• Energy Research

Abstract A mathematical model was established to analyze the heat transfer and thermal stress behavior of a segmented thermoelectric generator (STEG). Temperature gradient-induced thermal stress was studied with non-uniform steady heat flux (including Gaussian heat flux and parabolic heat flux), uniform heat flux, and transient heat flux applied to the surface of the hot end, respectively. The results showed that the heat fluxes applied to the hot end lead to uneven temperature distribution on the whole surface of the thermoelectric generator. Thermal stress in the horizontal direction is the major cause of fatigue damage and failures of STEG. When the heat concentration ratio increases, the horizontal temperature uneven distribution will also increase. The thermal stress on the hot end varied significantly reaching the maximum value as high as 16.3 GPa. In addition, the transient heat stress in the system gives rise to periodic stress fluctuations up to 0.6 GPa, which can seriously affect the life cycle of the system.

Abstract We introduce a novel optofluidic solar concentration system based on electrowetting tracking. With two immiscible fluids in a transparent cell, we can actively control the orientation of fluid–fluid interface via electrowetting. The naturally-formed meniscus between the two liquids can function as a dynamic optical prism for solar tracking and sunlight steering. An integrated optofluidic solar concentrator can be constructed from the liquid prism tracker in combination with a fixed and static optical condenser (Fresnel lens). Therefore, the liquid prisms can adaptively focus sunlight on a concentrating photovoltaic (CPV) cell sitting on the focus of the Fresnel lens as the sun moves. Because of the unique design, electrowetting tracking allows the concentrator to adaptively track both the daily and seasonal changes of the sun’s orbit (dual-axis tracking) without bulky, expensive and inefficient mechanical moving parts. This approach can potentially reduce capital costs for CPV and increases operational efficiency by eliminating the power consumption of mechanical tracking. Importantly, the elimination of bulky tracking hardware and quiet operation will allow extensive residential deployment of concentrated solar power. In comparison with traditional silicon-based photovoltaic (PV) solar cells, the electrowetting-based self-tracking technology will generate ∼70% more green energy with a 50% cost reduction.