Energy

New geothermal battery directly converts heat to electricity

New geothermal battery directl...
A new battery cell design could help us tap into the vast stores of geothermal energy beneath our feet
A new battery cell design could help us tap into the vast stores of geothermal energy beneath our feet
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A diagram demonstrating how the sensitized thermal cells work. Heat causes electrons to move from the semiconductor into the electron transport layer (ETM), then through an external circuit (the car) into the counter electrode, where redox reactions transport some copper ions back into the semiconductor to start the cycle over again
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A diagram demonstrating how the sensitized thermal cells work. Heat causes electrons to move from the semiconductor into the electron transport layer (ETM), then through an external circuit (the car) into the counter electrode, where redox reactions transport some copper ions back into the semiconductor to start the cycle over again
A new battery cell design could help us tap into the vast stores of geothermal energy beneath our feet
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A new battery cell design could help us tap into the vast stores of geothermal energy beneath our feet

One of the largest natural sources of renewable energy could be right under our feet – literally. The Earth itself is a big warm ball just waiting for us to tap into it, with vast stores of geothermal energy lying beneath Australia, the United States and plenty of other areas. Now researchers at Tokyo Institute of Technology and Sanoh Industrial have developed a new type of battery cell that can directly convert heat energy into electricity.

Most geothermal systems work using water heated by hot rocks a few kilometers below the Earth's surface. That water is either naturally present and pumped to the surface, or pumped down, heated and pumped back up. Such systems often need high temperatures, over 180° C (356° F), to work, and don't necessarily scale up that well.

But the Japanese researchers behind the new study say they've got a more direct method. Their design is made up of sensitized thermal cells (STCs), which are able to generate electricity at temperatures below 100° C (212° F) without needing a middle-ground carrier like water or steam.

The STC is a battery made up of three layers of material sandwiched between two electrodes. There's an electron transport layer (ETM), a semiconducting layer of germanium, and a solid electrolyte layer that transports copper ions. This battery is designed to be buried in the hot ground.

The idea is that the heat in the ground excites the electrons in the semiconductor, causing them to transfer to the ETM. That in turn passes them via the electrode through an external circuit and eventually back to the other electrode and into the electrolyte. There, oxidation and reduction (redox) reactions take place, which carries low-energy electrons back into the semiconductor, starting the cycle over again.

A diagram demonstrating how the sensitized thermal cells work. Heat causes electrons to move from the semiconductor into the electron transport layer (ETM), then through an external circuit (the car) into the counter electrode, where redox reactions transport some copper ions back into the semiconductor to start the cycle over again
A diagram demonstrating how the sensitized thermal cells work. Heat causes electrons to move from the semiconductor into the electron transport layer (ETM), then through an external circuit (the car) into the counter electrode, where redox reactions transport some copper ions back into the semiconductor to start the cycle over again

One question that the team wasn't sure about initially was how long the STC device could keep this cycle up, or even if it could keep going indefinitely. But during testing, they found their answer – eventually, the cycle dries up when the redox reactions do, because the different types of copper ions ended up in different places.

But interestingly, the team was surprised to find that the battery could fix this problem, as long as it's buried in a heat source. Then it's a matter of turning on the external circuit for a while to recharge it. This, the team says, could allow the battery to supply power "semi-permanently."

"With such a design, heat, usually regarded as low-quality energy, would become a great renewable energy source," says Sachiko Matsushita, lead researcher on the study. "There is no fear of radiation, no fear of expensive oil, no instability of power generation like when relying on the sun or the wind."

The team says that further refinements are needed for the design, but hopefully it soon joins the ranks for renewable energy options.

The research was published in the Journal of Materials Chemistry A.

Source: Tokyo Tech

11 comments
Bob Stuart
Have they really defeated the second law of thermodynamics, and created a heat engine that does not rely on a difference in temperature, but harvests molecular kinetic energy? If so, it should also work many places above ground, and win a Nobel.
rederje
Thermal physics second principle entropy needs at least 2 heat sources at different temperatures to convert earth heat into energy, by cooling the deep earth, by any method. Thus this battery after discharging at a low room temperature recovers because as they write in their abstract : " the battery characteristics were restored after discharging by placing or burying the battery in a heat source", i.e. this battery is recharged by heating it "buried" into earth. Thus to work, this battery need to be moved, up and down, between low and hot temperatures, i.e. moved between surface and deep hot rocks below earth surface ( at least 1 Km below at around 50°C at 1°C for each 30m deep ) and this is contrary to the statement "without needing a middle-ground carrier like water or steam", because moving up and down 1km, the battery is more difficult than moving the water. This new type of battery is interesting, but we must be careful to not overestimate its possibilities. Otherwise the efficiency, not indicated, is very likely quite small with respect to Carnot second principle maximum efficiency, already small, 50/350, ratio of diifference temperature 50°C to maximum temperature.
Nobody
Whatever happened to freon motors? Obviously some freons are a hazard to the ozone but there are many more chemicals that could fill the void for a low temperature heat cycle.
rederje
I agree with Bob Stuart, if proved true, "defeated the second law of thermodynamics", not only they win a Nobel, but a revolution in physics, turning all up down. It becomes possible to move on boats and motors extracting the energy of sea, leaving behing them icebergs, an nearly infinite energy !! Thus it is extremely unlikely, nearly impossible and we must search where are the basic errors !
Username
No laws are being broken. No free energy is being created. Convert the core's heat into electricity and the core (ever so slightly) gets colder.
mediabeing
Was there a valid reason that Thermocouples were completely left out? Explain that to us.
TechGazer
If it does require alternating hot and cold, then it's not a new phenomena. I read about it as an effect in lead-acid batteries, where the change in temperature boosted the charge (converted heat energy into electrical charge separation). As a heat engine, it wasn't very practical.
Nik
There is unlimited geothermal energy, worldwide, some is easy to access, some not, but like oil wells, eventually the more difficult will become viable. Drilling horizontally into volcanoes may be one way, with the right precautions. Otherwise, hot-spots like Yellowstone, Hawaii, and Iceland are obvious locations. Batteries tend to be expensive to produce, short-lived, and fragile, relative to steam power. So this invention may seem hopeful, but is also a long way from fruition.
Graeme S
what about other heat sources that do get very hot then cooler, say the exhaust system of the humble ICE?
MKO
Pilot these offshore of Japan where underwater vents from volcanic activity is present, then use the heat and surrounding colder water to make electrcity. Once the juice is running, put the electrcity to work by splitting water into Hydrogen and Oxygen. Pump the hydrogen to shore and put it to use Diffuse the oxygen in the ocean like a big fish aquarium keeping the fishes happy and healthier.