What is the difference between the 47mm, 58mm and 70mm tubes?
The standard tubes are 47mm, and are of twin wall construction. The 58mm tubes are also twin-walled, but longer (1.8m rather than 1.5m) and wider. This means that for a given number of tubes the 58mm tubes will produce 50% more heat than the same number of 47mm tubes (but the cost is 50% higher too!). The 47mm tubes are easier to transport, and are less fragile in handling due to their shorter length. The 70mm solar tubes are single-walled construction. This is more expensive to manufacture, but provides better performance in extreme conditions. A 10tube 70mm panel should produce around 90% of the output of a 20tube 47mm panel.
