Solar DC bus and solar ac bus for flywheel energy storage

Abstract

A direct current microgrid including a renewable energy source, a direct current (DC) bus in electrical communication with the at least one renewable energy source, a one supercapacitor in electrical communication with the DC bus, a drive motor in electrical communication with the at least one supercapacitor, a flywheel in mechanical communication with the drive motor, and a generator in mechanical communication with the flywheel and in electrical communication with the at least one supercapacitor.

Description

SOLAR DC BUS AND SOLAR AC BUS FOR FLYWHEEL ENERGY STORAGETECHNICAL FIELD

[0001] This disclosure relates generally to renewable energy devices, and in particular to mechanical renewable energy generation and storage systems for powering a DC bus and meeting energy loads of a building.BACKGROUND

[0002] Renewable energy has become an increasingly important source of electrical energy generation in many countries around the world. As the demand for electrical energy has increased, the impact of fossil fuels on the environment has become magnified and increasingly apparent. In an effort to overcome these obstacles, advancements in green energy generation have continued to accelerate, resulting in innovations such as hydrodynamic generators, wind turbines, geothermal energy, biomass energy, amongst others. However, mechanical energy storage and generation, despite its simplicity, has historically remained rather undeveloped. In traditional mechanical systems, as a load is placed upon the system, the mechanical device driving electrical generators loses momentum, resulting in a drop in electrical energy generation. To avoid this decrease in electrical energy generation, it is necessary to input additional energy to maintain consistency and therefore provide consistent electrical energy generation. As can be appreciated, the constant increase or decrease in energy required to maintain constant electrical energy generation using traditional mechanical systems is inefficient and wasteful.SUMMARY

[0003] One aspect of the disclosure is directed to a direct current microgrid. The direct current micro grid includes at least one renewable energy source; a direct current (DC) bus in electrical communication with the at least one renewable energy source, at least onesupercapacitor in electrical communication with the de bus, a drive motor in electrical communication with the at least one supercapacitor, a flywheel in mechanical communication with the drive motor, and a generator in mechanical communication with the flywheel and in electrical communication with the at least one supercapacitor. Other embodiments of this aspect include corresponding computer systems, apparatus, and computer programs recorded on one or more computer storage devices, each configured to perform the actions of the methods and systems described herein.

[0004] Implementations of this aspect of the disclosure may include one or more of the following features. The direct current microgrid further including a first inverter in electrical communication with the at least one supercapacitor and the drive motor. The direct current microgrid further including a variable frequency drive (VFD) in electrical communication with the inverter and the drive motor. The direct current microgrid further including a first switch selectively electrically connecting the inverter with the at least one supercapacitor. The direct current microgrid further including a second switch selectively electrically connecting the VFD with a natural gas generator, or electrically connecting the VFD with a grid connection. The drive motor, flywheel and generator are in mechanical communication with one another via a magnetic gear system. The direct current microgrid further including a first charge controller in electrical communication with the generator and the at least one supercapacitor. An inverter in electrical connection with the switch and the grid connection inverts energy output from the generator to a voltage to be fed to an electrical grid. The switch, when in an open position, allows energy to flow from the generator to the at least one supercapacitor. The direct current microgrid further including a plurality of light emitting diodes in electrical communication with the de bus. The renewable energy source is configured to directly power the DC bus. The direct current microgrid further including a full wave rectifier in electrical communication with the renewable energy source and the chargecontroller. The renewable energy source is one or more of a photovoltaic solar module or a wind turbine. Implementations of the described techniques may include hardware, a method or process, or computer software on a computer-accessible medium, including software, firmware, hardware, or a combination of them installed on the system that in operation causes or cause the system to perform the actions. One or more computer programs can be configured to perform particular operations or actions by virtue of including instructions that, when executed by data processing apparatus, cause the apparatus to perform the actions.

