Abstract:
A system for harvesting, storing, and generating energy includes a subsurface structure supporting machinery to convert received energy into potential energy, store that potential energy, and at a later time convert that potential energy into electrical energy. The system includes one or more buoyant chambers that support the subsurface structure and are maintained with an internal that is approximately equal to the ambient pressure at their deployed depth. The system is anchored to the seafloor with one or more mo lines. Suspended from the subsurface structure are one or more weights that are hoisted up or lowered down by one or more winches The one or more winches comprise a spooling drum, and one or more motors and/or one or more generators or one or more motor/generators.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to energy storage and more particularly, relates to a device that allows the efficient and low-cost storage and release of energy such as for use in electricity generating devices and electrical grids. 
       BACKGROUND INFORMATION 
       [0002]    Energy storage takes on many forms. Fossil fuels are the most ubiquitous and well known energy storage mechanism, having been formed of plant matter over millions of years and thereby storing solar energy. The key limitations of fossil fuels are that they take millions of years to store that energy and when you release it, such as through combustion, they emit massive amounts of greenhouse gases, which are harmful to the planet and human health. Other forms of energy storage include chemical storage such as in batteries, direct electrical storage such as in capacitors, kinetic energy storage such as in flywheels, mechanical storage such as in springs or compressed-gas energy storage, and lifted-mass storage such as pumped hydro. 
         [0003]    As well documented in the DOE—ARPA-E: DE-FOA-0000290 (GRIDS) solicitation from the US Department of Energy in 2010, all of these energy storage methods suffer from one or more of the following limitations: 1) the capital cost is too high to be economically viable; 2) the siting of the devices is too restrictive and/or narrow to be of commercial value; 3) the efficiency of the charge/discharge cycles are too inefficient to be of commercial value; 4) the amount of storage (kilowatt hours) per installation is not scalable for utility-scale deployment; 5) the estimated number of charge/discharge cycles or lifetime of the method is too short to support utility-scale infrastructure lifetimes; and/or 6) the length of time the energy could be stored is limited and degrades too severely over time (such as flywheels which lose up to several percent of their energy per hour due to friction and other issues). 
         [0004]    The US DOE ARPA-E noted that the current benchmarks for large scale energy storage for electrical grids were pumped hydro at $1,500 per kilowatt for capital cost and under $100 per kilowatt hour for storage, with other sources noting round-trip efficiency for pumped hydro of approximately 75%. They also noted that very few additional pumped-hydro plants could be built in the US due to their severe environmental impact and the limited number of locations that can support pumped hydro. However, they noted that in 2009 over 99% of electrical grid energy storage worldwide was in the form of pumped hydro. Utility experts involved with the construction of recent utility power plants state that a pumped-hydro plant such as the Northfield, Mass. 1GW plant would cost around $4,000/kW or $500/kWh to construct today, if it could be permitted, which they severely doubt. Similarly, ARPA-E noted that compressed-air storage at $600 per kW for capital cost and under $100 per kWh for storage, with other sources stating a round trip efficiency of 75-80%, was limited by the storage caverns or similar air storage mechanisms available, thereby making it a very limited option. After decades of compressed-air storage R&amp;D, it has not moved beyond the research and pilot-project stage. 
         [0005]    In the 2010 ARPA-E GRIDS FOA, reiterated in the ARPA E 2012 storage SBIR FOA, DOE set a high bar for advancing the state of the utility-scale energy storage marketplace. The goal was for proposers to develop technologies that would: 1) enable deployment near load centers; 2) be able to develop full power within 10 minutes; 3) provide rated power for at least 60 minutes; 4) have a round trip charge/discharge efficiency of greater than 80%; 5) be scalable to GW and GWhs of power and energy capacity; 6) have a capital cost of energy of less than $100/kWh; and 7) have at least 5,000 charge/discharge cycles before any storage capacity degradation. 
         [0006]    ARPA-E states that: “electric storage with a 5000-cycle lifetime, round trip efficiency of 80% and $100/kWh storage cost, the premium storage cost per storage cycle would be $0.025/kWh above the electricity cost, which is within the predicted cost range for technology adoption relative to the cost of alternative approaches to regulation power”. 
         [0007]    One of the main drivers for utility-scale energy storage is the fact that electricity has a very finite life. Once electricity is produced and transmitted, it must be used, or it will be lost. Equally important, if the amount of electricity being generated is not kept in close sync with the amount of electricity being consumed on the electrical grid, the frequency of the Alternating Current (AC) waveform on the transmission lines will go out of spec and equipment damage and large fines can quickly result. Since consumers of electricity expect electricity to be there when they need it, utility companies must have significant reserve capacity available and in some cases running, so that it can be supplied in the seconds and minutes response times that are needed to maintain grid stability. 
         [0008]    By contrast, most new renewable energy sources are intermittent in nature. In the case of wind farms, when the wind slows or picks up, the output of the wind farm changes quickly and drastically. The same is true for solar, as clouds come over, output changes drastically and quickly. This combination of intermittent generating sources and intermittent consumption causes the grid to be highly inefficient. Essentially, power generators such as wind and solar can be told to shut down if there is too much power on the grid. 
