Method And Apparatus For Forecasting Solar Radiation And Solar Power Production Using Synthetic Irradiance Imaging

Abstract

In an embodiment, measurements are simulated of direct normal irradiance, diffuse horizontal and global horizontal irradiance from groups of two or more photovoltaic arrays and/or irradiance sensors which are located in close proximity to each other and which have different tilt and azimuth angles. Irradiance measurements derived from solar power system power measurements are combined with measurements made by irradiance sensors to synthesize an image of ground level global horizontal irradiance which can be used to create a vector describing motion of that image of irradiance in an area of interest. A sequence of these irradiance images can be transformed into a time series from which a motion vector can be derived. The motion vector can be applied to a current image of ground level irradiance and that image can be projected to a future point in time to provide a solar radiation forecast. These forecasts can be converted into forecasts of solar power system power in the area of interest.

What is claimed is: 
     
         1 . A method comprising:
 collecting data, which is based on irradiance incident upon a surface, from a plurality of irradiance sensitive devices in a geographic area subdivided into a gridded pattern comprised of grid cells, each irradiance sensitive device having an irradiance sensitive surface, and each grid cell comprising a group of two or more irradiance sensitive devices whose respective irradiance sensitive surfaces have differing tilt and azimuth angles; calculating on a computer processor irradiance incident upon the plurality of irradiance sensitive surfaces from the collected data;   combining values of calculated incident irradiance from the two or more irradiance sensitive devices within the groups; and   calculating solar radiation from the combined values of incident irradiance.   
     
     
         2 . The method of  claim 1  further comprising:
 defining a solar radiation map by defining a grid of grid cells on the geographic area and associating values of the calculated solar radiation with particular individual grid cells. 
 
     
     
         3 . The method of  claim 1  wherein collecting data includes:
 defining time frames; 
 receiving asynchronous data which is proportional to irradiance incident upon a surface; 
 applying time stamps to the asynchronous data to match the time stamp of the nearest defined time frame. 
 
     
     
         4 . The method of  claim 2  further comprising:
 creating a time series of the solar radiation maps; 
 deriving a velocity vector from the time series of solar radiation maps; and 
 forecasting a future location of a solar radiation map based on a current solar radiation map and the velocity vector. 
 
     
     
         5 . The method of  claim 1  wherein collecting data includes:
 collecting power production data from a plurality of PV generating units which can measure and report energy production and which have communications capability to a central computer; 
 or 
 collecting power production data from a plurality of kilowatt-hour meters which meter output of PV generating units, and which have communications capability to a central computer; 
 or 
 collecting power production data from a plurality of data acquisition systems which monitor PV generating units, and which have communications capability to a central computer. 
 
     
     
         6 . The method of  claim 1  wherein collecting data includes:
 collecting irradiance data from a plurality of irradiance meters which have communications capability to a central computer; 
 or 
 collecting irradiance data from a combination of PV generating units, kilowatt-hour meters which meter the output of PV generating units, and data acquisition systems which monitor PV generating units. 
 
     
     
         7 . The method of  claim 1  wherein calculating irradiance incident upon the plurality of irradiance sensitive surfaces rom the collected data includes:
 collecting data indicating the power produced by a PV generating unit; 
 retrieving characteristics of the PV generating unit from a database; 
 deriving power produced by the PV generating unit based on the area of the PV generating unit's collecting surface and the system efficiency. 
 
     
     
         8 . The method of  claim 1  wherein calculating solar radiation from the combined values of incident irradiance includes:
 using a multi-pyranometer array method to solve at least two equations with at least two unknowns to calculate direct normal and diffuse horizontal irradiance; 
 calculating global horizontal irradiance from direct normal and diffuse horizontal irradiance. 
 
     
     
         9 . The method of  claim 8  further comprising:
 associating global horizontal, direct normal and diffuse horizontal irradiance values with cells of a grid defined on the geographic area; and 
 normalizing the gridded values of global horizontal irradiance by: 
 calculating clear sky model global horizontal value for each grid cell latitude and longitude, and each day and minute in the time series; and 
 dividing each grid cell global horizontal value by the clear sky model value of global horizontal irradiance. 
 
     
     
         10 . The method of  claim 9  further comprising deriving a velocity vector associated with the normalized gridded global horizontal irradiance image time series by creating matrices of normalized gridded global horizontal irradiance values for sequential gridded images:
 creating a plurality of shifted matrices from the first matrix by shifting the elements of the first matrix by one element in a clockwise or counterclockwise directions until all of the possible options, for a given step size, have been performed; 
 subtracting each of the shifted matrices from the second matrix and storing the resulting difference matrices in computer memory; 
 calculating the absolute values of the elements in the resulting difference matrices; 
 summing the absolute values of the elements of the resulting difference matrices and selecting the result with the lowest value; and 
 calculating the velocity vector using the time between the first and second matrices and distance and direction between the elements of the first matrix and the lowest value shifted matrix. 
 
     
     
         11 . The method of  claim 10  further comprising creating a forecast grid of global horizontal, direct normal and diffuse horizontal irradiance by:
 creating a matrix of global horizontal, direct normal and diffuse horizontal irradiance image values for the current grid of global horizontal irradiance values; 
 multiplying the current matrix of global horizontal, direct normal and diffuse horizontal irradiance values by the derived velocity vector; 
 mapping the forecast matrix of global horizontal, direct normal and diffuse horizontal irradiance values to the associated geographic surface; 
 and, optionally, 
 estimating PV power production values in the geographic area based upon the forecast grid. 
 
     
     
         12 . A system comprising:
 a computer processor configured to execute:   a collecting module for collecting data, which is based on irradiance incident upon a surface, from a plurality of irradiance sensitive devices in a geographic area subdivided into a gridded pattern comprised of grid cells, each irradiance sensitive device having an irradiance sensitive surface, and each grid cell comprising a group of two or more irradiance sensitive devices whose respective irradiance sensitive surfaces have differing tilt and azimuth angles;   an irradiance module for calculating irradiance incident upon the plurality of irradiance sensitive surfaces from the collected data;   a combining module for combining values of calculated incident irradiance from the two or more irradiance sensitive devices within the groups; and   a radiation module for calculating solar radiation from the combined values of incident irradiance.   
     
     
         13 . The system of  claim 12  further comprising:
 a map module for defining a solar radiation map by defining a grid of grid cells on the geographic area and associating values of the calculated solar radiation with particular individual grid cells; 
 and, optionally, 
 a time series module for creating a time series of the solar radiation maps; 
 a vector module for deriving a velocity vector from the time series of solar radiation maps; and 
 a forecasting module for forecasting a future location of a solar radiation map based on a current solar radiation map and the velocity vector. 
 
     
     
         14 . The system of  claim 12  wherein collecting data includes:
 defining time frames; 
 receiving asynchronous data which is proportional to irradiance incident upon a surface; 
 applying time stamps to the asynchronous data to match the time stamp of the nearest defined time frame. 
 
     
     
         15 . A computer readable storage medium containing a set of instructions that, when executed by a processor, perform a method comprising:
 collecting data, which is based on irradiance incident upon a surface, from a plurality of irradiance sensitive devices in a geographic area subdivided into a gridded pattern comprised of grid cells, each irradiance sensitive device having an irradiance sensitive surface, and each grid cell comprising a group of two or more irradiance sensitive devices whose respective irradiance sensitive surfaces have differing tilt and azimuth angles; calculating on a computer processor irradiance incident upon the plurality of irradiance sensitive surfaces from the collected data;   combining values of calculated incident irradiance from the two or more irradiance sensitive devices within the groups; and   calculating solar radiation from the combined values of incident irradiance.