3 Indian teens turn Class 9 science lesson into salt-powered fridge, win Rs 11.9 lakh

Three Indore teenagers transformed a Class 9 science lesson into an electricity-free refrigerator. Their salt-and-water invention won the 2025 Earth Prize for Asia and could support vaccine transport.

In Short

• Their research screened 150 salts before laboratory testing narrowed viable compounds
• A teacher suggested two compounds already covered in their Class 9 textbook
• Hospital trials kept vaccines cool inside Thermavault for 10 to 12 hours

For Dhruv Chaudhary, Mithran Ladhania and Mridul Jain, a school science lesson became the starting point for an invention that could help transport vaccines and medicines to remote villages.

The three teenagers from Indore, Madhya Pradesh, developed Thermavault, a refrigerator that uses salt and water to generate cooling without electricity, batteries or ice.

The idea emerged after they learnt about the difficulties of storing and transporting Covid-19 vaccines in rural areas without reliable electricity. With all three having parents working in the medical field, they became familiar with the challenges faced by healthcare workers in delivering temperature-sensitive medical supplies to remote locations.

Their invention won the 2025 Earth Prize for Asia, earning them $12,500 in prize money. The team plans to use the award to manufacture 200 units and send them to 120 hospitals for testing.

FROM 150 SALTS TO A NINTH-GRADE SCIENCE CONCEPT

The interesting part of the invention lies in the science behind it.

Certain salts produce a cooling effect when dissolved in water. During the process, the salts separate into electrically charged particles called ions. This separation requires energy, which is drawn from the surroundings, lowering the temperature of the water.

The students initially researched around 150 salts online before narrowing their list to approximately 20 promising options. They then borrowed laboratory facilities at the Indian Institutes of Technology (IIT) to test the compounds.

However, their initial experiments did not produce the cooling effect they needed.

The breakthrough came when their teacher suggested two compounds that were covered in their Class 9 science textbook: ammonium chloride and barium hydroxide octahydrate.

Their experiments showed that ammonium chloride could maintain temperatures between 2 and 6 degrees Celsius, a suitable range for storing many vaccines. Adding barium hydroxide octahydrate could bring temperatures below zero, potentially making the technology useful for certain other vaccines and transporting transplant organs.

Within approximately three months of identifying the right combination, the teenagers had developed a working prototype and begun testing it at local hospitals.

HOW DOES A FRIDGE RUN WITHOUT ELECTRICITY?

Thermavault is designed as an insulated plastic container with a copper lining on the inside. Medical supplies are placed within the copper-lined section, while a salt-and-water cooling solution occupies the space between the inner and outer walls.

Unlike conventional vaccine cold boxes that depend on ice packs, the device uses the cooling reaction of dissolved salts.

Another feature is the possibility of reusing the cooling material without electricity. The ammonium chloride solution can be removed from the container, heated to evaporate the water and leave the salt behind. The recovered salt can then be dissolved in fresh water to produce the cooling effect again.

According to Business Insider's report, a doctor who tested the device at V One Hospital in Indore found that vaccines could be kept inside Thermavault for around 10 to 12 hours.

The team believes the invention could eventually help transport vaccines, medicines and other temperature-sensitive medical supplies to places where conventional refrigeration is difficult.

FROM A STUDENT PROJECT TO A GLOBAL RECOGNITION

Winning the Earth Prize has given the three teenagers an opportunity to take their classroom experiment further.

The award recognises teenagers working on environmental projects, with regional winners selected from across the world. Chaudhary, Ladhania and Jain received the Asia award in 2025.

Their next goal is to obtain Performance, Quality and Safety certification through the World Health Organization (WHO). They also hope to present the technology to Gavi, an international alliance that works to improve access to vaccines.

The project also highlights how school-level science can extend beyond textbooks and laboratory experiments. A concept introduced in a classroom, when combined with research, experimentation and guidance from teachers, can become the foundation for solving problems outside school.

For these three students, a lesson on salts and chemical reactions did not remain confined to an examination. It became an attempt to address a healthcare challenge that affects communities far beyond their classroom.

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