Guwahati: In the sun-drenched summers of Ladakh and Himachal, Indian scientists have found a novel solution to the region’s freezing winters — bottle the sunlight. Researchers from the Indian Institute of Technology Bombay (IIT Bombay) have developed a prototype system that stores solar heat using strontium bromide, a salt compound, and releases it months later — offering a clean, smoke-free alternative to diesel heaters and firewood that many Himalayan communities still rely on.
The project, led by Dr Sandip Kumar Saha with collaborators Dr Rudrodip Majumdar and Dr Chandramouli Subramaniam, uses a thermochemical storage technique. During the summer, solar thermal collectors heat air, which is then used to dehydrate strontium bromide hexahydrate, turning it into a heat-storing monohydrate. In winter, humid air triggers a reverse reaction, rehydrating the salt and releasing stored heat in the process.
“The starry nights in the Himalayas are breathtaking, but the cold can be unforgiving,” recalls Dr Majumdar, who worked on the system as a postdoctoral fellow at IIT Bombay. “I saw people trekking long distances for firewood. Diesel is the only fallback, but it’s expensive and polluting. We wanted to offer a better option.”
A single modular unit — roughly the size of two LPG cylinders — can store up to 500 kilowatt-hours of energy, enough to heat a small home for four months, according to the team. These units are designed to be portable and rugged, with glass wool insulation to withstand Himalayan weather. Importantly, they can be charged in solar-rich regions like Gujarat or Rajasthan and transported to hill towns before winter sets in.
Unlike conventional batteries, the thermochemical salt doesn’t degrade easily. The researchers have successfully tested six full charge-discharge cycles in the lab and estimate the system can last for 500–600 cycles — or several years of use.
The study, published in Applied Thermal Engineering, found the Levelized Cost of Heating (LCOH) to range between ₹33 and ₹51 per kilowatt-hour across cities like Dehradun, Shimla, Srinagar, and Shillong — cheaper than diesel, especially when transportation and carbon penalties are included. In Leh, the cost dropped to just ₹31/kWh.
“We’re not reinventing the wheel,” says Dr Saha. “Solar collectors are proven. The real challenge was stabilising the salt and packaging the technology for daily life.”
The innovation is already being adapted for Indian Army camps at high-altitude, sub-zero locations, where diesel logistics are particularly challenging.
While the technology holds promise, scaling it for household use will require field trials, policy support, and local participation. Thermochemical storage is still a relatively new field, with pilot deployments in countries like Germany, but little real-world application in India.
“Energy poverty should not exist in the 21st century,” says Dr Majumdar. “With the right support, we can ensure even remote mountain villages are energy secure — without harming the environment.”
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