One of the next big things of the energy transition, power-to-X (P2X) technologies can be used to store surplus renewable energy in the form of clean fuels, such as hydrogen or ammonia. While these energy carriers and chemical products provide significant versatility in renewable energy storage, the tipping point for their conversion efficiencies and costs have often been a matter for debate.
Now, researchers at the University of Genoa have investigated and compared four green P2X solutions – hydrogen, methane, methanol, and ammonia – powered by various renewable energy sources in terms of their technical and economic viability. The analysis has been performed considering a PEM electrolyzer for hydrogen production of a fixed size of 10 MW.
In their energy analysis, they found that power-to-hydrogen (P2H) showed the highest efficiency of 61.5%, followed by power-to-methanol (P2M) 52.7% and power-to-ammonia (P2A) 51.4%, while power-to-gas (P2G) had the lowest value of 45%. On the other hand, P2H was found to be the less convenient storage solution (volume 316 m3). The best storage solution in terms of volume and energy density was the P2M (volume 30 m3, energy density 4.3MWh/m3), while P2A is the best in terms of H2 stored in the fuel (108 kgH2/m3).
From an economic perspective, the annual cost breakdown showed that, in all the cases, the major expenditures are related to the electrical energy purchase and capex and opex of the electrolyzer (around 90% of total costs). A 50% reduction in electricity cost and electrolyzer capex could lead to a reduction of about 30% and 18% on fuel production cost (FPC), respectively, the researchers found. But selling the co-produced O2 would allow for an improvement in the economic performance, reducing the FPC.
When considering different values of levelized cost of electricity (LCOE) and equivalent operating hours (EOH) characteristic of specific energy sources, the researchers compared hydrogen and ammonia production employing PV energy. They found that production costs ranged between €225 ($326)/MWh and €560/MWh for hydrogen and €250/MWh to €670/MWh for ammonia.
Finally, in terms of cost by mass, the hydrogen results in the most expensive product with €5.31/kg without the oxygen sale option, which is about 74% higher than gas production cost and even 420% higher than the methanol and ammonia costs that result in almost comparable (€1.02/kg and €1.04/kg, respectively). With that said, the resulting fuels 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), the researchers found.
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. Accordingly, the best result is obtained for the P2H case (€0.16/kWh), and intermediate results are obtained for 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,” which was recently published in Energy Conversion and Management.
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