Perfectly said August!
Dave Angelini Offgrid Solar
"we go where powerlines don't"
[3]https://offgridsolar1.com/ [4] [3]
e-mail offgridso...@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I have a soft spot for solar hot water, but alas it is obsolete in most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@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conclusion that solar thermal is obsolete.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@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 - d...@solarwork.com - 208.721.7003
On Jun 17, 2025, at 6:23 PM, Luke Christy via RE-wrenches
<re-wrenches@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
sgsrenewab...@gmail.com
On Jun 17, 2025, at 3:46 PM, jay via RE-wrenches
<re-wrenches@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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Links:
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[4] https://offgridsolar1.com/
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