“Green hydrogen” is hydrogen gas produced by using renewable electricity to split water into hydrogen and oxygen with little or no carbon emissions. Now, a demonstration project at the European Marine Energy Centre (EMEC) on the island of Eday in Scotland’s Orkney Archipelago [Google Maps] uses tidal energy to supply the renewable electric power for the hydrogen-oxygen splitting process.
Electrolysis, the process employed by EMEC on Eday, is a well-known technology that conducts electric current through water to produce hydrogen. What’s different about the EMEC center is their source of electricity: a tidal turbine located about a mile (1.6 kilometers) offshore, where it generates power from the strong tidal currents in the region. The 243-foot (74-meter) O2 tidal turbine, built by Orbital Marine Power, is tethered to the ocean floor and floats on the surface, deploying two 33-foot (10-meter) rotors that extract energy from tidal current flowing past its stationary hull. (The O2’s power capacity is 2 megawatts, enough to power about 2,000 homes.)
Hydrogen gas EMEC produces can be used for powering hydrogen fuel-cell vehicles, a carbon-free transportation mode. Hydrogen can also be used for fueling rockets, producing ammonia for fertilizers, and for several other industrial processes.
Electricity from the O2 turbines comes ashore by cable to EMEC, where it powers a 670-kilowatt electrolyzer made by ITM Power. During slack tides, when the O2 turbine has low output, vanadium redox flow batteries (VRFBs) by Invinity Energy Systems stand in to keep the process running until the next tide cycle. These batteries then recharge during high tidal flow times, when the O2 turbine produces more power than needed by the electrolysis process. (VRFB technology is particularly suited for large-scale electric energy storage because of its ability to be scaled up, its charge and discharge performance, and its long life.)
According to EMEC, this is the first time that tidal power, VRFB storage, and hydrogen production have been integrated into a single system.
For more details, visit EMEC’s website.