[0005] A further aspect of the disclosure is directed to an alternating current microgrid. The alternating current microgrid includes at least one renewable energy source; a first inverter in electrical communication with the at least one renewable energy source; an alternating current (AC) bus in electrical communication with the first inverter, where the ac bus is configured to meet an electrical demand of at least one building; a drive motor in electrical communication with the at least one renewable energy source; a flywheel in mechanical communication with the drive motor; a generator in mechanical communication with the flywheel; and at least one supercapacitor in electrical communication with the generator and the ac bus. Other embodiments of this aspect include corresponding computer systems, apparatus, and computer programs recorded on one or more computer storage devices, each configured to perform the actions of the methods and systems described herein.

[0006] Implementations of this aspect of the disclosure may include one or more of the following features. The alternating current microgrid further including a second inverter in selective electrical communication with the at least one renewable energy source via a switch and variable frequency drive in electrical communication the second inverter and the drive motor. The alternating current microgrid further including a second inverter in selective electrical communication with the supercapacitor via a switch and in electrical communication with the ac bus. The alternating current microgrid further including a secondinverter in electrical communication with the at least one renewable energy source and selectively in electrical communication with the ac bus. The grid connection enables energy stored in the flywheel to be transmitted to an electrical grid. The alternating current microgrid further including a grid connection in selective electrical connection with the ac bus and configured to supply grid power to the ac bus. Implementations of the described techniques may include hardware, a method or process, or computer software on a computer-accessible medium, including software, firmware, hardware, or a combination of them installed on the system that in operation causes or cause the system to perform the actions. One or more computer programs can be configured to perform particular operations or actions by virtue of including instructions that, when executed by data processing apparatus, cause the apparatus to perform the actions.BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the disclosure and, together with a general description of the disclosure given above, and the detailed description of the embodiments given below, serve to explain the principles of the disclosure, wherein:

[0008] FIG. l is a schematic diagram of a direct current microgrid in accordance with an aspect of the disclosure;

[0009] FIGs. 2A and 2B are a flow diagram of a control method of the direct current microgrid of FIG. 1; and

[0010] FIG. 3 is an alternating current microgrid in accordance with the disclosure.DETAILED DESCRIPTION

[0011] This disclosure is directed to systems and methods of mechanical renewable energy generation and storage for powering a DC microgrid and meeting energy loads of abuildings. In particular aspects of the disclosure are directed to systems connected to a variety of power sources including solar, wind, natural gas and diesel generators, and the grid to generate electrical energy, supply electrical energy to a direct current (DC) grid for lighting and other low voltage DC applications. Aspects of the disclosure are also directed to localized storage of energy from solar, wind, natural gas and diesel generators, and the grid to meet the varying daily alternating current (AC) energy demands of a building, while supplying the grid with the renewable portions of the produced energy when excess energy is available. These and other aspects of the disclosure are described in greater detail below. Embodiments of the disclosure are now described in detail with reference to the drawings in which like reference numerals designate identical or corresponding elements in each of the several views.

[0012] FIG. 1 depicts a DC microgrid system for directly supplying DC power for lighting (e.g., light emitting diode (LED)) systems and other applications employing DC from solar and other renewable energy sources. Current systems seeking to harness the energy produced by solar and other renewable energy sources, do not seek to directly convert the energy produced to a useable form that can be directly harnessed by loads such as LED lighting. And where there is some attempt at directly harnessing the energy from the renewable energy source (e.g., photovoltaic (PV) solar) a battery is required. LED lighting systems used in many buildings are often powered by DC microgrids rated at 380 VDC source and have converters (e.g., buck converters) which reduce the DC voltage to a useable level for the lighting and other applications. Even before the conversion to a lower DV voltage, the 380 VDC is often created either by rectifying an AC source (e.g., the grid) or from the conversion of the DC produced by the PV solar panels or other renewable source first to AC (e.g., with the use of an inverter) and then rectified to produce the 380 VDC. These multiple conversions generate a great deal of heat and result in energy losses in excessof 10%. In contrast, the system depicted in Fig. 1 directly connects the output of the renewable energy sources with the LED lighting (e.g., via a DC bus) and substantially eliminates the losses associated with the multiple energy conversions described above.

