Seasonal Solar Power Considerations
Earth is tilted at an angle of 23.45 degrees. which causes seasonal variations as the earth revolves around the sun. The sun takes different apparent paths across the earth's surface due to earth's the rotation while revolving.
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The rows in the table corresponds to the Spring/March Equinox, Summer/June Solstice, Fall (Autumn)/September Equinox, and Winter/December Solstice.
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The intensity of solar radiation, what is converted to electricity by solar panels, changes due to not just weather and atmospheric conditions, but the amount of atmosphere that it must travel through to reach a panel. The lower the sun's elevation, the less solar radiation gets through. This is true whenever the sun is lower in the sky, such as morning and evening, but also during winter compared to summer.
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The follow "stereograph" plots show the sun's elevation (angle above the horizon) versus azimuth (position from east to west for different times during different seasons for Page, Arizona. The darker red line corresponds to the June Solstice (longest day of the year). The point of these is to show the daylight duration and sun's elevation during different days of the year.
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Same thing for March and September Equinoxes, when day length is approximately 12 hours.
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Same thing for December Solstice (shortest day of the year).
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At Page, Arizona (for example):
Mar 20th, 12.2 hours day length, maximum sun elevation 53 degrees.
Jun 21st, 14.7 hours day length, maximum sun elevation 30 degrees.
Sep 22th, 12.2 hours day length, maximum sun elevation 53 degrees.
Dec 21st 9.6 hours day length, maximum sun elevation 77 degrees.
The point of all this is to emphasize that the amount of solar energy available to you during winter may be half or less than that available during summer. If you are getting much of your power from your vehicle's alternator, this may not be much of a concern, but must be considered if you plan on staying at a base camp for a number of days.
The following graph results from an analysis I did a few years ago for roughly 37 degrees north.
If you only have a panel pointing straight up (first column), the energy you'll harvest will be less than a third during winter. Keeping a panel pointed at where the sun will be at noon (fourth column) does much better but still much need supplementing.
It remains my opinion that the easiest way to harvest more solar energy is to simply get more [identical] panels in parallel. The voltage won't increase and your controller will take as much current as it can.
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Recommendation
- Take an inventory of geological formations and trees to determine where shadows are likely to fall. You may have significantly less time to harvest solar energy during the day.
- During summer, your roof tap panel pointing straight up is sufficient (depending on power requirements).
- During winter, wire in another panel in parallel.
- If possible, always at least point panels to where the sun will be at solar noon (azimuth 180 degrees in the northern hemisphere). See Solar Path Calculator below.
Solar Path Calculator
Solar Path Calculator
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