This blog outlines what hydrogen energy is, how it is produced and how it may be used to decarbonise key energy-intensive sectors. It is recommended that this blog is read alongside a second blog that describes how the Scottish Government anticipates using hydrogen to achieve net-zero greenhouse gas emissions by 2045.
Hydrogen is the most abundant element in the universe and can be used as a fuel, an energy carrier and store. Hydrogen does not release carbon when burned and therefore it has the potential to cut carbon emissions across a range of energy-intensive sectors, including transport, industry and heat generation. However, hydrogens use as a zero-carbon fuel depends on how it is produced, as hydrogen does not exist naturally in large quantities on Earth and must therefore be manufactured. Current commercial production of hydrogen releases carbon, and while technologies for low or zero-carbon are in development, they do not currently exist at a commercial scale. Independent advisors, the Climate Change Committee, suggest that large amounts of hydrogen energy will be necessary to meet the UK’s net-zero targets, and the UK Government has recently published its Hydrogen Strategy in which it outlines how it aims to meet up to a third of the UK’s energy consumption by 2050 using hydrogen energy. In December 2020, the Scottish Government committed to investing £100 million into the infrastructure needed to support the rollout of hydrogen energy in Scotland. Further detail is expected to be set out in a Hydrogen Action Plan later this year, which is anticipated to outline how the Scottish Government aims to meet its target of 5 gigawatts (GW) of energy generated from hydrogen by 2030, and 25 GW by 2045.
How is hydrogen produced?
The colours of hydrogen
Despite being the most abundant element in the universe, hydrogen gas does not exist naturally in the large quantities needed to generate energy and must therefore be extracted from other chemical forms. This process itself requires energy and often releases carbon; the most common method used globally today to produce hydrogen at scale (steam reforming, termed ‘grey’ hydrogen) emits carbon, negating the benefits associated with hydrogen being a zero-carbon fuel when burned. Low or zero-carbon methods of producing hydrogen do exist (termed blue or green hydrogen, explained further below), but rely on technologies that are still under development in Scotland and require significant amounts of surplus low-cost renewable energy. In some instances, it may be favourable to instead use this renewable energy directly to generate electricity that can be used to decarbonise key sectors (termed electrification), for instance in powering personal vehicles or generating heat in homes. However, hydrogen is seen to be a more compelling means of decarbonising sectors where electrification is not possible (e.g. due to high infrastructure costs). The following section outlines how the different forms of hydrogen — grey, blue and green — are produced.
Most of the hydrogen currently in use globally is produced through a process called steam reforming. In this process, natural gas (or methane – a fossil fuel) is heated in the presence of a chemical catalyst to produce syngas (a mixture of hydrogen and carbon monoxide) which is then processed to separate the hydrogen. This method of production — powered by fossil fuels — results in so-called ‘grey’ hydrogen and globally produces 830 million megatonnes of carbon dioxide equivalent (MtCO2) each year, equal to the emissions of the United Kingdom and Indonesia combined. Grey hydrogen is already produced in Scotland, for instance at the major industrial cluster at Grangemouth — one of Scotland’s largest localised sources of CO2 .
The carbon emitted during grey hydrogen production can theoretically be captured and stored elsewhere (for instance in geological formations) thereby making hydrogen a low-carbon form of energy. Storing carbon emitted from grey hydrogen production through Carbon Capture and Storage (CCS) technologies is known as ‘blue’ hydrogen. There are no active blue hydrogen projects in Scotland, as CCS technology is still under development, but there are plans to establish and support blue hydrogen projects in the near future. For instance, the flagship Acorn Project is expected to come online in the mid-2020s, with 200 MW production capacity predicted by 2025. This project will see blue hydrogen produced from natural gas landed at the St Fergus terminal based in northeast Scotland, with carbon dioxide captured and stored in the North Sea.
Concerns have been raised over whether the technical barriers in the rollout of CCS can be overcome in the short timescales outlined by the Scottish Government for the delivery of a hydrogen energy economy. In response to the Scottish Government’s Climate Change Plan update on 4 March 2021, the Environment, Climate Change and Land Reform Committee outlined:
“Whilst these technologies [CCS] have been proven in test facilities and at small scale, they do not currently exist at scales necessary to remove significant volumes of carbon. Timescales for developing and commissioning are therefore exceptionally tight….”
