PHOTOVOLTAIC POWER MANAGEMENT

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from U.S. Provisional Patent Application No.

62/578,385, filed on October 27, 2017, which is incorporated by reference herein in its entirety.

BACKGROUND

[0002] The present specification generally relates to solar power plants and, more specifically, to systems and methods for modulating energy production.

[0003] Solar power plants generate energy from arrays of photovoltaic modules. Energy production capacity from photovoltaic modules can vary due to factors such as weather and available light intensity. At times, energy production capacity can exceed energy demand, equipment load rating, or transmission capacity. Systems for regulating power generation and grid management are important for efficient and reliable energy production.

[0004] Accordingly, a need exists for alternative systems and methods to control photovoltaic energy production.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] The patent or application file may contain one or more drawings executed in color and/or one or more photographs. Copies of this patent or patent application publication with color drawing(s) and/or photograph(s) will be provided by the U.S. Patent and Trademark Office upon request and payment of the necessary fees.

[0006] The embodiments set forth in the drawings are illustrative and exemplary in nature and not intended to limit the subject matter defined by the claims. The following detailed description of the illustrative embodiments can be understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals.

[0007] FIG. 1 schematically depicts a solar power plant system according to one or more embodiments shown and described herein.

[0008] FIGS. 2A, 2B, and 2C depict an example of solar tracking for a PV array. [0009] FIGS. 3 A and 3B depict examples of reduced power output antitracking positions according to one or more embodiments shown and described herein.

[0010] FIG. 4 is a chart showing an example of power generation capacity relative to a set point.

[0011] FIG. 5 shows representative IV curves showing the relationships of current and voltage to MPP and Voc (top); and shows power output relative to voltage (bottom).

[0012] FIG. 6 graphically depicts power output reduction and module temperature data from an example system.

[0013] FIG. 7 shows a comparison of voltage change with curtailment in an example system with and without antitracking.

[0014] FIGS. 8 A and 8B show DC power and voltage, respectively, for a period following the application of curtailment, for selected curtailment levels, in an example system without antitracking.

[0015] FIGS. 9 A, 9B, 9C, and 9D show data for selected curtailment levels, in an example system with antitracking, for a period following the application of curtailment.

DETAILED DESCRIPTION

[0016] Provided are systems and methods for use in a solar power plant system. An exemplary system comprises photovoltaic (PV) arrays which generate direct current (DC) electricity from solar radiation. The arrays include mounted PV modules. The mounting system for the arrays may include solar trackers with actuators to angle the arrays toward incident light. The generated DC electricity is then transmitted to a power conversion station and through additional components to an electrical power grid or other distribution network.

[0017] The electrical power plant operator or grid operating authority may, from time to time, issue a power curtailment request inclusive of a power set point which varies with factors such as load demand, transmission capacity, and/or economic optimization. A state-of-the-art utility-scale solar power plant, connected to the grid, may utilize control capability to reduce energy output to a power set point in accordance with the operator request. Typical curtailment measures rely primarily on electronic methods of disconnection or of inverter voltage control to adjust arrays of PV modules causing the modules to deviate from a usual operating voltage and therefore reducing plant power output. These methods may result in higher temperature conditions and higher voltage levels for both modules and inverters, which in turn results in added operational stress, accelerated power output degradation, and increased risk of premature damage to these components.

[0018] Within an electrical power plant, pieces of equipment have operating parameters and power load ratings which may function as an upper or lower bound of capacity for a specific piece of equipment. For example, an inverter typically has maximum DC inputs (voltage, current) and maximum AC outputs (voltage, current) among others.

[0019] Methods and systems are described which provide energy output reduction using system processors coupled to the tracking system and the power sensor. Exemplary systems and methods may be combined with additional features or processes. Such features include control systems for photovoltaic power plants. Various embodiments of the system and operation of the system will be described in more detail herein.

[0020] Referring now to FIG. 1, an exemplary solar power plant system 100 is depicted.

It should be understood that the plant devices shown in FIG. 1 are only exemplary devices, and solar power plant systems may include other additional plant devices known in the art and may have one device performing the function of one or more depicted devices. The depicted system is simplified to show representative types of devices in the system and it is to be understood that the system includes pluralities of the devices shown.

[0021] The solar power plant system 100 includes PV modules 101. Multiple modules are connected in parallel or in series. Modules 101 are arranged into arrays 110 which are oriented at the same angle relative to the ground or a mounting surface. Multiple strings 105 of one or more arrays 110 can be connected in parallel to a single output at a combiner box 120. Combiner boxes 120 combine DC electricity received from multiple arrays 110 and transmit the DC electricity to a power conversion station (PCS) 125.

