Transportation technology has had a significant impact on the development of the world in the past, is still influencing it now, and will have a substantial effect on the development of the world in the future. Roads and other forms of transportation are costly and time-consuming to build, requiring a significant commitment of time and money.
However, the building, growth, and maintenance of communication routes have been on the agenda of many jurisdictions since ancient times because of the great interest in infrastructure development for economic and strategic purposes.
When the railway era began at the turn of the nineteenth century, land and maritime transportation had advanced significantly. In 1830, the first ever public railway transit system was implemented, displaying a travel speed of 30 kilometres per hour. Today, high-speed trains can reach speeds of more than 300 kilometres per hour because of advances in technology that have taken place over the last 185 years, including diesel-electric and electric-only locomotives. The Shinkansen train in Japan can reach speeds over 500 km/h. Although the 1435 mm gauge Stephenson recommended for the pioneering railroads is being used today, it is essential to note that this gauge has been accepted as a standard for railway construction across the globe. This demonstrates the long-term impact of a previous choice.
Rail transportation has several economic, social, energy, and environmental benefits, making it the finest land transportation alternative. Compared to other modes of transportation, rail offers several advantages, such as lower emissions and fuel consumption per passenger (or unit of freight) moved, less land usage (three times less land is needed than on highways), and a high rate of travel. Cargoes are often delivered on light rail and heavy-duty trains, although commodities may be moved by tram, funicular or monorail systems. The unit train, the carload, and the intermodal mode are all ways of rail transport that connect with maritime and road modes of transportation employing trailers, containers, and tanks today. Single fixed-type and dual-type rails are used to power the rail vehicles.
The advent of railroads in the industrialised world changed the course of human history. Georgescu-Roegen (1986) argues that the use of coal and wood in steam engines provided sufficient motive power in a ready-to-use manner, allowing for easier extraction and processing of minerals, construction of railroads facilitated by better technology using machines, and the development of more and better steam engines, railroad locomotives, and railcars. GHG emissions into the atmosphere surged “exponentially” during 150 years when steam locomotives dominated the transportation industry. The success of railroads in spurring technical advancement has rendered steam locomotives obsolete in favour of diesel-electric locomotives, which are now totally replacing them. There are just a few places in the world where electric railroads have been built to accommodate locomotives that can only run on electricity.
When an initial abundance of a resource spurs exponential consumption and development, Bejan and Lorente (2011) highlight the universality of the paradigm transition phenomena. Paradigm shift: Growth cannot be maintained owing to limiting resources; see Hubert’s peak hypothesis in Hubbert (1949). Today’s paradigm change in rail transportation is owing to civilisation having reached a point where fossil fuel supplies are depleting rapidly due to increased use and because of the increased detrimental effect of atmospheric pollutants due to global warming as a result.
With a predicted growth rate of 2.8 kt/year for the next 15 years, diesel-electric rail locomotive operating is now responsible for GHG emissions of approximately 120 kt of CO2 equivalent per year today. According to Dincer et al. previous . ‘s research, these facts exist (2015). Power generated by a regional power generating mix is delivered to the electric train in countries like Japan and the European Union. In other words, the electric train system is not entirely emission-free since the bulk of grid power production depends on fossil fuel burning (or even indirect fossil fuel combustion, such as nuclear power).
Energy usage per freight tonne and kilometre for rail transport is around 0.4%. According to this metric, coal-fired power plants release 150 g of CO2 for every tonne of energy they offer for a single kilometre of rail transit. According to previous years’ data and forecasts, transportation is expected to increase at a positive yearly rate soon. According to Mantzos (2003), rail transport in the European Union is expected to rise by 125% by 2020, equating to around 1% of Europe’s total energy consumption and the associated levels of greenhouse gas emissions.
The rise in train traffic is associated with a slew of environmental problems. Some pollutants contribute to air pollution, including carbon dioxide (CO), non-combusted hydrocarbons (NHCs), nitrogen oxides (NOx), and particle matter (PM). Acid rain, animal poisoning, stratospheric ozone depletion, ecological degradation, accidents, and risks are all linked, as are sulphur dioxide emissions and volatile organic compounds (VOC).
In recent years, the air pollution released by railroads in North America has risen as this industry has grown. Forty-eight thousand kilometres of track make up the Canadian rail network, making it one of the world’s most enormous. Rail freight services, which employ 3043 locomotives and 59,395 freight cars, comprise most of the rail transportation industry and provide 90% of its operating income. There has been a considerable rise in diesel fuel use in Canada during 2009, from 1.87 billion litres to over 2.11 billion litres, according to the Railway Association Canada (RAC). For 2015, RAC (2014) has set a goal of a 6% reduction in GHG emissions from freight rail transport in Canada compared to 2010. EPA (2012) advises that the maximum amount of air pollutants generated by line haul operation must be 0.14 g/bhp.hr for hydrocarbons, 1.3 g/bhp.hr of nitrogen oxides, 1.5 g/bhp.hr of carbon dioxide, and 0.26 g/bhp.hr of delicate particulate matter (PM). As a result of this pressure, new ideas and research and development in the railway industry are spawned.
Shunping et al. (2009) mainly focused on energy use and associated studies in a previous transportation review study. Malaysian transportation policy was also a subject of interest in this study (Ong et al., 2012). Rondinelli and Berry examine multimodal transportation’s logistical and environmental impacts (2000). The environmental effect of any economic activity, particularly the transportation industry, is becoming increasingly critical. As a result, Valipour et al.’s argument for using flow diagrams to analyse industrial sectors’ environmental effects is sound (2012). Valipour et al. explain their methodology in further detail.
To make clean rail operations more appealing from an economic and environmental standpoint, it is critical to discover feasible solutions and energy alternatives that link the industry to more stable energy sources with less reliance on imports and variable costs. This topic has not been addressed in previous sector assessments of transportation. In addition, no comprehensive reviews focus on rail transportation choices for a cleaner environment for their immediate or long-term relevance.
New energy choices for clean rail and civil possibilities are discussed in this article that concentrates heavily on natural gas as a feasible solution for immediate use.
Fig. 1 shows the diversified nature of transportation, including land, sea, air, freight, and people, and how hydrogen and fuel cells fit into each. There will be an increase from 1 billion to 2.5 billion passenger automobiles in the globe by 2050, which accounts for about half of global transportation’s energy consumption. (Lilly, 2022)
The UK must reduce its transportation CO2 emissions by half by 2030 to satisfy national carbon budget targets.
