Heat Transfer Modeling in a Counter-Current Moving-Bed Tubular Reactor for High-Temperature Thermochemical Energy Storage

An axisymmetric model coupling counter-current gas-solid flow, heat transfer, and thermochemical redox reactions in a moving-bed tubular reactor was developed. The counter-current flow enhances convective heat transfer and a low oxygen partial pressure environment is maintained for thermal reduction within the reaction zone by using oxygen depleted inlet gas. A similar concept can be used for the oxidation reactor which releases high-temperature heat that can be used for power generation or as process heat. The heat transfer model was validated with published results for packed bed reactors. After validation, the model was applied to simulate the moving-bed reactor performance, through which the effects of the main geometric parameters and operating conditions were studied to provide guidance for lab-scale reactor fabrication and testing.

A Comparative Study of the Influence of Different Wake Models on Wind Farm Layout Optimization

The accuracy of analytical wake models applied in wind farm layout optimization (WFLO) problems plays a vital role in the present era that the high-fidelity methods such as LES and RANS are still not able to handle an optimization problem for large wind farms. Based on a verity of analytical wake models developed in the past decades, FLOw Redirection and Induction in Steady State (FLORIS) has been published as a tool integrated several widely used wake models and the expansions for them. This paper compares four wake models selected from FLORIS by applying three classical WFLO scenarios. The results illustrate that the Jensen wake model is the fastest one but the defect of underestimation of velocity deficit is obvious. The Multi Zone model needs to be applied additional tunning on the parameters inside the model to fit specific wind turbines. The Gaussian-Curl wake model as an advanced expansion of the Gaussian wake model does not perform an observable improvement in the current study that the yaw control is not included. The default Gaussian wake model is recommended to be used in the WFLO projects which implemented under the FLROIS framework and has similar wind conditions with the present work.

Preliminary Techno-Economic Optimization Of 1.3 MWe Particle Heating Receiver Based CSP Power Tower Plant for the MENA Region

Due to increasing energy demand around the globe and potential environmental impacts of fossil fuels, it has become a crucial task for researchers to find alternatives to generate electricity from low-carbon resources at lower costs. Three types of advanced CSP are under consideration: systems heating salt, gas, or particulate. Particle heating receiver (PHR) based central receiver power tower CSP is an emerging technology that promises higher operating temperatures and more cost-effective thermal energy storage (TES) than feasible with existing or alternative CSP systems. For reasons stated above and others, we propose that the particle heating receiver (PHR) based CSP in the classic central receiver power tower (CRPT) configuration will be the most suitable especially in the promising Middle East and North Africa (MENA) region. Specifically, Duba, Al Wajih, and Wa’ad Al-Shamaal regions in Saudi Arabia have high direct normal irradiation (DNI) and represent potential locations. PHR based CSP power tower plant consists of a central receiver power tower with TES and cavity receiver, heliost at field, a high-temperature solar gas turbine with built-in fuel backup to operate in hybrid mode (using both fuel and solar-thermal resources). This study focuses on the optimization of a solar heat supply system (SHSS), consisting of a tower, cavity receiver, and heliostat field. SolarPILOT – Solar Power tower Integrated Layout and Optimization Tool is a field layout optimization tool developed by National Renewable Energy Laboratory (NREL). SolarPILOT is used in this study to generate the field layout of a 1.3 MWe power plant with a solar multiple (SM) of 2, 3, and 4. Cost models for the tower, receiver, and heliostats are developed using the data from research programs, contractors, manufacturing companies, and general cost engineering data and tools. System Advisor Model (SAM) is further used to simulate the annual performance of CSP tower plant including power block (high-temperature gas turbine) and TES using optical efficiency data from SolarPILOT to optimize PHR-based CSP tower plant. The results of this research are fundamental to the techno-economic analysis (TEA) of this and similar smaller-scale systems and will support the TEA of larger grid-connected and smaller off-grid systems operating independently or in conjunction with PV systems.

Sensitivity Analysis of the Levelized Cost of Electricity for a Particle-Based CSP System

This study presents a sensitivity analysis of the LCOE for a particle-based system with the costs of the most current components. New models for the primary heat exchanger, thermal energy storage and tower are presented and used to establish lower and upper bounds for these three components. The rest of component costs such as particle cost, cavity cost, lift cost and balance of power are set to lower and upper bounds estimating a 25% of uncertainty. Some relevant parameters such as lift efficiency and storage thermal resistance are also included in the analysis with a 25% uncertainty. This study also includes an upgrade to the receiver model by including the wind effect in the efficiency, which was not included in previous publications. A parametric analysis shows the optimum values of solar multiple, storage hours, tower height and concentration ratio, and a probabilistic analysis provides a cumulative distribution function for a range of LCOE values. The results show that the LCOE could be below $0.06/kWh with a probability of 90%, where the highest uncertainty is on the primary heat exchanger cost.

Using Molding to Fabricate Stable Salt Structures for Thermochemical Energy Storage

The present work investigates using a molding technique to fabricate stable salt structures for thermochemical energy storage. Two type of salts were investigated: pure MgSO4 and a blend of 53% CaCl2 with 47% MgSO4. These salts were mixed with two common binders and hot pressed. Various post-hot-pressing conditions were considered including the debinding temperature, whether the sample was sintered, and the sintering temperature. The samples were subjected to combined hydration and thermal cycling. The hydration reaction was monitored by measuring the relative humidity. The samples were visibly inspected for changes between each half cycle. The results indicate that molding can result in stable structures. All the samples of 53wt%CaCl2+47%wtMgSO4 and one sample of pure MgSO4 retained their integrity through the course of cycling. Of the samples that did not retain their integrity through cycling, the results show that fabrication parameters can be used to improve the cycle stability of the molded sample. The hydration data shows that, for the samples that retained their structure, stable hydration rates were achieved. This indicates that the structure stabilized. These results show the feasibility of using molding or similar manufacturing techniques to fabricate a stable structure of hygroscopic salts for thermochemical-based, thermal energy storage.

