Patent ID: 12255465

DETAILED DESCRIPTION

FIG.1illustrates system1for supplying power to an isolated grid, comprising both required and optional elements. The power grid, preferably an isolated grid that preferably only is provided with electric power from the power supply system1, is connected to the power supply system1by a busbar10. The grid connects to consumers that create a fluctuating AC power demand on the grid.

A master controller50(an electronic control unit), controls the operation of the power supply system1. The power supply system1comprises one or more fluctuating sources of AC power generated from renewable energy. These fluctuating sources of AC power are in the shown embodiment in the form of a wind turbine14and a solar energy collector12. However, it is understood that the fluctuating sources of AC power12,14generated from renewable energy may include other forms of renewable energy e.g. wave energy, tidal energy, or hydro energy. The wind turbines14comprise a terminal box15each and are coupled to the busbar10. The wind turbines14receives a control signal, e.g. via a signal line, from the master controller50, and the master controller50receives information about the operation of the wind turbine14. The controller50is powered by an auxiliary power supply unit18.

The solar energy collector12comprises one or more solar panels24and is coupled to an inverter22which is in turn coupled to the busbar10. The inverter22receives a control signal from the master controller50and the master controller receives information about the operation of the solar energy collector12from the inverter22, e.g. via a signal line.

At least one grid forming controllable inverter20is coupled to a rechargeable electric battery21, so that the controllable inverter20can, depending on need, receive electric power from the battery21and store electric power in the battery21. Several grid forming controllable inverters20can be arranged in parallel to obtain the required capacity and/or redundancy. The battery21can be of any suitable type comprising secondary cells, with a suitable capacity to store electrical charge and a sufficiently high C-rate. In an embodiment, the battery21is assisted by power from the fuel cell for the supply of electric power to the controllable inverter20. Several batteries21can be arranged in parallel to obtain the required capacity and/or redundancy.

The grid forming controllable inverter20is coupled to the master controller50, e.g. via a signal line, and the operation of the grid forming controllable inverter20is controlled by the master controller50. In an embodiment, the master controller50is an integral part of the grid forming controllable inverter20.

The grid forming inverter control structure incorporates a voltage regulator and its frequency is auto-generated. The controllable inverter20is grid forming, i.e. it is responsible for producing and maintaining voltage and frequency at the busbar10. Thus, the controllable inverter20ensures that the grid operates with a required voltage (Vref) and frequency (e.g. 230 V and 50 Hz or 110 V and 60 Hz) and this is in part achieved by the inverter control. The diagram of the inverter control scheme is shown inFIG.4. The voltage at the busbar10is sensed (Vm) and compared with the desired reference value (Vref) and the difference between them is sent to proportional plus integral (PI) controller27. A sine wave having amplitude 1 and frequency 50 Hz (or other desired value) wave generator28is multiplied in a multiplier29to generate the reference signal. This reference signal is sent to a pulse width modulator25to produce pulse width modulated (PWM) pulses to switch on/off a voltage source inverter20. An LC filter (not shown) is arranged in the controllable inverter20in order to eliminate the high frequency harmonics from output AC voltage.

A controllable energy bank40is coupled to the grid. The energy bank40is controlled by the master controller50, e.g. via a signal line. The energy bank40has a capacity to withdraw a variable amount of power from the grid, and the energy bank40preferably has a capacity to change the amount of energy withdrawn from the grid faster than the battery21can change the amount of power withdrawn from the grid. The energy bank40is a system that is coupled to the grid via the busbar10to provide rapid changes of resistive load on the grid. The energy bank40provides fast regulation with load steps in a binary range. In an embodiment, the energy bank40is a resistive load bank or a group of resistive load banks that are individually or groupwise selectively coupled to and decoupled from the grid.

The energy bank40provides a very fast absorbing capacity of excess electric power, in an embodiment the energy bank40comprising a number of resistors41, preferably air cooled or water cooled or a combination thereof. The resistors41are arranged to directly absorb electrical energy from the grid and convert it into heat. In an embodiment, the energy bank40comprises electrolysis units (not shown) instead of or in addition to resistors41for energy bank40.