Rising emissions and a drop in renewable energy use have prompted demands for more aggressive action in the United Kingdom’s transportation sector. (CCC, 2016) In addition to biofuels and electric cars, hydrogen is one of the three critical possibilities for low-carbon transportation (EVs). Hydrogen avoids the land-use and air-quality issues of biofuels and the restricted range and lengthy recharging periods associated with EVs by using hydrogen as its fuel. As a result of their lower prices and more easily accessible infrastructure, electric automobiles have a long way to go before hydrogen vehicles. Plug-in electric cars currently account for 30% of new vehicle sales in Norway and 2% in the United Kingdom. (Norsk elbilforening, 2017)
Figure 1:Global transportation energy use in 2015
Additionally, hydrogen-powered cars may enhance the quality of the air. Premature fatalities from particulates and NOx pollution kill more than half a million people in Europe each year. (EEA, 2016) There is a direct cost of roughly h24b per year in Europe owing to illness-induced output losses, healthcare, agricultural yield losses, damage to structures, and an estimated h330–940b per year in external expenditures. 92% of the world’s population is subjected to air quality that is worse than the standards set by the WHO. (WHO, 2016) Diesel-powered vehicles will be banned in major cities by 2025, and all pure combustion vehicles will be prohibited countrywide by 2040 in the UK and France. (Reuters, 2017)
Vehicles with electric propulsion powered by hydrogen
It is possible to convert conventional internal combustion engines (known as “HICEs”) to operate on pure hydrogen, which is far cheaper than fuel cells. As a result, it’s unlikely that hydrogen combustion will have a substantial long-term impact on transportation. In dual-fuel automobiles, hydrogen may be combined with natural gas (referred to as “hythane”) or diesel; in bi-fuel powertrains, it can be switched between the two. Existing infrastructure may be used, although they are not zero-emission and may be replaced by lower-carbon alternatives. (Hart et al., 2015)
FCEVs often employ PEM fuel cells because of their high efficiency, high power density and ability to start from cold.
European automobiles often use a 60 kW fuel cell, much bigger than the domestic fuel cells. (B1 kW). Most trips can be completed using only the vehicle’s onboard battery, with the option to switch to the engine or fuel cell for longer or more infrequent trips. Other alternatives include cars with conventional internal combustion engines (ICE), batteries, and plug-in hybrid systems (PHEVs, also called range-extender EVs). (Stewart and Stewart, 2016)
Table 1 compares hydrogen powertrains to alternatives and reveals the following differences: (Pollet, Staffell and Shang, 2012)
(1)Toyota Mirai and Hyundai ix3553 have a capital and operational cost of $60–75k, compared to $25–30k for the Renault Zoe and Nissan Leaf.
As production quantities increase, FCEVs have the potential to reduce costs significantly, making them more affordable alternatives to traditional vehicles. (Dodds and Ekins, 2014)
(2) FCEVs offer greater driving ranges and quicker refuelling periods than BEVs, making them equivalent to conventional cars in terms of their efficiency (ca. 500 miles and 3 minutes).
Driverless cars’ power-hungry computers, sensors, and air conditioning and heating for vehicles in hot and cold locations will significantly influence BEV range more than FCEV57. (Pollet, Staffell and Shang, 2012)
(3) Due to the extended range of FCEVs, hydrogen filling stations can accommodate many more cars than EV chargers.
58 However, hydrogen refuellers, presently costing roughly $1.5 million, will likely plummet by two-thirds when the technology improves.
(4) Overcharging, deep discharges, and high charging/discharging rates reduce battery life.
Most BEVs are just five years old, and Tesla expects the batteries in these vehicles to last 10–15 years. Fuel cell stacks are intended to outlast other parts of the powertrain, unlike batteries, which can only withstand repeated, severe discharges. (Scamman, Newborough and Bustamante, 2015)
(5) Regarding the driving experience, FCEVs are superior to ICEs (quieter, less vibration and no gear shifting).
(6) Due to their size and design, hydrogen tanks may limit the baggage carried. It is possible to make FCEVs with zero emissions at the point of use if they are manufactured from renewable-powered electrolysis or biomass or fossil fuels with carbon capture and storage (CCS). As for BEVs, the same holds, whereas ICEs have limited decarbonisation potential. Adding biofuels to gasoline and diesel does not enhance air quality in the immediate area. (Ammermann et al., 2015)
(7) It is unnecessary to modify the power network to use FCEVs and refuel infrastructure to a large extent, which may help balance the grid.
(8)Comparable but distinct safety concerns exist for FCEVs compared to BEVs and ICE vehicles. Although hydrogen is combustible (much more so than gasoline), flames caused by hydrogen may only cause little harm to the car. (Pollet, Staffell and Shang, 2012)
Other modes of transportation are via road.
In the case of heavy-duty vehicles like buses and trucks, FCEVs may be the only viable zero-carbon choice, despite stiff competition from ICE and BEV passenger cars. 25% of all transportation energy is used in these industries (Fig. 1 earlier). Hydrogen bus deployment is fueled by a growing desire to reduce urban air and noise pollution. 64 Back-to-base operation reduces initial refuelling expenses by lowering the required stations and increasing their use.
As a result of lower industrial quantities, the cost gap between ICE and heavy-duty transportation is narrower. In contrast to passenger automobiles, the US Department of Energy aims for a maximum operational duration of 25 000 hours for fuel cell buses. (Marcinkoski, Wilson and Papageorgopoulos, 2016) Battery technologies are expected to remain impractical outside of metropolitan areas due to their weight and driving range; fuel cell buses use ten times more hydrogen per kilometre than passenger vehicles, exacerbating range restrictions. (US Department of Energy, 2017)
Buses powered by fuel cell technology. At a Technology Readiness Level (TRL) of 7.84, fuel cell buses have received considerable attention and are considered a reasonably mature technology. Due to the decreased space constraints, hydrogen may be kept at 350 bar in the bus roof at a lower cost due to onboard tanks holding roughly 40 kg of hydrogen. A fuel cell bus may cost 10–20 per cent more to operate than a diesel bus by 2030 but might be more cost-effective if used at a large scale.
With 7 million kilometres of operating experience in Europe, fuel cell buses have seen significant early deployment.
In Europe, there are 83 fuel cell buses in operation; in North America, there are 44.
