Negative production from pv simualtion

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Negative production from pv simualtion


First of all, I'm very new to this software.

I'm trying to simulate PV production from my own weather file. It's a csv-file made in notepad that conatins
year,month,day,hour, GHI and DNI. The GHI-values are collected from a sensor, and the DNI values are calculated using the DISC model.

I'm only getting negative monthly production, no matter what size of the panels i choose.

EDIT: I have compared the DNI- data with data from an other city in my country (Bergen, Norway) from the SAM library. The data from Bergen gives complete different results (and off course positive production), but the energy from DNI is not extremely different( ~440kWh/year vs. ~ 380 KWh/year).

What can be the problem?


Paul Gilman


There are a couple of problems with the data in your weather file.

  • There are several hours with GHI values above 2,000 W/m2.
  • The weather file is missing wind speed and ambient temperature data.

Please see the "Weather Data Elements" topic in SAM's Help system for a list of weather data required by each of SAM's performance models.

You can use SAM's data viewer to examine the data in your file as follows:

  1. In SAM, on the Location and Resource page, click Folder settings and add the folder that contains your weather file to the list of solar data file folders.
  2. Click Refresh library and then you should be able to find your file in the solar resource library list.
  3. Click the weather file name in the list, and then click View data to open the data viewer.

You can also check the data in your file using SAM's built-in macro:

  1. In SAM, click Macros at the bottom left of the main window.
  2. In the list of macros, click Solar Resource File Checker, and then click Run macro at the top of the page.

Finally, you may be interested in the software developed by Angus King and described by him in the following thread. You may be able to use it to get meteorological data to go with your solar resource data:

Best regards,

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