SOLAR THERMAL ENERGY ARRAY AND DRIVE

Abstract

Disclosed are systems and methods for controlling arrays of solar thermal energy collectors. Rows of the array are actuated sequentially or consecutively rather than concurrently.

Description

FIELD OF THE INVENTION

The invention relates to solar thermal energy arrays, such as solar thermal trough arrays for collecting solar thermal energy.

BACKGROUND AND BRIEF SUMMARY OF THE INVENTION

Solar thermal energy collectors are often installed as arrays having a plurality of collector rows. Each row may be formed of a plurality of individual collectors, such that the array resembles a traditional array of cells arranged in columns and rows.

Tracking systems for solar thermal energy collectors enable the collectors to move to track apparent motion of the sun across the sky. Each collector in an array may be controlled individually to provide accurate tracking in a centralized control configuration, and therefore each individual collector in a “cell” of a row may be controlled individually so that each may separately track the sun's apparent movement to collect solar energy. Often, each collector moves continuously using a slow—but constantly—moving drive system.

The invention in one instance provides a solar thermal energy collector array which has a column comprising a plurality of adjacent solar thermal energy cells in which the individual cells each share a single row controller. Two, three, four, five, six, seven, eight, nine, ten, or more of these cells may share a single controller.

A cell in this instance may be a single solar thermal energy collector or may be a plurality of solar thermal energy collectors whose collector tubes are in fluid communication with one another, so that the working fluid passing through a first collector of the cell subsequently passes through a second collector of the cell to be heated further. A cell may therefore have two, three, four, five, six, seven, eight, nine, ten, twelve, fourteen, sixteen, or more collectors in a given row that are actuated by a single row controller.

The central controller may be configured so that the row controllers are actuated sequentially so that e.g. the first cell moves then remains stationary, the second cell moves then remains stationary, the third cell moves then remains stationary, and so forth until the last cell has been moved and the cycle repeats.

Alternatively, the controller may be configured to actuate row controllers consecutively but not in order so that e.g. the first cell moves then remains stationary, the third cell moves then remains stationary, the fifth cell moves then remains stationary, and so forth until the last cell in the column has been moved and a second part of the cycle begins with the second cell moving, followed by the fourth cell, etc.

There may be arrays adjacent to one another which form a complex array. Therefore, there may be plural row controllers arranged adjacent to one another in a row of the complex array. The row controllers in a row may be programmed identically or not. The row controllers in a row may be synchronized or not. The heated working fluid from one part of the row of the complex array may or may not be fed to the adjacent part of the row in the complex array.

The row controllers in a complex array may therefore be configured to operate independently of one another. Alternatively, plural adjacent row controllers such as two, three, four, or more adjacent row controllers may be configured to operate together.

Row controllers may be intelligent, stand-alone controllers that do not communicate with other controllers. Thus, in one configuration, each of the controllers is a stand-alone controller that receives various inputs and provides control outputs to the rows for which the controller is configured.

Row controllers configured as discussed above may be arranged in a distributed control system in which one or more control centers having e.g. a programmable logic controller, microprocessor, microcontroller, or computer communicates with each of the row controllers. In this instance, the row controllers do not stand alone and, instead, depend on the control center or centers for some information used to control the rows associated with that row controller.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 depicts rays parallel to the axis of symmetry reflecting to the focus of the parabola.

FIG. 2 illustrates a field of collectors consisting of rows oriented along the north-south longitude. Each trough collector rotates around the absorber tube to adjust the east-west orientation of the collector.

FIG. 3 shows an organization of controllers used to enable both large, field-level and small, row-specific commands. In the diagram, connections are labeled as “switches,” but routers may also be used to facilitate communication between controllers.

FIG. 4 illustrates an 18-inch sprocket as part of the chain-sprocket apparatus that rotates the collector row.

FIG. 5 shows a box containing an optical encoder, which sends the collector position to the Row Controller hardware.

FIG. 6 illustrates Row Tracker hardware which has a printed circuit board, CPU, motor power supply, and a 5- and 12-volt power supply.

FIG. 7 depicts a single board computer, which is programmed with the software to operate the collectors.

FIG. 8 illustrates one array of the invention with local control, with the row controller in the immediate vicinity of rows controlled by the row controller as opposed to being positioned at a more remote location such as a control room or periphery of a complex array.

FIG. 9 illustrates a complex array having four arrays, each with its row controller positioned in the immediate vicinity of rows controlled by the respective row controllers.

