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Posted by Mike on May 22, 2006, 10:54 pm
Hi Jeff

Very inefficient, I designed my system to run entirely off 12 volt DC so it
could be used in locations where no AC power is available, eg holiday
batches or cabins in the bush. Also if there is some emergency where the
mains power fails for a period, then it will continue to function. All the
commercial systems here in NZ use 230 Vac pumps.

The application requiring a 4M head is for a heating system for a pool, the
only place that panels can be positioned are high up on the roof. It is not
practical to run the main pool pump 6-8 hrs a day, so thought it better to
run an auxiliary pump. The panels are twinwall polycarbonate glued to 32mm
header pipes through slots in the pipes cut using a laser. They sit in a
simple wood frame and are painted flat black. Water is circulated through
the internal vertical honeycomb.
Very cheap to make, don't know how long they will last. Was advised to not
use copper constructed panels as the high chlorine content when the pool is
dosed can erode the copper and leave a brown deposit on the sides of tiled
pools that is very difficult to remove.

Most of the (cheap) AC pumps are not designed to run for extended periods,
thus my desire to use a magnetic drive pump, they usually have a life in
excess of 10,000 hours. For this application may use a good quality AC water
pump, needs about 120 watts to pump to the required head//flow.

Yeah I do have a white multi led flashlight running off AAA's, however am
definitely not Amish.


Posted by Gary on May 23, 2006, 1:08 am
Mike wrote:

Hi Mike,
Here are a couple thoughts -- I'm not at all sure any of them would actually
work :-)

Pressure Tank Start:
Do the initial startup with water from a flexible diaphragm  pressure tank of
the type used on well water systems.  The water from the prssure tank fills the
circulation loop initially so that the low head DC pump does not have to push
the water up the 4meters.  Once the circulation loop is full, the DC pump can
maintain flow?  You would have to have a way to charge the pressure tank -- e.g.
and RV diaphragm style water system pump -- some of these run on 12V and have a
built in pressure cutout switch ($0ish).

AC start -- DC run:
Install both the AC and DC pumps (not sure about the plumbing arrangement).
Startup on the AC pump (or both pumps).  Once flow is established, turn off the
AC pump and run on DC only.  This way the (cheap) AC pump runs little, lasts
long, and consumes power only on startup?

Pool Pump Start -- DC run:
I don't suppose the pool pump could be convinced to initiate flow through the
collector loop?  Once flow is established shut down pool pump, and let the DC
pump maintain flow?

Keep the circulation loop full:
Have an electrcally actuated valve where the pipe returns to the pool, and maybe
a 2nd one where the inlet pipe leaves the pool.  You would have to prime the
loop the first time.  After that the, the shutdown sequence is 1) close the two
electric valves, 2) shut down the pump.  The start up sequence is 1) turn on the
pump, 2) open the two electric valves.  This way the pump does not have to
overcome the 4m head at any time, and (maybe) could be a small DC pump.


I (and I'm sure others) would really like to hear how the twinwall PC collector
works out.




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Posted by Mike on May 23, 2006, 10:19 pm
 Hi Gary

Thanks for the helpfull hints, will look into using 2 pumps as suggested.

I have constructed a small sized twinwall PC panel 6 sq feet for testing,
and it certainly works ok, gets hot quite quickly. Holds a lot of water
though as they are 5mm thick, so will need back supports, thus the wooden
frame. Hardest problem is getting an effective seal to the headers, slots
can be cut at local laser cutting business, so are an exact push in fit.
Solvent mix is run down the joints and forms a very good seal, after
allowing 24 hrs to fully set then a non foaming structural adhesive is run
along the outer joint, this strengthens the joint and fills any pinholes.

Once I have made and installed the full size panels will let the group know
how I got on.


fills the

tank -- e.g.


off the

the two


Posted by DBlosse on June 12, 2006, 10:04 am
 Mike wrote:

Hi Mike,

Thanks for posting your efforts on the twinwall, I have been looking
into DIYing a few panels to heat my pool and keep the cost down, only
to be shocked at the rising cost of copper, and also the difficulty
finding cheap sources of rubber/PVC pipe fo that option.

And today was reviewing my options with my father, a retired Toolmaker,
who suggested I the twinwall. So I was looking to check the thermal and
UV resistance of the polycarbonate and methods of bonding that might be
available to join the header. This could be poly or even PVC as there
seems to be a variety of options.

I was intending to simply router some slots into the header tube, by
making a small jig to plunge the tube and slide it though.  And until I
read your message I was also intending to build a small prototype.

But now I think I will build a full 8' x 4' version with the following:
On a Timber frame enough to add spars only where needed, use 8mm
twinwall as the 6mm is very thin and flexible. Also paint the front of
the panel matt black. The wind may be a factor so I might cover the
timber with some thin ply or something and then have the option to
limit air from the rear.

I have some time coming up in July and might just get a panel up and
running by August.

Mean time if anyone has any advice, warnings or helpful hints please
pass them on.

If anyone else decides to construct a twinwall panel do let us know how
you get on.

Thanks for the info Guys.


Posted by Mike on June 13, 2006, 10:06 pm
 Hi Dave
For the top and bottom headers I used standard 32mm hard polyprop type
plumbing drainage piping.
To glue the twinwall to this you have to mix 2 solvents together, one
softens the poly tube and the other a solvent for polycarbonate type
Go to a sign company whom makes plastic signs, they will have the necessary
solvents. Once the twinwall is pushed inside your slots, hold it on a slant
and with a fine squeezer bottle run the solvent mix down the outside and
inside joints, this will soften both types of plastic and effectively bond
them together.
The joint will not be water tight if you hand cut the slots so fillet the
outside joints with a structural adhesive (use one that is solvent based -
not moisture cure, as these types will generally foam causing pinholes) This
will seal and strengthen the joint, give it a week to fully harden before
filling up with water.

We are in winter here so will be making the full sized panels later in the


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