailand, Malaysia, and the Philippines, the use of bioenergy results in substantial sustainability issues, such as food scarcity, loss of biodiversity, deforestation, destruction of peatland, greenhouse gas emission, soil erosion, social conflicts, and adverse public health [21,22,23,24,25,26,27,28]. For these same reasons, the use of biofuels for aviation (bio-aviation) is also ranked high in its impact on people, animals, and the environment.

2.2. Energy Trilemma Assessment

In setting its national energy policy, each national government must balance the triple goals of energy security, affordability, and sustainability [7]. Energy sustainability has been discussed in the previous section. Energy security addresses access to energy resources; energy affordability addresses the cost of energy. This energy trilemma is country-specific. In general, prosperous countries are more concerned about energy sustainability, while poorer countries are more concerned about energy affordability. All countries that lack energy resources are concerned about energy security. As ASEAN countries vary greatly in economic prosperity and in the distribution of energy resources, their considerations in addressing the energy trilemma vary greatly.

The criteria for energy security, affordability, and sustainability ranking are provided in

Table 4. Criteria for energy trilemma ranking.

Category/Ranking	Low	Medium	High
Security	Lacking in domestic energy resources	Some domestic resources but import needed	Sufficient domestic resources to be import independent
Affordability	Too expensive to be applied on a large-scale	Due to high cost, application is limited in scope	Readily affordable for application on a large scale
Sustainability	Ranked high in any category in Table 2	Ranked medium in any category in Table 2	Ranked low in all categories in Table 2

. For energy security, a technology is ranked low if there is no or very limited domestic resource. It is ranked medium if there is some domestic resource but imports were needed. It is ranked high if there are sufficient domestic resources to be self-dependent (Table 4).

For energy affordability, a technology is ranked low if it is too expensive to be applied on a large-scale in a country. It is ranked medium if its application on a limited scale is cost-effective. It is ranked high if it is cost-effective to apply the technology widely in the country (Table 4).

For energy sustainability (Table 4), a technology is ranked low if it has a high ranking in any of the five categories shown in Table 1. It is ranked medium if it has one or more medium ranking(s), but no high ranking, as shown in Table 2. It is ranked high if it has a low ranking in all five categories, as shown in Table 2.

2.3. Technology Readiness and Impact Mapping

The criteria for ranking technology readiness and impact are provided in

Table 5. Criterion for ranking in technology readiness and impact.

Category	Sector/Ranking	Low	High
Readiness	All	Never or unlikely to be used	Used or readily used based on results from other countries
Impact	Power	Low degree of power generation	High degree of power generation
	Transport	Usable in some vehicles, ships or planes	Usable in most vehicles, ships or planes
	Industry	Usable in some industrial plants	Usable in most industrial plants

. Technologies that are already in use or readily transferrable for local use are ranked high in readiness. Technologies that can be widely used in the country and have the biggest CO₂ abatement potential are ranked high in impact.

3. Country-Specific Assessment

3.1. Indonesia

Figure 4 gives the ranking of various decarbonization technologies (Figure 2) for Indonesia based on the aforementioned criteria. The following observations can be made from these figures.

• Ten technologies were ranked high in both readiness and impact (Figure 4b).
• Of these technologies, geothermal, EV, CP-CCS, GP-CCS, and Ind-CCS were ranked high in the energy trilemma, i.e., security, affordability, and sustainability. They have the highest potential to the applied in a large scale (Figure 4b).
• Coal→gas and coal→H₂-CCS had the second highest potential. However, the former ranked medium in sustainability, due to CO₂ emission.
• Indonesia would benefit from converting its coal to blue hydrogen by coal gasification. However, the current cost is too high for large-scale implementation. More research and development are needed to bring the cost down (Figure 4a).
• Hydroelectricity, biofuels, and biofuels for aviation all have potential to be applied in Indonesia. However, sustainability issues need to be resolved before they can be further applied at scale (Figure 4a).

3.2. Vietnam

Figure 5 gives the ranking of various decarbonization technologies (Figure 2) for Vietnam. The following observations can be made from these figures.

• Six decarbonization technologies were ranked high in both readiness and impact (Figure 5b).
• Of these technologies, Ind-CCS, CP-CCS, GP-CCS, and EV have the highest potential, because they were ranked high in energy security, affordability, and sustainability (Figure 5a).
• Coal→gas has the second highest potential. However, it had a medium ranking in the sustainability due to CO₂ emission (Figure 5a).
• Hydroelectricity has potential, but sustainability issues need to be adequately addressed before further large-scale application, as discussed earlier (Figure 5a).

