PV powered pond aerator - Page 2

jeff5may · 08-08-14, 07:33 PM

The only problem I imagine you will need to deal with is during sunrise / sunset / low lighting conditions. You will need something to limit your source voltage when there is not enough solar power available to start the motor or keep it from stalling. If the motor is not turning while the panels are pushing energy into it, the solar power will not be converted into mechanical energy. The solar energy will cook the stalled motor eventually (slowly if panel is small, much faster if big and strong).

IMHO, you have 2 options here:

1. Go big on your panels and add a battery, run 24/7/365. Your 35 watt motor will need 300 watts worth of panels and a trolling motor battery. Fish will be happy and full of life.

2. Run a timer with low voltage/over-current cutout device. Much experimenting may yield an acceptable device. The less panel power, the less time the motor can run.

Also, remember that a diffuser-based aerating head is a whole lot more efficient than an airstone or porous-block based head, due to its low pressure drop. Although more expensive up front, they push a lot more air through the water per watt. If you run a draft tube (sort of like a submarine smokestack), you can mount the diffuser just 2 feet underwater, and pump gobs of air at low PSI. The stack tube literally sucks stale water from below the thermocline of your lake or pond, mixing and aerating everything above the bottom of the tube!

This may sound like a gimmick or a plug, but it's honestly not. The cold water is somewhat aerated on its way up the tube, then contacts the surface, picking up more air and dragging warmer aerated water back down with it. This convection loop does way more to the pond than I care to describe. I have seen ponds saved this time of year using this method. I helped a buddy save his fish using a section of dryer hose and a raft inflator connected to a short length of soaker hose. Literally within seconds of commissioning the rig, his fish stopped gobbling air off the surface.

stevehull · 08-08-14, 07:53 PM

Jeff,

I misspoke wen I used the word "airstone". I actually use a number 60 drill and make a zillion holes in the last several inches of the 1/2 inch PVC tubing. The tubing is held down on the pond bottom 15 feet (~ 5 meters) by a concrete block and the far end comes out to the air pump.

The mechanical action of the rising air bubbles does several things. First it mixes deep cold water with the warm top layer and diffuses the thermocline. It also adds oxygen and increases the partial pressure of oxygen (pO2) in the water at all depths.

The convective action breaks up the algae mats, fish thrive and my dogs can swim and not come back into the house smelling like rotting algae.

Interestingly, you can buy pond aerators that have a solar cell (looks like 20 watt?) and an air pump in one box. They say it turns on in the daytime when the sun shines and off at night. Wonder how these avoid cooking the motor . . . .

But they also want several hundred dollars . . . .

I like the snorkel idea as the rising column is constrained in a small diameter and I bet it pulls a LOT of water up from the depths. Neat idea.

I may just have to get another deep cycle marine type battery . . . .

Steve

philb · 08-08-14, 09:35 PM

A cheap inverter will cut off the power if it's too low and will regulate the power to a lower voltage when it's too high. I'd look for the regulation info in the inverter's instructions to be sure. I've bought several at tool outlet locations in OKC. I like to buy inverters that are about double the watts I need because the motors starting requirements can be quite high.

philb · 08-08-14, 09:46 PM

I've had that same dissolved oxygen problem before. I tried air pumps and they wore out in less than one year.
My solution was to use a small submersible pump with a foot valve and a fountain head in the center of the pond. The fountain head was a 3/4" X 2 ft piece of pvc pipe with a thousand small holes drilled into the pipe at an upward angle. It was easy to tell if the pump was on even at several hundred yards.

stevehull · 08-09-14, 06:42 AM

Phil,

Good suggestion on small submersible pumps. Same issue as I want to use a PV panel to provide power. Any specific suggestions on specific devices on e-Bay?

Steve

jeff5may · 08-09-14, 03:03 PM

The floating fountain is good for a small pond, but you don't get the convective flow throughout the strata of a deeper body of water that you need to keep it aerated and cool. Before the airlift column was implemented in my dad's pond, he used airstones at the bottom of it, running 24/7 in summer off a 1 hp dual diaphragm pump. At 15 ft. depth, the thing had like 25 psi of back pressure. It couldn't keep up in the summer, so he used a gas-powered trash pump spewing water, fountain style, on the bridge. This is a 1 1/2 acre pond. He lost fish every year.

