What is Solar Constant?
Solar constant is the constant rate at which solar radiation hits the surface of the earth, which is accepted to be approximately 1,388 watts per square meter.
Key Takeaways:
- The solar constant is approximately 1,388 watts per square meter.
- It is not actually a constant and varies over the course of an 11-year cycle.
- It is expected to increase by 10% every one billion years.
Understanding Solar Constant
Solar constant is the constant rate at which solar radiation hits the surface of the earth, which is accepted to be approximately 1,388 watts per square meter on average at the Earth’s mean distance from the sun.
The solar constant is not actually a constant in the way that Planck’s constant or the speed of light are given to be constants because the solar constant actually does vary about 0.2 percent over the course of an 11-year cycle. During this cycle, sunspots that reduce the sun’s energy by a small amount, and plages which increase the sun’s energy by a small amount, vary the overall output of solar radiation.
This variance is enough to prevent the solar constant from being a formal “scientific” constant, but is consistent enough to be useful for calculating solar energy available for a photovoltaic array.
Finally, as the Sun burns up its hydrogen fuel, the solar constant is expected to increase by about 10 percent every one billion years.
Related Terms
Full Sun – An area that gets more than 6 hours of direct sunlight per day.
Solar Noon – Solar noon is the moment that the sun reaches its highest point in the sky at any particular location.
Peak Sun Hours – Defined as the number of one-hour units of time where the intensity of sunlight is at least 1kW per square meter.