3.3. Thailand

Figure 6 provides the ranking of various decarbonization technologies (Figure 2) for Thailand. The following observations can be made from these figures.

• Nine decarbonization technologies were ranked high in both readiness and impact (Figure 6b).
• Of these technologies, Ind-CCS, CP-CCS, GP-CCS, and EV have the highest potential, because they were ranked high in energy security, affordability, and sustainability (Figure 6a).
• Coal→gas, coal→H₂-CCS, and gas→H₂-CCS have the second highest potential. Both coal→H₂-CCS and gas→H₂-CCS were ranked medium in affordability, and coal→gas was ranked medium in sustainability because of CO₂ emission (Figure 6a).
• Bioenergy and biofuels for aviation have potential, but sustainability issues need to be adequately addressed before further large-scale application (Figure 6a).

3.4. Malaysia

Figure 7 provides the ranking of various decarbonization technologies (Figure 2) for Malaysia. The following observations can be made from these figures.

• Eight decarbonization technologies were ranked high in both readiness and impact (Figure 7b).
• Of these technologies, Ind-CCS, GP-CCS, and EV have the highest potential, because they were ranked high in energy security, affordability, and sustainability (Figure 7a).
• Coal→gas, CP-CCS, coal→H₂-CCS, and gas→H₂-CCS have the second highest potential. CP-CCS and Coal→H₂-CCS had a medium ranking in the energy security, as Malaysia has to import coal from other countries (Figure 7a). Gas→H₂-CCS had a medium ranking in affordability and coal→H₂-CCS had a medium ranking in both security and affordability, because Malaysia has to import coal and it is expensive to apply coal gasification on a large-scale. Coal→gas had a medium ranking in sustainability because of CO₂ emission during power generation.
• Hydroelectricity has good potential, but sustainability issues need to be adequately addressed before further large-scale application (Figure 7a).

3.5. The Philippines

Figure 8 provides the ranking of various decarbonization technologies (Figure 2) for the Philippines. The following observations can be made from these figures.

• Eight decarbonization technologies were ranked high in both readiness and impact (Figure 8b).
• Of these technologies, geothermal, Ind-CCS, GP-CCS, and EV had the highest potential because they were ranked high in energy security, affordability, and sustainability (Figure 8a).
• Coal→gas, CP-CCS, and coal→H₂-CCS have the second highest potential. Coal→gas had a medium ranking in sustainability, due to CO₂ emission. CP-CCS had a medium ranking in security because the Philippines has to import coal. Coal→H₂-CCS also had a medium ranking in security because coal is imported. It was also ranked medium in affordability, as coal gasification is too expensive to be applied on a large-scale (Figure 8a).
• Hydroelectricity has good potential, but sustainability issues need to be adequately addressed before further large-scale application (Figure 8a).

3.6. Singapore

Figure 9 provides the ranking of various decarbonization technologies (Figure 2) for Singapore. The following observations can be made from these figures.

• Six decarbonization technologies were ranked high in both readiness and impact (Figure 9b).
• Of these, EV has the highest potential, because it was ranked high in energy security, affordability, and sustainability (Figure 9a).
• GP-CCS, Ind-CCS, and solar PV have the second highest potential. However, they had a medium ranking in energy security, as Singapore has to import gas from other countries and Singapore has limited space for solar PV installation (Figure 9a).
• Bioenergy and its use for aviation has potential, but sustainability issues need to be adequately addressed before further large-scale application (Figure 9a).

3.7. Myanmar

Figure 10 provides the ranking of various decarbonization technologies (Figure 2) for Myanmar. The following observations can be made from these figures.

• Six decarbonization technologies were ranked high in both readiness and impact (Figure 10b).
• Of these technologies, Ind-CCS, CP-CCS, GP-CCS, and EV have the highest potential because they were ranked high in energy security, affordability, and sustainability (Figure 10a).
• Coal→gas has the second highest potential. However, it had a medium ranking in sustainability because of CO₂ emission (Figure 10a).
• Hydroelectricity has potential, but was ranked low in sustainability due to over-damming of the Mekong River, which needs to be resolved before further large-scale implementation (Figure 10a).

3.8. Cambodia

Figure 11 provides the ranking of various decarbonization technologies (Figure 2) for Cambodia. The following observations can be made from these figures.

