Do I need a vacuum breaker on my solar panel...or not?

[PrivatePilot]

Ok guys, I'm sure you can answer this lickedy split. Last year my solar install was temporary at best but I'm making it somewhat more "proper" this year. The panel is a single 4X20 Fafco, nothing fancy, but my experiences with it were very positive last year. It is mounted on an overhang on the back of our house which is almost a perfect fit for the panel.

I've read a lot about the need for vacuum breakers on solar panels, but here's my question. The panel sits width wise in it's location on about a 45 degree upward angle. The feed and return manifolds have plugs at both ends, look at it from a "top/bottom" perspective perhaps (so water can be fed from either top or bottom, simply remove the desired plug and plumb) although one is higher than the other. Last year I fed the water in from the bottom of the feed side manifold, and the return was from the top of the return manifold. This way the panel was always full of water and there would be no chance of drainback. I want this - The area where the panel is mounted is susceptible to extreme building-elevated (AKA, wind tunnel) high winds in storms and the extra weight of the water left in the panel is significant which without doubt helps keep it firmly in place.

So, if the panel is NOT having a vacuum drawn on it (if I had the return plumbed to the bottom/lower side of the return manifold), do I need to install a vacuum breaker anyways? It seems like it would be unnecessary as the way the panel is setup there's no way it can drain back on it's own.

At the end of the season I drain the panel manually, blow it out, and then roll it up and remove it from the roof, so I'm not worried about the fact it won't drain back automatically - it spends it's winters inside.

So, do I need one anyways installed at the top of the feed side manifold? (The highest point, basically the same height as the return however...)

 

[JasonLion]

If you specifically want the panel to stay full of water, then you should not install a vacuum breaker. However that will shorten the lifetime of the panel somewhat.

Regardless of that, I recommend that you have water enter the panel at the lowest point, and leave the panel at the highest point. It won't drain unless you have an air leak, but you at least have the option of draining it without removing it from the roof. Having the water flow up the panel will also improve the efficiency just a little.

 

[PrivatePilot]

If you specifically want the panel to stay full of water, then you should not install a vacuum breaker. However that will shorten the lifetime of the panel somewhat.

Regardless of that, I recommend that you have water enter the panel at the lowest point, and leave the panel at the highest point. It won't drain unless you have an air leak, but you at least have the option of draining it without removing it from the roof. Having the water flow up the panel will also improve the efficiency just a little.

Thanks, OK, as I suspected..and that is how it was plumbed and I planned to do again this year.

Regarding the lifespan of the panel being shortened, is that because of the constant water contact vs being evacuated, or something else I'm missing?

 

[jblizzle]

The water in the panel will get superheated if the solar is not running. This will soften the plastic and the weight of it trying to drain will pull a vacuum at the upper parts of the panel. If it gets soft enough, the vacuum will collapse the tubes.

 

[JasonLion]

The panel is heavier when it is full of water. When full of water and also hot it will tend to stretch a bit. Over time that stretching accumulates and eventually it can damage the panel.

 

[PrivatePilot]

Ok...I think that the extra weight holding the panel securely in place during storms outweighs the possibility of longterm damage. Having the panel damaged in a storm will bring it's life to an immediate end. Unfortunately due to the location it's mounted strapping options were limited - like I mentioned, the panel is basically the exact same size of the roof it lays upon, so securement was a challenge.

I did use it plumbed that way last year with no ill effects..and there was the occasional time when the panel was in the sun without flow. This year the system is going to be controlled by a GL235 automated system so I don't expect it to sit idle in direct sun that often. It receives direct sun for about 7 hours per day, 100% of the time which I expect it to be operating on a sunny day.

In the grand scheme of things a replacement panel is only a few hundred bucks a year or three down the road if this method causes premature death, so be it - still cheaper than a heater and the gas to feed it.