Quantification Of Solar Energy, Solar Power Calculator [Spreadsheet]

As solar energy we understand the energy that falls on the earth in the form of sunlight. The sun is the source of solar energy and it is renewable and virtually inexhaustible source of energy. The sun produces 1,1*10²⁰ kWh per second .

 

On the border of the earth's atmosphere the average solar energy varies from 1340 to 1390 W.m^-2. The average value of the energy is called the solar constant. Solar constant is the maximum quantity that can fall into the stratosphere, and this is the maximum value that can be obtained per square meter. This article will explain how to calculate direct, diffuse and total solar energy emitted from sun to earth surface and also parameters that determine position of the sun in the sky.

Spreadsheet in available for download in LibreOffice Calc and MS Office Excel format for easy and fast calculations.

1. Parameters determining the position of the sun in the sky

An important particularity regarding the use of solar energy is the movement of the sun the sky. Movement is caused by the Earth's rotation about its axis and changing the path of the sun the sky during the year.

An important parameter for determining the position of the sun in the sky are:

• Height of the sun above the horizon (h),
• Azimuth angle of the sun (α),
• Angle of incidence sunbeam (γ),

1.1 Height of the sun above the horizon

Height if the sun above the horizon is angle between horizon and sun and you can calculate it with the following formula:

Where:

δ solar declination [°]

Φ laditude [°]

τ time angle [°]

Spreadsheet calculator:
Spreadsheet calculates height if the sun above the horizon from 8:00 hours to 16:00 hours for every month of the year.

1.1.1 Solar declination

Values of solar declination are for every day differed in spreadsheet values of solar declination are only for specific dates of the month:

• 22.XII
• 22.XI and 21.I
• 23.X and 20.II
• 23.IX and 21.III
• 23.VIII and 21 IV
• 23.VII and 22.V
• 22.VI

Spreadsheet calculator:

In spreadsheet values of solar declination can be changed in “Sun azimuth and height” sheet.

1.1.2 Latitude

Spreadsheet calculator:

Latitude in spreadsheet is in WGS84 format and can be changed in “Home” sheet.

1.1.3 Time angle

Time angle is measured from 12:00 hours, one hour corresponds to an angle of 15 °.

Spreadsheet calculator:

In spreadsheet values of time angle can be changed in “Sun azimuth and height” sheet.

1.2 Azimuth angle of the sun

Azimuth angle of the sun can be calculated with the following formula:

Where: 

δ solar declination [°]

h height if the sun above the horizon [°]

τ time angle [°]

Spreadsheet calculator:

Azimuth angle from -180 to 180. East=-90, South=0

Spreadsheet calculates azimuth angle of the sun from 8:00 hours to 16:00 hours for every month of the year.

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