Patent Application
20110137481
The invention relates generally to power grid energy and more particularly to a system and method for efficiently providing battery energy to a power grid.
The supply of electricity and the demand for electricity must be well matched in order to maintain a stable power system. The energy delivered to the system is generally determined on a day-ahead basis; and the second-to-second mismatch between supply and demand is addressed by a separate function or a separate market (if applicable). This function (and/or market) is sometimes met by functions called frequency regulation, spinning reserve and other grid ancillary services. Further, this function is required to maintain a stable system frequency.
About 1% of the power generation at every second of a day is ramping up and down to address the short term imbalance between load and generation (demand and supply). Today, this function is primarily being served by combined cycle plant and gas turbine plants that are backed down to a lower (and less efficient operating point, delivering electricity sub-optimally) to provide both ramp up and ramp down capability. In return for providing the energy at a sub-optimal efficiency, a capacity payment (if a market exists for frequency regulation) is provided to the plant for ramping up and down in response to the needs of the grid. As the penetration of renewable energy increases, the amount of generation needed to provide frequency regulation will increase.
In view of the foregoing, it would be advantageous to provide a system and method for enhancing frequency regulation of a power grid supplied by renewable energy sources. It would also be beneficial if the system and method were to provide energy to the power grid in a manner to achieve optimal profitability.
Briefly, in accordance with one embodiment, a system for providing energy to a power grid comprises:
a renewable energy source comprising one or more power converters integrated therewith;
a battery-based energy storage system integrated with the renewable energy source; and
a control system comprising an algorithmic software, wherein at least one power converter together with the battery-based energy storage system are directed by the control system in response to the algorithmic software to supply stored battery energy to the grid when the cost of extracting the supplied energy from the battery-based energy storage system is less than the market price paid for the supplied energy extracted from the battery-based energy storage system.
According to another embodiment, a method of providing energy to a power grid comprises:
providing a renewable energy source comprising one or more power converters integrated therewith;
providing a battery-based energy storage system integrated with the renewable energy source;
providing a control system comprising an algorithmic software; and
directing at least one power converter together with the battery-based energy storage system via the control system in response to the algorithmic software such that stored battery energy is supplied to the grid when the cost of extracting the supplied energy from the battery-based energy storage system is less than the market price paid for the supplied energy extracted from the battery-based energy storage system.
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
While the above-identified drawing figures set forth alternative embodiments, other embodiments of the present invention are also contemplated, as noted in the discussion. In all cases, this disclosure presents illustrated embodiments of the present invention by way of representation and not limitation. Numerous other modifications and embodiments can be devised by those skilled in the art which fall within the scope and spirit of the principles of this invention.
The renewable energy source(s) 16 according to one embodiment generates a multi-phase AC voltage 34 that is converted to a DC voltage 24 that is subsequently reconverted into an AC voltage at a desired voltage level. A transformer 40 converts the AC voltage to a desired power grid AC voltage.
As the penetration of renewable energy increases, the amount of generation needed to provide frequency regulation of the power grid 26 will increase, as stated above. The renewable energy system 10 provides the foregoing frequency regulation by supplying additional energy to power grid 26; however, this additional energy is supplied to the power grid 26 when the cost of extracting the supplied energy from the battery-based energy storage system 12 is less than the market price paid for the stored battery energy supplied to the grid 26 according to one embodiment. According to one embodiment, battery-based energy storage system 12 includes one or more batteries 14 for storing a DC charge/voltage. Each battery 14 may be charged/recharged via a corresponding bi-directional DC-DC converter 35 connected to the DC bus voltage 24 or a corresponding bi-directional AC-DC converter 36 connected to the AC bus voltage 34. Each bi-directional converter advantageously allows energy to be supplied to the grid in alternating fashion from a renewable energy source and a stored battery energy source during periods when the supply of renewable energy is variable and not satisfactorily stable.
Control system 20 operates in response to algorithmic software integrated therein and described in further detail below with reference to
Each power converter/inverter pair (28, 29), (35, 37) and (36, 38) operates in response to the command signals generated via the control system 20. When so instructed via an algorithmic software such as described below with reference to
A control system 20 including an algorithmic software operates to control at least one power converter/inverter pair (28, 29), (128, 129), (35, 37), (43, 45) together with the battery-based energy storage system 210 to supply stored battery energy to the grid 26 when the cost of extracting the supplied energy from the shared battery-based energy storage system 210 is less than the market price paid for the stored battery energy extracted from the shared battery-based energy storage system 210 according to one embodiment.
Each renewable energy source 15, 16 in combination with its respective generator(s) or inverter(s) generates a respective multi-phase AC voltage 34, 134 that is converted to a respective DC voltage 24, 124 that is subsequently reconverted into an AC voltage at voltage level required by the corresponding power grid 26. A corresponding transformer 40, 140 converts the AC voltage to the requisite power grid AC voltage.
