Patent Publication Number: US-2019190445-A1

Title: Diagnostic vehicles for maintaining solar collector systems

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to U.S. Provisional Application No. 62/591,644, filed Nov. 28, 2017, the entirety of which is herein incorporated by reference. 
    
    
     FIELD 
     This disclosure pertains to solar photovoltaic (PV) power plants. 
     BACKGROUND 
     Photovoltaic panels have a front side and a back side and have in the past typically only collected light from the front side. The equipment designed to work with such monofacial photovoltaic panels has been designed to accommodate panels that receive light only from the front. Similarly, operation and maintenance processes have been designed for panels that only collect light from the front. 
     Some photovoltaic panels, known as bifacial panels, can collect light from both the front side and the back side. Embodiments described herein apply to solar collectors both monofacial and bifacial panels. 
     SUMMARY 
     A diagnostic vehicle for characterizing a solar collector system is presented herein. The diagnostic vehicle comprises a frame, one or more sensors positioned along the frame, and a control system. The one or more sensors measure and characterize attributes of the solar collector system and/or its environment such as a reflectivity of an area of ground around the solar collector system, an angular offset of a drive system of the solar collector system, and/or a degradation of structural components that support photovoltaic panels in the solar collector system. The control system is programmed to move the frame to one or more locations in the solar collector system and control the one or more sensors to acquire measurements at the one or more locations. 
     A method for characterizing a solar collector system is presented herein. In the method, one or more sensors positioned along a frame measure at least one of a reflectivity of an area of ground around the solar collector system, an angular offset of a drive system of the solar collector system, or a degradation of structural components that support photovoltaic panels in the solar collector system. A control system moves the frame to one or more locations in the solar collector system. The control system controls the one or more sensors to acquire measurements at the one or more locations. 
     A system that comprises a solar collector system and a diagnostic vehicle that traverses the solar collector system is presented herein. The diagnostic vehicle comprises a vehicle frame, one or more sensors positioned along the frame to measure and characterize a reflectivity of an area of ground around the solar collector system, and an applicator configured to distribute, based on the reflectivity, a reflective material on an area of ground around the solar collector system. The diagnostic vehicle further comprises a control system programmed to move the frame to one or more locations in the solar collector system and control the one or more sensors to acquire measurements at the one or more locations. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  schematically illustrates a perspective view of an embodiment of a diagnostic vehicle on a solar collector. 
         FIG. 2  shows a side view of a diagnostic vehicle on a solar collector. 
         FIG. 3  depicts a diagnostics vehicle with a camera positioned to observe a backside of solar panels, such as to observe a bar code on the panel. 
         FIG. 4  shows a side view of a diagnostic vehicle on a solar collector positioned to observe solar collector structure, solar collector foundation, nearby ground, and vegetation growth. 
         FIG. 5  depicts a diagnostic vehicle that can be used to measure degradation in a drive system of a solar tracker. 
         FIG. 6  depicts a diagnostic vehicle positioned under a solar collector. 
         FIG. 7  depicts another view of a diagnostic vehicle positioned under a solar collector. 
         FIG. 8  depicts a flow diagram for characterizing a solar collector system. 
     
    
    
     DETAILED DESCRIPTION 
     Solar collectors that use either monofacial panels or bifacial panels face issues of quality of installation, wear and degradation, electrical issues, plant growth around the structure, and a myriad of other problems. Diagnostics can be performed to improve decision making for plant managers, such as by helping to decide when to do maintenance activities. Unfortunately, making measurements or observations of solar panels can be very expensive and yet can also provide a much smaller sample size of observations than is desired. A crew takes time to drive far into the countryside to get to a solar plant and then has time to check only a small number panels or other equipment out of thousands on a typical utility-scale solar plant. Plant managers are left paying significant expenses without getting the information they desire to make good decisions. 
     Measurements and diagnostics can help managers of a solar plant in a variety of ways such as by identifying and characterizing problems, by optimizing plant performance, by observing the state of components for wear or degradation, or by simply observing what components are in which locations in a solar power plant. Measurements and diagnostics are important for solar plants with both monofacial panels and bifacial panels, and the following systems and methods apply to both kinds. 
