This invention is directed generally to apparatus and methods for locating and tracking a light source. More specifically, the present invention is directed to a system and method for optimizing the power generation of a photovoltaic power panel or array by utilizing a photovoltaic cell as both a power source and a solar tracking mechanism.
In concentrating photovoltaic (CPV) systems, optics are used to concentrate sunlight onto a relatively small solar cell. A primary optical element (such as a Fresnel lens) is used to concentrate the sunlight into a small spot on the aperture area of a solar cell. Typically, a tracking system is used to keep the spot of concentrated sunlight focused on the solar cell throughout the day.
In high-concentration CPV, where the concentration provided by the primary optical element is greater than 100x, a tracking system involving moving the photovoltaic panel or module in two-axes is used to keep the optical and cell surfaces perpendicular to the sun's rays during operation. Precise tracking, with a precision error of less than one degree is typically required in such systems to keep the spot centered on the cell area.
Tracking methods used to maintain the focused sun spot centered on the cell are generally divided into two methods: “open-loop” tracking, in which the system is pointed in a direction where the sun is expected to be, based on geographical location and the time of year, and “closed-loop” tracking, in which the location of the sun is determined by measuring its intensity and providing feedback to the tracker to allow it to follow the sun's apparent motion across the sky. Open-loop and closed-loop methods might be used separately, or they may be combined in larger systems. For CPV, some form of “closed-loop” tracking is required in order to achieve the necessary precision.
Generally some form of “closed-loop” tracking is required for the tracking precision necessary to optimize power generation in a CPV system. Closed-loop tracking systems utilize a sensor to detect the sun's position and align the system accordingly. For small systems, the sensor is may often be the photovoltaic module itself In such systems, the output of the module is connected to a monitoring system, such as computer or processor programmed with software designed to monitor the power output of the module. The processor typically applies a “perturb and observe” algorithm to the system. Using such an algorithm, the processor changes the position of the module slightly and evaluates the change in the power output of the module. The processor continues to cause the module to move in the direction of higher power output until the peak power is obtained. This is a form of maximum power point tracking (MPPT). While such a system is useful for small photovoltaic systems, it requires use of power to initiate movement of the module, and thus reduces the net power output of the module. Moreover, such a system is often inefficient when applied to a larger system, since it may be difficult to maximize the power of a large array.
For larger systems, an independent sun sensor is often used. Such a sun sensor measures the misalignment between the sun's rays and the system and moves the system to minimize the misalignment. One example of such a sun sensor is a quadrant sun sensor. Light falling on each quadrant generates electric current proportional to the intensity of sunlight. The current output by each quadrant of the sensor is measured; and when the current from each quadrant is equal, the sun is centered on the sensor. If the sensor is aligned with the system, then the system will also be aligned properly.
Until recently, both types of “closed-loop” tracking described above have suffered from significant limitations. For example, the modules employing such closed-loop systems must be aligned properly to the tracker mechanism during installation of the module. This process can be difficult, time consuming, and prone to error.
Another problems is that, once the modules are aligned and operating, the “perturb and observe” approach often results in a measurable decrease in power output before the monitoring software can detect an off-track condition and begin moving the system back into alignment. The frequent movement, or perturbation, of the system to “observe” the changes also results in significant power consumption in a system that is meant to produce, not consume, power. For these reasons, the “perturb and observe” method of closed-loop tracking is an unacceptable option for large systems where even small movements off track cause significant power losses, and which also require more power to move.
While the use of an independent sun sensor can eliminate the issues described above with respect to the “perturb and observer” approach, the use of a separate sun sensor presents difficulties of its own. For example, the use of a separate sensor unit adds cost and complexity to the system; moreover, the reliability of the sun sensor may require frequent maintenance or replacement.
