Backing Up the Power Grid With Green Methanol
A closed-loop storage-plus-power system stockpiles renewable energy wherever it's needed
It would be great if everyone could back up the intermittent power from wind and solar plants with energy stored as low-cost, zero-carbon hydrogen gas. But hydrogen can be hard to store.
Last month, when the Royal Society advised the British government to start building underground caverns to store megatons of hydrogen gas, it noted that the United Kingdom would need to store 1,000 times as much energy in this way as its pumped hydropower reservoirs can hold, and far more than batteries can feasibly provide. And the U.K. is fortunate to have hollowed-out underground salt deposits in which to put the gas. Others do not. The Pacific coast of the United States, for instance, has no appropriate geological formations. They are also rare across China, Africa, and South America.
Such cavern-challenged places may instead benefit from a creative workaround developed by German researchers: converting hydrogen to methanol. “Methanol presents a nice alternative to hydrogen, since as a liquid you can store it in tanks anywhere,” says energy-modeling expert Tom Brown, who heads the Department of Digital Transformation in Energy Systems at the Technische Universität Berlin.
Today in the journal Joule, Brown and Johannes Hampp, a doctoral researcher at the Potsdam Institute for Climate Impact Research, in Germany, report that storing energy as methanol can be cost effective. The key is to integrate equipment producing hydrogen, methanol, and electricity, all of which are being commercialized or are in industrial development.
Low-carbon methanol production is already scaling up to replace the dirty bunker fuel that propels big ships. And the specific type of power generator required has been demonstrated at a 25-megawatt plant in Texas.
The LaPorte, Texas, generating station, covered by IEEE Spectrum in 2018 along with process inventor Rodney Allam, burns natural gas with pure oxygen from a dedicated air separator. The Allam cycle, which bears his name, combusts fuel in a circulating stream of carbon dioxide that’s heated and compressed to form a pseudoliquid known as a supercritical fluid. After the supercritical gas expands to drive a turbine generator, excess carbon dioxide created by the combustion reaction is easily bled off. This allows a process to capture the carbon without the inefficiencies associated with separating carbon dioxide from a regular turbine’s exhaust.
NET Power, the LaPorte plant’s developer may sell the captured carbon dioxideto oil fields, which use it to boost petroleum extraction. That would diminish the Allam cycle’s climate-benefiting effect. But investors seem unfazed: NET Power raised over US $675 million earlier this year to build a 300-MW commercial-scale plant in Texas, which the company plans to start operating in 2026.
Repurposing the Allam cycle to burn methanol in an all-renewable energy system was first proposed in 2019 by engineers at the Netherlands’ University of Twente. Their integrated storage system, a closed loop that contains the Allam cycle, works as follows:
Electrolysis splits water molecules into their constituent elements, hydrogen and oxygen;
Hydrogen is made to react with carbon dioxide, producing methanol;
Methanol is stored in tanks until required as a backup for shortfalls in renewable power generation;
Methanol and oxygen are burned in the Allam cycle to generate power; and
Surplus carbon dioxide loops back to step No. 2, where it is used to synthesize more methanol.
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https://spectrum.ieee.org/methanol-energy-storage