FIG. 10 depicts a control strategy for arrays of FIG. 8 and FIG. 9.

FIG. 11 illustrates one array of the invention with distributed control, where a row controller in the immediate vicinity of rows controlled by the row controller receives setpoints from a more remote, central controller such as a field controller.

FIG. 12 and FIG. 13 illustrate complex arrays comprising e.g. four of the arrays of FIG. 11.

FIG. 14 depicts a control strategy for arrays of FIG. 11-13.

ADDITIONAL SUMMARY AS WELL AS MORE DETAILED DESCRIPTION, INCLUDING BEST MODE

There are a number of ways to track the apparent movement of the sun.

One way is to use or develop tables or data of the sun's position or utilize an equation that calculates the sun's position as a function of the time of day and day of year for the latitude at which the collector array is located. The time of day may be obtained from a clock within the controller, from a website on the World Wide Web, or from a radio transmission of time from e.g. a national bureau. Alternatively, tables that contain or equations that generate data representing the angle at which solar collectors of a row would ideally be positioned may be utilized.

Another way is to utilize global positioning satellite (GPS) data to assess the geographic position of an array or part of a complex array of collectors to calculate the angle of the sun and optionally obtain the time of day provided as part of a typical GPS signal. This data is useful in calculating the angle at which the collectors of a row of an array should be positioned.

Data as obtained above may be used to position and control solar thermal energy collectors. Alternatively, data as obtained above may be modified and used to position collectors to compensate for inaccuracies of measurement or movement.

One inaccuracy that may exist when comparing actual position of a solar thermal energy collector and theoretical position as obtained above is misalignment of an inclinometer used to provide a signal indicative of the angle at which the collector is positioned. It can be quite difficult to position an inclinometer at exactly the position it should be positioned during installation. One way to compensate for misalignment of the inclinometer is to measure the difference between the theoretical position and the position at which a collector row provides the greatest illumination of its collector tube and store this information for each collector or row as an “alignment offset” that may be added to or subtracted from the theoretical angle to provide a row controller set point. This modified set point may be calculated at the row controller, or the modified set point may be calculated at a central controller.

Another inaccuracy that may exist when comparing actual position and theoretical position for a collector is due to wear over time. Wear may be compensated for by incorporating a wear offset either directly into the alignment offset by adding it to or subtracting it from the stored alignment offset and storing the new number or by storing the wear offset separately in a database and adding to or subtracting from the modified set point above.

The alignment offset and wear offset may be measured manually, or these offsets may be calculated by providing alignment equipment in the solar array. For example, a collector tube of a row may have a brightness meter attached that indicates brightness of light shining on the tube. The row controller may periodically move the collector row to determine the position at which maximum brightness occurs and calculate either a new alignment offset or a new wear offset value that may be stored in a database.

Another source of inaccurate alignment is wind pressure on collectors of a row. A row of solar thermal energy collectors that are interconnected to rotate synchronously have a large surface area against which wind applies pressure. There are a number of ways to compensate for wind pressure.

One is to use information obtained from an on-site weather station that provides data about wind speed and direction to calculate a wind pressure offset. This value may be stored or may be calculated constantly to provide an offset value added to or subtracted from other values as discussed above to correct for current wind conditions.

Another way to compensate for wind pressure is to compare the collector row angle set point with either an instantaneous reading from the inclinometer or a time-averaged reading for a period of time during the day (e.g. the preceding five or ten minutes) as well as compare to wind speed and direction to calculate a wind pressure offset that can be used to adjust the set point as calculated above.

An additional way to adjust the position of the collector row is to measure temperature of the working fluid and moving the collector row slightly in one direction and then the other to assess change in temperature or rate of change in temperature of the working fluid. A working fluid temperature offset may be calculated by finding the position that maximizes the temperature or that maximizes the temperature and minimizes the rate of change of temperature near the position at which the temperature is at its maximum. This method may be used periodically to calculate a new wear offset value or a separate working fluid temperature offset value that may be stored separately and/or used in conjunction with other settings as discussed above.