Importantly, since the sensor output is independent of the system's generating power, there is no guarantee that the alignment of the sun sensor with the sun corresponds to alignment of the adjacent power modules to the sun. Accordingly, the sun sensor must be carefully aligned with the power module for the sun sensor to be effective in maximizing the power generation of the module. Delicate and time-consuming calibration of the sun sensor is required during installation, and ongoing maintenance is necessary to verify that proper alignment is maintained. For large systems involving many panels, there may also be significant variation in both the alignment and power output of each of the panels. Thus, it may become difficult to determine which alignment will provide the most overall system power and energy.
What has been needed, and heretofore unavailable, is a simple to install and calibrate, reliable and low cost system and method for aligning a large, high concentrating photovoltaic system. Such a system would provide reliable, precise tracking of the sun to maximize power generation by the system while minimizing power losses due to parasitic power consumption. The present invention satisfies these and other needs.
In its most general aspect, the present invention includes a specially modified power generating solar cell that includes two or more electrically isolated portions, with each portion capable of being independently monitored. The output generated by each independently monitored portion is analyzed to determine if the power generated by each portion is substantially equal, and if not, algorithms are applied that result in a processor or controller providing positioning signals to a mechanism designed to move an array of solar cells that includes the specially modified power generating solar cell into optimal alignment with the direction light rays incident on the cell from the sun.
In another aspect, the present invention includes a sun sensor configured to provide an indication of the position of the sun, comprising: a solar cell disposed on a moveable structure, the solar cell configured to have a plurality of electrical current generating portions; a plurality of electrical contacts, each of the plurality of electrical contacts configured to tap a signal generated by an individual electrical current generating portion of the solar cell; a plurality of electrical parameter monitors, each of the plurality of electrical parameter monitors in electrical communication with one of the plurality of electrical contacts, and each of the electrical parameter monitors configured to provide a signal representative of an electrical parameter generated by one of the plurality of electrical current generating portions of the solar cell. In an one aspect, the electrical parameter is a current; in another aspect, the electrical parameter is a voltage.
In yet another aspect, each of the plurality of power generating portions of the solar cell are separated from each other by an area having electrical resistance sufficient to electrically isolate each of the plurality of power generating portions of the solar cell from each other.
In still another aspect, the area of electrical resistance is a trench formed in a layer of the solar cell.
In yet another aspect, the solar cell is formed from a light absorbing electrical current generating semiconductor material disposed on an electrically insulated substrate. In a still further aspect, the plurality of electrical current generating portions are defined by electrically isolating separators disposed in the light absorbing electrical current generating semiconductor material to divide the light absorbing electrical current generating semiconductor material into the plurality of electrical current generating portions. In another aspect, an individual one of the plurality of electrical contacts is in electrical communication with an individual one of the plurality of electrical current generating portions.
In a still further aspect, the separator is formed by removing a portion of the light absorbing electrical current generating semiconductor material to define an electrically isolated portion of the light absorbing electrical current generating semiconductor material. In another aspect, the substrate is thermally conductive.
In yet another aspect, the present invention includes a sun sensor for tracking the location of the sun, comprising: a solar cell mounted on a moveable structure, the solar cell having a plurality of trenches that define electrically isolated electrical current generating portions of the solar cell; a plurality of electrical contacts, each one of the plurality of electrical contacts in electrical communication with a different electrically isolated electrical current generating portions of the solar cell; and a plurality of electrical parameter monitors, each of the plurality of electrical parameter monitors in electrical communication with one of the plurality of electrical contacts, and each of the electrical parameter monitors configured to provide a signal representative of an electrical parameter generated by one of the plurality of the electrically isolated electrical current generating portions of the solar cell. In one alternative aspect, the electrical parameter is a current.
