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Wednesday, April 22, 2015

Understanding solar insolation

Having solar power systems on one's home means that you become very conscious of the daily and seasonal cycles of the sun.  The word insolation is used to define the total amount of solar radiation energy received on a given surface area during a given time.  It is insolation that is used to calculate how much energy you can get from solar panels or collectors for any given location and time.

If you live on the equator you do not see significant
seasonal variations in insolation, but where I live at 44° latitude, it varies considerably throughout the year and it is important to understand this in order to correctly predict how much energy one can extract from the sun.

There is a very helpful web calculator produced by PVeducation.org that produces charts of available solar energy (insolation) for given locations.  I use this tool to create the animation below that shows the available solar energy in Watts/square meter in 10 day increments for the year at my location of 44° latitude North.
I made this animation by taking screenshots at ten-day intervals by adjusting the slider on the calculators webpage.

This clearly demonstrates how the available sun hours per day varies significantly at my latitude.  The chart below shows the predicted versus actual solar energy produced by my solar array and clearly shows the seasonal variations.  The predicted energy was charted using the calculator from National Renewable  Energy Labs called PVwatts which takes into account both seasonal variations and local weather conditions.  The actual data came from monthly energy production reports from my solar array. 
Over the years I have added panels to my solar power system which accounts for the annual increase in output.  If you are considering installing solar power or heating systems on your home it is important to be aware of the seasonal variations and the impact of local weather.