Frequently Asked Questions

The immediate need for Green ammonia is to replace the ‘brown’ ammonia currently produced using fossil fuels, mainly for fertiliser. Some 175 million tonnes of ammonia are currently made in this way every year, causing 2% of global greenhouse gas emissions.

But Green ammonia could have a far greater role in our zero carbon future as a medium for the storage and transport of renewable energy.

It could then serve as an energy-dense fuel for power stations, ships, trains, aircraft, steel making and other industrial uses.

See our page Uses of Green Ammonia.

Green ammonia could come from anywhere with abundant renewable power and water (including sea water) and the infrastructure for its transport to markets.

There are vast areas of the world with huge renewable energy potential. The lowest cost producers will mostly be in sunny arid zones, avoiding possible land use competition with farming, or precious ecosystems.

Multibillion dollar investments are currently being made in Green ammonia and hydrogen production in Australia, Africa and the Middle East, with facilities located near deep water harbours.

Also, any country generating most of its power from renewables is likely to have more than enough for its immediate needs when the sun is shining and / or the wind is blowing. Any surplus could be used for local production of Green hydrogen and / or ammonia.

Using local renewables to make Green hydrogen / ammonia in temperate industrialised countries is a good way to use excess renewable power.

However the world market in Green ammonia will be dominated by exports from renewable energy rich nations with the necessary export infrastructure, because they will be able to produce and export bulk Green ammonia at the lowest cost.

Green ammonia is ammonia made through all its production stages using only renewable energy.

These stages may include: desalination of seawater; electrolysis of water into hydrogen (and oxygen); separating nitrogen from air, and the Haber process, which combines hydrogen and nitrogen into ammonia.

There are also alternative processes for making Green ammonia, some of which may prove useful for ‘farm-scale’ ammonia production around the world.

Please see our page on Green Ammonia Production.

In our existing fossil fuel dominated global economy, there exists a huge de facto energy reserve from fuels in storage and transit - enough to keep the world supplied with energy for weeks even if all production is immediately cut off.

However there’s no such equivalent with wind and solar, which produce energy for mostly immediate use. If the sun stops shining and the wind stops blowing (as it can for a week or more in European winter), everything stops. Without fossil fuels, our biggest stores of energy are in large hydropower stations, and in the batteries of the world’s 40 million electric cars (April 2024).

Add Green ammonia into that picture and everything changes. Reserves will accumulate within the supply chain: on tankers, in pipelines, in bunkerage, in storage facilities close to power stations, ports, industrial centres, airports and other transport hubs. Nations may choose to create additional energy security by building up strategic reserves of the fuel, as has the USA with its Strategic Petroleum Reserve.

Simply put, ammonia can provide energy security in exactly the same way that fossil fuels do today.

Most ammonia is currently stored in pressure tanks at 8 bar (or atmospheres), high enough to liquefy the gas at ambient temperatures.

It may also be liquefied at ambient pressure (1 bar) by cooling to -34C or below. It should then be stored in insulated tanks, ideally at -50C or below.

This last option is inherently safer than ambient temperature storage under pressure. It may also be more cost-effective owing to the high cost of pressure vessels. (Salmon, 2021)

Ammonia gas is toxic if inhaled. Skin or eyes exposed to ammonia can suffer severe burns. Ammonia is also toxic to aquatic life.

However ammonia is widely used as an industrial refrigerant, and is directly applied to soils as a fertiliser, with few incidents. It’s also safely shipped around the world in large volumes, using both tankers and pipelines.

Ammonia is generally stored as a pressurised liquid but low temperature storage and transport of liquid ammonia (at -50C to -75C) is an inherently safer option.

In the event of a minor release of ammonia, its pungent odour is likely to be detected long before any harm is done.

See more information on Ammonia Safety.

The starting point for making Green ammonia is green hydrogen and nitrogen. Turning that H2 and N2 into ammonia needs energy and expensive equipment, and therefore carries a cost.

Hence ammonia must be more expensive than hydrogen - at the point of production.

However, ammonia is much easier and less expensive to store and transport than hydrogen, whose storage requires one or more of: very low temperatures; very high pressures; or very large volumes.

Moreover there’s no existing infrastructure at ports, and no commercial vessels, suitable for bulk hydrogen transport. Hence the bulk delivery of Green hydrogen is at present impossible.

It therefore appears that Green ammonia will, for the foreseeable future, generally be deliverable to market at a lower price per unit of energy than Green hydrogen from the same or an equivalent source.

Liquid Green ammonia can be shipped in an ordinary bulk gas carrier as used for LPG, propane, butane, butadiene, and vinyl chloride monomer.

Shipping costs are therefore at a similar level, in the region of $50-150 per tonne depending on distance and the demand for ships.

This is less than for LNG (liquefied natural gas), which needs to be stored at -161C or below to remain liquid; or indeed liquid hydrogen, which needs to be kept at -253C or below.

Further, there are also no existing port facilities for bulk hydrogen discharge / recharge or storage.

