Duda Solar Water Collector - 30 x 58mm x 1800mm Vacuum tubes - Winter Resistant w/45 degree stand30 x Duda 58mm x 1800mm Vacuum tubes for Active Solar Systems Winter Resistant Glycol System & Separated Tank SRCC Certified for 30% Federal Tax Rebate Standard 45 degree Stand A pump is utilized to transfer heat from the collectors to the water to be used, which is stored in a remote location away from the collector. This is also commonly known as a split tank system. The best tanks to use in these active systems have built in copper heat exchanger