The grid has selectively coupled thereto, in parallel with the controllable inverter20, at least one driven or nondriven alternators34for stabilizing grid frequency fluctuations by adding inertia and for improving grid voltage stability. Nondriven alternators are alternators that are rotating synchronously with the grid and are kept spinning by the grid and form a condenser. Nondriven alternators are not coupled to an engine, or can at least be disengaged from such engine. e.g. by a clutch, e.g. when the nondriven alternator is part of a hybrid generator set. In case the nondriven alternator is not part of a hybrid generator set, the nondriven alternators are typically connected to a motor, e.g. an electric drive motor, only for “soft” starting up of the nondriven alternator.

These alternators are controlled by the master controller50e.g. via signal lines. The alternator34is in an embodiment driven by an internal combustion engine32. This so-called hybrid genset solution30with a genset of the standard type equipped with clutch system36of standard type. Additional inertia mass may be added to the alternators, for example in the form of the flywheel (not shown), to increase the kinetic energy effect. The alternator34is connected to an internal combustion engine32on a common bedframe for engine power backup function. When alternator34is online (rotating in sync with the grid), engine start-up is fast as the internal combustion engine32only starts up itself and does not have to accelerate the alternator rotor from 0 rpm to synchronous rpm as alternator34is already connected and online. Engine clutch-in is performed at synchronous rpm between alternator34and internal combustion engine32. The alternator34may be equipped with an air duct system for ventilation air for connecting to nominated engine filter housing as described in EP0745186. The internal combustion engines32may be hybrid equipped for optimal operation in lower loads and for having fast response which may include the engine cooler system separated from the internal combustion engine as described in EP0745186.

A supervisory control and data acquisition system (SCADA) is 17 is coupled to the master controller50, e.g. via a signal line, for supervisory management and is connected to a large area network, e.g. the Internet via a wireless or wired connection.

An AUX supply14provides power for the master controller50and others auxiliary equipment including measurement equipment.

Grid supply16connects the busbar10to the grid.

FIG.2illustrates a first control principle that is implemented by the master controller50. The master controller50is configured to operate the at least one fluctuating source of AC power12,14as a slave to the grid, to measure grid frequency, to control grid frequency with the controllable inverter20as master controller to obtain a desired grid frequency, to supply power “+S3” from the electric battery21through the controllable inverter20to the grid when the measured grid frequency is below the desired grid frequency by more than a first lower margin, and to withdraw power “−S3” through the controllable inverter20from the grid to the electric battery21when the measured grid frequency is above the desired grid frequency by more than a second upper margin. The lower margin is at the root of the arrow+S3and the upper margin is at the root of the arrow −S3. The controllable inverter20allows the grid frequency to vary within the first lower margin and the first upper margin.

The main control principle is controlling via frequency. This results in a high-power quality typically within approximately +/−0.4-0.8 Hz.

The grid frequency is measured with a high number of impulses per secs giving a fast reading of the frequency trend variations, hence allowing for fast adjustments.

The amount of power supplied to the grid by the battery is increased according to a defined slope in kW/see illustrated by the orientation of arrow “+S3”, substantially proportionally, with increasing deviation of the measured grid frequency below the first lower margin and vice versa.

The amount of power withdrawn from the grid by the battery21is increased according to a defined slope in kW/see illustrated by the orientation of the arrow “−S3”, proportionally with increasing deviation of the measured grid frequency above the first upper margin and vice versa.

Power is in an embodiment withdrawn under control from the master controller50from the grid by the energy bank40when the measured grid frequency is below the desired grid frequency by more than a second lower margin, the second lower margin being smaller than the first lower margin, and power withdrawn from the grid under control of the master controller50by the energy bank40is increased when the measured grid frequency is above the desired grid frequency by more than a second upper margin, the second upper margin being smaller than the first upper margin, Thus, the energy bank allows grid frequency to vary within the second lower and the second upper margin.

