Solar and GARN

[Ecky]

I am going to hook up 6-4x8 solar panels to a GARN 1500. Looking for opinions whether to go with a drainback system and no heat exchanger issues or closed loop system with anti-freeze and a heat exchanger. I am located at the 45th parallel in central Ontario.

 

[benjamin]

I'd do the drainback if you can get away with it: location and height work out, regulations and incentives allow it, and you trust your water treatment plan to handle more aeration of the water.

The advantage of drainback in efficiency and simplicity outweighs the "picky" installation in my opinion.

 

[Ecky]

Thanks Benjamin. The drainback may not be that simple in my case since I would have to drain back to a different tank. Someone also pointed out that I would be dealing with a larger pump (and more electricity) to overcome the larger head - a valid point in my opinion. Good point about more aeration of the water. Thanks for your thoughts.

 

[DaveH9]

I have a closed loop pressurized, my collectors are on the ground so a drain back would not work. Are you talking about a drain back with no heat exchanger, pumping water through the collectors? I suggest a drain back closed loop. The few closed looped pressurized systems that get damaged are mostly from over heating in the summer, due to stagnation from pump or power failure. The few drain backs that get damaged are from freezing. The closed loop drain back is the most reliable, but it's a little more complex.


Here is a good article from Homepower

http://homepower.com/basics/hotwater/

 

[Ecky]

Thanks for the link. It is a good overview of the types. The closed loop drain back may not be the best in my situation since the panels are all below the GARN unit. As such I would have to put the drainback reservoir below the panels and insulate it very well. I would then need a bigger pump to overcome the head. There may also be the issue of the GARN unit trying to drain back into the panels and the reservoir. This could be overcome with 1-way valves I suspect. Pressurized glycol might be the way to go given my situation.

 

[markmudd]

Make sure you don't oversize tank to collector sq ft. I am fan of drainback without pressurized storage due to simplicity, but that is not always feasible. But if it turns out you need to have a smaller tank anyway, could it be considered. For 192 sq ft of collector, I wouldn't think you would want more than 250-300 gallons of storage.

 

[jimbom]

There are many references regarding size of storage vs panel square footage. There are so many variables but in general, one might start with the premise that one gallon of water storage for one square foot of panel is a good number. As I recall, the F-Chart method uses 1 to 1.5 gallons per square foot of storage as a reasonable starting place.