Property Value

Lower Heating Value (LHV): 18.6 GJ | 5.2 MWh/tonne

Higher Heating Value (HHV): 22.5 GJ | 6.25 MWh /tonne

Gas (20C)

Density: 0.73 kg/m3

Energy density: 14.6 MJ | 4.05 kWh/m3

Minimum auto-ignition temperature: 650C

Flame speed: 0.07 m/s

Liquid

Boiling point at 1 bar: −33.3℃

Pressure of liquefaction at 20C: 7.5 bar

Density at -33.3C: 682 kg/m3

Density at 25C: 626 kg/m3

Energy density: 12.7 GJ | 3.5 MWh /m3

Latent heat of vaporisation: 1.37 GJ | 0.38 MWh / tonne

Heat capacity: 4.7 kJ /kg/K

Solid

Melting point: −77.7℃

Latent heat of fusion: 300 MJ | 83.3 kWh/tonne

Heat capacity: 4.9 kJ/kg/K

On our page on Green ammonia production, we calculate that the total electrical energy input to make a tonne of Green ammonia is 10.6 MWh.

Ammonia has a lower heating value (LLV - excluding latent heat of vaporisation of steam produced in combustion) of 5.2 MWh /tonne. Hence the production efficiency of Green ammonia is about 50%.

Using the higher heating value (HHV) of 6..25 MWh /tonne (which includes the latent heat of the steam produced) the efficiency is almost 60%.

Let’s define round trip efficiency as (electricity delivered at point of use) / (total electricity inputs).

According to the Royal Society, efficiencies range from 16% to 39%, depending on the technologies used.

But this figure isn’t as important as it might seem. Solar and wind energy are free. The cost arises almost entirely from the capital employed - in solar panels, electrolysers, ammonia synthesis plants, ships, storage facilities and other infrastructure.

If the Green ammonia is made where renewable energy is very cheap, like Australia or southern Africa, it can still be competitive in markets, like northern Europe, where renewable energy is more expensive.

Batteries are a fantastic technology for all the many things they do well - powering low power devices (like phones), or high power devices (like cars) that are frequently discharged and recharged. They also have an increasingly important role in stabilising grids, smoothing spikes and troughs in power supply and demand.

If you use batteries every day or many times a day they are highly cost effective. But if you use them only a few times a year the cost of the energy they deliver is prohibitive. Lithium ion batteries typically store about 270 Wh/kg, compared to ammonia's lower heating value (HHV) of 5.2 kWh /kg. If converted to power at 50% efficiency ammonia holds almost 10 times more energy than batteries. The waste thermal energy can also be used for space and water heating

Long distance power transmission is increasingly important with the advent of large scale renewable power generation. That’s for two reasons:

1. to transmit energy from the often remote places where power is generated, to where it’s needed; and

2. to balance out the fluctuating power supply from renewables, and the power demand, over a wide distance spanning multiple time zones and weather systems.

In North America, Europe and the Far East, ‘supergrids’ are being built to connect centres of Green power generation to consumers.

To be carried out efficiently on a continental scale this requires the use of HVDC - high voltage DC - cables stretching over hundreds or thousands of kilometres. This is all good. However it doesn’t take away the need for a ‘renewable reserve fuel’ like Green ammonia.

Power lines re vulnerable. They may need to cross multiple countries or even oceans, making them prone to disruption and political interference. And they only go between fixed places.  Green ammonia, on the other hand, can be sourced from many places, can change where it goes from day to day, and, if moved by ship, doesn't depend on the goodwill of everyone along a route to allow safe transit.  

Hydrogen is a fantastic fuel, with a very high energy density by mass. But due to its very low molecular mass, it has a very low energy density by volume.

This makes hydrogen difficult and expensive to transport and store, needing very:

• large storage volumes, or

• high pressures (350-700 bar / atmospheres), or

• low temperatures (it liquefies at -253C).

Cooling and compressing hydrogen also carry high energy costs. Vessels capable of storing compressed or liquid hydrogen are expensive and either heavy or bulky. The most cost effective solution for hydrogen storage is underground salt caverns, however the appropriate geology is unevenly distributed - and you can't put a salt cavern on a ship or aeroplane!

One way of looking at ammonia is as a ‘molecular container’ for hydrogen - one that does the job at lower cost than available forms of physical containment.

In the future there will be a role for some biomass-derived fuels. One of these is in electricity or heat generation, but specifically in power stations making use of the Allam Cycle, which produces high purity CO2.

This CO2 will have value for the organic synthesis of lubrication oils, pharmaceuticals, plastics and other materials now derived from fossil fuels. Beyond that it can be consigned to permanent underground disposal, earning ‘carbon credits’.

However these biomass fuels should be derived from agricultural, forestry, industry and domestic waste streams. Farmland is already a scarce resource needed for growing food; and forests are needed both for timber, and for essential biodiversity, climatic and hydrological services.

Only if biomass crops are developed that are suitable for growing on arid lands unsuitable for agriculture and unable to support forests, could biomass become a large scale, sustainable alternative.