[0022] One or more arrays 110 are connected to a single PCS 125. The PCS performs

DC to AC power conversion, which is performed via an inverter 130. The PCS then increases the AC voltage output from the inverter 130 using a transformer 135. The output of multiple PCS devices are supplied to the photovoltaic combining switchgear (PVCS) 140.

[0023] The inverters 130 of the PCS 125 a control the DC power output of arrays by modulating voltage. Inverters may have maximum power point tracking algorithms. The inverters provide a fast response time to control AC output. Utility scale inverters include, for example, Power Electronics HEC-US V1500 and SMA Sunny Central 750CP-US. [0024] Accordingly, the output power from multiple PCSs are collected at the PVCS 140.

The PVCS 140 combines the output from the multiple PCSs and increases the current in a manner analogous to the DC combiner boxes. Additionally, the PVCS includes fused switch gear and metering transformers for monitoring current and voltage levels. The PVCS 140 transmits the output power to the substation 145 via collector lines, which have an increased wire diameter compared to the feeder lines.

[0025] The substation 145 serves as the point of common coupling between the solar power plant and the power grid. Specifically, the substation is connected to the transmission lines of the power grid 150. Since the transmission lines traverse much larger distances than the runs of the solar power plant, the substation operates to step up the voltage of the power received via the collector lines. The substation includes transformers that step up the voltage to a level suitable for the grid voltage specified for the transmission line. Accordingly, the power grid dictates the output of the substation. Additionally, the substation includes current and voltage metering equipment to monitor the amount of power supplied by the solar power plant to the power grid.

[0026] As an example, in a typical installation, multiple strings of about 1.5kV each are connected in parallel to a power conversion station (PCS) via a larger conductor. At the PCS, the inverter converts the voltage during the conversion step from about 1.5 kV DC to about 600 V AC. A second function of the PCS is to increase the AC voltage output from the inverter using a transformer to about 34.5 kV AC. Typically, each PCS is rated to output between about 1.6 and about 4 MW AC. The output of multiple PCS devices are supplied to the photovoltaic combining switchgear (PVCS). Each PVCS is rated to output between about 30 and about 40 MW AC. The substation includes transformers that step up the voltage from 34.5 kV to between 69 kV to 765 kV, depending on the grid voltage specified for the transmission line.

[0027] Components of the system 100 can be communicatively coupled by one or more communication channels 175 to one or more processors 165 and one or more memory components 160. As used herein, the term "communicatively coupled" means that the components are capable of exchanging data signals with one another such as, for example, electrical signals via conductive medium, electromagnetic signals via air, optical signals via optical waveguides, and the like.

[0028] According to the embodiments described herein, a processor 165 means any device capable of executing machine readable instructions. Accordingly, each of the one or more processors may be a controller (e.g., programmable logic controller (PLC) or proportional- integral-derivative controller (PID controller), an integrated circuit, a microchip, a computer, or any other computing device. The one or more processors can be configured to execute logic or software and perform functions that control the movement of the solar modules. Specifically, the one or more processors can be communicatively coupled to one or more memory components 160 that can store the logic and/or input received by the one or more processors. The memory components 160 described herein may be RAM, ROM, a flash memory, a hard drive, a non- transitory computer-readable medium, or any device capable of storing machine readable instructions.

[0029] Embodiments of the present disclosure comprise logic that includes machine readable instructions or an algorithm written in any programming language of any generation (e.g., 1GL, 2GL, 3GL, 4GL, or 5GL) such as, e.g., machine language that may be directly executed by the processor 165, or assembly language, object-oriented programming (OOP), scripting languages, microcode, etc., that may be compiled or assembled into machine readable instructions and stored on a machine readable medium. Alternatively, the logic or algorithm may be written in a hardware description language (HDL), such as logic implemented via either a field-programmable gate array (FPGA) configuration, an application-specific integrated circuit (ASIC), and their equivalents. Accordingly, the logic may be implemented in any conventional computer programming language, as pre-programmed hardware elements, or as a combination of hardware and software components.

[0030] The system includes manually generated SCADA or automated generation control

(AGC) inputs that may define power set points or other grid operator control functions.

[0031] The system 100 includes power sensors 170. The power sensors 170 receive information about grid conditions, such as DC or AC energy meters, current density, and voltage meters. The power sensors 170 may be placed in multiple locations throughout the system 100 to detect and monitor power conditions. The system may include other power management or storage components, such as batteries, and their associated metrology.

