A small defence research lab is actively finding solutions on how to efficiently tap solar energy to keep soldiers’ shelters warm during winters in the Ladakh sector. The Indian army is sitting in an eyeball-to-eyeball confrontation with the Chinese and needs warm habitations. The Defence Institute of High Altitude Research in Leh is developing solar thermal warming technology called Solar Thermal Energy Based Technology for Space Heating (Human Habitation) In High Altitude to keep the shelters warm for soldiers.

A renewable energy-powered solar thermal system has been developed by the Defence Institute of High Altitude Research (DIHAR), Leh to provide heat for shelters in cold, high-altitude environments, ensuring comfortable living conditions.

DIHAR said the power and heating requirements of the Ladakh region are mostly met with fossil fuel-based systems like bukhari (fire pot), Diesel Generator sets etc. The fossil fuels have to be transported to forward locations before the closure of roads from plain areas along with storage of the same.

The Defence Research and Development Organisation (DRDO), in its new mandate, is developing solar thermal energy-based technology for heating habitation units. Temperatures can drop to minus 40 degrees Celsius in Ladakh and Indian army units have to be warmed to plus 20 degrees Celsius. But Ladakh is endowed with sunshine and defence scientists are using solar energy which is then stored in thermi-fluids to provide heating at night. Special anti-freeze fluid is used to make sure the system does not freeze.

Mr Sarfraz Nazir, Scientist, Defence Institute of High Altitude Research, Leh told NDTV, “The system has an efficiency of forty per cent and a pilot plant is being made for the Indian Army unit at Hanle.”

According to DIHAR, Ladakh is a high altitude cold arid region with temperatures recorded as low as minus 40 degrees Celsius and the relative humidity ranges between 30 to 40 per cent. Low ambient temperature makes habitation difficult during winter periods without external heat supply. The region has scope for utilization of renewable energy particularly solar energy, for meeting power and thermal energy requirements. Ladakh has high solar irradiance which ranges between 1800 kWh/m2/year to 1900 kWh/m2/year and with an average annual sunshine duration of 7.9 hrs with 300 plus cloud-free days. 

High solar irradiance is when a high amount of solar power shines on a specific area at a given time.

Ladakh has ample scope for utilization of solar thermal energy for applications in space heating during peak winter seasons by installation of solar thermal technology for space heating using the Evacuated Tube Collector (ETC) technology.  

This solar thermal energy-based ETC technology comprises evacuated tube collectors (ETC) containing copper pipes connected in series and transferring thermal energy captured from solar radiation to fluid in contact by highly conductive copper pipes. This space heating system has been installed in an existing shelter of size 32 x 17 x 8 feet at DIHAR Leh. The average temperature inside the shelter has been recorded as 15 to 20 degrees Celsius when the minimum ambient temperature is minus 19 degrees Celsius.

The working mechanism of this technology comprises the evacuated tube collectors that convert the incident solar radiation into thermal energy through a low boiling point phase change material flowing inside a copper tube. The phase change material inside sealed glass tubes changes its phase from liquid to vapour upon receiving solar energy and comes in indirect contact with heat transfer fluid (Glycol water mixture) through copper tubes.

The phase change fluid transfers its thermal energy and changes its phase and settles down, which again on receiving thermal energy from solar irradiance rises and transfers thermal energy to heat transfer fluid. The process repeats and heats the heat transfer fluid throughout the sunny day time. The heated heat transfer fluid flows through insulated pipes and pumps and is stored in a polyurethane foam (PUF) insulated storage tank. The flow of heated fluid is auto-regulated so that its pump operates alternately every half hour throughout the day for extraction of heat from copper tubes containing phase change material (to avoid overload and breakdown). 

The heated fluid stored in the insulated tank is subsequently used to maintain the comfortable habitable temperature (15 degrees Celsius to 20 degrees Celsius) inside the shelter through a combination of insulated pipes, a pump and wall wall-mounted air fan coil unit.

Mr Nazir said “The whole system is automatically regulated with the help of sensors and related accessories to save the energy to prolong the heating effect of the stored thermal energy’.

He added that since the DIHAR plant is a pilot project it has cost about Rs 60 lakhs and is expected to last 15-20 years. It may sound expensive but once the system is installed it requires no fuel for its operation and it is based totally on renewable solar energy in less than three years it can pay back its costs.