Before the 2020 Olympic Games in Tokyo, Toyota plans to debut over 100 fuel cell buses from the company. (Toyota, 2016) Foshan City bought 300 fuel cell buses, making China the world’s biggest bus market.90 (quadrupling the global fleet of hydrogen-powered buses). As a point of reference, Shenzhen City’s fleet of over 16,000 buses has been electrified using BEVs. (Lambert, 2018)
Four London buses have already operated for more than 18 000 hours, demonstrating the progress in this area.
87 Nearing the DOE’s 25 000-hour goals, ten California buses have operated for more than 12 000 hours, with one surpassing 22 400 hours. It is now possible to find refuelling stations for fuel cell buses in 95 per cent of European countries (up from an initial aim of 85 per cent). (Madden, 2016)
Trucks. A lack of low-emission options means that fuel cells have a lot of promise in lorries. Battery and range-extender vehicles might be used for light goods trucks with short, low-speed travels, but long-haul heavy vehicles that demand high utilisation will likely need hydrogen. Although the Tesla Semi is planned to have a range of 300–500 miles for B$200 000, the competition for batteries is intensifying. (Tesla, 2017) With relatively modest production quantities, fuel cell vehicles might attain cost parity with other low-carbon solutions. While a single refuelling station might reduce fuel expenditures for return-to-base delivery trucks, a sufficient refuelling network is required for long-range HGVs.
High-mileage vehicles need a longer lifespan than other applications, with one programme seeking a stack lifetime of 50 000 hours.
In addition, it’s critical to have a vehicle with a minimal carbon footprint. In addition to Kenworth and Toyota, Nikola works on a long-distance HGV powered by liquid hydrogen in the United States. (Nikola Motor Company, 2016) HGV Auxiliary Power Units (APUs) are another use for fuel cells. Refrigeration units and “hotel” loads (such as cabin heating, cooling, lighting, and electrical gadgets) might be powered by these on parked HGVs to reduce engine idle.
Because the heavy-vehicle industry is very cost-sensitive, with no government backing or involvement, and hauliers are apprehensive of becoming pioneers, FCEV trucks have experienced lesser uptake than buses.
As a result, Anheuser-Busch InBev, a multinational beverage corporation, has bought 800 FCEV trucks to be in service by 2020. (Edie, 2018) Truck bans in large city centres might increase interest in alternative fuel vehicles.
Motorbikes. Passenger transportation in many locations is dominated by two-wheeled vehicles. A 4 kW fuel cell system created by Intelligent Energy and Suzuki is now being tested in the United Kingdom. (Intelligent Energy, 2017) Hydrogen canisters from vending machines may be used to recharge them because of their low fuel use. The use of FCEV motorcycles might help meet environmental and noise pollution goals.
Trains. Europe’s progress in electrifying its trains has stalled lately. For lines that are too long or too congested to electrify, hydrogen trains might be an alternative. A 500-mile-range fuel-cell powered train has started testing in Germany, with 101 and 40 trains expected to operate by 2020. By 2040, the UK government wants all diesel trains gone, and Alstom says it will do just that by converting a fleet of its electric trains to hydrogen-powered ones. (Gerrard, 2018)
In China, fuel cell-powered trams are being developed and put into service for use on the country’s light rail system.
This means that hydrogen trains will benefit from cost savings in the automotive industry since they are intended to utilise the same stacks and storage tanks as buses and trucks. In the long run, lower-cost hydrogen fuel and hydrogen that costs less than $7 per kilogramme will be necessary if hydrogen powertrains are to be economically viable. (Hart et al., 2016) According to recent research, FCEV trains are currently cost-competitive with diesel trains from a total cost of ownership standpoint.
Ships. Several marine applications, including ferries, have already begun using fuel cells to test the viability of hydrogen deployment. (Ballard Power Systems, 2015) If emissions-controlled zones (such as the Baltic Sea and urban ports) and hydrogen’s superior efficiency than LNG can drive early niches, hydrogen will likely gain momentum beyond 2030. It’s possible that the introduction of new propulsion technologies would be hampered by the fact that most boats have lengthy lifespans and are built in small numbers for very specialised purposes. Cryogenic storage is required due to the projected daily consumption of ferries of up to 2000 kg of hydrogen, and fuel costs are more crucial than upfront expenditure, with hydrogen costing much less than $7 per kilogramme. As with propulsion, port vehicles and auxiliary power might be the first to deploy fuel cells for a single refuelling station, which would help improve local air quality.
Aeroplanes. Aviation is one of the most challenging industries to decarbonise, and progress has been slow in lowering emissions from aircraft engines. The International Civil Aviation Organization (ICAO) decided in 2016 to put a ceiling on aviation emissions for the year 2020. However, this cap would be achieved chiefly via carbon offsets rather than low-emission fuels. (ICAO, 2016) A few hybrid electric designs are being researched, but their potential for reducing emissions is promising. (Gonzalez, 2016) The increased energy density of biofuels compared to hydrogen or batteries makes them an option. However, they are not emission-free and may stay expensive due to insufficient supply. For propulsion, hydrogen may be utilised; however, it must be liquefied for the requisite range. Fuel cells’ lack of takeoff power means combustion turbines are necessary. When it comes to aviation’s climatic advantages, hydrogen has been called into doubt due to its significant water vapour emissions, which add to net warming at high altitudes, even if they are short-lived. Effective hydrogen deployment is unlikely until 2050, except for tiny or low-flying aircraft. Developing low-emission aeroplane propulsion alternatives thus requires a great deal of effort.
Aviation-related industries. Using fuel cells, aviation auxiliary power units for taxiing aeroplanes to and from terminals have been tried. (Lawson, 2016) Air quality near airports is becoming more critical, and fuel cells might play a key role in powering ground vehicles and buses within 10 to 20 years, thanks to the necessity for a small number of refuelling stations with high utilisation. Unmanned aerial vehicles (UAVs) are becoming more popular for both commercial and military purposes. There are several advantages to using a fuel cell for UAVs, including quieter operation, more efficiency, and reduced vibration and infrared fingerprints than using a fossil fuel-powered UAV. However, the cost gap between fuel cell and battery UAVs will shrink with increased production volume. The fuel cell will maintain its edge in high-energy or long-duration applications.
