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I am using PVlib to simulate a PV plant but I don't understand the output I get.

For example, using the module 'Power_Electronics__FS2000CU__400V__400V__CEC_2018_' (available in the CEC database pvlib.pvsystem.retrieve_sam('CECMod')) it has a Maximum Power Point intensity Imp = 8.36 but the model calculates higher intesities (dc['i_mp'] up to 10.91).

I am using official irradiance component values, I have checked them and they have consistency. I don't know wind speed and temperature values for this location, so I set T=30ºC and wind speed 2.5m/s. So, the input is a complete year DataFrame (column names ['dni', 'ghi', 'dhi', 'wind_speed', 'temp_air']) every 15 minutes.

Here is the code I am running:

pv_system = pvlib.pvsystem.PVSystem(surface_tilt=23, 
                surface_azimuth= 0, 
                module_parameters=module, #(specified at explanation)
                inverter_parameters=inverter, #(doesn't matter for this example)
                modules_per_string=1, 
                strings_per_inverter=1)
mc = pvlib.modelchain.ModelChain(pv_system, location, aoi_model="no_loss",spectral_model='no_loss')
mc.run_model(times=weather.index, weather=weather)

This is a little set of the result I obtain:

datetime(UTC)   ghi     dni dhi temp_air    wind_speed  temp_cell   temp_module effective_irradiance    v_mp        i_mp    p_mp
======================================================================================================================================
Apr-03 09:00    826     568 385 30          2.5         56.62       53.94       892.66                  31.37       7.57    237.43
Apr-03 09:15    851     624 349 30          2.5         57.6        54.82       925.4                   31.2        7.85    244.84
Apr-03 09:30    1037    915 289 30          2.5         64.56       61.08       1158.68                 29.96       9.83    294.4
Apr-03 09:45    1146    973 334 30          2.5         68.38       64.52       1286.77                 29.24       10.91   319.12
Apr-03 10:00    940     881 190 30          2.5         61.52       58.35       1056.84                 30.51       8.96    273.48
Apr-03 10:15    664     245 443 30          2.5         50.41       48.36       684.4                   32.39       5.79    187.69
Apr-03 10:30    785     353 470 30          2.5         54.69       52.21       828.02                  31.71       7.02    222.46
Apr-03 10:45    836     446 442 30          2.5         56.85       54.15       900.41                  31.33       7.63    239.19
Apr-03 11:00    1069    800 364 30          2.5         65.59       62.01       1193.36                 29.76       10.12   301.27
Apr-03 11:15    976     674 383 30          2.5         62.22       58.98       1080.27                 30.39       9.16    278.39
Apr-03 11:30    957     731 317 30          2.5         61.79       58.59       1065.94                 30.46       9.04    275.4
Apr-03 11:45    692     357 378 30          2.5         51.96       49.76       736.51                  32.15       6.24    200.54
Apr-03 12:00    785     426 417 30          2.5         55.11       52.59       842.07                  31.62       7.14    225.75
Apr-03 12:15    842     541 388 30          2.5         57.44       54.68       920.24                  31.23       7.8     243.68
Apr-03 12:30    713     542 268 30          2.5         53.39       51.04       784.35                  31.91       6.65    212.1
Apr-03 12:45    792     687 257 30          2.5         56.69       54.01       894.95                  31.37       7.59    237.95
Apr-03 13:00    750     805 146 30          2.5         55.71       53.12       862.12                  31.53       7.31    230.41

The produced intensity is higher than the modules Imp at 9:30, 9:45, 10:00, 11:00, 11:15 and 11:30. The produced power p_mp is higher than the module's power (310W) at 9:45, when the intensity is the higher calculated by the model, but this is impossible, isn't it?

I presume the effective irradiance calculated by PVlib is too high at those cases and it makes the module produce more energy than the limit. But I don't know where the mistake is, I can't interpretate these results.

Dharman
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mdor
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    A module's effect is always specified with respect to a normal irradiance of 1000 W/m2. So in the case that you have a higher irradiance than this (which it looks like from the data) then a module will have a greater output than the specified effect. Where is your weather data from? Region and source? – Adam R. Jensen Sep 06 '19 at 14:07
  • Irradiance data is measured by an official BSRN project (https://bsrn.awi.de) weather station located in Gobabeb, Namib Desert, Namibia (-23.5614, 15.0420). This data is checked and is supposed to be correct, but in my opinion the calculated effective irradiance seems to be too high for this irradiance data... or maybe the problem could be related to the temperature and wind speed values I chose... – mdor Sep 11 '19 at 11:45
  • Anyway, if the irradiance is higher than 1000W/m², is the module able to produce more than 310W? So the modules haven't got any limit? Thank you for your help @AdamJensen – mdor Sep 11 '19 at 11:52
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    Yes exactly! Of course it depends also on the inverter size - lookup inverter clipping. From the Wikipedia page on 'Nominal power (photovoltaic)': "The power a module generates in real conditions can exceed the nominal power when the intensity of sunlight exceeds 1000 W/m2 (which corresponds roughly to midday in summer in, for example, Germany), or when sun irradiation close to 1000 W/m2 happens at lower temperatures." – Adam R. Jensen Sep 12 '19 at 15:08

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