[RE-wrenches] Solar thermal covering

Wed Jun 18 14:24:51 PDT 2025

I have a soft spot for solar hot water, but alas it is obsolete in most if
not all circumstances. We stopped doing it probably 10 years ago in the Bay
Area after finding a) a loss in demand, b) maintenance often costing more
than the calculated savings, and c) PV costs and reliability substantially
improving. The cost and reliability of a few PV mods and a heat pump water
heater beats the pants off of a comparable solar hot water system. I used
to regularly teach a solar hot water class for PG&E and the last time we
did it I think there were only 8 attendees compared to hundreds that would
attend energy storage classes. I believe I was the last NABCEP Solar
Heating Installer in California when I finally let that certification
lapse. There clearly aren't many folks doing it any more.

Anyway, for the right offgrid DIY remote living type situation, I can see
where SHW still makes sense. For mainstream applications, I don't think so.

August
Luminalt

On Wed, Jun 18, 2025 at 12:54 PM Solar Energy Solutions via RE-wrenches <
re-wrenches at lists.re-wrenches.org> wrote:

> We have been installing solar hot water heating system since 1987.
> Previous to 87, during the Carter years, there were 100 solar companies in
> the Portland Oregon area. So far as we can tell, we are the last man
> standing doing solar thermal in Portland. Subsequently, we don’t know how
> to advise people on what to do with their solar thermal systems. The
> plumbing industry never embraced solar  thermal, solar electric has sucked
> up all the solar thermal people, and heat pump hot water heaters have come
> along, which bring people to the same resource footprint as thermal brings
> people down to.  I have slowly come to the painful conclusion that solar
> thermal is obsolete.
>
> Thoughts?
>
>
>
> *Andrew Koyaanisqatsi*
> President
>
>
> *Solar Energy Solutions, Inc.The BRIGHT CHOICE*
>
> *Since 1987,** helping you and your *
> *Portland neighbors move** towards an environmentally sustainable future.*
>
>
> *503-238-4502 <503-238-4502>www.SolarEnergyOregon.com
> <http://www.solarenergyoregon.com/>*
>
> On Jun 18, 2025, at 4:12 AM, Dana Orzel via RE-wrenches <
> re-wrenches at lists.re-wrenches.org> wrote:
>
>  I have not read all of the comments on this thread so please excuse any
> repeats.
>
> The valley that I live in has so many drain back systems it’s amazing. I
> have inherited the service on them not that I wanted to.  The trick seems
> to be that you need a pump that gets the Evac tube manifold full of water &
> pushes the air out very quickly in order to eliminate the possibility of
> steam lockup. The taco 2699 series of pumps were used here for a lot of the
> systems .
> There are many up sides to employing evac tubes in general & many down
> sides.
> Upsides include:
> Higher temperatures at colder air temps (if not covered with snow).
> Lighter weight at installation .
> Smaller footprint on roof or area of installation .
> Production of hot water in less than desirable weather conditions.
> Production of higher water temps.
>
> The down sides of evac tube systems with drain back are:
> When the tank gets hot & the circ pump to the collector gets turned off as
> long as it’s sunny the manifold is too hot to restart & resume to make
> additional hot water as it steam locks.  This Of course limits the overall
> efficiency of the system & comprises this the systems production, not good
> as you get 1 tank of hot water/ day unless very cloudy conditions for a bit
> & the manifold cools.This requires a controller that will not restart the
> pump or you burn out pumps.
> Avoiding shut down requires having a very large tank(s).The systems here
> have oversized atmospheric tanks 300-800+ gallons each with dual heat
> exchangers one for solar & one for DHW  before the backup source.
> Pollution during the production of the tubes
> All are Made in china due too pollution during tube production pollutionp
> Steam lockup
> Tubes Still covered in snow long after the sun has returned after the snow
> storm has cleared out
>
> Evac tubes have their uses though I tend to not install them In
> residential systems. I think that high water/ higher temperature
> requirements usage applications all day like schools, jails, commercial
> production facilities, dairies, etc .
>
> That all said. I tend to install flat plate  collectors appropriately
> sized for system needs, with some kind of way to address overheat when
> people go on vacation midsummer so I don’t have to go rescue the system
> when I am on a vacation!
>
>
> Dana Orzel - dana at solarwork.com - 208.721.7003
>
> On Jun 17, 2025, at 6:23 PM, Luke Christy via RE-wrenches <
> re-wrenches at lists.re-wrenches.org> wrote:
>
>  Hi Jay,
> I agree with Brad that Evacuated tubes are not a good (or even a
> reasonably possible) candidate for a drainback retrofit. If they are
> pass-through tubes, then they cannot fully drain as piping connections
> typically come through header connections at the tops of the tubes. If they
> are sealed heat-pipe tubes, then not only is the header unlikely to drain
> properly, but the tubes themselves will stagnate at a very high temperature
> without heat transfer fluid flow.
>
> I recommend a diversion heat- dump arrangement such as Todd suggests.Use
> paralleled runs of conventional hot water baseboard fin tube for the heat
> dissipator. This stuff is readily available at almost every plumbing supply
> house and it works well.
>
> Diversion can be activated by either an electric 3-way valve and a set
> point controller, or the passive wax-thermostat 3-way valve that you
> mention. I have used both methods extensively with good results. The wax
> thermostat will probably be significantly harder to find. Some years ago I
> ordered them through Low Energy Systems in Denver. Reach out to me off list
> and and I can supply some contact information.
>
> -Luke
>
> Luke Christy
> Renewable energy consultant
>
> NABCEP Certified PV Installation Professional™:
>
> Solar Gain Services, LLC
> PO Box 531
> Monte Vista, CO 81144
> 719.588.3044
> sgsrenewables at gmail.com
>
>
>
> On Jun 17, 2025, at 3:46 PM, jay via RE-wrenches <
> re-wrenches at lists.re-wrenches.org> wrote:
>
> In doing research today I found the following, not sure where I can buy
> them at this point.
>
> 1. solar dissipation tubes.  that will do about 12,000 btu or at least
> this one does.
>
> 2. 3 way thermostatic valve which uses a type of wax that opens and closes
> it at a specific temp and routes the heat through the dissipation tube vs
> the heat exchanger down below.
>
>
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