This invention is an improvement to the shape of liquid storage tanks, in particular to unpressurized molded polymer tanks used for thermal storage in solar systems. All aspects of this invention are well suited to solar storage tanks, and individual aspects are suited to other liquid tank applications. This invention provides a formed horizontal extension at the bottom of the tank. From the top of this lower extension, a hollow vertical stub provides a reliable connection to a circulator pump. Thermal performance is enhanced by ensuring the lowest and coolest water is delivered to the array of rooftop solar collectors without entraining debris from the bottom of the tank. At the top of the tank, a similar horizontal extension is used to distribute hot water returning from the solar collectors. Flow velocity is eliminated and a curving lower edge allows return water to find the matching thermocline to avoid de-stratifying.
STATEMENT REGARDING STATE OF CALIFORNIA SPONSORED RESEARCH OR DEVELOPMENT
 This invention was made with State of California support under California Energy Commission grant number PIR-08-012. The Energy Commission has certain rights to this invention.