The second technology (GEN 2) has significant long-term importance in terms of ammonia economics, but is limited by non-scalability and the significant plant investments required. The second technology is based on Haber-Bosch technology but using renewable or blue hydrogen rather than fossil fuels. This has the advantage of being able to convert existing Haber-Bosch systems quickly and without large plant costs.
The cost will also include the equipment for the electrolysis of water or by adopting PEM technology the cost will be significantly reduced due to the intrinsically higher current densities obtainable >1 A cm-2. The efficiency of the calorific value exceeds 75% and it is plausible to hypothesize further improvements.
Still within the scope of the second technology, in the future it will probably be possible to opt for high-temperature solid oxide electrolysis (SOE) by exploiting the heat resulting from the Haber-Bosch process. This variant will have an overall energy efficiency of more than 70%. In addition to generating H2 with an efficiency close to 100%, SOEs can be used to generate pure N from air by replacing traditional air separation units, reducing the final energy cost of ammonia. To date, the SOE variant is still being developed and it will first be necessary to find how to stabilize the electrolysers during long-term operation at 700°C-900°C as well as how to harmonize them with intermittent mode operation caused by power supply from renewable.
In fact, the Haber-Bosch process ideally works continuously, which does not combine well with the day-night cycle of photovoltaics or with the intermittency of the wind, creating the need for an intermediate solution for energy storage with further increases in expense.
