If you ignore the price issue heat pipe solar collector may be the best one for us since heat pipe solar collector features advantages: (1) it can transfer heat 1000 time faster than other types of sola collector. (2) The pipe will not freeze even though it works in an extremely cold weather. (3) Its working pressure suited for existing government cold water supplier which working pressure is 6.0bar and 9.0bar for testing.(4) It is safer than other types of solar collector because there's no water in it.(5) The highest working temperature is almost at 350 degree. (6) The storage tank is large so it can provide enough energy.