Hi! I'm quite intrigued with your discussion. But can I ask something regarding this topic? We are actually conducting a research about integrating peltier module and smart film in uPVC window panel powering a charging port and how it can generate electricity by using the indside and outside temperature of living spaces. Do you think u can give me some insights in how we make it happen or how can we generate energy from this?

Moderator edit: New thread created from this.

 

In a Peltier device, heat is transferred by current flow. So to generate current, heat flow is required. Providing heat flow is not quite so simple as it sounds. Making things worse, there are resistance losses present whenever current is flowing. So the process is not 100% efficient. So now for the application you have, you need to decide on the power it requires, and then use the math to see how much heat flow you will need. The formulas should be available from the suppliers of the Peltier junction devices.. Probably the heat flow required will exceed the solar energy impacting whatever you are collecting it with. GOOD LUCK!!!

 

Do peltier's work in reverse? I thought they were consumers of electrical joules to do the work of moving heat from one side to the other. Solid state AC.

If they could be used in reverse, then still no free lunch here. If say outside is 0F and inside is a toasty 73F, you need to consume energy to make the inside +73F above the outside. Then the peltier uses the developed heat diff to make electric (moving you inside heat to the outside. Super not efficient way to do it.

 

Do peltier's work in reverse? I thought they were consumers of electrical joules to do the work of moving heat from one side to the other. Solid state AC.

If they could be used in reverse, then still no free lunch here. If say outside is 0F and inside is a toasty 73F, you need to consume energy to make the inside +73F above the outside. Then the peltier uses the developed heat diff to make electric (moving you inside heat to the outside. Super not efficient way to do it.

Yes, you can use the Seebeck effect to generate power from heat.

 

In a Peltier device, heat is transferred by current flow. So to generate current, heat flow is required. Providing heat flow is not quite so simple as it sounds. Making things worse, there are resistance losses present whenever current is flowing. So the process is not 100% efficient. So now for the application you have, you need to decide on the power it requires, and then use the math to see how much heat flow you will need. The formulas should be available from the suppliers of the Peltier junction devices.. Probably the heat flow required will exceed the solar energy impacting whatever you are collecting it with. GOOD LUCK!!!

One thing that may make this all moot are the annoying laws of thermodynamics. If the only reason for doing this is to be able to place a charging port where these is no easily accessed electrical outlet then maybe it is worth pursuing. But if it is intended as some sort of “green” effort, well, there’s no free energy and it is going to cost something to keep the cool side… cool.

If the temperature differential is used to generate power, something will have to be done to maintain that—and it means using power. In the end, most schemes of this sort completely fail at being “greener” than straightforward alternatives in that any imaginary gains are turned into losses because everything costs something. But if the motivation is power where power is hard to come by, and the price and extra energy consumption don’t matter—it might have a shot at being useful (if not for the huge amount of heat needed to produce anything worth using).

 

ive done some messing with these as well and the temperature differential needed to either, get a high enough voltage to be useable, or to get enough current to boost up to that voltage and be useable is just too much. Even with a 70 degree differential you get very little usable power out. You'd have to have some sort of energy harvesting to store a usable amount, for use. Being able to plug into and charge a device usefully would require a very decent sized area with a high temperature differential.
I'm not going to say its impossible. I'd say the power bank you can stick to a window in winter and charge it up wouldn't be too crazy. As long as you don't mind it taking a day to charge. There are some integrated chips made specifically to harvest low levels of energy from devices including peltier devices to charge a battery or super capacitor. Like THIS ONE from analog. Link provided as a starting point, not as a solution to the problem. The specifics of the application may point at a different one.

 

Do peltier's work in reverse? I thought they were consumers of electrical joules to do the work of moving heat from one side to the other. Solid state AC.

If they could be used in reverse, then still no free lunch here. If say outside is 0F and inside is a toasty 73F, you need to consume energy to make the inside +73F above the outside. Then the peltier uses the developed heat diff to make electric (moving you inside heat to the outside. Super not efficient way to do it.