       FIG. 1  schematically illustrates a perspective view of an embodiment of a diagnostic vehicle  100  on a solar collector  120 . The diagnostic vehicle  100  includes a structure  104  on four sets of wheels  106 , two sets on each side of the solar collector. Each of the four wheel sets  106  consists of a weight-bearing wheel that rides on the top of the solar collector&#39;s concrete ballast  110  or other track and also a guide wheel that rolls along the sides of the concrete track. One or more of the weight-bearing wheels  106  can be a driving wheel that is powered directly or via a transmission by an electric motor or combustion engine. The diagnostic vehicle  100  can also be pulled or pushed by workers, by another vehicle, by a cable, or by other means. The diagnostic vehicle  100  can be powered by one or more solar panels  102  which can charge an onboard battery to store energy. The diagnostic vehicle  100  can alternatively be powered by a battery that is occasionally electrically connected to a charger to recharge the battery or swapped out for a fresh battery. Alternatively, the diagnostic vehicle  100  can be powered by a combustion engine with a fuel tank, can be powered manually, by other means, or by a combination of the above methods. 
     The diagnostic vehicle  100  can include a control system, memory, and a wireless communication system as well. The diagnostic vehicle  100  can be remotely programmed and directed to drive to one or more specific locations, to acquire images and store them as data, and to transmit the data to other computer systems. The diagnostic vehicle  100  also can be equipped with means of determining its position via GPS, via using RFID reader and RFID tags that are placed in its path, via using optical observations of its surroundings, by proximity sensors interacting with corresponding targets, or by other means. The diagnostic vehicle  100  can have a variety of other components too, such as implements for a maintenance process, storage of consumables, an onboard pretreatment system to treat consumables before depositing them, or other components or systems. 
     Continuing with  FIG. 1 , the diagnostic vehicle  100  can carry one or more cameras or other optical sensors  112 . The cameras  112  can take images of solar panels  102  in the infrared (IR) spectrum, in the visible spectrum, or in other sections of the electromagnetic spectrum. Multiple cameras  112  can take multiple images at once. A solar panel typically comprises a number of solar cells. The vehicle frame  104  is configured to position the camera  112  sufficiently far away from the solar panels  102  so a number of cells fits in the camera&#39;s field of view at the same time. The camera  112  can also be angled to look down the row of solar panels  102  to further increase the number of cells or panels that fits inside the camera&#39;s field of view. The extent of an example field of view is diagrammed with dashed lines  114 . 
       FIG. 2  shows a side view of the diagnostic vehicle  100  on a solar collector  120 . The vehicle frame  104  can be shaped like a circle in the direction of this view, and the azimuthal position of the camera  112  around the frame can be adjusted so that the camera  112  can be positioned anywhere along this circle. If the diagnostic vehicle  100  is operating on a fixed-tilt solar collector, the camera  112  can be set in a single position, such as aligned with the normal vector of the solar panels  102 , to take images of the solar collector. If the diagnostic vehicle  100  is operating on a tracking solar collector, as is shown in  FIGS. 1 and 2 , the camera&#39;s azimuthal position on the vehicle frame  104  can be continually or intermittently adjusted to account for the movement of the solar panels  102 . The camera  112  can be moved by an electric motor with a chain or belt transmission, by manual repositioning, by pneumatics, or by other means. As shown in  FIG. 3 , the camera can also be positioned to capture images of the rear of the panels or positioned to capture whatever other images are desired. 
     The camera  112  can be an IR camera, a visible-spectrum (normal) camera, or a combination of both. Infrared spectrum images of operating solar panels can be helpful to show cell temperature, variations of temperature within a cell, and variations of temperature between cells. Temperature measurements can help an operator deduce problems with electrical performance. Combining an IR image with a visible-spectrum image can further aid an operator in understanding solar cell and solar panel performance. With such a camera tool, this diagnostic vehicle  100  can be used to drive along a row of operating solar collectors and collect images in the IR and visible spectra. A computer program can then be used to process the images where results can include flagging anomalies for further attention or generating statistics on a large batch of samples. In this way, an operator can program the diagnostic vehicle  100  to drive through an operating solar plant, capture a number of IR and visible images, to store the data, to process the data on board, and to transmit the data to another computer for further processing, storage, and investigation by the operator. This system and method would be a substantial improvement over other methods of recording images. It would be much cheaper than sending a person to walk around the field with a camera. Besides cost, many solar plants are impractically large to pay people to capture images of all of the panels. Another advantage of the diagnostic vehicle  100  is that the camera is held still and at a uniform position, thus improving image quality and easing image processing. As opposed to aerial vehicles that carry cameras, this land-based vehicle can stop and become motionless to take a picture. This can increase the flexibility in the photography process, for example by allowing a longer exposure duration without blurring the picture. 
     In an alternative embodiment, the camera  112  in  FIG. 3  can be a bar code reader or matrix bar code reader and can be positioned to observe the backside of the panels  102  at the position where the panel&#39;s bar codes are positioned. In this embodiment, the diagnostic vehicle  100  can drive along a row of solar collectors and capture images of panel bar codes. Combining the bar code data with the sequence of when pictures were taken or with the vehicle position can enable a computer program to make a map or catalogue of a solar field of thousands of solar panels to show which solar panels are in which locations. This can be helpful for diagnostic purposes because, for example, electrical problems identified via IR imaging or by other means can be matched to manufacturing batches of panels. Furthermore, construction crews typically do not record panel identification and location when installing them. 