         [0009]    Alternatively, utility companies must keep large amounts of fossil fuel capacity running in the background so it can be quickly added to the grid as needed. This increases fossil fuel use and greenhouse gases and reduces the viability and effectiveness of intermittent clean-energy sources. This tremendous problem is what the US and global governments and industry are trying to tackle with advances in grid-scale energy storage R&amp;D efforts. So far, according to ARPA-E and the US DOE, there has been limited success in meeting the goals. Accordingly, a device and method for usage is needed which enables the deployment of energy-storage systems that meet the needs of energy-generation devices, particularly intermittent ones, and grid operators to store energy, at both device and grid scale. 
         [0010]    Although the concept of a hanging weight to store energy has been around of hundreds of years, such as is exhibited in clocks that use hanging weights to store the energy needed to run the clock for long periods of time. At a larger scale, in 1901 we see U.S. Pat. No. 680,038 by Gore 1901 that employed lifting weights to store the renewable energy of a windmill for later use in pumping water. 
         [0011]    More recently, refined concepts have been introduced aimed at storing electrical energy from renewable sources in the potential energy associated with raising weights. In 2011, Scott was granted U.S. Pat. No. 7,973,420 where weights are hoisted inside vertical cylinders or through elaborate means of lifting and supporting weights in a storage structure. 
         [0012]    In 2011, Boone received U.S. Pat. No. 7,944,075 for a vertical axis wind turbine that drives a potential energy storage system involving heavy weight or rail cars on inclined tracks. In the same year, Simnacker was granted U.S. Pat. No. 7,956,485 for a means of storing energy from a wind turbine by raising a fluid to an elevated tank. 
         [0013]    It is important to note that each of the foregoing examples of prior art do not involve the use of the ocean&#39;s depths to provide the hoist (lift) height that is needed for large-scale and economical potential-energy-based storage. 
         [0014]    More relevant to the current invention is a 2010 patent application by Morgan (US2010/0107627) where the concept of submerging a buoyant volume under water is introduced. This being the reverse process of lifting a weight, it nonetheless captures the value of the height offered by a body of water in potential-energy-based storage. 
         [0015]    Equally relevant is another 2010 patent application by Ivy (US2010/0307147) where a fluid is pumped underwater and/or under backfill that provided the resistive force to maintain pressure in the fluid, thereby storing it as potential energy. 
         [0016]    A 2009 application by Fiske (US2009/0193808) combines the idea of a suspended weight being raised and lowering them over the depth of the ocean to provide energy storage in the form of potential energy. Fiske also suggests combining this storage means with a wind turbine. 
         [0017]    However, in all proposed forms there is a floating portion that is at the surface and therefore subject to the waves and other hazards on or near the surface. Fiske also specifies the suspended weight to be constructed of a dense material such as concrete, reinforced concrete or steel. 
         [0018]    A 2010 application by Howson (US2010/0283244) describes a system similar to Morgan mentioned above where buoyant volumes are pulled to greater depth underwater in order to store potential energy, the power to do so being provided by an offshore, bottom-mounted wind turbine. 
         [0019]    The present invention provides significant advantages over the prior art described above. None of them include the concept of submerged buoyancy provided by low-cost containment that is enabled by having the internal pressure match the ambient external pressure at the deployed depth. This design attribute contributes to an unprecedented low cost of energy storage that is needed to meet the market demands. 
         [0020]    In addition, the present invention provides significant advantages over the prior art described above by introducing the concept of extremely low-cost mass enabled by the use of flexible fabric structures filled with dredged materials such as sand or gravel. This mass remains constant, regardless of the depth to which it is submerged. By contrast, inverted systems that use a buoyant volume will experience either a decrease in volume with depth or, if designed to be rigid, an increase in external pressure with depth. In either case the cost effectiveness of such a system will be impaired. 
         [0021]    A further advantage of the present invention over the prior art is full submergence. The present invention has nothing at the surface that could couple the energy-storage system to the potentially destructive excitations of surface waves. 
         [0022]    Specifically, application US 2010/0107627 by Morgan proposes a barge with a motor/generator, attached via cable to a pulley on the seafloor and via the pulley, to a buoyant body, attached to the end of the cable. The system suffers from a number of potentially fatal flaws, including 1) the cost, size, ruggedness and movement of the surface barge, which counteracts the buoyancy of the buoyant body at the far end of the cable, essentially doubling the amount of buoyancy needed in the system; 2) the need for a very large anchoring mechanism which will counteract twice the actual buoyancy of the buoyant body and movements of both the buoyant body and the barge; 3) the fact that the buoyant body at the far end of the cable will need to be crush resistant (and expensive) or it will collapse as it is pulled deeper into the water, reducing its buoyancy as it descends and increasing it as it ascends, dramatically altering the rate at which energy can be stored over a given depth; 4) the need to provide a tether between the buoyant body and the barge which has a length twice the depth of the body of water that the system is deployed in. 
         [0023]    Neither Fiske nor Morgan describes a system with the ability to address the current needs for cost-effective energy storage at the system or grid scale. As with other mass-based energy-storage concepts, the cost of the structure needed to obtain height over which the mass can travel and the cost of the mass itself are cost drivers that will determine commercial viability. The present invention innovatively and uniquely addresses both of these drivers by: 1) introducing novel and innovative low-cost buoyancy, 2) exploiting deep water to obtain low-cost height and 3) utilizing low-cost mass via cost-effective containers for the mass combined with a novel and innovative manner to acquire, collect and load mass by the millions of pounds, at practically no cost, into the containers. These three attributes of the present invention i.e. relatively inexpensive buoyancy, height, and mass, enables a significant breakthrough in the commercial viability of large-scale energy storage. 
