Abstract:
A renewable electric power system includes a high temperature superconducting wind turbine using high temperature superconducting yttrium-barium-copper oxide for the rotor and stator windings as well as a superconducting bearing. Power from the turbine is stored in a high temperature superconducting magnetic storage system that also uses HTS YBCO. Also included is a regenerative solid oxide fuel cell/electrolyzer with steam turbine cogeneration. The system operates on a managed day/night cycle. During daytime, the energy produced by the wind turbines and fuel cells is transmitted to the grid. During nocturnal hours, the wind turbine is used to provide low cost electricity to the reversible fuel cells operating in the electrolysis mode producing hydrogen and oxygen that is stored for later use. Alternatively, the fuel cells can remain in electrolysis mode producing hydrogen and oxygen for the market. A modified interactive system generates power on a continuous twenty-four hour cycle.

Description:
BACKGROUND OF THE INVENTION 
     The present invention is directed toward a renewable energy electric power generating system and, more particularly, toward an integrated renewable energy system comprised of high temperature superconducting wind turbines and regenerative or interactive solid oxide fuel cells/electrolyzers with superconducting magnetic energy storage based on a managed demand cycle. 
     The world is facing a major energy and clean air challenge. Renewable energy systems using wind, sun, and water and utilizing advanced energy generating technology offer some potential solutions. Unfortunately, the current state of the art of conventional wind turbine generators, energy storage systems, as well as fuel cell/electrolyzer technologies have individually not been fully developed from a standpoint of efficiency and cost effectiveness to meet the challenge. 
     Current wind turbines for utility use are huge machines that use conventional generator designs that include troublesome gear systems and lack of a commercially viable nighttime off-peak energy storage system. Low temperature superconducting energy storage systems use two-stage liquid helium cryorefrigeration to cool their metallic niobium-titanium or niobium-tin coils and are not cost effective. Also, current first generation high temperature superconducting coil wound energy storage units do not function efficiently at liquid nitrogen temperature. Solid oxide fuel cell systems that generate electricity for utility use are generally designed to use natural gas or methane as the base fuel for hydrogen, thus contributing to air quality degradation. Integrated electrolysis systems have not been fully developed to use the high temperature steam, a byproduct of fuel cell operations, in combination with low priced off-peak produced renewable energy for producing hydrogen in a cost effective manner. The challenge is to effectively integrate a combination of advanced renewable energy systems where the strength of each individual system is utilized to offset the shortcomings of other components of the overall system thus creating a more efficient synergistic result. 
     SUMMARY OF THE INVENTION 
     The present invention is a concept for meeting America&#39;s growing energy demand through the use of non-polluting electric generating technology utilizing renewable energy. The concept consists of three major advanced energy technologies that are uniquely integrated so as to significantly enhance their overall efficiency for the production of electric power. They are:
         1.) A high temperature superconducting wind turbine generator,   2.) A high temperature superconducting magnetic energy storage system,   3.) Either a regenerative or a modified interactive solid oxide fuel cell/electrolyzer.       

     The conventional wind turbine is being increasingly recognized as a low cost generator of renewable energy. However, the economic potential of high temperature superconducting wind turbine technology has not been fully exploited particularly when operationally integrated with a regenerative solid oxide fuel cell/electrolyzer system to operate on a day/night cycle. In order to optimize wind turbine system efficiency, a number of supporting subsystems are required. A high temperature superconducting magnetic energy storage system compensates for the effects of variable and intermittent winds. High temperature superconducting power conditioning equipment and the connecting power cables are also critical components of the integrated wind-hydrogen system. 
     This integrated system is specifically designed to operate on a managed day/night or 24 hour cycle. The regenerative system generates electricity during the day when demand is high and creates hydrogen and oxygen at night when demand is very low. However, it is operationally flexible and when provided with an external source of low cost energy generated by the wind turbines can remain in extended electrolysis mode producing hydrogen and oxygen for off-site distribution. The direct interactive system generates only electricity around the clock, feeding its output to the superconducting magnetic energy storage units during the periods of low demand. 
     A cryogenic system design will employ a multi-use cryorefrigeration system that cools the current carrying high temperature superconducting cables as well as the wind turbine generator coils and bearings and the magnetic energy storage units. Supporting the regenerative fuel cell system are storage vessels for hydrogen and oxygen, the product of the electrolysis process, and the byproduct high temperature steam produced by the fuel cells. The modified solid oxide interactive system does not require hydrogen, oxygen, or high temperature steam storage systems but would require superconducting energy storage units with larger capacity for increased off-peak use. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For the purpose of illustrating the invention, there are shown in the accompanying drawings forms that are presently preferred; it being understood that the invention is not intended to be limited to the precise arrangements and intrumentalities shown. 
