Is hydrogen a ‘clean’ energy source?

Not all hydrogen is created equal, and hydrogen production is a major decarbonisation problem as a result. 99% of hydrogen produced today is made from fossil fuels without carbon capture – responsible for more emissions than the global aviation industry.

Both green and blue hydrogen are often presented under the banner of ‘clean’ or low-emission hydrogen. But there is emerging consensus that green hydrogen, produced from renewable electricity, is the only near-zero emission form of hydrogen.

Blue hydrogen, produced from fossil fuels with carbon capture and storage (CCS), should be approached with caution. This is because its production relies on fossil fuels, carbon capture is always partial, and researchers have found the significant fugitive methane emissions along its supply chain may make it worse for the climate than simply burning fossil fuels outright.

To be defined as ‘clean’, blue hydrogen must at least meet the same emissions levels as green hydrogen – a difficult task. You can read more about our definition of clean hydrogen here.

Is hydrogen a greenhouse gas?

Hydrogen is an indirect greenhouse gas. Recent research has shown its global warming potential once released into the atmosphere is 35 times that of carbon dioxide (CO2) in the first 20 years, and 12 times over 100 years after release.

Because hydrogen is a much smaller molecule than natural gas, it is even more prone to leak from pipelines or storage tanks. The climate consequences of this require further study.

Hydrogen is also often billed as a ‘clean-burning’ fuel that produces only water vapour as a by-product. However, this is only the case when it is used in a fuel cell and converted to electricity ‘electrochemically’ – without combustion.

While burning or combusting hydrogen does not produce CO2 emissions, it can produce high levels of nitrogen oxides (NOx) – a potent pollutant with impacts on human health.

What does science say about hydrogen’s role in the energy transition?

Science shows that hydrogen is not a silver bullet for the energy transition.

The Intergovernmental Panel on Climate Change (IPCC) estimates that hydrogen will represent just 2% of global energy consumption by 2050, with it often being more risky, expensive, energy inefficient or emissions-intensive than already available alternatives like electrification.

Renewable or green hydrogen is a niche solution that must be used wisely for a small number of essential applications, where direct electrification is not possible.

This is due to the fact that it is very energy inefficient, requiring vast amounts of electricity to produce. As a result, it is also very expensive – about four to six times the cost of natural gas per unit of energy per HSC calculations. It remains in scarce supply today, with large-scale projects yet to be fully realised and ‘low-emission’ hydrogen accounting for just 0.7% of total demand, according to the IEA.

Decarbonising fossil fuel hydrogen where it will still be needed in a net-zero future, by replacing it with renewable hydrogen, will require an enormous amount of energy – almost three times the amount of wind and solar electricity that the world produced in 2019.

As a result, renewable hydrogen must be prioritised to replace this emissions-intensive hydrogen where it is already widely used today: as an essential feedstock in the fertiliser, chemical and iron industries where hydrogen is necessary for its chemical properties.

Elsewhere, it is always more efficient to use renewable electricity directly wherever possible. For example, heating buildings with boilers using renewable hydrogen takes 5.5 times more electricity than electric-powered heat pumps, while powering a hydrogen fuel cell vehicle with renewable hydrogen uses three times more electricity than one running on a battery.

Are there wise new uses of renewable or green hydrogen?

Yes – these uses generally require hydrogen for its chemical properties, rather than for use as a fuel or energy storage medium. This justifies the energy losses involved in making renewable hydrogen from electricity.

One example is for the production of green steel. Renewable hydrogen can be used to replace fossil natural gas-derived syngas currently used in the direct reduction of iron ore to iron metal (DRI), a raw material for steelmaking. DRI removes the need for traditional blast furnaces powered by coal-derived coke in the steelmaking process, slashing carbon emissions.

While direct electric iron reduction technologies are under development, they are at an early stage and will take at least a decade to commercialise – making this an application where the new deployment of renewable hydrogen makes sense for decarbonisation.

Why haven’t we already scaled up renewable or green hydrogen production?

The scale-up of renewable hydrogen production faces multiple challenges, including high costs, a shortage of electrolysis equipment, and an insufficient supply of renewable electricity generation.