The amount of power withdrawn from the grid by the energy bank40is in an embodiment increased according to a defined slope in kW/see illustrated by the orientation of the arrow “+S2, proportionally, with increasing deviation of the grid frequency above the second upper threshold and vice versa. The amount of power withdrawn by the grid from the energy bank40is decreased according to a defined slope in kW/see illustrated by the arrow “−S2”, proportionally, with increasing deviation of the grid frequency below the second lower threshold and vice versa.

Reactive power, inertia, and/or short-circuit effect in the grid are in an embodiment controlled by the master controller50selectively coupling and decoupling the at least one or more selectively driven or nondriven alternators34to the grid in parallel with the controllable inverter20. The alternators34act as condensers and the alternators34can be replaced or supplemented by other forms of condensers.

Reactive power drawn from the controllable inverter20is in an embodiment measured, and at least one driven or nondriven alternator34is coupled by the master controller50to the grid in parallel with the controllable inverter21when reactive power drawn from the controllable inverter21exceeds a first reactive power threshold, preferably coupling one or more additional driven or nondriven alternators34to the grid in parallel with the controllable inverter20when reactive power drawn from the controllable inverter20remains above the first reactive power threshold.

One or more additional driven or nondriven alternators34are in an embodiment coupled to the grid by the master controller50in parallel with the controllable inverter20when wind turbines14or other electric drives coupled to the grid are started up, preferably upon detection or notification of the wind turbines14or other electric drives starting up.

According to an embodiment the master controller50receives measurements of active power and reactive power, and the master controller50is configured to minimize active power drawn from the controllable inverter and covering reactive power with the at least one driven or nondriven alternator34when reactive power is above a reactive power threshold. Reactive power is covered with the at least one fluctuating source of AC power when reactive power is below a predetermined threshold.

According to the second control principle illustrated inFIG.3, which is combined with the first control principle, the master controller50is configured to start increasing power production through one or more internal combustion engine driven alternators34according to a defined slope in kW/see shown by the orientation of the arrow “−S1” when the measured grid frequency is below the desired grid frequency by more than a third lower margin, the third lower margin being smaller than the second lower margin. The root of the arrow “−S1” corresponds to the third lower margin. The master controller50is configured to start reducing power production through one or more internal combustion engine driven alternators34when the measured grid frequency exceeds the desired grid frequency by more than a third upper margin according to a defined slope in kW/see shown by the orientation of the arrow “+S1”. The third upper margin is smaller than the second upper margin and corresponds to the root of the arrow “+S1”. The master controller50allows the operation of the internal combustion engine driven alternators34and effected the grid frequency varies within the third lower and the third upper margin.

In an embodiment, the master controller50is configured to control the battery charge level of the battery21within a nominated control band, by increasing power withdrawn from the grid by the energy bank40when the battery charge level is above the upper limit of the control band and/or for a grid having the alternator34driven by an internal combustion engine coupled thereto, starting and/or increasing engine power when the battery charge level is below a lower limit of the control band.

In an embodiment, the master controller50is configured to charge the battery21by withdrawing energy from the grid when surplus power is available from the fluctuating source of AC power12,14.

In an embodiment control principle1, is active in parallel with control principle2.

The energy balancing function is in an embodiment based on the grid-forming battery inverter20operating in frequency control mode in parallel with controlling the alternators34. In an embodiment where the alternators are coupled to an internal combustion engine32via clutch36, the internal combustion engine32is clutched out and stopped when 100% or more renewable energy is available for the grid. In this scenario, the alternator34continues online drawn by the renewable energy or the energy from the battery21. In an embodiment, energy bank control is used to assist to dampen fast and/or large energy fluctuations. In an embodiment, the energy bank40is frequency controlled. The master controller50is configured to charge the battery21by surplus renewable energy and not from energy from an internal combustion engine32.

When there is more than a hundred percent renewable energy available to the grid, the master controller50is configured to operate according to dynamic control principle1. 100% and more renewable energy surplus is a situation where there is more renewable energy available than consumption on the consumer side. In this scenario, the master controller50is configured to clutch out and stop the internal combustion engines32while the alternators34continue online rotating in parallel with the controllable battery inverter20. The master controller50is configured to increase and decrease the amount of power consumed by the energy bank40to assists dampen energy fluctuations caused e.g. by the fluctuating sources of renewable energy and/or fluctuations in consumer demand.

