Flat Plate collectors have been commercially available since 1870.  The reason for the invention of the Vacuum Tubes more than 100 years later, is explained by the following diagrams:

The Difference in reflection

Even though a round tube will always be perpendicular to the sun rays, our Vacuum Tubes have 9 extra coatings that prevents reflection like seen in this diagram.  With very intelligent chemical coatings sun rays are prevented from reflecting out of the vacuum tube - they are forced to remain inside and transfer their heat to the water (in the case of a Low Pressure system), or to the Heat Pipe (in the case of a High Pressure System).

With special coatings UV is converted to a heat wave to heat up the water, and Infra-red is converted to a heat wave to heat up the water.  All of the sun's energy is harnessed through this break through in technology.

The Difference in Absorption

A test was done in the United Kingdom that shows how each system is differently effected by the Ambient Temperature.  The reason for the big difference in efficiency is the very reason why the vacuum tube was invented:

Inside a Vacuum Tube there are 2 glass tubes, called the Inner Tube, and the Outer tube.  What separates these 2 tubes is a vacuum.  The reason for this is because if there is no medium to transfer heat to the outside, heat cannot be lost!  This means that when the inner tube is heated up with sun rays, the outside temperature will have no effect on that heating, since a vacuum separates the inner tube from the outer tube.  Therefore, as seen in the diagram below, the advantage of the vacuum tube is that even in winter, or in cold and cloudy weather, water can be heated very effectively, thus giving you a balanced all year production of hot water!

Claims from Flat Plate suppliers that "Vacuum Tube Systems generate too much heat" is therefore misunderstanding the very intent for the technology.  Oversized systems will generate too much heat, irrespective of the technology.  Vacuum Tubes will generate more heat than a Flat Plate in winter - that is the point!  At EfTech we have taken steps to prevent over sizing, so that temperature and pressure problems will not be incurred.