To ensure that renewable hydrogen is truly green, its source electricity must be truly green. This means that not only must wind or solar power be used, but it must be new power built expressly for this purpose – otherwise it would be best used to decarbonise the existing electricity grid.

It is also important that grid electricity is not used to back up the renewable electricity used, otherwise fossil fuel power sources will end up making the hydrogen. While the grid can be used to deliver power to make the hydrogen, it must be made exactly when renewable power is available.

As a result, electrolysers must be able to work with varying levels of electricity input to make the most of fluctuating renewable energy and avoid further driving up production costs – a feature they have yet to fully demonstrate, according to an analyst note from BloombergNEF.

All this, plus the cost of hydrogen electrolysis equipment, makes it very expensive to make renewable hydrogen. It cannot currently compete with fossil-derived hydrogen on a cost basis, reinforcing the need to prioritise its use for niche sectors and for effective hydrogen policy to kickstart the renewable hydrogen industry.

Can we make renewable or green hydrogen when there is excess electricity in the grid?

Producing renewable hydrogen when there is excess renewable electricity in the grid is a popular idea with difficult economics.

As electrolysis plants using renewable electricity to produce green hydrogen are very expensive, using them only part of the time means that their high capital cost must be recovered from comparatively fewer kilograms of hydrogen, making each kilogram expensive – even though the cost of energy to make the hydrogen is low, zero, or even sometimes negative.

While electrolysers will become cheaper with time, not all parts of an electrolysis plant are likely to improve dramatically in cost. It is unlikely that electrolysis plants will become cheap enough to operate on a part-time basis, even if running exclusively on excess renewable electricity.

As a result, producers would need to be paid or otherwise incentivised to operate their electrolysis plant on a part-time basis and to stop production whenever demand on the grid is high.

Can the efficiency of renewable or green hydrogen be improved?

The inefficiency of renewable hydrogen when it is used as a fuel or energy storage medium is largely due to the laws of thermodynamics, the branch of science that deals with heat, work, temperature and energy.

While electrolysers and fuel cells will improve in efficiency with time, the efficiency of using hydrogen as a fuel will not change significantly in the future as the engineering of these systems is relatively mature and the laws of thermodynamics do not change. You can read a further explanation of why even the most efficient electrolysers won’t solve hydrogen’s efficiency problems when used as a fuel here.

Is blending hydrogen into the existing natural gas grid a decarbonisation solution?

Blending hydrogen into the existing natural gas grid will have a very limited impact on greenhouse gas emissions, while driving up costs for consumers.

Existing pipelines can carry no more than a 20% mix of hydrogen with natural gas before requiring expensive infrastructure retrofits. Blending hydrogen with natural gas reduces the energy content, meaning more of the mix is needed to deliver the same amount of energy to the end consumer.

Studies show that blending 20% renewable hydrogen into existing natural gas pipelines will result in emissions savings of just 7%. Given how valuable renewable hydrogen is, blending it into the existing natural gas grid does not make sense to deliver such limited emissions savings.

Recent research also suggests that blending hydrogen into the gas grid increases nitrogen oxide (NOx) emissions, which are associated with a higher risk of respiratory illnesses – further calling into question the safety of burning hydrogen in domestic environments.

Is renewable or green hydrogen a decarbonisation solution for aviation?

Renewable hydrogen as a direct liquid fuel for aviation is not a decarbonisation solution due to its enormous renewable electricity requirements.

While one large wind turbine could provide 6,000 homes with electricity for a whole year, it could at best power only one flight per month of a Boeing 787-9 at maximum range with liquid hydrogen.

As a result, all short and medium range aviation up to around 2,000 or 3,000 kilometres can be more effectively decarbonised by switching to batteries. Flights of longer distances will likely switch to biofuels.

Are hydrogen vehicles more sustainable than battery electric vehicles?

Hydrogen fuel cell vehicles (HFCVs) today are not zero-emissions and are most often powered by hydrogen made from fossil fuels.

Though widely billed as ‘zero tailpipe emissions’ vehicles because hydrogen produces only water vapour as a by-product when used in a fuel cell, the manufacture of the hydrogen fueling these vehicles is an emissions-intensive process.

