Solar Radiation Estimation based on Digital Image ProcessingHARSH VARDHAN MALL16EC65R22

Solar Radiation Estimation

Quantifying the total solar radiation incident in the solar field

Forecasting cloudy situations.

Why Solar Radiation Estimation?

Expansion in solar energy applications Information of atmospheric conditions is the major

requirement to improve system performance Information is used to adapt solar plant's strategic

operation to the meteorological conditions

Components of Solar Radiation

3 components - Beam, Diffuse and Global Solar Radiation

Beam Radiation – Solar radiation travelling in a straight line directly to the surface of the earth

Diffuse Radiation – Solar radiation reaching the surface after being scattered by atoms and molecules in atmosphere

Global Radiation – Total radiation reaching the surface. It includes both Beam and Diffuse radiation

.Courtesy – www.cspalliance.org

Sky Camera

Sky Camera is used for solar radiation estimation Hemispherical vision is represented in JPEG images Images collected over 1 minute periods when solar

altitude is higher than 5 degrees Dataset made with sky camera images and solar

radiation data

Image taken from sky cameraCourtesy - www.niwa.co.nz

Division of image into three areas

Distance Matrix

Division of image into three areas

Division of image into three areas

Area around the sun is more saturated and dilutes as we move away from "Sun pixel"

This area varies according to the time of the day After image splitting, pixel values are studied for

cloudless and overcast situations Different databases were created for both situations Data of 4 clear and 4 cloud covered days (for each

season) was collected 

Study of Image values

Digital values of RGB(red, green, blue) and HSV(hue, saturation, value) are collected for each pixel

Beam, Diffuse and Global solar irradiance values are also collected for each pixel

These values are stored at the databases

HSV

Courtesy - infohost.nmt.edu

Study of image values

Obtaining data from sky camera

Range of RGB and HSV value recorded

Channel values based on solar altitude Correlation between different image and solar altitude

was analyzed. It is done for each type of sky condition and each area

Correlation of digital image levels with solar altitude

Plotting Solar Irradiance versus ND valuesFor Beam, Diffuse and Global Solar Radiation Values

Estimation of Solar Radiation components Area 1 is considered the most representative in terms

of Beam solar radiation component Area 2 and 3 better define the diffuse and global solar

radiation components To estimate beam radiation, the values of beam

radiation from pixels of area 1 are averaged To estimate diffuse and global radiation, pixels from all

three areas are averaged 

Errors

RMSE (Root Mean Square Error) Normalized RMSE (nRMSE) MBE (Mean Bias Error) Normalizes MBE (nMBE)

Formulae Definitions

Test data

Four years of data was accessed Out of total number of days – 318 corresponded to

clear skies (216,243 images) 304 corresponded to partially cloudy skies (193,889

images) 86 to overcast skies(51,161 images)

Component RMSE nRMSE MBE nMBE

Beam 214.17 20.64 169.01 16.28

Diffuse 44.12 5.85 6.77 0.10

Global 66.45 6.46 32.92 3.20

For cloudless sky conditions

Component RMSE nRMSE MBE nMBE

Beam 106.50 11.13 48.97 0.87

Diffuse 122.09 16.31 43.47 0.38

Global 152.72 11.81 55.64 0.66

For overcast sky conditions

References

 J. Alonso-Montesinos,  F.J. Batlles "The use of a sky camera for solar radiation estimation based on digital image processing"           Energy 2015;90: Page 377-386

Escrig H, Batlles FJ, Alonso J, Baena FM, Bosch JL, Salbidegoitia IB, et al. "Cloud detection, classification and motion estimation using geostationary satellite imagery for cloud cover forecast."  Energy 2013;55 Page 853-859

Rusen SE, Hammer A, Akinoglu BG. "Estimation of daily global solar irradiation by coupling ground measurements of bright sunshine hours to satellite imagery." Energy 2013;58 Page 417-425