How to Calculate Solar Energy Production

Before you consider installing solar panels, you may want to calculate the solar energy production in your region.  That will help you determine the efficiency of solar panels in generating electricity for your home or business.  You’ll also be able to determine how many solar panels you’ll need for your energy demands.

Efficiency of solar panels depends in part on the angle of their positioning, but perhaps more importantly, the amount of solar irradiation in your area.  Overall solar energy production is influenced by the number of clear, sunny days, but also latitude and longitude.

If you want to learn how to calculate solar energy production where you live or work, there are several methods of doing so.

Perhaps the easiest approach is to use the tools from the National Renewable Energy Laboratory.  As stated on NREL’s PV Watts page:

The PVWatts calculator works by creating hour-by-hour performance simulations that provide estimated monthly and annual energy production in kilowatts and energy value. Users can select a location and choose to use default values or their own system parameters for size, electric cost, array type, tilt angle, and azimuth angle. In addition, the PVWatts calculator can provide hourly performance data for the selected location.

There are two versions of the NREL PVWatts calculator:

Version 1 allows users to select a location from a map or text list of pre-determined locations throughout the world. Version 2 allows users to select any location in the United States.

The calculations take into consideration several decades of recorded irradiance values.  You can pinpoint your area pretty well using its maps, which are developed based on local weather, sun angles and local microclimate cells.

There are some formulas to help you calculate solar radiation

Some believe that you can get a more accurate total energy production by using your own formula.  Engineers and scientists will enjoy putting pen to paper and crunching the numbers to calculate solar energy production.

Now, I’m not a scientist, but I did find this formula at SolarPanelTalk:

PV STC value *.8 (80% of STC) times hours of usable light (5 is a normal number) The sun may be up 12 hours a day in the summer, but the 3 morning and 3 evening hours, carry little power, so you can’t count them.
Figure in a number for clouds.

2KW array =(1600 *5) = 8000w day x 365 = 2,920,000 watts year, of sunny days, no clouds, no rain, perfect sun angle. You will NEVER exceed this #, and almost always fall short of it because of bad weather.

No matter how you do it – using the NREL links, or crunching your own numbers – calculation of solar energy production is an important step before you install solar panels.