PV array for Heat Tape

[cwmielke]

Hello,

I am looking into a project for a home high in the rocky mountains which has a very high sun exposure on the Southwest facing roofs and eves, the trouble is that this exposure helps in the creation of ice dams on the NE roof valleys of this home. The simple solution is plug in heat tape. However, being an electrical engineer who likes to tinker I would like to look into hooking 12V heat tape to a 12V solar array. I have no need for batteries or constant heat, I am fine with this tape only working while I have direct sunlight. I only want to melt simple channels down the valleys of my roof (5 feet of tape) and further I do not care to melt all the ice I only want a "drain" to allow for any trapped water to escape below the ice. I am thinking of some 12V-5W/ft heat tape for 2 valleys, so simple math tells me I need around 50W of power (2 valleys X 5 ft X 5 w/ft).

Does anyone have any recommendations for waterproof 12V heat tape (obviously not in bulk) and a small 60W solar array? Is there anything I am overlooking? I know I will probably never recoup my investment in electricity savings but hey everyone needs a hobby right?

Thanks!

Chris

 

[Noway2]

I don't have suggestions for products to buy, but I have a suggestion for a potential alternate approach to consider if the electrical method doesn't work out. Get some black plastic pipe and create a set of loops that runs through the sunny area and then to the area where you want to melt the ice. Fill the pipe with a glycol (antifreeze) solution and use a little pump to circulate the water. You can then run the pump off solar array. You would need to calculate the pressure loss of the pipe, which is a function of diameter, and get a pump that can overcome that pressure drop. You wouldn't be too worried about flow as in GPM, so you could run the pump nice and slow, using less power. The water in the pipes would be heated by the sunlight and then used to melt the ice. You could even build a little solar box with mirrors to concentrate the heating of the pipes.

 

[OperaHouse]

12V solar panels are not 12.000V The power point is closer to 18 or 19V. As it gets colder actually they produce more voltage. Not likely you will burn out the tape but you will consume more power than you counted on. Calculate the current needed for your string which will likely be 80-100W.

 

[VEBill]

50 watts isn't much heat. If you shop carefully, it's pretty cheap to go above and beyond 50 watts.

http://www.costco.com/Grape-Solar-100W-Solar-Panel.product.11760095.html

In these parts (E. Canada) we just install rubber membranes under the shingles and can often ignore any ice dams.

 

[cwmielke]

NoWay, Thanks for your suggestion but I'd like to try it electrically.

OperaHouse, I did not consider the voltage profile of a PV array, though I don't think it will be a large deal with a pure resisvite load. V²/R however wouldn't the voltage be dependent upon the load?

VE1Bill, I wish my contractor would have installed rubber but the roof is too new to rip it up. A single hole in the valley would drain any trapped water. I like the attached link and similar, my biggest problem is finding waterproof 12V heat tape

 

[SceneryDriver]

For 50-100w, losses from using an inverter to step up to 120v wouldn't be too bad. You can find 300w inverters at most home centers for about $25 or so.



SceneryDriver

 

[OperaHouse]

There are 12V heat tapes available that can be cut to any length. They also self regulate temperature like a PTC solid state fuse, when they heat up the current drops. In full sunlight a solar panel operates like a constant current source from the power point down to a short. So select the panel for the desired current.