Location and Interval Load Data Errors

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Location and Interval Load Data Errors

Hi Guys,

I've gone through your webinars and followed your steps pretty closely. I'm getting a bunch of errors when I go to run a simple PVWatts, commercial simulation. I believe the errors are caused by two of my own inputs, as when I use the inbuilt inputs I do not get the same errors.

The first error comes from the location data I have used, taken from AUSTELA as per the recommendations on your website, it seems to load the data fine into the viewer and populate the fields automatically, but it is causing an error when I run the simulation. I'm based in Australia and trying to used data for Halls Creek (see attached SAM file).

The second error comes from the electric load data tab. When using the Download Electric Load Macro to populate the fields I have no issues, but when I manually input the data into the energy usage field (I am using 15min increment data), again the Simulation fails.

I have also attached the error log. Any help you could provide would be greatly appreciated.



Paul Gilman

Hi Dan,

There are two problems here. First, the weather file does not contain diffuse horizontal irradiance (DHI) data (the values in that column are all set to -9900 -- I think because these files were originally designed for modeling CSP systems that only require DNI data). The PVWatts model requires a weather file with both direct normal irradiance (DNI) and DHI data, so it will not run with that file. Second, the time step of the weather file and load data must be the same. If you use 15-minute load data, you must also use 15-minute weather data.

Fortunately, there is a way around these problems.

1. If you use the Detailed Photovoltaic model instead of PVWatts, you'll be able to use a weather file with DNI and global horizontal irradiance (GHI). That requires providing more technical details about the system design than you need to with PVWatts. For example, you'll need to choose a brand of module and inverter, and provide the number of modules per string, and number of strings in parallel. If you do that, on the Location and Resource page, under "Albedo - Sky Diffuse Model - Irradiance Data (Advanced)", choose the DNI and GHI option.

2. You can run the Solar Resource Interpolation script to convert the weather file from hourly data to 15-minute data. First, you'll have to convert the file from EPW format to SAM CSV format using the Solar Resource File Converter macro. (Note that this latter macro saves the SAM CSV format file with a different filename than the original EPW file.)

If you decide to try this, you can save some time by duplicating your original case (click the little carrot next to the Case name to show the Case menu, and then click Duplicate), and then changing the performance model from PVWatts to Detailed Photovoltaic (Case Menu, Change Model). That will preserve your inputs for the financial model including the load data so you only need to change the inputs for the performance model.

Best regards,

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