         [0024]    The present invention enables the adoption of intermittent renewable energy sources that are highly problematic for utilities. As a result of this problem, the power from these renewable sources is currently less valuable to the utility companies. By incorporating energy storage through the adoption of the present invention, intermittent sources such as wind power, solar power, tidal power, and wave power can provide very-high-value peaking power to the grid. This ability to store renewable power (or excess power from other generating sources) at times of low electrical power prices and sell it to the grid at peak rates (often 3-5 times the rate paid by utilities for intermittent power) completely changes the market dynamics for renewable energy. Using the present invention, project developers can get significantly more revenue for each megawatt hour their project produces, while the utility company does not have to have standby fossil-fuel plants running to smooth out the amount of power on the grid. 
         [0025]    Accordingly, an object of this invention is to provide a device and method of energy storage that is applicable where capital cost, ubiquitous deployment, efficiency of storage/release of energy, and energy storage/release cycle times are major factors in economic viability. 
         [0026]    A further object of this invention is the integration of several innovative solutions to the drawbacks of competing energy-storage systems, thereby allowing a reduced-cost device to be easily deployed, quickly placed in service, and readily maintained over its lifetime, at sizes ranging from tens of kilowatt-hour individual systems to multi-unit gigawatt-hour utility-scale farms. 
         [0027]    A still further object of this invention is to enable a new class of low-cost energy storage, uniquely characterized by novel low-cost buoyancy and mass, taking advantage of the ubiquitous hoist heights available at ocean depths convenient to load centers and locations suitable for ocean-based renewable energy device deployment. 
         [0028]    A still further object of this invention is to enable the economic viability of intermittent sources of renewable energy generation, such as solar, wave, tidal and wind, both at the device and the grid level. 
         [0029]    A still further object of this invention is to provide a stable subsurface platform for mounting various ocean-based renewable energy generation devices, thereby reducing their deployment costs and providing co-sited energy storage to increase the utility and therefore the value of the energy produced. 
         [0030]    A still further object of this invention is to provide an energy-storage capacity in the deep ocean that can enable the economic exploitation of the US Exclusive Economic Zone by various ocean-based industrial and marine agronomy activities that would benefit from a consistent source of power. 
       SUMMARY 
       [0031]    The present invention combines a novel and disruptively low-cost buoyancy system and a novel and disruptively low-cost weight mechanism, with enabling motor/generator technology and enabling software, to provide a highly scalable and cost-effective energy-storage system for use in water-based deployment locations. This invention directly addresses the needs outlined by government agencies and industry groups alike for cost-effective energy storage. The invention stores energy by powering a motor that drives a large-capacity winch drum that pulls in a cable and thereby lifts a weight resulting in electrical-energy input being converted into potential (stored) energy. The invention releases this stored potential energy by allowing the weight to lower, thereby turning the winch drum and driving a generator, which produces electrical power. 
         [0032]    The weight may be in the form of fabric containers filled with sand, rocks and other material dredged from the ocean or other water body floor at or near the deployment location of the system. The weight may alternatively be in the form of rigid or semi-rigid containers preferably filled with weighted material at or near the deployment site of the system. In this manner, no additional cost and difficulties are encountered in obtaining weight material and transporting the weighted material and/or containers to the deployment site. The weight material may also include material conveniently gathered not from the ocean or water—but rather from say a gravel pit nearby the launch location. 
         [0033]    The buoyancy component of the invention includes relatively lightweight buoyancy units made from fiber-reinforced plastic (FRP) laminates. These buoyancy units are large, having 100 s to 1,000 s of cubic meters in volume and are operated in a way that maintains the internal pressure at or close to the ambient pressure at the depth under the ocean they are positioned. This results in a large economy of materials and low-cost compared to more conventional submerged buoyant structures that are operated as pressure vessels and must withstand the stress resulting from a significant pressure difference between their interior and exterior. 
         [0034]    The mass component of the invention includes low-cost non-structurally-rigid containers that are filled with locally abundant ballast material that can be obtained at little or no cost. In one preferred embodiment, this mass is dredged material obtained from a suitable underwater location along the route between the system launch site and the ultimate deep-water deployment location or at/near the deployment location itself, preferably in shallow water although this is not a limitation of the invention. In this embodiment the mined sand or gravel comes at a cost that is trivially low and generally readily and accessible compared to other sources and methods of obtaining the hundreds of millions of pounds needed for cost-effective gravity-based energy storage. In still other embodiments, the mass is obtained within economically viable towing distances of the deployment site of the system. The low-cost containers, in one preferred embodiment, would be made of non-rigid synthetic material that is specially designed for use in subsea environments such as woven polyester fabric of high tensile strength. 
         [0035]    Similar synthetic materials are utilized worldwide in the manufacture of marine ropes, commercial fish netting, geotextiles, and other applications where strength and durability are important. This material can be woven to make a high-strength fabric that can be assembled into three-dimensional cylindrical containers with rounded bottoms that make efficient use of the material while providing high-volume capacities. Suitably reinforced with webbing straps that lead to attachment means, these assemblages offer unique abilities for providing the many hundreds of tons of mass needed for utility-scale energy storage. These woven materials need not be watertight, requiring a coated fabric. Indeed in one preferred embodiment the porosity of the woven fabric is such that seawater and fines are allowed to pass through the containment wall thereby increasing the total density of the contained volume. 
