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Passive Electrical Generator


Nitack

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I have a friend who built a completely passive, zero electricity required air conditioning system for his home. The gist of it is this. He dropped steel pipe five feet into the ground running through his backyard. One end stuck up above ground, the other end connected directly into his basement. He then went through and made sure that his house could be as completely air tight sealed as possible with the exception of a vent out of the top of his roof. From there it is basic physics. Hot air flowed up and out of the roof vent, the resulting pressure change drew air in from the pipe that was running through the ground. Once you hit three feet below ground the temperature is a relatively constant 56ish degrees F. So all the air moving into the house was cool. Hello the beauty of science at work! Zero electricity required and his house maintained a relatively constant 70 degrees during the summer no matter how warm it was outside.

 

First of all, I very much want to set up a system like that in my own house, but foresee some issues given my location. He was in the desert of Arizona (dry air), I am in Virginia, and it is VERY humid during the summer. I still need to figure out how to make it work and not allow water from the air to condense and lead to mold problems.

 

For now, I want to put the same principals to work to create a passive electrical generator. With any liquid or gas, the higher temperature liquid or gas will rise to the top of a given system due to the expansion and lower mass to volume ratio. I want to develop a closed loop system, where water in aluminum piping will heat, by virtue of it's lower mass to volume ratio, move to a higher point, where it can cool, and cycle back into the heating area. This should create a current that could be tapped to generate electricity. Here is my rough schematic:

 

 

The gist of it is this. The entire closed loop system is filled with water. The area marked 1. or Heating Assembly is a series of blackened aluminum pipe that folds back on itself creating a rectangular area that is placed in a full sun area. The line out 2. of the Heating Assembly will carry heated, and less dense, water to a higher elevation. The Cooling Assembly or 3. can be a coil of pipe that is in a shaded area that will naturally be cooler than the water that was in the sun (I have a perfect area for this that is in an enclosure under my second story deck). That water will then be allowed to drop down into 4. the Electricity Generator(slightly incorrectly labeled in the diagram). The Electricity Generator will be a converted water pump that utilizes a permanent magnet motor to generate electricity from the current that will develop in the loop. The water will then go into either piping or a tank, the Feed (also shaded) will then feed back into the Heating Assembly. I am not sure if I will bury the Feed in order to allow it to cool the water faster or if I need to leave it level with the Heating Assembly so as not to try to fight gravity. The pressure changes and current that develops should cause it to draw water either way but I am still hazy on if the system will lose power to gravity if it has to draw the water up from under ground. There is only so much practical application my brain can calculate at once.:hihi:

 

Thoughts? Is this practical? Could it be accomplished? I know some one is going to say that the amount of electricity produced in a system like this will not be tremendous, but that is not my concern at the moment. I am curious it my concept is sound first.

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Sounds like a good direction to investigate but remember the ground isn't the same temperature everywhere, where I live ground water is low 70's. Humidity is very high almost year round. Air conditioning is as much a factor of low humidity as it is low temperature. If I ever build a house I plan to use open loop geothermal AC, it's much more efficient than regular AC.

 

Geothermal heat pump - Wikipedia, the free encyclopedia

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I question whether with water would actually get any flow through the system in a loop, especially against gravity. Seems like you might have cool water moving from the cooling tank back to the warming tank at the same time warm water is moving up...IF the temperature differential is great enought to generate such convection currents.

 

Otherwise the heat transfer would be mostly radiation and conduction...

 

Heat Transfer

 

Also, if the system is a closed loop full of water, heating up one side of it would just cause an increase in pressure throughout the system. If you heat it up enough, it would explode.

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I question whether with water would actually get any flow through the system in a loop, especially against gravity. Seems like you might have cool water moving from the cooling tank back to the warming tank at the same time warm water is moving up...IF the temperature differential is great enought to generate such convection currents.

 

Otherwise the heat transfer would be mostly radiation and conduction...

 

Heat Transfer

 

Also, if the system is a closed loop full of water, heating up one side of it would just cause an increase in pressure throughout the system. If you heat it up enough, it would explode.

 

There are a couple of items I wanted to ask about. Yes, the water moving up would be going against gravity, but wouldn't it be both pushed and pulled in that direction due to pressure in the system? After all, there would also be water at the other side of the system being pulled down with gravity.

 

As for pressure in the system. Because it is closed loop, the warm water would naturally flow to the highest point in the system as it was displaced by the denser cold water.

 

Explosion... :hihi: I had considered that possibility but did not think it would be too likely considering we are only heating with sunlight and not a more robust source of heat. That being said, I have an idea how to minimize the possible issue with pressure. Even though it is a closed system, I will require a few access points to the system. Probably one at the highest point (filling) and one at the lowest point (draining). If I left the access point at the highest point open until the middle of a hot day, the system should be at peak pressure and if I sealed it at that point the pressure would only be able to decrease, but never pass that level.

 

Thanks for pointing this stuff out overdog. I was really hoping to bounce this idea around a bit to work out kinks in the concept phase rather than once materials had already been invested in.

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Pressure can be reduced to safe levels with a pressure release valve. (if you remember, we discussed this when we were talking about using a sealed cast iron pot to heat up the stuff to be pyrolysized by the fresnel)

 

Basically you just need something that will open up the system when a certain PSI is reached (think pressure cooker).