As the penetration of renewable energy increases, the amount of generation needed to provide frequency regulation of the power grid 26 will increase, as stated above. The renewable energy system 200 provides the foregoing frequency regulation by supplying energy to power grid 26 during periods when the cost of extracting the supplied energy from the battery-based energy storage system 210 is less than the market price paid for the stored battery energy supplied by the battery-based energy storage system 210 to the grid 26 according to one embodiment. According to one embodiment, battery-based energy storage system 210 includes one or more batteries 114 for storing a DC charge/voltage. Each battery 114 may be charged/recharged via a corresponding bi-directional DC-DC converter 35, 43 connected to a respective DC bus voltage 24, 124.
Control system 20 operates in response to algorithmic software integrated therein and described in greater detail below with reference to
Each power converter/inverter pair (28, 29), (128, 129), (35, 37) and (43, 45) operates in response to the command signals generated via the control system 20. When so instructed via an algorithmic software such as described below with reference to
Algorithmic software 300 includes an optimization algorithm 302 that determines control system 20 command signals 314 based upon market price forecast data 304, renewable energy forecast data 306 such as wind forecast data, and battery energy storage system (BESS) economic and performance data 308 according to one embodiment. The market price forecast data 304 is based on previous market data provided via a third party according to one embodiment. The wind forecast data 306 is based upon turbine plant constraints such as estimated available wind turbine inverter capacity 310 based on wind power forecast data according to one embodiment. The BESS economic data 308 is based on 1) battery life data 312 that determines battery percent depth of discharge required for meeting particular energy demands of the power grid according to one embodiment, 2) the market price forecast data 304, and 3) battery replacement/recharge time based on the estimated available wind turbine inverter capacity. More particularly, the BESS economic data 308 determines the cost of using the battery-based energy storage system 12, 210 to supply energy to the grid 26.
The optimization algorithm 302 then compares the market price forecast data 304 with the cost of extracting the stored battery energy supplied to the power grid 26 via the battery-based energy storage system 210 as determined from the BESS economic model 308 and makes a determination as to whether the cost of extracting the supplied energy from the battery-based energy storage system 12, 210 is less than the market price paid for the supplied energy.
Control system commands 314 are then generated and communicated to the renewable energy source power converter(s)/inverter(s), and each corresponding battery-based energy storage system 12, 210 power convert/inverter to control whether energy is supplied to the power grid 26 via a renewable energy source or a battery-based energy storage system. A renewable energy source 15, 16 may be used when available, even during periods when stored battery energy is available, in certain applications if the cost of extracting the supplied energy from the battery-based energy storage system 12, 210 is greater than the market price paid for stored battery energy.
The cost of using stored battery energy is dependent upon the depth of battery discharge required to supply the energy to the grid, because the battery(s) then need to be recharged via a renewable energy source or the grid itself to replace the energy extracted from the battery(s) and thus restore the battery(s) to their full potential. If the cost to recharge the battery(s) is greater than the cost of discharging the battery(s), then a cost benefit is not achieved, and stored battery energy will not be extracted from the battery-based energy storage system 12, 210.
In summary explanation, a system embodiment has been described for providing energy to a power grid. The embodiment includes at least one renewable energy source and one or more power converters integrated therewith. A battery-based energy storage system is also integrated with the renewable energy source. A control system includes an algorithmic software such that at least one power converter together with the battery-based energy storage system are directed by the control system in response to the algorithmic software to supply stored battery energy to the grid when the cost of extracting the supplied energy from the battery-based energy storage system is less than the market price paid for the supplied energy extracted from the battery-based energy storage system.
The embodied methodologies described herein estimate the optimal amount of energy to dispatch from a battery-based energy storage device/system based on the opportunity cost of providing energy, regulation response or both. Since the energy storage device/system can share an inverter with a renewable energy source such as a wind turbine, there is a decision that needs to be made about whether the combined system should provide energy from a battery or from the wind rotor according to one embodiment. Factors of consideration include 1) information about the impact of a single charge and discharge cycle on the life of the storage device/system and a comparison of this impact to the perceived benefit of offering this additional energy in the form of regulation service to a power system/grid from the storage device/system; 2) information about near-future (day ahead to hour ahead) energy and ancillary prices to quantify the value of providing energy at the expense of ancillary services or vice versa and/or information about the opportunity cost of other generation providing ancillary services compared to the cost of energy storage providing this service; and 3) information about the forecasted wind power which can be refined and incorporated into an updated forecast as the timeframe is approached to quantify the value of providing energy at the expense of ancillary services or vice versa.
While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