[0032] The system 100 includes ambient condition sensors 155. The ambient condition sensors 155 receive information about real-time conditions, such as temperature, wind, and light- intensity. The ambient condition sensors 155 may be placed in multiple locations throughout the system 100 to detect and monitor real-time ambient conditions, including environmental information. Collected data may include, but is not limited to: light intensity, wind speed, wind direction, air temperature, module temperature, tilt angle, array position, module location, light spectra, precipitation, and humidity. [0033] The system 100 includes trackers 115. Trackers tilt one or more arrays 110 and may use a plurality of actuators and motors in communication with a tracker controller, comprising memory 160 and processors 165. Controllers may use various methods, such as preprogrammed sun-path data supplemented with GPS sensor timing or real-time clock to establish tracking path and timing logic. Tracker controllers may use data from ambient condition sensors 155 with a light-intensity sensor and algorithm to dynamically 'hunt' for optimal tilt angle maximizing incident light. A tracker controller 160/165 sends instructions to individual or ganged motor, pneumatic, or alternate drive mechanisms to alter array tilt to follow the sun for highest energy production. The tracker controller 160/165 may use wind sensor input to detect conditions that could damage a panel and actuate the tracker 115 to move arrays 110 to a 'stow' position to protect against high wind damage. Trackers may include single axis or dual axis tilt construction and control.

[0034] FIGS. 2A, 2B, and 2C depict an example of solar tracking. The tracker 115 tilts the array 110 to an angle to receive solar irradiance. In typical conditions, the tracker tilts the array surface substantially normal to the path of incoming sunlight 200 to maximize incident light. The angle of the sun, or the path of peak irradiance 200, relative to the array changes in a predictable manner based on daily and seasonal changes.

[0035] State of the art trackers may operate with a nominal 90-120 degree range of motion and can traverse the full range of motion in less than 5 minutes. Some trackers may operate with a 45 degree range of motion and traverse the full range of motion in about 20 minutes.

[0036] Under typical operating conditions, the tracker 115 tilts the array 110 to optimize energy production by optimizing incident irradiance under most usual ambient conditions. When multiple rows are placed in an installation, early and late day low sun angles combined with maximum tracker tilt angles may cause shading of modules in adjacent rows. Crystalline silicon PV modules have a non-linear response to shading of modules and can lose much more power in partially shaded conditions than from a suboptimal angle of incident light. For example, in some single crystalline modules, 10% shading reduces power production by 30%. Thus, a capability, often called back tracking, may include tracking the sun position but tilting the array at an angle that is offset from a directly perpendicular incident irradiance angle to avoid row-to-row module shading. Back tracking may reduce irradiance received by a module or set of modules, but increases, or seeks to maximize, total irradiance received by the array or system. In some instances this tilt is approximately 1-30 degrees offset. Tilt may be adjusted periodically, continuously, at set intervals, and/or in response to conditions detected by the ambient condition sensors.

[0037] In high wind conditions that approach the design limits of trackers, regardless of sun position, the tracker may move the array to a stow position to mitigate wind load damage risk. The stow position may comprise a horizontal position relative to the ground.

[0038] When series-connected strings of modules are grouped together in parallel to comprise an array, the operating behavior can be represented by an IV curve. The power output (P) of a PV array is the product of the current (I) and voltage (V) at a given operating point on its IV curve, which is represented in the top chart of FIG. 5. The lower chart of FIG. 5 shows power output as a function of voltage.

[0039] Two IV curves are shown on the top chart with current increasing along the y-axis and voltage increasing along the x-axis. The point where the IV curve meets the y-axis indicates the short circuit current (Isc). The Isc is the maximum current that the array can provide and it occurs when the array is short circuited and no power is produced. The point where the IV curve meets the x-axis indicates zero current or "open circuit" (Voc). At Voc a maximum voltage is produced with no power production.

[0040] An example of an array operating under an irradiance condition of full sun with an irradiance of about 1000W/m ² is represented in one IV curve. The other IV curve shows an example of the same array operating under an irradiance condition of half sun with an irradiance of about 500W/m ² . Irradiance levels can decrease due to factors such as clouds, haze, dust, or when the sun is near the horizon. Isc is directly proportional to the irradiance, while irradiance has only a small effect on Voc.

[0041] Along the x-axis at zero current or "open circuit," a maximum voltage is produced

(Voc) 520 with no power production, and along the y-axis at zero voltage or "short circuit," a maximum current is produced (Isc) with no power production. At any other operating conditions, the product of these is the total power (P). The achievable maximum power output (PMAX or MPP) is defined by the MPP point 500, 505 on each IV curve that gives the largest product of current multiplied by voltage, I * V. The voltage associated with MPP is shown on the x-axis as VMP 510. The lower chart of FIG. 5 shows power output as a function of voltage for the array in full sun and half sun irradiance levels.