The control system may be localized to the central controller. In one local control system as illustrated in FIG. 8 and FIG. 9 (illustrating multiple arrays, each having an individual row controller), the time, row angle, and calibration offset are calculated or stored at each row controller, and little or no information or instruction is received from other controllers. Information that might be received from other controllers is e.g. stow (park) the collectors by turning them to face earth or another safe position, track the sun, lag the sun by maintaining the collector stationary for a period of time that the apparent motion of the sun would otherwise be tracked, and defocus the collectors by moving them off of the set point at which the collectors obtain maximum solar energy by e.g. five degrees. In the system depicted in FIG. 8, the row controller receives information from the inclinometers of each of the rows and adjusts an individual row at a time to position the row at the desired angle. Signals indicating the temperature of heated working fluid (in one instance, heated oil from a trough array) from each of the rows discharging heated working fluid to a common pipe are sent to a field controller via a sensor module and optional sensor router, which communicates information about the temperatures of each of the rows to a field controller that compares the temperature values to established values to instruct the row controller to stow, track, lag, or defocus. The field controller optionally receives information from weather sensors and/or the process utilizing the working fluid (e.g. a power plant) to also make decisions on whether a row should stow, track, lag, or defocus.

FIG. 9 illustrates multiple arrays in which each of the row controllers operates independently of a central controller.

The local controller will therefore calculate solar angle from latitude, longitude, time of day and date, utilize weather information directly, and perform other responses as discussed above and below for this type of array.

All logic and controls may be provided at each local row controller.

A row controller sequentially actuates each of its associated rows as discussed above.

Row controllers may each comprise an enclosure; a logic board with its microcontroller; a plurality of relays, each relay interfacing with the logic board and wired to a motor of a row; and one or more power supplies for the logic board and for the motors. Each logic board receives inputs such as signals representative of weather condition, inclinometer position, and/or working fluid temperature, and each logic board uses this information along with e.g. time of day and date information to calculate what action to take (e.g. move solar thermal energy collector 1 degree; place collector row into “stow” condition, where reflector row points to ground rather to the sky) and when.

A particular control scheme is illustrated in FIG. 10. In this control scheme, each row controller receives a command such as stow, track, lag, wash, or defocus from the field controller, and the row controller takes the indicated action in response. While tracking, the row controller calculates a solar angle at which to set the row. The calculated angle is compared to a minimum value and a maximum value. If the calculated angle is less than the minimum value or greater than the maximum value, the row is placed in the stow position. If not, the row is moved to the calculated angle, and the cycle is repeated. If the row controller receives a command other than the “track” command, the row controller positions the collector row as instructed until the row controller receives a different instruction from the field controller. If no instruction is received, the collector row proceeds to a “stow” position.

The optional field controller in this instance receives signals from various sensor modules to decide what instruction to send to the various row controllers. For instance, if weather sensors indicate that there is sufficient wind and/or rain, the field controller instructs all row controllers to stow their respective rows. If a wash command has been entered by e.g. a user interface, the field controller instructs selected or all row controllers to move their respective rows to a wash position. Likewise, if the working fluid exit temperature from one or more rows is at or above a threshold for the maximum fluid temperature, the row controller or controllers associated with those rows are instructed to defocus that row or those rows. If the working fluid temperature nearing the threshold for a “nearing maximum” working fluid temperature, the particular row controller is instructed to lag the particular row (i.e. not track the sun and remain in its present position) for one cycle. Otherwise, the field controller sends the row controllers a signal to track the sun, and the row controllers run through their cycles of controlling the position of each row individually until an instruction to the contrary is received from the field controller.

A distributed control system is illustrated in FIG. 11 and in FIG. 12 (illustrating dedicated control wires from the central or field controller to row controllers for multiple arrays) as well as in FIG. 13 (illustrating a “daisy-chain” arrangement of field controller and row controllers for multiple arrays). Time and collector row angle for all rows are generated at the field controller, and an optional GPS system provides location data as well as a reference time signal. A row controller comprising a microcontroller receives the angle set point and actuates each row individually to move the row to a desired position by comparing the set point to the angle received from the inclinometer and actuating the row motor as needed. The microprocessor can utilize a communication protocol such as Bacnet to directly communicate with the central field controls. The temperature of the working fluid from each row discharging to the common discharge pipe is also provided to the field controller or to the microcontroller to adjust the position of the collector row as described herein. Likewise, information from the process that uses the heated working fluid and/or weather sensors is processed by the field controller and/or the row controller to provide changes to set points for the various rows or directions to stow, track, lag, or defocus a row, selected rows, or all rows.

