Harvested Energy Maximization Research Articles

Extraction of Energy from Small Thermal Differences near Room Temperature Using Capacitive Membrane Technology

Extracting electric energy from small temperature differences is an emerging field in response to the transition toward sustainable energy generation. We introduce a novel concept for producing electricity from small temperature differences by the use of an assembly combining ion exchange membranes and porous carbon electrodes immersed in aqueous electrolytes. Via the temperature differences, we generate a thermal membrane potential that acts as a driving force for ion adsorption/desorption cycles within an electrostatic double layer, thus converting heat into electric work. We report for a temperature difference of 30 °C a maximal energy harvest of ∼2 mJ/m2, normalized to the surface area of all the membranes.

Increasing the output from piezoelectric energy harvester using width-split method with verification

This paper proposes a new scheme for piezoelectric energy harvesting maximization. The proposed enhancement relies on a new topology of splitting a specified dimension piezo composite bender into beams with smaller width and, therefore, higher quality factor (or Q factor). The increase of Q factor allows a much more effective energy conversion process. It is shown that the proposed method, based on single splitting, increases the harvested power by a factor of up to √6, and up to √7.62 for two even-splitting compared to with no splitting. The wideband operation is accomplished by using different resonating benders in such a way that individual benders are each tuned to a different resonance frequency. Taking the configuration of single even-splitting as an example, the power output of the prototype was 39 μW at 27.2 Hz with 8 Hz bandwidth under 2 mm peak-to-peak input displacement and 3 Hz variation in resonant frequency. This corresponds to more than 2 times of power output with no splitting as well as about 23% increase in bandwidth. Such power output is sufficient to power up electronics devices such as a “2 AA dry cells-powered” digital clock with the wider range operating frequency.

A TEG Efficiency Booster with Buck–Boost Conversion

A thermoelectric generator (TEG) efficiency booster with buck–boost conversion and power management is proposed as a TEG battery power conditioner suitable for a wide TEG output voltage range. An inverse-coupled inductor is employed in the buck–boost converter, which is used to achieve smooth current with low ripple on both the TEG and battery sides. Furthermore, benefiting from the magnetic flux counteraction of the two windings on the coupled inductor, the core size and power losses of the filter inductor are reduced, which can achieve both high efficiency and high power density. A power management strategy is proposed for this power conditioning system, which involves maximum power point tracking (MPPT), battery voltage control, and battery current control. A control method is employed to ensure smooth switching among different working modes. A modified MPPT control algorithm with improved dynamic and steady-state characteristics is presented and applied to the TEG battery power conditioning system to maximize energy harvesting. A 500-W prototype has been built, and experimental tests carried out on it. The power efficiency of the prototype at full load is higher than 96%, and peak efficiency of 99% is attained.

Modeling of a concentrating photovoltaic system for optimum land use

ABSTRACTConcentrating photovoltaic solar power plants using dual‐axis trackers are in increasing demand. In a utility‐scale photovoltaic system, both capacity factor and ground coverage ratio are widely used to characterize systems in view of the land use efficiency. Current system modeling approaches lack accurate location‐specific direct normal irradiance (DNI), miss a reliable electrical model for power optimization and conversion and are inadequate for optimizing the tracker array configuration. In this paper, a comprehensive modeling of a concentrating photovoltaic system is introduced. First, a more accurate estimation of hourly DNI is obtained by considering location‐dependent DNI and air mass changes according to the sun's elevation. Second, mismatch effects of modules are factored in. Third, various power optimization and conversion levels are taken into account for optimization with self‐shading in each module. The tracker array configuration has been optimized to maximize energy harvest by getting a maximum capacity factor for a given ground coverage ratio. Copyright © 2011 John Wiley & Sons, Ltd.

Ultra-Low Power Control System for Maximal Energy Harvesting From Short Duration Vibrations

With the advent of ultra-low power sensor packages, there is renewed interest in harvesting vibration energy to power them, thus creating a self sustaining battery-less sensor system. The optimal algorithms previously developed in literature to harvest vibration energy are complex and hence require controllers that consume a significant amount of power. The relatively high power requirement combined with the inherent complex design of these algorithms would also limit them to only applications in which sustained vibration energy is available for harvesting. To address these issues, this paper presents new control systems to optimize the amount of energy harvested from short duration vibrations. Only algorithms that can be implemented using simple ultra-low power analog electronic components are considered. The first algorithm termed ¿fixed threshold switching¿, has been adapted from literature on harvesting energy from sustained vibration. The second and third algorithms are new optimal control algorithms termed ¿maximum voltage switching¿ and ¿switched inductor¿, respectively. The three algorithms are theoretically evaluated and compared for a short duration vibration application. The final section of this paper presents experimental results from the implementation of all the three algorithms on a new battery-less wireless traffic sensor.

Energy harvesting efficiency of III–V triple-junction concentrator solar cells under realistic spectral conditions

In this paper we present a methodology that uses the detailed balance method to determine the optimum bandgap combination of III–V triple-junction solar cells for the highest yearly energy production. As an example of the methodology, we analyze two geographical locations on Earth with distinct spectral conditions. For these places the monthly average of the measured aerosol optical depth and the precipitable water are used to calculate direct solar spectra with a discretisation of one spectrum per hour. The model is used to analyze the spectral sensitivity of the bandgap design of four practical III–V triple-junction solar cell structures. Furthermore, the ideal bandgap combination for a maximal energy harvest is calculated for each location. It is shown that the metamorphic solar cell structure of Ga0.35In0.65P/Ga0.83In0.17As/Ge with transparencies optimized for the standard AM1.5d reference spectrum leads to the highest energy harvesting efficiencies and shows the lowest spectral sensitivity. The standard lattice-matched structure of Ga0.50In0.50P/Ga0.99In0.01As/Ge shows the highest spectral sensitivity with up to 10%rel difference in the yearly energy harvesting.

Efficient energy transfer in Langmuir-Blodgett monolayers by optimized quantum capture

Energy transfer in Langmuir-Blodgett monolayers called J-aggregates is explained by direct exciton capture to bound states on acceptor molecules. The condition for maximal energy harvesting is found.