How hydrogen can be harnessed to help the decarbonization effort – Monash Lens
Hydrogen should play an important role in the deep decarbonisation of transport and industry, in particular for energy services which will be difficult or expensive to electrify.
The utility value of hydrogen derives from its versatility as an energy carrier, storage medium and chemical feedstock. Hydrogen has the potential to intervene in the provision of electricity, mobility, heat and work.
If hydrogen is to contribute to decarbonisation efforts, attention should be paid to several aspects of green hydrogen production:
Energy, material and emissions flows integrated into the hydrogen supply chain
The scale of the deployment of green hydrogen needed to contribute to a carbon-free global energy supply
Net energy from hydrogen production
The challenges of powering electrolysers with a variable power source.
Life Cycle Assessment (LCA) and Net Energy Analysis (NEA) are tools to address these aspects. The dilemma for LCA practitioners is that there are no large-scale renewable electrolysis plants in operation from which to collect operational data and plant specifications.
To fill this gap, we have carried out a net environmental and energy assessment of a hypothetical large-scale solar electrolysis plant.
Hydrogen can be produced from a wide variety of primary energy resources, including renewable and nuclear energy, biomass, natural gas, coal, and petroleum.
The “clean” and “low carbon” labels can be applied to several production sectors; however, the “green” label is generally reserved for hydrogen produced almost entirely from renewable energies.
Much of the international policy discussion has focused on the deployment of green hydrogen, with a growing number of jurisdictions announcing policies to accelerate deployment. Australia announced a national hydrogen strategy to develop a “clean hydrogen” industry.
Wind-powered water electrolysis and solar photovoltaic (PV) are promising candidates for large-scale green hydrogen production in Australia.
Emissions contained in hydrogen
Unlike hydrogen produced from fossil fuels, electrolysis powered by renewable energies produces virtually no direct emissions during operation. However, the infrastructure is energy intensive and consumes materials.
To the extent that fossil fuels are used to manufacture, build and operate infrastructure, the impacts of the extraction and combustion of these fossil fuels will be indirectly incorporated into hydrogen. A global transition from fossil fuels will, of course, reduce these integrated impacts.
Hydrogen certification programs generally recognize “low carbon” as a reduction of at least 60% in greenhouse gas emissions compared to steam methane reforming (currently the method of producing gas). dominant hydrogen).
However, the measured reduction in emissions depends on the system limits used for the environmental assessment. the European CertifHy system applies the “well-to-door” system boundary, which is relatively narrow, but captures most of the emissions from the production of hydrogen from fossil fuels.
This limit includes the direct emissions emitted within a hydrogen production facility, as well as the immediate upstream emissions associated with the supply of raw materials and the production of electricity from fossil fuels.
Australia’s proposed certification system, or Guarantee of Origin (GO), has yet to determine the limit of the system, but stakeholder feedback generally supports the “well-to-door” limit adopted for CertifHy.
The broadest system boundary used for environmental assessment, the “cradle to grave” boundary, includes full life cycle impacts during fabrication and construction, and subsequent decommissioning, of production facilities. hydrogen.
Read more: Mapping the future of hydrogen in Australia for large-scale production and delivery
Regardless of system limitations, estimating emissions of hydrogen from fossil fuels is straightforward, as most emissions result from combustion in clearly identified industrial plants and power generators.
In contrast, almost all emissions associated with renewable electrolysis are integrated into global supply chains. Since the environmental impacts are diffused in a network of energy and material flows, it is much more difficult to identify and measure the impacts.
Nonetheless, the plant and equipment supply chain is critical to the sustainability of green hydrogen.
Energy return on investment
Another factor is that there has been a marked decline in the energy return on investment (EROI) of the global energy system over the past decades, raising fears that a further decline may hamper the energy transition.
The EROI is the ratio between the energy returned by an energy supply process and the energy invested in this process over the entire life cycle. It is conceptually an energy profit ratio, and based on the fundamental principle that any supply system must return more energy than what has been diverted from other uses to obtain that energy.
Depletion of resources tends to reduce EROI, while technological improvement tends to increase it. To date, technological improvements in oil and gas extraction, significant technological developments in renewables and smart grids have not been able to reverse the global decline of EROI.
As a physical metric, the EROI can be useful in identifying physical constraints that may not be evident from technical-economic analyzes alone.
The extent of the move upmarket required
An important consideration in the context of climate change mitigation is the enormity of the scale-up required – both globally in terms of investment, area, materials and gray energy; and at the project scale with respect to the potential localized impacts of gigawatt-scale plants.
Assuming that hydrogen was to provide 5% of final energy in 2050, around 5,000 GW of wind and solar power would need to be spent on hydrogen production. This implies that perhaps hundreds of gigawatt-scale wind and solar power plants will need to be operational by 2050.
The targets for hydrogen demand beyond 2050 are much higher. Along with the production and use of hydrogen, the energy transition will involve the synchronous ramp-up of renewable electricity, batteries and energy use technologies. The materials and metals demanded by a low carbon economy are expected to be immense, creating challenges along the supply path.
Electrolysis of water supplied by a variable power source
A related consideration is understanding how renewable electrolysis plants will operate as integrated plants.
The electrolysis of water, the compression of hydrogen, the liquefaction and the production of ammonia are subject to physical and thermodynamic operating constraints. Chemical plants are generally optimized for steady-state operation at medium to high operating capacity.
Read more: A breakthrough in green production and storage of hydrogen gas
The challenges of powering electrolysers with a variable power source are known, but the main strategy for managing the renewable variability of pilot plants has been network buffering. However, grid buffering can dramatically increase hydrogen GHG emissions, even when grid imports represent a minor share of the energy.
Another strategy is the buffering of electricity through batteries or other electricity storage technology.
All of these factors tend to increase environmental impacts and reduce net energy.
A necessary integrated approach
Design for sustainability implies that environmental assessment parameters should be treated as objective functions in the optimization of facilities.
We recommend that life cycle analysis and net energy analyzes be incorporated into project planning, as well as conventional techno-economic analysis, to inform decision making to ensure that hydrogen meets the objectives of sustainable production.