         [0036]    It is important to note that the present invention is not intended to be limited to a device or method which must satisfy one or more of any stated or implied objects or features of the invention. It is also important to note that the present invention is not limited to the preferred, exemplary, or primary embodiment(s) described herein. Modifications and substitutions by one of ordinary skill in the art are considered to be within the scope of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0037]    These and other features and advantages of the present invention will be better understood by reading the following detailed description, taken together with the drawings wherein: 
           [0038]      FIG. 1  represents a prior-art stabilized-platform design; 
           [0039]      FIG. 2  represents a subsurface low-cost suspended-mass energy-storage system with the motor/generator/winch positioned on a buoyancy platform; 
           [0040]      FIG. 3  represents a subsurface low-cost suspended-mass energy-storage system with the motor/generator/winch positioned on the suspended mass; 
           [0041]      FIG. 4  represents a subsurface low-cost suspended-mass energy-storage system with a single-point mooring that acts as a suspended-mass guide; 
           [0042]      FIG. 5  represents a subsurface low-cost suspended-mass energy-storage system with a wind turbine hosted on the buoyancy platform; 
           [0043]      FIG. 6  represents a subsurface low-cost suspended-mass energy-storage system with a water current turbine hosted on a buoyancy platform; 
           [0044]      FIG. 7  represents a side view of a subsurface low-cost suspended-mass energy-storage system with a water current turbine with a counterbalance hosted on a buoyancy platform; 
           [0045]      FIG. 8  represents a subsurface low-cost suspended-mass energy-storage system with wave-energy converters hosted on a buoyancy platform; 
           [0046]      FIG. 9  represents a networked redundant-membrane buoyancy system; 
           [0047]      FIG. 10  represents an embodiment utilizing multiple roto-molded plastic tanks; 
           [0048]      FIG. 11  represents an embodiment utilizing multiple fiber-reinforced plastic (FRP) tanks; 
           [0049]      FIG. 12  represents the way modular buoyant chambers are mounted to frames; 
           [0050]      FIG. 13  represents a method for adding mass to a subsurface low-cost suspended-mass energy-storage system; and 
           [0051]      FIG. 14  represents a deployed kinetic-energy conversion system with structure, mooring, support vessel and ROV. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0052]    Referring to  FIG. 1 , there is shown a legacy or prior-art stabilized platform  100  that uses steel or other rigid material to form a submerged buoyant volume  101 . In the example shown, the stabilized platform  100  supports a wind turbine  33  that is mounted on a tower  31  that penetrates the sea surface  27 . Buoyant volume  101  is held submerged by mooring tendons  7  that lead to seafloor anchors  5 . Buoyant volume  101  operates as pressure vessels and must be designed and built to withstand the external pressure associated with its depth below the surface as well as the rigors of operating at or near the surface due to passing waves  103 . Large buoyant steel structures such as what is portrayed can cost $2 to $4 per pound of displacement plus the costs of proper corrosion-preventive coatings. 
         [0053]    Referring now to  FIG. 2 , one embodiment of the subsurface low-cost suspended-mass energy-storage system  10  of the present invention is shown. The invention includes a buoyancy component or platform  13 . In this embodiment, each of the multiple modular buoyant chambers  11  that make up the buoyancy component  13  are made of synthetic membrane, roto-molded plastic, or glass-reinforced plastic. The chambers  11  can be filled or vented of air in order to add and remove buoyancy from the system. Each chamber  11  is attached to a frame  12 , which together forms the main structural members of the buoyancy platform  13  that is positioned below the sea surface  27  to avoid waves and maritime activity. 
         [0054]    In this embodiment the motor/generator/winch  21  is mounted on the buoyancy platform  13 , a position that would allow easy maintenance when the buoyancy platform  13  is surfaced. In this configuration, the power cable  19  leads from buoyancy platform  13  to the seafloor  29  where it can lead to shore. Alternatively, power cable  20  could lead from buoyancy platform  13  in a generally horizontal direction to a neighboring energy-storage system or a renewable-energy device. 
         [0055]    The platform structure  13  is moored to the seafloor  29  via mooring lines  7  and anchors  5 , thereby maintaining its position. This mooring mechanism, and those depicted in subsequent figures, can be of various configurations known in the art, such as Tension Leg Platform (TLP), catenary, weighted catenary, single point mooring and others. Two mooring lines  7  are shown, however, there may be more spaced equally around the platform structure  13  or in specific directions depending on the prevailing oceanic conditions. 
         [0056]    Umbilical cable  19  that connects to the motor/generator/winch  21  and various other power and control components facilitates the transfer of power to the grid or other demand load and serves as a communication link between an off-platform or shore-based control center that operates the system in optimal fashion. 
         [0057]    Hanging below the buoyancy platform  13  we see multiple mass modules  25  that are together supported by a tension member  23  to the motor/generator/winch  21  and the buoyancy platform  13 . When the mass modules  25  are being raised, energy is consumed by the system via the motor element of motor/generator/winch  21  and when the mass is being lowered, energy is generated via the generator element of motor/generator/winch  21 . The motor and the generator elements can be the same device, just run in different modes or they can be separate devices. 
         [0058]    In addition to the conversion of the potential energy stored in the lifted masses  25  to electricity and the transmission of the energy via the electrical cable  19 , other methods can be utilized to act as the carrier for the stored energy. 
