Solar energy/Resource availability
Introduction
The amount of sunlight that will strike the Earth's surface will depend on a few factors, some of which are periodic and others can be considered variable. Some periodic factors:
- Seasonal
- Day/night
- Urban shade
Some variable factors
- Cloud coverage
- Other natural weather events
Solar declination
Throughout the annual orbit of the Earth around the Sun, the distance between the two bodies is around 150 million km. Because the Earth's orbit is elliptical, the actual distance between the Sun and the Earth will vary somewhat. The Earth takes around 365.25 days to completely orbit the Sun.
The solar declination, δ, is the angle at which the sun Earth is inclined relative the plane of orbit around the Sun. For the northern hemisphere, the angle of declination varies from +23.45 degrees in Winter to -23.45 degrees in Summer.
The solar declination angle can be calculated at any point of the year with the following equations:
Where J is the day of the year, with January 1st being n=1.
The amount of sunlight that will strike the Earth's surface will depend on a few factors, some of which are periodic and others can be considered variable.
Some periodic factors:
- Seasonal
- Day/night
- Urban shade
Some variable factors
- Cloud coverage
- Other natural weather events
Latitude and longitude
In addition to the position of the planet around the sun, the amount of sunlight available at any point on the Earth's surface will also depend on the longitude and latitude of the geographic position. Latitude is a measure of how far north or south you are, and varies from -90° (90° south) to +90° (90° north). The longitude is a measure of how far east or west one is, and varies from -180° (180° west) to +180° (180° east).