solar thermal collector,25mm Hail Resistance Includes Vacuum Tubes, Heat Pipes, Manifold, Frame,Silica Gel. solar thermal collectorSpecifications: Manifold: ... of vacuum tube: SS-C/CU 3-high vacuum tubes Heat preservation: 72 hours Hail resistance: 25mm Insulation: polyurethane/rock ... rate: 0.1L/minute/tube or 0.026G/minute/tube Heat pipe: anti-freezing less than -35 degrees Glass tube dimensions: ...