A particular control scheme for the distributed control system is illustrated in FIG. 14. In this particular control strategy, a field controller may perform the same or similar decisions as discussed above. For instance, the field controller verifies whether it has received an instruction or information indicating that collector rows should move to a stow position, such as an operator's instruction to stow collectors or weather information indicating there is sufficient precipitation and/or wind. In this instance, the field controller may send row controllers an angle set point that the row controllers use to move collector rows to the desired angle, effectively parking the rows. A wash command received by the field controller results in the field controller sending out an angle set point to row controllers to place selected or all rows to an angle appropriate to wash the collectors of the rows. If the working fluid exit temperature is at a threshold for a maximum working fluid temperature, the field controller may provide an angle set point to the selected row controller or controllers to effectively defocus the desired row or rows. In one instance, the field controller uses a proportional-integral-derivative control loop to determine a target angle offset from a calculated desired solar angle to provide a corrected angle set point to the row controller(s). In addition, if the field controller in comparing the set point or target angle to a “stow” condition maximum or minimum value finds that the calculated angle is above the maximum or below the minimum value, the field controller sends selected or all row controllers target angles that effectively move the collector rows to a stow position. Row controllers in this instance receive target angles from the field controller and perform limited functions with the target angles. A row controller may optionally compare the target angle to maximum and minimum positions as discussed above and stow the controller's rows as discussed above as well as optionally send an alarm to a control panel. Alternatively, the row controller may not make any adjustment to row position and may just send an alarm signal. The row controller may then optionally compare the row angle as provided by a row's inclinometer to a maximum acceptable and a minimum acceptable value stored locally or obtained via the network connecting the controllers and, if not acceptable, stop taking action and send an alarm. Otherwise, the row controller simply controls row position to the set point received from the field controller as discussed above.

Various conditions may be measured and used as inputs to the central controller. These include:

• • for weather:
    • Wind speed
    • Wind direction
    • Air temperature
    • Humidity
    • Precipitation
    • Cloudiness
    • Cloud factor
    • Direct normal irradiance;
  • inclinometer angle, to both reposition accurately and to assess whether the row is stuck;
  • angle of sun or sun location (as measured by e.g. brightness or heat or row temperature);
  • row temperature (to control to a set point, to lag, to defocus, or, if too high, to point the row, selected rows, or all rows away from the sun);
  • Temperature of working fluid
    • from entire array
    • from selected rows of the array
    • from each row of the array
  • Limit switch inputs to prevent collector rows from moving to positions that would damage equipment; and
  • GPS input for very accurate time and site location

User inputs may also be accommodated by the central controller. These include:

• • Over-ride values for
  • Temperature set point
  • Offset
  • Shut down rows or array
  • Move to wash or maintenance position

In addition, limit switches may be used as an input to the central controller or row controller to shut off power to a collector row motor, or limit switches may be used in series with relay actuator wiring to interrupt power to the relay to stop the motor for a collector row.

Communications from sensors and among controllers may occur a number of ways. There may be dedicated cables from the central controller to each row controller or sensor. Alternatively, the row controllers are daisy-chained, allowing the central controller to communicate with some or all row controllers using a single control cable. Likewise, inputs such as working fluid temperature and inclinometer angle may be daisy-chained with their respective cables. Communications may instead or additionally be performed using e.g. wireless mesh communications (802.15.4) or other RF protocols.

Solar Thermal Energy Collectors

The systems discussed above are well-suited to various solar thermal energy collectors, such as trough collectors or linear Fresnel array collectors.

For instance, a trough collector array may be formed using solar thermal energy collectors as described in PCT/US2009/041171, entitled “SUPPORT STRUCTURE FOR SOLAR ENERGY COLLECTION SYSTEM”, the contents of which are incorporated by reference herein as if put forth in full below. Such collectors may be comparatively small when compared to previous trough collectors used in generating process steam for e.g. power generation, air conditioning, food processing, or oil recovery from earth formations.

An aperture of a solar collector such as a trough collector may be less than about 2 or 3 meters.

A trough or other type of collector of an array such as the one referred to in the PCT application cited above may have a chain and sprocket drive. Such drive is not typically considered to be sufficiently precise to use in accurately positioning a collector. Often, more precise drives such as worm gear drives are used. A system as described herein may often utilize less precise positioning means such as chain and sprocket drives.

