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Power Devices For Efficient Energy Conversion


Researchers measure the performance of a photovoltaic (PV) device to predict the power the cell will produce. Electrical power is the product of current and voltage. Current-voltage relationships measure the electrical characteristics of PV devices. If a certain "load" resistance is connected to the two terminals of a cell or module, the current and voltage being produced will adjust according to Ohm's law (the current through a conductor between two points is directly proportional to the potential difference across the two points). Efficiencies are obtained by exposing the cell to a constant, standard level of light while maintaining a constant cell temperature, and measuring the current and voltage that are produced for different load resistances.




Power Devices for Efficient Energy Conversion



In this study, we applied microwave annealing (MWA) to fabricate amorphous In-Ga-Zn-O (a-IGZO) thin-film transistors (TFTs) without thermal damage to flexible polyimide (PI) substrates. Microwave energy is highly efficient for selective heating of materials when compared to conventional thermal annealing (CTA). We applied MWA and CTA to a-IGZO TFTs on PI substrate to evaluate the thermal damage to the substrates. While the PI substrate did not suffer thermal damage even at a high power in MWA, it suffered severe damage at high temperatures in CTA. Moreover, a-IGZO TFTs were prepared by MWA at 600 W for 2 min, whereas the same process using CTA required 30 min at a temperature of 300 C, which is a maximum process condition in CTA without thermal damage to the PI substrate. Hence, MWA TFTs have superior electrical performance when compared to CTA TFTs, because traps/defects are effectively eliminated. Through instability evaluation, it was found that MWA TFTs were more stable than CTA TFTs against gate bias stress at various temperatures. Moreover, an MWA TFT-constructed resistive load inverter exhibited better static and dynamic characteristics than the CTA TFT-constructed one. Therefore, MWA is a promising thermal process with efficient energy conversion that allows the fabrication of high-performance electronic devices.


The United States' power plants consumed 39.5 quadrillion Btus of energy and produced 3.675 trillion kWh of electricity. What is the average efficiency of the power plants in the U.S.?


Yet the energy efficiency of a power plant is about 35%, and the efficiency of automobiles is about 25%. Thus, over 62% of the total primary energy in the U.S. is used in relatively inefficient conversion processes.


Thermophotovoltaic approaches that take advantage of near-field evanescent modes are being actively explored due to their potential for high-power density and high-efficiency energy conversion. However, progress towards functional near-field thermophotovoltaic devices has been limited by challenges in creating thermally robust planar emitters and photovoltaic cells designed for near-field thermal radiation. Here, we demonstrate record power densities of 5 kW/m2 at an efficiency of 6.8%, where the efficiency of the system is defined as the ratio of the electrical power output of the PV cell to the radiative heat transfer from the emitter to the PV cell. This was accomplished by developing novel emitter devices that can sustain temperatures as high as 1270 K and positioning them into the near-field (


Beta-voltaic radioisotope power sources (RPSs) are devices that directly convert beta particles (electrons) from a beta-emitting radioisotope source (such as nickel-63) into electrical energy. These devices have high power density, meaning they can release a large amount of power quickly when needed. They also have high energy density, meaning they store large amounts of power. They are ideal for applications like spacecraft that need power sources that can operate for many years under harsh conditions without human intervention. Researchers recently explored a new approach for making beta-voltaic RPSs more efficient at converting heat into electricity. These NextGen RPSs apply isotopes in new ways to improved converters. This gives NextGen RPSs excellent potential for providing long-term, compact power in remote and extreme environments.


Small sensors often used in remote and/or extreme environments on land and in space require power sources that supply high energy and power density to operate continuously for 3 to 25 years. Chemical batteries can only provide short-term solutions. A beta-voltaic RPS is an alternative to a chemical battery. These RPSs can store 1,000 times as much as a chemical battery, allowing them to supply small sensors with power for many years. This research shows how beta-voltaic RPS performance can be enhanced by improving the efficiency with which they convert radioactive decay into electricity. This advance will help make RPSs even more effective for small devices that require small amounts of power and represents a promising first step to increase nuclear battery power density from microwatts to milliwatts per 1000 cm3 with the implementation of higher energy beta sources.


