Researchers from the University of Genoa conducted a techno-economic analysis to evaluate green hydrogen produced by electrolysis of water and its conversion into three alternative fuels – methane, methanol and ammonia. They looked at the efficiency, storage capacity, annual costs and production costs of the different fuels, which they found to be significantly higher than market benchmarks.
One of the next big projects in the energy transition, power-to-X (P2X) technologies can be used to store excess renewable energy in the form of clean fuels, such as hydrogen or ammonia. While these energy carriers and chemicals offer great versatility in storing renewable energy, the tipping point of their conversion efficiencies and costs has often been debated.
Today, researchers from the University of Genoa studied and compared four green P2X solutions – hydrogen, methane, methanol and ammonia – powered by various renewable energy sources in terms of technical and economic viability. The analysis was performed considering a PEM electrolyser for hydrogen production with a fixed size of 10 MW.
In their energy analysis, they found that power-to-hydrogen (P2H) had the highest efficiency of 61.5%, followed by power-to-methanol (P2M) 52.7% and power-to- ammonia (P2A) 51.4%, while power-to-ammonia (P2A) 51.4% -to-gas (P2G) had the lowest value of 45%. On the other hand, P2H proved to be the least practical storage solution (volume 316 m3). The best storage solution in terms of volume and energy density was P2M (volume 30 m3, energy density 4.3 MWh/m3), while P2A is the best in terms of H2 stored in the fuel (108 kgH2/ m3).
From an economic point of view, the distribution of the annual costs showed that, in all cases, the major expenses are linked to the purchase of electrical energy and to the capex and opex of the electrolyser (approximately 90% of the costs totals). According to the researchers, a 50% reduction in the cost of electricity and capital expenditure of the electrolyser could lead to a reduction of around 30% and 18% in the cost of production of the fuel (FPC), respectively. But selling the co-produced O2 would improve economic performance by reducing the FPC.
When examining different values of Levelized Cost of Electricity (LCOE) and Equivalent Operating Hours (EOH) characteristic of specific energy sources, researchers compared the production of hydrogen and ammonia in using photovoltaic energy. They found that production costs varied between €225 ($326)/MWh and €560/MWh for hydrogen and between €250/MWh and €670/MWh for ammonia.
Finally, in terms of mass cost, hydrogen is the most expensive product with €5.31/kg without the option to sell oxygen, i.e. around 74% more than the cost of producing gas and even 420 % more than the costs of methanol and ammonia which result almost comparable (respectively 1.02 €/kg and 1.04 €/kg). That said, the resulting fuel production costs are significantly higher than market reference values (€3/kg for H2, €1/kg for CH4, €0.5/kg for MeOH, €0.6/ kg for NH3), found the researchers.
Considering the production cost in terms of energy content, the highest value is for the P2G process (€0.22/kWh) due to the lower energy efficiency compared to the other process. Thus, the best result is obtained for the P2H case (0.16 €/kWh), and intermediate results are obtained for the P2M and P2A plants (0.19 €/kWh and 0.2 €/kWh, respectively).
The researchers described their findings in “A comparative techno-economic and sensitivity analysis of Power-to-X processes from different energy sources”, recently published in Energy conversion and management.
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