Hydrogen can be formed by splitting water into hydrogen and oxygen in a device called an electrolyser, using electricity generated through renewable sources (such as wind and solar power). This form of hydrogen is called ‘green’ hydrogen and does not emit any carbon and is therefore considered to be the gold standard when it comes to reducing carbon emissions. In Scotland, there are a handful of preliminary projects which are successfully producing green hydrogen to fuel small-scale local transport and energy demands, such as the Orkney ‘Surf ‘N’ Turf’ project. As with blue hydrogen, the Scottish Government has laid out plans to expand the capacity of green hydrogen production.
However, as with blue hydrogen, technologies for green hydrogen production and distribution remain in development. Green hydrogen additionally requires a surplus of electricity generated from renewable resources, but the scale and availability of these resources are uncertain, as it will depend on the renewable capacity and the extent of other grid management and demand-side response technologies.
How can hydrogen be used?
Hydrogen can be used in two key ways:
(1) Energy: Hydrogen can be burned as a fuel to provide heat in homes, generate electricity or as a transport fuel in the form of a fuel cell.
(2) Feedstock: As an industrial feedstock (a raw material used to produce materials like fertiliser or plastics)
Hydrogen to be also be stored — as a liquid or compressed gas — for months or longer, meaning that it may help energy supply when seasonal demand for energy varies, or energy supply from renewable resources (such as wind and solar) is sporadic. Hydrogen can additionally be transported as a liquid or compressed gas using existing natural gas pipelines, meaning that it can potentially be exported to other parts of the world, with economic benefits.
The use of hydrogen, if produced in a zero-carbon way, is attractive to those planning for net-zero as it releases large amounts of energy when burned without emitting carbon at point of use. This property makes it particularly suitable for decarbonising industrial processes which have historically relied on fossil fuels to achieve high temperatures.
In the transport sector, hydrogen fuel cells can be used as an alternative to internal combustion engines, especially in larger vehicles such as buses, heavy goods vehicles, trains and ships, which are less suited to electrification. A fuel cell is a device that works like a battery, converting chemical energy (in this case hydrogen) into electrical energy. Fuel cells are seen to provide an advantage over electric vehicles in heavy fleet vehicles because of the greater weight to energy ratio of hydrogen (which better supports longer-distance haulage or heavy-duty vehicles) and quicker refuelling times compared with electric batteries. Hydrogen buses and refuelling stations have been operating in Aberdeen since 2015 as part of an £8.3 million project funded by Aberdeen City Council, the Scottish Government, and the European Union.
While hydrogen can be used to replace natural gas in domestic and commercial heating, decarbonising domestic heat demand is considered challenging and does not necessarily provide any additional benefits over electrification of heating. For instance, use of air or ground source heat pumps alongside district heating systems in more urban or heat dense areas may be a more cost-efficient alternative to hydrogen.
The future of Scotland’s hydrogen energy landscape
Hydrogen has a wide range of potential applications, but there are still significant technical and policy challenges that need to be overcome before low-carbon hydrogen can be produced at scale. In addition, the precise role of hydrogen in decarbonising key sectors across the UK — from a variety of implementation, technical and policy perspectives — is still a source of ongoing debate and consultation. For instance, concerns have been raised by academics as to whether hydrogen is the most financially viable option for decarbonisation, given that per kilogram it provides a third of the energy when compared to natural gas. Experts have therefore suggested hydrogen will more likely play a larger role in decarbonising the industrial and transport sectors where increasing energy efficiency and electrification isn’t possible or cost-effective. The high energy demand of the industrial sector is especially important to decarbonise as it contributes significantly to Scotland’s carbon emissions (explained in more detail in Part II of this blog series).
In Scotland, the emerging picture is that there are large challenges for the technologies required to produce blue and green hydrogen to be sufficiently developed in time to support the move to a hydrogen-based economy in time – but that there is the potential for development of the technology to play a part in a just transition from fossil fuels. Are Scotland’s plans to reach net-zero with hydrogen more aspirational than realistic? What might Scotland’s future hydrogen energy economy look like? Is it achievable?
Roxana Shafiee, Researcher (Marine Environment, Climate Change and Energy)