Types of Solar Thermal Energy Collectors

• • Trough
  • Configured to rotate more than 180 deg, especially more than 200 or 220
  • Even up to 270 deg rotational configuration
  • Chain drive

If collectors are comparatively small, it is helpful to provide a more precise control system such as one disclosed herein. The smaller rotational mass (especially where the axis of rotation for a row is located within the parabola defined by the mirror, such as coaxially with the collector tube or at the center of mass for the reflector in cross-section) in combination of a more precise control system as disclosed herein allows better control over temperature of the working fluid exiting the array and improved efficiency in collection of solar energy. While a more precise control system as disclosed herein may be applied to larger solar collectors, the gains in collection efficiency and/or temperature control may not be as large for a larger solar collector as for a smaller solar collector.

Discussed below is a particular implementation of a control configuration and strategy.

Micro Concentrated Solar Power (Micro CSP) can utilize trough solar collectors with a parabolic shape to reflect sunlight onto an absorber tube located at the focus on the parabola. The absorber tube is filled with a liquid that is pumped through a thermal loop, which could be used for solar process heating, air conditioning, or power generation, among other uses. Rays that are directed toward the collector in parallel with the axis of symmetry reflect to the focus of the parabola. Adjusting the collectors to face the sun throughout the day maximizes the amount of sun rays that are parallel to the axis of symmetry and, thus, maximizes the amount of solar power directed to the absorber tube. Since this technology relies on rays parallel to the axis of symmetry, it is important that the collectors continually face the sun to maximize the energy harvested in a day. The SopoTracker maximizes the solar power collected, which is especially important to large scale solar power solutions.

In a typical field deployment, rows of collectors are positioned so that their absorber tubes are oriented along a North-South line. Not only does this arrangement allow efficient use of space and prevent/reduce collectors from casting shadows on neighboring collectors, but it also enables the collectors to change their East-West direction by simply rotating about the absorber tube. The SopoTracker can accommodate large fields by using a system of Controllers, as explained below. However, it can also be used for smaller applications, including a single-collector system sometimes referred to as the SopoLite—for example a small-scale thermal loop that sits on a portable trailer, which can be used for data collection. SopoTracker applications are not limited to just parabolic collectors, but could also be applied to pyrheliometers to collect direct measurements of solar radiation and to enhance other technologies that benefit from directly facing the sun, among other uses.

Advantages of the SopoTracker

Features and advantages of the SopoTracker over other solar trackers can include some or all of the following:

A rapid stow function that enables the collectors to return to a protective HOME position (in which the collector faces downward or other position away from the sun) within seconds.

Rotates at least 270 degrees to capture as much sunlight as possible as well as stow the collector in a safer, earth-directed position.

Built-in safety features to prevent over rotation, which could result in self-inflicted damage to the SopoTracker, the solar collector, and/or to elements in the thermal loop.

Complete solar tracking system that can control large fields in a systematic fashion and enables both large scale and specific commands (e.g., Send all collectors to the HOME position in the event of a storm or defocus a single row or even a single collector that is overheated).

Adaptable hours of operation that may be specific to the location, time of year, etc., to capture the most sunlight for the amount of energy expended on controlling the collectors.

Integrative system that can integrate, analyze, and respond to information such as time, sun angle, wind speed, weather conditions, heat generation, manual commands sent via internet, etc., to optimize solar collection and intelligently respond by, for example, adjusting the collectors to track the sun, defocus when too hot, or return to HOME in a protective manner.

Data collection and transmittal, which can help assess the efficiency of the thermal loop or help foresee and prevent any potential problems.

Reducing the need for drive train accuracy and allowing the use of e.g. sprocket and chain drive.

Using Field Controllers and Plant Controllers for Large Fields

One approach to controlling large fields of collectors while maintaining the specificity of control is by implementing a hierarchy of controllers. For example, in one example architecture, the SopoTracker includes Row Controllers, Field Controller(s) and a Plant Controller. Each Row Controller maintains the tracking for a cluster of one or more rows of collectors. The Row Controller typically would be responsible for basic control in keeping a cluster of collectors aligned with the sun's angle. A Field Controller could facilitate communication between multiple Row Controllers, a Plant Controller and the internet. This communication could, for example, utilize Ethernet hardware, including Ethernet switches or Ethernet routers. Both the Plant Controller and Field Controller could, for example, run on Linux. In one implementation, the Plant Controller might monitor information such as weather conditions, flow rate, heat generated by each row of collectors, etc. and send commands via the Field Controller and Row Controllers to collectors when a response to these factors is necessary. By taking in commands from the Plant Controller and the internet (i.e. sending manual commands from afar), the Field Controller can relay commands to override the Row Controller's basic solar tracking to account for other factors, either as an entire field or as a single row or as a set of rows. The Field Controller can change the start and stop times for tracking since it is communicating with many Row Controllers. Thus, accounting for different hours of operation for the changing seasons and for daylight savings would be relatively easy. Another example of field-wide controls would be if the weather station indicates that the amount of energy use is less than what is being generated, the Plant Controller could send a command that the entire field of collectors should be sent to the HOME position to conserve energy. However, in the event that a single row of collectors is overheating, then the Plant Controller could send a specific command to the affected row to return to the HOME position to defocus. The connection to the internet could also enable the Field Controller to send information out to the solar field operator, to the power generator or to others. This information could be analyzed to calculate efficiency or to predict and/or prevent potential problems.

