Experimental study on the transient response of a solar micropower thermoelectric generator using wet-fabric evaporative cooling

Efficient cooling of the shadowed side of concentrated solar thermoelectric generators (STEGs) remains a major challenge, particularly at the micropower scale, where active cooling is not practical because its power consumption can exceed the power generated. Passive cooling using a simple heat sink is inadequate to maintain the necessary temperature difference. This challenge becomes even more critical when the application targets only the transient impulse period of the TEG (i.e. immediately after exposure to a heat source before output declines to steady state). Hence, this study experimentally investigates the transient response of a solar-driven micropower TEG equipped with an innovative ultrathin self-wicking passive fabric cooling system and compares its performance with a conventional finned heat sink. The fabric, coated with a hydrophilic layer, passively draws water to its surface, forming a thin film that enhances cooling through evaporation. Using a parabolic dish collector to focus sunlight, key parameters including hot- and cold-side temperatures, generated current, heat losses, and conversion efficiency were measured at one-second intervals from initial exposure through steady-state operation. The results demonstrate that, while the hot-side temperature stabilizes near 92 °C in both cases, the wet fabric keeps the cold side over 10 °C cooler than the heatsink, sustaining a larger temperature gradient. This translates into around 14% higher peak current in the transient stage and 147% greater steady-state current. Heat-loss analysis further confirmed that, although the heatsink rejected more sensible heat, the wet membrane achieved superior performance through latent evaporative cooling. Overall, the study establishes wet-fabric cooling as a highly effective passive alternative to conventional heatsinks for solar-driven TEGs under natural convection condition. By leveraging evaporative cooling, it enhances both impulse power and long-term output, offering strong potential for powering portable devices, off-grid systems, and IoT applications that rely on intermittent bursts of energy.