[0013] Referring now to the Fig. 1 there is depicted a DC microgrid 100 in accordance with the disclosure. The DC microgrid 100 includes a flywheel 102, a flywheel is a mechanical energy storage device. In accordance with aspects of the disclosure the flywheel 102 includes a rotor weighing between 4,000 and 10,000 lbs. spinning at between 6,000 and 10,000 RPM and store therein between 15 and 50 kWh of energy. The flywheel 102 may include magnetic lift bearings which suspend the rotor and eliminate substantially all friction as employed in traditional mechanical bearings. The rotor is enclosed within a housing on which a vacuum is drawn approaching or even exceeding 29 inHg (29.92 inHg being a perfect vacuum). The drawing of a vacuum further reduces friction within the flywheel 102 associated with windage on the rotor as it spins at high speed.

[0014] The magnetic bearings, not only lift the rotor to reduce the friction, but also act as a radial bearing to maintain the vertical alignment of the rotor within the housing while spinning at high speeds. In some embodiments, the rotor is formed of a high strength steel such as an armor rated steel commonly used to reinforce bulldozer blades and the like.

[0015] The flywheel 102 may also incorporate a magnetic gear system. The magnetic gear system magnetically connects the rotor to a magnetic bull gear located outside of the housing and due to the magnetic coupling spins at the same RPM as to rotor. In some implementations, the magnetic gear system includes one or more magnetic idler gears magnetically coupled to the magnetic bull gear. One magnetic idler gear may be coupled to a magnetic driven gear 104 coupled to a generator 106. By coupling the rotor of the flywheel 102 to the generator 106 via the magnetic drive gear 104, mechanical energy stored in the flywheel 102 can be converted into electrical energy output from the generator 106.Depending on the gear ratios of the magnetic bull gear, magnetic idler gear, and magnetic driven gear 106, the speed of the generator 106 and the power available for output form the generator 106 can be maintained within a range and capable of achieving a determined power output e.g., 15-50 kW.

[0016] Another aspect of the magnetic gear system is a drive gear 108 coupled to a motor 110. The motor 110 rotates the drive gear 108 and in turn transfers energy from the motor 110 to the flywheel 102. This configuration is unique among energy storage systems in that it can be simultaneously charged and discharged. A battery, for example, cannot be simultaneously charged or discharged. Thus most battery systems require complicated electronics and switching to allow some batteries or cells to charge while others discharge. Further details of the flywheel 102, the magnetic bearings, and the magnetic gear system as well as their interaction with the generator 106 and the motor 110 can be found in PCT / US2023 / 027355 titled MECHANICAL RENEWABLE GREEN ENERGY PRODUCTION filed July 11, 2023, and incorporated herein by reference in its entirety regarding the construction and features of these elements of the DC microgrid 100.

[0017] As noted above, and in accordance with the disclosure, the flywheel 102 can be supplied with power from a variety of sources including the grid 112 or a natural gas or diesel generator 114. When selectively employed, switches 116 close to connect one of these energy sources are electrically connected to a variable frequency drive (VFD) 118. The VFD 118 allows the frequency and voltage of the electrical energy applied to the motor 110 to be varied to control the speed of the motor 110. This can be particularly beneficial when starting the motor and ramping up the speed of the motor 110 on initial start-up of the flywheel 102.

[0018] The generator 106 is electrically connected to a charge controller (e.g., a DC-DC converter) 120. The charge controller 120 controls the charging of supercapacitors 122.The supercapacitors 122 are an energy storage device which can both charge and discharge very quickly. The supercapacitors 122 help to stabilize fast transient changes in conditions as will be described in greater detail below. The supercapacitors 112 may have a voltage of for example between 2.2 and 3.8 volts (V) and a capacitance of between about 100 and 12,000 farads (F) The charge controller 120 is selectively coupled to an inverter 124 via switches 116. The inverter 124 outputs high voltage AC to connect to the grid 112. As a result of this interconnection of the output of the generator 106 through the inverter 124 any excess energy produced by the renewable energy sources (described below) in excess of the requirements of the DC microgrid 100 is fed to the grid 112. This energy offsets energy that might otherwise require the use of fossil fuels to generate and can provide excess capacity to the grid 112 in times of high demand (e.g., summertime during daylight hours).

