TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Components: The temperature-controlling and temperature-keeping devices are a solar heat pump system comprising a solar radiation plate, a heat-insulating layer, a heat pump machine unit, a temperature-controlling circulation pump, a heat storage device, a radiation device and a temperature-controlling controller. The temperature of the heat supplying medium in the heat storage device of the temperature-controlling and temperature-keeping devices is 50-80 degrees C. The stirring device comprises a stirring shaft passing through the whole tank body, a stirring arm and an impeller blade at the end of the stirring arm, where the stirring shaft is an electric stirring shaft. The stirring shaft is a closed hollow shaft, where the hollow part is filled by gas or air. The stirring arms are evenly distributed at periphery in radial direction of the stirring shaft; where the opposite angle alpha between the adjacent two stirring arms in the radial direction is 30-90 degrees . The stirring arms are distributed in transverse direction of the shaft, and the density of stirring arms at the inlet and the outlet is high. The stirring arms are distributed in middle, and one end of the stirring arm far away from the shaft is provided with an impeller blade. The heat exchanging device comprises multiple groups of heat exchangers, where each group of the heat exchangers is formed by connecting multiple heat exchanging water covers or multiple heat exchanging pipes in series. One end of each group of the heat exchangers is connected with the heat exchanging pipe of the temperature-controlling and temperature-keeping device through the control valve, and the other end of each group of heat exchangers is connected with the reflowing pipe of the temperature-controlling and temperature-keeping device. The multiple groups of the heat exchangers are evenly on the outer side wall of the horizontal fermentation device, where each group of heat exchangers is formed by connecting at least two heat exchanging water covers or at least two heat exchanging pipes in series. The temperature-measuring device comprises at least two temperature automatic monitoring probes, and more than two temperature automatic monitoring probes are evenly distributed along the tank body. The probes are 0.3-1 meter deep in the horizontal fermentation device. The horizontal fermentation device is a steel structure, where the heat exchanging device is connected on the outer wall of the fermentation tank or the fermentation tank is a reinforced concrete structure. The heat exchanging device is at the bottom and side wall of the fermentation tank, and is covered by using a plain concrete layer or a solar radiation plate. The step (a) comprises heating and keeping temperature of the horizontal fermentation device, where the temperature is controlled through the reflowing of the residue generated in the step (b).