Hydrogen: the key to a zero-carbon energy system
Chris de Beer, Hydrogen leader
It’s 2050 and the world has risen magnificently to the challenge of halting climate change. Globally, an affordable and workable zero-carbon energy system has been created, with hydrogen providing the backbone.
Hydrogen is an essential counterpart to renewable generation, providing a means of storing energy to overcome intermittency and balance supply with demand. It is also supremely versatile, meeting electricity supply, transportation, industrial and domestic needs.
Developing a hydrogen-based energy system will not be easy, however. Several technical, policy and investment steps are still needed to evolve the hydrogen industry, alongside continued rapid expansion of renewables.
This is the first of three articles looking at the issues that must be addressed.
Hurdling barriers to renewable generation
The debate over manmade global warming has been won almost everywhere. The 2015 Paris Agreement was signed by 195 nations – very nearly every country in the world. When it comes to action to implement the Paris Agreement, European nations are most advanced. Many are working out the best way of transitioning to a zero-carbon energy system by 2050. However, the falling cost of renewables, and solar photovoltaics especially, has seen a surge in zero carbon electricity generation.
In 2018, nearly two thirds of all new power generation capacity added worldwide was from renewables; at the end of the year total renewable energy generation capacity reached 2351GW, around a third of total installed electricity capacity.*
On the supply side, seasonal and weather-related intermittency of wind and solar power is the chief obstacle to renewables’ total dominance of electrical energy, with supply-demand balance and grid frequency regulation challenges also presenting barriers.
On the demand side, barriers are principally the huge potential cost of electrifying heating systems and the energy-intense nature of high temperature industrial processes.
It is becoming apparent that the most cost-effective way of addressing these issues is to use hydrogen. In a hydrogen-based energy system, renewable electricity would be converted to hydrogen by splitting water – H2O – into its molecular components. Hydrogen would be stored and transported via modified gas networks to provide both back-up to renewables, and a primary fuel.
Converted back to electricity via fuel cells or direct combustion in thermal power units, hydrogen would respond rapidly to meet peaks in demand, or fill longer troughs in supply. It would also supply residential, commercial and industrial customers with energy in the form of hydrogen for heating, cooking and industrial processes – creating, by 2050, a zero-carbon system across heating as well as power. Meanwhile, in the transport sector hydrogen fuel cell vehicles would compete with those powered by electric battery.
“Hydrogen can act as a storage medium and as an energy carrier – like conventional hydrocarbons. As an energy carrier, it has different uses in a variety of sectors, including the ability to take surplus renewable energy generated during the summer and store it for winter, reducing dependence on natural gas as a backup to renewables in the power sector,” says Chris De Beer, energy storage engineer at Mott McDonald. To get there, large-scale hydrogen production plants must be piloted, while pipeline networks and end-use appliances need to be converted to use hydrogen.
Currently most hydrogen is made from natural gas, through steam reforming. Most experts anticipate that electrolysis will become the main zero carbon hydrogen production option, as opposed to adding carbon capture and storage to methane conversion (or other emerging methane-to-H2 processes).
The first step is to cut the cost of electrolysis, which currently is expensive and consumes more energy than can be produced by the hydrogen product. Next generation electrolysis promises higher performance. Powered by renewable energy, hydrogen production costs should tumble.
Polymer electrolyte membrane (PEM) electrolysis is a working technology, but only at the early commercial stage, and is still undergoing refinement before wider large-scale deployment. PEM produces hydrogen at higher pressures, enabling it to be injected directly into the gas network, saving costs on compression. In Germany, Siemens is most advanced in this field, with a commercial multi-megawatt system. ITM Power is among the active companies in the UK.
More novel approaches include using solid oxide electrolysis or direct photo electrolysis – a modified photovoltaic system that has an electrolysis process embedded in it. This involves sunlight hitting a panel with water circulating around it, which is split into hydrogen and oxygen. This approach has already been trialled at small scale with some success, but still needs to be proved at scale. A further direct solar-to-hydrogen approach being tested at bench scale is photoelectrochemical water splitting (artificial photosynthesis).
The second area of focus is the gas pipeline and storage network, which must be able to hold the hydrogen. Because it is a far smaller molecule than methane, this can require considerable modification. Initially, countries such as Germany and the Netherlands have raised the safe proportion of hydrogen permitted to be mixed with methane to 12%. Although the UK is currently at just 0.1%, studies have concluded that up to 20% hydrogen is unlikely to harm the gas network. The HyDeploy project at Keele University aims to run a live trial of blended hydrogen and natural gas on a private gas network.
Similarly, end-use appliances must be checked to ensure suitability at low hydrogen concentrations, and eventually switched to run on 100% hydrogen. This includes gas turbines for power generation – with recent models from major manufacturers designed to be hydrogen compatible. At the residential level, several funding programmes have been considered to trial boilers and cookers using hydrogen as the fuel source.
And if hydrogen is to be used as a transport fuel, recharging infrastructure needs to be set up, alongside generation and storage. Hydrogen vehicles have greater range than electric vehicles and, as the hydrogen economy grows can be expected to become competitive on cost too. Development of a failsafe onboard hydrogen storage vessel is key, with Toyota most advanced. Its carbon fibre vessel operates at high temperature and pressure using liquid hydrogen. Solid hydrogen fuel options are possible, but some way off. Environmental impact may also favour hydrogen fuel cell electric vehicle versus battery vehicles given the significant negative impacts of mining and disposal of materials used in lithium-based batteries.
Because hydrogen is such a low density gas, transportation is an issue at scale (also because much of the renewable power could be well away from demand centres). So, as well as local gas pipeline and storage networks, other transportation mediums need to be considered.
Options under development include cryogenic liquefaction of hydrogen – although this has major costs and risks. A carrier process using ammonia is more practical. Splicing nitrogen and hydrogen together to create ammonia (NH3) is a simple and easily reversible chemical engineering process. An ammonia trading network already exists globally, serving the fertiliser industry, although existing networks would need to be expanded dramatically and modified to include conversion facilities.
Hydrogen molecules can be chemically bonded into a class of materials known as hydrogen carriers (HC), which come in both liquid and solid forms. Liquid organic HCs enable transportation in regular tankers and pipelines; solid HCs can be transported as freight. These HCs can be non-toxic and fully inert, and very cheap if produced at mass scale. HCs can be charged and depleted repeatedly. The cost comes in the process of bonding and separating hydrogen from them – hydrogenation and dehydrogenation – and from transporting the depleted HC back to source for recharging.
From today’s vantage point, some of the challenges look significant, but the renewables market has shown the extraordinary commercial progress achievable with research, development, investment and the development of applications at scale.
All these milestones are achievable, and once they are the hydrogen economy will be ready to roll – driven perhaps by cheap solar from the world’s deserts, which could provide the bulk of the world’s hydrogen through a new global trade network to users in the power, heating and transport sectors.