• Six decarbonization technologies were ranked high in both readiness and impact (Figure 11b).
• Of these technologies, Ind-CC and EV had the highest potential because they were ranked high in energy security, affordability, and sustainability (Figure 11a).
• Solar PV has the second highest potential, but was ranked medium in security because of a medium level of irradiance (Figure 11a).
• Coal→gas, CP-CCS, and hydroelectricity have potential. However, the first two had a low ranking in energy security, as Cambodia has to import coal and gas from other countries (Figure 11a). Hydroelectricity had a low ranking in sustainability due to over-damming of the Mekong River, which needs to be resolved before large-scale future application (Figure 11a).

3.9. Laos

Figure 12 provides the ranking of various decarbonization technologies (Figure 2) for Laos. The following observations can be made from these figures.

• Five decarbonization technologies were ranked high in both readiness and impact (Figure 12b).
• Of these technologies, Ind-CCS, CP-CCS, and EV have the highest potential, because they were ranked high in energy security, affordability, and sustainability (Figure 12a).
• Coal→gas and hydroelectricity have the second highest potential. However, Coal→gas had a low ranking in energy security, as Laos has to import gas from other countries (Figure 12a). Hydroelectricity had a low ranking in sustainability because of over-damming of the Mekong River, which needs to be resolved before large-scale future application.

3.10. Brunei

Figure 13 provides the ranking of various decarbonization technologies (Figure 2) for Brunei. The following observation can be made from these figures.

• Four decarbonization technologies were ranked high in both readiness and impact (Figure 13b).
• Of these technologies, EV, GP-CCS, and Ind-CCS have the highest potential, as all of them were ranked high in the energy trilemma (Figure 13a).
• Solar PV has the second highest potential, but was ranked medium in security due to the moderate level of solar irradiance (Figure 13a).

4. Decarbonization Roadmaps

The decarbonization pathways for the ten ASEAN countries obtained by using this study’s assessment tool are summarized in

Table 6. Decarbonization roadmaps for ASEAN countries by sector.

Country	Power Sector	Transport Sector	Industry Sector
Indonesia	Coal→gas 3 Geothermal Hydro 3 Bio 3 CP-CCS GP-CCS	EV Bio-aviation 3	Ind-CCS Coal→H2-CCS 2
Vietnam	Coal→gas 3 Hydro 3 CP-CCS GP-CCS	EV	Ind-CCS
Thailand	Coal→gas 3 CP-CCS GP-CCS Bio 3	EV Bio-aviation 3	Ind-CCS Coal→H2-CCS 1,2 Gas→H2-CCS 1,2
Malaysia	GP-CCS CP-CCS 1 Coal→gas 3 Hydro 3	EV	Ind-CCS Coal→H2-CCS 1,2 Gas→H2-CCS 2
Philippines	Geothermal Coal→gas 3 CP-CCS 1 GP-CCS Hydro 3	EV	Ind-CCS Coal→H2-CCS 1,2
Singapore	GP-CCS 1 Solar PV 1 Bio 1,3	EV Bio-aviation 1,3	Ind-CCS 1
Myanmar	CP-CCS GP-CCS Coal→gas 3 Hydro 3	EV	Ind-CCS
Cambodia	Coal→gas 1,3 CP-CCS 1 Hydro 3 Solar PV 1	EV	Ind-CCS
Laos	CP-CCS Coal→gas 3 Hydro 3	EV	Ind-CCS
Brunei	GP-CCS Solar PV 1	EV	Ind-CCS

¹ Security issues exist; ² affordability issues exist; ³ sustainability issues exist.

. These are the technologies ASEAN countries should focus on to obtain the most benefits for decarbonization. Note that some of these technologies have remaining security, affordability, or sustainability issues that need to be addressed before large-scale future application. Technologies that have no such issues should be given a higher priority. Below is a discussion of the roadmap for individual ASEAN countries.

4.1. Roadmap for Indonesia

In the power sector, the decarbonization technologies with the highest potential are implementing CCS in existing and future coal- and gas-fired power plants and promulgating policies that encourage private sector investment in geothermal power plants. The second-highest potential benefit will come from switching from coal to gas for power generation. The third highest potential benefit will come from increasing the share of hydropower and bioenergy in power generation after their respective sustainability issues are resolved. In the transport sector, replacing ICE vehicles by EVs should be the primary focus. The second focus should be using biofuels for aviation after resolving their sustainability issues. In the industry sector, using CCS to decarbonize industrial plants should be the focus. In the long term, replacing fossil fuels by blue hydrogen generated from coal is the preferred solution.