In this scenario, the controllable inverter20operates in frequency control mode and controls the frequency within a deadband between the +S3Hz to −S3Hz frequency setpoints. The renewable energy sources12,14are controlled by the master controller50in response to battery charge level of the battery21within a nominated kW band in battery+S4kWh to −S4kWh. The master controller is in an embodiment configured to activate the energy bank40within deadband+S2Hz to −S2Hz frequency setpoints depending on the need for damping energy fluctuations. The deadband+S2Hz to −S2of the energy bank40can, as shown, be chosen to be within the deadband+S3to −S3of the controllable inverter20, for reducing wear and tear on the battery21and also to dampen large power variations on the grid. However, the deadband+S2Hz to −S2of the energy bank40can be chosen or adjusted to be outside the deadband+S3to −S3of the controllable inverter20, in particular to assist to dampen large power variations on the grid.

When less than 100% renewable energy is available the master controller50is configured to operate according to this second control principle. Less than 100% renewable energy is the situation where the grid demand is larger than the power available either directly from wind and or PV and/or from stored in the battery21. Internal combustion engines32are in operation and coupled to the alternators34operating with controlling the voltage and frequency of the grid in parallel with the controllable inverter21. The master controller50is configured to control the generator sets (genset)30within the deadband+S1Hz to −S1Hz frequency setpoints, to control the controllable inverter20within the deadband+S3Hz to −S3Hz setpoints, and to optionally control the activation of the energy bank40within the deadband+S2Hz to −S2Hz frequency setpoints, depending also on the need for damping energy fluctuations.

When the grid frequency increases, e.g. due to increasing renewable energy and or decreasing consumption the master controller50is configured to:decrease energy production from the combustion engine driven alternators34(gensets30) at +S1Hz,increase our consumption by the energy bank40at +S2Hz, andto increase battery charge at +S3Hz.

If the last genset30cannot operate down to zero load, the master controller50will load energy bank40with a load similar to the least genset minimum load, where after the internal combustion engine34is clutched out and stopped (preferably after a period of time (delay) in which the grid has been stable for a nominated period). Alternatively, the master controller50may charge increased charging of the battery21. Battery charging may be increased until this charging level is similar to minimum load on last genset30before internal combustion engine32is clutched out and stopped, preferably after a period of time (delay) in which the grid has been stable for a nominated period.

The active energy bank controlling40is optional. Activation of the energy bank40depends on fluctuations or risk of periods with large fluctuations or depending on the condition of the battery21. In a scenario where the grid frequency decreases, e.g. due to decreasing renewable energy and or increasing consumption the master controller50is configured to:increase production using the internal combustion engine34at −S1Hz, andto increase production from the battery21at −S3Hz.

In an embodiment in which there is no energy bank40or the energy bank40is non-active, its functionality above is eliminated in the main control method and system function without energy bank40.

If the energy bank40is loaded it can increase and decrease load. If non-loaded, the energy bank41can only increase load.

In an embodiment, a continuous load on energy bank40is used for heating purposes.

The additional storage solution is in an embodiment integrated into the above control logic and instead of reducing PV and wind, the surplus energy is the capturing into the storage solution. Additional storage may feed storage energy back into the system via the nominated grid-forming battery inverter system or by its own electrical energy generation system depending on the type of technology.

A battery21charge level band is nominated, where battery charge level is kept for having both capacity available for energy production to cover load 100% and energy charging to absorb surplus energy 100% to balance the load variations. The master controller50uses the charge level band in the battery21for control of the renewable energy production by continuously providing a maximum power reference. The charge level band is defined based on a kW-charge level band operation area in the battery21where there is the least wear and tear on the battery. The renewable energy sources12,14. e.g. wind, solar are slaves and operate within (and up to) a controlled maximum power output limit.

In an embodiment the master controller50is configured to: operate the at least one fluctuating source of AC power12,14as a slave to the grid up to a controlled maximum power output limit, to measure grid frequency, to control grid frequency with the controllable inverter20as master controller to obtain a desired grid frequency, to monitor the charge level of the battery21, and to reduce the controlled maximum power output limit when the charge level of the battery21exceeds an upper battery charge level threshold.