[0019] The DC microgrid 100 also includes an array of PV solar modules 126 connected to a full wave rectifier 128 and feeding a charge controller 120. A wind turbine 130 may also be connected to its own full wave rectifier 128 and a charge controller 120. The charge controllers 120 connected to the PV solar modules 126 or the wind turbine 130 both feed a DC bus 132, the DC bus as a result of being connected to the output of the two charge controllers 120 are at the voltage necessary to power the LED lights 134. Also connected to the DC bus 132 are the supercapacitors 122. Thus the supercapacitors 122 are charged via the DC bus 132. Switches 116 connect the supercapacitors 122 to an inverter 124 to the VFD 118. In this manner the DC voltage output from the supercapacitors 122 is fed as an AC voltage output from the VFD 118 to the motor 110 to drive the flywheel 102 and store energy therein. As a result, the PV solar panels 126 provide not just power to directly power the LEDs 134 via the DC bus 132, charge the supercapacitors 122, and excess energy is stored in the flywheel 102. When the PV solar modules 126 are producing more energy than can be used by via the DC bus 132 and can be stored in either the supercapacitors122 or the flywheel, excess energy is provided via an inverter 124 to the grid 112. Further, the DC bus 132 may be fed by more than one renewable source simultaneously.

[0020] Unlike prior systems that require multiple conversions, inversions, and storage (e.g., via a battery) prior to supply to the DC bus, the DC microgrid 100 employs just a single DC-DC charge controller (for each renewable energy source) thus the efficiency of the DC bus 132 and the overall efficiency of the lighting for a building is greatly increased. In part this is achieved by eliminating the batteries commonly employed in DC bus installations. By utilizing the supercapacitors 122 the “absorb: and “float” voltage settings of the charge controllers 120 are set very close to one another. This closeness of the absorb and float voltages yields a narrow voltage range that is supplied to the DC bus 132 and to the supercapacitors 122. As is known, when batteries are employed , the absorb and float voltage values can’t be close to one another without causing the batteries to quickly fail.

[0021] The supercapacitors 122 also play a role in stabilizing the entire DC microgrid 100 because of their ability to charge and discharge very quickly. The controlled use of the supercapacitors helps to limit in-rush and out-rush current to and from various components of the DC microgrid 100. Thus, in the event clouds quickly appear and the voltage of the DC bus 132 begins to drop, the supercapacitors 122 can discharge, maintaining the voltage of the DC bus 132 for a predetermined duration. Simultaneously, switches 116 connecting the generator 106 to the grid 112 via an inverter 124 can be opened to allow the charge controller 120 and the generator 106 to continue charging the supercapacitors 122 and therewith the DC bus 132. This can continue until, the PV solar modules 126 or the wind generator 130 once again start outputting sufficient energy that the charge controllers 120 connected thereto can maintain the DC bus 132 voltage power. Once the output of the charge controller 120 is sufficient to maintain the DC bus 132 voltage, the flywheel 102 can be recharged via inverter 124 and VFD 118 by closure of switch 116 connected thereto. This configuration can bemaintained until the flywheel 102 is fully recharged and the connection of the generator 106 to supply the grid 112 via switch 116 and inverter 124 reestablished. In this way the DC microgrid 100 and the DC bus 132 can operate within tightly regulated DC voltage despite being powered by irregular and unsteady renewable energy sources such as PV solar modules 126 and wind turbines 130. Further, this can be achieved while substantially simultaneously providing energy to a building (e.g., for power the LEDs 134) and providing excess energy from the renewable sources back into the utility grid 112.

[0022] Further, if the energy in the flywheel 102 becomes sufficiently depleted (e.g., at night) the switches 116 connecting either the natural gas or diesel generator 114 or the grid 112 can be closed to recharge the flywheel 102 and continuously power the DC bus 132 such that observation of the LEDs 134 cannot detect the changes in the source of energy powering the DC bus 132. Indeed, due to the unique nature of the flywheel 102, the grid 112, the natural gas generator 114 and the PV solar modules 126 cab be simultaneously connected via the VFD 118 to the flywheel 102 to charge the flywheel 102 and bring it to its maximum RPM (e.g., 10-12,000).

