Ammonia as an energy carrier: avoiding environmental problem shifting

The current energy system is highly dependent on fossil fuels, the most significant contributor to GHG emissions. The opportunity is enormous, and the science is crystal clear: how we produce and manage energy must change.

We have reached a tipping point in the deployment of renewable energy: solar panels cost $100 per watt in 1975, they're now less than 30 cents per watt.

Why do we need energy vectors?

It’s not enough to generate cheap, clean energy - it has to be made available on demand: when and where we need it. Energy demand depends on the climate, geography, social habits, and seasonal changes. Energy demand is usually achieved through energy storage and transportation: we produce extra energy when demand is low, store it, and deliver it via a suitable vector when needed.

But renewable supply is as variable as demand - it literally changes with the weather. And not all places have the right conditions for wind or solar production. A reliable global renewable energy system needs a practical way to store and transport energy.

The challenge of a new energy carrier

To date, we have relied on fossil fuels, whose chemical bonds hold energy made available through combustion. Coal, gas, and oil have been stored and transported through existing networks. Substituting fossil fuels also means finding a replacement for how the energy is stored and moved.

Electrification and energy transport via the grid and most other methods, such as electrochemical batteries, are not suitable for long-term, large-scale storage or long-distance transport or are too expensive. So, we look for clean chemical storage—specifically hydrogen and ammonia.

Hydrogen’s potential as a carbon-free fuel, its high energy content and clean combustion make it a cornerstone of sustainable energy transition strategies. However, it has severe drawbacks for long-distance energy carriers or long-term energy storage. A lot of hydrogen has to be transported to produce a limited amount of energy. It is also dangerous and costly to handle, requiring pressure conditions only found at the bottom of the Earth’s oceans or temperatures than anywhere in our solar system [5].

Ammonia: the versatile vector

Ammonia, on the other hand, is a Hydrogen derivative with several advantages over it. It’s much easier to handle, requiring much milder conditions of about 10 bar at -25C. Its structure makes it more efficient at transporting hydrogen than using hydrogen itself. It also burns as a carbonless fuel.

While hydrogen transportation is a ‘lossy’ process with many technical unknowns, ammonia has a mature existing infrastructure as a critical ingredient of global fertiliser and less technical risk. All these factors make it a more practical, versatile vector that could realise the hydrogen economy.

A pillar of the global energy transition

In the IEA Net Zero scenario, hydrogen is responsible for 6.5% of cumulative emissions reductions from 2021-2050, avoiding up to 60 Gt CO2. A quarter of global hydrogen demand in 2050 (614 Mt) could be internationally traded, requiring new supply chains and transport routes for energy carriers.

Most hydrogen projects that have identified a hydrogen carrier molecule have chosen ammonia, and up to 10% of total global hydrogen produced could be transported over large distances in the form of ammonia by 2050. This represents up to 20% of total ammonia demand by 2050: 110-127 Mt.

Direct power generation from uncracked ammonia could also be cost-effective. By 2050, it could account for 35–105 Mt of ammonia, eliminating up to 478MtCO2eq.

Some ways ammonia could have an essential role as an energy carrier are:

• Transporting hydrogen from distant generating sites (i.e. offshore wind) to end users
• Allowing stable export of low-carbon energy from countries with non-intermittent, low-cost sources
• Storing large amounts of energy generated by renewable sources when supply exceeds demand, balancing the energy system in places with intermittent energy resources
• Delivering green energy to remote locations and regions, including direct power generation
• In the transport section, after decomposition into hydrogen

Ammonia could play a huge role in decarbonising energy systems. But carbon dioxide is not the only problem in our current ecological crisis. In addressing climate change, we must take care not to shift the burden to other planetary systems.

Clean ammonia production: avoiding environmental problem shifting

Generating renewable energy for hydrogen production requires land and water, depending on the technology - bioenergy is incredibly demanding. Extracting materials to produce solar panels or wind turbines degrades ecosystems and harms biodiversity. Deployment of these technologies can put pressure on wildlife. Producing hydrogen from electrolysis also demands water.

If this is not considered, deploying renewable energy shifts the burden from climate change to other systems, mainly biodiversity loss and ecosystem functioning. Since solar power is land-intensive, it poses risks to biodiversity, while hydropower affects freshwater availability and aquatic ecosystem functioning. Wind power disturbs local ecosystems and pressures wildlife conservation and biodiversity.

Producing clean ammonia overall could impact all systems identified by researchers as essential for maintaining life on Earth. A study with an electrified Haber-Bosch system showed that even clean ammonia can be unsustainable when considering a broad environmental view.

The extent of these impacts highly depends on the production route: sources of hydrogen and energy. Water electrolysis powered by wind, solar, and hydropower were found appealing, while using bioenergy improves climate change at the expense of significantly damaging the biosphere integrity, nitrogen flow, and freshwater use.

Nium’s technology is expected to have fewer impacts since it requires 16x less energy for the ammonia synthesis step than electrified Haber-Bosch. Nevertheless, impacts from hydrogen production could still be significant.

Using clean ammonia sustainably

Once ammonia is produced, leakages during transport could impact ecosystems due to its toxicity, as well as causing aerosol loading and ozone depletion. But ammonia transport is a much less leaky process than hydrogen, which is an indirect greenhouse gas. Transporting ammonia instead of hydrogen can avoid indirect climate change effects equivalent to 0.6% of current fossil systems for every 1% leakage rate.

If powered with fossil fuels, transport would also impact climate change and ocean acidification. Cracking ammonia back to hydrogen and using hydrogen as a power source in fuel cells usually require heat, which can impact climate change depending on the energy source. Clean energy should be prioritised for all steps.

Using ammonia as a direct power source, in alkaline or solid fuel cells also requires heat; and combustion of ammonia requires fuel for ignition, as well as emitting NOx and particulate matter, impacting climate change, and aerosol loading. This requires control equipment for these emissions.