In a further aspect, the present invention includes a sun sensor for use in controlling the movement of a photovoltaic array to maintain the alignment of the photovoltaic array with the sun as the sun moves across the sky during a day, comprising: a sun sensing solar cell mounted on an insulating substrate, the insulated substrate disposed on a moveable support structure as part of an array of power generating solar cells, the sun sensing solar cell having a plurality electrically isolated electrical current generating portions defined by areas of areas of increased electrical resistivity disposed between the plurality electrically isolated electrical current generating portions, the sun sensing solar cell also contributing to a power output of the array of power generating solar cells; a plurality of electrical contacts, each one of the plurality of electrical contacts in electrical communication with a different electrically isolated electrical current generating portion of the sun sensing solar cell; and a plurality of electrical parameter monitors, each of the plurality of electrical parameter monitors in electrical communication with one of the plurality of electrical contacts, and each of the electrical parameter monitors configured to provide a signal representative of an electrical parameter generated by one of the plurality of the electrically isolated electrical current generating portions of the sun sensing solar cell.
In yet another aspect, the present invention further comprises a processor configured to receive the signals from the plurality of the electrical parameter monitors and also configured to analyze those signals and to provide appropriate control signals to the moveable structure to position the solar cell in relation to the sun so as to substantially equalize the electrical parameter generated by each of the electrically isolated electrical current generating portions of the solar cell.
In still another aspect, the present invention includes a sun sensor for use in controlling the movement of a photovoltaic array to maintain the alignment of the photovoltaic array with the sun as the sun moves across the sky during a day, comprising: a sun sensing solar cell mounted on an insulating substrate, the insulated substrate disposed on a moveable support structure as part of an array of power generating solar cells, the sun sensing solar cell having a plurality electrically isolated electrical current generating portions defined by areas of areas of increased electrical resistivity disposed between the plurality electrically isolated electrical current generating portions, the sun sensing solar cell also contributing to a power output of the array of power generating solar cells.
In yet another aspect, the present invention includes a sun sensor configured to provide an indication of the position of the sun, comprising: a solar cell disposed on a moveable structure, the solar cell configured to have a plurality of electrical current generating portions; a plurality of electrical contacts, each of the plurality of electrical contacts configured to tap a signal generated by an individual electrical current generating portion of the solar cell; a plurality of electrical parameter monitors, each of the plurality of electrical parameter monitors in electrical communication with one of the plurality of electrical contacts, and each of the electrical parameter monitors configured to provide a signal representative of an electrical parameter generated by one of the plurality of electrical current generating portions of the solar cell; and a processor configured to receive the signals from the plurality of the electrical parameter monitors and also configured to analyze those signals and to provide appropriate control signals to the moveable structure to position the solar cell in relation to the sun so as to substantially equalize the electrical parameter generated by each of the electrical current generating portions of the solar cell.
Other features and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the features of the invention.
Referring now to the drawings in detail, in which like reference numerals indicate like or corresponding elements among the several figures, there is shown in
High concentrating photovoltaic cell 10 typically has a housing 12 having sides that are sloping and/or reflective to assisting in focusing solar radiation or rays 18 onto a solar cell 16. Such a high concentrating cell 10 also includes a primary optical element 14, which may be, in some embodiments, a Fresnel lens. As shown in
A quadrant sun sensor in accordance with the various embodiments of the present invention may be introduced into a photovoltaic array or module without significant impact on the operation of the system. Those skilled in the art will recognize that a variety of techniques exist for manufacturing such a quadrant sun sensor solar cell. For example, the solar cell may be manufactured using current techniques, with electrical resistance increased between the quadrants by forming separators, such as, for example, narrow trenches 80, 82 into the cell to form the quadrants. Typical cell forming technology using photolithographic techniques, wet or dry chemical etching, laser scribing, and/or saw dicing may be used.
It is not necessary that the trenches penetrate the full thickness of the cell to provide sufficient isolation between the quadrants of the solar cell. For example, the depth of the trench may be less than the thickness of the top solar cell junction, that is, less than a few micrometers. For increased isolation between the quadrants, the trench may extend deeper into the thickness of the cell.
