Energies 2023 , 16 , 280
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Thus, more long-term stringent measures have to be put forward. According to the Inter- governmental Panel on Climate Change (IPCC), the 1.5 °C goal requires a global realization of net zero CO 2 emissions by 2050—a goal collectively termed “reaching carbon neutrality”. Carbon neutrality refers to the balance between CO 2 emissions and absorptions within a specific period to achieve “net zero emissions of carbon dioxide” [10]. Carbon neutrality means the output of CO 2 is offset by other approaches and thus has neutral effects on the environment. Today, a total of 194 countries have joined the Paris Agreement [11]. Countries like the United Kingdom, Germany, Canada, France, South Africa, South Korea, and Denmark have pledged to reach carbon neutrality by 2050, Iceland and Sweden by 2040 and 2045, respectively, China by 2060, India by 2070, and more countries are expected to make similar pledges in the near future [12,13]. The development of carbon-neutral fuels is very crucial in reaching carbon neutral- ity, especially in decarbonizing the major energy-consuming sectors such as heavy-duty transport, power, industry, etc. [14–16]. Carbon-neutral fuels are carbon-based fuels that do not increase the atmospheric CO 2 when combusted. A net zero amount of atmospheric carbon is achieved from the combustion of these fuels in the sense that they are typically produced with CO 2 as a key component in the process—implying that there is no net gain of carbon in the atmosphere. There are several carbon-neutral fuels and all these fuels are important to the realization of a net zero future. However, the remaining discussions in this perspective paper are limited to green hydrogen, green ammonia, and renewable methanol. There are several existing reviews on their production technologies and pathways such as hydrogen [17–19], ammonia [20–22], and methanol [23–25]. Despite the key contributions of such reviews, there is a limited holistic summary of the role of these fuels in reaching a net zero future. Our current perspective is thus developed to provide a brief overview of the interconnected roles of all three fuels. These are arguably the three most often consid- ered carbon-neutral fuels to significantly contribute to the realization of carbon neutrality within the next three decades, especially in hard-to-abate sectors like long-range transport, energy-intensive industry, and parts of residential heating. The coupling of these sectors with the power sector through the production and consumption of these fuels helps solve one of the most challenging tasks with renewable electricity generation (i.e., matching time of generation to time of load consequently leading to energy curtailment), especially from intermittent sources such as solar and wind energy. The technologies for their production stage to end-use are well understood and have been around for quite some time albeit with certain inherent challenges such as commercialization and large scale-up. Undoubtedly, these three carbon-neutral fuels considered in this perspective have a crucial role to play in reaching the 1.5 °C target by mid-century, and these roles and potential applications will become apparent in the subsequent sections. Figure 1 highlights the energy transition from today’s fossil fuel-dominated system to tomorrow’s net zero carbon emissions system powered mainly by renewable energies and carbon-neutral fuels.
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