Thermal - PV and diff controller? [RE-wrenches]

[Tom DeBates]

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good day Geoff,
 ...sorry about the delay in replying.
  This Winter I installed a PV-powered solar thermal system for my 
residence.  I have a 32 watt Unisolar powering 4 ElSid pumps. Currently 
there are only 3 pumps installed as I have not completed the small 
radiant heating loop. There is a 10 watt pump on the collector loop, a 5 
watt on the storage tank loop, and a 5 watt on the heating loop (HX 
side). The other 5 watt pump will be on the heating side of the HX.
  Although I need to do more insulating and fine-tuning, so far I am 
satisfied with the performance of the system. Initially I felt that I 
was "missing" some late afternoon gain as the collectors had more 
"thermal inertia" than the PV could extract during that period. I 
considered adding a small module facing west, but have decided that the 
storage tank and collectors are almost at equilibrium at that point 
anyway and I am not losing much gain.
  ElSid does make a differential controller. It is a small board that 
attaches to the side of the pump. It is set for ~ 8 to 10 degrees 
(non-adjustable) and seems to work well....nice and simple. I inquired 
as to a set-point controller and Dan (ElSid) said that he could do this.
  I can send a schematic and pics if you want.
good luck,
Tom
  

geoff at third-sun.com wrote:
> 
> I like the PV direct approach for typical residential solar thermal... 
> nice
> 20 watt panel and an el-sid and away we go.  Flow rate increases with
> sunlight (and collector temp in theory?). Usually an 80 gallon with 
> built in
> HE.
> 
> My question - how may of you add a differential controller to the 
> system?  I
> didn't have a good answer for a savvy customer who asked the somewhat
> obvious question... "What keeps us from dumping heat on a sunny but 
> super
> cold day?"
> 
> For a brighter energy future,
> 
> Geoff Greenfield
> NABCEP Certified Energy Practitioner
> 
> THIRD SUN SOLAR & WIND POWER Ltd.
> 340 West State Street
> Athens, OH 45701
> 
> www.third-sun.com
> (740) 597-3111
> 
> 


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