In one implementation, the Field Controller is an FTP server to which files are written and read by both the Row Controller and the Plant Controller. The following lists example communications that the different controllers may send to each other:

Plant Controller to Field Controller:

• • Home (at evening, excess wind, low sun, or some other error)
  • Start tracking (usually in morning)
  • Defocus row# (over heat)

Field Controller to Plant Controller:

• • Error in row#
  • Status report

Field Controller to Row Controllers:

• • Start
  • Defocus row#
  • Home
  • Off row#

Row Controller to Field Controller:

• • Report row encoder position
  • Error row#

Row Controller

In one implementation, the Row Controller can adjust multiple rows of collectors (a cluster) to track the sun. In a large field, many of these Row Controllers can be used to control numerous rows, which are also controlled by a Field Controller. In a smaller application, as in the SopoLite, a single Row Controller may also play the roles that the Plant Controller and Field Controller play in a larger field. This would enable the Row Controller to use weather station information, temperature measurements, etc. to determine how the collectors should function. In this section, however, the description below will provide an example of how a Row Controller could be designed to meet the basic function of controlling rows of collectors to track the sun and receive commands from a Field Collector.

One version of the Row Controller directs a cluster of up to six rows of collectors. The collector rows are rotated by a chain-sprocket apparatus that is driven by a motor controlled by the Row Controller hardware, which includes a single board controller, power supply, motor power supply, and driver/selector board. An encoder installed on one collector in each row measures and encodes the row's position, which is read by the software programmed in the single board controller. The software will use an algorithm to calculate the sun's angular position and then rotate each of the rows individually, looping through the six rows throughout the day, to match the calculated angle position.

The collectors in a row are connected to a crank shaft by a few chain-sprocket apparatuses, which have a gear ratio of 9:1. The chain-sprocket apparatus includes a chain link that wraps around an 18-inch drive sprocket that connects to the end arm of the collector and a 2-inch drive sprocket that is attached to the crank shaft. The crank shaft is rotated by a ½ horsepower DC motor, which runs on a 90 volt DC power supply activated by the Row Controller hardware. The 18-inch sprocket also has a safety feature called a limit switch. The limit switch prevents over rotation of the collector by creating a non-conducting gap between the sprocket and a metal switch. In FIG. 4, there is a white semi-circular piece of material over the blue sprocket. This white piece prevents a metal switch from touching the sprocket. If the collector over rotates, the metal switch will exceed the white semi-circle and will cause the switch to close. When the switch closes, an electrical signal is sent to the hardware through a RJ45 Ethernet wire. Alternatively, the limit switch may be bolted to collector panel stands, and an arm on the panel impacts the switch prior to impacting the panel stand. The signal may be a simple voltage or lack thereof, and therefore either presence or absence of voltage is sensed.

Each row has a encoder that detects the angle at which the collector is positioned. The encoder communicates using e.g. a 5-volt level of RS232 signal. An encoder may transmit e.g. 2 bytes of data every 10 milliseconds. Data may be sent 56K, no parity, 1 stop bit, for instance.

The data format is as follows:

High ordered byte transferred first.

Bit 7 is set to 1 to indicate high order

Bit 6 to 0 are high order data

Low order byte transferred immediately after

Bit 7 is set to 0 to indicate low order

Bit 6 to 0 are low order data

A high bit indicator is used to make it easier for the receiver to identify the bytes, which saves considerable computation and uncertainty.

After installing the encoder, the collector is placed upside down or right side up while the encoder is reset. The upside down position of the collector is set as the origin and 0 degrees. It is also referred to as home. A full rotation of 360 degrees is counted in 2̂14 (14 bit binary) positions, which results in a resolution of approximately 45 positions per degree.