After we experimented around with the airlift pump rig, and found how much more air it actually dissolved into the water, as well as dropping the thermocline like 5 feet, he abandoned the stones in the muck approach. I believe the rig is running at around 5 or 6 psi now. He uses two 10 foot columns made out of old black plastic drain tile, I believe they are 5 inch diameter. He got a couple of 12 inch rubber diffusers, which refuse to clog up. The things move so much water that we had to put leaf screens at the bottom. His pump runs on half the power than before. The only time he lost fish is when the lawnmower man ran over the power cord and no one noticed until the next day.

stevehull · 08-09-14, 04:35 PM

Jeff,

The air pressure is about right as 33 foot water depth is 1 atmosphere or 14.7 lb (760 mmHg). Then add in the resistance with the air stone and you are spot on.

But with the "stack" device, you don't need the bubbler at the bottom, just the end of the pipe need to be down there. My pond is about 15-18 feet deep, but with the stack, I can put the bubbler at only 5-8 feet down - lots less power as you observed.

My problem is this pond is ~ 1000 feet from any ac power source; thus the need to do this with a PV panel.

e-Bay has a lot of small capacity 12 V air pumps; some with brushless motors and with 30,000 hour life.

Steve

jeff5may · 08-09-14, 06:58 PM

Yep, you got the main idea with the airlift stack. The pond bottom absorbs the surface heat faster than the sun can supply it with just a little convective flow.

The other big point is that there is no need to go more than a foot or two down the tube with your bubbler head. Since there is no head pressure for the water flow to overcome, placing the bubbler lower just builds up back pressure at the air pump. The water flow rate is more a function of the stack diameter, length, and texture than anything else. Every foot below the surface adds 1/2 psi of pressure to overcome for hardly any more water flow through the column. Since you are using basically a gas burner for your bubbler head, it has nearly no restrictive effect.

At this extra low back pressure, the diameter and length of your supply hose has a larger effect on the airflow rate. As you go deeper in the water with your bubbler head, the pump power increases exponentially to achieve the same airflow rate, and the price of the air pump and solar array skyrockets quickly. A HVLP pump that maxes out at, say, 12 psi is much cheaper and draws less power than one that will push 50 psi.

I found a page that describes these systems better than I can. It reads like a sales ad (because it is), but this setup has a high potential for mega-efficiency if configured correctly. They don't bloat their figures or lie about how these things work. What seems like swagger and boasting on the page actually carries weight.

solar aerator

A brushless DC motor would definitely be worth looking into in this situation. It could solve most of the problems associated with the direct-drive, brushed DC motor. Soft start would be a dream come true in this application.

philb · 08-10-14, 11:23 PM

Quote:

Originally Posted by stevehull

Phil,

Good suggestion on small submersible pumps. Same issue as I want to use a PV panel to provide power. Any specific suggestions on specific devices on e-Bay?

Sorry Steve, I don't have any specific suggestions on an inverter. The one I bought a year ago was from Harbor Freight. They have a new one coming out about every 3 months it seems. So the info I have with mine probably won't be the same as what's available now.

From my experience with solar panels, I would suggest purchasing double the PV wattage you will need to power your pump. Today my 7100 watts of solar was putting out almost 5000 watts at solar noon. That's unusually high for this time of the year. There was a 10 mph wind out of the east. Normal is 3600 Watts. Hot panels don't produce as much electricity as cool or cold ones do.

Submersible water well pumps with LARGE intake screens will also work well provided you keep the screen clean. Otherwise they will overheat and melt.

Little Giant makes great submersible pumps. The liquid filled ones worked best for me. If the inlet gets clogged, the pump won't burn out from lack of cooling water. The last one had a 5 year 24/7 run before I replaced the impeller. They aren't much bigger than a softball.

I hooked the pump to a jet pump bottom assembly and foot valve. It all floated on a piece of EPS (styrofoam). It was tethered to an overhead steel cable along with a game feeder to feed 500 catfish. I didn't like having a line going from bank to bank at water level because it could cause problems with cattle.

There are new variable speed water pumps on the market and on Ebay that operate directly off PV panel voltage. They are made for domestic hot water panels and are very pricey. I saw them on Ebay.

