NOVELTY - Producing biogas using solar heat, comprises taking a solar collector system, a digester circulation heating system (4) and a control system (3), and collecting solar heat using solar collector systems, and feeding into digester circulation heating system by tubes, and controlling constant temperature of solar heat by using control system, and heating the digester circulation heating system made of tubes whose inner side walls are surrounded the heating units, or directly heating the digester using heat transfer tubes.    USE - The method is useful for producing biogas using solar heat (claimed).    ADVANTAGE - The method utilizes digesters producing biogas temperature reaching certain range; and prevents the operation during northern winter cold weather, where product is not produced during low temperature conditions.    DETAILED DESCRIPTION - Producing biogas using solar heat, comprises taking a solar collector system, a digester circulation heating system (4) and a control system (3), and collecting solar heat using solar collector systems, and feeding into digester circulation heating system by tubes, and controlling constant temperature of solar heat by using control system, where the solar collector system includes a heat insulation tank (1) and a solar flat plate collectors (2), taking a buffer for saving energy of solar flat plate solar collectors, where an inlet pipe and an outlet pipe of the solar flat plate collectors are parallelly connected to each other, and the solar flat plate collectors has an installation angle of 45 degrees , and the outlet pipe and inlet pipe of the solar flat plate collectors are connected to middle and lower portions of heat insulation tank, and heat insulation tank is located on the solar flat plate collectors, and heating the digester circulation heating system made of tubes whose inner side walls are surrounded the heating units, or directly heating the digester using heat transfer tubes, where one end of the outlet pipe is connected to the bottom of the heat insulation tank by heat transfer tubes which are connected to inlet pipe and side of the heat insulation tank, and the digester circulation heating system is located below the flat plate solar collector.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic representation of the device utilized in the above mentioned method.    Heat insulation tank (1)    Solar flat plate collectors (2)    Control system (3)    Digester circulation heating system (4)