3 teens invented a salt-powered refrigerator that doesn't need electricity. They're building 200 of them for hospitals to use.

3 teens invented a salt-powered refrigerator that doesn't need electricity. They're building 200 of them for hospitals to use.

Three teenagers designed a mini refrigerator that cools itself with salt and doesn't require an outlet. They're bringing it to hospitals to help transport medical supplies to rural areas without electricity.

Dhruv Chaudhary, Mithran Ladhania, and Mridul Jain live in Indore, India, and all have parents working in the medical field. The boys decided to find a salty refrigeration technique after hearing how challenging it was to bring COVID-19 vaccines to rural areas without electricity.

Their invention, which they call Thermavault, won them the 2025 Earth Prize on Saturday. The award comes with $12,500, which they plan to use to build 200 of their refrigerators and send them to 120 hospitals for testing.

Finding the right cooling salt

Some salts can have a cooling effect when they're dissolved in water.

That's 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, thus cooling the water around them.

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

To their disappointment, none of the salts cooled the water enough.

After all — their teacher recommended trying two different salts: barium hydroxide octahydrate and ammonium chloride.

The trio says they 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 subzero Celsius temperatures, which is ideal for some other vaccines and sometimes for transplant organs.

About three months later, they'd built a prototype and were testing it in local hospitals.

(A mock-up of a Thermavault prototype.Dhruv Chaudhary/Mithran Ladhania/Mridul Jain)

The fridge itself 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 the copper inner wall.

Cold boxes and coolant packs are already in widespread use for bringing vaccines to rural areas without electricity. Those carriers typically rely on simple ice packs.

One advantage of the ammonium chloride solution, the trio of teens said, is that it's reusable in the field without electricity. You can remove the saltwater from the box, boil away the water, and collect the salt in its solid form, ready to dissolve in new water and produce its cooling effect all over again.

Ref: 3 teens invented a salt-powered refrigerator that doesn't need electricity. They're building 200 of them for hospitals to use.