Author Topic: Generating electricity from ice?  (Read 12361 times)

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Offline ArtlavTopic starter

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Generating electricity from ice?
« on: November 09, 2014, 07:06:33 pm »
Ice.
Lots of ice around, such is the nature of Russia.
So, how about making electricity out of it?


Just having some fun with a thermoelectric generator i made.

A TEG is said to produce electricity from heat, but since it is running on a temperature difference, it's equally valid to say that it produces electricity from cold.
However, i don't think i ever heard it described that way.
And for a good reason - the energy is, in the end, coming from the furnace that heats up the house.

Are there circumstances where it would make sense to say that the power is coming from the cold?
Even in places where heat and cold co-exist, it's more precise to say that the heat is carrying the energy (be it from fire, solar, geothermal, nuclear, body heat, etc), and not the cold.
 

Offline SeanB

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Re: Generating electricity from ice?
« Reply #1 on: November 09, 2014, 08:45:40 pm »
However the energy to the hot side comes from your central heating........... Will not work if you do not pay that bill and the heat is turned off.
 

Offline Macbeth

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Re: Generating electricity from ice?
« Reply #2 on: November 09, 2014, 09:42:04 pm »
I believe running air conditioners in reverse is more efficient at generating heat in the home than the usual resistive electric heating methods. Kind of like air-con is so energy inefficient at reducing room temps compared to the power in, it's actually pretty good using the heat exchanger the other way around?

I'm not sure, I live in the UK and use a gas boiler for our radiators in the winter. Far cheaper than electricity.

I have a portable AC that I only really use in the rare summer heatwaves we have. It is a godsend when temps, and worse, humidity, are high.
 

Offline PlainName

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Re: Generating electricity from ice?
« Reply #3 on: November 09, 2014, 10:16:11 pm »
Quote
I believe running air conditioners in reverse is more efficient at generating heat in the home than the usual resistive electric heating methods.

Yes, it is. I used to have a fan heater in my office and replaced it with aircon specifically for the heating part (in summer it's cheaper to open the windows, although I have used cooling once or twice). Cost about £300 and paid for itself in 2-3 years (hard to be precise because they bump the energy prices every year, but even so my bills are still coming in low).

It is not for everyone - takes a while to get up to speed from cold, so you wouldn't want it if you're just heating up the place to watch a TV prog, say. But it is much more smooth heat, so you don't feel extra cold when the extra hot fan blowing up your trousers turns off.
 

Offline rob77

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Re: Generating electricity from ice?
« Reply #4 on: November 09, 2014, 10:18:12 pm »
I believe running air conditioners in reverse is more efficient at generating heat in the home than the usual resistive electric heating methods. Kind of like air-con is so energy inefficient at reducing room temps compared to the power in, it's actually pretty good using the heat exchanger the other way around?

I'm not sure, I live in the UK and use a gas boiler for our radiators in the winter. Far cheaper than electricity.

I have a portable AC that I only really use in the rare summer heatwaves we have. It is a godsend when temps, and worse, humidity, are high.

AC is a heat pump, nothing less nothing more ;) the problem running the AC in reverse is the efficiency.... you can't extract enough heat from the freezing cold air with acceptable efficiency.... that's the reason why the heat pumps designed for heating houses are pumping the heat from a exchanger buried in the ground or submersed in a well.
 

Offline ArtlavTopic starter

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Re: Generating electricity from ice?
« Reply #5 on: November 09, 2014, 10:25:38 pm »
However the energy to the hot side comes from your central heating........... Will not work if you do not pay that bill and the heat is turned off.
Yep, like i said below the video. :)
I mostly wondered if it would make sense to say the energy is coming from the cold.

I.e. if you made liquid nitrogen, you stored a fraction of the energy spent making in it.
So, when it vaporises it can spin a turbine and give some of that energy back (at 1% system efficiency or so).
However, sources of energy don't naturally occur in the "cold" variety, AFAIK.
Thus, the question.

I believe running air conditioners in reverse is more efficient at generating heat in the home than the usual resistive electric heating methods. Kind of like air-con is so energy inefficient at reducing room temps compared to the power in, it's actually pretty good using the heat exchanger the other way around?
Yes, in general.
However, when it's -30*C outside, it tends to get difficult.
Even if it is designed to run that cold, it still will be only marginally more efficient than a resistive heater, at many, many times the complexity.
We are talking about refrigerating the cold outside air to even colder temperatures to bring heat inside, and that is a difficult task.
So, at some point the complexity outprices the gains.
 

