Hydrogen Generation
Hydrogen is an energy carrier, not an energy source. Hydrogen can store and deliver usable energy produced using ocean energy technologies.
Hydrogen, chemical symbol H, is the simplest element on earth. An atom of hydrogen has only one proton and one electron. Hydrogen gas is a diatomic molecule - each molecule has two atoms of hydrogen (which is why pure hydrogen is commonly expressed as "H2").
Hydrogen is an energy carrier, not an energy source. Hydrogen can store and deliver usable energy, but it doesn't typically exist by itself in nature; it must be produced from compounds that contain it.
Storing and Transporting Energy as Hydrogen
Offshore wind, solar, and wave energy do not always produce energy at the time at which it is needed. In addition, the energy produced at remote offshore locations using these technologies and ocean current technology must typically be brought to onshore consumers. To address the sporadic nature of energy production from these sources at offshore locations, feasible methods for storing excess energy until it can be used and for transporting it must be developed. Currently, the most attractive approach is the use of hydrogen as a storage medium. Hydrogen can be generated on location on a variety of scales, and it can be stored and transmitted for later consumption in fuel cells in vehicles or converted into electricity. At this time, however, hydrogen is not being used to store or transport energy produced with ocean energy technologies in commercial applications.
Hydrogen Production
In future commercial applications, hydrogen could be produced offshore at the point of energy generation in a co-located facility, or it could be produced at an onshore location, utilizing the energy generated at the offshore power generation facility. Because all four alternative energy sources under analysis in the OCS Alternative Energy Programmatic EIS are capable of producing electricity, electrolysis is currently the most viable means of producing hydrogen from any of the four alternative energy sources. Electrolysis involves the dissociation of water into hydrogen and oxygen by passing a current through an electrochemical cell, and has been available commercially for decades.
Transmission and Storage of Offshore Energy as Hydrogen
If the hydrogen production is co-located at the offshore power generation facility, the hydrogen must be stored and transmitted to an onshore location for eventual use. Hydrogen could be delivered to onshore facilities through one of three means: as a gas, in liquefied form, or in a hydrogen carrier. In gaseous form, hydrogen would be compressed and transferred onshore through a pipeline or in pressurized containers on a ship or tanker. Compressed gas technology is well-established in the United States. Also, dedicated hydrogen pipelines exist, having been converted from those previously carrying oil or natural gas, and offshore pipelines are an established technology. The transport of hydrogen raises some technical concerns, however, that do not occur with the transport of natural gas or oil. Some potential obstacles include the need for improved seal technology and techniques to control permeation and leakage in general. Because of its low molecular weight, hydrogen molecules are much smaller than oil or gas molecules, and it is difficult to control leakage of hydrogen from equipment.
Liquefaction of hydrogen and its transport in containers are established technologies; however, the liquefaction process is energy-intensive and precludes the use of pipelines. Thus, transport from offshore locations would have to be by ship or tanker. Because of its added complexity and expense for both generation and transport, the use of liquid hydrogen is not an attractive option. A hydrogen carrier is any substance that can be used to store and transport hydrogen in any chemical state other than free hydrogen molecules. The carrier would be charged with hydrogen at the offshore generation site and then sent onshore where the carrier would be stripped of its hydrogen and sent back for recharging (two-way carrier) or decomposed at the point of hydrogen use (one-way carrier). Examples of carriers include ammonia (one-way) or liquid hydrocarbons and metal hydrides (two-way). Depending on the carrier and its form, it could be transported by pipeline, ship, or tanker. While considerable research has been and is being conducted on hydrogen carrier technology, no commercial process has yet been introduced.
Transmission of Offshore Energy as Electricity
Direct transmission of electricity from offshore locations is more straightforward and more energy-efficient than using hydrogen as an intermediate stage, but demand is not always concurrent with supply. Submarine cables are used to provide power to island communities and are used extensively in offshore oil and gas exploration to provide power, communication, and control lines to offshore platforms. Submarine cable technology is already used to provide electricity from offshore wind farms to onshore electric power substations, but over relatively short distances; there are technical challenges involved in transmitting electricity by submarine cables for the much longer distances to the Outer Continental Shelf (OCS).
Environmental Considerations for Offshore Energy Transmission
Potential environmental impacts that would need to be considered in evaluating the options for transmission of energy generated on the OCS to shore would include the impacts associated with the disturbance of the ocean floor while laying electrical cables or pipelines, potential interference with shipping lanes and other uses near the shore, the effects of electromagnetic radiation emanating from the underwater cables on aquatic organisms, and the health and safety concerns associated with the embrittlement of hydrogen pipelines and the release of hydrogen to the environment. While release of hydrogen to the environment is not inherently hazardous, the accumulation of hydrogen in confined volumes poses an explosion and fire hazard.
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