Modeling and optimization of solar thermoelectric generators for terrestrial applications

In this paper we introduce a model and an optimization methodology for terrestrial solar thermoelectric generators (STEGs). We describe, discuss, and justify the necessary constraints on the STEG geometry that make the STEG optimization independent of individual dimensions. A simplified model shows that the thermoelectric elements in STEGs can be scaled in size without affecting the overall performance of the device, even when the properties of the thermoelectric material and the solar absorber are temperature-dependent. Consequently, the amount of thermoelectric material can be minimized to be only a negligible fraction of the total system cost. As an example, a Bi[subscript 2]Te[subscript 3]-based STEG is optimized for rooftop power generation. Peak efficiency is predicted to be 5% at the standard spectrum AM1.5G, with the thermoelectric material cost below 0.05 $/W[subscript p]. Integrating STEGs into solar hot water systems for cogeneration adds electricity at minimal extra cost. In such cogeneration systems the electric current can be adjusted throughout the day to favor either electricity or hot water production

A review of cermet-based spectrally selective solar absorbers

Spectrally selective solar absorbers harvest solar energy in the form of heat. Solar absorbers using cermet-based coatings demonstrate a high absorptance of the solar spectrum and a low emittance in the infrared (IR) regime. Extensive work has been done to optimize cermet-based solar absorbers to achieve high performance by exploring different cermet (ceramic–metal composite) materials and film configurations through different preparation techniques such as electrodeposition, sputtering, pulsed laser deposition, and solution-based methods. In this article, we review the progress of cermet-based spectrally selective absorbers with high solar absorptance and low thermal emittance, such as Cr[subscript 2]O[subscript 3], Al[subscript 2]O[subscript 3], AlN, SiO[subscript 2], and ZrO[subscript 2] based cermets as absorption layers. We also present an outlook for cermet-based spectrally selective absorbers with high thermal stability and high conversion efficiency from sunlight to heat.United States. Dept. of Energy (SunShot CSP Grant Award DE-EE0005806

Optical cavity for improved performance of solar receivers in solar-thermal systems

A principal loss mechanism for solar receivers in solar-thermal systems is radiation from the absorbing surface. This loss can be reduced by using the concept of directional selectivity in which radiation is suppressed at angles larger than the incident angle of the sunlight striking the absorber. Directional selectivity can achieve efficiencies similar to high solar concentration, without the drawbacks associated with large heat fluxes. A specularly reflective hemispherical cavity placed over the absorber can reflect emitted radiation back to the absorber, effectively suppressing emission losses. An aperture in the cavity will still allow sunlight to reach the absorber surface when used with point focus concentrating systems. In this paper the reduction in radiative losses through the use of a hemispherical cavity is predicted using ray tracing simulations, and the effects of cavity size and absorber alignment are investigated. Simulated results are validated with proof of concept experiments that show reductions in radiative losses of more than 75% from a near blackbody absorber surface. The demonstrated cavity system is shown to be capable of achieving receiver efficiencies comparable to idealized spectrally selective absorbers across a wide range of operating temperatures.United States. Dept. of Energy (“Concentrated Solar Thermoelectric Power”, a DOE SunShot CSP Grant, under award number DE-EE0005806

Concentrating solar thermoelectric generators with a peak efficiency of 7.4%

Concentrating solar power normally employs mechanical heat engines and is thus only used in large-scale power plants; however, it is compatible with inexpensive thermal storage, enabling electricity dispatchability. Concentrating solar thermoelectric generators (STEGs) have the advantage of replacing the mechanical power block with a solid-state heat engine based on the Seebeck effect, simplifying the system. The highest reported efficiency of STEGs so far is 5.2%. Here, we report experimental measurements of STEGs with a peak efficiency of 9.6% at an optically concentrated normal solar irradiance of 211 kW m⁻², and a system efficiency of 7.4% after considering optical concentration losses. The performance improvement is achieved by the use of segmented thermoelectric legs, a high-temperature spectrally selective solar absorber enabling stable vacuum operation with absorber temperatures up to 600 °C, and combining optical and thermal concentration. Our work suggests that concentrating STEGs have the potential to become a promising alternative solar energy technology.United States. Department of Energy (DE-EE0005806)Solid-State Solar-Thermal Energy Conversion Center (DE-SC0001299)Solid-State Solar-Thermal Energy Conversion Center (DE-FG02-09ER46577

Electrocatalytic hydrogen evolution using amorphous tungsten phosphide nanoparticles

Amorphous tungsten phosphide (WP), which has been synthesized as colloidal nanoparticles with an average diameter of 3 nm, has been identified as a new electrocatalyst for the hydrogen-evolution reaction (HER) in acidic aqueous solutions. WP/Ti electrodes produced current densities of −10 mA cm^(−2) and −20 mA cm^(−2) at overpotentials of only −120 mV and −140 mV, respectively, in 0.50 M H_2SO_4(aq)

Enhancement of thermoelectric performance in n-type PbTe1−ySey by doping Cr and tuning Te:Se ratio

Lead telluride and its alloys have been extensively studied for medium temperature thermoelectric applications due to decent figure-of-merit (ZT) at temperature close to 900 K. However, little emphasis has been given to improve the ZT near room temperature. In this investigation, we report a systematic study of Cr doping in PbTe[subscript 1−y]Se[subscript y] with y=0, 0.25, 0.5, 0.75, 0.85, and 1. We found the peak ZT temperature increased with increasing concentration of Se. The highest ZT of ~0.6 at room temperature in Te-rich Cr[subscript 0.015]Pb[subscript 0.985]Te[subscript 0.75]Se[subscript 0.25] was obtained due to a lowered thermal conductivity and enhanced power factor resulted from high Seebeck coefficient of about −220 µV K[superscript −1] and high Hall mobility ~1120 cm[superscript 2] V[superscript −1] s[superscript −1] at room temperature. A room temperature ZT of ~0.5 and peak ZT of ~1 at about 573–673 K is shown by Se-rich sample Cr[subscript 0.01]Pb[subscript 0.99]Te[subscript 0.25]Se[subscript 0.75]. This improvement of the room temperature ZT improved the average ZT over a wide temperature range and could potentially lead to a single leg efficiency of thermoelectric conversion for Te-rich Cr[subscript 0.015]Pb[subscript 0.985]Te[subscript 0.75]Se[subscript 0.25] up to ~11% and Se-rich Cr[subscript 0.01]Pb[subscript 0.99]Te[subscript 0.25]Se[subscript 0.75] up to ~13% with cold side and hot side temperature at 300 K and 873 K, respectively, if matched with appropriate p-type legs

The Archaeology of a Discipline and the Discipline To Come

A review of Michael Allan's "In the Shadow of World Literature.