Pump and Panel for Solar DHW system

3 Posts
Nov 16, 2011 10:47 am
Pump and Panel for Solar DHW system

I am in the processing of engineering a DIY solar DHW system as described on the site www.builditsolar.com.  This will be a drainback system, with a storage tank in the basement, with panels (collectors) on the roof.   
I would like the circulation pump to be driven by a PV solar panel.  The challenge I've encountered is finding an appropriate pump that can develop the initial 25 ft of head at startup.  The operating head, once the circulation is going, is on the order of 3.5 psi, with a desired flow rate of 2.9 gpm.
I am wondering if a system consisting of 2 Laing D5 strong pumps installed in series, powered by something like the SUNTECH STP180S-24/ADB+ 180W 24V SOLAR PANEL.
Any feedback on this, or any other aspect of my proposed system, would be most appreciated.
462 Posts
Nov 16, 2011 05:46 pm
Re: Pump and Panel for Solar DHW system

Gregory, I usually recommend using a battery, small inverter and controller in conjunction with a PV panel to power a pump. That way there enough power is always available rather than intermittant power from direct sunlight alone...eg. a few clouds go by and the pump stops even though the panels are hot. Then you can use a converntional off the shelf pump suitable to overcome the head needed. TACO and Grundfos both make high head models.  It also gives you a small backup system for other uses when power goes out.
1 Posts
Nov 19, 2011 01:13 am
Re: Pump and Panel for Solar DHW system

Recommend any good quality and long lasting battery in order to power a pump. Looking forward for reply.

3 Posts
Nov 19, 2011 11:54 am
Re: Pump and Panel for Solar DHW system

Thanks very much for the reply.    I have done some research into this, and can believe it is the better solution, but it certainly seems s to be somewhat more expensive.   

I just came across the Taco 009 VT pump however, which is apparently new and looks like it could be part of a solution.

 Could I use for example this panel
 Suntech STP180S-24/Adb+ 180W 24V 

with this MPPT controller

this battery
12V 73.6AH

and this inverter

as components of a balanced system?

462 Posts
Nov 19, 2011 06:17 pm
Re: Pump and Panel for Solar DHW system

Gregory, you don't have to get that big of a panel or controller. You only need to maintain the battery based upon  your pumps power draw.  Just figure the amount of watts needed per day, amps x voltage and how long the pump will run, maybe 2-6 hrs at best, based on the rating of the pump you choose, and then buy a panel that will replace this power based upon the amount of sun you get each day.
 check out the Morningstar sunsaver series controllers here at alte...they're cheap., 30-50 bucks..Only need one that will handle the PV panel amperage output.....
    ..choose a 12 volt panel, not a 24 volt as you suggest,  20 -whatever watts, (20 Watts..around 1.5 amps...60 watts...5 amps)
   small inverter available here or your local auto store, 100 bucks or less (GoPower as you have suggested) and deep cycle battery (like you also suggest) and you should be all set.
  You can also charge the battery with a regular battery charger should the sun hours not be sufficient.
  Or skip the whole setup all together and just use you regular house power for the pump, the amount of power draw is really minimal if paying for electricity is not that big of a concern. 
3 Posts
Nov 19, 2011 06:57 pm
Re: Pump and Panel for Solar DHW system

I wondered if I was oversizing things.   The  pump specs show a draw of 1.4 amps at 115v = 160 watts, so that was the basis for selecting that size panel.  I assume that the pump should be running nearly all the time that the sun is shining and that therefore there will be pretty much a steady-state situation between the pump and panel, except for momentary cloud cover as you mentioned in your original post.    The battery would seem to be acting as a very short term (a few minutes generally) buffer, not providing significant storage for any length of time.

That panel I selected seemed to be the cheapest at that output, and I figured that the MPPT charge controller could manage the 24-12 v business.

Re the whole solar thing- certainly power cost is not the motivation since its pretty minimal as you say.  Rather its the doomer side of me that would like have this operate without needing grid power.  In case of no power, I can run a generator just enough to get water from the pump to charge my fairly large pressure tank, and then I'd have hot water, sans electricity.

Thanks for  your continued dialog.  I've been doing some research, but there's nothing like talking this stuff through with someone.

462 Posts
Nov 20, 2011 12:52 pm
Re: Pump and Panel for Solar DHW system

Your welcome Gregory, just remember the pump will not run continously, especially if you use a differential controller, which you should. Other wise, if you just use a pv panel to run the pump, you may be losing heat. A differential controller ensures that the pump only runs when the panels are hotter than the water in the tank. With just a pv running the pump it will circulate whenever there is enough power from the pv panel irregardless of temperature differences, drawing heat from the tank and losing it through the panels. Just think of a sunny winter morning, the hot water panels may be cold but the pump turns on based on the sun hitting the pv panel.

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