Solar water heater
The space between the double glass is in vacuum and therefor the heat is held extremely well (think of a thermos).
A special absorbing coating has been applied to the inner wall, which converts infrared radiation into heat in the case of diffuse light (clouds).
The upper, copper end of the Heat Pipe is pushed into the collector and the heat is transferred to the flowing water.
Even when it's minus 20 degrees, this collector delivers - if enough radiation - hot water.