Storage reservoirs for liquids heatable by solar energy

A domestic hot water heater comprising:

• an upright tank having a cold water inlet adjacent the bottom of the tank and a hot water outlet adjacent the top of the tank;
• a separating wall spaced from the bottom and the top of the tank and defining and separating an upper tank chamber and a lower tank chamber, the wall including only two, first and second, spaced apart apertures in respective quadrants of a surface of said wall which fluidly connect the chambers;
• a flow tube in communication with the first aperture and having a length at least equal to half the depth of the lower tank chamber and extending from said wall towards the tank bottom for guiding cold water from the upper tank chamber into the lower tank chamber;
• a heat exchanger positioned in the lower chamber proximate the tank bottom including means for connecting the heat exchanger to a solar energy receiving fluid circuit so that heated fluid from the circuit can flow through the heat exchanger to thereby heat the cold water in the vicinity of the bottom of the tank;
• and auxiliary heating means in the upper chamber for maintaining the water temperature in the upper chamber at a predetermined level above the ambient temperature;
• whereby the water temperature in the lower tank chamber proximate the tank bottom and the heat exchanger is at all times the lower water temperature in the tank so as to maximize the temperature gradient between the heat exchanger operated with solar energy and the surrounding water and to thereby maximize the efficiency of the heat exchanger, and whereby further water at the predetermined temperature level can at all times be withdrawn from the heater.