The Row Controller hardware in this example includes a single board controller, power supply, motor power supply, and driver/selector board, which enable the tracker (i.e., Row Controller) to control 6 rows of collectors.

The driver/selector board in this instance is a printed circuit board (PCB) and may include some or all of the following:

• • 6 optical decoders
  • selector
  • connectors/sockets to ethernet, RS232, power
  • AC power switch
  • manual/automatic mode switch or outboard terminal block-connection switch
  • manual motor power switch
  • manual reverse/forward switch
  • dip switch for manual row motor select
  • 8 RJ45 sockets or screw terminal blocks
  • reset switch for single board computer
  • 12 v and 5 v LED to indicate proper voltage.
  • Relays to select directions and row to power specific motor
  • power to single board computer
  • POD to control output level of motor power supply
  • inhibitor to disable motor power supply

One of the RJ 45 sockets may provide connection to Ethernet. Six of the RJ 45 sockets may provide power to the encoder as well as a limit switch. Limit switches prevent collectors from moving beyond a safe limit in the event of a single-board computer or other electronic failure. At least two limit switches may be used per row. One may be serially connected to the motor while another may be serially connected to the relay driver. In alternate versions, limit switches connected to the drivers may be replaced with limit switches that are connected to the logic of the circuit.

In one implementation, the PCB has the potential to control six rows of collectors, and multiple Row Controllers are linked via switches to accommodate large field size. Other versions can expand to control 10 or more rows.

One version of the single board computer (SBC) is a picoFlash CPU with a 186 compatible processor that runs on a limited version of DOS operating system. Since the Field Controller could run on LINUX, other versions of Row Controllers can use CPUs running on Linux instead of DOS to simplify communication between the two computers.

This specific software implementation operates in the following manner—

• • Execution Sequence:
    • BIOS of SBC starts and execute batch file in A: drive
    • STARTUP.BAT file in B: drive executes
    • Reset IO lines so that motor is off
    • Environment variables are set
    • Ethernet Packet Driver is loaded
    • Serial Port Driver is loaded
    • Timer interrupt TSR is loaded
    • Program to read date/time/operational commands from Field Controller loaded.
    • CHOICE selection routine run
    • User has choice of N dos prompt or,
    • if there are no user input in few second, TRACKER software is run
  • Tracker Software:
    • Initializes various routines
    • Places IO ports to motor off state
    • Serial Communications
    • Ethernet/FTP Communications to Field Controller
    • Reads configuration file
    • Reads date using standard C routine and compute solar day and solar correction angle for the day
    • Initializes interrupt for millisecond time interrupt and counter
    • Turn on watchdog timer which will automatically restart SBC in case if it hangs
  • Loop through each row
    • Set output to select proper row of optical decoder for serial input
    • Reset serial port
    • Wait one second
    • Reads encoder for two second and accept average as current position
    • Compute current expected position from second from midnight and correction.
    • Compute millisecond to turn motor on for difference between current position of collector vs. optimal position to align to sun (approx. 170-500 ms)
    • Turn on proper row selection relay
    • Turn on forward direction relay
    • Turn off motor power inhibitor relay (turn motor on) for computed millisecond
  • Tracker
  • During each row or between loops for whole entity of 6 rows, Row Controller reads and writes to FTP server in Field Controller.
  • Writes:
    • Normally report position of encoder for all rows
    • If there are stuck or error, it will report errors
  • Reads:
    • Command file containing:
    • Home all
    • Defocus row
    • Home row
    • Off row

Internally, the Row Controller program cooperatively multitasks. The timer counter increases in increments of approximately one millisecond. The Delay function waits for the delay counted in ms, while still multitasking (mainly reads serial port). The millisecond count is divided by 1024 to approximate a second and coordinate one-second events. One-second events include resetting the watchdog timer, resetting the display of the raw encoder position during large moves that are not routine mini tracking moves, and blinking of the LED.

Other Methods of Tracking and Calibration

Another method of tracking, among others, uses photovoltaic (PV) cells. PV cells produce electrical current from light, such that the amount of electricity generated provides a quantitative measurement of light received by the PV cells. A ring of PV cells could be placed around the absorber tube to indicate the amount of sunlight that each particular part of the collector is reflecting toward the tube. The ring of PV cells could be grouped into the two halves of the reflector. By measuring the amount of light reflected by each half of the collector, which is correlated with the amount of electricity generated by each half of the PV cell ring, a SopoTracker could adjust the angle of the collector so that both sides reflect equal amounts of sunlight.

