NOVELTY - A solar collector, comprises first flat plate for collecting solar energy; second flat plate which fixed along edges (31, 32, 33) on underside of first plate; space between the two plates; an inlet for feeding a liquid to space; and outlet for discharging liquid from space. The liquid can flow from inlet to outlet. The space between the plates is formed in that a profile defining zigzag form of space is arranged in at least one of plates.    USE - The solar collector is used for storing solar energy in a liquid medium.    ADVANTAGE - The space provides a high heat transfer from the plate to the medium such as water. A relatively high throughflow speed is also possible. These aspects provide the option of providing the water with a relatively high final temperature at a relatively low level irradiation, where efficiency is optimal. The storage container can be manufactured in relatively simple manner. The storage container is here very light, durable and insulates well. This is an open vessel where the whole collector system can be given a pressureless form. The collecting efficiency can be increased in that irradiation can be effected at an optimum angle.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (A) a method for manufacturing a solar collector, comprising manufacturing plates for an upper side and an underside of the solar collector; arranging a profile comprising edges and ribs in at least one of the plates, which profile, after assembly of the heat exchanger, defines a space on the inside of the heat exchanger, which space has a zigzag form for allowing a fluid to flow; and fixing the plates to each other along the ribs and edges by laser welding;    (B) a storage container for a liquid, comprising an inner wall and an outer wall, each comprising a bottom wall for the storage container, which are molded from a plastic; a closing cover for closing the container which is also double-walled and filled with a foaming insulating mechanism; passage openings for passage of supply and discharge conduits for the liquid; passage openings for passage of supply and a discharge for a heat exchanger; and an insulating unit such as PUR foam which fills the space between the inner wall and the outer wall by foaming during or after introduction between the inner wall and the outer wall;    (C) a system comprising a solar collector; a storage container; and conduits for transporting a liquid from the storage container to the collector and vice versa; and a pump for driving the liquid through the conduits;    (D) a method for manufacturing a storage container for a liquid, comprising introducing a liquid curable plastic into a mold defining an outer wall, an inner wall and a connection; rotating the mold such that the plastic is distributed over the whole surface of the mold; curing the plastic; and arranging a foaming, heat-insulating plastic in the space between the inner wall and outer wall, where the plastic fills the whole space between the inner wall and the outer wall;    (E) a sun following system for optimizing the orientation of a solar collector relative to the sun during the course of a day, comprising a support; a first rotation frame which is arranged in the frame and which is mounted about a first rotation axis on the support frame; a second rotation frame which is arranged in the first rotation frame by a second rotation axis for mounting of a solar collector; drive unit for driving the first and second rotation frames for movement; and a controller for controlling the drive unit; and    (F) a method for orienting a collector in a direction considered optimal relative to incident solar radiation by device, comprising determining the direction of incident solar radiation, rotating the solar collector in a first direction to this direction, and rotating the solar collector in a second direction to this direction.    DESCRIPTION OF DRAWING(S) - The figure is a top view of solar collector.    Ribs (21)    Barriers (26, 27)    Flap (28)    Edges (31, 32, 33)