Colloquia

Summary

Global effort to reduce carbon emissions has stimulated growth of renewable technologies internationally. In The Netherlands, renewable technologies have significantly increased their share in total electricity generation over the last two decades as well. Due to the intermittent nature of some renewable energy technologies (in particular wind and solar), the electricity network is under significant stress during periods of heavy production or heavy demand. Addressing this requires large-scale energy storage and conversion technologies capable of balancing fluctuating supply and demand.

One of such technologies might be the carbon-neutral Power-to-Gas/Gas-to-Power (PtG/GtP) system developed by EmmetEnergy. This system integrates a reversible solid oxide cell with a methanation process. in Power-to-Gas mode, renewable electricity drives electrolysis to produce hydrogen, which reacts with carbon dioxide to form storable methane. In Gas-to-Power mode, methane is re-converted into hydrogen, carbon dioxide is recaptured and hydrogen is used to regenerate electricity. The PtG/GtP process chain could play a significant role in future renewable energy technologies. However, it lacks perspective combining technology with economic feasibility and potential consequences thereof. In this study, a PtG/GtP process chain was assessed using the software Reves DSE, allowing for design space exploration across a wide range of parameter configurations.

A reference case of 3 kW PtG and 1.5 kW GtP originating from EmmetEnergy was modeled and subsequently scaled to a 30 MW PtG and 15 MW GtP design. 1825 hours of PtG loading are divided into seasonal storage and immediate daily cycling equally. Efficiencies of components are given. Model results show that system roundtrip efficiency is heavily influenced by the reversible solid oxide cell, lowering the maximum attainable roundtrip efficiency to 59.8% according to the reference case. If condensers operate entirely using once-through cooling, roundtrip efficiencies may range between 22.1% and 36.4% for varying heat exchanger effectivenesses. As there is still a significant roundtrip efficiency reduction compared to the maximum attainable roundtrip efficiency, the process setup may have to be improved. The model also shows a Levelized Costs of Electricity range from 0.49 €/kWh to 0.81 €/kWh at a discount rate of 6%. The system could reduce national emissions by 99.2 kilo tonnes CO2 eq. to 194.4 kilo tonnes CO2 eq. in its 20 years lifetime, yet practical challenges remain, including sulfur filtration, cooling impacts on marine ecosystems, duality of components, load and unload strategies and economic competitiveness.