The same ring of PV cells could be used to calibrate the SopoTracker. This would give quantitative measurements of the amount of light that is reflected onto the absorber tube.

Another method could use tubes fitted around the absorber tube to provide pyrheliometer readings. In both instances, the quantitative measurement of light/radiation that is reflected onto the absorber tube can be used to determine the angle at which the collection is at its maximum. By making a comparison to the sun angle position derived from the SopoTracker software, an offset can be determined to send a zero position to the encoder.

In some implementations, the functions of the Field Controller and Plant Controller could be integrated into a single computer that would control plant information while also facilitating the necessary communication, regardless of the amount of collectors being used. Thus, a single Controller would integrate information from the weather station, temperature readings, flow measurements, etc., and send commands directly to the Row Controller.

Claims

1. A solar thermal energy collector array comprising a) a plurality of rows of solar thermal energy collectors comprising a first solar thermal energy collector row and a second solar thermal energy collector row,b) a plurality of electric motors comprising a first motor configured to position the first solar thermal energy collector row and a second motor configured to position the second solar thermal energy collector row,c) a plurality of inclinometers comprising a first inclinometer and a second inclinometer, the first inclinometer being coupled with the first solar thermal energy collector row and the second inclinometer being coupled with the second solar thermal energy collector row,d) a row controller in communication with the plurality of electric motors and the plurality of inclinometers, the row controller being configured to sequentially actuate i) the first motor to position the first solar thermal energy collector row according to a position of the first solar thermal energy collector row as indicated by the first inclinometer, andii) the second motor to position the second solar thermal energy collector row according to a position of the second solar thermal energy collector row as indicated by the second inclinometer.

2. An array according to claim 1 wherein the row controller comprises a field-mounted enclosure in the immediate vicinity of the plurality of rows.

3. An array according to claim 1 and further comprising a central controller in communication with the row controller, the row controller being configured to calculate a setpoint for the row controller and the central controller not being configured to calculate a setpoint for the row controller.

4. An array according to claim 3 wherein the central controller is configured to provide an instruction to the row controller to position the rows controlled by the row controller to a position selected from a stow, track, lag, defocus, and wash position.

5. An array according to claim 4 wherein the central controller is configured to provide said instruction in response to a temperature of a working fluid in said array.

6. An array according to claim 4 wherein the central controller is configured to provide said instruction in response to a weather sensor.

7. An array according to claim 4 wherein the central controller is configured to provide said setpoint in response to a signal indicative of an operating condition of said facility that extracts work from heated working fluid of said array.

8. An array according to claim 1 and further comprising a central controller in communication with the row controller, the central controller being configured to provide a setpoint representative of row angle to the row controller.

9. An array according to claim 8 wherein said setpoint representative of row angle is sufficient to place the rows controlled by the row controller to a position selected from a stow, track, lag, defocus, and wash position.

10. An array according to claim 9 wherein the central controller is configured to provide said setpoint in response to a temperature of a working fluid in said array.

11. An array according to claim 9 wherein the central controller is configured to provide said setpoint in response to a weather sensor.

12. An array according to claim 9 wherein the central controller is configured to provide said setpoint in response to a signal indicative of an operating condition of said facility that extracts work from heated working fluid of said array.

13. An array according to claim 1 wherein the plurality of rows comprises a number of rows, said number being at least five, the plurality of electric motors comprises at least said number of motors respectively coupled to said rows, the plurality of inclinometers comprises at least said number of inclinometers respectively coupled to said rows, and said row controller is configured to sequentially but not simultaneously actuate any of said number of motors.

14. An array according to claim 13 wherein said number is at least ten.

15. An array according to claim 13 wherein said number is at least fifteen.

16. An array according to claim 1 wherein the solar thermal energy collectors are trough collectors.

17. An array according to claim 16 wherein the trough collectors each have a chain and sprocket drive coupling the electric motors and the collector troughs.

18. An array according to claim 16 wherein the trough collectors each have an aperture less than about 3 meters.

19. An array according to claim 18 wherein the aperture is less than about 2 meters.

20. A method of positioning a plurality of rows of a solar thermal energy trough collector array comprising sequentially and not simultaneously positioning any of the number of rows of the array, the number being at least two.

21. The method of claim 20 wherein the number is at least five.

22. The method of claim 20 wherein the number is at least ten.

23. A method according to claim 20 wherein the rows are positioned consecutively.