     In an alternative embodiment such as diagrammed in  FIG. 3 , the camera  112  can take visible-spectrum or IR images of any structural members or electrical connections behind the solar panels  112 . These images can be processed to identify construction quality issues, wear marks on the bearing surfaces, other degradation issues, or other problems. For example, images of all of the electrical connections in a solar field can be taken and processed after construction to check that they were all made correctly. Images of all of the metal parts of a solar field can be taken and processed from time to time to check for corrosion. Images of drive system components can be taken and processed to check for wear or increased gaps at bearing surfaces or for other signs of degradation. 
       FIG. 4  shows a side view of a diagnostic vehicle  100  where the camera  112  is positioned on the vehicle&#39;s frame  104  and is rotated on its mount such that its field of view (denoted by dashed lines  114 ) includes the solar collector&#39;s concrete track  110  or other foundation, the solar collector&#39;s mounting structure  108 , the connection between mounting structure  108  and the foundation, and the area of ground around the concrete track  110 . In this configuration, the diagnostic vehicle  100  can be used to drive along and capture images of the foundation, track, structure, and connections between foundation and structure. This can be used to check for quality or defects during installation, such as of an epoxy joint between the concrete and support structure. It can also be used to check for concrete track wear, concrete cracking, track deterioration, and for metal corrosion. It can further be used to check for debris or obstructions on the vehicle track  110 . By capturing images either in IR or visible spectrum of the ground near the solar collector and with subsequent image processing, the diagnostic vehicle  100  can be used to survey how much plant growth  430  has occurred and to help determine whether cutting the plants is necessary. This can also be useful for surveying for other issues like snow accumulation, water pooling, settlement of the ground, animal activity, or other natural phenomena. Conducting surveys with the diagnostic vehicle  100  and subsequent image processing can result in significant cost savings over sending work crews to site to go out and walk the site to check for issues. 
     In  FIG. 4 , the camera  112  can alternatively be a pyranometer, radiometer, or other sensor to measure light. It is possible to deposit agricultural lime or other material to increase the reflectivity of the ground, also called its albedo. By increasing the ground&#39;s reflectivity, the solar panels  102 , and especially bifacial panels, will receive more light reflected from the ground. However, natural phenomena, like rain, can deteriorate the reflectivity benefit of such a ground treatment. A diagnostic vehicle  100  with a sensor to measure light oriented downward at the ground can be used to measure the albedo to help a plant manager decide whether to reapply the treatment that increases albedo. 
     Another way to use the diagnostic vehicle  100  is to measure a degradation in a drive system of the solar tracker  120 , as diagrammed in  FIG. 5 . The solar tracker  120  can use a single drive motor coupled to a long drive shaft or torque tube to provide power and torque to a number of solar tracker sections or a single tracker section, as shown in  FIG. 5 . The torque tube or drive shaft is not perfectly stiff. Torsional flexibility can arise from mechanical fastener tolerances at connection points in the drive shaft, from inherent flexibility in the material, or from other causes. Over time the stiffness of the solar tracker  120  can reduce with wear. 
     In  FIG. 5 , the solar panels  102  are supported by two purlins  124 . The purlins  124  are connected by two pivot arms  118 , which are perpendicular to the purlins  124 . The pivot arms  118  rotate about an axle at the top of a support structure  122 . The support structure  122  is supported by the ballast foundation  110 . 
     A method to measure the flexibility of a tracker row is as follows. The diagnostic vehicle  100  can be positioned at a tracker section of the row furthest from the drive motor. The diagnostic vehicle  100  can be positioned so that the camera&#39;s field of view  114  includes the rotating structural components of the solar tracker  120 , such as the pivot arm  118 , relative to the structural components  122  that are fixed to the foundation. The drive motor can rotate all of the tracker sections to their furthest rotational position away from the diagnostic vehicle&#39;s camera  112 . Then, the motor can slowly rotate the tracker back toward horizontal. The angle of the motor&#39;s encoder can be compared with the angle observed at the last tracker section observed by the camera  112  to estimate the twist in the drive shaft or torque tube between the motor and the last tracker section. Image processing can be used to compare the relative angle of the rotational components such as the pivot arm  118  with the stationary structural components  122  to calculate the flexibility of the drive system. 
