DIFFERENCE BETWEEN GHI AND DNI
Irradiance is defined as the amount of power received by a surface per unit area and is measured in W/m2. Irradiation is defined as the amount of power received by a surface per unit area on a given period of time and is measured in Wh/m2.
There are two different irradiation’s to be considered while measuring the amount of radiation incident on a surface. They are, Global Horizontal Irradiation (GHI) and Direct Normal Irradiation (DNI). Solar radiation available at Earth’s surface consists of Direct (Beam), Diffuse, and Albedo radiation.
Global Horizontal Irradiation (GHI) is the sum of Direct irradiation and Diffused irradiation. The yearly sum of the GHI is of particular relevance for PV power plants, which are able to make use of both the diffuse and beam components of solar irradiance. GHI is typically of most interest to PV project developers. This is clearly explained from the below fig.
Direct Normal Irradiation (DNI) is the direct beam radiation of the sun excluding the diffused irradiation that is incident on the surface. DNI is the total solar energy received on a unit area of surface directly facing the sun at all times. The DNI is of particular interest for solar installations that track the sun and for concentrating solar technologies (as concentrating technologies can only make use of the direct component of irradiation).
Diffuse Horizontal Irradiation (DHI) is the energy received on a unit area of horizontal surface from all directions when radiation is scattered off the atmosphere or the surrounding area. The irradiation measurements is of two different types. They are Land based and Satellite based measurements.
The global horizontal and diffused irradiation values loaded from Meteonorm are listed down for the site in Visakhapatnam, Andhra Pradesh.
| Month |
Horizontal Global radiation |
Horizontal Diffused radiation |
|
January |
149.4 |
51 |
|
February |
153.6 |
54.5 |
|
March |
185.6 |
71.8 |
|
April |
192.2 |
74.9 |
|
May |
188.2 |
88.4 |
|
June |
146.8 |
86.4 |
|
July |
141.7 |
89.6 |
|
August |
140.3 |
87.5 |
|
September |
142.9 |
77.6 |
|
October |
152.1 |
72.9 |
|
November |
139 |
49.4 |
|
December |
138.2 |
55.2 |
Annual Mean Horizontal Solar Irradiation for Visakhapatnam
The global horizontal and diffused irradiation values loaded from NASA-SSE are listed down for the site in Visakhapatnam, Andhra Pradesh.
| Month |
Horizontal Global radiation |
Horizontal Diffused radiation |
|
January |
151.6 |
39.4 |
|
February |
159.3 |
38.9 |
|
March |
197.2 |
51.1 |
|
April |
200.7 |
57.3 |
|
May |
191.3 |
68.5 |
|
June |
139.2 |
71.4 |
|
July |
130.2 |
73.2 |
|
August |
129.9 |
72.2 |
|
September |
131.4 |
65.1 |
|
October |
142.6 |
56.4 |
|
November |
134.7 |
44.4 |
|
December |
142 |
38.1 |
Annual Mean Horizontal Solar Irradiation for Visakhapatnam