In an embodiment where the fluctuating source of AC power comprises a solar panel12and a wind turbine14, the master controller50comprising reducing power from the solar panel12before reducing power from the wind turbine14when reducing the maximum power level and vice versa. In an embodiment, the master controller50is configured to increase power absorbed by the energy bank40when the battery charge level exceeds the battery charge level threshold.

In an embodiment, the master controller50is configured to activate a motor and/or engine driven alternator34coupled to the grid by starting the motor or engine by coupling a running motor or engine to the alternator34when the battery charge level is below a lower battery charge level threshold.

In an embodiment the master controller50is configured to operate the at least one fluctuating source of AC power12,14as a slave to the grid up to a controlled maximum power output limit, to measure grid frequency, to control grid frequency with the controllable inverter20as master controller to obtain the desired grid frequency, to monitor the temperature of the battery21, and to absorbing surplus power with the battery21when the battery temperature is below a first battery temperature threshold, to absorb surplus power with the energy bank40when the battery temperature is above a first battery temperature threshold and/or absorb surplus power with the energy bank40when an increase in surplus power accelerates above a level defined by a first surplus power acceleration threshold. The master controller50can in this embodiment further be configured to reduce power from the at least one fluctuating source of AC power12,14when the battery temperature is above the first threshold and/or when the energy bank40is absorbing energy at a level above a first energy bank absorption capacity level.

The controllable inverter20is controlled to preferably only cover active power. The reactive power is covered by the online alternators34. Voltage can be set to be covered by the controllable inverter20and/or the online alternators34, depending on circumstances.

When power from the alternators34approaches 0 kVar, wind turbine14and or solar inverters22will be ordered to absorb a small amount of reactive power.

The number of alternators34of the total alternator fleet remaining online is determined by, but not limited to, below requirements that are constantly calculated:1. Reactive power requirements2. Short circuit effect requirements3. System electrical stability requirements incl. stability in inverter systems

For system electrical stability, the master controller50makes active use of the mechanical inertia (kinetic energy) and electrical cadence of the online alternator fleet. If no genset30with clutch36is available, then a separate condenser system (not shown) can take over the role of disengaged online alternator capacity with a similar operation strategy. Additional condenser capacity is be added if there is too little available alternator capacity in the system.

At a first nominated setpoint for reactive power in the total energy system, the master controller50commands the photovoltaic unit12and or wind turbines14to assist in reactive power production. Preferably, the wind turbines14are started before the photovoltaic unit12.

At a second nominated setpoint for reactive power in the total energy system, the master controller commands the controllable inverter20to assists in reactive power production.

The master controller is configured to monitor temperatures and cell voltage of the battery21

If battery21reaches temperature max setpoint power from the photovoltaic sources12,22is reduced before reducing power from the wind turbines until a minimum charge level in the nominated control band of the battery21is reached.

When the battery reaches a high temperature threshold, the master controller50controls the energy bank40within deadband+S2Hz to −S2Hz. The master controller50also activates the energy bank40to dampen energy fluctuations in battery21.

To protect the battery21master controller applies the following strategies:1. The controllable inverter20is set to allow increase in frequency at large power increases. For this strategy, the energy bank40will have an activation set point after +S3Hz and will here start to assist to dampen the large power increase.2. The energy bank increases load based on charge level in battery21increasing above upper charge level setpoint in control band in battery+S4kWh at the same time as power from the wind turbines14wind and/or solar panels12is reduced.3. The energy bank41is commanded to put in load as per ramp based on increase in power into battery21when a fast increase in power to the battery21or an increase in frequency is identified.

The system comprises one or more fuel generating units, configured for generating a fuel for use in the internal combustion engine (s)132from power from surplus energy from the fluctuating sources of renewable energy12,14, a fuel storage tank for storing the generated fuel, and a system for supplying the stored fuel to the internal combustion engine (s)132when operation of the internal combustion engines132is needed to drive the selectively driven alternators32. In an embodiment, the system is provided with one or more hydrogen generating units (electrolysis units)64. Preferably, the one or more electrolysis units64are powered exclusively from the sources of renewable energy, i.e. the fluctuating sources of renewable energy in the form of the photovoltaic source12,22and/or the wind turbines14. The electrolysis unit (s)64can be directly electrically coupled to one or more of the sources of renewable energy12,14or can be coupled to the busbar10as shown inFIG.5.

