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What to do when the power goes out?

charlie_16 Member Posts: 9
I have a solar hot water system for domestic and a bit of radiant floor heating.  The pump (Taco 011 I think) draws about 300watts when running.  So here and all over the area, the power has been unreliable of late, and it is always a struggle to run the pump during daylight hours...nice to have a hot shower after spending the day cutting up the downed trees in the yard.

We've tried a 400 watt inverter run off the car battery: it will do the job, but only for a couple hours without starting the car every hour or so.  PV powered DC pump is kinda pricy and would require cutting into the system and running wire for the PV...

Gas generator does fine, but noisy and kinda overkill for the energy needed...

Its a circulating glycol/water system, not drainback- I'm very reluctant to just let it stagnate (and not have hot water).

Just wondering what other solar hot water folks are doing during our frequent power outages?


  • SWEI
    SWEI Member Posts: 7,356
    DC pump

    Direct PV powered pumps are an elegant solution.  Sizing is critical if you want variable flow dependent on insolation.

    You can use a DC pump on batteries if your controller is also powered by DC -- preferably by the same voltage.  A 0011 moves a *lot* of water -- a thorough review of the system design would be in order before you start changing parts.
  • Kevin_in_Denver_2
    Kevin_in_Denver_2 Member Posts: 588
    New affordable DC pump

    This pump is rated to 30,000 hrs of service and only costs $58 including shipping.

    (Chinese of course) http://sun-pump.com/

    I've been testing it extensively, and I think it will produce about 3gpm for your system, which should be enough unless you have more than 5 panels or so.

    BONUS: Your power consumption will be reduced 3300%, since this thing draws only an amazing 9W.

    Another solution is just to let it "steam back". The only thing you need is a properly sized expansion tank. http://www.homedepot.com/webapp/wcs/stores/servlet/ProductDisplay?productId=100533020&storeId=10051&langId=-1&catalogId=10053&ci_sku=100533020&ci_kw=%7bkeyword%7d&kwd=%7bkeyword%7d&cm_mmc=shopping-_-googleads-_-pla-_-100533020&ci_gpa=pla#.UJ1bleQqaqk

    But that strategy has the downside that you don't collect any solar energy when there is a blackout. For more info, search this site for "steamback".
    Superinsulated Passive solar house, Buderus in floor backup heat by Mark Eatherton, 3KW grid-tied PV system, various solar thermal experiments
  • charlie_16
    charlie_16 Member Posts: 9
    Thanks and more info

    Thanks for your responses- inexpensive DC pump is intriguing.  (Laing and El Sid are way more$).  I've wondered about current pump- Sized it using Silicon Solar's guidelines; followed their guidelines for  85 tube Evac tube array.  (its split on two roofs, 2x30 on high roof, 1x25 on lower roof).  The high roof is 30 ft above storage/pump station, but this should not matter if it is a closed, circulating system, yes?  I checked the link you provided- couldn't find what power it would need.  1.2A @12V would be 14.4 watts?  So 10-20 Watt 12V PV should do?  Again, thanks for your thoughts.
  • Kevin_in_Denver_2
    Kevin_in_Denver_2 Member Posts: 588
    Sun-15 pulls 15W

    Yes, a 15-20W solar PV panel should do it. If you have 3/4" pipe that should be enough flow.

    BTW those are excellent tube collectors, and they work great with a low flowrate since their efficiency doesn't drop off much, but short cycling is reduced.
    Superinsulated Passive solar house, Buderus in floor backup heat by Mark Eatherton, 3KW grid-tied PV system, various solar thermal experiments
  • charlie_16
    charlie_16 Member Posts: 9
    more details

    OK- thanks for the confirmation.  Yes- 3/4in to the large array, 1/2inch to the smaller one. 

    Next question is controls.  Right now a Eagle 2 Diff controller...just leave that for monitoring but have the PV output determine the flow rate? 

    Can this pump be mounted in any orientation? Guess that is a question for its manufacturer, eh?)  Doesn't look like it has flanges... just adapt it to flange or cut them out I guess.
  • rt_2
    rt_2 Member Posts: 86
    Lost of electricity

    What I did was tie my solar circulating pump into the same circuit as my pellet stove. I have a battery backup system for my stove with a convertor with two deep cycle batteries. If I just ran my circulator, I believe it would run off both batteries for at least 6 hrs.

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