Air bubbles lift rooftop solar-hydrogen output in India

On a rooftop in Tiruchengode, Tamil Nadu, a small solar setup spent seven summer days doing two jobs at once: producing electricity and making hydrogen. Researchers from K.S. Rangasamy College of Technology and SRM Institute of Science and Technology report that injecting air bubbles into the circulating coolant raised the system’s reported electrical efficiency to around 11.1% and hydrogen production to approximately 15.5 ml/min.

The device combines a photovoltaic-thermal system — a solar panel that also collects heat — with water cooling and a Hoffman electrolyzer fitted with platinum electrodes. A spiral-flow thermal collector sat behind the module. Air was injected into the circulating water at mass flow rates of 0.006, 0.008, and 0.011 kg/s, allowing the researchers to test whether bubbles improved cooling independently of the hydrogen-generation process.

The strongest result came at 0.011 kg/s. Peak thermal efficiency reached around 45.5%, compared with about 30% for the air-cooled photovoltaic-thermal configuration. Electrical efficiency was around 11.1%, versus 8.1% for the conventional photovoltaic module. Hydrogen output reached approximately 15.5 ml/min, compared with a maximum of 8.3 ml/min for the conventional setup.

The tests used the same 20 W, 36-cell polycrystalline module across four configurations: conventional photovoltaic, air-cooled photovoltaic-thermal, water-cooled photovoltaic-thermal, and water cooled with injected air bubbles. Measurements covered solar irradiance, temperatures, flow rates, electrical output, and hydrogen production under outdoor conditions. The researchers also tested the systems at constant irradiance of 600 W/m² and an ambient temperature of 26 C.

So what changes in practice? The experiment points to one integrated way of extracting more value from a compact solar installation: water removes heat from the panel, bubbles help that heat transfer, and the connected electrolyzer produces hydrogen. But this remains a rooftop prototype tested over seven days. The researchers say the optimal injection rate is still unknown for different conditions and system designs, and that advanced control algorithms are needed before the system can manage energy and hydrogen production more effectively.