Hi,

I am not sure that is the right rationale for thinking about how this works.
That's because it would be VERY rare that you would heat your whole house JUST to keep a Peltier device happy. The more reasonable assumption is that you were already heating your house and you needed just a little more electrical current so you add a thermoelectric device.
Another reasonable scenario is that you have some waste heat, such as from an unwanted but unavoidable resistance, that you wanted to convert back into electrical current for use in RAISING the efficiency of some process. This has actually been done already.
Still yet another reasonable and practical scenario can be found in some spacecraft. These generate power for the spacecraft using nuclear decay to generate heat. They may not use Peltier devices they may be using thermocouples, but same idea as I think they are just the reverse in the use of each other strictly speaking. In fact, the effect is sometimes combined into the Seeback-Peltier Effect.

In the practical use the efficacy is not as important as the function itself. There may be little output, but it's better than no output at all.

 

ive done some messing with these as well and the temperature differential needed to either, get a high enough voltage to be useable, or to get enough current to boost up to that voltage and be useable is just too much. Even with a 70 degree differential you get very little usable power out.

Right, the unit as non-consumer of joules produces very little output, and you need near 100F diff to get something.

I am not sure that is the right rationale for thinking about how this works.
That's because it would be VERY rare that you would heat your whole house JUST to keep a Peltier device happy. The more reasonable assumption is that you were already heating your house and you needed just a little more electrical current so you add a thermoelectric device.

I was doing the simple joules math. Energy (joules) that you heat the inside air with, now needs to leak across the the device in order to get provider of electrical energy. The efficiency of the device is poor to begin with. My conclusion was, find some other way to get the electrical energy needed.

And in the original model, it assumes the differential never flips 180, in some locations like south TX the outside ambient may become 30F higher than inside, and in that case you need to flip the device over, and then you leak joules into the inside cooler room, which you then use HVAC to pump out.

 

FWIW, there are devices specifically designed to be “thermoelectric generators”. I don’t know how much different they would be from a Peltier but I suspect they’re meant to withstand higher temperatures. More efficient? Maybe

 

FWIW, there are devices specifically designed to be “thermoelectric generators”. I don’t know how much different they would be from a Peltier but I suspect they’re meant to withstand higher temperatures. More efficient? Maybe

This concept works like automotive turbo, harness the expelled heat. Makes me wonder why the hybrid vehicle makers don't slap these devices onto the exhaust pipes and couple the heat from that to make electric joules to help charge the batts.

 

The more reasonable assumption is that you were already heating your house and you needed just a little more electrical current so you add a thermoelectric device.

You are missing the point. Extracting that electrical power cools the inside of the window, meaning you need more power to heat the house. The extra power is minuscule, but still larger than the power extracted.

 

You are missing the point. Extracting that electrical power cools the inside of the window, meaning you need more power to heat the house. The extra power is minuscule, but still larger than the power extracted.

That's still not a reasonable argument, read why I posted that. It's because it sounded like he was going to heat his house just for the thermoelectric conversion.

Also, you seemed to have missed the other two "points" and concentrated on that one point.

Do you have a thermoelectric device for making electric current from your home heating?
What, no you say?
Then you don't have to heat your house

 

Right, the unit as non-consumer of joules produces very little output, and you need near 100F diff to get something.


I was doing the simple joules math. Energy (joules) that you heat the inside air with, now needs to leak across the the device in order to get provider of electrical energy. The efficiency of the device is poor to begin with. My conclusion was, find some other way to get the electrical energy needed.

And in the original model, it assumes the differential never flips 180, in some locations like south TX the outside ambient may become 30F higher than inside, and in that case you need to flip the device over, and then you leak joules into the inside cooler room, which you then use HVAC to pump out.

Hi,

Yeah I think it would be hard to generate any useful electrical energy from one of those unless it was really big or something.

Yes if it flips 180 then it generates negative energy