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Air Mass(AM), one of the parameters that affect solar photovoltaic modules yield

image credit: The credits for the picture goes to Renewables Academy (RENAC)

There are several parameters that affect a photovoltaic (PV) module yield amount such as Irradiance, Cell Temperature, Air Mass

Many people ask about the meaning of AM(Air Mass) in the STC conditions. Air mass is ratio of the actual atmospheric mass through which solar radiation travels to the minimum possible atmospheric mass at sea level. In the following formula "hS" is the sun's height angle. where "P" is local air pressure and "P0" is air pressure at sea level.

Scietific formula
AM calculation formula

But to be honest , it's just mathematical interpretation. AM is defined as light spectral characteristic which is in nonlinear relation to the distance light travels through atmosphere. Longer waves will be less absorbed/scattered, that's why morning/evening sky is red (AM is bigger).

So "What is AM ?"

The answer has been depicted here, Air Mass (AM) is actually the proportional distance the solar radiation must pass through when the sun is in a specific solar elevation angle, in comparison with the condition when the sun is exactly overhead (90° solar elevation angle)


Shayan Razaghy's picture

Thank Shayan for the Post!

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Matt Chester's picture
Matt Chester on May 17, 2019 11:16 pm GMT

Thanks a ton for sharing, Shayan. I'm wondering if you could give an example about how this priniciple comes into play practically for solar installations. How can solar professionals use this information?

Shayan Razaghy's picture
Shayan Razaghy on May 18, 2019 7:26 pm GMT

Thanks for reading the post, Matt .

Predicting PV plant yield in different scheduling horizons ( time intervals of yield prediction ) plays a significant role in grid management. This will be of much more importance in grids with high PV penetration.

Sometimes the predictions and yield forecasts are not accurate enough , the common reason is AM's effect in PV system yield has been neglected.

In this post , the context of AM was expressed. I will go through the topic on "AM's effect on PV system yield" in another post ASAP.

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