InFIG.1a hydrogen generating unit (electrolysis unit)64is powered by electric power from the photovoltaic sources12,22, another electrolysis unit64is powered by electric power from the wind turbines14, and yet another electrolysis unit64is powered by AC power from the busbar10. However, it is understood that is not required that the system has more than one electrolysis unit64. The electrolysis unit64has an inlet for water and hydrogen outlet and an oxygen outlet. As illustrated inFIG.5, the hydrogen outlet of the electrolyzers unit64is connected to a hydrogen inlet of a hydrogen storage tank136by a feed conduit that includes a compressor unit140driven by an electric motor66. The hydrogen is either stored at high pressure in the hydrogen storage tank136, or the hydrogen is liquefied stored in liquid form in the hydrogen storage tank136. The hydrogen storage tank136part of the hydrogen fuel system70. The hydrogen fuel system70comprises a hydrogen supply line that connects a hydrogen outlet of the hydrogen storage tank136to the internal combustion engine132, preferably to the hydrogen fuel valves of the internal combustion engine132.

A high pressure hydrogen pump134driven by an electric motor138raises the pressure of the hydrogen in the hydrogen supply line to the required injection pressure. In an embodiment, the fuel valves of the engine may include a pressure booster for further increase of the pressure of the hydrogen fuel for injection into the engine. In an embodiment, the engine is a compression-ignition engine, in which the hydrogen is injected at or near the top dead center of the pistons. In another moment the engine is a spark-ignition engine, in which the fuel is mixed with the charging air the air-fuel mixture is compressed and ignited by a spark for other ignition means at or near top dead center (TDC) of the pistons. If the hydrogen is stored in liquid form in the storage tank136, the hydrogen supply line will include a vaporizer135for vaporizing the hydrogen before supplied to the internal combustion engine/fuel valves of the internal combustion engine. In an embodiment the internal combustion engine is a dual fuel engine, that is configured in one mode to operate on hydrogen and in another mode to operate on a conventional fuel, e.g. fuel oil.

The cells of the electrolysis unit64comprise in the present embodiment polymer electrolyte membrane cells (PEM) or alkaline electrolysis cells (AECs). Alkaline electrolysers generally use nickel catalysts and are inexpensive but not very efficient. PEM electrolysers, generally use platinum group metal catalysts are more efficient and can operate at higher current densities. PEM electrolysis cells typically operate below 100° C. and are comparatively simple and accept widely varying voltage inputs which renders them suitable for use with renewable sources of energy such as solar PV or wind turbines. AECs operate optimally at high concentrations electrolyte (KOH or potassium carbonate) and at high temperatures, typically near 200° C.

The fuel cell85comprises an electrochemical cell that converts the chemical energy of the hydrogen with an oxidizing agent, preferably oxygen from air, into electricity through a pair of redox reactions. The fuel cell85is coupled to the hydrogen fuel system70. A hydrogen supply line connects a hydrogen inlet of the fuel cell85to the outlet of the hydrogen storage tank136. In an embodiment, the engine supply line includes a vaporizer84and a control valve82that controls the flow of hydrogen from the hydrogen storage tank136to the fuel cell85. The control valve82is coupled to the master controller50.

The one or more selectively driven alternators34, are selectively operably couplable by a clutch36to the internal combustion engine132operated on hydrogen (or a mixture of hydrogen and another fuel). The clutch36is controlled by the master controller50. When the role of the one or more selectively driven alternators34needs to be changed from a role of creating inertia to a role of also maintaining the network frequency, the master controller50will start up the internal combustion engine132and thereafter engage the clutch36so that the already rotating alternator34is coupled to and driven by the internal combustion engine132. Thus, the master controller50is configured to clutch-in the internal combustion engine132when the internal combustion engine132is at synchronous rpm with the selectively driven alternator34.