Beta-voltaic batteries are a type of RPS. Radioisotopes utilized in beta-voltaic batteries (e.g., Ni-63, Pm-147) are produced by the DOE Isotope Program. In traditional beta-voltaic batteries, the radioisotope is deposited onto a metal foil that is placed on top of a semiconductor converter. The interaction between the radioisotope and the converter can limit RPS performance. This research demonstrated an approach where long-lived beta-emitting radioisotopes can be used to match the power density (the ability to release power) of chemical batteries while surpassing them in energy density (the ability to store power). Researchers investigated how the converter geometry and beta-conversion can influence performance by improving on the source efficiency and surface power density. Researchers focused on a beta-voltaic battery configuration consisting of nickel-63 directly applied onto a 4-H silicon carbide polytype (4H-SiC) beta-voltaic cell. Changing from a planar converter geometry to a textured 4H-SiC beta-voltaic cell improved power density by seven times. Converter efficiency increased by two times compared to a silicon cell when researchers directly applied nickel-63 to the textured 4H-SiC beta-voltaic cell. The beta-conversion can be captured on both sides of the radioisotope source. This permits two cells to collect the beta-conversion instead of one cell and increases surface power density. This research demonstrated that the interaction between the radioisotope and converter is critical to efficient energy conversion. These NextGen beta-voltaic RPSs have excellent potential in fulfilling long-duration, compact power needs for applications in remote and/or extreme environments.


Overall, we highlight that it is the combination of CTL thickness, PLQE and absorption coefficient that is decisive for determining the attainable efficiency of ET. In particular, stronger parasitic light-absorption coefficients may still be tolerated for CTLs, if these layers are thin and exhibit high PLQE. This finding is important, given that exploration of sun-facing front CTL materials so far has concentrated exclusively on materials that are transparent (i.e., absorb as little as possible across the sun spectrum) to avoid parasitic absorption in the CTL58. Our findings suggest that less transparent materials with high PLQE may be equally tolerable as CTL materials for MHP-based solar cells because absorbed energy is efficiently transferred to the MHP. This approach opens up a larger material space suitable for CTLs, allowing selection of previously unexplored candidates that share further positive characteristics, such as higher charge-carrier mobilities or more optimised energy-level alignment, which can reduce charge-extraction losses. Regardless of the specific selection, any efficient ET process between the front-facing CTL and the active MHP layer will enhance device performance, as it mitigates parasitic light absorption by transferring excitations to the MHP, from where they can be harvested as photocurrent.


Power electronics is the engineering study of converting electrical power from one form to another. At a world-wide average rate of 12 billion kilowatts every hour of every day of every year, more than 80% of the power generated is being reprocessed or recycled through some form of power electronic systems. A lot of energy is wasted during this power conversion process due to low power conversion efficiency. It is estimated that the power wasted in desktop PCs sold in one year is equivalent to seventeen 500MW power plants! It is therefore very important to improve the efficiency of these power conversion systems. It is estimated that with the widespread use of efficient and cost-effective power electronics technology, the world could see a 35% reduction in energy consumption.


Electric Machines and DrivesThe electric machine is an electromechanical energy conversion device that processes and delivers power to the load. The same electric machine can operate as a motor to convert electrical power to mechanical power or operate as a generator to convert mechanical power to electrical power. The electric machine in conjunction with the power electronic converter and the associated controller makes the motor drive. The power electronic converter is made of solid state devices and handles the flow of bulk power from the source to the motor input terminals. The advances in the power semiconductor technology over the past several decades enabled the development of compact, efficient and reliable DC and AC electric motor drives.


With the introduction of electric propulsion, a completely new drivetrain is introduced in the vehicle requiring multidisciplinary research into system components. The Electric vehicle system is comprised of electric motor, power electronics converters, and energy storage devices such as batteries. In addition, the overall system must be optimized to maximize overall system efficiency. Finally, to reduce the overall transportation emissions, the vehicle energy storage device should be recharged at times when the grid power production is most efficient and non-polluting. 041b061a72


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