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Sustainable Alternatives: solar water pump

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cathy4
St. Louis County, MO
(Zone 5a)

March 6, 2009
3:01 AM

Post #6227439

Hi everyone,

Has anyone used one of the small solar water pumps that are sold for yard fountains? I'm mulling over a hot water heating set up for my small greenhouse, and think a small pump might be the key ingredient to move the cooled water from the water buckets back into the solar heater. I don't want to move the water after dark, so that part wouldn't be a problem. Thanks!
dparsons01
Albuquerque, NM
(Zone 7b)

March 11, 2009
4:49 PM

Post #6251827

I'm not specifically familiar with them, but would be concerned about a couple items.

1) If your solar panels are higher than the fountain height the pump can handle, then you will definitely need a pump that can deliver more pressure. The solar panels should also have some type of head loss (pressure drop) specification and a throughput spec as well. For the vertical part, you gain a little under 1/2 psi per foot but can round up to account for friction losses in the pipes. If the top of your solar heaters is at 8 feet you need 4 psi to push the water that high. Add in the panel pressure loss and you get a minimum number for a pressure requirement for the pump. Pick a pump that delivers the throughput and is capable of 1.5 to 2 times your pressure need (means pump won't be overloaded).

2) The overall quality and durability of the product. The resource saving is nil if it wears out in a year or two. Sometimes end-user products market to the general public are pretty cheap.

I like the solar aspect. I'm getting a solar fan for my greenhouse. No need to run wires.
cathy4
St. Louis County, MO
(Zone 5a)

March 11, 2009
6:12 PM

Post #6252177

dp, I've been looking at the fans, too. I've found really big one$ or tiny ones, there seems to be nothing in the middle. I'm hoping to only use electric in the very dead of winter. The solar lighting is great, I got the older fashion wired ones and they light all night, even on cloudy days.

The solar pump would be to move water from my water storage to an add-on solar water heater to get the water in the greenhouse hotter than it would get just from whatever sunlight hits it. I have a small electric pump but I don't want to run electric to the GH if I can avoid it. So the lift would be only about 18 - 24 inches, then gravity would take it through the heater and back into the storage tank.

Even if I have to run electric, the pump is very cheap to run vs. a heater.

Thanks for the input, Cathy4

darius

darius
So.App.Mtns.
United States
(Zone 5b)

March 29, 2009
3:35 PM

Post #6335366

A good old fashioned convective loop should do the job... and no moving parts.
cathy4
St. Louis County, MO
(Zone 5a)

March 29, 2009
7:34 PM

Post #6336369

darius, do you have information on how to set one up or a place I can learn about it? I'm bound and determined to make this as power-grid free as possible. Thanks (maybe do an article?)

darius

darius
So.App.Mtns.
United States
(Zone 5b)

March 29, 2009
8:10 PM

Post #6336551

Setting one up is easy... just hook everything together with tubing, garden hose, whatever... NO valves although a shut-off valve is convenient to have.

As long as the cold water container is above the solar collector, the warmer water will rise into the cold container as the colder water drops into the collector. As long as there is a temperature differential, the water will keep looping. How fast it moves will depend on the size of the tubing/pipe/hose. Obviously a tiny tubing won't let much water pass through very quickly.

There are books and internet articles that explain convective loops. Try 'breadbox' solarwater heaters, although most 'batch' solar water heaters have a more complex storage tank in the loop for household water. Also google 'thermosiphon'... here are a couple...
http://en.wikipedia.org/wiki/Thermosiphon
http://www.a-spi.org/tp/TP9.htm
cathy4
St. Louis County, MO
(Zone 5a)

March 29, 2009
9:32 PM

Post #6336897

thanks darius, i'll learn all i can by fall, i have a source for free heavy garden hose sections. I can get all the free 5 gallon buckets i could want, hopefully i can figure out how to work it all together. it seems pretty basic, thankfully.

darius

darius
So.App.Mtns.
United States
(Zone 5b)

March 29, 2009
9:39 PM

Post #6336922

Well if you get stuck, just shoot a dmail my way. I have LOTS of solar DIY books from the 1970's (most are out-of-print); I'm just short of time right now.
dparsons01
Albuquerque, NM
(Zone 7b)

March 30, 2009
3:59 AM

Post #6338578

Nice idea.

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