Forklifts and other machinery. More than a dozen forklift trucks in the United States, and a few worldwide are powered by fuel cells. (US Department of Energy, 2016) Forklifts manufactured by Plug Power account for 85 per cent of FC forklifts sold in the US. A typical high-throughput warehouse may save TCO 24 per cent with FC forklifts since they produce no emissions and can be used inside. FC forklifts can also be refuelled quicker than their battery-powered counterparts. (Ballard Power Systems, 2010) Additionally, FC forklifts can operate in temperatures down to 40 C. Predominantly, direct methanol fuel cells (DMFCs) have shorter lives. Still, they have a cheaper cost of ownership in low-usage applications where PEMFCs can’t compete. (Ahmad Mayyas, Chan and Lipman, 2014) Agriculture is one of the few markets for fuel cells showing promise, where tractors114 and recreational vehicles like RV APUs and golf carts might benefit from their use.
Hot temperatures and heavy industry
Final energy use in European homes and businesses is 60–80 per cent heat and hot water.
Heat-related emissions must be drastically decreased, if not eliminated, by the year 2050. This will be difficult for several reasons: (Eyre, 2016)
(1) In many temperate nations, heating is the primary source of energy use, which creates an issue of scale.
(2) no one solution can fulfil all of the heat needs, which range from scattered low-temperature home heating to enormous high-temperature industrial loads;
(3) Because of the daily and seasonal variations in heat demand, a highly adaptable supply is required; (Staffell, Hamilton and Green, 2015)
(4) Low-carbon heating options are less competitive and might increase energy poverty, while fossil fuels give this flexibility at a cheaper cost.
Winter peak heat demand, which is much greater and more volatile than peak power demand, is a problem for low-emission heating in temperate nations (Fig. 2 and 3). Because of their cheap per-kW capital cost, current gas heating technologies are frequently enlarged for buildings, and the gas network (including geological storage) can store a month’s worth of use. They are well-suited to deal with the considerable seasonal variance that exists. (Richard, 2016)
Figure 2: Major Energy Vector Demand in Britain
Figure 3: British Household heat demand Variation
Thermal storage, more insulation, and more efficient devices might lower peak demand, but they need strict regulation that has not yet been implemented.
A decarbonised gas-based strategy may be more cost-effective than other low-carbon solutions like electrification or district heating for meeting peak heat demand.
Decarbonising heating has therefore lagged far behind other sectors in terms of progress. Because of its heavy reliance on gas, the United Kingdom may fail in its renewable heat goal for 2020. By 2030, it may only be able to decrease emissions from buildings and industry by roughly 20%, compared to a goal reduction of 57%. (CCC, 2015) Fig. 4 shows that, in many counties, natural gas has replaced coal and oil as the primary source of home heating fuel since it is now less expensive, more convenient, and cleaner-burning. There are over a billion electric heat pump systems heating residences in Asia, North America, and portions of Europe, while district heating is extensively employed in Russia and Scandinavia.
Figure 4:The DESSTINEE model estimates the percentage of fuels used for heating in 10 countries.
Alternatives to conventional heating that emit no carbon dioxide
Table 2 and below summarise the five major strategies for decarbonising heat worldwide (GEA, 2012). Although a few of them have acquired popularity in individual nations, none of them is commonly utilised on a worldwide level. The following are the most common choices:
(1) Reduction of demand. Energy consumption may be reduced by insulating, using high-efficiency equipment, and modifying demand behaviour (e.g., via smart metres and price). Residential heat demand might decline by 20% by 2050, which is a substantial contribution and a facilitator for other low-carbon heating solutions but inadequate in isolation. In affluent nations, 80–90% of the 2050 housing stock has already been built; (CCC, 2016b). Some houses are unsuited for retrofitting insulation, and family size (people per building) is reducing due to lifestyle choices.
(2) Green gas. Low-carbon gases might replace natural gas using the existing gas network assets and possibly decreasing costs and disruption. (MacLean et al., 2016) Anaerobic digestion and gasification of garbage, sewage, landfill gas, energy crops, etc., may produce biogases. Several factors stand in the way of widespread use: the lack of readily available resources, the possibility for emission reduction, the presence of local emissions, and the quality of the gas itself. As a result, the UK Bioenergy Strategy sets a 15% heating uptake cap. H2O is an alternative that can be injected into the current gas network in tiny amounts, or the existing gas network may be modified to distribute 100% hydrogen rather than natural gas.
(3) Electrification. Global CO2 emissions might be reduced by 8 per cent with the widespread use of heat pumps, which are popular in many nations. (Staffell et al., 2012) They may be unable to fulfil peak winter demand and customer preferences because of their low-grade heat and restricted production, and rapid uptake may compel electrical network modifications. However, prices may come down as the implementation continues, limiting acceptance. In rural areas without access to district heating or gas networks, which utilise costly, high-carbon fuels like heating oil, heat pumps may still be a significant option, especially if the residence has room for a more extensive system. High-density urban dwelling complexes may also benefit from electric heating since gas is not permitted for fire safety reasons and space heating needs are reduced. (MacLean et al., 2016)
(4) Thermodynamics. Only a few nations have a frigid environment and an openness to collaborative solutions allowing district heating. This technology might provide ten to twenty per cent of household heat by 2050 in highly populated nations like Britain. Installing retrofitted heat networks is expensive and disruptive; transmission lengths are limited to 30 kilometres. (Lidstone, 2016) However, they are 30 per cent cheaper to heat than gas boilers and are best suited for urban new construction. Geothermal heat or industrial and data centre waste heat may be used. Individual CHP systems are more expensive and less efficient than large-scale district heating CHP installations.
(5) Onsite renewable energy sources. Ninety per cent of the world’s heat is produced by modern renewable energy, with the rest coming from solar thermal and geothermal. (REN21, 2017) Some drawbacks to small-scale home solar thermal systems exist, including a lack of biomass supply and the high concentration of localised pollutants that may result from their use.
Technical feasibility, cost, appropriateness, compatibility across geographies and building types, and user acceptability and safety are some challenges or uncertainties connected with each low-carbon heating method. A single technology is typically the driving force of a country’s economy. Although this is a new development, the UK has an 84 per cent penetration of gas (Fig. 5). Natural gas or electricity heats almost all new American family dwellings. (US Census Bureau, 2014) Previous research has consequently focused on broadly implementing a particular technology to satisfy decarbonisation requirements.
