Heliostat Control Scheme Using Cameras

Abstract

A heliostat control system includes a heliostat having a reflective surface and at least one reflective element, the reflective surface having a different radius of curvature than the at least one reflective element, a receiver configured to receive sunlight reflected from the reflective surface, and a camera configured to receive sunlight reflected from the at least one reflective element and to generate an image including pixels having a brightness dependent on an orientation of the reflective surface.

1 . A heliostat control system, comprising:
 a heliostat having a reflective surface and at least one reflective element, the reflective surface having a different radius of curvature than the at least one reflective element;   a receiver configured to receive sunlight reflected from the reflective surface; and   a camera configured to receive sunlight reflected from the at least one reflective element and to generate an image including pixels having a brightness dependent on an orientation of the reflective surface.   
     
     
         2 . The heliostat control system of  claim 1 , wherein the at least one reflective element has a greater radius of curvature than the reflective surface. 
     
     
         3 . The heliostat control system of  claim 1 , wherein the at least one reflective element is circular in shape. 
     
     
         4 . The heliostat control system of  claim 1 , wherein the at least one reflective element is convex. 
     
     
         5 . The heliostat control system of  claim 1 , wherein the at least one reflective element is on the reflective surface. 
     
     
         6 . The heliostat control system of  claim 5 , wherein the at least one reflective element is located proximate to a center of the reflective surface. 
     
     
         7 . The heliostat control system of  claim 5 , wherein there are a plurality of reflective elements, and wherein at least some of the reflective elements are located proximate to corners of the reflective surface. 
     
     
         8 . The heliostat control system of  claim 1 , wherein the at least one reflective element includes a first portion and a second portion, the first portion having a lower reflectivity than the second portion. 
     
     
         9 . The heliostat control system of  claim 8 , wherein the first portion of the at least one reflective element is closer to a center of the reflective surface than the second portion. 
     
     
         10 . The heliostat control system of  claim 1 , wherein the at least one reflective element is generally tubular in shape. 
     
     
         11 . The heliostat control system of  claim 10 , wherein the at least one reflective element is bowed outward from the reflective surface. 
     
     
         12 . The heliostat control system of  claim 1 , wherein there are a plurality of heliostats, the receiver is configured to receive sunlight reflected from a reflective surface of each of the plurality of heliostats, and the image includes pixels having a brightness depending on an orientation of each of the reflective surfaces. 
     
     
         13 . The heliostat control system of  claim 12 , further comprising a controller configured to receive the image from the camera and calculate an error in the orientation based upon the image. 
     
     
         14 . The heliostat control system of  claim 13 , wherein the controller is further configured to associate pixels of the image with the at least one reflective element. 
     
     
         15 . The heliostat control system of  claim 13 , wherein there are a plurality of reflective elements, and wherein the controller is configured to calculate the error by determining whether a brightness of pixels associated with one reflective element differs substantially from a brightness of pixels associated with a different reflective element. 
     
     
         16 . The heliostat control system of  claim 13 , wherein the controller is further configured to send a signal to change the orientation of the mirror based upon the determined error. 
     
     
         17 . The heliostat control system of  claim 16 , wherein there are a plurality of reflective elements, and wherein the controller is configured to repeat the steps of receiving an image, calculating an error, and sending a signal until a brightness of pixels associated with one reflective element is substantially equivalent to a brightness of pixels associated with each of the other reflective elements. 
     
     
         18 . The heliostat control system of  claim 13 , wherein the controller is configured to associate a portion of the image with the heliostat. 
     
     
         19 . The heliostat control system of  claim 1 , further comprising a plurality of cameras positioned on different sides of the receiver and a controller configured to receive images from the cameras, and wherein the controller is configured to generate a error signal from a comparison of intensity values from the images from the cameras. 
     
     
         20 . The heliostat control system of  claim 19 , wherein the controller is configured to cause the heliostat to point toward a location off-center of the receiver. 
     
     
         21 . The heliostat control system of  claim 20 , wherein the controller is configured to subtract an intensity value from a first image from a first camera of the plurality of cameras from an intensity value from a second image from a second camera of the plurality of cameras to generate an error signal, and wherein the controller is configured to control orientation of the heliostat so that the error signal reaches a non-zero target value. 
     
     
         22 . A method of heliostat control, comprising:
 receiving sunlight in a receiver, the sunlight received in the receiver reflected from a reflective surface of a heliostat;   receiving sunlight in a camera, the sunlight received in the camera reflected from at least one reflective element of a heliostat, the at least one reflective element having a different radius of curvature than the reflective surface;   generating an image from the sunlight reflected into the camera; and   determining an error in an orientation of the reflective surface based upon the image.   
     
     
         23 . The method of  claim 22 , wherein the sunlight is reflected from a plurality of reflective surfaces, each reflective surface having a corresponding heliostat, and wherein determining comprises determining an error in an orientation of each of the reflective surfaces. 
     
     
         24 . The method of  claim 22 , further comprising associated pixels of the image with the at least one reflective element. 
     
     
         25 . The method of  claim 24 , wherein there are a plurality of reflective elements, and wherein calculating the error includes determining whether a brightness of the pixels associated with one reflective element differs substantially from a brightness of pixels associated with a different reflective element. 
     
     
         26 . The method of  claim 22 , further comprising sending a signal to change the orientation of the reflective surface based upon the determined error. 
     
     
         27 . The method of  claim 26 , wherein there are a plurality of reflective elements, the method further comprising repeating the steps of generating an image, determining an error, and sending a signal until a brightness of pixels associated with one reflective element is substantially equivalent to a brightness of pixels associated with each of the other reflective elements. 
     
     
         28 . The method of  claim 22 , further comprising associating a portion of the image with the heliostat. 
     
     
         29 . The method of  claim 22 , further comprising cooling the camera with a cooling system. 
     
     
         30 . The method of  claim 22 , wherein determining an error comprises comparing images generated from a plurality of cameras. 
     
     
         31 . The method of  claim 22 , wherein determining an error comprises comparing the image with an expected image. 
     
     
         32 . The method of  claim 22 , further comprising controlling the heliostat to point toward a off-center location of the receiver. 
     
     
         33 . The method of  claim 32 , wherein controlling the heliostat includes subtracting an intensity value from a first image from a first camera of a plurality of cameras from an intensity value from a second image from a second camera of the plurality of cameras to generate an error signal, and adjusting orientation of the heliostat so that the error signal reaches a non-zero target value. 
     
     
         34 . A method of heliostat control, comprising:
 receiving sunlight in a receiver, the sunlight received in the receiver reflected from a reflective surface on a heliostat;   receiving sunlight in a camera, the sunlight received in the camera reflected from at least one reflective element of a heliostat;   oscillating the reflective element at a frequency;   generating first image from the sunlight reflected into the camera; and   assigning a portion of the image to the heliostat by detecting the frequency of oscillation in the first image.   
     
     
         35 . The method of  claim 34 , further comprising:
 generating a second image from the camera;   locating in the second image the assigned portion; and   determining an error in an orientation of the reflective surface based upon the assigned portion.   
     
     
         36 . The method of  claim 35 , further comprising sending a signal to change the orientation of the reflective surface. 
     
     
         37 . The method of  claim 34 , further comprising:
 receiving sunlight in the receiver, the sunlight received in the receiver reflected from reflective surfaces of a plurality of heliostats;   receiving sunlight in the camera, the sunlight received in the camera reflected from reflective elements of a plurality of heliostats;   oscillating each of the plurality of heliostats at different frequencies;   assigning a different portions of the image to each of the plurality of heliostats by identifying the different frequencies of oscillation in the first image.