3 Indian Teens Win $12,500 Earth Prize 2025 For Inventing Salt-Powered Fridge That Doesn't Need Electricity

Three Indian teenagers have built a salt-powered fridge to help bring vaccines and medical supplies to rural areas. Indore’s Dhruv Chaudhary, Mithran Ladhania, and Mridul Jain have won the Earth Prize of $12,500 this year and plan to test 200 units in 120 hospitals.

As covered in detail in a Business Insider story, the refrigerator does not need electricity. Instead, it uses salts that pull heat from the environment when they dissolve in water.

After hearing how challenging it was to bring COVID-19 vaccines to rural areas without electricity, these boys decided to find a salty refrigeration technique.

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More about the salt-powered fridge

Their invention is called Thermavault. They are planning to build 200 of those refrigerators and send them to 120 hospitals for testing with the $12,500 award money they earned.

The Thermavault is designed to help transport vaccines, other medicines and supplies, and even transplant organs.

"We have been able to keep the vaccines inside the Thermavault for almost 10 to 12 hours," Dr. Pritesh Vyas, an orthopaedic surgeon who tested the device at V One hospital in Indore, says in a video on the Thermavault website.

With some improvements like a built-in temperature monitor, the surgeon added, "It will be helpful, definitely useful in the remote places, the villages."

 Some salts have a cooling effect when dissolved in water because when those salts dissolve, the charged atoms, or ions, that make them up break apart. That separation requires energy, which the ions pull from the environment, cooling the water around them.

Chaudhary, Ladhania, and Jain searched the internet to make a list of about 150 salts that might work, then narrowed it down to about 20 that seemed most efficient.

They then borrowed a lab at the Indian Institutes of Technology to test those 20 salts. To their disappointment, none of those salts cooled the water enough.

"While we did scour through the entire internet to find the best salt possible, we kind of just ended up back to our ninth-grade science textbook," Chaudhary said.

Finally, the trio found that ammonium chloride maintained temperatures of around 2 to 6 degrees Celsius (about 35 to 43 degrees Fahrenheit), which is ideal for many vaccines.

Adding barium hydroxide octahydrate to the mix produced sub-zero Celsius temperatures. This is ideal for some vaccines and transplant organs.

About three months later, the boys built a prototype and started testing it in local hospitals.

The Thermavault is an insulated plastic container with a copper wall lining the inside, where the vaccines or organs would sit. The cooling solution, made by dissolving the salts in water, is poured into a space between the plastic outer wall and its copper inner wall.

Usually, cold boxes are used for bringing vaccines to rural areas which rely on simple ice packs.

The ammonium chloride solution used in the Thermavault is reusable in the field without electricity. The trio said it would not need a freezer to pull ice from. 

The Earth Prize, awarded by The Earth Foundation, is an annual environmental sustainability competition for secondary education students from each world region. Chaudhary, Ladhania, and Jain of Indore won the prize for Asia. A global winner will be chosen by public vote, which closes on April 22.

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