         [0059]    In one embodiment, the stored energy can be turned back into electricity via the generator and that electricity can be utilized to generate a liquid or gaseous energy carrier such as via electrolysis of water to create hydrogen and oxygen, or conversion to products, which have high-energy storage density such as anhydrous ammonia. This conversion to non-electrical energy carriers is especially useful in areas of great depths but limited access to those in need of electricity. Since it is not economically practical to run a high capacity (Gigawatts) subsea cable over very long distances (many hundreds to thousands of miles), the non-electrical energy carrier enables the locally collected energy to be converted to a suitable carrier fuel. This fuel can be loaded onto a transport ship, utilized on-board, as well as transported in bulk on ships to locations globally where the energy can be utilized via the energy carrier (such as the anhydrous ammonia or others). 
         [0060]    This embodiment of the present invention allows the system to be deployed in these remote areas, where it stores energy generated over long periods of time via a kinetic-energy-conversion device(s) such as the wave-energy system described herein, with ships or other transport mechanisms being used to distribute the energy in a cost effective manner to global users of energy. In this manner, very limited bulk storage of the liquid or gas is needed on the platform, as the conversion from potential energy to electricity to gas or liquid can be done at the time the transport is ready to receive it. 
         [0061]    Referring now to  FIG. 3 , there is shown one embodiment of the subsurface low-cost suspended-mass energy-storage system  10  with multiple modular buoyant chambers  11  attached to a frame  12 , which together forms the main structural members of the buoyancy platform  13  that is positioned below the sea surface  27  to avoid waves and maritime activity. 
         [0062]    In this embodiment, the motor/generator/winch  21  is not mounted on the buoyancy platform  13  and instead is mounted on the suspended mass  25 . In this position, the mass of the motor/generator/winch  21  contributes to the overall mass of the suspended-mass energy-storage system  10 . In this configuration, the power cable  19  leads from suspended mass  25  to the seafloor  29  where it can lead to shore. Power cable  19  is supported in an intermediate location between suspended mass  25  and seafloor  29  by support means  18 , which provides both mechanical support and a means for power and control signals to reach the buoyancy platform  13 . Alternatively, power cable  19  could lead to the buoyancy platform  13  and thence in a generally horizontal direction to a neighboring energy-storage system as was shown in  FIG. 2 . 
         [0063]    Referring now to  FIG. 4  is an embodiment of the present invention which utilizes a single-point mooring system wherein the mooring line(s)  22  both anchor the buoyancy platform  13  to the seafloor  29  and serve as a guide for the suspended mass  25  as it is raised and lowered by motor/generator/winch  21  and tension member  23 . In this figure the motor/generator/winch  21  is shown mounted on the suspended mass  25 , contributing to the overall mass of the suspended-mass energy-storage system  10 . In this configuration, the power cable  19  leads from suspended mass  25  to the seafloor  29  where is can lead to shore. Power cable  19  is supported in an intermediate location between suspended mass  25  and seafloor  29  by support means  18 , which provides both mechanical support and a means for power and control signals to reach the buoyancy platform  13 . Alternatively, power cable  19  could lead to the buoyancy platform  13  and thence in a generally horizontal direction to a neighboring energy-storage system as was shown in  FIG. 2 . 
         [0064]    The motor/generator/winch  21  is guided along mooring line(s)  22  thereby preventing undesirable horizontal motions that could be induced by ocean currents. A single mooring line  22  is shown; however, two, three, four or more mooring lines  22  could be employed depending on the situation and the selection of materials. Multiple mooring lines  22  not only would prevent undesirable swinging of the suspended mass  25 , but it would also prevent rotation. 
         [0065]    The embodiment shown in  FIG. 4  would work equally well if the motor/generator/winch  21  were mounted on the buoyancy platform  13  as exemplified in  FIG. 2 . 
         [0066]    Referring now to  FIG. 5  is shown an embodiment of the present invention in which the buoyancy platform  13  is host to a kinetic energy conversion device such as a wind turbine that is mounted vertically by means of a tower  31  that penetrates the sea surface  27  presenting the rotor  33  to the prevailing winds. In this case, the subsurface low-cost suspended-mass energy-storage system  10  can be directly utilized to store the intermittent energy produced by the wind turbine rotor  33 . 
         [0067]    Referring now to  FIG. 6  is illustrated an embodiment of the present invention in which the buoyancy platform  13  is host to a kinetic energy conversion device such as an underwater tidal or ocean current turbine that is mounted vertically by means of a tower  31  presenting the rotor  34  to the prevailing currents. As with the wind turbine shown in  FIG. 5 , the subsurface low-cost suspended-mass energy-storage system  10  can be directly utilized to store the intermittent energy produced by the hydrokinetic energy-conversion rotor  34 . In addition, the subsurface low-cost suspended-mass energy-storage system  10  can be utilized to store more uniformly produced energy such as in ocean currents, in order to utilize that energy at times where that energy is of more value to the various players in the electricity value chain. 
         [0068]      FIG. 7  is the same embodiment shown in  FIG. 6  except that the rotor  34  has been rotated 90 degrees atop the tower  31  to reveal a counterbalancing arm  124  that supports a counterbalancing buoyancy module  120 . This assembly helps both orient the tidal current turbine into the direction of flow and reduces the clockwise torque caused by the drag of rotor  34 . 