4.2. Roadmap for Vietnam

In the power sector, implementing CCS in existing and future coal- and gas-fired power plants will have the highest benefit. The next highest benefit will be from switching from coal to gas for power generation. The third highest benefit will be from increasing hydropower after resolving its sustainability issues. EVs should be the key focus for the transport sector, while implementing CCS in industry plants is the key focus for the industry sector.

4.3. Roadmap for Thailand

In the power sector, implementing CCS in existing and future coal- and gas-fired power plants will have the highest benefit. The next highest benefit will come from switching from coal to gas for power generation. The third highest benefit will come from increasing the use of biofuel for power generation after resolving its sustainability issues. EVs should be the focus for the transport sector, followed by biofuels for aviation after resolving their sustainability issues. In the industry sector, implementing CCS in industry plants should be the focus. In the long term, using blue hydrogen for heating is the preferred solution for industry.

4.4. Roadmap for Malaysia

In the power sector, installing CCS in existing and future gas-fired power plants is the best solution. The next-best solution is switching from coal to gas for power generation and installing CCS in existing coal-fired power plants. The third solution is increasing hydropower after resolving its sustainability issues. EVs should be the focus for the transport sector, followed by biofuels for aviation after resolving their sustainability issues. Installing CCS in industry plants should be the focus for the industry sector. In the long run, use of blue hydrogen to replace fossil fuels for heating is the preferred solution.

4.5. Roadmap for the Philippines

In the power sector, installing CCS in gas-fired power plants and encouraging private sector investment in geothermal power plants should be the main focus. The next focus is switching from coal to gas for power generation and installing CCS in coal-fired power plants. Increasing hydropower can be considered after resolving its sustainability issues. EVs should be the focus for the transport sector, while installing CCS in industry plants should be the focus for the industry sector. The long-term solution for industry is to use blue hydrogen from coal for heating.

4.6. Roadmap of Singapore

In the power sector, the biggest benefit will come from installing CCS in gas-fired power plants. The next benefit will come from increasing the share of solar PV. The third benefit will come from using biofuels for power generation, provided that sustainability issues can be resolved. EVs should be the focus for the transport sector, followed by biofuels for aviation, provided that sustainability issues are resolved. Installing CCS in industry plants should be the focus for the industry sector.

4.7. Roadmap for Myanmar

In the power sector, installing CCS in gas- and coal-fired power plants should be the main focus, followed by switching from coal to gas for power generation. The third focus is increasing hydropower after its sustainability issues are resolved. In the transport sector, the focus should be on the use of EVs. In the industry sector, the focus should be installing CCS in industry plants.

4.8. Roadmap for Cambodia

In the power sector, installing CCS in coal-fired power plants should be the main focus, followed by switching from coal to gas for power generation in the long term, with imported gas. The third focus is increasing hydropower, if sustainability issues are resolved. The fourth focus is increasing solar PV capacity. In the transport sector, the focus should be on the use of EVs. In the industry sector, the focus should be installing CCS in industry plants.

4.9. Roadmap for Laos

In the power sector, installing CCS in coal-fired power plants should be the main focus, followed by switching from coal to gas for power generation in the long term, with imported gas. Hydropower can be considered, if sustainability issues are resolved. In the transport sector, the focus should be on the use of EVs. In the industry sector, the focus should be installing CCS in industry plants.

4.10. Roadmap for Brunei

In the power sector, the main focus should be installing CCS in gas-fired power plants, followed by installing solar PV. In the transport sector, the focus should be on the use of EVs. In the industry sector, the focus should be installing CCS in industry plants.

5. Discussion

Several important observations can be made from the technology pathways provided in Table 6. First, in the power sector, switching from coal to gas for power generation is a priority for Vietnam, Malaysia, Indonesia, and the Philippines, which are countries that rely heavily on coal [2]. This switch alone can reduce CO₂ emissions by about one-half, as the burning of gas emits only half the CO₂ of burning coal. Second, installing CCS in existing or future fossil fuel power plants is also a key to decarbonization. Recent research has shown that there is enough storage space in the saline aquifers and in the oil and gas fields in Southeast Asia to store at least two centuries of anthropogenic CO₂ from the power and industry sectors [2,3,4,5,6,7]. Consequently, implementation of large-scale CCS projects is a necessary part of decarbonization for most ASEAN countries. Third, hydroelectricity and bioenergy are the key renewable energies in most Southeast Asian countries. However, they have substantial sustainability issues, such as the over-damming of the Mekong River [19,20] and the deforestation caused by palm oil plantations [21,22,23,24,25,26,27,28,29].

