Basic knowledge on clean hydrogen and its derivatives
Clean hydrogen is expected to play a large role in mitigating emissions from otherwise hard-to-decarbonize sectors, while also providing an alternative for long-duration energy storage.
Hydrogen is a gaseous chemical element that can act as an energy carrier and be used as fuel to store, move, and deliver energy. In its combustion, it emits only water as a by-product and is hence seen as key to decarbonizing otherwise greenhouse gas-emitting sources of energy. Hydrogen is projected to significantly help decarbonize hard-to-abate sectors such as iron and steel production, the chemical industry, as well as heavy-duty transport. Employing clean hydrogen in current industrial uses focusing on petroleum refining and ammonia production could also bring significant reductions in global CO2 emissions. Looking beyond emissions reduction as a key characteristic of hydrogen production, clean hydrogen can also bring resilience to countries that are pursuing energy independence and diversification, thanks to the fact that it can be produced domestically from multiple feedstocks using diverse technologies.
Production technologies for clean hydrogen
Clean hydrogen is first and foremost defined by the low carbon footprint of its production. It can be produced by using different feedstocks and technologies. In recent years, many have referred to the production pathways using a color scheme, the “hydrogen rainbow.” The colors used to this end are not standardized, and some colors end up being used for multiple technologies or fuels in different contexts. International organizations and think tanks like the International Energy Agency (IEA), IRENA, the Hydrogen Council, and others have thus moved away from this approach, focusing instead on carbon intensity as the main criterion for the evaluation of production technologies. They have consequently switched to the terms “clean hydrogen” or “low-emission hydrogen.” H2Global has adopted “clean hydrogen,” which encompasses a variety of different production pathways using diverse feedstocks, all with a lower carbon intensity than the conventional hydrogen currently being used. Nevertheless, the providers of funds of H2Global Foundation’s work have at times preferred using a color-based terminology, which is why we sometimes talk about “green” hydrogen, for example.
Energy system services: Seasonal storage and flexible production
A major challenge in the energy transition is the volatility of the two most important renewable energy sources: wind and solar power. While solar power naturally fluctuates with the day-and-night cycle as well as seasonal changes in solar radiation intensity, wind availability changes with the weather, and thus also with the seasons. In some regions, their patterns may be complementary, meaning that winds are blowing stronger and more steadily in the winter when solar radiation is low. The effect, however, is not perfect and not fully reliable. Thus, energy must be stored to enable a sufficient supply of clean energy.
To store energy, a range of technologies is available. This includes, among others: batteries, compressed air, pumped hydropower, and hydrogen. Different types of storage will be needed to serve different purposes. For example, battery storage allows for a high frequency of loading and discharging cycles, making it a great option for short-term storage. On the other hand, batteries suffer from low energy density and significant energy losses over time, which limits the utility for heavy transport solutions and long-term energy storage. This is where hydrogen and its derivatives enter the market: gaseous or liquid storage has limited losses once leakage is addressed, and it is able to hold large amounts of energy for a long period of time.
If hydrogen production is timed right, it not only helps to cover cold, dark periods (times with lack of wind and solar power) but also to make maximum use of the times when there is a renewable energy surplus through flexible production.
Special uses in the industry sector
Outside the energy sector, hydrogen and its derivatives can perform specific functions for both the industry and transport sectors. Several hard-to-abate sectors cannot use direct electrification to reduce the carbon intensity of their production. There are several reasons for this:
Chemical Industry
The chemical industry already produces and uses hydrogen in large quantities to produce basic chemicals like methanol, ammonia, and various acids, as well as to further refine these basic chemicals to build more complex molecules. These in turn are the basis to produce plastics, fertilizer, pharmaceutical products, etc. The amounts of hydrogen needed for these processes are mostly produced through steam reformation of natural gas, which implies greenhouse gas emissions if CO2 is not captured and stored.
Steel Industry
The steel industry needs to replace natural gas or coking coal to decarbonize the production of raw steel. In conventional blast furnaces, coking coal is used to solve the oxygen bound in the iron ore. In modern, direct reduction units, the same purpose is achieved by using natural gas. With few modifications, the latter can use hydrogen to substitute natural gas, leading to an almost emission-free process resulting in directly reduced iron.
Cement and Glass
In the cement, glass, and ceramics industries, blast furnaces provide the process heat of more than 1,000°C that is necessary for smelting and sinter processes, and hydrogen can replace the fossil fuels conventionally used to fire the furnaces. In case of some glass and ceramics processes, hydrogen may also contribute to product qualities that would be lost if electrification was used to decarbonize the process.
Special uses in the transport sector
Similar to the industry sector, hydrogen also has a role to play for special purposes in the transport sector. Just like in industries, some aspects of transport are hard to abate and cannot easily resort to the electrification of engines:
Aviation
In aviation, batteries present a problem in that they are too heavy and voluminous for economically viable uses. The low energy density of batteries is a particular problem for long-distance flights even if there might be battery-based solutions for very short distances. The solution to this problem is still in nascent stages but involves the use of sustainable aviation fuel (SAF). SAF includes the use of hydrogen-based engines for short to medium distances, or the use of synthetic kerosene for medium to long distance flights.
Railways
In railway transport, there are niche applications for hydrogen in regions that are too remote for cost-effective electrification solutions or that entail tunnels that have not been sized for overhead lines and thus prevent electrification.
Heavy-duty transport
In heavy-duty transport, such as in long-haul trucks, agriculture, or mining, the need for energy-intensive and long, uninterrupted performance provides a use case for hydrogen and electrofuels (e-fuels) based on hydrogen.
Efficiency of hydrogen-based solutions
In the initial phases of the hydrogen market creation, clean hydrogen and its derivatives have been particularly scarce, which warrants a critical assessment of the solutions for clean energy carriers. From a macro-economic perspective, an efficient use of clean hydrogen is imperative, as its productionalways entails energy losses.Following discussions on macro-economic efficiency, heating in residential and commercial buildings has been removed as an application in several models by international institutions estimating future clean hydrogen demand.
While there is general consensus that clean hydrogen will play an important role in the energy transition, there is some disagreement with respect to the size of its contribution. Analysts draw diverging conclusions based on different assumptions of the technological readiness and economic viability of alternatives such as carbon-capture technologies, direct electrification of high-temperature process heat, or heat pumps in private and business buildings. Estimates for the scope of the use of clean hydrogen in power generation and the transport sector have also been scaled down in some studies. For the transport sector, this is based on considerations regarding the macro-economic utility of e-fuels and emerging limitations for producing SAF. However, the jury is still out on which technology will succeed. Ultimately, we will need a mixture of diverse clean technologies if we are to achieve our climate goals.