         [0069]    Referring now to  FIG. 8  is an embodiment of the present invention in which the buoyancy platform  13  is host to a kinetic energy conversion device such as a wave-energy conversion mechanism. Two types of wave energy conversion mechanisms are portrayed in  FIG. 8 , both types connected to the buoyancy platform  13  by cables  37 . Wave-energy conversion mechanism  36  is a simple floating buoy that heaves up and down depending on the height of the water surface. This up and down movement of the buoy  36  yields useful power at the buoyancy platform  13  that can be used to drive a generator or some other form of energy extraction system that can be cabled to shore via power cable  19  or stored using the suspended-mass energy-storage system. 
         [0070]    Wave energy conversion mechanism  35  is a simple submerged chamber that changes volume due to the change in pressure under passing waves. The change in volume results in a vertical movement of the chamber  35  relative to the stationary portion  39  that can be used to drive a generator or some other form of energy extraction system. The basic wave energy conversion concept is very well documented art and commonly utilizes either at surface or near-surface buoyancy devices, with dozens of companies working with the basic concept, sometimes referred to in the art as point absorbers. 
         [0071]    Examples of such legacy concepts are being developed by companies such as AquaEnergy Group, LTD (AquaBuOY) and Ocean Power Technologies (PowerBuoy), as documented in: Wave Energy Potential on the US Outer Continental Shelf, US DOI, MMS May 2006. 
         [0072]    The use of the buoyancy platform  13  to create a false seafloor for attaching the conversion system  35  and  36  allows several advantages including a shorter length of cable  37 , the ability to be economically located in deep offshore locations where there is greater wave energy compared to shallow water, and the ability to utilize the subsurface low-cost suspended-mass energy-storage system  10  to store the intermittent energy produced by the wave energy converters  35  and/or  36 . 
         [0073]    As with the embodiment shown in  FIG. 4 , the advantages for the energy storage system in a dual-use platform are also significant versus stand-alone energy-storage concepts, as there are a number of capital-intensive infrastructure pieces that the energy-storage system is sharing with the wave or wind or other energy-conversion system, which reduce the overall Cost of Electricity for the storage system in this dual-use platform case. Alternatively, the ability for co-hosting to reduce the number of key components needed to be supplied by the kinetic-energy conversion system by 40-70% can completely change the economics of the deployment of the kinetic-energy conversion system, making it economically attractive versus economically non-viable. 
         [0074]    One particularly useful embodiment of the present invention, not shown, but similar to  FIGS. 5 through 8 , utilizes the kinetic energy conversion to generate electricity, stores that energy in the subsurface low-cost suspended-mass energy-storage system and utilizes that stored energy, as needed, to power electronic systems on-board the platform. This innovation has many practical applications, including the powering of sea-based remote Department of Defense systems, oil and gas platforms, deep-sea mining systems, marine fish farms, marine agronomy facilities, and stationary fish capture systems. Currently, such systems must rely on various combinations renewable and/or fossil fuel generation capabilities coupled with batteries to provide a continuous supply of power. As with grid-based storage and retrieval of electrical energy, on a standalone basis, the present invention is low cost, scalable and very compelling. 
         [0075]    The relatively uneven power output from the generation mechanisms portrayed in  FIG. 8  can be directly stored in subsurface low-cost suspended-mass energy-storage system providing, inter-wave, wave to wave, as well as long-term energy storage (minutes, hours and days) of the output of the wave energy conversion mechanisms  35  and  36 . 
         [0076]    In the embodiments shown in  FIGS. 5 through 8 , mechanisms other than electrical power can be used to transfer the extracted kinetic energy from the kinetic-energy-conversion device to the task of lifting the mass. These mechanisms include hydraulic and direct mechanical coupling. 
         [0077]    The storage of short term (wave to wave and within each wave cycle) energy of the present invention in a novel, scalable, and low cost manner is a step-function breakthrough for the harnessing of what the US Government has estimated as thousands of Terawatt-hours (TWhs) of wave energy available globally each year. This is partially due to the fact that electrical systems do not tolerate highly varying and impulsive kinetic energy well, without some sort of smoothing or energy-storage mechanism to serve as a buffer or aggregator of the energy for delivery to the grid. 
         [0078]    Referring now to  FIG. 9  is shown a preferred embodiment of the present invention that utilizes an innovative and highly cost-effective buoyancy-control system. In this embodiment multiple flexible watertight containers  110  are arranged on structural framework  114 . These flexible watertight containers  110  are similar in construction to underwater salvage bags that are commonly used in marine salvage and construction, exemplified in products by Subsalve USA (http://www.subsalve.com/) or Carter Lift Bag, Inc. (http://carterbag.com/). These flexible watertight containers  110  are attached to structural framework  114  by reinforcement strap  112  around their lower perimeter. Each flexible watertight container  110  is networked to a gas distribution unit (GDU)  118  via hoses  116 . 
         [0079]    Unlike prior art buoyancy-control systems that are designed around steel or other rigid pressure vessels, the use of this upwardly suspended network of flexible watertight containers  110  provides a durable solution to providing low-cost buoyancy. The gas distribution unit  118  can be fed gas from on-board cylinders, an attached compressor, or a remote supply line (all three not shown). A fully redundant gas distribution and monitoring system, with dual lines, controllers, attachment points on the bladders and communications and sensor mechanisms is utilized in the preferred embodiment of the buoyancy-control system. To avoid the need for emergency repair and potential platform loss, should one flexible watertight container  110  fail, redundant unused units would be inflated to retain the needed overall buoyancy. 