Where the semiconductor layers of the solar cell have high enough lateral resistance, it may only be necessary to provide the four separate contacts 70, 72, 74 and 76. In this embodiment, the relatively high lateral resistance minimizes “cross-talk” between adjacent quadrants. The relatively high lateral resistance between quadrants ensures that separate independent contacts 70, 72, 74 and 76 will provide sufficiently independent electrical signals to allow for sensor operation. If greater isolation is required, one or more of the previously described techniques may be used to separate the quadrants.
Where a physical separation of quadrants 62, 64, 66, and 68 is required to ensure electrical isolation between the quadrants, the physical separation is typically in the range of 25 micrometers (μm) if a dicing saw is used to form the trenches between each quadrant. Where chemical etching is used to form the trenches, the trench width might be just a few micrometers in width. The depth of the trench may range from about 100 nanometers (nm) to approximately twenty percent (20%) of the cell thickness. For example, the trench formed in a 200 μm thick cell may be 40 μm deep. Typically, the depth of the trench will be selected to increase electrical isolation in part or all of the electrical junctions that comprise the various embodiments of the solar cell present invention. The resulting loss of power generating area of the solar cell caused by the formation of the trenches 80, 82 could be less than 0.5% of the total area of the cell, which is typically within the range of acceptable cell performance. If greater tracking precision is required, the power generating area of the solar cell may be further divided, or pixelated, to include more than four quadrants. Such an arrangement will continue to function without increasing the parasitic power demands on the cell where the monitoring technology used has low impedance, such as with an ammeter. Therefore, the sun sensor is enabled to simultaneously function as an integrated part of a power-generating solar array.
Returning now to
A Y-axis drive mechanism may be used to automatically move the array 40 about the Y-axis. Similarly, an X-axis drive mechanism may be used to automatically move the array 40 about the X-axis. The drive mechanisms typically comprise drive motors mechanically coupled to drive gears or hydraulic actuators configured to rotate the array about the axes. In some embodiments, the drive motors are stepper motors or servo-motors, and the drive gears are worm gears. In other embodiments, the drives may be hydraulically actuated.
Generally, the drives are electrically coupled to a drive processor or computer that controls drive rates at which the array 40 rotates around each of the axes. The drive processor is configured to communicate drive signals to the drive mechanisms or actuators so as to control the pointing, tracking, and guiding of the array 40. For example, some embodiments of the drive mechanisms include position sensing devices such as, for example, rotary encoders for sensing the angular position of the axes. The rotary encoders may comprise mechanical, optical, or magnetic encoders. The drive processor may communicate drive signals through an electric connection such as a wire or may use wireless signals such as, for example, infrared or radio frequency signals.
Various embodiments of the drive processor may include electronic circuitry to control the drive mechanisms according to programming established to provide for sensing the position of the sun in relation to the pointing direction of the array 40, and then provide from movement of the array in the suitable axis or axes to optimize the power generation of the array. The drive processor may include a set of logic instructions for converting programming commands into electronic drive signals.
In block 110, the signals from the quadrant sensor may be communicated to an (optional) comparator by wired and/or wireless techniques. The wires that carry electrical power in the solar module or modules may also be used to carry the signals form the quadrant sensor. The wireless techniques may include transmitting and/or receiving electromagnetic signals, such as, for example, infrared or radio frequency signals. In some embodiments, the comparator comprises a microprocessor that implements a set of logic instructions for processing and/or analyzing the signals from the quadrant sensor. The logic instructions used by the comparator may be encoded in hardware, firmware, or software. The logic instructions may implement algorithms that use information from the signals to estimate parameters relating to the solar cell or individual quadrants of the solar sensor. For example, the parameters may include one or more of a current, voltage, power, brightness, flux, fluence, intensity, or other aspect relating to the sensor. Typically the parameter estimated will be an electrical current.
In
In optional block 110, the comparator produces one or more signals indicative of the parameters relating to the sun sensor. For example, the comparator signals may represent the amount of current being produced by each of the quadrants 62, 64, 66, and 68 of the sun sensor.
