System For Correlating Satellite Imagery Through Bounded Area Variance For Use In Photovoltaic Fleet Output Estimation

Patent metadata

Field	Value
Publication number	US-2016349407-A1
Application number	US-201615231701-A
Country	US
Kind code	A1
Filing date	Aug 8, 2016
Priority date	Jul 25, 2011
Publication date	Dec 1, 2016
Grant date	—

Abstract

The calculation of the variance of a correlation coefficient matrix for a photovoltaic fleet can be completed in linear space as a function of decreasing distance between pairs of photovoltaic plant locations. When obtaining irradiance data from a satellite imagery source, irradiance statistics must first be converted from irradiance statistics for an area into irradiance statistics for an average point within a pixel in the satellite imagery. The average point statistics are then averaged across all satellite pixels to determine the average across the whole photovoltaic fleet region. Where pairs of photovoltaic systems are located too far away from each other to be statistically correlated, the correlation coefficients in the matrix for that pair of photovoltaic systems are effectively zero. Consequently, the double summation portion of the calculation can be simplified to eliminate zero values based on distance between photovoltaic plant locations, substantially decreasing the size of the problem space.

First claim

What is claimed is:

1 . A system for correlating satellite imagery through bounded area variance for use in photovoltaic fleet output estimation, comprising:
a storage comprising a set of pixels in satellite imagery data of overhead sky clearness that have been correlated to a bounded area within a geographic region, each pixel representing collective irradiance over a plurality of points within the bounded area, each point suitable for operation of a photovoltaic system comprised in a photovoltaic fleet; and a computer coupled to the storage and comprising a processor configured to execute code in a memory, the code comprising:
a conversion module adapted to convert the collective irradiances, as represented by the set of pixels correlated to the bounded area, into a set of point clearness indexes for the plurality of the points under each pixel, relative to clear sky irradiance;
an averaging module adapted to average the point clearness indexes in the set of point clearness indexes for all of the points within the bounded area into an area clearness index;
a variance module adapted to determine a variance of the area clearness index as a bounded area variance through an evaluation module adapted to sequentially evaluate only the points within the bounded area that have not already been evaluated, the evaluation module comprising:
a selector module adapted to choose a point within the bounded area not yet evaluated, and to determine a zero correlation value for the chosen point;
a pairing module adapted to pair the chosen point with each of the points remaining within the bounded area that have not already been evaluated, and to find a correlation coefficient for each of the point pairings; and
a covariance module adapted to calculate a covariance for each of the point pairings whose correlation coefficient exceeds the zero correlation value, and to add those point pairings' covariances to the variance of the area clearness index; and

a correlation module adapted to determine, for each of the points within the bounded area, a variance of the point clearness index for that point as a ratio of the variance of the area clearness index and the physical area relative to the point clearness index for that point, cloud speed over the geographic region, and a time interval relating to a time resolution of observation for the collective irradiance.

2 . A system according to claim 1 , further comprising:
a derivation module adapted to determine cloud speeds between the chosen point and each of the remaining within the bounded area that have not already been evaluated, and for each point pairing, to derive the zero correlation value as a function of the cloud speed between the point pairing.

3 . A system according to claim 1 , further comprising:
a cloud speed module adapted to determine cloud speeds across the geographic region, and to select a minimum cloud speed of the cloud speeds; and a derivation module adapted to derive the zero correlation value as a function of the selected minimum cloud speed, and to set the zero correlation value thus derived as being applicable to evaluating all of the points within the bounded area not yet evaluated.

4 . A system according to claim 1 , further comprising:
a cloud speed module adapted to determine cloud speeds across the geographic region, and to evaluate whether the cloud speeds are substantially constant; and a derivation module adapted to derive, when substantially constant, the zero correlation value as a function of the substantially constant cloud speed, and to set the zero correlation value thus derived as being applicable to evaluating all of the points within the bounded area not yet evaluated.

5 . A system according to claim 1 , further comprising:
a coordinates module adapted to convert the zero correlation value into degrees, to specify coordinates of the chosen point in terms of longitude and latitude, and to define a rectangular region around each chosen point comprising the longitude coordinate±the degrees and the latitude coordinate±the degrees.

6 . A system according to claim 1 , further comprising:
an upper bound module adapted to set an upper bound of unique combinations C of each chosen point with each of the points remaining within the bounded area that have not already been evaluated relative to the chosen point in accordance with:

C
=

N
×

(

Correlation_region
-
1

)

2

where N comprises a number of points within the bounded area and Correlation_region comprises a number of equal-sized divisions of the bounded area.

7 . A system according to claim 1 , wherein each correlation coefficient ρ i,j is defined as a continuous probability density function of distances between each point pairing.

8 . A system for correlating satellite imagery through average point variance for use in photovoltaic fleet output estimation, comprising:
a storage comprising a set of pixels in satellite imagery data of overhead sky clearness that have been correlated to a bounded area within a geographic region, each pixel representing collective irradiance over a plurality of points within the bounded area, each point suitable for operation of a photovoltaic system comprised in a photovoltaic fleet; and a computer coupled to the storage and comprising a processor configured to execute code in a memory, the code comprising:
a conversion module adapted to convert the collective irradiances, as represented by the set of pixels correlated to the bounded area, into a set of point clearness indexes for the plurality of the points under each pixel, relative to clear sky irradiance;
an averaging module adapted to average the point clearness indexes in the set of point clearness indexes for all of the points within the bounded area into an area clearness index;
a variance module adapted to determine a variance of the area clearness index as an average point variance through an evaluation module adapted to sequentially evaluate only the points within the bounded area that have not already been evaluated, the evaluation module comprising:
a selector module adapted to choose a point within the bounded area not yet evaluated, to determine a zero correlation value for the chosen point, and to find a zero correlation distance as a function of the zero correlation value;
a pairing module adapted to pair the chosen point with each of the points remaining within the bounded area that have not already been evaluated and which are located within the zero correlation distance of the chosen point, and to find a correlation coefficient for each of the point pairings; and
a covariance module adapted to calculate a covariance for each of the point pairings and to add those point pairings' covariances to the variance of the area clearness index; and

a correlation module adapted to determine, for each of the points within the bounded area, a variance of the point clearness index for that point as a ratio of the variance of the area clearness index and the physical area relative to the point clearness index for that point, cloud speed over the geographic region, and a time interval relating to a time resolution of observation for the collective irradiance.

9 . A system according to claim 8 , further comprising:
a derivation module adapted to deter

Assignees

• Clean Power Res L L C

Inventors

• Hoff Thomas E

Classifications

• H02J3/004 Primary

  Generation forecast, e.g. methods or systems for forecasting future energy generation · CPC title

• H02J3/38

  Arrangements for feeding a single network from two or more generators or sources in parallel; Arrangements for feeding already energised networks from additional generators or sources in parallel · CPC title

• H02J2103/30

  Simulating, planning, modelling, reliability check or computer assisted design [CAD] of electric power networks · CPC title

• H02J2101/24

  Photovoltaics · CPC title

• G06Q10/04

  Forecasting or optimisation specially adapted for administrative or management purposes, e.g. linear programming or "cutting stock problem" (market predictions or forecasting for commercial activities G06Q30/0202) · CPC title