Several studies on heat pipes integrated with solar thermal col-lectors have been conducted. Hammad [20] studied flat-plate heat pipe collectors, and the results of his study indicated that the ther-mal efficiency of a heat pipe collector is comparable with that of a water-cooled solar collector. Furthermore, the transient thermal performances of wickless heat pipe, flat-plate solar collectors are affected by various parameters, such as solar radiation intensity, temperature of cooling water, absorber plate material and thick-ness, and the ratio of condenser-section length to total wickless heat pipe length [21]. Hiroshi and Yasuhito [22] designed a vertica