In block 120, the comparator signals may be communicated to a drive processor. The drive processor may also receive signals from one or more drive mechanisms that are used to move the array 40 about one or more axes. For example, one or more encoders coupled to the array axes may communicate the angular position of the array axes to the drive processor. The drive processor may further process or analyze the signals received from different components in the sun sensor system. The drive processor may be separate from or integrated with the comparator, and either or both may be implemented in hardware, software, or firmware. In certain embodiments, the drive processor is disposed in or on the array. In other embodiments, the drive processor may be disposed remotely from the array, as described above with reference to the comparator.
In block 130, the drive processor communicates with the array drive mechanisms so as to move the array as needed. In some embodiments, the drive processor generates one or more signals that are communicated to drive actuators coupled to the axes of the array. The drive processor can communicate signals so as to cause the array to point toward the sun and/or to track the sun as it moves.
The flowchart illustrated in
In the various embodiments of the invention, the signals A, B, C, and D from the quadrants of the sensor are communicated to a comparator, as described above. The comparator is configured to use the signals to estimate a location and/or direction of the sun. As described previously, the comparator can communicate information relating to the sun's position to a drive processor and/or array drive mechanisms to move the array about the X and Y axes of the array in order to point to and/or track the sun.
In an embodiment, process 200 may be implemented by a comparator such as that described in optional block 110 in
As used herein with reference to the description of
A software code block may be compiled and linked into an executable program, installed in a dynamic link library, or may be written in an interpreted programming language. It will be appreciated that software code blocks may be callable from other code blocks or from themselves, and/or may be invoked in response to detected events or interrupts. The code blocks described herein are preferably implemented as software, but may be represented in hardware or firmware.
As shown in
Additionally, the signals A, B, C, D may be converted from one electrical form to another, for example, a current may be converted to a voltage. In certain preferred embodiments, the signals A, B, C, and D are currents that may be amplified to enable more precise measurements. Some embodiments may utilize one or more amplifiers to convert the currents into measurable difference voltages.
The conditioned signals are communicated to the X-axis tracking code block 220 and the Y-axis tracking code block 230, which are configured to communicate output signals to the drive processor and/or the drive mechanisms to move the array. For example, the output signals may include instructions to move the array about a particular axis, in a particular direction, and at a particular rate. As described herein, X-axis directions such as “right” or “left,” and Y-axis directions such as “upward,” “above,” “downward,” or “below” are measured with respect to the plane of the quadrants 62, 64, 66, and 68 looking outward along the optical axis toward the sun.
In block 250 of the Y-axis tracking code block 230, the sum of signals A and B are compared to the sum of the signals C and D. If the sum of signals A and B is greater than the sum of signals C and D, the sun is above the optical axis, and the Y-axis tracking code block 230 transmits an instruction to slew the array upward. Conversely, if the sum of signals A and B is less than the sum of signals C and D, the sun is below the optical axis, and the Y-axis tracking code block 230 transmits an instruction to slew the array downward. If the sum of signals A and B equals (to within a tolerance) the sum of signals C and D, no action is taken.
In block 260, an inquiry is made whether to continue to move the array. If the answer is yes, the process 200 loops back either to the signal conditioning code block 210, if used, or to the entry of code block 220 to receive further inputs from the quadrant sensors, and if the answer is no, the process 200 stops. In some embodiments, the process 200 may include code blocks configured to display information related to the inquiry on a screen, monitor, or other display, and which may be conveyed to a user audibly, tactilely, or visually. The user may input an answer to the inquiry via a keyboard, keypad, buttons, switches, or sensors. For example, the user may input a “stop” answer when the sun is located within the field of view of the array and the user has determined that the power generation of the array has been maximized. The user may also use the sun position information from the sun sensor to mechanically align the solar module with the sun.