If you do go with the air type pumps, you might Google "Ebay aquarium pumps". One of the first selections are "EcoPlus Commercial Air 5 - 80 Watts Single Outlet". They have a free floating piston assembly driven by stator coils that compress the air. Pretty neat. I aerate waste water with them, so a fountain is definitely out! They have outlasted the traditional piston and rod pumps and they are very quiet. Ebay has several vendors of this type of pump.

Gary has useful info on builditsolar.com Solar water pumping

08-08-14, 07:33 PM	#11
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,428 Thanks: 431 Thanked 619 Times in 517 Posts	The only problem I imagine you will need to deal with is during sunrise / sunset / low lighting conditions. You will need something to limit your source voltage when there is not enough solar power available to start the motor or keep it from stalling. If the motor is not turning while the panels are pushing energy into it, the solar power will not be converted into mechanical energy. The solar energy will cook the stalled motor eventually (slowly if panel is small, much faster if big and strong). IMHO, you have 2 options here: 1. Go big on your panels and add a battery, run 24/7/365. Your 35 watt motor will need 300 watts worth of panels and a trolling motor battery. Fish will be happy and full of life. 2. Run a timer with low voltage/over-current cutout device. Much experimenting may yield an acceptable device. The less panel power, the less time the motor can run. Also, remember that a diffuser-based aerating head is a whole lot more efficient than an airstone or porous-block based head, due to its low pressure drop. Although more expensive up front, they push a lot more air through the water per watt. If you run a draft tube (sort of like a submarine smokestack), you can mount the diffuser just 2 feet underwater, and pump gobs of air at low PSI. The stack tube literally sucks stale water from below the thermocline of your lake or pond, mixing and aerating everything above the bottom of the tube! This may sound like a gimmick or a plug, but it's honestly not. The cold water is somewhat aerated on its way up the tube, then contacts the surface, picking up more air and dragging warmer aerated water back down with it. This convection loop does way more to the pond than I care to describe. I have seen ponds saved this time of year using this method. I helped a buddy save his fish using a section of dryer hose and a raft inflator connected to a short length of soaker hose. Literally within seconds of commissioning the rig, his fish stopped gobbling air off the surface. Last edited by jeff5may; 08-08-14 at 07:41 PM..

08-08-14, 07:53 PM	#12
stevehull Steve Hull Join Date: Dec 2012 Location: hilly, tree covered Arcadia, OK USA Posts: 826 Thanks: 241 Thanked 165 Times in 123 Posts	Jeff, I misspoke wen I used the word "airstone". I actually use a number 60 drill and make a zillion holes in the last several inches of the 1/2 inch PVC tubing. The tubing is held down on the pond bottom 15 feet (~ 5 meters) by a concrete block and the far end comes out to the air pump. The mechanical action of the rising air bubbles does several things. First it mixes deep cold water with the warm top layer and diffuses the thermocline. It also adds oxygen and increases the partial pressure of oxygen (pO2) in the water at all depths. The convective action breaks up the algae mats, fish thrive and my dogs can swim and not come back into the house smelling like rotting algae. Interestingly, you can buy pond aerators that have a solar cell (looks like 20 watt?) and an air pump in one box. They say it turns on in the daytime when the sun shines and off at night. Wonder how these avoid cooking the motor . . . . But they also want several hundred dollars . . . . I like the snorkel idea as the rising column is constrained in a small diameter and I bet it pulls a LOT of water up from the depths. Neat idea. I may just have to get another deep cycle marine type battery . . . . Steve __________________ consulting on geothermal heating/cooling & rational energy use since 1990

08-09-14, 06:42 AM	#15
stevehull Steve Hull Join Date: Dec 2012 Location: hilly, tree covered Arcadia, OK USA Posts: 826 Thanks: 241 Thanked 165 Times in 123 Posts	Phil, Good suggestion on small submersible pumps. Same issue as I want to use a PV panel to provide power. Any specific suggestions on specific devices on e-Bay? Steve __________________ consulting on geothermal heating/cooling & rational energy use since 1990

08-09-14, 04:35 PM	#17
stevehull Steve Hull Join Date: Dec 2012 Location: hilly, tree covered Arcadia, OK USA Posts: 826 Thanks: 241 Thanked 165 Times in 123 Posts	Jeff, The air pressure is about right as 33 foot water depth is 1 atmosphere or 14.7 lb (760 mmHg). Then add in the resistance with the air stone and you are spot on. But with the "stack" device, you don't need the bubbler at the bottom, just the end of the pipe need to be down there. My pond is about 15-18 feet deep, but with the stack, I can put the bubbler at only 5-8 feet down - lots less power as you observed. My problem is this pond is ~ 1000 feet from any ac power source; thus the need to do this with a PV panel. e-Bay has a lot of small capacity 12 V air pumps; some with brushless motors and with 30,000 hour life. Steve __________________ consulting on geothermal heating/cooling & rational energy use since 1990 Last edited by stevehull; 08-09-14 at 05:13 PM..

