Wind Resources for RET

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 — Land


Dedicated wind farms producing hydrogen from RET can be constructed in any remote area so long as there is a relatively constant source of wind. As shown in the figure below, water availability is not an issue since even unfiltered rain water caught in basins can be a source of hydrogen. Expensive grid connection is not necessary, eliminating a high capital cost item. Hydrogen as well as oxygen can be sent to customers via pipeline as shown by label B or via truck as shown by label A. Local economics will dictate which option is more viable.  


Remote Land Farm


There are different scenarios in which the eRET can be used. If it is desired to have a hybrid system where hydrogen and electricity is sold simultaneously, there are several ways in which one can accomplish that. This option only makes sense if the grid is located near the wind farm. In that case, hydrogen could be produced during non demand hours and electricity sold to the grid during high peak hours. Alternatively, the wind farm can be used as a base load plant where a predictable electricity flow could be established if hydrogen is produced in conjunction with a fuel cell. In this scenario, hydrogen is produced and stored and the fuel cell supplies electricity to the grid in even amounts to satisfy base load needs. One advantage of this option is the generation of useful by products such as argon and nitrogen. Local production of fertilizer can be made a reality if the wind farm is located in an agricultural area. The figure below illustrates this approach. A 1 MW wind turbine would permit the use of about 15,000 eRETs to operate giving a total of around 600 MW of power.


WindRET H2


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.






Centralized hydrogen production as illustrated in the figure below would be most suitable for wind farms close to the shore. Once again, two options for hydrogen delivery are available. Their implementation would be a function of the local infrastructure and other economic factors.




RET is superior to electrolysis especially in ocean based hydrogen production. As the table below enumerates, RET can use unfiltered seawater as a feedstock for hydrogen production. The elimination of expensive water filtering substantially reduces operating and capital costs. In addition, since the RET is a solid state system, there is no fear of a toxic leak from corrosive chemicals as is commonly used in electrolysis systems. RET systems are modular, so scale-up to a variety of turbine sizes is simple and cost effective. The compression of hydrogen takes place in a metal alloy hydride system tailored to the thermodynamics of the site. The exothermic nature of the metal hydriding process can be used to vaporize the seawater for RET hydrogen generation. High pressure dispensing could be accomplished on a just in time schedule. As the barge approaches the loading facility of the turbine/RET system, cooling water from the ocean can initiate hydrogen desorption from the metal alloy in order to pressurize and fill tanks for shipping. The temporary storage of hydrogen in metal hydride containers allows the safe storage of this gas at atmospheric conditions. The salt residue left after the generation of the vapor can be sold as a byproduct.


The pie chart below shows the cost breakdown of an offshore wind plant. About 15% of the capital cost is due to submarine cabling and integration with a land electrical grid. This would not be necessary if a RET/wind turbine combination is used. The capital cost of a deep offshore wind farm is quite large and therefore any capital reduction would be welcome.


In comparing dedicated production of hydrogen using RET in an offshore wind farm versus generating electricity for a land based grid there are several outstanding differences that should be noted. The capital cost of submarine cabling and transmission to land is very expensive. RET is a low cost system that can be tailored to the peak production of power of the wind turbine. Generating hydrogen exclusively allows the maximization of energy collection from the turbine enhancing its availability and capacity, thereby justifying the high initial capital cost of the offshore wind farm. Also, it should be pointed out, that there are no losses of hydrogen when transported to the shore via tanker or barge. Typically there is a 10 to 15% loss in transmitting power from the wind farm to the land-based grid. Offshore wind farms dedicated solely for the production of hydrogen are not limited to distance from the shore since expensive cabling or piping is absent. Lastly, the infrastructure of producing hydrogen in an offshore setting is similar to offshore oil operations. We have the benefit of over 50 years of experience and technology to make this combination a near term reality. Unfortunately, the deepwater generation of electricity has a very short span of experience where the first deep water project generating electricity occurred in September, 2009. As an example, there is a proposed offshore wind farm to be located off the Maine coast that is projected to produce 5 GW of power. If this farm is dedicated to hydrogen production, assuming a 75% efficiency of the RET, this farm could produce about 250,000,000 kilograms of hydrogen per year. This would satisfy half the transportation needs or half the electrical needs for the state of Maine on a permanent basis. 
The Problems with Salt Water Electrolysis

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.
Sea Electrolyzer