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Posted by markkate on January 22, 2008, 5:09 pm
 
Hello all;
I want to build a near total solar heat system for my farm house in
Portugal. There is a lot of sun here, and temperatures aren't too
bad.
Factory built collectors are rather expensive here, at about 700 Euros
[US$000] for a 2 sq.meter unit. I recon I'll need 8 [ie 16 sq.meters]
to provide double my heat requirement on a clear day, half to use and
half to store.
So I will have to build my own collectors. Research I have done
indicates that copper is expensive; aluminum plate at double the
thickness will work about as well for a fraction of the cost. But I
fear copper tubes bonded [soldered] to an aluminum plate will be
destroyed by thermal cycling due to dissimilar expansion rates.
Does anyone have direct experience? Have you tried it?
I have no faith in the long term efficiency of a mechanical [crimped,
clamped] bond. Has anyone succeeded that way?
I've found sunstrip on the web, looks pretty good and cheap compared
to an all copper plate/tube setup I could fabricate myself. But does
anyone know where to get it retail? Europe preferably.
Any links or experience appreciated, especially with costs of
different systems. I've seen too many "blue sky" academic works, where
the budget seemed to be set by NASA. I'm looking for a real world,
real price, durable design.
My roof is large, unobstructed, and faces due south.
Regards, Mark Holden
My inventions; www.amsterdamhouseboats.nl , links at the bottom of the
page

Posted by Jeff on January 22, 2008, 7:08 pm
 
markkate@hotmail.com wrote:

That I don't know, but you will have a limited contact area, that being
at the solder point. A high silver content solder is probably going to
be very strong. The wider the bond or gap the more silver content you
will need. I've never soldered aluminum...



Some have suggested just using a silicone caulk. The collectors I've
built I've coated the copper risers with (non silicone, it doesn't
migrate) heatsink compound. I have a flat sheet of aluminum on top and a
sheet wrapped around the tube in back and then riveted to the front
sheet. This gives a very wide thermal bond. It's not up yet, but is
based on Solar Mikes designs and he's quite experienced.

   You can get an idea of what the bond needs to be by running a simulation:

<URL: http://sel.me.wisc.edu/codepro/new_codepro.html>

   The commercial products are welded, either ulrasonically or some
other method. High setup costs but efficient and cheap in the long run.


   Jeff



Posted by Morris Dovey on January 22, 2008, 7:13 pm
 markkate@hotmail.com wrote:
| Hello all;
| I want to build a near total solar heat system for my farm house in
| Portugal. There is a lot of sun here, and temperatures aren't too
| bad.
| Factory built collectors are rather expensive here, at about 700
| Euros [US$000] for a 2 sq.meter unit. I recon I'll need 8 [ie 16
| sq.meters] to provide double my heat requirement on a clear day,
| half to use and half to store.
| So I will have to build my own collectors. Research I have done
| indicates that copper is expensive; aluminum plate at double the
| thickness will work about as well for a fraction of the cost. But I
| fear copper tubes bonded [soldered] to an aluminum plate will be
| destroyed by thermal cycling due to dissimilar expansion rates.
| Does anyone have direct experience? Have you tried it?
| I have no faith in the long term efficiency of a mechanical
| [crimped, clamped] bond. Has anyone succeeded that way?
| I've found sunstrip on the web, looks pretty good and cheap compared
| to an all copper plate/tube setup I could fabricate myself. But does
| anyone know where to get it retail? Europe preferably.
| Any links or experience appreciated, especially with costs of
| different systems. I've seen too many "blue sky" academic works,
| where the budget seemed to be set by NASA. I'm looking for a real
| world, real price, durable design.
| My roof is large, unobstructed, and faces due south.
| Regards, Mark Holden
| My inventions; www.amsterdamhouseboats.nl , links at the bottom of
| the page

I build vertical passive air-heating panels - and if you're not set on
a roof-mounted panel system you're welcome to look at
www.iedu.com/DeSoto/SC_Madison for ideas.

I have a sketch for a four-peice press fixture for forming either
copper or aluminum fins into which you can snap tubing at
www.iedu.com/DeSoto/Projects/FinPress

There's a wonderful collection of DIY information at
www.builditsolar.com - and Gary, the site owner, is a regular here.
Gary, BTW, has photos of a DIY fin press on his site.

--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto/



Posted by Niels Erik on January 22, 2008, 8:55 pm
 

I have build a collector using these strips and I am very satisfied with it.
The price in Denmark is less than 100 euro pr m2

http://www.batec.dk/_da-DK/Content/Data/PDF-dokumenter/Brochurer%20og%20prislister/UK-CuStrip%20Prospect.pdf

I don't know the price in Portugal but they are sold by

Sociedade Portuguesa
De energia solar
Rua Pascoal de Melo 81-4ESQ
P-1000 lisboa
Tlf. 00351 1 3555067

Regards
Niels



Posted by gary on January 23, 2008, 7:44 pm
 On Jan 22, 10:09 am, markk...@hotmail.com wrote:

Here are a few ideas you might think about:

1) Use air heating collectors for part of the load.  Air collectors
are much cheaper and easier to build, and lower maintenance.  They
don't offer storage (except in the thermal mass or your house), but
they can meet the daytime heat loss, and if you let the house
temperature drift up, the heat will last a ways into the night.
If designed well they have about the same efficiency as water heating
collectors.

Some plans here:
http://www.builditsolar.com/Projects/SpaceHeating/Space_Heating.htm

This is the one I use -- $ per sqft -- a one year payback on
materials cost in my climate with propane at $ per gallon:
http://www.builditsolar.com/Projects/SpaceHeating/solar_barn_project.htm

2) Buy the absorber sheets and build the rest of the collector.   I'm
not sure what the high price of copper has done to this solution, but
it worked out well for me about 2 years ago.  By integrating the
collector with the building wall (thus saving some wall costs), the
net cost of the collector was about $ per sqft -- about 1/4 of the
then cost of commercial collectors.
http://www.builditsolar.com/Projects/SpaceHeating/SolarShed/solarshed.htm

3) substitute direct gain or a sunspace or attached greenhouse for
some of the collector area.  This gives you some heat and some plant
or living space as well.  These can be very cost effective depending
on how fancy you get with the construction:
http://www.builditsolar.com/Projects/Sunspace/sunspaces.htm
http://www.builditsolar.com/Projects/SpaceHeating/SolarGarageCollector/garcol.htm

--
There are some notes from people who built their own collectors here:
http://www.builditsolar.com/Projects/WaterHeating/water_heating.htm
They range for a bit sketchy to works of art -- to see the high end,
search for "Kris's Collector"

There are some high thermal conductivity silicone caulks.  I don't
remember the brand, but it had a significantly larger thermal
conductivity.  I did not get it because it had to be shipped from
Europe, so it might work out well for you :)

Gary


















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