         [0080]    By filling a specific flexible watertight container  110  with gas, it is inflated, resulting in increased buoyancy. By controlling which flexible watertight containers  110  are inflated, via the computer-controlled GDU  118 , the attitude of the structural framework  114  can be maintained. In an alternate embodiment (not shown), the flexible watertight containers  110  could be fitted such that, once inflated, they would seat underneath the structural framework  114  held in place by their own buoyancy. 
         [0081]    The embodiment shown in this figure has very favorable lift-per-dollar and lift-per-weight ratios, both of which are much higher than other conventional methods of supplying buoyancy, such as steel. For example, the SubSalve model PF70000, provides 77,000 lbs of lift, at a cost of $6,000 retail and weighs 410 lbs. This yields a lift-per-dollar ratio of 77,000/6,000=12.8 lbs per dollar, and a weight-per-pound-of-lift ratio of 77,000/410=188 pounds of lift per pound of weight. Importantly, in the present invention, multiple of these types of bladders are networked in order to provide as much buoyancy as needed, in the case of some versions of the present invention, 100&#39;s of tons or millions of pounds of lift. This compares very favorably with more conventional methods of providing buoyancy where the ratio is $2 to $4 per pound and the lift-per-weight ratio for steel that ranges from 8 to 15. 
         [0082]    Referring now to  FIG. 10  is a second preferred embodiment of the present invention that utilizes multiple roto-molded plastic tanks  111  to provide low-cost buoyant volumes. These tanks  111  are arranged on structural framework  114 . These roto-molded plastic tanks  111  common in process and bulk storage industries and exemplified in products Peabody Engineering &amp; Supply, Inc. (http://etanks.com/) and Chem-Tainer Industries (http://www.chemtainer.com). These roto-molded plastic tanks  111  offer some advantages over the flexible watertight containers  110  shown in  FIG. 9  in that they offer some resistance to internal or external pressure, they provide the ability to be formed in advantageous shapes, and they offer excellent lift-per-dollar and lift-per-weight ratios. Each roto-molded plastic tank  111  is networked to a gas distribution unit (GDU)  118  via hoses  116 . Valve-controlled vents at the bottom of each roto-molded plastic tank  111  allows their controlled flooding or emptying. By controlling which roto-molded plastic tanks  111  are flooded via the computer-controlled GDU  118 , the attitude of the structural framework  114  can be maintained. 
         [0083]      FIG. 11  illustrates a third preferred embodiment of the present invention that utilizes multiple fiber-reinforced plastic (FRP) tanks  112  arranged on structural framework  114  to provide low-cost buoyant volumes. These FRP tanks  112  are common in liquid storage applications and as underground storage tanks. They are exemplified in products made by Xerxes Corp. (http://www.xerxes.com/) and Containment Solutions, Inc. (http://www.containmentsolutions.com/). 
         [0084]    Each FRP tank  112  is networked to a gas distribution unit (GDU)  118  via hoses  116 . Valve-controlled vents at the bottom of each FRP tank  112  allows their controlled flooding or emptying. By controlling which FRP tanks  112  are flooded via the computer-controlled GDU  118 , the attitude of the structural framework  114  can be maintained. 
         [0085]    These FRP tanks  112  offer additional advantages over the roto-molded plastic tanks  111  shown in  FIG. 10  and the flexible watertight containers  110  shown in  FIG. 9  in that they offer significant resistance to internal and external pressure. This feature allows for a fixed buoyant volume that does not change in magnitude with changes in submerged depth, thereby requiring less active buoyancy control interventions by the gas distribution unit  118 . These FRP tanks  112  also offer excellent lift-per-dollar and lift-per-weight ratios. 
         [0086]    Referring now to  FIG. 12  are modular buoyant chambers  11  mounted to frame(s)  12 , which is part of the buoyancy platform  13 . These modular buoyant chambers  11  are preferably mounted in a way that minimizes the overall frontal area that is exposed to the flow, thereby minimizing their fluid drag and improving the performance of the system when positioned in a current. Whether fabricated from synthetic membrane, roto-molded plastic or fiber-reinforced plastic, attachment to the frame(s)  12  is done in a way to prevent stress concentrations in the buoyant chambers  11 . 
         [0087]    Referring now to  FIG. 13  is an embodiment where the mass or weight modules  25  are being filled with low-cost ballast such as sand, gravel, rock or other non-rigid material that is supplied from a surface vessel or barge  15  on the surface  27 . This process is preferable undertaken after the subsurface low-cost suspended-mass energy-storage system  10  has been launched and is in transit to or actually at or near its deep-water deployment location. The sand or gravel is pumped down the pipe  17  as a slurry and into each mass module  25 . In another preferred embodiment, a small offshore workboat  16 , with an air compressor aboard, is positioned near the subsurface low-cost suspended-mass energy-storage system  10 . Compressed air is sent down the hose  3  to the seafloor  29  were the air is released into a larger hose  18 , which leads to one of the mass modules  25 . As the air rises in the hose  18  it creates a rapid upward flow of the seawater it contains which sucks up seawater and sand or similar materials from the seafloor  29 . At the other end of the hose  18  the sand is deposited into the mass module  25  until it is full, at which point the hose  18  is moved to another mass module  25  and the process is repeated. In this manner, each of the mass modules  25  is filled to capacity with hundreds of thousands of pounds of sand or similar material in an extremely low-cost manner. Not only is the material that serves as the mass low cost but there is no added cost in obtaining and transporting the mass or weight to the deployment site. 
