Abstract: The experimental study of natural convection for solar collectors with different coating materials and being equipped with guide plate is carried out step by step through the experimental platform of solar-assisted fuel cells under the research background of renewable total energy systems, which mainly include solar energy comprehensive utilization, solid oxide fuel cells, gas turbine and Kalina refrigeration cycle. The three-dimensional mathematical model on natural convection and forced convection of solar collectors is established to study the flow and heat transfer data with the field synergy and entransy principle on the basis of experimental verification. The natural convection results show that the thermal efficiency and the entransy increment rise gradually with the absorption rate increasing from 0.95 to 1.0 and the emission rate decreasing from 0.06 to 0.16, and the thermal efficiency of experiment for high absorption is 1.17% higher than that of low absorption. The thermal efficiency of experiment for solar collectors increases by 2.17% after equipped with guide plate, because the mixed flow in the vacuumvacuum tube disappears and the guide plate strengthens the flow at the bottom of the vacuum tube. The reasonable plate thickness of guide plate for all-glass vacuum tube water heaters is 2 mm, the reasonable plate length of guide plate is 60-100 mm distance from the bottom of the vacuum tube, and the reasonable position of guide plate is 16-20 mm above the axial line of the vacuum tube. The forced convection results show that the Reynolds number and the Nusselt number decrease gradually after the fluent flow into manifold but the Reynolds number and the Nusselt number increase gradually at the exit of manifold. Although the fluent is extremely volatile along the vacuum tube, the Reynolds number and the Nusselt number of horizontal double collectors are higher than that of vertical single collector. The angle between speed vector and temperature gradient vector is 0° with downward fluid and 180° with upward flow, because the collector overall temperature is gradually reduced from vacuum tube bottom to manifold. It makes more fluid absorb the bottom heat, because the internal flow of vacuum tube is smooth and the mixed flow in vacuum tube disappears. Manifold velocity gradually decreases because there is backflow interiorly, but temperature increases because fluid absorbs solar radiation, and the field synergy in collector outlet is higher than others because temperature field is consistent with velocity field according to numerical simulation. Although the entransy increments of vertical single collector and horizontal double collectors are negative values in initial period, they gradually rise with the heat time increasing. There are 2 parts for entransy dissipation in the vacuum tube. The entransy dissipation of horizontal double collectors (from 0.2 to 1.8 m) is less than that of vertical single collector along the vacuum tube axis because the definite condition is to give heat flux boundary. The entransy dissipation of horizontal double collectors (from 0 to 0.2 m) is less than that of vertical single collector along the vacuum tube axis because the definite condition is constant temperature when hot water in vacuum tube flows into water tank and heat transfer occurs between hot and cold water. Enhancement of heat transfer effect of horizontal double collectors is better than that of vertical single collector, because its entransy increment is higher than that of vertical single collector and its entransy dissipation is better than that of vertical single collector. It is determined that the solar collectors with guide plate can be adopted in natural convection and the horizontal double collectors can be employed in forced convection in the thermal field of solar-assisted fuel cells with low and medium temperature.