In March , the UK's Hydrogen and Fuel Cell Supergen Hub published a white paper that systematically assessed the current status and future prospects of hydrogen and fuel cells in future energy systems. It builds upon previous holistic reviews of hydrogen and fuel cells, 32—34 and takes the novel approach of considering how they might be integrated together across the energy system.
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- 1 Introduction.
The UK must halve its transport CO 2 emissions between and to meet national carbon budget commitments. Hydrogen avoids the land-use and air quality impacts of biofuels, and the limited range and long recharging times associated with EVs. In addition to tackling climate change, hydrogen vehicles can improve air quality. This is an urgent priority with over half a million premature deaths per year across Europe due to particulates and NO x emissions.
Fuel cell electric vehicles FCEVs predominantly use PEM fuel cells, offering high efficiency, high power density and cold-start capabilities. Competing powertrains includes conventional internal combustion engines ICEs , battery electric vehicles BEVs and plug-in hybrid vehicles PHEVs, also known as range-extender EVs , which allow most journeys to be completed using a battery, and switch to the engine or fuel cell for less-frequent longer journeys.
Hydrogen powertrains are compared to alternatives in Table 1 , and differ in the following ways: 49, Blending biofuels with petrol and diesel can reduce CO 2 emissions, but not improve local air quality. Hydrogen is flammable more so than petrol but hydrogen fires can cause little damage to the vehicle due to their localised nature.
Platinum is a key contributor to capital cost, as mid-sized fuel cell vehicles require ten times more circa 30 g than a diesel autocatalyst.
Passenger FCEVs are believed to require production volumes of around units per year and hence considerable financial support to approach cost parity. Deployment could be accelerated by targeting powertrain configurations with smaller initial hurdles. Globally, there are hydrogen refilling stations as of , half of which are in Japan and the US 76 Fig.
The various European H2Mobility programs have suggested a rollout of refuelling stations at critical locations, with a network of 65 refuelling stations for the UK by to start the market, growing to stations by to cover the whole country. Return-to-base fleets such as delivery vans and taxis, or passenger cars in a future car-sharing economy will see high utilisation and benefit from single refuelling depots with fast, infrequent refuelling. The requirement for less infrastructure could enable distribution costs to fall more rapidly than in the passenger FCEV sector, suggesting deployment in these sectors should be targeted.
Three key differences for heavy-duty transport are low manufacturing volumes meaning the cost gap with ICE is smaller , and the need for greater longevity and energy density. The US DOE targets 25 hour operating lifetime for fuel cell buses, versus just for passenger cars.
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Fuel cell buses have seen substantial early deployment, with 7 million kilometres of operational experience so far in Europe. Good progress is being made with longevity, with four London buses operating more than 18 hours. Higher longevity is required than for other applications due to the high mileage expected of trucks, with one program targeting 50 hour stack lifetime. FCEV trucks have seen lower adoption than buses due to the HGV market being highly cost sensitive with limited government support or intervention, and highly conservative with hauliers wary of being pioneers.
Light rail also presents opportunities for hydrogen, with fuel cell-powered trams being developed and operated in China.
Integration and dynamics of a renewable regenerative hydrogen fuel cell system
A particular challenge for low-emission heating in temperate countries is meeting winter peak heat demand, — which is considerably higher and more variable than peak electricity demand Fig. This strong seasonal variation is easily met by prevailing gas heating technologies, as low per-kW capital cost means they are routinely oversized for buildings, and the gas network including geological storage can store a month's worth of consumption.
Improved insulation, residential or communal thermal storage, and more efficient conversion devices could reduce peak requirements, but require strong regulation which has not been forthcoming. Hence progress in decarbonising heating has lagged severely behind other sectors. For example, the UK relies heavily on natural gas and is likely to miss its target for renewable heat. Electric heat pumps are well established in Asia, America and parts of Europe, with over a billion systems heating homes; whilst district heating is widely used in Russia and Scandinavia.
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Insulation, higher efficiency devices and changing demand behaviour e. Natural gas could be replaced by a low-carbon gases, utilising the existing gas network assets and potentially reducing costs and disruption. Nevertheless, heat pumps may play an important role, particularly for rural homes too remote for district heating or gas networks, which use expensive high carbon fuels such as heating oil, and with space for larger systems. District heating is only commonplace in a handful of countries, which typically combine a cold climate with an acceptance of collective solutions.
Large district heating CHP schemes are cheaper and more efficient than individual residential systems. Each low carbon heating technology exhibits barriers or uncertainties associated with technical feasibility, cost, suitability across regions and building types, user acceptance and safety. Individual countries are often dominated by a single technology.
Development of controllers using FPGA for fuel cells in standalone and utility applications
However, a portfolio of complementary heating technologies used to be more prevalent, and is now regaining recognition. FC-CHPs are currently expensive, but costs have halved in the last six years and lifetimes have grown with increasing rollout in Japan and also more recently in Europe. Tens of thousands of non-residential GDHPs have been sold across Europe and Asia; costs are currently high, but should come down significantly.
