PV powered circulator pump for AET solar hot water system undersized PV panel

28 Posts
Jan 10, 2008 02:42 pm
PV powered circulator pump for AET solar hot water system undersized PV panel

Any folks have experience with the March pumps supplied with the AET hot water system kits? My system was supplied with a 12 volt 20 watt sunwise panel and a 12 volt March pump. The panel was substantially undersized for installation in northern NH and would only run the pump uncoupled for about an hour on a sunny day (in December). My short term solution was to install a spare 12 volt Siemens 48 watt panel. The system is running well now but the concern is "am I going to cook the pump" later in the year when there is more sun? Guy Marsden mentioned a similar problem in his Home Power articles about an install along the Maine coast and he doubled up on his panels.
 
578 Posts
Jan 10, 2008 02:55 pm
Re: PV powered circulator pump for AET solar hot water system undersized PV pane

probably wont cook the pump, but has potential to cool already heated watter off.  by increasing pv size, you increase the likelyhood that the pump runs before the collector is hot enough to heat the water that is already warm in the house in its tank.  trial and error it, 48w is not obscene, and will likely be fine.  with pv direct to pump, you have no control over high limit, so you may or may not want to switch back in summer based on your results.  make sure t & p valve in tank is good before summer when overheating may be more likely.

others in the community may have more experiece with this, especially mr. mayrand.  i'd bet we see some more answers soon.

james
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163 Posts
Jan 10, 2008 04:51 pm
Re: PV powered circulator pump for AET solar hot water system undersized PV pane

probably wont cook the pump, but has potential to cool already heated watter off.  by increasing pv size, you increase the likelyhood that the pump runs before the collector is hot enough to heat the water that is already warm in the house in its tank. 

I use an El Cid 5w pump in my system that I tested by putting it on a 12V car battery. The only thing that it did was pump a whole lot faster that what it does on the 5W solar panel. I suspect the March pump is the same and will not draw any more current than it can handle, provided the PV panel is still a nominal 12V.

Early startup should not be a problem if he has a temperature differential switch controlling the pump, which I suspect he would. My setup is very simple (no freeze to worry about) and it pumps as soon as the sun comes up and continues pumping until the sun goes down. I'm considering purchasing one of those temperature differential switches myself now that the temperatures have been dropping down to the low 70's at night. lol.
 
578 Posts
Jan 10, 2008 05:36 pm
Re: PV powered circulator pump for AET solar hot water system undersized PV pane

i dont think he has a dtt, because the pump is controlled solely by the pv module, no?

james
Alt-E staff

AltE
"Making Renewable Do-able"
http://www.altEstore.com/

Tel: 877.878.4060 x107  or +1.978.562.5858 x107
Fax: 877.242.6718  or +1.978.562.5854
 
163 Posts
Jan 10, 2008 09:08 pm
Re: PV powered circulator pump for AET solar hot water system undersized PV panel

I think the AET systems come with them standard.
 
28 Posts
Jan 11, 2008 07:05 am
Re: PV powered circulator pump for AET solar hot water system undersized PV panel

Thanks for the input, I have an ArTec PV powered differential switch on order to take care of the concern of early morning and late afternoon operation. The 48 watt panel is part of a 16 panel array that is getting installed this summer so it will be replaced with a smaller unit, possibly another 20 watt panel. I plan to cover over a portion of the panels in the summer when I dont need the heat.   
 
462 Posts
Jan 11, 2008 01:22 pm
Re: PV powered circulator pump for AET solar hot water system undersized PV panel

Since James figured I could help, I guess I will try. First you should have done a little homework before purchasing the PV powered pump with the system. I checked other sites for the cost of the March pump and they were pretty expensive compared to your regular Taco or Grunfos pumps. If you truly wanted to use PV to power the pump, you could have purchased a small battery and controller along with a small inverter and regular AC pump at pretty close to the cost of the March pump alone. Since you live in northern NH, a differential controller should be a must. It would have freeze circulation and other features to ensure your system would operate as efficient and safely as possible.
 You mentioned you are purchasing a diff. switch to run off the PV. You still may run into the same probem if the unit runs directly off the PV, where shading from clouds or whatnot could cause adverse effects on proper water circulation.
  I think the best thing for you to do is to incorporate a battery and charge controller into the system. Use the diff. switch to switch the load lines from the controller to the pump. Use the PV to charge the battery and then at least you will have enough power coming from the battery to operate the pump correctly and consistently as needed, instead of intermittent or fluctuating power from the PV alone.
 
28 Posts
Jan 11, 2008 05:55 pm
Re: PV powered circulator pump for AET solar hot water system undersized PV panel

I understand your concept, but elected to go with a direct driven DC pump as it has a lot fewer failure modes than an AC system. Over the years I have encountered several abandoned solar hot water systems and inevitably the controls are the second faulure mode (stuck check valves enabling cold weather reverse thermocycling was the number one issue). Usually I find a wire got broken to a sensor or the controler had a melt down and the system stopped functioning.

Replacing that with a glycol based closed loop system,a seal less pump, an indirect heat exchanger, redundant check valves and not having any controls to fail was a pretty attractive trade off to me. The trade off for adding a PV driven differential controller is that I will gain some system efficiency, at the risk of an added failure mode. The odds are good that if the PV controller fails in the off position and the glycol in the panels overheat, the relief blows so the system is "protected".

Of course the DC motor has brushes so that is a negative.

What the heck             
 
462 Posts
Jan 12, 2008 10:52 am
Re: PV powered circulator pump for AET solar hot water system undersized PV panel

  Yes some of the older system's components did fail. I've seen fried controller boards, sensor wires, pumps etc. The control you mention that failed in the past is basically what you are purchasing now, the differential controller. Todays controllers are a lot better. And I've seen stuck check valves from system neglect. Proper maintenance will prevent that. There weren't too many system installers and service people back then, up until now, to do it, if you couldn't do it yourself.   
  Your original question was about power to the pump. The main reason I mentioned including a battery, along with a PV charge controller, (something like the Moriningstar, "Sunsaver" series), is to ensure that the pump has enough power to circulate the fluid. Especially on start up, when the system continually surges from rapidly cooling panels. The pump is drawing maximum power each time. Not having sufficient power could promote early wear and tear. As I mentioned, just use the wire coming from the positive load, off the charge controller to the pump, as the source of power you are switching with the differential controller.   
   Hopefully everything works out okay for you, just be careful with an open loop, especially in Northern NH. You could still use glycol as the agent going up to the panels. (I assume you have an external heat exchanger with a reservoir/drainback tank). It would help on freeze protection and cleaning of the lines and panels.
 
2 Posts
Sep 27, 2010 10:34 am
Re: PV powered circulator pump for AET solar hot water system undersized PV panel

You should always size your PV panel so that you have at least double the watts of the pump in northern latitudes.  EG. 20W panel with 10W pump. 

But then you also should install a PV powered differential controller to guarantee that the pump never runs when the collectors are cooler than the tank.  Also to limit the max temperature in your tank.

You can get a PV differential controller direct from ArtTecSolar.com
 

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