Evacuated Tubes [RE-wrenches]

[Kurt Albershardt]

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Good points, but I am not as convinced on the cost.  The combination of 'new improved' copper pricing and overseas ET production the differential has narrowed quite a bit.

We are planning a 52 ET collector array in southern NM (6000', but snow is rare) which should meet ~50% of the mid-winter heat load on a 1938 mid-rise brick/concrete building.  If suitable roof area is a limiting factor, ET quickly becomes the obvious solution.



--On Saturday, November 17, 2007 9:59 PM -0500 Wilco Vercoelen <w.vercoelen at dommelvalley.ca> wrote:

>
> Dear Howie,
>
> We believe that there is a great difference in quality of these tubes.
> So basically saying, evacuated tubes are better or worse than flat plate is
> not recommended.
> However...
> In a snow belt region we recommend flat plates over evacuated tubes, because
> like the others wrote, there is very little heat loss, so snow cover is an
> issue and you want the heat during the winter, unless you put them
> vertically or at a steeper angle which would be preferable, the sun's angle
> is lower in the sky in Fall and Winter anyways and this way it reduces the
> overheating in the summer.
>
> Generally you can say that ET performance (Net area) is much better, not
> less, check SRCC & SPF, but to achieve the same results with flat plates,
> from a financial point of view it is often wise to install more net surface
> area of flat plates, because ET systems generally costs more, but it also
> depends on what is available in your area and what the costs are.
> There are many different manufacturers' out there and there good and bad
> apples.
>
> Wilco Vercoelen
> Dommelvalley Green Power
>
>
> 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
> --
> Howie Michaelson
> NABCEP Certified Solar PV InstallerT
>
> Sun Catcher, LLC
> Renewable Energy Systems Sales and Service
> http://www.SunCatcherVT.com
> (cell) 802-272-0004
> (home) 802-439-6096



-- 
Kurt Albershardt
Eastern Sierra Energy Engineering
Reno, NV
775-853-1800







.


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