Understanding Solar Vacuum Tube Technology Used for Solar Water Heaters Solar vacuum tubes have been used since the early 1900s. But they’re used for solar heating purposes. Nowadays, most solar water heaters utilize solar vacuum tubes for their operation. You must be careful as the vacuum tube temperature can be two times higher than flat panel collectors. Solar vacuum tube technology works like a thermos bottle that traps heat inside and provides insulation barrier against heat loss. Vacuum tubes work effectively in cold climates especially the places that experience freezing temperatures. Generally, Northern Lights use SunRain solar evacuated tubes for solar water heating purposes. They utilize a copper heat pipe in the center of the tube.