Abstract: A latent heat storage tank is filled with antifreeze solution such as ethylene glycol, propylene glycol, calcium chloride and a plurality of bundles of cylindrical latent heat containers in the form of tubes or pipes which float perpendicularly to the antifreeze surface. The antifreeze solution is circulated by a refrigerator provided outside the latent heat storage tank. Each cylindrical latent heat container contains water or other liquid which is cooled to become ice by said antifreeze solution which has been cooled by said refrigerator driven by inexpensive night time electric power.