Solar Hot Water Tank, Drainback Tank, and pumps. AET DX-96-120 - Alternative Energy Technologies Drainback 96 square feet collector area (3 4x8 panels) 120 gallon storage tank. The drainback tank is 15 gallons. The drainback tank protects from both freeze and overproduction (My system is oversized and is able to run off-grid 98% of the time).