Living Sustainably
in the shadow of climate change

March 2015
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Solar energy seasonal cycles
Filed under: General, Solar Power
Posted by: Guy @ 4:16 pm

Here in Maine, we are approximately at the 45th parallel which means that we have significant seasonal changes in solar elevation from winter to summer.  At the spring and fall equinoxes the sun is approximately 45° elevation at noon.  This means that the available solar energy in the winter is approximately 25% of the maximum solar energy available in the summer.  This is best explained graphically by this chart taken from my TED energy monitor:

The blue bars show the kilowatt hours that we import from our electric utility. The yellow bars show the amount of solar energy actually produced by our 5.7 kW solar array, and the green bars show the net amount of energy that we pay for.  Clearly our electric bills drop to near zero in the summer, and since we have an electric vehicle we need to charge your round our bills peak at around $100 per month in the winter.  At this time of year it is always nice to see our solar energy increasing, and our electric bills dropping.

The amount of solar energy we produce is significantly affected by the weather and cloud cover as the chart below demonstrates.  I have the impression that climate change is changing faster than the models can keep up with.  But the chart clearly demonstrates the significant seasonal variation in solar energy available here at the 45th parallel.  Clearly, people who live further south gain a much greater benefit from solar panels on their roofs.  For instance, if you lived at the equator you would have around 12 hours a day of sunlight available with no seasonal variation other than cloud cover. 

2 Responses to “Solar energy seasonal cycles”

  1. rj Says:
    I would not mind $100 average electric bills but I would need 15kw to get there with the Texas AC requirements. Maybe in five more years the pricing and power density per module will get there, but there are some who believe the Chinese have subsidized the pricing to capture the market. Otherwise I need to move to a new passive house quality house and then 5kw and a minisplit heat pump would do it easily.
  2. Guy Says:
    Our *average* bill is around $45.00, and if we didn’t have the Volt it would be around $10/month. This is for 2 efficient buildings and 2 home based businesses FYI.