Renewable hydrogen is set to play a key role in the decarbonisation of hard-to-abate sectors, whether in heat generation or as a feedstock where fossil-based hydrogen is currently used. Although “green hydrogen” tends to be identified with that produced from renewable electrolysis, there are other CO2-neutral pathways capable of producing renewable (green) hydrogen. Among them is steam reforming of biomethane, which has the great advantage of using existing infrastructures and fully mature techniques. This process is based on replacing natural gas with biomethane, so that the CO2 released in the process is neutral, being of biogenic origin. A further step would be to capture this biogenic CO2, thus generating negative emissions. We have called this hydrogen with negative emissions from biomethane reforming “golden” hydrogen, since it comes from “green” hydrogen from which the “blue” colour has been removed (associated with fossil hydrogen from which carbon capture is carried out to obtain low-carbon hydrogen). This colour subtraction would result in “yellow”, which is associated with electrolysis production from the electricity grid. Hence, we have modified it to “gold”, in order to also highlight the negative emissions character. Figure 1 shows this process.

Figure 1. Phases of golden hydrogen production.

The Fundación Repsol Chair of Energy Transition at Comillas-ICAI participates, in collaboration with other research groups at Comillas-ICAI, in the characterization of this type of renewable hydrogen, having published a scientific article with the cost model for golden hydrogen in Spain, of which the most relevant information is collected here.

Figure 2 shows the golden hydrogen supply chain. On the one hand, and in a decentralized manner, biomethane is produced and injected into the existing gas network with certificates of guarantee of origin, which allow it to be redeemed at the centralized SMR plant with carbon capture. To avoid transporting hydrogen over long distances, the SMR plant is located in a hydrogen valley with the presence of large industrial consumers. The captured CO2 is transported to the geological storage (in Spain, the CO2 storage capacity in deep saline aquifers is estimated at 11 Gt). Regarding the use of biomethane, for each GWh-PCS of biomethane, 18.54 t of golden hydrogen can be produced, with a generation of negative emissions of 8.64 kg of CO2 for each kg of hydrogen.

Figure 2. Golden hydrogen supply chain.

The cost model takes into account both investment (CAPEX) and operating (OPEX) costs. CAPEX has been obtained from existing plants, while OPEX has taken into account the cost of biomethane (biogas production, its enrichment and subsequent injection into the grid); the operation and maintenance of the reforming plant with capture and finally the cost associated with the management of captured CO2 (transport, injection into storage and income from CO2 tax).

An important aspect is the cost of biogas, as well as its potential to be ultimately transformed into hydrogen. Table 1 shows four scenarios considered in Spain: scenario 1 assumes that only the organic fraction of municipal solid waste (MSW) is used, with the SMR plant placed next to the treatment plant; scenario 2 proposes a mix consistent with the forecasts of the Government of Spain; Scenarios 3 and 4 are based on estimates by SEDIGAS, with scenario 3 being more conservative than scenario 4 in terms of the amount of biogas from intermediate crops. Based on these potentials, the production capacity of golden hydrogen in Spain is obtained, as shown in Table 2. Note that the negative emissions generated would range between 1.27 Gt/year in scenario 1 and 26 Gt/year in scenario 2. As regards cost, the developed model generates Figure 3. As can be seen from it, after including the negative cost for the CO2 credits obtained, the standardised cost of this hydrogen is between €2 and €3/kg, close to that of fossil hydrogen and below that of green hydrogen from renewable electrolysis.

Table 1. Biogas potential in Spain in different scenarios, together with the weighted average cost in each case.

Table 2. Production of golden hydrogen in Spain according to the scenarios contemplated in Table 1.

Figure 3. Normalized costs of golden hydrogen in the scenarios considered.

In conclusion, it can be said that golden hydrogen allows for the production of renewable hydrogen on a large scale, with a reasonably achievable potential (scenario 3) in Spain of about 2.15 Mt/year (about 3.6 times the current demand for hydrogen and approximately double the forecasts of the Renewable Hydrogen Roadmap). The negative emissions it produces (8.64 kg CO2/kg H2) allow for the compensation of unavoidable emissions, with geological storage facilities in deep saline aquifers in Spain with a capacity of up to 11 Gt of CO2, equivalent to more than 400 years of production in the most optimistic hypotheses (scenario 4).

This note summarizes the article “Yagüe, Linares, Arenas and Romero, Levelized Cost of Biohydrogen from Steam Reforming of Biomethane with Carbon Capture and Storage (Golden Hydrogen)—Application to Spain, Energies (2024) 17(5), 1134” https://doi.org/10.3390/en17051134