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Wednesday, March 9, 2011

Solar efficiency: Deserts vs. forests

By Bob Difley
By the end of this month snowbirds will be heading north, retreating from the increasing heat of the desert sun into the cooler climes of the northern forests. As a boondocker, most of your livability habits don't change too much--except for electricity if supplied by solar panels.

Most winter desert campsites are open to the sky, so your panels charge when the first rays of the morning sun hit your panels until it has passed out of view in the western sky. But since the angle of the sun is lower in the winter, you will not get full charging unless you tilt your panels toward the sun's trajectory across the sky, and position your RV horizontal to the sun's movement.

You must also verify that your panels--or other roof top equipment--do not shade the charging (silicon) part of the panel. Since the days are also shorter, your total charging time will be shorter, and fewer amps will make their way into your batteries. Therefore, you may have to schedule more electricity-using hours (meals, showering, computer use) during daylight, so as not to deplete too much from your batteries overnight.

But when you move from the desert to a Ponderosa pine forested campsite, your challenges change. Since the sun during the summer months passes more directly overhead, your panels do not have to be elevated to take advantage of the suns' rays throughout the day.

Days are longer so you have many more charging hours every day than in the desert, and since the number of nightime dark hours roughly equals the eight hours of sleep needed, most electricity-using can be accomplished while the panels are charging to some degree. If you coordinate your sleeping and rising times with the sun's you will not draw excessive juice from the batteries.

But now comes the hard part. Since you are camping in a forest, you will undoubtedly have periods of the day when the sun is blocked from reaching your panels by the magnificent (and tall) trees surrounding your campsite. Short of camping out in the middle of a meadow (which is nice too) you will have to hazard a guess at how many daylight hours the sun is actually reaching your panels--without any part being shaded, which reduces the amount of amps that pass into your batteries--and calculate accordingly so you don't find yourself with batteries that have not re-charged.

The remaining consideration in both desert and forest is the number of overcast or rainy days which will produce far fewer amps. It is therefore a good idea to oversize your system to account for all the variables. And sweep off the pine needles from time to time.

Check out Bob Difley's Boondocking and Snowbird Guide eBooks at

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