[0042] Referring now to FIG. 4, a solar power array produces power which can be represented graphically to show a ramp up period in the morning, a peak output during the day and a decreasing output in the late afternoon or evening. In mid-day clear-sky conditions, a power output of an array may exceed a set-point or load capacity of its inverter. Likewise, in good conditions, an entire power plant may have generation capacity that exceeds an output set- point or target level. FIG. 4 shows a set point 400, excess power generation capacity 410 above the set point, and start 420 and end 430 times associated with the excess power generation capacity 410. At a plant-level, reducing the AC power output is called curtailment. At the level of inverters and an associated array, reducing the DC input power is called clipping.

[0043] A power plant operator or grid system operator may from time to time need to partially or fully reduce the output power of a power plant due to economic or grid reliability factors. A manual plant control signal or automated grid control signal may be generated inclusive of a plant power output set point and required response time. The power set point and required response time may vary with economic or physical factors such as load demand and transmission capacity. The power set point may be a forecast signal for day-ahead operation, or may be realtime. When power provided by the power plant is greater than the power output set point, curtailment measures are taken to reduce energy output.

[0044] One established curtailment method includes reducing plant power by

disconnecting one or more inverters entirely with all modules connected to that inverter forced into open circuit. As shown in FIG. 5, in the Voc condition, current is reduced to zero while voltage is increased to a peak Voc voltage point 520 above the optimal operating voltage or MPP voltage (VMP) 510.

[0045] A variant of this curtailment method may equally curtail the plant level output by partially reducing the output level of many inverters in the plant rather than disconnecting them entirely. In this case, the inverter typically adjusts DC voltage away from the MPP to reduce the DC power. This is typically done by increasing voltage above the MPP voltage, but below the Voc voltage, thus moving the operating point of the module array to a different point on the IV curve where the output power of the DC array is reduced. For example, in FIG. 5, a half-power 515 point by this method is shown on the IV curve and power output curve. Both higher voltage and higher temperature are known stressors which can accelerate power output degradation and increase failure risk for PV modules. Maintaining the high voltage in the open circuit condition, and associated heating, for long periods may cause damage or degradation to PV modules. It can also damage some types of inverters.

[0046] Another relevant and common operating condition, commonly referred to as

"clipping," occurs when the DC power from the PV array exceeds the maximum rated input level for the inverter. When an inverter is clipping, its AC output is held at its maximum, while the DC power from the PV array is controlled to avoid exceeding the inverters' rated input limits. This clipping behavior is the result of hardware design and cost optimization practice of installing a higher level of DC capacity than allowed by the inverters' maximum ratings to maximize energy production in all non-peak production hours while sacrificing some DC capacity during the relatively fewer clipping hours. Rather than a forced plant control signal common to curtailment, clipping is typically controlled by the inverter, and protects the inverter from input in excess of its rating. In response to this clipping condition, the inverter typically behaves in the same fashion as the partial curtailment scenario about, and adjusts DC voltage away from the MPP to reduce the DC power. This is typically done by increasing voltage above the MPP voltage, but below the Voc voltage, thus moving the operating point of the module array to a different point on the IV curve where the output power of the DC array is reduced.

Increasing the DC array module voltage above the MPP voltage can also cause a higher module operating temperature. Both higher voltage and higher temperature are known stressors which can cause power output degradation and higher risk of failures of PV modules.

[0047] Referring now to FIGS. 3A-3B, a method to achieve controlled AC energy output reduction can use system processors which combine the tracking system function with inverter functions and ambient sensor inputs to modify DC power input level, and therefore modify resulting AC power output generation. By using the trackers 115 to tilt the array 110 and reduce incident irradiance, energy output of the DC array is reduced, therefore reducing the AC output of the inverter or the power plant, without creating DC array voltage levels above the MPP level. FIG 3A and 3B shows tilt angle for receiving incoming light purposely adjusted to a selected antitracking tilt angle for a reduced DC power output position. As described in FIGS. 2A-C, a standard single-axis tracking system optimizes insolation by tilting the array substantially perpendicular to the light source at a sun-following angle toward peak irradiance 200. In the power reducing mode, surface normal 310 of the array 110 is tilted at a selected antitracking angle 320, or angle of incidence, away from peak irradiance 200, a peak light-receiving angle, as illustrated in FIGS. 3A-B.

