EVACUATED TUBE SOLAR PANELS
The advantage this design has over the flat-plate type is that the constant profile of the round tube means that the collector is always perpendicular to the sun's rays and therefore the energy absorbed is approximately constant over the course of a day. Ideally the panel wants to face south, so it can catch light all day, however it will still function well if it is at South East or South West. When this is not possible, it is recommended to have two panels, one facing East and the other facing West.
Although they work best in direct sunlight evacuated tubes do not rely on it to function. They work much like a thermos flask. In a double walled tube there are two layers of glass which has a vacuum between them. This is shown on the diagram below with the light grey area.
Cross section of an Evacuated Solar Tube