Wind energy is intermittent and variable. However, electrical demand is stable and predictable. In order to maximize wind resources, it is important to remove the variability of the energy source in order to optimize allocation and distribution to customers on a regular and predictable basis. The only means of doing that is to fully dedicate the collection of energy in the form of a stable, energy dense fuel (hydrogen) from a primary feedstock (waste or seawater) that is readily available and inexpensive and allocate and distribute that captured energy source (in this case hydrogen) to synchronize with customer demand. The figure below illustrates this point. The data was taken from a group of wind farms located in South East Australia. In the label marked A, one can see that the supply of wind energy exceeds demand. Unless a method of storing this excess energy is implemented, the additional generated energy is lost. Label B shows a peak in energy production at the same time of minimum energy demand. This represents a complete mismatch in the energy supply and demand cycle. Excess supply in this scenario is also lost. Label C represents the exact opposite of B in that the demand is very high but the supply is low. This reduces the availability of the wind farm for energy production, idling expensive capital equipment. Label D represents the synchronization of supply and demand. As one can see in the example shown below, that condition is not a common event.
As shown in the figure below, the change of the seasons clearly demonstrate the complete change in the wind resource availability from the above figure. On the contrary, demand is constant and predictable although at a higher level due to the change of season. Once again, the synchronization of supply and demand occurs in only a handful of days in the month.
Wind Farms — Ocean
Wind farms located close to the shore or in deepwater are ideal venues for the production of hydrogen using the RET. There is a clear similarity between offshore oil drilling and hydrogen production using RET from offshore wind. The infrastructure of both would be identical. The capital cost, however, would be a lot less for the production of hydrogen using RET for many reasons. Some of them are the unnecessary requirement for expensive exploration and drilling at great depths for a depleting and finite resource or the use of submarine cabling to attach to a land electrical grid. There is no physical limitation as to the size of a deepwater wind farm or its location further from land since the RET/wind turbine combination is self contained and the infrastructure of transporting hydrogen is well established. There are two ways of generating hydrogen in an offshore scenario; centralized or distributed. The decentralized or distributed approach is considered superior for ocean applications. The opposite is true for land based hydrogen production. As shown in the figure below for decentralized hydrogen production, there are two types of hydrogen delivery to the shore. As shown in the figures, labeled A or the figure below labeled C, a tanker or barge* collects the compressed hydrogen in the form of cylinders (composite or otherwise), and transports them to a port on the coast for land based distribution. This is more suitable for distant offshore hydrogen generation. Land distribution of hydrogen could take the form of tanker or conventional flat bed vehicles. The other option, namely a hydrogen pipeline, label B in the figure, would be more suitable for offshore farms closer to the shore.
*Commercial ships already employ hydrogen. Both represent different approaches. The Hydrogen Challenger produces its own fuel so it doesn't compete with the RET hydrogen production. See also the H Ship.
As shown in the figure below, chlorine generation becomes predominant in the region where the electrode potential lies between about 1.8 and 2.6 volts. The transport of Cl- ions to the electrode is limited, whereas there is no corresponding problem with the availability of water to produce oxygen. There is a potential sufficiently high at which Cl2 production becomes limited by mass transfer; oxygen continuing to evolve as a function of the increasing electrode potential. If the cell potential is increased > 0.2 volts above the limiting current of Cl-, the amount of chlorine generation drops to less than 1% of the evolved gas (O2/Cl2). One can conclude from the figure below that up to about 1.8V, chlorine evolution can be neglected and that after 2.2V, it will predominate. However, after 2.6 volts it will become a rapidly decreasing component of the product gas.
The higher range of potentials in which chlorine evolution rates increase no more, but hydrogen and oxygen increase exponentially with the applied potential, is not an economically practical range. Additional energy (from electrical sources) is necessary to operate at higher potentials. Therefore, the aim is to achieve oxygen evolution at potentials < 1.8V for economic reasons. Unless a super active catalyst is discovered to achieve a kinetic regime that makes economic sense, direct seawater electrolysis will not be a viable means of converting seawater into hydrogen and oxygen in the near term. There has been work on new electrodes to improve the speed of the reaction. They involve the use of expensive precious metals (e.g. iridium and platinum) and the kinetics are still not in the realm of commercial realization. Also, at these low potentials, the current density for the reaction is diminished. Larger electrode surface areas are needed to compensate for the smaller current densities. The use of precious metals for these electrodes would make the capital cost of the electrolyzer prohibitive. It should finally be pointed out that it is necessary to maintain 100% selectivity to oxygen over chlorine in order to prevent the toxic emission of this halogen gas into the atmosphere. There is no such process technology to date that can fulfill the above requirement.
