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post #47 of Old 11-28-2017
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Re: Solar heating element for water heater

Originally Posted by misfits View Post
You know that would be a pretty cool idea.
IF your PV system completed charging your house bank & there were still a couple hours of good sunlight left, this would work providing your PV system had the nugget to drive a 300 watt element.

The 300 watt DC element is capable of raising the temperature in a 6 gal tank 20 degrees in an hour.
One watt equals 3.413 BTU's in my world. A 300 watt element would equal 1023 Btu's per hour.
One BTU raises the temperature of a pound of water one degree. Water weighs 8.34 pounds per gallon.
6 gallons X 8.34 X 20 degree rise= 1000 Btu's

So if you were some place that the ambient water temperature of your heater was 70 degrees, hour later it's at 90. Not a bad deal in my book.

It would also be pretty easy to make a small open loop thermal solar panel & just let it work by convection. You'd have to valve it off so at night it didn't operate the opposite way. All the above sounds like a good science experiment to me
It might be sound science in a lab, but not so much on a sailboat somewhere between 36 to 42 feet, especially in the Frisco area, as in the OP's case. You are talking about approximately 25 amps of 12 volts to get your 300 watts, sometime after peak operating hours, at which time we can assume the batteries are fully charged. With a fixed system that is at best 65% efficient in the tropics over the daylight hours, just how many panels and how much surface area are you expecting to get on a boat somewhere between 36 to 42 feet?

"Any idiot can make a boat go; it takes a sailor to stop one." Spike Africa aboard the schooner Wanderer in Sausalito, Ca. 1964.
“Believe me, my young friend, there is nothing - absolutely nothing - half so much worth doing as simply messing about in boats.” ― Kenneth Grahame, The Wind in the Willows

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