solar vacuum tube 1.Excellent performance of absorbing but low loss 2.Excelleng resistance of burst 3.Excellent resistance of 4. Reducing the fouling on the tube wall, keeping water clean. 5. Evacuated tubes are aligned in parallel, the angle of mounting depends upon the latitude of your location. In a North South orientation the tubes can passively track heat from the sun all day. In an East West orientation they can track the sun all year round. 6. The efficiency of a evacuated water heater is dependent upon a number of factors, one important one being the level of evacuated radiation (insolation) in your region.