To solve the global energy and freshwater crises, interfacial solar evaporation has received more and more attention. However, constructing 3D evaporators in a facile and cost-effective way is still a crucial challenge. In this work, we propose a cost-effective approach to construct 3D biodegradable foams by combining melt blending and surface coating for simultaneous solar-vapor and thermoelectricity conversion. Benefiting from the fast water supply and super-photothermal conversion, the foam attains an evaporation rate of 4.33 kg m-2 h-1 and electric power density of 0.8 W m-2 under 1 sun irradiation. In outdoor environments, the electricity produced by eight devices can power a small fan or a LED display. Moreover, the foam can be degraded in 2% NaOH solution after use. The proposed method presents a promising approach for the mass production of 3D evaporators to solve freshwater and electricity shortages in off-grid or remote areas.