I believe high efficiency conversion of small temperature differences to energy would be a breakthrough technology.
Geothermal power is the first that springs to mind.
Geothermal doesn't really convert small deltas into power. It takes a small delta, then amplifies it using compression/expansion to alter the temperatures into a usable delta. So it is subject to all sorts of inefficiencies as it compresses/expands/moves the medium around.
The real breakthrough would be a machine that can harvest power without a temperature gradient/delta, something that could take the vibration of molecules and convert it directly to electricity. Something like this...
"The idea of harvesting energy from graphene is controversial because it refutes physicist Richard Feynman's well-known assertion that the thermal motion of atoms, known as Brownian motion, cannot do work. Thibado's team found that at room temperature the thermal motion of graphene does in fact induce an alternating current (AC) in a circuit, an achievement thought to be impossible."
> "The idea of harvesting energy from graphene is controversial because it refutes physicist Richard Feynman's well-known assertion that the thermal motion of atoms, known as Brownian motion, cannot do work. Thibado's team found that at room temperature the thermal motion of graphene does in fact induce an alternating current (AC) in a circuit, an achievement thought to be impossible."
The crucial question here is: Can this alternating current do work?
Without overwhelming evidence there's no reason to think this isn't just another mirage like emdrive. The second law has stood up to everyone everywhere who ever made a machine being on the lookout for a single counterexample starting from well before we had science.
Am I correct in understanding that if you could use a heat pump to convert electricity to heat at 300% efficiency, and then convert that heat back to electricity at 50% efficiency, you’d basically get “free” energy by cooling the air? Is this even feasible?
Heat pumps move heat from one place to another. They pump the heat. That is how they achieve 300% returns, they move 300% of the heat energy that they consume to operate.
But that heat isn’t free. It has to be produced somewhere. You must “consume” the heat to produce electricity.
If you tried to generate power in the way you postulated, you would ignore the 300% number and instead look at the conversion rate between the energy it takes to produce that heat and the energy output.
To frame this another way since I missed part of the point on first read: the heat pump has the same maximum theoretical efficiency (Carnot efficiency) as the heat-to-electricity generator does (just in the opposite direction), and cannot exceed it. If you model the two parts independently, then in the ideal scenario, your 300% efficient component is balanced by something that physically cannot exceed 33⅓% × some-other-variable efficiency. You therefore model the system as just a heat-to-electricity generator that consumes the atmospheric heat directly at some-other-variable efficiency.
(I believe this to be accurate, but I am speaking far beyond my expertise and invite correction if I have erred.)
If you're pulling heat from the air though, you're just absorbing solar power efficiently. And this wouldn't be a bad way to do it if you could make it work: at any given time, there's always sun shining somewhere on Earth, just not where we need it. A heat pump which could extract enough of a differential to power itself using a turbine, isn't impossible.
The real issue is such a thing at scale would functionally be a storm generator: you'd be pulling warmer air in the upper troposphere down to ground level, chilling it, and then releasing it.
Lots of comments here jumping at impossible/perpetual motion machine etc
Think of it as mining the air/water for heat energy and turning it to electricity. No one said energy is being made from nothing. This is not being touted as a solution to climate change.
To rephrase the idea, is the following equation possible:
This is the problem with characterising heat pumps as '300%' efficient.
They're not, they're actually around 30-60% efficient like most other heat engines. It's just the thing they do is move heat so people characterise the 'output'/ work as efficiency when in reality the relevant factor is something like output / output_of_reverse_carnot_cycle.
A 100% efficient heat pump would produce exactly as much electricity putting the heat back where it started as it used in the first place.
A heat pump moves heat from one pool to another and adds whatever input energy required to move the heat to the whole system.
When you have two pools at different temperatures you can harvest energy from that difference but only as much as is there because harvesting the energy involves bringing the two pools closer in temperature.
There is nothing you can do to cheat this, whatever you do will bring the two pools closer together. If you bring in outside energy you will always be able to harvest less than you brought in.
Don't you need an external source of heat for a heat pump? They move heat from one place to another, rather than generate heat directly, so all you would be doing is moving existing heat, and then converting that into electricity, but we can already do that without the heat pump.
I get that, but you need fairly high grade heat to generate power. The idea would be to move enough heat from lower grade sources to a reservoir that is then hot enough to generate more power than is required to move the heat in the first place. It's effectively harvesting the ambient air temperature. I don't know that you could pull in that much heat, and I suspect that an analysis of the system might show that it can't yield useful work.
That would be a perpetual motion machine, so no. Separating room-temperature air into hot and cold fractions removes entropy from that air, and that needs more energy input than can be extracted by a heat engine working from that temperature difference.
Saw this effect demonstrated at room temperature by an acquaintance at Ames Laboratory over 20 years ago. Have long wondered about its practicality.
https://www.eurekalert.org/news-releases/854806
I worked at a company a few year ago that makes adiabatic demagnetization refrigeration (ADR) systems for milliKelvin temperature cooling. The magnetic cooling system cooled a small payload from sub 4K to mK temperatures... company sells a fair number of system each year.
I have been hearing about "magnetic cooling fridges" for almost 30 years now. Generally when it takes something that long to reach the market, there are inherent problems with the technology that prevent it from going mainstream.
There are. But I think this company is more self aware and honest than most I’ve seen. Check there latest blog post - “ you have to start somewhere”
The issue is cost of magnets, you need 1000’s dollars of magnets to make a small fridge like a home refrigerator. This group is well know for their work on recycling magnets, which can cut down costs easily 10x if they crack the code to down to 100x suddenly you have a fridge that is silent Freon free etc and a compelling value proposition.
Maybe the recycling tech that results from this startup will be more valuable than the refrigerator tech.
It took a while for general purpose computers, but limited purpose computers like programmable looms or machines to help with arithmetic existed long before the difference engine. And general purpose computers only took so long because there were inherent difficulties with building them mechanically.
https://www.geandr.com/collections/magnetocaloric-materials/...
You can buy magneto-caloric materials starting from $175
(Found it by reading through this presentation: https://www.hydrogen.energy.gov/pdfs/review19/in012_ihnfeldt...)