The internal combustion engine132is equipped for pre-pressuring and heating for optimal operation in lower loads and for having fast response and startup with one or more of below technical solutions—but not limited to—as follows:

For pre-pressuring the engine, the selectively driven alternator34is equipped with an air duct system for ventilation air for connecting to nominated engine filter housing as m described in EP0745186 or alternatively, the internal combustion engine132is equipped with a separate pre-pressuring system for similar pressure effect to nominated engine filter housing.

For control of heating of the internal combustion engine132the air cooler system is separated from the engine and controlled by temperature as per system described in EP0745186.

For control of heating of the internal combustion engine132the internal combustion engine132is equipped with a pre-heating system described in EP0745186.

The master controller50is configured to powering said at least one hydrogen generating unit64with power from said at least one fluctuating source of electric power12,14when, and preferably only when, actual electric power generated by said at least one fluctuating source of electric power12,14exceeds actual consumer AC power demand and battery charge level have reached an upper charge level set point and simultaneously hydrogen storage capacity is available in said hydrogen storage unit136, so that hydrogen (and oxygen) is generated with said at least one hydrogen generating unit64. The hydrogen generated by said at least one hydrogen generating unit64is stored in said hydrogen storage unit, e.g. hydrogen storage tank136.

The master controller50is also configured to generate AC power with said at least one selectively driven alternator34by combusting hydrogen from said hydrogen storage unit136(or a mixture of hydrogen from said hydrogen storage unit136and another fuel) in said internal combustion engine132, when actual electric power generated by said at least one fluctuating source of electric power12,14is less than the actual consumer AC power demand and battery charge level has reached a lower charge level set point and simultaneously the amount of hydrogen in said hydrogen storage unit136is above a hydrogen amount threshold. The hydrogen amount threshold is greater than or equal to 0.

The master controller50is configured to generate AC power with said at least one selectively driven alternator34by combusting hydrogen from said hydrogen storage unit136(or a mixture of hydrogen from said hydrogen storage unit136and another fuel) in said internal combustion engine132, when the charge level of said electric battery21is below a first battery charge level threshold.

The master controller50is configured to ramp up and down hydrogen production with said electrolysis system64as a function, preferably a proportional correlation, of the availability of actual surplus electric power generated by said at least one fluctuating source of electric power12,14. The actual surplus electric power is defined as the amount to which the actual power generated by said at least one fluctuating source of electric power12,14exceeds the actual consumer AC power demand. The master controller50is in an embodiment configured to ramp up and down hydrogen production with the said hydrogen generating unit64as a function, preferably a proportional correlation, of the frequency of the grid. Both methods of ramping up and down the activity of the hydrogen production unit64can be combined.

In an embodiment, hydrogen generated by said hydrogen generating unit64is pressurized using a high-pressure pump140driven by an electric drive motor66. In an embodiment, the hydrogen is also liquefied in the process. The master controller50is configured to powering said electric drive motor138with electric power generated by at least one fluctuating source of electric power12,14.

In embodiment, the internal combustion engine132operates on a mixture hydrogen from the hydrogen storage unit136and another fuel such as fuel oil (pilot oil). The fuel oil can be supplied to the internal combustion engine separately from the hydrogen. The fuel oil can be supplied as a pilot oil, i.e. as an oil that ensures ignition. Preferably the fuel oil is injected at high pressure from fuel valves and the injection of the fuel oil can be timed for timed ignition.

In an embodiment, the internal combustion engine132is a compression ignited engine, i.e. an engine operating to the Diesel principle, and fuel is injected when the piston (s) is (are) at or near top dead center.

In an embodiment, the internal combustion engine132operates according to the Otto principle, and a mixture of fuel and charging air is compressed during the stroke of the piston (s) from bottom dead center to top dead center.

In an embodiment the mixture of hydrogen from the hydrogen storage unit and another fuel comprises a mixture of hydrogen from the hydrogen storage unit and one or more of petroleum gas, natural gas, syngas, biogas, ammonia. Biogas can be a mixture of gases, primarily consisting of methane, carbon dioxide and hydrogen sulphide, produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste and food waste.