In the transport sector, the replacement of ICE vehicles by EVs is a key technology that is widely applicable to ASEAN countries. All ASEAN countries have set targets for EV usage. This step will mean more demand for electricity, necessitating the construction of new low-carbon power plants. A “smarter” power grid using digital technologies will also be needed to prevent power outages due to unbalanced electricity supply and demand. In addition, the construction of adequate numbers of EV charging stations will be needed before EVs become the norm for road transport. Decarbonization of marine transport will take a longer time, and will probably involve the use of hydrogen for marine fuels. Before this happens, the supply chain for hydrogen first needs to be made available. This probably will not happen until road transport is electrified.

Using biofuels to replace petroleum-based fuels for aviation will be a key way to decarbonize the aviation industry [15]. Before this happens, sustainability issues of biofuels based on first generation biocrops, such as palm oil, needs to be resolved. This is particularly relevant for Indonesia and Thailand.

In the industry sector, installing CCS in existing or future industry plants is needed. In the long term, replacing fossil fuels by blue hydrogen for high-temperature heating is the preferred solution. Even in this case, the use of CCS to mitigate the CO₂ emitted from coal gasification or SMR plants will be needed.

Figure 1 illustrates the current energy usage in the power, transport, and industry sectors. Figure 14 summarizes what happens when decarbonization technologies are applied to these sectors. One key decarbonization technology is CCS, which can be applied to coal- and gas-fired power plants, refineries, biorefineries, petrochemical plants, coal gasification plants, and SMR plants. Renewable energies can be used to provide electricity and green hydrogen for all sectors. In particular, bioenergy can be used to produce biofuels for the transport sector. Both natural gas and coal can be used to produce blue hydrogen for the industry and the transport sectors. Conventional industry plants that use coal or natural gas for high-temperature heating can be replaced by plants that use hydrogen for high-temperature heating. There may also be some legacy industry plants that still use fossil fuels for heating, which are not shown in Figure 14. For these plants, CCS can be used to mitigate the emitted CO₂. Figure 14 can be adapted for each ASEAN country using the results shown in Table 6.

There are several limitations to this study. First, this study considered only the decarbonization technologies listed in Figure 2 and Table 2. Some technologies were not included in this list, such as direct CO₂ capture from air (DAC) [29,30,31] and improvements in energy efficiency. DAC was excluded because it has a low technology readiness level. It can be included later when its technology readiness level increases. Improvement in energy efficiency is needed to reduce energy demand. However, since this study deals only with the supply side of decarbonization, it is outside the scope of this study. Second, technology mapping-based readiness and impact can be refined to include not just low and high rankings, but also low, medium, and high rankings. In addition, technology mapping is best done by a group of experts who are familiar with decarbonization technologies.

6. Conclusions

The following conclusions can be made from this study.

• A new integrated assessment tool is proposed for the screening of decarbonization technologies, taking into account the energy trilemma (sustainability, security, affordability) as well the technology’s readiness and impact for a specific country.
• This tool was applied to a set of decarbonization technologies to derive a technology pathway for each ASEAN country. The result is an inventory of technologies that have both high impact and readiness for decarbonizing the power, transport, and industry sectors of each country. The tool also reveals each technology’s remaining issues regarding security, affordability, and sustainability, which require more research and development.
• CCS is a key technology for large-scale CO₂ emission in the power and industry sectors.
• For Indonesia, the Philippines, Vietnam, Malaysia, Cambodia, Laos, and Thailand, switching from coal to gas for power generation can halve their CO₂ emission and should be given a high priority. However, for some of these countries, construction of LNG terminals and securing long-term LNG contracts will be needed.
• Although hydropower and bioenergy have high potential for ASEAN, sustainability issues arising from the damming of the Mekong River and from deforestation due to palm oil plantation need to be resolved.
• In the road transport sector, replacing ICE vehicles by EVs is the overarching theme for ASEAN countries. However, this change will require building of charging stations and increasing low-carbon electricity capacity.
• In the medium to long term, use of hydrogen for marine fuel and biofuels as aviation fuel will be the preferred solution. However, the former will require the building of a hydrogen supply chain and infrastructure; the latter will require solving sustainability issues with biocrops.
• For the industry sector, installing CCS in industrial plants should be given priority. In the long term, replacement of fossil fuels by blue hydrogen for high-temperature heating is the preferred solution. However, building of a hydrogen infrastructure and supply chain will be needed.