Solar Water Heater Set Up

[sailawayrb]

sailawayrb:

 About using a 120 volt pump:

 I have SIX of them sitting for use, its is just that I don't want another 120 volt load if there is a way around it.

 I was chagrined to discover, after I did lots of research, that the Xantrex solar controller would not control the six set of panels to NYSEG's satisfaction - I have, finally, with mike90045's guidance, settled upon a MidNite Solar Classic that WILL let me use the full set of six panels that I can deploy, and make NYSE happy.  Another reason not to jump off of the high board until your sure how deep the water is LowGear!!!  I was a day or two from having the Xantrex irretreivable on order and shipped before I solved the most recent problem.

 About the 120Volt panels: Lets suppose that the duty cycle is 50% (though I can't see how the panel will not overheat if it isn't given continuous flow of coolant in the sun - but that's another argument!  <grin>).  And, lets suppose eight hours of sunshine in the winter. So that will be four hours of 1/12 HP (what my pumps are) or 746+losses=900 watts(?)* 1/12 = 75 watts.  75 watts x 4 hour = 300 watt hrs/day.  The DC pump that I sited would use about 1/3 of that electricity and would do it without tying up ANY of the available 7200 watts of inverter power available from the XW6048.  I have this nagging feeling that if i just keep adding things on to the inverter, electric pancil sharpener's, electric floor buffers, electric toothbrushes, electric knife sharpener, etc., etc. without giving any concern to whether or not I have the power available for it, I will soon have 15,000 watts of load trying to drive off of a 7200 watt inverter.  Direct DC driving of the circulator pump is one small way of keeping one small load out of the inverter system.

 If there is no other way to do it, of course I will use the inverted 120 V AC, I MUST have some sort of circulator pump and if I can't do it via a reasonable DC load, it will have to be AC, even if it's three times what the DC load would be.  Since I have the 1/12 HP circulator pumps sitting there, it is an easy, if inelegant,  "fix".

Wayne Stayton

I understand your issue given where you now find yourself.  However, the power required to accomplish a given mission is the same whether one uses DC or AC.  It sounds like you built your power system without first considering how much power you would need to accomplish your mission.  I can understand that some people are prone to mission scope creep...  Normally one would figure out exactly how many KW-H per day one expects to need and then perhaps multiply that by 1.5 (or perhaps even by 2 if you are especially prone to scope creep...) and then design and build the power system to meet that power requirement.

Bob B.

[bschwartz]

    "However, the power required to accomplish a given mission is the same whether one uses DC or AC"

True, but with DC he doesn't incur the conversion losses that he would with DC to AC.

May not be much, but every little bit adds up.

[WStayton]

Hi All!

  A quick post before I go buy my bathtub!!!

bschwartz said:  "May not be much, but every little bit adds up."

  Therein lies the problem!!!

  I started out with the constraint of my roof, which has ONE south facing slope that is about 15' x 36'.  On this surface I have to fit solar electric panels, solar heat panel(s) and any ancilliary solar panels to drive the solar heat panels.

  I could just populate the WHOLE surface with solar electric panels and use a the instant-hot gas water heater, which is present and planned for backup, as THE hot water source, but since solar costs less than gas (I'm CHEAP, remember! <grin>) AND is fun to play with, I decided to build my own solar heat panels.

  The other problem with populating the whole surface with solar electric panels, and I THINK that I could squeeze in something like three "ranks" of 12 panels each, if I put nothing else on the surface and let the panels hang off of the peak and the eaves a few inches, but 36 panels exceeds the ability of my finances to BUY them!!!  So, I settled on two "ranks" of nine panels per "rank" as being something that was affordable, if you can call $5,000 affordable, and leave me enough room to 1) move around on the roof without stepping on/in some part of the installation every time I moved and 2) fit in the solar heat panel(s) for domestic water and some heat.
 
