Energies 2023 , 16 , 280
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3. Application of Carbon-Neutral Fuels (Power, Transport, Heat) As discussed above, carbon-neutral fuels have critical roles to play in the realization of carbon neutrality in the next three decades. Today, they are already in application in several sectors of the energy system as summarized in Figure 10. In terms of power generation, these fuels offer cleaner pathways by using technologies such as fuel cells, reciprocating engines, or gas turbines to replace high-carbon fuels. Hydrogen can be utilized in fuel cells and turbines for the generation of power and heat. There are several existing and planned hydrogen-based combined heat and power (CHP) projects. At NREL’s Flatinos Campus, a fuel cell generator as part of the ARIES MW-scale hydrogen system is being designed and commissioned. The flexible system comprises a 1.25 MW PEM electrolyzer, a 600kgH 2 storage system, and a 1 MW fuel cell generator. The platform is designated to demonstrate direct green hydrogen generation, energy storage, power production, and grid integration at MW scale [55]. Across the world, more than 800 MW of large stationary fuel cell systems (rated power >200 kW) have been installed for distributed generation and CHP applications, with the largest shares of installation located in the US and South Korea. More than 4100 fuel cell units for CHP applications have been installed in Europe and a 1.4 MW stationary fuel cell powerplant is the largest in Europe. The transport sector alone is responsible for 20% of the global primary energy demand, and about 96% of this demand is met with petroleum [56]. Due to the progressive growth of fossil fuel consumption, the sector was responsible for 37% of CO 2 emissions from end-use sectors in 2021 [57]. Sectors such as aeronautics, long-haul road, maritime transport, and railways require highly dense fuels and the direct electrification of these sectors with batteries or grid is challenging. The range, capacity, and refueling time of batteries do not make them suitable for these sectors but carbon-neutral fuels, on the other hand, meet the fuel requirement of these hard-to-abate transport sectors and they can directly replace the fossil fuels or indirectly electrify these sectors. The International Maritime Organization (IMO) has plans to reduce shipping carbon intensities by an average of 40% by 2030 and by 70% by 2050 and cut maritime emissions by at least 50% by 2050 in reference to 2008 levels. In addition, as of January 2020, the global sulfur content of marine fuels has been limited to 0.5 wt% [38,58]. These targets have created an important opportunity for the penetration of carbon-neutral fuels in the shipping sector. In the shipping sector, for example, ammonia’s popularity is growing significantly. The world’s first ammonia-based fuel cell for shipping is being developed by the Fraunhofer Institute in collaboration with 13 European consortium partners as part of the ShipFC project [59]. The project comprises an offshore vessel retrofitted with a large 2 MW ammonia fuel cell that will allow it to sail 100% on ammonia for up to 3000 h per year [60]. Similarly, green ammonia is being developed in the Ammonia Zero Emissions Project (AMAZE) as a substitute ship engine fuel. The project was launched in early 2022 by Bergen Engines to develop technology for a fuel-flexible ICE with green ammonia as the primary fuel [61]. Net carbon-renewable methanol will meet IMO’s goal of reducing GHG emissions by 50% by 2050. By using methanol as a marine fuel compared to diesel, emissions of SO x , NO x , and PM reduce by 99%, 60%, and 95%, respectively [46]. The application of carbon-neutral fuels in road transport is also gaining momentum in recent years. China has a goal to produce between 100,000 and 200,000 tons of green hydrogen annually and to have around 50,000 hydrogen- powered vehicles on the roads by 2025. Currently, M100 (100% methanol) vehicles are in operation in some countries with China having the largest share of such vehicles. In Italy, methanol-derived fuels such as A20, methanol (15%)-bio-ethanol (5%)-gasoline blends are being trialed. The US has for some time been using methanol regularly in motorsports, and Iceland is fuelling a fleet of cars with renewable methanol [46]. Methanol fuel cells do not only substitute fossil fuels and reduce both CO 2 emissions and fuel consumption but they are also designed to ensure long-range, fast refueling, zero harmful emissions, and lower costs. The range of battery electric vehicles can be extended from 200 km to over 1000 km with methanol fuel cells. An eco-friendly alternative fuel for heating is methanol. As a substitute fuel for cookstoves and boilers, methanol has been adopted in some parts
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