How to POA irradiance for tilted surface

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vshyam1992
vshyam1992's picture
How to POA irradiance for tilted surface

Hi

I am working on a masters thesis, In here I used TMY2 and TMY3 format to get the hourly GHI irradiance(W/m2).I am trying to find the hourly POA irradiance(W/m2) from whether a file, its showing "NAh". Can you please help what am I doing wrong in here. Is there any way to find the hourly POA irradiance?
Please suggest me

Paul Gilman

Hello,

SAM's photovoltaic models report the POA irradiance for each subarray. For a system with one subarray, the variable for the solar irradiance incident on the top of the module surface is "Subarray 1 POA total irradiance nominal."

The "Irradiance POA from weather file" variable is for a weather file that includes POA data. SAM can run simulations using POA data measured in the field at the array. If your weather file does not contain POA data, SAM displays "NaN" for "not a number" for that variable's value.

Best regards,
Paul.

vshyam1992
vshyam1992's picture

Hello Paul,

Do you have any tutorial how to get the POA whether data (W/m2)? I want the hourly data of solar irradiation for the tilted surface in W/m2. Is it "subarray 1 POA total irradiance nominal data "

Thank you in advance,
Shyam Busineni

Paul Gilman

Dear Shyam,

Yes, that is correct. You can export that data from the Data Tables tab on the Results page.

Best regards,
Paul.

vshyam1992
vshyam1992's picture

Hello Paul,

I am working on the comparison between SAM and RETScreen software. In this, I am trying to find Solar irradiance for the tilted surface on PV module for both software. In RETScreen, I have monthly solar irradiance for the tilted surface in KW/m2/d (very straightforward results). In SAM, I used hourly "subarray 1 POA total irradiance nominal" and then converted to monthly (Kw/m2/d). In this analysis, there is a huge variation in the results. IN SAM, it is showing total annual irradiance as 4.0kw/m2/d and in RETScreen, its showing annual irradiance as 2.84KW/m2/d.

I am not sure where I am making mistake, am I making mistake in inputting data in SAM. But, I watched webinars for inputting data. Is there any problem with TMY3 weather file? or Do I have to use any DHI, DNI data to convert in POA irradiance?
Can you please help this analysis, I can attach the attachment if it is needed

Thanks in advance
Shyam

Paul Gilman

Dear Shyam,

SAM can read weather files in the TMY3 format. Are you using the same weather file for both models? Also, please check that the tracking, tilt, and azimuth inputs are the same in both models.

SAM reports the monthly "POA irradiance total nominal (kWh/mo)" that may help you confirm that your calculation is correct. You can find that on the Data Tables tab on the Results page.

By default, SAM uses the DNI and GHI data from the weather file to calculate the POA irradiance.

Best regards,
Paul.

vshyam1992
vshyam1992's picture

Hello Paul

Is SAM using DNI and GHI data from the weather file to calculate the POA irradiance which is " subarray 1 POA irradiance total nominal? just making sure?

Regards
Shyam

Paul Gilman

Hi Shyam,

Yes. If your system has one subarray, then the POA irradiance at the surface of the array is the value SAM reports as "Subarray 1 POA irradiance total nominal."

Best regards,
Paul.

vshyam1992
vshyam1992's picture

HELLO PAUL,

I am using Subarray 1 POA irradiance total nominal for calculating tilted surface solar irradiance at angle- 45 and azimuth -180 degrees. I am using 1-subarray to calculate, but the results are very different from RETScreen compared SAM. I am using same parameters. I am getting a huge variation in the monthly and annual data as well. I don't know what I am doing wrong. Please suggest me

Paul Gilman

Dear Shyam,

I am not familiar with the values that RETScreen reports. Be careful with the units and make sure you are comparing equivalent values. For example are you comparing total monthly values to average daily values by month?

Also, check the azimuth angle convention: For SAM 180 degrees is due south, regardless of the hemisphere. Some models use zero degrees as due south in the Northern hemisphere and due North in the Southern hemisphere.

Best regards,
Paul.

vshyam1992
vshyam1992's picture

HI PAUL,

In order to get the POA irradiance, do I have change any settings in Albedo- Sky Diffuse model- irradiance data( advanced). I am trying to get POA irradiance data from pyronometer and the reference cell, but I am getting an error here, It's not letting me simulate the results.

vshyam1992
vshyam1992's picture

Hi paul
I figured it out. Thank you

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