  Back to bschwartz's statement:  If I just keep adding one loads, even if they are only 25 or 50 watts at the time, eventually I will exceed the capabilities of my limited solar electric installation.  I figure that the ONLY way to solve this problem is to really get "religion" about adding loads to the panels if there is ANY other way around it - hence my try at something that is on the fringes of what is available and, maybe, cutting edge.  In general I try not to use something that is the latest and greatest because it has been my experience that the "bugs" only get worked out after something is in use for ten or twenty years and lots of users have added their experience to the manufacturer's limited testing before placing the item on the market - but i thought that the pump in question, here, was worth at least looking at, since it was a more-or-less novel design, and had the benefit of using half of the electricity of any other pump I could find.  The TWO complaints of diminishing performance have made me shy of the pump, but absent any "hard" data of degradation of performance over time, I MAY take a flier - I can always sue the manufacturer if if doesn't work out!  <grin>  (That IS a joke, BTW!)

  I feel strongly that ANYBODY who builds a solar set up, that doesn't have unlimited funds/deployment-area/etc., and isn't vigilant about keeping loads down is going to, ultmately have problems - a system that will only service half of the load is not really very effective, since you have to have the very 120 volt mains line that you are trying to eliminate, to pick up the slack!!

  Yea, I have to have the line so that i can get the governments contribution to my folly, but I have written that off as the price I have to pay - I am really shooting for a stand-alone system that is tied to the net only to make the Government happy and to sell them some solar electricity in the summer, when I SHOULD have excess!

  Okay, I'll get down off of my soapbox now and go buy my bathtub - on sale for $59.00, BTW! Good things come to thoise who wait - SOMETIMES!!!   <grin>

  Thanx for the input - as always!

Regardz,

Wayne Stayton
 

[cujet]

Wayne,

I understand and relate to your line of reasoning. Optimization of a system is always a worthwhile goal.

In my line of work (aircraft), out chief pilot loads up our planes with equipment. Then we suffer the consequences when performance matters. Our EC-135 helicopter is 400 pounds heavier due to "options" and therefore limited in capacity by the same amount.

My reasons for suggesting the Grundfos circulation pump are the reliablity/cost ratio is excellent and it's simply plug n play. Placed on a timer, it's consumption could be managed.

But, you are 100% correct. A dedicated 20-30 watt panel, with DC pump is a simple and viable option. There are plenty of more expensive options here! That's half the fun of designing such a system. Making it "Optimal".

[miket]

have you looked the El Sid pumps, they are very efficient?

http://www.altestore.com/store/Solar-Water-Heaters/Circulating-Pumps/El-Sid-Brushless-DC-Pump-for-10W-Module/p485/

[WStayton]

Hi All:

  Seeking to get a comment from somebody who might know and didn't have a dog in this fight, I sent an email to Solar Gary, who has a VERY comprehensive do-it-yourself sight.

  His comment was that he had no direct knowledge of the product, but that he judged that it was the cadillac of the available direct-solar-panel options.  He was also very circumspect of the "low-degraded-performance" reports that I found which had NO objective measure except to say that they THOUGHT that the performance degraded over a few months.

  He seemed to think that the pump in question is one of the better, if not the best, option around.

  That's his opinion, FWIW.

  On that basis, I have ordered one - I'll let you know in three months, or so, if it was a good decision, or not!  <grin>

  I DO appreciate everybody opinion!

Regardz,

Wayne Stayton

[cujet]

Wayne,

Who is "Solar Gary" and can you provide a link? I googled but did not find.

[Carlb]

here is a link to his site.  He has many projects from others as well on his site.  Great reading and Gary is a good guy.

http://www.builditsolar.com/

[Rom]

http://shop.solardirect.com/product_info.php?products_id=880

This is the unit I have been using for about 2 years now. It lives in my Lister shed and the panel is just laying on the roof with a big vacuum tube collector. Works a treat!

Look around though, I am sure I didnt pay that much for it.

Rom

[Rom]

Ah, I see the difference, mine does not have the ball valve, purge valve etc. That must explain the price.

Rom