[0048] In some embodiments the displacement angle is greater than 30 degrees. In some embodiments the displacement angle is greater than about 50 degrees. In some embodiments the displacement angle is in a range of about 1-180 degrees, 20-120 degrees, 30-90 degrees, or 45-90 degrees. In some embodiments a maximum displacement angle for a particular installation is 45 degrees, and a selected antitracking displacement angle is between about 1-45 degrees, 10-45 degrees, 15-45 degrees, 20-45 degrees, 25-45 degrees, 30-45 degrees, 35-45 degrees, or 40-45 degrees. In some embodiments the displacement angle is about 45 degrees. [0049] The antitracking displacement angle is selected to reduce total irradiance received by the array or system. In some embodiments the albedo, clouds, or reflected light may alter module positioning and ambient condition sensors may be used in calculating array position. In some embodiments, the selected antitracking angle may be adjusted periodically, continuously, dynamically, at set intervals, in response to conditions detected by the ambient condition sensors and/or in response to conditions detected by the power sensors.

[0050] In an embodiment, a dual-axis tracking system is employed and the displacement angles may combine a full range of motion available for both axes of rotation.

[0051] In an embodiment of the invention, a form of inverter DC input limiting functionality, or clipping, is produced. Rather than relying on the inverter to shift DC array voltage to limit DC input, an equivalent DC clipping functionality is produced by using the tracker array position to achieve some or all of a DC array power reduction that limits DC power input to the maximum inverter rated power. For example, upon generation of the inverter input limit signal that would usually trigger the inverter' s clipping mode, the integrated power plant tracker controller determines a tracker displacement angle necessary to reduce solar input and therefore DC array power output to the target level. The tracker displacement angle and resulting DC output is monitored along with ambient conditions by the system processor to continuously adjust the tracker displacement angle to dynamically remain in close proximity to the inverter maximum input without exceeding it. By using both inverter and tracker together, the duration of time PV modules are not in MPP can be reduced from hundreds or thousands of hours to a de minimis amount of time during the life of power plant. As a result, the cumulative beneficial reduction in excess voltage exposure and excess operating temperature becomes significant.

[0052] Referring now to FIG. 6, data from modules in a solar installation is shown for power output, module temperature data, and ambient temperature at a range of power output reduction levels for an example system. Power reduction by percent is shown and indicated by the line with circular data points rising from left to right. The line with triangular data points shows module temperature relative to ambient for a system using antitracking to accomplish power reduction. The antitracking angle is shown on the x-axis. A comparable module having the same structure but accomplishing power reduction by increasing voltage above VMP is also shown. The data empirically shows that power output reduction using anti-tracking angles results in less heating of the modules by about 5 degrees C. The data points of FIG. 6 for a system using antitracking shows the effectiveness of a purposely adjusted tilt angle to produce a reduced DC power output. [0053] As shown in FIG. 5, the antitracking half-power point 505 is associated with a voltage that is not elevated above VMP, while the standard half-power point 515 is associated with a voltage elevated above VMP. In this example, the array is positioned by the tracker into an antitracking position aproximately 60 degrees offset from the sun-tracking position. By using antitracking, the power output can be reduced from 0-100% by altering the MPP value without increasing voltage above VMP.

[0054] Module temperature reduction is achieved by anti-tracking. Under typical operating conditions, incident sunlight on a module operating at MPP causes operating temperatures to rise. Increasing light intensity leads to higher temperatures. Additional heating occurs when a module voltage is increased above VMP toward Voc. In a typical system with sun tracking, a module may operate at 25C above ambient. Anti-tracking mitigates heating both by reducing incident light available and by operating in MPP rather than at an elevated voltage, including an open current voltage. In an embodiment, a module temperature in an anti-tracking system operating by the described methods is 4-6 degrees C below an equivalent module using sun tracking and operating under equivalent environmental conditions.

[0055] Referring now to FIGS. 7-9 data from modules in an example solar installation is shown. In this example, the range of tracker movement is limited to 0-45 degrees of

displacement from sun facing.

[0056] FIG. 7 shows a comparison of voltage change with curtailment in an example system with and without tracker mitigation using antitracking. The top solid line shows an example of voltage change, y-axis (left), with percent curtailment x-axis (bottom) using the prior art method of shifting voltage up, past the maximum power point, to reduce total power, as previously described. The bottom solid line shows an example of voltage change, y-axis (left), with percent curtailment x-axis (bottom) using antitracking. The dotted line shows

corresponding values for tracker angle away from sun-following with curtailment, where the displacement angle is shown (right) for the associated curtailment percent (bottom). The data set for the example corresponding to FIG. 7 is shown in Table 1, showing DC voltage change relative to an initial 0% curtailment value of 1149V. [0057] Table 1: Comparison of voltage change with and without tracker mitigation:

[0058] FIGS. 8A and 8B show DC power and voltage, respectively, for a period following the application of curtailment, in the example system using the prior art method of shifting voltage up, past the maximum power point, to reduce total power. Curtailment levels of 5 percent, 10 percent, 15 percent, 20 percent, 22 percent, 25 percent, 30 percent, 35 percent, and 50 percent are shown. In comparing FIGS. 8A and 8B, it can be seen that, at corresponding time points, higher levels of curtailment correspond to greater increases in DC voltage. The data for the example corresponding to FIGS. 8 A and 8B is shown in Table 2.