Figure 5:Over forty years, the heating technology utilised in UK homes
Complementary heating systems, formerly more common, are gradually gaining popularity.
It has been shown in a UK case study that a 50% immersion of fuel cell micro-CHP may balance power requirements from a 20% penetration of heat pumps when used in conjunction with heat pump consumption. (Dodds et al., 2014) Even though no one can agree on the best technological mix for long-term transformation, the UK recognises that evidence must be reassessed and new methods tested. Based on geographical availability and building type, this technology combination might be tailored to offer a safety net in the face of technological uncertainty and fluctuating fuel prices.
Technology that utilises hydrogen and fuel cells
Hydrogen and fuel cell technologies were not included in most energy systems or building stock models for decades.
The majority of UK heat demand by 2050 might be met by hydrogen, according to recent research (Hodges et al., 2015), which shows that it plays an essential role in decarbonising heat. To provide warmth, a variety of H2FC methods are available.
Boilers that use hydrogen as a fuel. Hydrogen may be used in gas boilers and furnaces in low quantities. High quantities of hydrogen have a comparable Wobbe index to natural gas; however, a separate burner tip is needed because of hydrogen’s increased flame speed. (Hodges et al., 2015) The development of catalytic boilers, which prevent NOx formation 48 but need higher-grade hydrogen and are less powerful, is also underway. As a result, switching to hydrogen would require a complete overhaul of all appliances and their components. It’s nothing new: Many nations have changed from town gas to natural gas in recent decades, with the UK replacing 40 million appliances at $8 billion in 2015 dollars during an 11-year conversion programme. (Dorrington et al., 2016)
CHP uses a fuel cell. Engines or fuel cells may be used in CHP systems to generate electricity and heat efficiently while using a wide range of fuels. In different technologies, the balance between electrical energy and heat production is different (Fig. 6). IC and Stirling engines produce more heat than electricity and are thus better suited for significant buildings with high heat demands. Still, they also emit particulates and NOx into the atmosphere. (Staffell and Entchev, 2015)
Figure 6:CHP thermal and electrical efficiency
The ‘conventional frontier’ of utilising average power plants with condensing gas boilers offers better-combined efficiency than all CHP methods. Fuel cell CHP can only exceed energy efficiency with the finest gas-fired power plants and ground source heat pumps. (Staffell, 2015) Fuel cell CHP systems are more efficient and emit fewer pollutants than conventional CHP systems (Table 3). SOFCs, PAFCs, and MCFCs are the most often utilised in business applications, whereas PEMFCs, SOFCs, and MCFCs are more commonly found in residential ones. Fuel cells’ excellent power-to-heat ratio makes them more suited for buildings with lower heat demands that are also well-insulated. Costs have been reduced in the past six years, and lifespans have increased as more FC-CHPs have been deployed in Japan and, more recently, Europe. (Ellamla et al., 2015) Currently, most CHP systems use natural gas, but if hydrogen becomes accessible with minor alterations, existing systems might transition to using it (or even simplification).
Although costs for specific technologies (home PEMFCs in Asia) have decreased, they have not reduced for others (wind turbines in Europe) (large MCFC and SOFCs in the US). Solar PV modules hit a pricing threshold of $10 000 per kW in 1990, and prices are now convergent at about that level. (IRENA, 2012) Other aspects, such as product life and dependability, have improved dramatically. A fuel cell CHP unit is comparable to a contemporary gas-fired boiler in both areas.
Other means of communication. Gas-driven heat pumps (GDHPs), which use an engine that runs on hydrogen to power the heat pump, are another alternative for generating heat. There are presently GDHPs on the market that can save up to 43% on energy costs compared to conventional condensing boilers. (Richard, 2016)
Non-residential GDHPs have already been sold in Europe and Asia, and prices are expected to fall dramatically soon.
Electric heat pumps may provide the bulk of a building’s yearly heat demand (60–95 per cent), but a gas boiler can be kept to meet peak demand. Hybrid heat pumps are another alternative. Several studies have shown that hybrid heat pumps are acceptable for many buildings in 2050; (Dodds et al., 2014); however, these systems need extra capital investment and connection to electric and gas networks. However, there are many hydrogen-powered fireplaces on the market.
Burners and hydrogen grills are being developed, allowing for various culinary possibilities.
It will be necessary to use food-safe odorants and colourants when using hydrogen for cooking, and the increased water vapour that hydrogen creates when burned will affect cooking times.
Heating systems for both private residences and business establishments
Over 225 000 micro-CHP systems have been constructed worldwide using residential fuel cells, which have experienced tremendous acceptance in the micro-CHP sector. All of these attributes make PEMFCs the dominating technology in the market today. They are also very energy efficient, have a long lifespan and can be used in part-load applications at temperatures up to 80 C. (Hawkes et al., 2009). Electrical efficiency (35 per cent) is lower than other fuel cells, while thermal efficiency (50 per cent) is better (55 per cent). Individual buildings may benefit from their low-temperature heat production. Systems with SOFCs159, which may take up to 12 hours to boot and shut down, account for around 7 per cent of all systems in Japan. Because of the higher operating temperatures and consequently lower catalyst costs, they have higher electrical efficiency (B40–60%), greater fuel flexibility, lower purity requirements, and lower catalyst costs. They also produce heat at a higher temperature, making them better suited to older buildings with smaller radiators.
Capital and stack replacement expenses dominate the price of residential systems, so compact systems are chosen to get the most bang for their buck.
Between 2025 and 2050 (Berger, 2015), when fuel prices dominate, fuel cell micro-CHP might be cost-competitive with conventional heating technologies. There is a limited market for larger multi-family and commercial units (2–20 kW) that might be viable at lower production levels.
CHP systems are also popular in the business sector, with hundreds of MWs built worldwide, mainly in the United States and South Korea.
Since they operate reliably and have lower catalyst costs, but their complicated subsystems do not scale well for smaller applications, MCFC and PAFC fuel cells have risen to the top of the commercial system leaderboard (e.g. needing to remain heated whilst off to prevent electrolyte freezing). Because of the corrosive electrolytes and short lives (20 000 hours), and significant degradation rates caused by MCFCs’ greater electrical efficiency (450 per cent), they produce less heat, but they are rigid (Table 3). This makes them unsuitable for using hydrogen, but it offers new carbon capture and storage options because of their need for carbon dioxide for basic electrode processes. Compared to MCFCs, (Stolten, Samsun and Garland, 2015) PAFCs have lower electrical efficiency but a better thermal efficiency and overall higher efficiency (Table 3). They are more durable (80 000–130 000 hours), degrade less quickly, and are more adaptable, allowing them to keep up with changing demands. If just 100 units per year of PAFCs are produced, they might be cost-competitive with ICE-CHP by 2025.
