CODEWITHSUNDEEP
pvlib
Oscar
Oscar

Reputation: 129

POA "weird" outcome (IMHO)

I have gathered satellite data (every 5 minutes, from "Solcast") for GHI, DNI and DHI and I use pvlib to get the POA value. The pvlib function I use:

def get_irradiance(site_location, date, tilt, surface_azimuth, ghi, dni, dhi):
    times = pd.date_range(date, freq='5min', periods=12*24, tz=site_location.tz)
    solar_position = site_location.get_solarposition(times=times)
    POA_irradiance = irradiance.get_total_irradiance(
        surface_tilt=tilt,
        surface_azimuth=surface_azimuth,
        ghi=ghi,
        dni=dni,
        dhi=dhi,
        solar_zenith=solar_position['apparent_zenith'],
        solar_azimuth=solar_position['azimuth'])
    return pd.DataFrame({'GHI': ghi,
                         'DNI': dni,
                         'DHI': dhi,
                         'POA': POA_irradiance['poa_global']})

When I compare GHI and POA values for 12 June 2022 and 13 June 2022 is see the POA value for 12 June is significantly behind the GHI. The location is in The Netherlands, I use a tilt of 12.5 degrees and an azimuth of 180 degrees. Here is the outcome (per hour, from 6:00 - 20:00):

12 Juni 2022
             GHI         DNI         DHI         POA
6      86.750000  312.750000   40.500000   40.277034
7     224.583333  543.000000   69.750000   71.130218
8     366.833333  598.833333  113.833333  178.974322
9     406.083333  182.000000  304.000000  348.272844
10    532.166667  266.750000  346.666667  445.422584
11    725.666667  640.416667  226.500000  509.360716
12    688.500000  329.416667  409.583333  561.630762
13    701.333333  299.750000  439.333333  570.415438
14    725.416667  391.666667  387.750000  532.529676
15    753.916667  629.166667  244.333333  407.665794
16    656.750000  599.750000  215.333333  293.832376
17    381.833333   36.416667  359.416667  356.317883
18    411.750000  569.166667  144.750000  144.254438
19    269.750000  495.916667  102.500000  102.084439
20    134.583333  426.416667   51.583333   51.370738

And

13 June 2022
             GHI         DNI         DHI         POA
6       5.666667    0.000000    5.666667    5.616296
7     113.500000    7.750000  111.416667  111.948831
8     259.500000  106.833333  208.416667  256.410392
9     509.166667  637.750000  150.583333  514.516389
10    599.333333  518.666667  240.583333  619.050821
11    745.250000  704.500000  195.583333  788.773772
12    757.250000  549.666667  292.000000  798.739403
13    742.000000  464.583333  335.000000  778.857394
14    818.250000  667.750000  243.000000  869.972769
15    800.750000  776.833333  166.916667  852.559043
16    699.000000  733.666667  167.166667  730.484502
17    582.666667  729.166667  131.916667  593.802853
18    449.166667  756.583333   83.500000  434.958210
19    290.083333  652.666667   68.666667  254.048655
20    139.833333  466.916667   48.333333   97.272684

What can be an explanation of the significantly low POA compared to the GHI values on 12 June?

I have this outcome with other days too: some days have a POA much closer to the GHI than other days. Maybe this is "normal behaviour" and I do not reckon with weather influences which maybe important...

I use the POA to do a PR (Performance Ratio) calculation but I do not get "trusted" results.. Hope someone can shine a light on these values.

Kind regards, Oscar The Netherlands.

Upvotes: 1

Views: 104

Answers (1)

Oscar
Oscar

Reputation: 129

I'm really sorry, although the weather is unpredictable in the Netherlands I made a very big booboo in using dd-mm-yyyy format instead of mm-dd-yyyy. Something I overlooked for a long time...(I never had used mm-dd-yyyy, but that's a lame excuse...)

Really sorry, hope you did not think about it too long..

Thank you anyway for reacting!

I've good values now!

Oscar (shame..)

Upvotes: 3

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