[0023] Through the use of the DC microgrid 100 a target performance of 96-98% efficiency in converting energy from renewable sources such as the PV solar modules 126 or a wind turbine 130 to power the DC bus 132 and the LEDs 134 is expected. This represents an average 7-17% increase in efficiency over existing (solar power to LED lighting conversion systems). Further, by improving the efficiency of the DC bus 132, an additional 2.5-6% decrease in energy consumption of a building can be expected due to the reduced HVAC cooling necessary to mitigate the heat generated by inverters, transformers, and other electrical and power electronics components of such systems. For a single flywheel 102, the expected efficiency in converting excess renewable electric power to AC power feeding thegrid / building is in excess of 80%. The round-trip efficiency of just the flywheel (e.g., energy into energy out) is in excess of 90%.

[0024] For a given DC microgrid 100, the PV solar modules 123 employed to power the DC bus 132 and powering at least the LED lighting 134 should be sized to provide sufficient power to power the LEDs 134 during daylight hours and charge the flywheel 102 sufficiently to allow the flywheel 102 to provide energy to the DC bus 132 during nondaylight hours. The PV solar modules 126 can be installed to have some quantity biased to the east, some biased south, and some biased west to match the contour of the expected timebased lighting demand curve of the particular building. Matching the diurnal illuminance to the diurnal demand for lighting helps optimize the efficiency of the DC microgrid 100 minimizes power needed from the grid 112. As noted above, wind turbine generators 130 can be added with PV solar modules 126 to improve the efficiency to between 96-98 % in converting electric power from renewable sources to DC LED 134 lighting systems and other DC bus 132 loads.

[0025] As will be appreciated, a variety of software and control systems are employed in the DC microgrid 100 to maintain operational balance of the system and the powering of the DC bus 132 from the multiple sources of energy available to provide the necessary power. Some of these software and control systems are described in connection with the flow diagram of Figs. 2 A and 2B. Though not shown in Fig. 1 computer including a processor and a memory storing thereon software code executable by the processor is in communication with most or all of the elements of the DC microgrid 100. This may be a wired or a wireless connection (e.g., Wi-Fi, Bluetooth®, Zigbee and others). In addition a variety of sensors, including photodiodes to detect light conditions effecting the PV solar modules 126, wind speed detector for the wind turbine 130, revolution counters for the flywheel 102, and a variety of voltage and current detectors to detect the voltage and current between any twoelement can all be incorporated in the DC microgrid 100 to provide data on which the software applications stored in the memory of the computer can act to open or close one or more of the switches 116 (e.g., relays) and alter the source of power to the DC bus 132 or allow the DC microgrid 100 to provide excess power to the grid 112.

[0026] With respect to Fig. 2A, once the DC microgrid is brought on-line with the flywheel 102 spinning at its maximum rated RPM (e.g., 10,000 RPM) with the PV solar modules 126 and / or the wind turbine 130 providing operational power to the DC Bus 132 to power the LED lights 134. The switches 116 connecting grid 112 and the natural gas or diesel generator 114 are open isolating the DC microgrid 100 from using these as energy sources. And the supercapacitors 122 are fully charged and the switches 116 connecting the generator 106 to the grid 112 via inverter 124 closed allowing the DC microgrid 100 to feed power to the grid 112. In this position, as can be expected the DC microgrid 100 to achieve at some point after the sun has risen on a sunny day, the PV solar modules 126 are directly supplying the LED lights 134 and the DC microgrid 100 is at a substantially steady state the method 200 is commenced.

