The tubes are made from high strength Borosilicate Glass, they are very strong. The Vacuum is what makes them very efficient, insulating the heat inside from the "cold climates" outside. If the vacuum does fail, then the performance of the tube effectively drops to that of a Flat Plate Collector!
There are 30 tubes in each of our collectors, The most likely time the tube will be damaged is during installation, once its in place, then its very unlikely to break. The tubes are warranted by the factory for 10 years from manufacturing defects.
If a single tube does break, the system continues to function normally (even if the Evacuated tube breaks, it will still produce heat, just not as much. Also to replace the tube, the system does not need to be drained down. Single tubes can be replaced very easily.
If a Flat Plate Collector breaks, the whole house system needs to be drained and the panel removed from the roof and repaired.
It is a common misconception that the tubes will break with hail stones. its like the windshield on your car. You can get hit many times by hailstone or rock chips from the road and your windshield doesn't break.
However if a small stone hits it, at the right angle your windshield can crack. The same will apply to both Flat Plate and Tube type collectors, they can break, but its very unlikely. They can be replaced quite easily.
A recent large hail storm in Calgary (summer 2010) resulted in NON of our tubes breaking. The hail was golf ball sized and bigger but the tubes were OK.
Saying that there is no Guarantee the tubes will not break due to some weather event. We do not guarantee the tubes from breakage like this. Just like your car windshield is not warranted against breakage. You buy insurance to cover these events.
If the Flat Plate Panels break the whole panel needs to be removed from the roof and replaced.
Hail Stones? - These tubes are tough. This video is of Apricus Tubes. The dimensions of our tubes are the same as the apricus tubes. Same thickness, same diameter, same vacuum. Most tubes are made with the same dimensions and are more or less identical. In fact its remarkable how similar the tubes are of most the main manufacturers - you wounder if there is one company making all the tubes!