The controller is configured to determine said actual consumer AC power demand the actual electric power generated at least one fluctuating source of electric power12,14and said actual consumer AC power demand with the actual electric power generated by at least one fluctuating source of electric power12,14.

The master controller50is configured to generate AC power with said at least one selectively driven alternator34by combusting fuel other than hydrogen from the hydrogen storage unit136, e.g. fuel from a fuel oil tank90, in said internal combustion engine132, when simultaneously the amount of hydrogen in said hydrogen storage unit136is below a hydrogen amount threshold and simultaneously battery charge level has reached a lower charge level set point, and preferably actual electric power generated by said at least one fluctuating source of electric power12,14is less than the consumer AC power demand.

The master controller50is configured to generate AC power with said at fuel cell85by converting hydrogen from said hydrogen storage unit136into DC power and converting said DC power into AC power with said inverter when said when actual electric power generated by said at least one fluctuating source of electric power12,14is less than the consumer AC power demand and simultaneously the amount of hydrogen in said hydrogen storage unit136is above a hydrogen amount threshold, said hydrogen amount threshold being greater than or equal to 0.

In an embodiment the master controller50is configured to controlgrid frequency with the controllable inverter20as master controller to obtain a desired grid frequency, supply power from an electric battery21through the controllable inverter (20) to the grid when the measured grid frequency is below the desired grid frequency by more than a first lower margin, and withdraw power through the controllable inverter20from the grid to the electric battery20when the measured grid frequency is above the desired grid frequency by more than a second first upper margin.

In an embodiment the master controller50is configured to increase AC power production with said fuel cell85and said inverter20according to a defined slope when the measured grid frequency is below the desired grid frequency by more than a fourth lower margin, decreasing AC power production with said fuel cell85and said inverter20according to a defined slope when the measured grid frequency exceeds the desired grid frequency by more than a fourth upper margin.

FIG.6shows another embodiment of the system. In this embodiment, structures and features that are the same or similar to corresponding structures and features previously described or shown herein are denoted by the same reference numeral as previously used for simplicity. In this embodiment, the system comprises a two-stage power to gas system170, in which the hydrogen that is generated in the hydrolysis unit64is converted into fuel gas, e.g. syngas, methane, or liquid petroleum gas (LPG) by a hydrogen to fuel gas conversion unit164. The hydrogen to fuel gas conversion unit164is powered e.g. by a connection with the busbar10. The fuel gas that is generated by the fuel conversion unit164is stored in a fuel gas storage unit176. In this embodiment, the master controller50is configured in a similar fashion to the embodiment above, to use only electrical power for generating fuel gas when there is a surplus of power from the fluctuating sources of renewable energy. The fuel gas stored in the fuel gas storage unit176is supplied to the internal combustion engine via a fuel pump174that is driven by an electric motor178, and that is under control of the master controller50. The operation and control of the two-stage power to gas system170, is essentially identical to the operation of the hydrogen fuel system70.

In an embodiment (not shown), the system comprises a two-stage power to liquid fuel system, in which hydrogen that is generated in the hydrolysis unit64is converted into a liquid fuel, e.g. methanol by a hydrogen to liquid fuel conversion unit. The operation and control of the two-stage power to gas system, is essentially identical to the operation of the hydrogen fuel system70.

In an embodiment the system uses a single-stage power to gas system to produce methane using such as reversible solid oxide cell (ReSOC) technology. In this embodiment, methane produced using surplus energy from the fluctuating sources of renewable energy12,22is stored in a methane tank and supplied by the fuel supply system to the internal combustion engine (s)132when needed. The operation and control of the one-stage power to gas system, is essentially identical to the operation of the hydrogen fuel system70.

The various aspects and implementations have been described in conjunction with various embodiments herein. However, other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed subject-matter, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. A single controller or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage.

The reference signs used in the claims shall not be construed as limiting the scope. Unless otherwise indicated, the drawings are intended to be read (e.g., cross-hatching, arrangement of parts, proportion, degree, etc.) together with the specification, and are to be considered a portion of the entire written description of this disclosure.