         FIG. 1  illustrates the general arrangement of the components of a large-scale integrated renewable energy generating system; 
         FIG. 2  shows the renewable energy power generating system in daytime, peak period, fuel cell operational mode; 
         FIG. 3  shows the renewable energy power generation system in nighttime, off-peak, electrolyzer operational mode; 
         FIG. 4  shows the renewable energy generating system with a modified interactive solid oxide fuel cell and electrolysis system for continuous 24 hour power production, and 
         FIG. 5  is a schematic view of a self contained vertically integrated renewable energy power system housed within a stand-alone wind turbine structure. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings in detail wherein like reference numerals have been used throughout the various figures to designate like elements, there is shown in the  FIGS. 1 ,  2  and  5  a renewable energy electric power generating system constructed in accordance with the principles of the present invention and designated generally as  10 . The general arrangement of the various components of an integrated large-scale renewable energy power generating system  10  is illustrated in  FIG. 1 . However, the specific details of the high temperature superconducting wind turbine generator are illustrated in  FIG. 5 , which is a schematic view of a vertically integrated renewable energy power generating system housed within a stand-alone wind turbine structure. 
     The renewable energy electric power generating system  10  is comprised of three major components incorporating advanced energy technologies that are uniquely integrated so as to significantly enhance their overall efficiency for the production of electric power through the use of non-polluting renewable energy. These three major components include a high temperature superconducting air gap wind turbine generator  12 , a high temperature superconducting magnetic energy storage system  14  and either a regenerative or a direct interactive solid oxide fuel cell/electrolyzer  16 . 
     The major components are supported by a number of subsystems that are critical components of this wind-hydrogen-electricity generating system. They include high temperature superconducting power conditioning equipment  18  that includes a superconducting transformer and high temperature superconducting multi-use interconnecting power cables. 
     The high temperature superconducting air gap wind turbine generator  12  is comprised of high temperature superconducting YBCO or other REBCO wire coil windings for both the rotor  20  and the stator  22  (see  FIG. 5 ). The wind turbine generator and the superconducting non-contact magnetically levitated bearings are preferably contained within a double-walled vacuum vessel  24  that provides insulation for the maintenance of the cryogenic temperature. 
     Multi-use superconducting electric power cables  26  serve to connect the wind turbines  12  to the high temperature superconducting magnetic energy storage  14  units via the superconducting power conditioning system  18 . The superconducting power cables include internal ducts that circulate liquid nitrogen coolant to the wind turbine generators as well as to the SMES system. The power conditioning system  18  includes a superconducting transformer as well as inverters and rectifiers and appropriate and necessary switchgear and protective devices (not shown). The high temperature superconducting magnetic energy storage units  14  are contained within walled vessels  28  that provide vacuum insulation. 
     A centralized cryogenic refrigeration system  30  circulates liquid nitrogen at an optimum temperature of 65° Kelvin to the superconducting wind turbines and magnetic energy storage units. 
     The integrated renewable energy system includes regenerative (reversible) or modified interactive solid oxide fuel cell/electrolyzer units  16 . The regenerative system uses a single stack of cells that works alternately in the fuel cell mode producing electricity or in an electrolysis mode creating hydrogen and oxygen. The byproduct of the fuel cell cycle is high temperature steam which is forwarded to a storage vessel  32 . In the electrolysis mode hydrogen and oxygen are produced which also are piped to the storage vessels  34  and  36 , respectively. The byproduct high temperature steam can be used as an option to produce electricity by cogenerating with a steam turbine  38 . 
     The modified interactive solid oxide fuel cell and electrolyzer system  16  consists of two distinct units that are interconnected and that directly feed the hydrogen, oxygen, and high temperature steam to the respective unit without any need for short-term storage. 
     An electronic control system  40  connects with all components and is used to manage the integrated operation of the complete system. 
     The foregoing general description is schematically illustrated in  FIG. 5  which is in the form of a self-contained, stand-alone vertically integrated renewable energy power generating system housed within a wind turbine structure. It contrasts with the other figures which depict a large-scale integrated renewable energy power generating system with multiple units of wind turbines and regenerative fuel cells. However, in the large-scale configuration the storage vessels, electronic control system, cryorefrigeration system, power conditioning and SMES storage units are all also preferably consolidated in a central location. 
     The major high temperature superconducting components of the overall integrated system require cooling by a unitary cryogenic refrigeration system that may use liquid nitrogen as the coolant to maintain an optimum temperature at approximately 65 Kelvin. These components include the high temperature superconducting wind turbine generator and its bearing system, superconducting magnetic energy storage units, the power conditioning system that includes a superconducting transformer as well as the connecting system of multi-use superconducting YBCO electric cables which contains ducts for the circulation of the coolant to all superconducting components of the overall system. 
     The vacuum insulation system along with the vacuum pump apparatus  42  is shown in the schematic details on  FIG. 5 . These details of the cryogenic and vacuum systems would also apply, though not shown, to all similar superconducting components illustrated in the large-scale system in the remaining figures. 
     The large-scale integrated renewable energy generating system  10  of  FIG. 1  is capable of three different operational modes. The first is illustrated in  FIG. 2  which shows the renewable energy power generating system in operational mode during the daytime peak period.  FIG. 3  shows the system during the off-peak nighttime operational mode.  FIG. 4  shows the integrated renewable energy power generating system with a modified interactive solid oxide fuel cell and an electrolyzer system for continuous 24 hour power production. 