At present, 99% of hydrogen is made from fossil fuels and responsible for more emissions than the global aviation industry. Near-zero emission renewable or green hydrogen is, and will remain, in scarce supply. As a result, hydrogen vehicles are likely to lock us into continued fossil fuel use.

Crucially, hydrogen vehicles are about three times less efficient than battery-powered electric vehicles when running on near-zero emission renewable or green hydrogen. The ‘wind-to-wheel’ energy efficiency of hydrogen-powered vehicles, from hydrogen’s production through to its use in a fuel cell, is just over 30% – compared to around 80% for an electric vehicle.

This means that hydrogen vehicles use three times more electricity, require three times more energy-generating infrastructure, and involve at least three times higher costs than battery electric vehicles.

Furthermore, hydrogen vehicles require entirely new refuelling infrastructure that will add considerable cost to every mile driven, as the infrastructure’s costs are recovered in the price of the fuel.

What will happen if scientific evidence on hydrogen’s role in the energy transition is ignored?

Ignoring what science indicates about hydrogen in the energy transition will have implications in terms of excessive energy consumption, high carbon emissions and high economic costs.

Governments that decide to use hydrogen to provide a significant proportion of their country’s energy supply will be destined to pay large subsidies to the hydrogen industry for the indefinite future.

Globally, if a move to deploy hydrogen for inappropriate uses is satisfied by manufacturing renewable hydrogen, there will be a severe shortage of renewable electricity for decarbonising other sectors of the economy. This will significantly delay the energy transition and worsen global heating.

If the demand for hydrogen is satisfied at scale by making hydrogen from fossil fuels, with or without carbon capture, carbon emissions will likely rise significantly and emissions targets are unlikely to be reached.

Is hydrogen safe?

Hydrogen has been used in industrial applications for well over a century. Industrial hydrogen users have, over time and often in response to past accidents, established strict rules and practices related to hydrogen in order to reduce its risk. These rules are expensive to implement, and set limits on how hydrogen should be transported, handled and stored in order to ensure safety.

Hydrogen is a small molecule with high diffusivity, making it more difficult to contain than natural gas – especially at high pressure. It can diffuse through intact materials, such as plastic pipe, and also reduces the fracture toughness in steels of the sort used in gas transmission pipelines.

Hydrogen’s intrinsic properties make it considerably more dangerous than methane, the main constituent of natural gas, when it comes to fires and explosions. It has a very wide range of concentrations where it may be ignited, and the energy required to ignite it is about one-eighth that of methane. Hydrogen’s flame speed is also about eight times that of methane, meaning that it can generate more damaging explosions when ignited inside a confined space.

The types of ‘stenching agents’ added to natural gas to help detect leaks are damaging to the catalysts used in hydrogen fuel cells. As a result, replacing natural gas with hydrogen would require considerable safeguards beyond those commonly used for natural gas in order to protect against fire and explosion.

Is water use for hydrogen production a concern?

Current hydrogen production from fossil fuels uses a considerable amount of water to produce steam and also for cooling. Renewable hydrogen production requires a similar, if slightly higher, amount of water for the process of electrolysis.

Renewable hydrogen is the most water-efficient form of hydrogen among those aiming to cut greenhouse gas emissions, according to a report from the International Renewable Energy Agency (IRENA). As carbon capture and storage (CCS) systems increase hydrogen production’s water demand, even the most water-intensive renewable hydrogen uses almost one third less water per kilogram of hydrogen produced than blue hydrogen made from natural gas with partial CCS.

Since renewable hydrogen requires large amounts of renewable energy, and the best renewable wind and solar resources are often found in desert regions, water use by hydrogen projects has been raised as a concern.

However, the real problem with hydrogen production is not water use, but energy use. Desalinating enough seawater to produce one kilogram of hydrogen would require about 0.035 kilowatt-hours (kWh) of electricity to run a reverse osmosis unit. Producing one kilogram of hydrogen from that pure water requires 50 to 65 kWh.

If water is scarce, the best option would be to find a way to avoid producing one kilogram of hydrogen, which would save enough electricity to desalinate 14,000 litres of pure water – once again reinforcing the need to prioritise renewable hydrogen’s use for niche sectors where direct electrification is not possible.