The quiet and low-emission nature of FC-CHP systems makes them suitable for urban environments.
Fuel costs are a significant part of TCO and drive efficiency improvements.
Some 7 PEMFCs and SOFCs are also being used in the business sector.
Too far, industry has made very little progress toward decarbonisation, relying on fossil fuels for three-quarters of its fuel mix and contributing to one-fifth of direct global greenhouse gas emissions (see Fig. 7). As a result, low-carbon options for industry must be found quickly; options identified to date include CCS, biomass as a fuel, electrification, energy efficiency and heat recovery, industrial clustering and the switch to hydrogen – noting that it can be used as both a fuel and a feedstock. CCS is a low-carbon option that can be both a fuel and feedstock. The change will be sluggish in conservative industries because of the long equipment lifespans and investment cycles.
Figure 7:Fuel-specific carbon emissions from industry.
As a chemical feedstock (such as ammonia production and oil refining) and a byproduct (such as chlorine creation) of chemical manufacturing processes, hydrogen is frequently employed in industry as a chemical feedstock rather than an energy vector. (Lidstone, 2016)
While burners and furnaces may need to be replaced, they don’t need to be very pure to use hydrogen as a source of heat and electricity. However, commercialisation of hydrogen will not be possible until 2030 owing to the high costs and complexity of redesigning plants, the sluggish turnover of existing systems, and the low maturity and uncertainty of hydrogen’s costs. Regarding industrial equipment, the primary considerations are technical performance and economic rationale, with aesthetics and space limitations playing a much smaller role. (Dodds et al., 2014)
Infrastructure for the production and distribution of hydrogen
For H2FC technologies to be widely adopted, hydrogen infrastructure has to be developed. Many believe that an all-encompassing “hydrogen economy” must be built at a great expense and the duplication of current energy infrastructure. (Balat and Kirtay, 2010) However, as shown in Fig. 8, many production and distribution options don’t need a complete overhaul of the infrastructure. An enormous task lies in constructing a long-term infrastructure that can adapt to changing demands while being cost-effective. (Turner, 1999)
Centralised manufacturing techniques relying on new distribution networks may be seen in the top part of Fig. 8. It is possible to use existing gas or electricity grids to decrease upfront expenditures, but at the penalty of lesser efficiency, as seen in the bottom part of the picture. The H2Mobility study found that in the early phases of the transition to fuel cell cars, just 60 small refuelling stations with onsite hydrogen generation would be adequate to feed the majority of the UK’s population. As demand rose, more infrastructure would be needed. This shows that building infrastructure may not be as complex as some claim.
A method of producing hydrogen.
The biggest obstacle to developing a hydrogen energy system is the inability to produce low-carbon hydrogen at cost-competitive scales.
As a feedstock for the chemical and petrochemical sectors, around 45–65 Mt year one hydrogen is generated worldwide each year, comparable to 5.4–7.8 EJ, or 1 per cent of the global energy supply. (Wawrzinek and Keller, 2007) Steam reforming natural gas accounts for around half of this, followed by partial oxidation of crude oil products (30%), coal gasification (18%), and water electrolysis (4%). High-temperature steam electrolysis, solar thermo-chemical water splitting (artificial photosynthesis), and biological hydrogen generation are a few of the newer hydrogen-generating methods in the early phases of development. (Poudyal et al., 2015)
Carbon dioxide and methane from fossil fuels. Hydrocarbons and steam are converted into hydrogen and carbon monoxide via reforming” (known as syngas). Because it is an endothermic reaction slower than a transient one, it responds poorly to brief or stop/start cycling.
Figure 8:This paper’s hydrogen delivery routes. This simplified and non-exhaustive graphic highlights the alternatives available at each system level.
The incomplete burning of a fuel-rich combination to create syngas is known as partial oxidation. However, the hydrogen yield is lower (which means that more hydrocarbon feedstock is required), and the resultant gas requires additional cleaning compared to reforming, making it less versatile. It also proceeds quickly without requiring external heat input, allowing for smaller reactors. (Gupta, 2008)
Coal or biomass is partly combusted to form syngas at high temperatures and pressures. Steam reforming yields a quicker reaction, but at the expense of higher expenses since the solid fuel must first be treated before it can be used, and the resultant syngas must be further processed. (Holladay et al., 2009)
Carbon dioxide emissions are a function of feedstock and conversion efficiency since fossil fuels account for the overwhelming bulk of hydrogen production.
It is possible to use bioenergy feedstocks to capture and store carbon dioxide (CCS), potentially reducing CO2 emissions. 239,240 For this to work, CCS must mature to the point where it can be widely deployed after a “lost decade.” Sustainability challenges in bioenergy supply chains are being closely monitored, as well as (Slade, Bauen and Gross, 2014)
Electrolysis of water. While alkaline electrolysis cells (AEC) have been around for over a century, polymer electrolyte membranes (PEMEC) are fast maturing and hold great promise for power-to-gas applications, while solid oxide electrolysers are moving from the laboratory to the demonstration stage. (Carmo et al., 2013)
Alkaline electrolysers are the most established, long-lasting, and cost-effective method.
A direct voltage current connects an anode and a cathode immersed in an alkaline electrolyte. There are numerous MW-sized units. However, they have a restricted operational range (from a minimum of 20% to 150% of design capacity) and long startup periods. (Lehner et al., 2014) As the need for renewable energy integration grows, efforts are being made to enhance the system’s ability to operate dynamically. After being developed in the early 1960s, PEM systems were commercialised throughout the previous decade. They are more suited for intermittent power supply since they respond and start up quicker and have a broader dynamic range (0–200 per cent). (Carmo et al., 2013) Because of their solid plastic electrolyte and high output pressure (e.g. 80 bar), they have a greater power density (and hence are smaller) and need less energy for compression farther down the line. AEC’s capital expenditures are about twice as high as IC’s, and cell longevity must be improved.