[0059] Table 2: Example of voltage increase - trackers not used to control Vdc:

[0060] FIGS. 9A and 9B show DC power and voltage, respectively, for a period following the application of curtailment, in the example system using an embodiment of the antitracking method to reduce total produced power. Curtailment levels of 5 percent, 10 percent, 15 percent, 20 percent, 22 percent, 25 percent, 30 percent, 35 percent, and 50 percent are shown. FIG. 9C shows angular displacement angle on the y-axis over the period following the application of curtailment for selected curtailment levels and FIG. 9D shows corresponding irradiance levels. From top to bottom the curtailment levels shown on FIGS. 9C and 9D are: 0 percent, 5 percent, 10 percent, 15 percent, 20 percent, and 50 percent. The data for the example corresponding to FIGS. 9A, 9B, 9C, and 9D is shown in Table 3.

[0061] Table 3: Example of curtailment using trackers to control DC Voltage:

[0062] The example data sets of FIGS. 7-9 show benefits of antitracking to control DC voltage production and array temperature. While these details relate to one example system, it will be understood that the system and method may be used with various photovoltaic devices, environmental conditions, and curtailment demands.

[0063] In an embodiment, if superseding tracker stow position or other overriding system factors render the tracker position unable to singularly reduce DC array power to the required level, the traditional inverter clipping functionality may supplement the DC array power reduction to the degree required to maintain the total required limited DC array output.

[0064] In some embodiments, the tracker function, inverter function, and ambient sensors are integrated with plant grid control functions and used together.

[0065] In an embodiment, the inverter reduces the power output using traditional disconnect or shifting off MPP for a short duration, to achieve the needed reduction nearly instantaneously, while the tracker moves the array into a first position for reduced output, the power output level at the first position is compared to a target set point, the tracker controller determines an adjustment and the array is angled to a second position for reduced output, the power output level at the second position is compared to a target set point, and the reduction of power at the inverter is reduced or stopped. A tracker usually achieves its maximum DC power reduction contribution within about 5 to 30 minutes of initiated displacement, during which time the inverter may supplement the reduction further. In some embodiments, over the course of the daylight period or power-generation period of a day, the inverter power output reduction is maintained for a continuous duration period of no more than 5-25 minutes, 0-30 minutes, 0-25 minutes, 0-20 minutes, 0-15 minutes, 0-10 minutes, 0-5 minutes, or between about 1-300 seconds. In some embodiments, a daily duration of inverter power output reduction is no more than 5-60 minutes, 5-30 minutes, 0-60 minutes, 0-45 minutes, 0-30 minutes, 0-15 minutes, or between about 1-600 seconds, per 24 hour period.

[0066] In some embodiments, the maximum DC power reduction contribution of the tracked array can reach a level that effectively turns off the inverter by reducing DC array voltage to a level below the inverter turn off voltage.

[0067] In some embodiments, target power curtailment is achieved by combination of the inverter and tracker, simultaneously positioning the array to reduce irradiance, achieving a portion of the power reduction, while the inverter operates at a level slightly above MPP to achieve the remaining reduction with precision. In an embodiment 1-99% of curtailment is achieved by the reduced power position of the array, while the inverter method contributes the remaining balance of the required power reduction. A dual contribution embodiment, using antitracking with inverter power reduction, may be used to reduce power production for a period ranging from milliseconds to a full solar day. In an embodiment, a curtailment power reduction order, to reduce power output by 5-25%, is fully achieved by antitracking within 30 minutes, 25 minutes, 20 minutes, 15 minutes, 10 minutes, or 5 minutes, of a curtailment request. In an embodiment, a curtailment power reduction order, to reduce power output by 10-50%, is fully achieved by antitracking within 30 minutes, 25 minutes, 20 minutes, 15 minutes, 10 minutes, or 5 minutes, of a curtailment request.

[0068] In an embodiment, antitracking contributes a first portion of the required power reduction while inverter power reduction contributes a second portion. The second portion may be greater than the first portion during some or all of a period of tracker re-positioning. The first portion may be greater than the second portion following a period of tracker re-positioning.

[0069] In some embodiments, the displacement angle of all trackers in a system may be uniform. In a system having several sub-systems including a plurality of inverters, signals from one sub-system can be used to make highly accurate and correct adjustment on neighboring subsystems.

[0070] In some embodiments, the displacement of particular trackers associated with selected modules of the multiple strings of arrays comprising a system may be individually controlled at different displacement angles to provide additional dimensions of power output control levels and/or response time.

