EME 810
Solar Resource Assessment and Economics

4.7 Typical Meteorological Years: A Mosaic of Data


Reading Assignment

  • J.R. Brownson, Solar Energy Conversion Systems (SECS), Chapter 8: Measure & Estimation of the Solar Resource (Focus on Meteorological Years: Collage of Data.)
  • Kalogirou, S. (2011) Ch 2 (section 2.4.1-2.4.2) pp 106-117. Typical Meteorological Year [available on eReserves]

Your reading in Ch 8 of SECS will introduce the concept of Meteorological Years, while the Ch 2 reading in Kalogirou offers a condensed description of how a TMY data set is formed and how the files are formatted. The Supplemental readings address the most recent version of the TMY data sets in the USA (TMY3), and point to the National Solar Radiation Database maintained by NREL.

The data that you will find in your SAM simulation software, and the data that is all over the web in resources like the NREL Dynamic Maps of the USA solar resource, come from a single database, called the NSRDB, or the National Solar Radiation Database. There are currently three generations of TMY.

What is a Typical Meteorological Year? Why would we use a synthesized year of data for solar resource simulations?

A typical meteorological year (TMY) data set provides designers and other users with a reasonably sized annual data set that holds hourly meteorological values that typify conditions at a specific location over a longer period of time, such as 30 years. TMY data sets are widely used by building designers and others for modeling renewable energy conversion systems. Although not designed to provide meteorological extremes, TMY data have natural diurnal and seasonal variations and represent a year of typical climatic conditions for a location. The TMY should not be used to predict weather for a particular period of time, nor is it an appropriate basis for evaluating real-time energy production or efficiencies for building design applications or solar conversion systems.

...The TMY data set is composed of 12 typical meteorological months (January through December) that are concatenated essentially without modification to form a single year with a serially complete data record for primary measurements. These monthly data sets contain actual time-series meteorological measurements and modeled solar values, although some hourly records may contain filled or interpolated data for periods when original observations are missing from the data archive.

Wilcox and Marion (2008) NREL/TP-581-43156

Estimation can often be evaluated relative to 30 year averages of weather conditions at specific locations, termed the Typical Meteorological Year (TMY). These data are not reasonable estimates of extreme conditions (e.g., hurricanes, tornadoes) and may also be inaccurate for evaluating site or time-specific data. The most common database is TMY3, now collected from the period of 1991 to 2010.

TMY data was initially developed to aid in building simulation, for modeling the energy demands in counterpoint with the solar/meteorological gains. As in your software SAM (and the source code, TRNSYS), TMY is also used by SECS design teams for initial estimates of energy and financial returns on investment. We can use SAM's TMY data set to evaluate PV, solar hot water, and CSP systems.

The source data for the TMY set in the USA comes from the NSRDB, or the National Solar Radiation Database.

Try This!

SAM Location and Resource Help

Let's go back to the SAM software and explore the solar resource data in its browser.

  1. You can open up SAM at this point and click the button "Start a new project"
  2. Click on "Photovoltaics (Detailed)" on the left of the pop-up window ("Choose a performance model").
  3. Click on "Residential (Distributed)" on the right of the pop-up window ("then choose from the available financial models").
  4. Hit "OK."
  5. You will now have a default residential PV project, based in Phoenix, AZ. There will likely be a SunPower (California company) PV module, and an SMA America dc-ac power inverter listed on the left column of shortcut tabs. They're not really "tabs" like the tab at the top of the window, but I'm going to use that term for convenience in the class.
  6. Click on the shortcut tab called "Location and Resource" (will list "Location," latitude ($\phi$), longitude ($\lambda$), and elevation above sea level in the shortcut.
  7. Leave the location on Phoenix.tm2 and look inside the section "Tools."
  8. Click the button "View hourly data...," and a new window will pop up.

Reminder: This information will be used when you create your final project.

Optional Reading