I thought I could use my solar panel to heat a drum full of water. I would put a hole near the bottom for the element and another at the top for a pressure release valve. My cabin is off grid and fully insulated with thermal windows, so a small, constant supply of heat might do the trick. I have all the components to set this up for the winter, and I like the passive approach - no pump.
So i wouldn't completely rely on this system. I know where i am some times we do not get any usable sun for days. Sometimes we can get a few hours of sun per week.
I also am somewhat worried about the galvanized tank off gassing the galvanization process from being heated. Maybe with the water it will not reach the temperature for that however.
In all honesty if it is easy and does not require retrofitting your house. I would give it a go.
How are you going to control the extra power from the 350w panel? Maybe you are going to use a battery and charge controller?
I believe if you put a 350w solar panel to a 150w element it wouldn't be good. Why not get a 300w element?
Where we are. We have a residential water tank for our hot water. Its most likely 30 gallons. When the sun is out we can heat it with 1 of the elements in the tank. It takes about 3 hours to get the water to 140* Maybe longer if the water tank hasn't been heated at all. The element draws about 1000 watts.
I suspect if you are heating the tank up and the tank is than radiating out to the room 150w might not be enough due to the tank giving off most of its heat.
Are you going to have a water line plumbed to the tank? or just take the top off and fill it up weekly?
If you could use all 350 watts, and you have a lot of sunny weather, then you might be able to get 35 gallons of water warm. You would get a lot more gain by just letting some of the sunlight inside - could you add an extra window to your cabin?
If the climate is often cloudy, then forget it. Your your water will not heat. If you wire a 150w rated load to a 350w panel, you will simply burn it out. I suspect that the idea with the water is to create some sort of thermal storage? In that case, it is likely much too small to make a meaningful contribution to heating overnight, unless you sleep next to it. You can get wire wound resistors that can handle up to 1000 watts which will heat the air in the cabin, but again, if the sun is shining, you are going to be much better off using the sunlight directly - solar panels are only about 15 - 20% efficient.
Assuming your panel and battery can power the heating element 24 hours per day: 300W = 1023 BTU. That's not a lot.
A Mr. Heater Little Buddy puts out 3800 BTU. A plug-in 110V 1500W heater puts out just over 5000 BTU. A Portable Buddy puts out up to 9000 BTU. Even my antique Coleman backpacking stove puts out 8000 BTU.
It's a neat idea, but I don't think you have nearly enough energy input to heat your space.
I have an insulated 5 gallon bucket with 3 x 25 watt elements in it. It will keep 3 gallons of water from freezing down to about 20 deg f. In the winter 40 deg f water feels mighty cold. From my tinkering it would take a couple thousand watts to keep an uninsulated drum in a house above a temperature that feels warm. To me it only feels warm 85 deg f and up. I like your idea, and I keep trying different ways to do this too. I like to do this sort of thing when I have a surplus of sunshine.
The best place to pray for a good crop is at the end of a hoe!
I think there are some good reasons to get a little heat out of a PV panel. Sure a person could hook up a mini split heat pump and make four times as much heat, but then it would take quite a bit more money than some solar panels and a space heater.
One 35o watt panel is just not much heat, but maybe four panels and 15 dollar space heater from walmart. Start the system up late in the summer when there is more sunshine and blow the heat into a rock pile under the cabin. Slip a cover off the rock pile in October to let the heat rise. 3.41 BTUs a Watt times maybe 1000 watts times four hours a day times seven days starts to add up to some heat(95,000BTUs)
Maybe don't think of it as a reliable heat source though but that many less logs to split and that much less smoke to breath. Might as well just store the heat in living space objects if its not too much heat.
Thanks for the helpful comments. My experiment will be to heat my 3" (insulated with recycled styrofoam and vapor barrier) 12x16 cabin with different kinds of thermal mass. I am seeing more potential with filling the crawl space with rocks and ducting and connecting a rocket stove to it. Because my cabin is between 1' and 3' above grade I have realized i have to close up and insulate underneath and around the periphery if I want to have a radiant floor above, which would be half a yard or 32 bags of concrete to make a 1" floor. And if that crawl space was filled with thermal mass waiting to be heated by fire during the day it would accumulate enough heat to get through the night with the assistance of the floor which could be heated by different methods. My solar panel dump would keep the floor above freezing while I was away and then I would be able to switch it over to a copper coil on a rocket stove when there.
The amount of power a solar panel generates usually depends on the amount of sunshine absorbed. For example, if two houses situated in different regions require the same amount of power, the house with the sunniest weather will require fewer solar panels.
That's a very big dog. I think I want to go home now and hug this tiny ad:
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