Hourly Output from Multi-Year P50/P90 Simulation

Hi Mark,

I think the limitation has expired, but we still haven't implemented a feature in SAM to make time series data for each year in a P50/P90 simulation available. I've created an issue on GitHub to get it on our To Do list:

github.com/NREL/SAM/issues/212

The single_year_simulations.lk sample script I mention in my previous post is still a good workaround solution. I updated the link and instructions for downloading it.

Best regards,
Paul.

Hi Paul,

Wondering if you can provide a little guidance on how to use the multiple_weather_files.lk script your wrote to extract hourly generation data from a P50/P90 simulation. I think i'm probably misusing or misunderstanding the script. I followed the instructions using 23 years of weather day for New Orleans downloaded via SAM. I was expecting the script to result in in a simulated 8760 at P10, P50, and P90 exceedances using the 23 weather files to develop the empirical cumulative distribution functions.

What I found was the script generated an 8760 for each year for which there is a weather file. Can you provide some guidance as to how to use these results to derive a simulated 8760 at a P90 exceedance probability?

Thanks in advance for any help you can provide!

Best regards,
Chris

Hi Chris,

The Pxx values are based on total annual values. For example, to calculate the P90 value for annual energy, SAM uses the following method (described in detail in Dobos (2012) "P50/P90 Analysis for Solar Energy Systems Using the System Advisor Model" available here sam.nrel.gov/weather-data/weather-data-publications.html ):

1. Run an 8760 simulation for each year to calculate the total annual energy production for each year.

2. Sort the resulting annual energy values in increasing value, and assign each value a probability equal to 1 divided by the number of values. For example, the table below shows results for 18 years, so each value is assigned a probability of 1 / 18 = 0.056.


3. Determine the Pxx values. For these results, the P50 value for annual energy is 57,430,500 kWh, meaning that 50% of the annual energy values are greater than that number, and 50% are less. The P90 value is between 52,685,900 kWh and 53,637,500 kWh. SAM uses linear interpolation over all the values to estimate the P90 value, in this case 53,447,200 kWh, so 90% of the energy values are greater than that value.

That means there isn't really a set of hourly 8760 (or subhourly) results for a given Pxx value. In this case, the P50 value happens to correspond to the results for Year 2000 because there is an even number of years, but the P90 value does not correspond to results for a particular year. You could choose 1998 or 2011 to represent the P90 year, as long as you keep in mind that its the total annual energy value that is the P90 value, not the hourly generation values.

Best regards,
Paul.

This is really really helpful. Thank you Paul!

Hello Paul and All 
From a location outside of US, using the recomended source  re.jrc.ec.europa.eu/pvgis.html , is there a script or a way to generate CSV files for each year in SAM format from a timeserie with multiples years in PVGIS5 format? 

I tried to use Solar Resource Converter macro but I think only works with TMY time serie. 

Best Regards,
Nico

Hi Nico,

We did not write a converter for the the single year weather data from PVGIS because those files do not include the time zone, which SAM's weather file format requires.

It is not too difficult to convert a CSV file from the PVGIS CSV format to the SAM CSV format (after you look up the location's time zone) using the format description in SAM's Help system: samrepo.nrelcloud.org/help/weather_format_sam_csv_solar.htm

Best regards,
Paul.