Production efficiencies. Various techniques of hydrogen generation are summarised in Table 4, which shows their nominal efficiencies and energy needs. However, early demonstrations have shown substantially lower efficiency in reality than expected. For example, many hydrogen filling stations in California and Japan have averaged 55.8 per cent efficiency from natural gas. In comparison, electrolysers have averaged 55.9 per cent LHV efficiency from natural gas (for those with 44 operating hours per day). (Okazaki, 2005)
Trade-offs. Trade-offs between production size, cost, and GHG emissions may be found among the many production methods. Hydrogen created from natural gas, oil, and coal is the most cost-effective at large sizes, but it is also the least environmentally friendly. Hydrogen from natural gas has minimal emissions and low prices, but only if CCS equipment is available. GHG emissions may still be significant, but the carbon capture rate and the embodied upstream supply chain emissions will determine how much is released into the atmosphere. Environmental impacts from shale gas extraction vary substantially throughout the country and contribute significantly to global warming potential. (Balcombe, Brandon and Hawkes, 2008)However, because of the increased startup costs, biomass gasification may not be viable for large-scale centralised hydrogen generation. (Speirs et al., 2018) Natural gas hydrogen produces less emissions than biomass hydrogen, although they are still considerable and highly reliant on biomass fuel. Hydrogen produced using electrolysis has the most significant production cost, but since electrolysers are modular, it is better suited for small-scale generation. Low-carbon power (e.g., paired with offshore wind) may reduce total greenhouse gas emissions, and electrolysis is a vital technology if cost profiles improve.
Compression of hydrogen as a fuel source
There are a variety of pressures at which hydrogen may be produced, and high-pressure electrolysers can create hydrogen up to 15–80 bar.
Hydrogen pipelines often function at such pressures, with frequent compressors employed to maintain pressure across long distances in the pipeline. Gases such as hydrogen must be transformed into denser forms before storing them for long periods. Highly compressed gas is presently being used for onboard vehicle storage because of its cost and boil-off losses and because of the technical immaturity of hydrogen carriers (hydrides) compared to liquefied gas. Using high-pressure hydrogen tanks (825–950 bar) at refuelling stations allows quick refills despite the decrease in pressure across dispensers. 265 It is necessary to cool compressed hydrogen to a temperature between 20 and 40 degrees Celsius to prevent damaging the vehicle’s tank. (Speirs et al., 2018)
Compression up to 875 pressure has a considerable energy cost, estimated at 2.67 kW h kg1 from 20 bar onwards.
The energy content of the hydrogen is thus reduced by 7% when a 700-bar vehicle is refuelled. A 70 per cent compressor efficiency standard is still considered poor compared to several other compressor technologies, even if the US DOE has set an efficiency goal of 80 per cent by 2020. (Parks et al., 2014) Liquefaction requires far more energy than this, but it still contributes significantly to this fuel’s cost and carbon intensity. Compressor expenses add up to $1.50 per kg when using pipelines and onsite manufacturing, while tube trailers add up to $0.40 per kg. Because compressor technology is well-established, there is no reason to believe this will alter much. (IEA, 2105)
Despite their low dependability, mechanical compressors are the most often used method for recharging hydrogen at stations.
The centrifugal and piston compressors used in centralised production and pipelines fall into this category, which also includes high-pressure fueling stations.
Hydrogen may be produced at up to 200 bar pressures via electrolysis, compared to mechanical methods.
Technologies not ready for prime time include electrochemical, ionic, and hydride compressors (Table 5). (Staffell and Entchev, 2015)
Liquefaction. The energy density of hydrogen may be considerably increased by liquefaction, enabling large-scale transportation by road tanker or ship, which is especially appealing over vast distances when pipelines are not economically practical. Liquefaction technology has matured so that over 90% of commercial hydrogen is carried as liquid in the United States. (US Department of Energy, 2015)
Because liquefaction uses so much more energy than compression, this is seen in Table 6. Large-scale liquefaction in the United States is expected to use 11 kW h kg-1 of energy by 2020, with a long-term reduction of 6 kW h kg-1. Even though various other designs have been developed, “they are neither more efficient nor practical”. All large-scale hydrogen liquefaction facilities rely on the precooled Claude system. Liquefaction adds 0.66 units of primary energy consumption per unit of released hydrogen if the power input is generated with a 50 per cent efficiency rate.
A high degree of purity in hydrogen
ISO 14687-2 mandates a hydrogen purity of 99.97 per cent for transport PEMFCs, (14:00-17:00, n.d.), and all fuel cell systems have strict input purity criteria to maintain cell lifespans (Table 7). As the most fuel-flexible technology, high-temperature SOFCs and MCFCs may utilise methane and carbon monoxide directly as fuel in certain instances. PAFCs tolerate CO, but the Pt catalyst in the PEMFC is readily poisoned. Therefore, the CO present in syngas has to be removed or converted. Because sulphur is used as an odourant in natural gas for safety reasons, it is poisonous to all fuel cells.
They are using electrolysis to produce hydrogen. As recombination catalysts eliminate oxygen that penetrates the membranes, hydrogen generated from water electrolysis is usually clean enough for FCEV applications. (Ito et al., 2016) Even though it’s necessary for fuel cell humidity, water vapour is a significant pollutant that damages the equipment used to compress, store, and transport it. It may also freeze, causing damage to pipes and valves in cold weather. Dryers, such as regenerative desiccant towers, are often used in electrolysers since they are low-cost and use little electricity. The two most common regeneration methods are electrical heating or sending some dry gas back through the wet towel to mop the collected moisture. Both reduce yield by around 10%, although there is room for improvement.
It reforms steam methane into hydrogen. Suppose hydrogen from reformed natural gas is to be utilised in low-temperature fuel cells. In that case, it must first go through a series of cleaning processes, as seen in Fig. 9. Pressure-swing adsorption (PSA) is the current method for separating hydrogen from carbon dioxide and other pollutants. It can obtain purity levels of 499.9 per cent at the cost of a reduction in yields. In 2025, the cost of hydrogen purification using SMR is expected to drop from $0.70 per kilogramme to $0.40 per kg, saving people money.
Figure 9:An overview of fuel cell fuel processing.
Pressure-driven diffusion membranes, primarily palladium-based, are an alternative to PSA. Because they are very costly and need working temperatures of 400°C and pressure differentials of 10–15 bar, current palladium filters diminish yield by 3–5 per cent and may have limited lifespans. They attain extraordinarily high purity. Further research is needed to establish the potential of diffusion membranes and electrochemical compressors for separating palladium and other metals from aqueous solutions.
