abnormal weather condition

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abnormal weather condition


How can I simulate system for 25 years that in one year weather condition is severe and significantly different from other years?


Paul Gilman


For now, SAM runs a simulation using a single weather file. The performance model runs once to calculate the hourly (or sub-hourly) electrical output of the system over one year, and then the financial model assumes that the system's output is the same for each year of the project life. (You can specifiy a degradation rate to model a reduction in the system's annual output over time.)

SAM is designed to run with typical meteorological year (TMY) data, so that the data in the weather file represents the solar (or wind) resource over a long historical period. That ensures that the cash flow calculations are made based on the expected "typical" performance of the system. If the period of record for the data used to develop the TMY data is long enough, it will include severe weather years and their impact will be accounted for in the analysis.

In the past, weather data for simulation models like SAM was hard to find, but now it is becoming more common. NREL and other data providers provide both TMY and single-year data files. If you have access to a TMY file and the historical single-year files it was developed from, you can run simulations with the TMY and single-year files for years with extreme weather conditions and then compare your metric of interest (annual energy, capacity factor, levelized cost of energy, etc.) to see explore the differences.

If you have a set of single-year weather files, SAM's P50/P90 simulation option runs a simulation for each weather file and calculates statistical summaries of the results. See SAM's help system and the video listed Parametric and Statistical Analysis page for details.

See the Weather Data page for more on the different kinds of weather data SAM uses, and Sengupta (2015) "Best Practices Handbook for the Collection and Use of Solar Resource Data for Solar Energy Applications" (PDF 8.9 MB) an excellent overview of solar resource data and modeling.

In the future, we plan to modify SAM so that the cash flow model will be based on a separate simulation for each year (when enough specific-year data is available) rather than on a single year of data.

Best regards,


Thank you Paul. Your response was very helpful.

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