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Pressure can be reduced to safe levels with a pressure release valve. (if you remember, we discussed this when we were talking about using a sealed cast iron pot to heat up the stuff to be pyrolysized by the fresnel)

 

Basically you just need something that will open up the system when a certain PSI is reached (think pressure cooker).

 

As Always, you rock

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There are a couple of items I wanted to ask about. Yes, the water moving up would be going against gravity, but wouldn't it be both pushed and pulled in that direction due to pressure in the system? After all, there would also be water at the other side of the system being pulled down with gravity.

 

As for pressure in the system. Because it is closed loop, the warm water would naturally flow to the highest point in the system as it was displaced by the denser cold water.

 

Explosion... :shrug: I had considered that possibility but did not think it would be too likely considering we are only heating with sunlight and not a more robust source of heat. That being said, I have an idea how to minimize the possible issue with pressure. Even though it is a closed system, I will require a few access points to the system. Probably one at the highest point (filling) and one at the lowest point (draining). If I left the access point at the highest point open until the middle of a hot day, the system should be at peak pressure and if I sealed it at that point the pressure would only be able to decrease, but never pass that level.

 

Thanks for pointing this stuff out overdog. I was really hoping to bounce this idea around a bit to work out kinks in the concept phase rather than once materials had already been invested in.

 

I think that what would happen in the closed system would just be an increase in pressure throughout the system in all directions, with some heat transfer going on, but no uni-directional flow of water through the loop. What is missing is a differential in pressure (which can be caused by temperature differences) that would cause the fluids to move through the closed loop system in one direction or the other.

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I think that what would happen in the closed system would just be an increase in pressure throughout the system in all directions, with some heat transfer going on, but no uni-directional flow of water through the loop. What is missing is a differential in pressure (which can be caused by temperature differences) that would cause the fluids to move through the closed loop system in one direction or the other.

 

So perhaps the solution is to not actually seal the system. :shrug: If, it were not actually sealed, but instead towards the top there was a holding tank with room left for water levels to rise an fall based on changes in pressure that would alleviate the question of pressure building. It also should not interfere with the current I am trying to establish as the density changes in the water will still work the same way in either an open or closed system. As long as we give the heated water a way to move to a higher position, and ensure that once at that higher position the water is able to cool and move to a lower position that will then feed the heating assembly shouldn't the current develop?

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Ah, but with my end goal, it matters very little how much power I can remove from such a system, only that I can actually remove some power at a relatively constant pace (however minor that may be).

 

I am interested in this design because it is pretty passive. Once it is set up it will start up on it's own every day, wind down ever day as the sun/temperatures go down every day, and produce electricity (however small the amount). There is another question, will it actually produce anything though. If the current does not create enough friction to turn the water pump it may produce nothing, which i was hoping some one with more experience could address.

 

The end goal is to feed that electricity back into my house (and possibly the grid if I can produce more than I need at any given time). I know that this will require a complex setup of diodes, fuses and an inverter, but I am not at that planning stage yet. Gotta figure out how to create the electricity before you can figure out how to use it. This is already done with solar panels for most grid tie systems. As I do not have $20k to invest in a PV system, I have been thinking about this poor mans solar electric system design. Don't worry, i have a lot of steps I have to get through first before I tried connecting this thing to my house :shrug:

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The bigger problem is the design depends on the water sinking/flowing downhill, sunlight isn't going to make that water flow back up-hill (unless it boils it into steam).

 

EDIT:

 

You should be able to build a cheap prototype and test the idea (at least with respect to getting the sunlight to power the water flow) without spending too much money...

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The bigger problem is the design depends on the water sinking/flowing downhill, sunlight isn't going to make that water flow back up-hill (unless it boils it into steam).

 

EDIT:

 

You should be able to build a cheap prototype and test the idea (at least with respect to getting the sunlight to power the water flow) without spending too much money...

 

But it is not "flowing" up hill. It is simply flowing to a higher position as it is displaced by denser (lower temp) water. In that sense, i don't think we are actually fighting gravity at all, but i may be wrong.

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But it is not "flowing" up hill. It is simply flowing to a higher position as it is displaced by denser (lower temp) water. In that sense, i don't think we are actually fighting gravity at all, but i may be wrong.

 

Ah, I see what you are saying. So the question is whether the flow would sufficient to turn a turbine to produce electricity?

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I think what you are describing would be a type of Heat Engine.

 

Heat engine - Wikipedia, the free encyclopedia

 

This one actually sounds very similar to what you are thinking about...

 

ORC TurbinexxGenerator xx System - Solar Thermal Energy Version

The FREEPOWER system has been developed as a cheap reliable alternative to photovoltaic systems. It consists of a micro turbine generator that is driven by a closed loop of working fluid. The working fluid is pumped by a small electrical pump through a solar array, where it is heated and vaporised. The vapor drives a micro turbine generator, and then condenses back to a liquid and the whole cycle recommences. A small ancillary circuit of the same vapor provides cooling for the alternator.

 

Heat Engine Projects

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The biggest problem I see is that the temperature in the water will reach equilibrium quicker than the water can migrate based on density. Now, if you brought a fresnel lens into the equation...:jumpforjoy:

 

Yes, the water would have to cool off at least as fast as it heats up or it would reach equilibrium.

 

I remember reading somewhere that water really doesn't work well for heat engines unless you actually heat it to steam, but I can't find that anywhere now. I recall the ideal substance is something which goes from a liquid to a gas and back during the process...

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