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Recommendations for pump and controller for Solar Hot Water System?

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Posted by Uglow on August 13, 2004, 4:16 pm
 
I'm planning to build a solar hot water system to pre-heat my DHW. Can
anyone recommend a suitable DC pump that can be run off a small PV panel?
The flow does not have to be very great and the storage tank will be level
with the panels on the roof. Would the pump run at varying speeds depending
on the light level and therefore the power output of the PV panel?

I am also looking for a relatively cheap control unit (differential
controller) for the pump. I would be prepared to build one myself from
circuit diagrams if there are no cheap ready-made controllers already
available.

I was thinking that if the pump was controlled directly by the PV panel then
only one temperature sensor (on the hot outlet of the solar panel) would be
required to prevent the system loosing
heat (e.g. on cold winters days when there is still enough light to power
the pump but no direct sunlight).  Is this setup possible or would it be
simpler just to buy/make a differential controller?

Any advice would be very much appreciated.
Chris





Posted by Gary on August 14, 2004, 4:11 am
 
Uglow wrote:

The Tom Lane book on solar hot water heating likes the El-Sid pumps
made by Ivan Labs for direct operation on a PV panel -- this outfit
(and many others) sell them:
http://www.solarsupply.com/DCPumps.htm
Or, google something like "El-Sid pump Ivan Labs".
Ivan Labs does not seem to have a website, but the phone number is
listed as: 561 747-5354   Jupiter, FL

March Pumps also makes DC pumps that should work with PV panels.
http://www.marchpump.com/

This pdf manual for one of the SunEarth solar hot water systems has
some details on using El-Sid and March pumps with PV:
http://www.sunearthinc.com/Solaray-PV.pdf

This pdf from a HomePower article is pretty interesting -- shows a
"homebrew" system that heats water and uses the El-Sid pumps on PV.
Quite a bit of installation and some design info:
www.arttec.net/Solar/SolarHeating.pdf


The Goldline controllers seem pretty popular, but I'm not sure you
need one if you use a PV panel powered pump.  The PV panel only drives
the pump when the sun has reached a certain intensity.


I don't think you need the temperature sensor if the PV panel and the
pump are well matched, and the PV panel is correctly oriented (i.e.
parallel to the collector).

You might also want to post your question on alt.solar.photovalic

Gary


Posted by Uglow on August 14, 2004, 4:50 pm
 Thanks for the links Gary. There was plenty of useful info in the pdf's
generally, although I can't see how the SunEarth system prevents cooling
without any temperature sensors. What characteristics does a solar PV panel
need to ensure correct operations in this case?

My location is: UK 51N (thats the south of England)   in case it's
relevant.

Chris



Posted by Gary on August 15, 2004, 2:21 am
 Uglow wrote:


I think that you need a PV panel that does not generate enough power
to drive the circulation pump until there is enough sun to heat the
water.  I suppose the system can't be perfect, in that enough sun to
heat the water will vary with ambient temperature, while sun to drive
the pump is probably pretty constant.  But, people seem to get good
results with this arrangement.  I have heard of people biasing the PV
panel to face a little east of south to get the pump started earlier,
or doing other tailoring to get things working right -- so, it may
take some tinkering.
I think that Ivan Labs recommends a 20 watt panel for the El-Sid pumps
-- so this would seem like a good starting point.

There is also a check valve in the feed line from the storage tank to
the collector to prevent hot water from rising up to the cold
collector at night.

The Tom Lane book on Solar Water Heaters (which is written from the
very practical point of view of an installer/maintainer :-) shows the
same kind of diagrams for solar water heaters with PV powered pumps,
and he does not mention any problems.   If you are going to build your
own system, this might be a good book to own -- it contains a mountain
of practical info -- its available from his website.


Had no idea England was so far North!

Good Luck with your project -- Gary



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