Automated heliostat reflectivity measurement system
Methods and systems for measuring heliostat reflectivity with a control processing unit configured to receive an image of a heliostat, receive an image of the Sun, process the received images, and determine a reflectivity estimate based on a comparison of the processed images.
1. A heliostat reflectivity measurement system comprising:
a control processing unit comprising a processor and addressable memory; the control processing unit configured to:
receive an image from a imaging device having a field of view;
receive a reading of total energy absorbed by a thermopile having a field of view within the field of view of the imaging device;
determine a total number of pixels in the received image containing part of an image of the solar disc; and
determine a reflectivity estimate based on the determined total number of pixels in the received image containing part of the image of the solar disc and the received reading of total energy absorbed by the thermopile.
2. The heliostat reflectivity measurement system of claim 1 wherein the determined reflectivity estimate is further based on an angular size of a pixel in the received image and a surface brightness of the solar disc.
3. The heliostat reflectivity measurement system of claim 2 wherein the control processing unit is further configured to:
calibrate the angular size of a pixel based on the number of pixels in a received image of an object with a known size and wherein the object is a known distance from the imaging device.
4. The heliostat reflectivity measurement system of claim 2 wherein the control processing unit is further configured to:
receive a measurement of the direct normal insolation provided by the solar disc;
receive an angular size of the solar disc; and
determine the surface brightness of the solar disc based on the received measurement of direct normal insolation and received angular size.
5. The heliostat reflectivity measurement system of claim 1 wherein the control processing unit is further configured to:
determine a scaling factor based on a received reading of total energy absorbed by a thermopile for a received image of a surface with a known reflectivity.
6. The heliostat reflectivity measurement system of claim 5 wherein the determined reflectivity estimate is further based on the scaling factor.
7. The heliostat reflectivity measurement system of claim 6 wherein the scaling factor is the product of the total number of pixels in the received image containing part of an image of the solar disc and the known reflectivity of the surface divided by the received reading of total energy absorbed by the thermopile.
8. The heliostat reflectivity measurement system of claim 6 wherein the determined reflectivity estimate is the received reading of total energy absorbed by the thermopile divided by the product of the total number of pixels in the received image containing part of an image of the solar disc and the scaling factor.
9. The heliostat reflectivity measurement system of claim 2 wherein the determined reflectivity estimate is the received reading of total energy absorbed by the thermopile divided by the product of the total number of pixels in the received image containing part of an image of the solar disc, the angular size of a pixel in the received image, and the surface brightness of the solar disc.