         [0088]    In another embodiment, a bulk material pump or similar mechanisms, including but not limited to those utilized in dredging systems, can be utilized in place of the compressed air pumping mechanism noted above. It should be noted that the process of filling mass modules  25  does not need to occur at the final system deployment location, but can happen in relatively shallow water and can be done at any location that is economically proximate to the deployment location. 
         [0089]    Referring now to  FIG. 14  is shown a preferred embodiment of the present invention in a deployed location showing the buoyancy platform  13 , the suspended mass  25 , a support vessel  16 , and a remotely operated vehicle (ROV)  26  engaged in system inspection or maintenance. Through the use of materials with a density less than or equal to that of water and the incorporation of buoyant volumes, many components of the present invention can be rendered neutrally buoyant to facilitate the removal and replacement of such components using ROV  26 . 
         [0090]    The present invention is similar to a modern elevator, enabling both long (hours) and short (seconds) term energy storage. The present invention provides cycle times between storage and retrieval of energy that are measured in seconds, scalability from kilowatt hours (kWhs) to megawatt hours (MWhs) per device and MWhs to tens of gigawatt hours (GWhs) per installation, all at a fraction of the cost of other device-level or utility-scale storage solutions. For example, a recent (April 2011) US DOE grant to Duke Energy, for an energy storage solution of 36 megawatts and purportedly 10 MWh will cost $44M or approximately $1,200 per kilowatt and $4,400 per kilowatt-hour. 
         [0091]    Based on data from eXtreme Power, the supplier of the Duke battery based system, the system will rather quickly lose capacity over time, as the batteries are cycled, presenting a further significant cost and maintenance problems at utility-scale product lifetimes of 10-20 years. A recent 20 MW flywheel-based storage system in NY, also funded by a US DOE grant, cost approximately $65M or $3,250 per kilowatt, according to company officials. It is anticipated that the present invention will deliver device and grid-scale energy storage at a cost that is approximately one tenth of the cost of these most recent government and industry-funded utility-scale storage solutions. Unlike legacy energy-storage systems noted elsewhere in this application, the current invention can cost effectively (as specified in the US DOE ARPA e FOA noted elsewhere in this application) both store and release energy at the platform level. 
         [0092]    Those with expertise in the areas of knowledge required for large offshore platforms will recognize the applicability of this novel innovation for other applications such as offshore wind, as well as other applications needing cost effective but highly stable marine platforms. A further embodiment of the present buoyancy platform of the present invention has a hydrokinetic turbine mounted below the buoyancy platform and a wind turbine mounted above the platform, with the tower of the wind turbine penetrating the water surface. In this dual-use embodiment, a particularly cost effective offshore renewable energy resource is created, which taps not only water currents, but also wind currents, in locations that happen to have both of these resources in the same geographic area. Of course this configuration could be further integrated with the primary aspect of the present invention, the energy storage means creating a triple-use embodiment and further cost savings. 
         [0093]    The advantages of the invention described herein will be apparent to those of expertise in the fields of ocean platforms. Reports created by the US National Renewable Energy Laboratory, a division of the US Department of Energy, such as report NREL/CP-500-34874, released in 2003 and titled Feasibility of Floating Platform Systems for Wind Turbines, as well as NREL/CP-500-38776, released in 2007 and titled Engineering Challenges for Floating Offshore Wind Turbines, clearly highlight many of the long-standing technical and economic barriers which the present invention solves. 
         [0094]    The ability to cost effectively store and release energy at the megawatt level, per platform, at low cost, over seconds to hours, for years on end, over many thousands of cycles, with a round trip efficiency of 90+ percent, that can be deployed in Gigawatt and Gigawatt-hour-size farms that are near most of the world&#39;s population centers, makes the present invention a game changer in the utility-scale energy-storage marketplace. 
         [0095]    The advantages of the invention described herein will be apparent to those with expertise in related fields. The present invention solves numerous deficiencies in the prior art providing a novel and non-obvious way to enable a whole new class of water-deployed low-cost mass and low-cost buoyancy-based utility-scale energy-storage systems and multi-use platforms. The subsurface energy-storage system of the present invention is advantageously used to store various time frames of energy to meet the needs of one or more of the following; managing peak power demand, load balancing, or voltage management, and wherein this stored energy being used on timescales of seconds to hours. In addition, the subsurface buoyancy components and the suspended-weight components are preferably fabricated from materials such as fibers, fabrics, and resins that allow their manufacture and/or assembly at or close to the launch site, eliminating the logistical complexities and costs associated with the transport of large objects. 
         [0096]    While the benefits of one element or another will quickly be obvious to an experienced energy or marine engineer, the particular innovation itself is not obvious due to the detailed multidisciplinary analysis needed in order to understand the limitations of prior-art energy-storage systems, their development, deployment and ongoing cost. The isolation of the full-life-cycle cost drivers and non-traditional highly multi-disciplinary design approaches led to the novel and unique innovation with the desired and unprecedented cost/benefit of the present invention. 
         [0097]    The present invention is not intended to be limited to a device or method which must satisfy one or more of any stated or implied objects or features of the invention and should not be limited to the preferred, exemplary, or primary embodiment(s) described herein. Modifications and substitutions by one of ordinary skill in the art are considered to be within the scope of the present invention, which is not to be limited except by the allowed claims and their legal equivalents.