How does a “vacuum tube collector” work?

A vacuum tube collector is made up of rows of parallel, transparent glass tubes. Each tube consists of a glass outer and glass inner tube. The inner tube is covered with a selective coating that absorbs solar energy well but inhibits radiative heat loss. The air is withdrawn ("evacuated") from the space between the two glass tubes to form a vacuum, which eliminates conductive and convective heat loss.

What does “thermosiphon” mean?

Due to the larger proportion of hot water to cold water, cold water flows downwards and hot water moves upwards. Water will be heated continuously and the hot water will be kept in the storage tank. As the tank is higher than the collector and higher than your shower or bath tub, the thermosiphon system doesn't need a pump to supply your house with hot water.

Sunlabob gives a 5-year warranty for the collector and the tank.