08-09-14, 06:58 PM	#18
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,428 Thanks: 431 Thanked 619 Times in 517 Posts	Yep, you got the main idea with the airlift stack. The pond bottom absorbs the surface heat faster than the sun can supply it with just a little convective flow. The other big point is that there is no need to go more than a foot or two down the tube with your bubbler head. Since there is no head pressure for the water flow to overcome, placing the bubbler lower just builds up back pressure at the air pump. The water flow rate is more a function of the stack diameter, length, and texture than anything else. Every foot below the surface adds 1/2 psi of pressure to overcome for hardly any more water flow through the column. Since you are using basically a gas burner for your bubbler head, it has nearly no restrictive effect. At this extra low back pressure, the diameter and length of your supply hose has a larger effect on the airflow rate. As you go deeper in the water with your bubbler head, the pump power increases exponentially to achieve the same airflow rate, and the price of the air pump and solar array skyrockets quickly. A HVLP pump that maxes out at, say, 12 psi is much cheaper and draws less power than one that will push 50 psi. I found a page that describes these systems better than I can. It reads like a sales ad (because it is), but this setup has a high potential for mega-efficiency if configured correctly. They don't bloat their figures or lie about how these things work. What seems like swagger and boasting on the page actually carries weight. solar aerator A brushless DC motor would definitely be worth looking into in this situation. It could solve most of the problems associated with the direct-drive, brushed DC motor. Soft start would be a dream come true in this application. Last edited by jeff5may; 08-09-14 at 07:04 PM..

08-08-14, 09:35 PM	#13
philb Apprentice EcoRenovator Join Date: Nov 2010 Location: Oklahoma City Posts: 155 Thanks: 58 Thanked 17 Times in 14 Posts	A cheap inverter will cut off the power if it's too low and will regulate the power to a lower voltage when it's too high. I'd look for the regulation info in the inverter's instructions to be sure. I've bought several at tool outlet locations in OKC. I like to buy inverters that are about double the watts I need because the motors starting requirements can be quite high.

08-08-14, 09:46 PM	#14
philb Apprentice EcoRenovator Join Date: Nov 2010 Location: Oklahoma City Posts: 155 Thanks: 58 Thanked 17 Times in 14 Posts	I've had that same dissolved oxygen problem before. I tried air pumps and they wore out in less than one year. My solution was to use a small submersible pump with a foot valve and a fountain head in the center of the pond. The fountain head was a 3/4" X 2 ft piece of pvc pipe with a thousand small holes drilled into the pipe at an upward angle. It was easy to tell if the pump was on even at several hundred yards.

08-09-14, 03:03 PM	#16
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,428 Thanks: 431 Thanked 619 Times in 517 Posts	The floating fountain is good for a small pond, but you don't get the convective flow throughout the strata of a deeper body of water that you need to keep it aerated and cool. Before the airlift column was implemented in my dad's pond, he used airstones at the bottom of it, running 24/7 in summer off a 1 hp dual diaphragm pump. At 15 ft. depth, the thing had like 25 psi of back pressure. It couldn't keep up in the summer, so he used a gas-powered trash pump spewing water, fountain style, on the bridge. This is a 1 1/2 acre pond. He lost fish every year. After we experimented around with the airlift pump rig, and found how much more air it actually dissolved into the water, as well as dropping the thermocline like 5 feet, he abandoned the stones in the muck approach. I believe the rig is running at around 5 or 6 psi now. He uses two 10 foot columns made out of old black plastic drain tile, I believe they are 5 inch diameter. He got a couple of 12 inch rubber diffusers, which refuse to clog up. The things move so much water that we had to put leaf screens at the bottom. His pump runs on half the power than before. The only time he lost fish is when the lawnmower man ran over the power cord and no one noticed until the next day.