Size of the current market
Based on the data in Tables 8 and 9, it is clear that H2FC technologies have been adopted more widely in nations with more robust policies (Table 8). As of 2017, the United States has sold more fuel cell cars than Japan and Europe combined, with 2750 FCEVs sold. There might be worldwide ramifications for China’s fuel cell policy, which includes a modest 2020 objective of 5000 FCEVs, but a massive 2030 aim of millions of FCEVs. (Pan, 2017)
As shown in Figure 8, Japan is a global leader in fuel cell combined heat and power (CHP) deployment: South Korea and Europe lag by a decade, while adoption in the United States is relatively low. When fuel cells outsold engines for the first time in 2012, they accounted for 64% of the worldwide market. 333 98 per cent of the world’s home fuel cell systems have been sold in Japan as of October 2017, with more than 223 000 systems sold. Bloomberg predicted that just a quarter of Japan’s 2020 goal of 1.4 million fuel cell installations would be met because subsidies had declined too rapidly to overcome high prices and competition from rooftop solar, as seen in Fig. 10. Only two EneFarm manufacturers remain after Toshiba’s recent departure from the market. Only 1046 systems were deployed as part of the Enfield project, and 2650 further units will be installed by 2021 as part of the PACE demonstration, compared to the EU’s initial expectation of 50 000 systems by 2020.
Figure 10:Installed home micro-CHP systems (solid lines) and future forecasts (dotted lines).
As seen by Japan’s adoption of home heating systems and cars and the success of Japanese businesses, strong policy signals may bring significant advantages. As with previous technologies, the price of H2FC technology has had to be reduced via demonstration projects that allow for learning-by-doing through industrial scale-up. On the other hand, such demonstration programmes have been primarily insignificant outside of Japan. To put things in perspective, the two most significant demonstration projects in Europe (Enfield and PACE) aim to reach just 3% of the 100,000 houses in Germany that got solar PV panels as part of the country’s 100 000 rooftops initiative a decade earlier. (Dewald and Truffer, 2011)
Policies that encourage the use of hydrogen fuel cells
Promoting hydrogen and fuel cells in energy policy is essential because they can increase energy system resiliency, lower environmental impact, and create new low-carbon jobs and skill sets. Sustainable development may be measured regarding ecological, social, and economic factors, and H2FC technology can contribute to all three.
Many European governments strive to establish green hydrogen standards, demonstrating a concern for the environmental advantages of fuel cells rather than merely their adoption.
354 Depending on the criteria, hydrogen from renewable or low-carbon sources may be required (including nuclear and CCS). If a pan-European or worldwide certification process is to be agreed upon, these disagreements must be overcome.
Climate change, natural catastrophes, conflict, and vulnerabilities in the internet’s security can severely disrupt the world’s energy supply networks.
H2FC technology may help the power grid balance weather-dependent renewables, and hydrogen can boost national energy self-sufficiency because of its multiple manufacturing paths. Hydrogen is an intriguing alternative fuel for oil-rich nations since it can be generated everywhere, making it a viable long-term substitute for oil and natural gas. (European Commission, 2014)
Low-carbon alternatives such as hydrogen and fuel cells are generally more costly. However, they have several advantages over their rivals that may help decarbonise personal energy consumption and gain public acceptance. H2FC technology may benefit from programmes to promote research, development, and implementation, as shown by the sharp cost reductions achieved in Asia. This trend is notable for the Japanese Hydrogen and Fuel Cell Roadmap, the US DOE Hydrogen and Fuel Cells Program, and the European FCH-JU.
A marginal energy system choice, hydrogen has fallen and rebounded in and out of favour since the 1970s oil crisis. Although mainstream goods are coming, the first mass-produced hydrogen fuel cell automobiles have been released by Honda, Toyota, and Hyundai, and fuel cells are already used to heat 225 000 households. Many Japanese enterprises are taking advantage of the attractive export market.
Combined with electricity, hydrogen may play a significant role in a low-carbon economy by providing heat, transportation, and power system services. It offers low carbon flexibility and storage for deeper decarbonisation, allowing for various complimentary decarbonisation paths. Complex trade-offs between cost, emissions, scaleability, and needs for purity and pressure are presented by a wide range of hydrogen production, distribution and consumption methods, which may be used based on local conditions (e.g. renewable energy or suitable sites for CO2 sequestration).
There is a distinction between hydrogen and fuel cells, which may be used together or independently. Natural gas may be used to power fuel cells, eliminating combustion and, as a result, 90% of the pollutants in the air. In engines and boilers, hydrogen produces no CO2 and almost little NOx when burned. Hydrogen fuel cells are zero-emission at the point of use when used in conjunction with each other. Still, the total emissions of the fuel-producing process will determine the overall emissions (as with electricity).
Fuel cell car costs are higher than battery electric vehicles, but this will change once mass manufacturing begins in earnest in the mid-to-late 2020s. Premium electric cars have much less range and refuelling time, making them ideal for heavy-duty vehicles such as buses and forklifts. Fuel cell cars, like electric vehicles, but unlike biofuels, have no exhaust emissions; therefore, they may help improve urban air quality. This might be a game changer in cities, trains, airports, sea ports, and warehouses.
Heat decarbonisation innovations lag behind other industries as heat pumps, district heating, and biomass burning confront several obstacles. Powerful, compact, rapid-response heating systems that may be converted to utilise hydrogen are commonplace in homes. Fuel cell CHP can run on today’s natural gas network; however, the carbon reductions are modest. The long-term decarbonisation of this network is possible with the use of hydrogen.
Intermittent renewables and electric heating demand may be supported by hydrogen technology. The controlled capacity of fuel cells may mitigate the higher peak demand of heat pumps. The large-scale, long-term storage necessary to move renewable energy from periods of excess to deficit might be provided by turning electricity into hydrogen or other fuels (power-to-gas) and regulating short-term dynamics.
At the beginning of the process, there is no need to make significant, risky expenditures in hydrogen applications and infrastructure. Refilling stations and fuel cell heating may use existing power and gas infrastructure. Captive vehicle fleets (e.g., city buses with central refuelling facilities) might offer the high utilisation and demand certainty required for investment by focusing on particular customers. Hydrogen and fuel cell technologies may be introduced cost-effectively if a clear plan is devised.
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