NOVELTY - Increasing biogas output by solar energy, where a circulating loop of hot medium water is formed by a biogas fermenting kettle, a solar energy collector, a heat-insulating water box, a heat exchanger and a hot medium water circulating pipe; the heat exchanger is arranged inside the biogas fermenting kettle and is fixed between the fermented liquid level and the kettle bottom; a hot medium water circulating pump is laterally connected between the heat exchanger and the heat-insulating water box; and the heat exchanger is provided with a mechanical descaling device.    USE - The method and device are used for increasing biogas output by solar energy (claimed).    ADVANTAGE - The method and device are capable of realizing a purpose of recycling the hot medium water, eliminating scaling of the heat exchange pipe, increasing the heating efficiency, guaranteeing stable biogas output of the biogas fermenting kettle in four seasons, and prolonging the service life.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is a device for strengthening biogas output by the solar energy, where the mechanical descaling device is constituted by a descaling ring component capable of moving along the surface of the heat exchange pipe, and a power transmission mechanism for driving the descaling ring component to move; a descaling part of the mechanical descaling device forms a chain wheel group by a chain wheel, two guide chain wheels and a chain; wheel axles of the two guide chain wheels are respectively in fixed connection with the two master hot medium junction pipes; circular parts on the upper part of the multiple descaling ring components are respectively sleeved on the parallel heat exchange pipes and are capable of transversely moving along the outer surface of the heat exchange pipes in a contacted friction manner; the top of each descaling ring component is fixedly connected with a connection rod, and the lower end is hinged with the chain and can be driven by the chain to move transversely.