     Reference will first be made to  FIG. 2  which illustrates the system operations during the daytime peak period part of the cycle. A large part of the United States is within reasonable transmission distance of areas currently deemed appropriate for the generation of wind energy. These areas provide average annual wind speeds desirable for the commercial production of electricity. High temperature superconducting wind turbine generators  12  are up to two-thirds to three-fourths lighter and smaller than conventional generators and along with their air-gap design eliminate the need for gears or transmissions. Wind energy turns the blades on the levitated superconducting shaft of the turbine. 
     The YBCO or REBCO superconducting wound rotor and stator work to produce electricity more efficiently since current generator designs generally use a non-superconducting warm copper wound stator coil. The direct current generated by the wind turbine is transmitted with appropriate power conditioning  18  to the high temperature superconducting magnetic storage system (SMES)  14 . However, since wind is highly erratic, wind speeds can vary greatly. The effective moderation of these variations is critical if the optimum competitive position of wind turbine energy is to be fully realized. 
     The dc energy stored in the high temperature SMES  14  provides a power leveling function, offsetting the variable peaks and valleys of energy production by the wind turbines  12  caused by variable wind speeds and thereby minimizing any instability in the transmission of power to the grid  44 . The electricity stored in the SMES  14  continuously circulates in a series of YBCO or other REBCO wound high temperature superconducting cryogenically cooled non-resistant coil system with very high power energy. The SMES  14  releases a level load of electricity to the power conditioner  18  that modifies the load to appropriate voltage levels and converts the power to alternating current for transmission to the grid  44  during the peak period daytime hours. 
     During the high demand daytime hours, the regenerative solid oxide fuel cell  16  functions in an electric generating mode using the stored hydrogen and oxygen produced by the system when operating in electrolysis mode during the low demand nighttime cycle. When operating in the power generating fuel cell mode, it produces as a byproduct high temperature (up to 1000° C.) steam. There are two options for the use of this steam. If stored and the temperature is maintained, it can be used during the nighttime reverse electrolysis process, thus significantly reducing the amount of electricity required for the disassociation of the hydrogen and oxygen. If used to cogenerate electricity using a steam turbine  38 , the efficiency of the fuel cell system is enhanced. 
     The dc electricity produced by the fuel cell system  16  is at a constant level and unlike the variable produced by the wind turbine  12  can be sent directly to the power conditioning unit  18  for any needed modification and then is converted to ac for transmission to the grid. If the steam turbine cogeneration option  38  is introduced, then the same process is followed. 
       FIG. 3  shows the integrated renewable energy power generating system  10  during the low demand nighttime operational mode. The reversible solid oxide fuel cell  16  functions in the electrolysis mode to produce hydrogen and oxygen during off-peak periods. Also, during the low demand nighttime cycle, the high temperature superconducting wind turbine generator  12  does not primarily produce energy for transmission to the grid  44  due to the reduced value of the product. The wind turbine generated dc energy is transmitted to the SMES storage unit  14  after appropriate power conditioning  18 . The off-peak electrolysis process is energy intensive and is economically viable when provided with low cost dc electricity produced by the wind turbine  12  during nocturnal hours. The option which utilizes the high temperature steam for the electrolysis process draws on the temperature controlled steam storage system. 
     It should be noted that there are a number of different storage technologies (not shown) for hydrogen and oxygen that include compressed gas, liquefaction, metal hydrides, etc. If the high temperature steam cogeneration option  38  is exercised, then an external source of deionized water is required for electrolysis. This would also require a greater use of off-peak low value electricity to offset the unavailability of the byproduct steam for electrolysis. 
     The operational flexibility of the regenerative system is demonstrated by the fact that it can remain in the electrolysis mode producing hydrogen and oxygen over an extended period again using low value, off-peak wind turbine generated stored electricity along with an external source of deionized water. 
     The third operational mode of an integrated renewable energy power generating system  10  uses a modified interactive solid oxide fuel cell  16  with an integrated but separate solid oxide electrolyzer for continuous 24 hour power production. It is shown in  FIG. 4 . The hydrogen and oxygen produced by an interactive solid oxide and electrolysis unit is fed continuously to the integrated interactive solid oxide fuel cell  16 . The high temperature byproduct steam produced by the fuel cell is likewise fed continuously to the electrolysis unit. The 24 hour requirement for electricity for the electrolysis unit is provided by the SMES system  14  which stores off-peak low cost electricity produced by both the wind turbine  12  and the fuel cell systems  16  during the low demand nighttime hours. 
     During the high demand high-value daytime hours, both the interactive fuel cell  16  with its level load of electricity and the superconducting wind turbines  12  send their combined dc power to the power conditioner  18  for voltage adjustments and conversion to ac and subsequent transmission to the electric grid  44 . Depending on wind conditions, the wind turbine generated power may first have to pass through the SMES system  14  for load leveling purposes. 
     The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and accordingly, reference should be made to the appended claims rather than to the foregoing specification as indicating the scope of the invention.