In other embodiments, the process 200 may utilize a feedback loop to automate pointing the array toward the sun. For example, in certain embodiments, process 200 may repeat the procedures implemented in the code blocks 210, 220 and 230 until each of the signals A, B, C, and D is substantially equal to within an error tolerance. When the four signals are substantially equal, the sun has been located to within the error tolerance, and the array has been accurately pointed toward the sun to maximize the power generated by the array.
Returning again to
In the example of
It will be apparent to those skilled in the art that the various embodiments of the present invention may also be used to point the array toward the sun, and then begin tracking the sun. This embodiment of the present invention is particularly useful at the beginning of a day. In some “open-loop” embodiments, the expected position of the sun at dawn of any given date and spatial local on earth can be stored in a memory associate with the processor charged with controlling the movement of the array. The system could, for example, turn off tracking of the sun at sun down, enter a hibernation state during the night to conserver power, and then, shortly before dawn, move the array into position to capture the first rays of the sun. Active or “closed-loop” monitoring would then begin to ensure optimal power generation by the array as the sun moves across the sky during the remainder of the day. Alternatively, an operator could enter appropriate coordinates for the array to position the array for the start of the day. A similar procedure may be used during initial installation of the array. In other embodiments, open-loop and closed-loop sun tracking may be combined.
After the array 40 (
In other embodiments present invention, the system may utilize algorithms and processes that are additional to and/or different from those illustrated in
In this embodiment, the system transmits instructions to the drive processor or the drive mechanisms so as to reduce the coordinate values in Equations 1 and 2 to zero (within an error tolerance). The sun is located when the x-y coordinates are substantially equal to zero. Such an algorithm may be readily implemented in a feedback loop that monitors the x-y coordinates and makes adjustments to the X-axis and Y-axis drive mechanisms to ensure the x-y coordinates remain substantially equal to zero.
In other embodiments, the process 200 may include additional or different hardware or software code blocks than shown in the sample flowchart of
The code blocks and functions of process 200 may be implemented in electronic circuitry comprising hardware, firmware, and/or software. The set of logic instructions implemented by the electronic circuitry may be embodied by a computer program that is executed by a processor or electronics as a series of computer- or control element-executable instructions. These instructions or data usable to generate these instructions may reside, for example, in random access memory (RAM), on a hard drive or optical drive, or on a disc.
A typical concentrating photovoltaic array contains hundreds of solar cells arranged into parallel and series strings in order to generate power. Sun sensors in accordance with the various aspects of the present invention are incorporated into the array of solar cells to provide sun position information. In general, the number of sun sensors deployed in each array could be relatively small, and their position among the solar cells of the array could be pre-determined, or could be placed according to an random assignment. Since the sun sensor cells are dispersed among the solar cells, the signals from the suns sensor cells may be useful in aligning and calibration of the array during installation of the array.
An additional advantage of the sun sensor/solar cells of the various embodiments of the present invention is that each of the sun sensor cells also generates power similar to an ordinary solar cell. Any loss in power from the sun sensor solar cells would be within the range of power generation variation expected from the operation of ordinary solar cells. Thus, there can be a large number of suns sensor cells dispersed in the array without decreasing the efficiency of the array. Further, not all of the sensor cells dispersed within the array would be needed to track the sun. This feature add redundancy and would allow the processor monitoring the sun sensor cells to be programmed to use only the number of cells necessary to adequately track the sun, ignoring the signals from the rest of the sensors. Should one or more of the monitored cells fail, the processor would simply begin actively monitoring a sun sensor cell or cells located in the approximate area of the failed cell. In some embodiments, every solar cell in the array could be a sun sensor/solar cell. In other embodiments, only a single sun sensor/solar cell might be incorporated into the array to provide sun tracking information to the processor control the tracking process.
While several particular forms of the invention have been illustrated and described, it will be apparent that various modifications can be made without departing from the spirit and scope of the invention.