Offline IanB

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Re: Generating electricity from ice?
« Reply #6 on: November 09, 2014, 11:17:18 pm »
A TEG is said to produce electricity from heat, but since it is running on a temperature difference, it's equally valid to say that it produces electricity from cold. However, i don't think i ever heard it described that way. And for a good reason - the energy is, in the end, coming from the furnace that heats up the house.

If you put your generator outside with a black painted aluminium panel facing the sun on one side and the cold ice on the other, you could generate some solar powered electricity.
 

Offline Rufus

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Re: Generating electricity from ice?
« Reply #7 on: November 09, 2014, 11:50:41 pm »
If you put your generator outside with a black painted aluminium panel

Does that mean it is powered by dark?
 

Offline suicidaleggroll

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Re: Generating electricity from ice?
« Reply #8 on: November 09, 2014, 11:53:52 pm »
I mostly wondered if it would make sense to say the energy is coming from the cold.
No, it doesn't, because it's not.

I.e. if you made liquid nitrogen, you stored a fraction of the energy spent making in it.
No, you make liquid nitrogen by pulling energy OUT of in, not by putting energy INTO it.

So, when it vaporises it can spin a turbine and give some of that energy back (at 1% system efficiency or so).
The liquid nitrogen is not vaporizing itself and spinning the turbine.  The energy required to vaporize the liquid nitrogen and spin the turbine is coming from the heat in the surrounding air.  You're not extracting energy from the liquid nitrogen, the cold temperature of the liquid nitrogen simply gives you a conduit through which you can extract energy from the surrounding (read: warmer) air.

However, sources of energy don't naturally occur in the "cold" variety, AFAIK.
That's because there's no such thing.  Cold, by definition, is the absence of energy, not the presence of "cold energy".

Think of it like a waterfall.  High temperatures are like the water in the river at the top of the falls, low temperatures are like the water in the river at the bottom of the falls.  The temperature (height of the water) is its potential energy.  The higher it is, the more potential energy it has, but you can only extract that energy by allowing it to fall to a lower height.

Same with a TEC, it allows you to extract some of the thermal energy on the hot side as it transitions from hot to cold.  A perfect TEC wouldn't heat the cold side at all, it would just act like a sink on the hot side and all of that thermal energy would turn into electricity.  Since a TEC is not perfect, some of that heat makes it through and warms up the cold side as well.
« Last Edit: November 09, 2014, 11:57:02 pm by suicidaleggroll »
 

Offline suicidaleggroll

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Re: Generating electricity from ice?
« Reply #9 on: November 10, 2014, 12:00:13 am »
If you put your generator outside with a black painted aluminium panel

Does that mean it is powered by dark?

It's powered by solar radiation, black just happens to have a higher emissivity than shiny silver, which makes it more efficient.
 

Offline calexanian

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Re: Generating electricity from ice?
« Reply #10 on: November 10, 2014, 12:29:56 am »
Dave just recently did a video on the Seebeck effect. Also Thermopile generators. The voyager probes have one each that are amazing.
Charles Alexanian
Alex-Tronix Control Systems
 

Offline Rufus

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Re: Generating electricity from ice?
« Reply #11 on: November 10, 2014, 02:35:09 am »
If you put your generator outside with a black painted aluminium panel

Does that mean it is powered by dark?

It's powered by solar radiation, black just happens to have a higher emissivity than shiny silver, which makes it more efficient.

I think you are taking the thread too seriously.
 

Offline LukeW

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Re: Generating electricity from ice?
« Reply #12 on: November 11, 2014, 04:42:48 am »
You've got the ambient environment on the "hot side" of the system, and something that is cold below room temperature (eg ice, or liquid nitrogen or whatever) on the cold side of the system.

The energy comes from the hot side... so you could say that the energy comes from the temperature of the room.
However, you've spent energy to create a system that is colder than room temperature, putting energy in to make the ice or whatever.
So you can't (of course) get a free lunch in the thermodynamic sense.

You can do the same thing using a small low-temperature-gradient Stirling engine, with the heat source at room temperature and ice on the heat sink, or a thermoelectric pile like you've used.
 


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