Wall-mounted fires are waning in popularity, but several hydrogen-powered fireplaces have been designed. There is considerable scope for hydrogen usage as a cooking fuel, with burners and barbecues under development today. The cost of residential systems is dominated by capital and stack replacement costs, with small systems used to maximise utilisation.
Larger multi-family home and commercial units 2—20 kW e could be competitive at smaller production volumes, but have a smaller market. Their reliance on carbon dioxide for fundamental electrode reactions also make them unsuitable for operating on hydrogen, 48 but opens up new possibilities for carbon capture and storage. They last longer 80 — hours with lower degradation rates and are more flexible, giving scope for load-following capability.
FC-CHP systems are quiet and low-emission making them ideal for urban areas. Hydrogen is already widely used in industry as a chemical feedstock e. Hydrogen could replace natural gas as a fuel for providing heat and power in a number of industries; burners and furnaces may need replacement, but would not require high purity.
Hydrogen could also be introduced into several high-temperature industries including steelmaking and cement, although commercialisation is not expected before due to low maturity, uncertain costs, the likelihood of needing fundamentally redesigned plant and the slow turnover of existing systems. Unlike other sectors, electricity generation has available a range of low-, zero- and even negative-carbon alternatives already available. Wind and solar power are forms of intermittent renewable energy: their output cannot be fully controlled or predicted as they rely upon the weather.
Balancing supply and demand requires new solutions if electricity systems are to fully decarbonise whilst maintaining current levels of cost and reliability.
Electricity has the fundamental constraint that supply must always balance demand, and system reliability is paramount as outages cause severe economic and social damage. Hydrogen technologies are able to assist with both the integration and expansion of low-carbon electricity generation and with the electrification of heating and transport sectors. Power generation from hydrogen is gaining ground — global capacity reached the milestone of 1 GW in , as seen in the bottom right corner of Fig. If this were maintained, fuel cells would reach 10 GW capacity in , and 30 GW in However despite this growth, no company has yet turned a profit through sale of stationary fuel cells.
It is important to note that the decarbonisation potential depends on the hydrogen feedstocks and supply chains. Any use of fossil fuel-derived natural gas to produce hydrogen without CCS will necessarily lead to carbon emissions that are at least at the level of a new CCGT power station. A key advantage of fuel cells is that they retain their performance at smaller scales. Energy Servers have received large subsidies from US green generation incentives e.
Vehicle-to-grid V2G describes a system for communication with electric vehicles, allowing grid operators and utilities to access the energy stored within electric vehicles to meet demand and provide other grid services. Even with current lifetimes, it is expected that the fuel cell stacks would not be a chief determinant of lifetime in FCEVs.
Surplus electricity is used to power hydrogen production via water electrolysis. The resulting gas may then be stored and used when required, for instance by a fuel cell, or undergo further processing to produce methane, also known as synthetic natural gas SNG. Equally, it can then be converted back to electricity or used to displace demand for natural gas in the heating and power sector, or indeed for transport.
There are two commercially available processes for water electrolysis: alkaline electrolysis cells AEC and polymer electrolyte membranes PEMEC ; while solid oxide SOEC offers the possibility of high efficiency but are still at a development stage.
Thesis defence F. Alavi: fuel cells
Onward conversion of the hydrogen to methane is a less efficient and significantly more complex process. Methanation of hydrogen is achieved via either a catalytic or a biological process, and requires a source of CO or CO 2 , plus compression and storage of the hydrogen feedstock. Globally, the energy storage capacity of the natural gas network is in excess of TW h, approximately three times the global production from wind and solar power combined in There is a growing number of power-to-methane pilot projects in progress globally, with Europe leading the way in driving forwards development of the technology.
Looking further ahead, several authors have examined the role that P2G might play in future national electricity markets with very high penetration of renewables. The upper half of Fig. Incremental and less infrastructurally-intensive routes also exist the lower half of the figure , which utilise existing gas or electricity networks and reduce large up-front costs, albeit at the expense of lower efficiency.
Indeed, H2Mobility concluded that only 60 small refuelling stations with onsite hydrogen production would be sufficient to supply most of the UK population in the early stages of a transition to fuel cell vehicles, with additional infrastructure deployed as demand increased. Partial oxidation is the incomplete combustion of a fuel-rich mixture to produce syngas.
It is more versatile than reforming, allowing a greater range of fuels to be used, and proceeds more rapidly with no need for external heat input allowing for smaller reactors ; however, the hydrogen yield is lower meaning more hydrocarbon feedstock is required , and the resulting gas requires additional cleaning. Gasification is the process of partially combusting coal or biomass at high temperature and pressure to produce syngas.
This gives a faster reaction than steam reforming, but has higher costs as the solid fuel requires pre-treatment and the resulting syngas requires greater treatment. The vast majority of hydrogen is produced from fossil fuels, with CO 2 emission intensities depending on the feedstock and conversion efficiency. Alkaline electrolysers are the most mature, durable and cheapest technology.
PEM systems were introduced in the s and became commercialised in the last decade. However, capital costs are currently approximately twice those of AEC, ,, and cell lifetimes need to improve.