[0027] At step 202, with the DC microgrid 100 in the steady state described above a voltage of the DC bus 132 is detected and at step 204 a determination is made whether the voltage is above a pre-determined value. If yes, the method returns to step 202, if no the software application at step 206 opens switches 116 connecting supercapacitors 122 to the inverter 124 and VFD 118 thus preventing the flywheel 102 from receiving power from the DC bus 132. At step 208, a time check is conducted to determine whether the position of the sun is the cause of the drop in voltage. If yes, at step 210 which may optionally occur simultaneously with step 206, switches 116 connecting the supercapacitors 122 generator 106 to the grid 112 are opened, isolating the flywheel 102 from the grid 112 to preserve the energy in the flywheel 102 for charging the supercapacitors 122 and for use by the DC bus132. If no, at step 212 a whether check is conducted to determine whether the drop in voltage of the DC bus 132 is expected to be transient. This determination may be based in part on weather forecast data that is received by the application for the location of the DC microgrid 100 or local weather detection sensors such as wind, rain, photodetectors, etc. If the drop in voltage is determined to be non-transitory (e.g., a prolonged weather event extending to near or beyond sundown, the method reverts to step 210 described above. If the DC bus 132 voltage drop is determined to be transient (e.g., cloud shading of the PV solar modules 126), then at step 214 a periodic check of the output of the renewable energy sources (e.g., PV solar modules 126) is undertaken. This periodic check may be for example every minute. At step 216 the application may make periodic checks of the power stored in the flywheel and compare the stored power to expected necessary power before the transient condition is overcome. If the stored power in the flywheel 102 drops to a specified level, at step 218 switches 116 connecting the supercapacitors 122 generator 106 to the grid 112 are opened, isolating the flywheel 102 from the grid 112 to preserve the energy in the flywheel 102 for charging the supercapacitors 122 and for use by the DC bus 132. Once output of the renewable energy sources returns such that the renewable energy source can directly power the DC bus 132, the periodic checks ends and at step 220 switches 116 connecting the supercapacitor 122, and therewith the DC bus 132 to the inverter 124, VFD 118 and the motor 110 can be closed allowing the flywheel 102 to be recharged. In addition, once the power stored in the flywheel is sufficient, at step 222 the switches 116 connecting the generator 106 to the grid 212 via the inverter 124 may be closed and the flywheel 102 is able to feed power to the grid 212 while still being charged by the PV solar modules 126 or the wind turbine 130.

[0028] Referring back to step 210, where following determination that the drop in voltage of the DC bus 132 is due to the time of day at step 212, the power stored in theflywheel 102 is monitored at step 224 to ensure that the DC bus 132 can be powered. If at any point the power stored in the flywheel drops to a specified level switches 116 connecting either the natural gas or diesel generator 114 or the grid 112 to the VFD can be closed at step 224 and the flywheel 102 charged at step 226. Once the flywheel 102 is adequately charged as detected at step 228, the switches 116 may be again opened isolating the grid 112 or the natural gas generator 114 from the VFD 118 and the flywheel at step 230. At step 232 as the sun rises the following morning a determination is made whether the output of the renewable energy sources (e.g., PV solar modules 126 or wind turbine 130) are sufficient to directly power the DC bus 132. Steps 224-232 may be repeated periodically throughout the nighttime hours to ensure that the DC bus 132 is adequately powered and the flywheel is adequately charged. Once the renewable energy sources are outputting sufficient power to directly power the DC bus 132 and the LEDs 134, the switches 116 connecting the supercapacitors 122 to the VFD 118 via the inverter 124 may be closed at step 234 and the flywheel 102 charged via the renewable energy sources. At step 236 a determination is made whether the flywheel 102 is fully charged. If no, the charging of the flywheel continues, but if yes, the switches 116 connecting the generator 106 to the grid 112 via inverter 124 may be closed t step 238 such that excess power generated by the renewable energy sources in excess of demand on the DC bus 132 and the charging requirements of the flywheel 102 can be fed to the grid 212. At this point the DC microgrid 100 is returned to the substantially steady state at which method 200 started and the entire method may continually repeat by returning to step 202. As will be appreciated, the series of steps outlined in connection with method 200 are not exhaustive and may be performed in a different order than specified here without departing from the scope of the disclosure. Further, one or more detection of voltage or power steps may occur out of order or autonomously to advance the method 200 to a different aspect of the method without departing from the scope of the disclosure.

[0029] If yes, which may be the result of a determination that the PV solar modules 126 are temporarily shaded as detected by a photodetector, for example by a cloud, or a measured drop of wind speed reducing the output of the wind turbine, then the application may wait a predetermined period at step 210 (e.g., 30s, 1 min, 2min, 5min, etc.), and at step 212 a determine is made whether an output voltage of the PV solar modules 126 and or wind turbine 130 exceeds a threshold indicating that the transient condition has passed.