[0071] In embodiments, the displacement of trackers and contribution of inverters work in concert to increase DC power of the array to the degree capable to respond to the plant control commands to reinstate full power plant output when a power plant is issued a signal to return to full output. This is accomplished by implementation of inverse logic of all above curtailment scenarios.

[0072] In embodiments, the displacement of trackers and contribution of inverters work in concert to increase DC power of the array to the degree capable to respond to the plant control commands to ramp power output to a higher setpoint level after a previously lower setpoint level. This is accomplished by implementation of inverse logic of all above curtailment scenarios.

[0073] A controller may be used for determining target point. In an embodiment, the controller checks actual conditions of the DC system, the inverter of the PCS, the ambient environment as detected by the ambient condition sensors, the grid, and required set points. In an embodiment, the controller sends individual instructions to each inverter and tracker based on location, losses, and performance. The system may receive control signals from manual or automated grid control operators, or plant level control signals and/or use supervisory control and data acquisition (SCADA) control system architecture, using computers, networked data communications and graphical user interfaces for high-level process supervisory management, and other peripheral devices such as programmable logic controllers and discrete PID controllers.

[0074] A controller may be used for planned or scheduled curtailment. In a planned curtailment the control system can manage tracker angle and inverter settings to assure that planned ramp rates are achieved and not limited by tracker slew rate. The scheduled curtailment may be modified by a feedback loop to adjust for unplanned conditions, such as clouds or other weather, and dynamic factors such as unplanned changes in power demand.

[0075] The system and method has the benefit of reducing wear and degradation of PV modules, inverters, and other system components affected by cumulative higher operating temperatures or cumulative higher operating voltage.

[0076] It is noted that the terms "substantially" and "about" may be utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative

comparison, value, measurement, or other representation. These terms are also utilized herein to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue. [0077] According to the embodiments provided herein, a system for providing solar power can include: a solar array; a tracker coupled to the solar array, wherein the tracker adjusts an angle of a surface normal of the solar array; a power sensor communicatively coupled to the solar array; and one or more processors communicatively coupled to the tracker and the power sensor, wherein the one or more processors executes machine readable instructions to: receive a measurement signal from the power sensor indicative of a power output from the solar array in a first position; determine, from the measurement signal, that the power output exceeds a setpoint; transmit a control signal to the tracker to cause movement of the solar array from the first position to an antitracking position, wherein the surface normal of the solar array is displaced from solar angle of incidence, thereby reducing a power output from the solar array.

[0078] According to any of the embodiments provided herein, an antitracking position may comprise tilting the solar array to an antitracking angle defined by the surface normal of the solar array and the solar angle of incidence; and wherein the antitracking angle in a range selected from: about 1-180 degrees, about 20-120 degrees, about 30-90 degrees, about 1-45 degrees, about 10-45 degrees, about 15-45 degrees, about 20-45 degrees, about 25-45 degrees, about 30-45 degrees, about 35-45 degrees, about 40-45 degrees, or about 45-90 degrees.

[0079] According to any of the embodiments provided herein, a system for providing solar power can include at least one inverter receiving the power output from the solar array.

[0080] According to any of the embodiments provided herein, the setpoint can correspond to an inverter load limit.

[0081] According to any of the embodiments provided herein, the setpoint can corresponds to a grid curtailment request.

[0082] According to any of the embodiments provided herein, the one or more processors can execute machine readable instructions to: receive a second measurement signal from the power sensor indicative of a power output from the solar array in a second position; determine, from the second measurement signal, whether the power output exceeds a setpoint; and transmit a control signal to the tracker to cause movement of the solar array to increase or decrease an antitracking angle.

[0083] According to any of the embodiments provided herein, a system for providing solar power can include a plurality of ambient condition sensors, wherein the plurality of ambient condition sensors provide environmental data, and wherein the environmental data is selected from the group consisting of: light intensity, wind speed, wind direction, air temperature, and module temperature. [0084] According to any of the embodiments provided herein, a system for providing solar power can include a plurality of power sensors, wherein the plurality of power sensors provide data on one or more power system conditions, and wherein the power system data is selected from the group consisting of: DC energy measurement, AC energy measurement, current density, voltage measurement, power rating, power threshold, grid conditions, power set point, and fault conditions.

[0085] According to any of the embodiments provided herein, a system for providing solar power can include a plurality of arrays, wherein one or more of the plurality of arrays are indexed to a reference array, whereby the one or more processors executes machine readable instructions to: receive a signal indicative of an antitracking position from the reference array; and transmit a control signal to the tracker to cause movement of the plurality of arrays to a corresponding antitracking position.

