[RE-wrenches] Solar thermal covering
Dave Angelini Offgrid Solar
offgridsolar at sti.net
Wed Jun 18 14:38:38 PDT 2025
Perfectly said August!
Dave Angelini Offgrid Solar
"we go where powerlines don't"
[3]https://offgridsolar1.com/ [4] [3]
e-mail offgridsolar at sti.net
text 209 813 0060
On 2025-06-18 2:24 pm, August Goers via RE-wrenches wrote:
> I have a soft spot for solar hot water, but alas it is obsolete in most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 conclusion that solar thermal is obsolete.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 [1]
> www.SolarEnergyOregon.com [2]
>
> 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(tm):
>
> 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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------
[1] tel:503-238-4502
[2] http://www.solarenergyoregon.com/
[3] http://members.sti.net/offgridsolar/
[4] https://offgridsolar1.com/
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