One of the concerns people have about solar thermal as a means of providing effective space heat is its ability to produce during the winter months. In the U.S. Northeast, the upper plains, and certain parts of the Midwest, winter temperatures can easily dip below zero for extended amounts of time. Well, now we know that solar thermal can get the job done even in some pretty harsh conditions. Thanks to a test conducted in the mountains of northern India, solar thermal has proven its winter mettle.
The real-world test of the solar thermal system was conducted by the Indian Defense Institute of High Altitude Research (DIHAR) at a troop shelter built at Chang La, a mountain pass that stands more than 17,000 feet above sea level. Moreover, tests were conducted during the winter months to see how well the system would perform in providing adequate space heat.
Researchers set up the system to store solar heat during the daylight hours using a phase-change storage tank. The stored energy was then used to produce the heat necessary to keep the shelter warm overnight. Throughout the test period, the ambient temperature inside the 295-square foot shelter remained between 44 and 50° despite exterior temperatures that reached as cold as -22°.
Saving Oil and Diesel
DIHAR officials say there were some points during the test when a diesel generator had to be operated to compensate for temperatures below -22°. Those occurrences were mainly in the coldest months of January and February. Still, the evacuated tube design of the solar thermal system performed well because they rely on ultraviolet “A” (UVA) rays from the sun, not the warm infrared (IR) rays that are not effective in cold or cloudy conditions.
Under normal conditions, the troop shelter is kept warm with wood, diesel and paraffin oil burners. Heating the shelter in the dead of winter consumes hundreds of thousands of gallons of diesel and oil every year. Researchers estimate that using the solar thermal system overnight could save as much as 10 liters of paraffin oil per day for every system installed.
Solar Thermal Suitable for Winter Climates
The solar thermal industry is very pleased with the results achieved by the Indian study. The study proves that our technology is more than suitable for winter climates, even when temperatures dip well below freezing. If an evacuated tube system can generate sufficient heat to keep a Himalayan shelter at 50° despite outside temperatures of less than -20°, imagine how well it might work here in the U.S. where most winter environments are not nearly as harsh
The key to the success of the Indian test was the evacuated tube design of the solar collector panels. Evacuated tubes, which happens to be the same technology the patented SunQuest 250®™ solar thermal collector is based on, make for the most efficient collection and transfer of solar energy for both space heat and hot water.
Evacuated tubes are glass tubes with an enclosed absorption surface surrounded by a vacuum. That surface absorbs solar energy which is transferred to a thermal liquid to be then sent to a heat exchanger for heat extraction. Extracted heat is either used immediately for space heat or hot water or forwarded to a highly insulated storage tank for later use.
Solar thermal space heat built around evacuated tube solar collector panels has proven up to the task in harsh winter environments. It has worked so well that DIHAR plans to begin installing the systems in several hundred buildings. All being well, what they have learned will improve the technology worldwide. In the meantime, there are a lot of buildings here at home that would benefit from a solar thermal solution for space heat and hot water.
1.Solar Thermal World – http://www.solarthermalworld.org/content/india-vacuum-tube-system-pcm-storage-tank-heats-troop-shelter