[0086] According to any of the embodiments provided herein, the one or more processors can execute machine readable instructions to: receive a measurement signal from the power sensor indicative of a power output from the solar array; compare the measurement signal to the setpoint; if the measurement signal indicates that the power generated by the solar array is greater than the setpoint, initiating an incremental adjustment to increase the antitracking angle; if the measurement signal indicates that the power generated by the solar array is less than the setpoint, initiating an incremental adjustment to decrease the antitracking angle; and if the measurement signal indicates that the power generated by the solar array substantially equal to the setpoint, maintaining the antitracking angle.

[0087] According to the embodiments provided herein, a method can include receiving, by one or more processors communicatively coupled to at least one tracker and at least one power sensor, a power sensor measurement indicative of a power output from a solar array in a first position; determining that the power output exceeds a setpoint; and initiating movement of the solar array from the first position to a second position, in response to determining that the power output exceeds the setpoint, wherein the second position is a selected antitracking position, wherein surface normal of the array is displaced from solar angle of incidence, thereby reducing a power output from the array.

[0088] According to any of the embodiments provided herein, the selected antitracking position can comprise an antitracking angle between surface normal and solar angle of incidence, and the antitracking angle can be in in a range selected from: about 1-180 degrees, about 20-120 degrees, about 30-90 degrees, about 1-45 degrees, about 10-45 degrees, about 15-45 degrees, about 20-45 degrees, about 25-45 degrees, about 30-45 degrees, about 35-45 degrees, about 40- 45 degrees, or about 45-90 degrees.

[0089] According to any of the embodiments provided herein, a method can include receiving the setpoint.

[0090] According to any of the embodiments provided herein, determining the selected antitracking position can comprise: receiving a power setpoint; comparing the setpoint to a power generating capacity for the array; determining an antitracking position whereby the surface normal is displaced from a solar angle of incidence by a selected angle, and the determining can include using data from one or more sources selected from: an ambient condition sensor, a power sensor, a clock, a global positioning system, a look-up table, and historical trends.

[0091] According to any of the embodiments provided herein, a method can include receiving from a power sensor a measurement of power generation from the solar array;

comparing the measurement of power generation to a setpoint; and initiating an angle tilt change in the array to a second antitracking position.

[0092] According to any of the embodiments provided herein, the power output can be direct current to an inverter, and a voltage of the direct current does not exceed a voltage corresponding to a maximum power point (MPP) for the solar array.

[0093] According to any of the embodiments provided herein, the power output can be direct current to an inverter, and a voltage of the direct current may exceed a voltage

corresponding to a maximum power point (MPP) of the solar array for a duration of 5 minutes or less.

[0094] According to any of the embodiments provided herein, a method can include: receiving a measurement signal from the power sensor indicative of a power output from the solar array; comparing the measurement signal to the setpoint; if the measurement signal indicates that the power generated by the solar array is greater than the setpoint, initiating an incremental adjustment to increase the antitracking angle; if the measurement signal indicates that the power generated by the solar array is less than the setpoint, initiating an incremental adjustment to decrease the antitracking angle; and if the measurement signal indicates that the power generated by the solar array substantially equal to the setpoint, maintaining the antitracking angle. In an embodiment the incremental adjustment can be in a range of about 0-20 degrees, 1-15 degrees, 1-10 degrees, or 1-5 degrees. [0095] According to the embodiments provided herein, a method for limiting current transmitted from an array of photovoltaic modules to an inverter, can include: providing an array of photovoltaic modules electrically connected to an inverter and configured to transmit power to the inverter; and initiating an angle tilt change in the array to a selected antitracking position.

[0096] According to the embodiments provided herein, a system for providing solar power can include: an array of solar modules; a tracking system coupled to the array of solar modules, the tracking system can adjust a tracking angle of the solar modules; a power sensor communicatively coupled to the array of modules, the power sensor can communicate a power signal indicative of power generated by the array of solar modules; and one or more processors communicatively coupled to the tracking system and the power sensor, the one or more processors can execute machine readable instructions to: receive the power signal; determine that the power signal indicates that the power generated by the array of solar modules is greater than a target power level; cause the tracking system to actuate to reduce the power generated by the array of solar modules; and cause the tracking system to stop, when the power generated by the array of solar modules is less than or equal to the target power level.

[0097] While particular embodiments have been illustrated and described herein, it should be understood that various other changes and modifications may be made without departing from the spirit and scope of the claimed subject matter. Moreover, although various aspects of the claimed subject matter have been described herein, such aspects need not be utilized in combination. It is therefore intended that the appended claims cover all such changes and modifications that are within the scope of the claimed subject matter.