Ammonia

Ammonia--chemically NH₃--is a critical ingredient in fertilizers, and it could play a much larger role in a future energy economy. As we show below, producing ammonia today with carbon capture and sequestration is cost-effective, and so is production by clean energy electrolysis if the electricity source is sufficiently cheap.

Ammonia Economy

Over 80% ammonia is used for fertilizer today, with the remainder used for explosives, solvents, nitric acids, and other industrial chemicals ¹.

Source: ².

In the future ammonia may play several important roles in the energy system.

Potential roles for ammonia in a low-carbon energy system. See references on ammonia in transportation ³, for load balancing ⁴, and for other roles ⁵.

In an energy system with high volumes of variable renewable energy and/or hydrogen, ammonia may be the best option for seasonal energy storage and long-distance energy transportation ⁵. While ammonia can be used directly as transportation fuel, its low gravimetric and volumetric density, toxicity, and other drawbacks may limit this role.

Cost of Production

The cost of producing ammonia is estimated as follows.

Levelized cost of ammonia, which is the price that the ammonia producer must receive for the given method to be profitable. Values are reported by the IEA ⁶. The wide range in the cost of ammonia by electrolysis depends on the price of electricity.

Because the cost of ammonia from electrolysis is dominated by the cost of electricity, rather than equipment capital costs, it is possible to produce ammonia intermittently to match low electricity prices. This may be useful for load balancing on a high renewable grid.

Cost of producing ammonia by electrolysis varies by the cost of electricity and the level of usage of the electrolyzers. Source: Philibert ⁴.

There are novel ammonia production methods under development that may reduce further reduce costs. Examples are biological nitrogen fixation, mimicking the processed used by natural bacteria; electrochemical methods that would produce ammonia directly from nitrogen and water without producing hydrogen; and chemical looping methods ⁷. Each of these methods is still far from commercial production.

Ammonia Distribution

Ammonia is much easier to transport than hydrogen, which makes it particularly attractive for long-duration transport and storage of intermittent energy.

Estimated cost of shipping ammonia from the Middle East to Japan. It is cheaper both than producing ammonia locally or shipping hydrogen. Source: IEEJ ⁸.

Energy and Environmental Impacts

Modern ammonia production is efficient, and there is potential for modest further efficiency improvements. The following are estimates of the onsite energy requirements for current and future ammonia production methods.

Sources: Brown ⁹ and Cefic ¹⁰.

Electricity is a higher quality fuel than coal, natural gas, or biomass, and there may be more primary energy behind the electricity than what is consumed onsite. Nuclear thermochemical electrolysis and solid state ammonia synthesis are not yet commercial methods.

For electrolysis ammonia to serve a role in a low carbon energy system, a low cost and low carbon electricity source is needed. Most of the energy for electrolyzed ammonia is used for the splitting of water to produce hydrogen.

Source: Dana et al. ¹¹. Note that Dana et al. and Cefic ¹⁰ differ slightly in total energy required for ammonia by electrolysis.

Ammonia production methods show the following life cycle greenhouse gas emissions.

Source: Singh et al. ¹², with information about SMR with CCS supplied by Young et al. ¹³.

Ammonia is highly toxic, necessitating a high level of care in an expanded ammonia distribution system and potentially creating a public acceptance barrier ⁵. If used at a large scale, nitrous oxide emissions ¹⁴ and ozone depletion ¹⁵ will be challenges.

Ammonia as a Transportation Fuel

With an energy density significantly higher than lithium-ion batteries, ammonia, including from low-carbon production, is suitable for most forms of transportation except long-haul aviation.