# Can we generate electricity efficiently from a peltier device by supplying heat?

Is it possible to generate electricity from a Peltier device by only supplying heat (not ice)(something above 343 K )?

How efficient can it be?

Which is more efficient?- Using Peltier device or using the heat to convert the water to steam and then to electricity(heat is obviously not 343K in this case, it's something above 373 K)?

• Yes, it is possible. No, it is not efficient compared to most other methods. – Dave Tweed Dec 17 '19 at 16:08
• Have you done your basic calculations? Pick a number of joules and figure out what output you get in each case and compare. Add the calculations and numbers into your question. – Transistor Dec 17 '19 at 16:09
• Oh, you had to use that word "efficiently" didn't you... – Harper - Reinstate Monica Dec 17 '19 at 16:23
• Look up what a radioisotope thermoelectric generator is. Very inefficient, but reliable and long lasting and only used in exotic situations where nothing else will work like deep space probes Galileo, and Voyager 1 and 2...and uhhh lighthouses. – DKNguyen Dec 17 '19 at 16:31
• 343K is only 70'C which isn't even boiling hot for water. It's just evaporating faster than room temp. Heat extraction depends on the temperature difference. REad Rankine cycle – Tony Stewart Sunnyskyguy EE75 Dec 17 '19 at 17:26

Is it possible to generate electricity from a Peltier device by supplying heat (not ice)(something above 343 K )? How efficient can it be?

Yes, that is possible. The mechanism that generates electricity (seebeck effect) is dependent on the temperature gradient (temperature drop or $$\\Delta T\$$) across the module. Typical peltiers are roughly 3% to 8% efficient, but the efficiency is dependent on many factors like temperature gradient, heat moving through the device, and the load on the peltier or current and voltage that the device is operated at.

Most steam conversion is 30% to 50% efficient, much more efficient than a peltier.

• It might be worth mentioning, if you know, how the efficiency of low-ΔT stirling engines compares, since they would be the most direct replacement for small-scale things. Steam turbines are only really worth it at large scales. – Hearth Dec 17 '19 at 16:41
• @Hearth, you can also have small steam engines, you just don't see many anymore because of combustion engines. – Voltage Spike Dec 17 '19 at 18:12
• I'm talking more about scale of temperature; you won't have any steam engines operating at 50°C (unless you use something other than water as the fluid, of course!) but you can definitely have Peltier modules or low-ΔT Stirling engines. – Hearth Dec 17 '19 at 18:14
• In a carnot engine we need the sink to be cold and the source to be hot so is there anyway to use peltier device in it ? (Obviously in an ideal case else the device would melt)so that one side is hot(by the source) and other side cold(to the sink) – Sidhant Mishra Dec 19 '19 at 12:20
• They have special peliters that work with delta T's in the 600C range, the consumer ones will die at around 200C. You can use a peliter to recover waste heat, there aren't good reasons to do this because of cost vs preformance. – Voltage Spike Dec 19 '19 at 16:38

Peltier devices are notoriously inefficient - only about 5%.

However, steam requires an army of skilled engineers present at all times the boiler is running (and hours before and after). It doesn't matter if you're making 500 milliwatts or 500 megawatts, you still need the army of engineers to avoid a deadly BLEVE (boiling liquid expanding vapor explosion). You can get 30-40% efficiency from a well-optimized steam boiler/turbine.

Note that 343K is much too cold for a steam plant to operate efficiently. You might be able to make it work with lower boiling point liquids like pentane if you can access an ultimate heat sink that is sufficiently cool. However, most of those fluids are flammable.

Even operating in efficient temperatures, steam is economically impracticable (depending on the cost of labor in your country) below a break point of 10 megawatts to 200 megawatts. At the lower ends of that range, you are much better off using gas turbines or plain diesels, which require a much smaller engineering staff, because they can't explode in the violent manner of a BLEVE. These run about 30-40% thermally efficient, net.

If you have a gas turbine installation large enough, you can use the rather hot exhaust to boil steam and run a steam plant alongside. This is called a combined-cycle plant. In this case, the boiler management staff are managing a number of small boilers (at each turbine exhaust) feeding into one large steam turbine. These combined-cycle plants have efficiency of 50% or even as high as 55-60%.

• What does BLEVE stand for? I can guess what you're talking about (the dangers of boilers are well known) but I don't know that acronym. – Hearth Dec 17 '19 at 16:42
• @Hearth Boiling Liquid Expanding Vapor Explosion. – Harper - Reinstate Monica Dec 17 '19 at 16:44
• I figured something along those lines. Nice convenient acronym for "your entire facility is out of commission for the foreseeable future and several people are probably severely injured if not dead". – Hearth Dec 17 '19 at 16:45
• @Hearth Also, you'll need a new boiler :) and it'll take awhile to talk the regulators out of a new operating permit. – Harper - Reinstate Monica Dec 17 '19 at 16:49

Heat engines with a low temperature differential will always be inefficient. The theoretical maximum is the ratio of the absolute temperatures of the source and sink. With a room temperature sink of 293K and 343K source, the maximum efficiency will be (343-293)/293 = 17%.

This is known as the Carnot limit (Carnot cycle).

Peltier devices will get much lower than that - a large source of inefficiency is the conduction of heat directly from the source to the sink side of the Peltier.

• In a carnot engine we need the sink to be cold and the source to be hot so is there anyway to use peltier device in it ? (Obviously in an ideal case else the device would melt)so that one side is hot(by the source) and other side cold(to the sink) – Sidhant Mishra Dec 19 '19 at 12:09
• @SidhantMishra - If you supply heat to a Peltier device and cool the other side it is subject to Carnot rules - it is a heat engine. – Kevin White Dec 19 '19 at 15:23
• what if we consider it in a practical scenario?(assuming no carnot rules but only the practical part of it) – Sidhant Mishra Dec 20 '19 at 20:01