Evacuated Tubes [RE-wrenches]

[Todd Cory, Mt. Shasta Energy Services]

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A local contractor also loves these. He claimed there was a 40 degree 
delta T on a sunny day with the panel under 3' of snow. I **seriously** 
doubt that is anywhere close to being accurate.

The evacuated tube marketing folks are evidently doing a good job, but I 
prefer the trusted flat plate technology. Been around forever, very 
robust and long lived.

The last time this thread went around here, the consensus was to steer 
clear of them. Perhaps the folks at AAA or Tom Lane might have more hard 
data, which I would also love to see.

Todd


Howie Michaelson wrote:

>Hi All,
>
>I'm looking for experiential as well as "non-biased" info on Evacuated
>tubes.  I have installed them a few times in the past, but have pretty
>much steered clear of them since for several reasons:
>
>1. Here in snow country, I've seen them not shed snow for significant
>periods of time, and have also seen them break from ice/snow movement down
>the roof.
>
>2. From what I've seen/heard their output is in most cases not any better
>than flat plate collectors, and due to lack of snow shedding capabilities,
>sometimes substantially worse.
>
>3.  They are more expensive than flat plates, and are rated lower by SRCC
>so in Vermont are given less incentive money (which is based on the
>ratings).
>
>A client saw the Solar Decathlon and noticed that almost all the
>competitors used evacuated tubes (ET's).  He also said that one
>manufacturer was whacking a tube very vigorously against hard objects with
>no damage resulting.  He wants to put in the reasonably best collectors he
>can with an eye toward Return on Investment, but is now enamored with
>Evacuated tubes since they would fit well on the south wall of his home at
>a very steep angle (near vertical), and was told that there is virtually
>no output penalty for doing so.  Placing them near vertical probably goes
>a long way toward answering the snow shedding issue, but I'm mostly
>ignorant about the rest of these issues.
>
>Any info about any of these concerns or leads to a place where I can get
>good comparative info on ET's vs. flat plate collectors would be much
>appreciated.
>
>Thanks,
>Howie
>  
>

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