questions about solar powered circulator pump for solar hot water system

9 Posts
May 13, 2008 08:33 am
questions about solar powered circulator pump for solar hot water system

I’m planning a new solar evacuated tube hot water system and had a question about the circulator pump, which I’d like to run directly on solar PV.  I’m considering the Ivan El Sid DC hot water pump, 3.3 gpm solar direct and two 10 Watt 12 Volt Solar Panels instead of one 20 Watt panel.   With two panels I could orient them at slightly different angels, plus have some redundancy.  Will this configuration work?  Are the panels large enough?  Do I need a controller?  Should I use a battery instead of running the pump directly frpom PV?  Any other suggestions?  My location is Maryland.  Thanks for the help.
 
163 Posts
May 13, 2008 10:14 am
Re: questions about solar powered circulator pump for solar hot water system

Jerry,

I've been using an El Cid to circulate water here in the Cayman Islands for over a year and it works great. I pump using PV power only, and in my case I have found that it works best to use only the 10 watt panel that is matched to the pump. When the sun is shining bright and the water is hottest then the pump is operating at max throughput, and on cloudy days when the panel gets shaded and the water not so hot, the pump circulates the water much slower.

I haven't purchased any yet, but in your case I would recommend a couple of sensors and a temperature differential switch to prevent the water from circulating early in the morning before it has heated up, and again late in the evening after the sun has stopped heating the water but is still light enough for the PV to operate the pump.

John
 
9 Posts
May 13, 2008 11:31 am
Re: questions about solar powered circulator pump for solar hot water system

John,

Thank you for the response.  Excellent suggestions.   Using only one panel will save $$$ too.  The only reason I was thinking about two panels was because I'm concerned (probably overly) about the pump failing and the collectors overheating.  Are you using evaculated tubes for your solar hot water panels?  I'm looking at the Sunda http://www.sundasolar.com/
 
163 Posts
May 13, 2008 12:14 pm
Re: questions about solar powered circulator pump for solar hot water system

Jerry,

I use a single 3' x 7' AET flat panel. Evacuated tubes are more efficient (and expensive!), but when you live in the tropics there is not a great deal of need for hot water. Other than the washing machine and dishwasher we could easily get by without it.

I have a single pressure/temperature relief valve installed at one end of the AET solar collector. When I first installed my system I got some air in the lines and the El Cid pump was just spinning and not actually pumping the water. After a short while the temperature reached 210F and the valve opened up spraying hot water everywhere. Luckily nobody was near it. This also cleared the air out of the lines and it has not given a single problem since the day that I installed it.

You might want to run a piece of hose from the pressure/temperature relief valve into a gutter to avoid a similar problem.

The El Cid pump is very quiet and you almost have to put your ear next to it to hear it running, although it does have small led lights to indicate that it is on. If you can hear the pump (as I now know!) then it has air in it and you are probably looking at the situation described above.

My system just circulates water from the hot water storage tank through the collector so it is a very simple setup, whereas you will probably need some sort of heat exchanger and also have to take freezing temperatures into consideration.
 
9 Posts
May 13, 2008 04:01 pm
Re: questions about solar powered circulator pump for solar hot water system

Ah - the tropics - I've visited the Cayman's once on a cruise - very beautiful - I'm quite envious. Here in Maryland, I have to worry about freezing and less sunlight in winter. 

Your input has been most helpful.  Good tip about the hose on the pressure relief.  Thank you again.  Jerry
 
462 Posts
May 19, 2008 01:08 pm
Re: questions about solar powered circulator pump for solar hot water system

Jerry, make sure you take the height of the panels with respect to the tank into consideration if you plan on using an El Cid pump. I believe it is rated for a head of only 3 ft. (Great for a radiant heat zone at the same level as the tank.) Here in the NE area, pumps such as a Grundfos or Taco are used in closed loop systems...
 
9 Posts
May 20, 2008 04:07 am
Re: questions about solar powered circulator pump for solar hot water system

Tom, thanks for the feedback.  After further research on the subject, I'm seriously thinking about going with the Velux hot water system that has just recently been introduced into the US. I've read that these systems have been used in Europe for years. Aesthetically, they are perfect for the front of a house because they look just like skylights, and the SRCC rating is very good. Anyone have any experience with the Velux system? (I think I'll start another post)
 
1 Posts
Jul 4, 2008 02:06 pm
Re: questions about solar powered circulator pump for solar hot water system

Hi I,m new to this forum, I just wanted to intoduce you to a different type of system that doesn't require a pump, glycol, or a seconday tank within your house.  go to www.greenenergyinnovations.ca
 
9 Posts
Jul 5, 2008 08:09 am
Re: questions about solar powered circulator pump for solar hot water system

Barry, thanks for the link.  I've seen these types of systems but they aren't a good fit for the front roof of a house where I'm installing. As a matter of fact, I've given up on the evacuated tubes in favor of flat panels for aesthetics reasons only.  I’ve decided to go with a German-made Schuco system with 4 panels and a dual transfer tank – the extra transfer to heat my hot tub.  The Velux system that I was looking at didn't support dual transfers - the company didn't recommend but I never did find out why.
 
462 Posts
Jul 5, 2008 04:33 pm
Re: questions about solar powered circulator pump for solar hot water system

Jerry, before you make your expensive purchase from the company you mention, check out the pricing here at the Alternative Energy Store for your panels and controller. Then check at your local plumbing supply for a double heat exchanger tank and other related plumbing materials needed. I think you will find that you can purchase and install a complete system for the price of purchasing only half the components needed from the source you are considering. At least then all the components will be locally purchased and easily replaced, rather than trying to deal with an overseas company, just in case anything is missing or goes wrong. Of course, check with your installer to make sure he is okay with your purchases or just hire an experienced plumber to help you with your purchases and/or installation.
« Last Edit: Jul 5, 2008 04:37 pm by Tom Mayrand »
 

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