     A solar tracker  120  can have a stow position to address strong wind conditions. The stow position can be designed so that the tracker structure can be made much stronger, much stiffer, or better protected from wind forces, or so that the drive system can be decoupled. The diagnostic vehicle  100  of  FIG. 5  can be used to verify on a regular basis that all of the tracker sections  120  of a solar plant properly enter and exit the stow position. The camera  112  can be used to capture images of the drive components or other critical components. Then, imaging software can be used to process the data and to flag those few tracker sections that are not performing properly. Because a large solar plant can have thousands of tracker sections, such verification would otherwise be prohibitively expensive. 
     In  FIGS. 6 and 7 , an alternative diagnostic vehicle  600  is shown positioned under a solar collector  120 . The diagnostic vehicle includes a body  602  which can be carried by four wheel sets  604 . A wheel set  604  can include a weight-bearing wheel which rolls on the top of the solar collector&#39;s concrete track  110  and a guiding wheel that rolls along the inside of the concrete track  110 . The diagnostic vehicle  600  can be solar powered with battery energy storage, powered with a battery and plug-in charger, powered with a battery that can be swapped out for a fresh battery, powered by an engine, or powered by other means such as manually or by a cable. The diagnostic vehicle  600  has a control system, memory, and a communication system as well. The diagnostic vehicle  600  can be programmed and directed remotely to drive to one or more specific locations, to acquire images and store them as data, and to transmit the data to other computer systems. The diagnostic vehicle  600  also has means of determining its position by GPS, by using RFID reader and RFID tags, by using optical observations of its surroundings, or by other means. 
     Continuing with  FIGS. 6 and 7 , the diagnostic vehicle  600  also includes a camera  606 . The camera  606  can be positioned to point upward at the solar panels  102 , support structure, and drive system of the solar collector  120 . The camera  606  can be oriented to look down the line of solar panels  102  to increase the field of view (denoted with dashed lines  610 ) so that the entire width of the solar panels  102  is in view. An angular position of the camera  606  can be changed by onboard motors to observe different view of the solar collector  120 , for example to keep the solar panels  102  in view as they track the sun. The camera  606  can be an IR camera that observes the solar cells for temperature, a visible-spectrum camera and an IR camera, or a visible-spectrum camera. The camera  606  can be directed and focused to observe the solar panels  102 , structural members of the solar collector, or drive system members of the solar collector. The diagnostic vehicle  100  can take images during an operation of the solar collector  120  or when the solar collector  120  is not operating. This diagnostic vehicle embodiment can be used to observe tracker section movement, driveshaft twist, and other mechanical behavior in the same methods as the diagnostic vehicle of  FIGS. 1-7 . 
       FIG. 8  depicts a flow diagram for characterizing a solar collector system. At  802 , one or more sensors positioned along a frame measure at least one of a reflectivity of an area of ground around the solar collector system, an angular offset of a drive system of the solar collector system, or a degradation of structural components that support photovoltaic panels in the solar collector system. A control system moves the frame to one or more locations in the solar collector system at  804 . At  806 , the control system controls the one or more sensors to acquire measurements at the one or more locations. 
     In the descriptions above and in the claims, phrases such as “at least one of” or “one or more of” can occur followed by a conjunctive list of elements or features. The term “and/or” can also occur in a list of two or more elements or features. Unless otherwise implicitly or explicitly contradicted by the context in which it is used, such a phrase is intended to mean any of the listed elements or features individually or any of the recited elements or features in combination with any of the other recited elements or features. For example, the phrases “at least one of A and B;” “one or more of A and B;” and “A and/or B” are each intended to mean “A alone, B alone, or A and B together.” A similar interpretation is also intended for lists including three or more items. For example, the phrases “at least one of A, B, and C;” “one or more of A, B, and C;” and “A, B, and/or C” are each intended to mean “A alone, B alone, C alone, A and B together, A and C together, B and C together, or A and B and C together.” In addition, use of the term “based on,” above and in the claims is intended to mean, “based at least in part on,” such that an unrecited feature or element is also permissible. 
     The subject matter described herein can be embodied in systems, apparatus, methods, and/or articles depending on the desired configuration. The implementations set forth in the foregoing description do not represent all implementations consistent with the subject matter described herein. Instead, they are merely some examples consistent with aspects related to the described subject matter. Although a few variations have been described in detail above, other modifications or additions are possible. In particular, further features and/or variations can be provided in addition to those set forth herein. For example, the implementations described above can be directed to various combinations and subcombinations of the disclosed features and/or combinations and subcombinations of several further features disclosed above. In addition, the logic flows depicted in the accompanying figures and/or described herein do not necessarily require the particular order shown, or sequential order, to achieve desirable results. Other implementations may be within the scope of the following claims.