Water pumping and Peltier units

Telco
Telco Solar Expert Posts: 201 ✭✭✭✭✭
in Solar Water Pumping #1
Hey folks, long time no speak, but there's only so many hours in a day. Quick question, is it possible for a Peltier generator to make enough power to run a low pressure water pump as might be used in a radiant heating system?

My thinking is that I would need a pump to pump water through a radiant heating system, so if a Peltier or three could be added to the radiant heating system, that might make enough power to run the pump. On the surface this might appear to be perpetual motion device, except that it would not be. The Sun would be providing the heat for the hot water, and the temp differential between the hot water line and outside temps would produce the temp differential needed for a Peltier to make juice. The setup would just need a battery to provide ready power with the Peltier keeping the battery topped up.

My standing plan would have approximately 4000 to 5000 gallons of hot water at all times heated by the sun with a backup wood fired boiler, so I'd not have to worry much about heat loss from the Peltier with the hot water system. In fact, the heat loss the Peltier causes might be beneficial to the radiant system.

I have no idea if this would be more cost effective than a solar panel running the water pump or not, so if anyone knows on that would appreciate a post.
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #2
    Re: Water pumping and Peltier units

    I think you are going to have a tough time getting enough power out of TED to power any water pump. I tried a ton of them wired together in series/parallel to try to run a 5 watt computer fan to no avail. (Putting the hot side on the wood stove, and the cold side with ice wouldn't do the trick).

    The last units I looked at were ~.5 volts at some time miliamperage. 3 together would run the eco-woodstove fan.

    Good luck,

    Tony
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  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    #3
    Re: Water pumping and Peltier units

    Using Petier devices to power a pump would require more devices and far more cost than solar panels. One of the many problems of Peltier devices is stopping the side you are heating making the other side just as hot and stopping the process. Same when they are used for cooling . if you just sit one on a table and appply electricity for first few seconds one side will be cold other side hot then after that both sides hot. they need massive heatsink usually fan cooled on the cold side . They are very inificient devices.
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #4
    Re: Water pumping and Peltier units

    The wood stove fans work, because they control the cold side effectively by having a large heat sink in the slip stream of the fan. The fan draws cooler air through the cooling fins, keeping a relatively constant Delta T.

    If you want graphic proof of how what JohnP is talking about, take a eco-fan wood stove fan, and put it on the front of the stove instead of the back. The effect of which is that it is pulling the warmest air off the stove through the heat sink. You will soon notice that the fan slows to nearly stopped. The instructions caution you to make sure the fan draws cooler room air over the heat sink, and then blow over the hot part of the stove to move the heat off the stove.

    From what I know of TEDs they have a fairly critical Delta T range. It is not the absolute temperature that counts, but the proper Delta to make them work properly. And indeed they are very inefficient.

    Tony
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
    Re: Water pumping and Peltier units
    icarus wrote: »
    The wood stove fans work, because they control the cold side effectively by having a large heat sink in the slip stream of the fan. The fan draws cooler air through the cooling fins, keeping a relatively constant Delta T.

    If you want graphic proof of how what JohnP is talking about, take a eco-fan wood stove fan, and put it on the front of the stove instead of the back. The effect of which is that it is pulling the warmest air off the stove through the heat sink. You will soon notice that the fan slows to nearly stopped. The instructions caution you to make sure the fan draws cooler room air over the heat sink, and then blow over the hot part of the stove to move the heat off the stove.

    From what I know of TEDs they have a fairly critical Delta T range. It is not the absolute temperature that counts, but the proper Delta to make them work properly. And indeed they are very inefficient.

    Tony

    Tony,

    my Eco-fan sits at the front and runs full speed just fine. Works better than the built-in electric fan (which is why it sits at the front) and makes far less noise.

    But blowing a stream of air around is no place near as difficult as moving any volume of water. Water is a lot more dense than air.

    So am I. :p
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #6
    Re: Water pumping and Peltier units

    Marc,

    some time just for grins, fire up your stove to "normal" temp, put the fan on the front and measure the rpm (with a laser tach if you've got one) or just count if you can follow the blades.

    The start over with the fan cooled and put it on the back. It will turn faster! (to be clear, front/back isn't the issue, the issue is the fan should pull cool air from the room, and then blow over the stove, rather than the reverse. You can put the stove on the side or the back or the front, just as long as the cool(er) air comes over the heat sink).

    I have two identical units on my stove, which I move around as I wish to blow air one direction or another. A side by side comparison always reveals that the one drawing cooler air turns faster. As a control, I have switched them.

    Tony
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  • Telco
    Telco Solar Expert Posts: 201 ✭✭✭✭✭
    #7
    Re: Water pumping and Peltier units

    Hmm... so it might be possible, but would likely be far more trouble than it would be worth with no guarantee that it would work. OK thanks then. I may play with it for a project sometime down the road but for now will forget about it.
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  • Brock
    Brock Solar Expert Posts: 639 ✭✭✭✭
    #8
    Re: Water pumping and Peltier units

    I think you would be better off somehow setting the system up to use a thermo siphon. Or heck even a small 12v pump directly connected to a solar panel.
    3kw solar PV, 4 LiFePO4 100a, xw 6048, Honda eu2000i, iota DLS-54-13, Tesla 3, Leaf, Volt, 4 ton horizontal geothermal, grid tied - Green Bay, WI
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