Using PVWatts to Find Stationary and Tracker PV Output

In the following it is assumed the solar site has good access to sunshine.   For stationary that means sunshine is mostly good between 9 and 3 sun time and for trackers from about an hour after sunrise to an hour before true sunset.  More on this later.

Go to http://rredc.nrel.gov/solar/codes_algs/PVWATTS/version1/  and click on the location nearest you and with a climate most like your location.  Select your system size in “DC Rating”.  This is the total nameplate rating of the modules you plan on using.  If you don’t yet know the modules or size just pick 1 KW and you can multiply your results by whatever size you eventually decide on later.  Leave all other boxes with the default values and click “Calculate” at the bottom of the page.  This will give you a very accurate estimate of the real world output of a PV array of the size you specified with a normal stationary array tilted to latitude.  Read the “AC Energy” column which shows the kWhs (kilowatt hours) per month your system will produce.  Next hit the back button and change the “Array Type” to “2-axis tracking” and again click on the “Calculate” button.  This will give you the output of the same size array installed in a tracker.  You can compare the total output to the stationary results to get a sense of how much a tracker will help.  For projects off grid it is good to compare the amounts month by month to see if the totals match your usage for that time of year.

If the above comparison shows a good gain using a tracker, it is worth looking into using a tracker in detail.  You can make a more precise site survey to tell just how much shading there is at your intended installation site.  And you can look into trackers available and their cost.  If you fill out the following form, we will do our best to explain some of the options and details available and give you our recommendation.  Please go back to the rest of this web site and read pertinent information especially “Tracker Types”