[0030] Figs. 1 and 2A-2B are primarily focused on the creation of a DC microgrid 100 and a DC bus 132 to be used to powering LED lights 134 and other DC loads without necessitating the muti-step conversion, inversion, and transformation steps commonly employed to power LED and other DC loads in buildings and other applications. However, the disclosure is not so limited.

[0031] Fig. 3 depicts a similar microgrid 300 configured for meeting the AC loads of, for example, a building. The microgrid 300 may be combined with the microgrid 100 to enable the PV solar modules 126 to directly power both the DC bus 132 as well as a building’s AC loads. As with microgrid 100, microgrid 300 includes a flywheel 102 as described above. In microgrid 300 the flywheel 102 may be for example a cluster of 2-4-8 or more flywheels 102 forming a flywheel group. The magnetic gear system as described above connects the flywheel 102 to two generators 106. A first generator 106 is connected to a set of supercapacitors 122 and via an inverter 124 to an AC bus 302. The AC bus 302 may be for example a three phase 440 VAC bus, capable of supporting a building 304. A power meter 306 may be located on the bus to measure the power used by the building 204. In an alternative, the power meter 306 may be located between a grid connection 112 and a switch 116, such that the power meter 306 only measures power received from the grid 112. Further two or more power meters 306 may be employed without departing from the scope of the disclosure.

[0032] A second generator 106 may be directly connected via an inverter 124 to a grid connection 112 so that energy from the PV solar modules 126 in excess of the requirements of the flywheel 102 and the supercapacitors 122 can be fed to the grid 112 to meet the grid demand.

[0033] The PV solar modules 126 are connected to a full wave rectifier 128 and a solar inverter 124 to directly feed the AC bus 302. As noted above switches 116 are employed to allow energy to flow from the inverter 124 to the AC bus 302 and isolate the AC bus from the grid 112. Where the PV solar modules 126 are generating power in excess of the needs of the building 304, switches 116 connect the output of the full wave rectifier 128 to a solar inverter 124, that may optionally not include maximum power point tracking features, to a variable frequency drive (VFD) 118. The output of the VFD 118 is supplied to an AC drive motor 110 which is magnetically coupled to and drives the flywheel 102. The spinning mass of the flywheel 102 stores energy from the PV solar modules 126. The flywheel 102 may also be supplied with energy from the grid 112. The flywheel 102 may include multiple AC drive motors 110, each of which can provide energy to the flywheel 102 from one or more sources (e.g., the grid 11, PV solar modules 126, a wind turbine 130, or a natural gas or diesel generator 114).

[0034] A computer control system 308, shown schematically in FIG. 3 may receive inputs from a variety of sensors (e.g., photo sensors 310) to provide control signals to a variety of elements of the microgrid 300. These control signals can be input to each of the VFDs 118 and the switches 116. In addition, the computer control system 308 may receive a variety of data from various elements of the microgrid 200 including outputs from the power meters 306, voltage outputs from the PV solar modules 126 or wind turbine 130, charge state of the supercapacitors 122, load on the AC bus 202, load on the AC drive motors 110, speed of the flywheel 102 (e.g., energy stored), etc. The computer control system 208 may alsoimplement applications and methods such as that described in connection with the DC microgrid 100, above, to similarly maintain supply of energy to the AC bus 302 to meet the demands of the building 204 and the changing output of the renewable energy sources.

[0035] The AC microgrid 300 is expected to have an overall target performance of 97% efficiency during times of 100% solar power, 90% when solar is providing 50% of building demand, and 85% when solar is providing 25% of the building demand. At times when there are excess renewables, the efficiency in feeding these back into the grid will be 70-85% with higher power favoring higher efficiency due to electrical generator efficiency characteristics. The round-trip efficiency of just the flywheel system is about 90%. The PV solar modules 126 may be oriented so as to match the time-based solar irradiance curve to the demand profile curve of the buildings needs for times of maximum electrical demand. This orientation minimizes energy storage required, maximizes efficiency, and lowers system initial capital costs for both flywheel 102 and PV solar modules 126. Wind turbine power can be simultaneously added directly to the flywheel and can be used to help power the building at efficiencies of 85% and / or be fed into the grid as excess at efficiencies of 70 to 85%. If a building manager wishes to over-generate with renewables and specify adequate energy storage to power the building through the entire nighttime, they can maintain off-the- grid status for days with adequate sun and wind generated power.

