Global incident coll.plane

[Konstantina]

Hello dear Andre,

I would like to ask how the global incident coll.plane is calculated.Does it depend from the geographical coordinates or the irradiance?

Also in order to find the effective irradiance on collectors, this global incident in coll.planes is added to the irradiance or not?

Thank you very much.

[André Mermoud]

The Global incident is computed from the Horizontal Global and Diffuse irradiances in hourly values, using a model (Perez or Hay model, may be chosen in the "Preferences").

It depends on the solar geometry, therefore on the geographical coordinates of course.

It is the full irradiance as received ("viewed") by the tilted plane.

We define the "Transposition factor" as the ratio GlobInc/GlobHor.

[Gayathridevi]

Hi,

Greetings. I am new to this forum, today only I joined.

I have one doubt. My location latitude is around 42 deg N. I have given tilt to the modules 30 deg towards south.

For this location sun will be always in south throughout the year. In this location, If collector tilted towards south, Global incident coll. plane will be always greater than

the horizontal global irradiation know. But why GlobInc less than GlobHor (GlobInc < GlobHor) for three months (May June July) in the year.

If it is not correct optimal tilt also at least facing the sun through out the year know. Then why it is decreasing. I attached that page also for your reference.

Please Clarify.

Thank you.

Doubt page

[André Mermoud]

This is quite normal.

Evaluating the average irradiance over the whole day (including beam, diffuse and even albedo) is not intuitive !

As an example, in summer at these latitudes, the sun goes far beyond east in the morning and west in the evening: with planes as tilted as 30°, the sun is behind the plane or at very high incidences. This is a significant loss by respect to the horizontal irradiance, which is not affected.

Using "Tools" / "Meteo tables and Graphs", you can plot the meteo data (Global horizontal, and Global on 30° plane), in hourly values. Please observe a clear day in June: you will see that the Global plane is slightly higher around midday, but significantly lower during the morning and the evening. And not very different for cloudy days.

[Gayathridevi]

Hello André Mermoud,

Thank you for your fast reply and clearing my doubt. As you said, i checked with hourly values in june month.

my doubt is cleared now.

Thank you

[rraja]

Hello Andre Mermoud,

Please share the steps to be followed in Hey / Perez Model and Inputs, Formula/Algorithm to be used.

Thank you.

[André Mermoud]

The Hay model is fully described in the help:

"Physical models used > Incident irradiation models > The Hay transposition model".

For the Perez model, it is more complicated, you have to follow the original article:

R. Perez, P.Ineichen, R. Seals, J. Michalsky, R. Stewart:

Modeling Daylight Availability and Irradiance Component from Direct and Global Irradiance.

Solar Energy 44, no 5, pp 271-289, 1990.

[rraja]

Thank you Andre ,.

Can u please explain How to calculate these two variables (mentioned below) In Hay's Model,

Hsol = Sun height on horizontal plane

Hsoli = Sun height on the plane (= 90° - incidence angle)

[André Mermoud]

The Solar geometry calculations are fully described in the help "Physical models used > Solar Geometry"

[Msajeilat]

Hi Andre,

So when calculating PR from measured values, does the POA (plane of array) pyranometers installed on site reflect the Global Incident irradiation used to calculate the PR in the PVsyst report? Or are there other other values we need to measure in order to “compare apples to apples”

Thanks