[0036] While several embodiments of the disclosure have been shown in the drawings, it is not intended that the disclosure be limited thereto, as it is intended that the disclosure be as broad in scope as the art will allow and that the specification be read likewise. Therefore, the above description should not be construed as limiting, but merely as exemplifications of embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.

Claims

WHAT IS CLAIMED IS:

1. A direct current microgrid comprising: at least one renewable energy source; a direct current (DC) bus in electrical communication with the at least one renewable energy source; at least one supercapacitor in electrical communication with the DC bus; a drive motor in electrical communication with the at least one supercapacitor; a flywheel in mechanical communication with the drive motor; and a generator in mechanical communication with the flywheel and in electrical communication with the at least one supercapacitor.

2. The direct current microgrid of claim 1, further comprising a first inverter in electrical communication with the at least one supercapacitor and the drive motor.

3. The direct current microgrid of claim 2, further comprising a variable frequency drive (VFD) in electrical communication with the inverter and the drive motor.

4. The direct current microgrid of claim 3, further comprising a first switch selectively electrically connecting the inverter with the at least one supercapacitor.

5. The direct current microgrid of claim 4, further comprising a second switch selectively electrically connecting the VFD with a natural gas generator, or electrically connecting the VFD with a grid connection.

6. The direct current microgrid of claim 1, wherein the drive motor, flywheel and generator are in mechanical communication with one another via a magnetic gear system.

7. The direct current microgrid of claim 1, further comprising a first charge controller in electrical communication with the generator and the at least one supercapacitor.

8. The direct current microgrid of claim 7, further comprising a switch selectively coupling the first charge controller to a grid connection, wherein an inverter in electrical connection with the switch and the grid connection inverts energy output from the generator to a voltage to be fed to an electrical grid.

9. The direct current microgrid of claim 8, wherein the switch, when in an open position, allows energy to flow from the generator to the at least one supercapacitor.

10. The direct current microgrid of claim 1, further comprising a plurality of light emitting diodes in electrical communication with the DC bus.

11. The direct current microgrid of claim 10, further comprising a charge controller in electrical communication with the at least one renewable energy source and the DC bus, wherein the renewable energy source is configured to directly power the DC bus.

12. The direct current microgrid of claim 11, further comprising a full wave rectifier in electrical communication with the renewable energy source and the charge controller.

13. The direct current microgrid of claim 12, wherein the renewable energy source is one or more of a photovoltaic solar module or a wind turbine.

14. An alternating current microgrid comprising: at least one renewable energy source; a first inverter in electrical communication with the at least one renewable energy source; an alternating current (AC) bus in electrical communication with the first inverter, wherein the AC bus is configured to meet an electrical demand of at least one building; a drive motor in electrical communication with the at least one renewable energy source; a flywheel in mechanical communication with the drive motor; a generator in mechanical communication with the flywheel; and at least one supercapacitor in electrical communication with the generator and the AC bus.

15. The alternating current microgrid of claim 14, further comprising a second inverter in selective electrical communication with the at least one renewable energy source via a switch and variable frequency drive in electrical communication the second inverter and the drive motor.

16. The alternating current microgrid of claim 14, further comprising a second inverter in selective electrical communication with the supercapacitor via a switch and in electrical communication with the AC bus.

17. The alternating current microgrid of claim 14, further comprising a second inverter in electrical communication with the at least one renewable energy source and selectively in electrical communication with the AC bus.

18. The alternating current microgrid of claim 14, further comprising a second inverter in selective electrical communication with the generator via a switchand in electrical communication with a grid connection, wherein the grid connection enables energy stored in the flywheel to be transmitted to an electrical grid.

19. The alternating current microgrid of claim 14, further comprising a grid connection in selective electrical connection with the AC bus and configured to supply grid power to the AC bus.

20. The alternating current microgrid of claim 19, further comprising a variable frequency drive in selective electrical communication with the grid connection and configured to power the drive motor and flywheel with energy from an electrical grid.

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