Sustainability Assessment of Aviation Fuel Blends

Stakeholders in the aviation industry committed to a goal of 50% reduction in carbon emissions by the year 2050, to be achieved by reducing emissions 1.5% each year from 2020 onwards. There are multiple pathways to achieve this goal however; with, the most promising technology being Sustainable Aviation Fuels (SAF), which are biofuels blended with kerosene. As the industry shifts towards SAF, it is important to evaluate these fuels in terms of their long-term sustainability, and this is the objective of the current study. Sixteen types of fuels were assessed which include fossil, natural gas, electric, and SAF. A Multi Criterion Decision Making methodology was adopted which considers three categories, namely environmental, economic, and social aspects which in turn are broken up into 8 indicators in all (such as ecological footprints, cost of transportation, investment cost, operating costs, employment generation, and health & safety). A Monte Carlo analysis was also performed to analyze sensitivity of the results to the weights attributed to the three categories. The most sustainable fuel was found to be Hydrogen, with a score of 0.91 out of 1.0. The least sustainable were determined to be the military kerosene-based fuels (with the experimental fuel JP-8 + 100LT being the poorest with a normalized score of 0.50).

Fluttering Amplitude Amplification by Utilizing Flapping Moment in Flutter-Driven Triboelectric Nanogenerator

Flutter-driven triboelectric nanogenerator (FTENG) is one of the most promising methods to harvest small-scale wind energy. Wind causes self-fluttering motion of a flag in the FTENG to generate electricity by contact electrification. A lot of studies have been conducted to enhance the energy output by increasing the surface charge density of the flag, but only a few researches tried to increase the converting efficiency by enlarging the flapping motion. In this study, we show that by simply replacing the rigid flagpole in the FTENG with a flexible flagpole, the energy conversion efficiency is augmented and the energy output is enhanced. It is found that when the flag flutters, the flagpole also undergoes aerodynamic force. The lift force generated from the fluttering flag applies a periodic rotational moment on the flagpole, and causes the flagpole to vibrate. The vibration of the flagpole, in turn amplifies the flutter of the flag. Both the fluttering dynamics of the flags with rigid and flexible flagpoles have been recorded by a high-speed camera. When the flag was held by a flexible flagpole, the fluttering amplitude and the contact area between the flag and electrode plates were increased. The energy enhancement increased as the flow velocity increased and the enhancement can be 113 times when the wind velocity is 10 m/s. The thickness of the flagpole was investigated. An optimal output of open-circuit voltage reaching 1128 V (peak-to-peak value) or 312.40 V (RMS value), and short-circuit current reaching 127.67 μA (peak-to-peak value) or 31.99 μA (RMS value) at 12.21 m/s flow velocity was achieved. This research presents a simple design to enhance the output performance of an FTENG by amplifying the fluttering amplitude. Based on the performance obtained in this study, the improved FTENG has the potential to apply in a smart city for driving electronic devices as a power source for IoT applications.

Enhancement the Solar Still Performance Using Chimney Exhaust Gases

In this paper, a theoretical study is presented on enhancement of the solar still performance by using the exhaust gases passing inside a chimney under the still basin. The impact of the exhaust gases temperature on the solar still temperature, productivity, and efficiency are considered. The performance of solar still with chimney is compared with that of conventional solar still. The study is carried out under the hot and climate conditions of Upper Egypt. A complete transient mathematical model of the physical model including the solar still regions temperatures, productivity, and heat transfer between the solar still and the exhaust gases are constructed. The mathematical model is solved numerically by using fourth-order Runge-Kutta method and is programmed by using MATLAB. The mathematical model is validated using an experimental work. The results show that the solar still saline water temperature increases and productivity with using and rising the exhaust gases. Furthermore, the impact of using exhaust gases on the still performance in winter is greater than in summer. using chimney exhaust gases at 75 °C and 125 °C enhances the daily freshwater yield of the conventional still by more than three times and about six times in winter, respectively, and about two and half times and more than three times in summer, respectively.

Least Cost Microgrid Resource Planning for the Natural Energy Laboratory of Hawaii Authority Research Park

The Natural Energy Laboratory of Hawaii Authority’s (NELHA) campus on The Island of Hawai’i supplies resources for a number of renewable energy and aquaculture research projects. There is a growing interest at NELHA to convert the research campus to a 100% renewable, islanded microgrid to improve the resiliency of the campus for critical ocean water pumping loads and to limit the increase in the long-term cost of operations. Currently, the campus has solar array to cover some electricity needs but scaling up this system to fully meet the needs of the entire research campus will require significant changes and careful planning to minimize costs. This study will investigate least-cost solar and energy storage system sizes capable of meeting the needs of the campus. The campus is split into two major load centers that are electrically isolated and have different amounts of available land for solar installations. The value of adding an electrical transmission line if NELHA converts to a self-contained microgrid is explored by estimating the cost of resources for each load center individually and combined. Energy storage using lithium-ion and hydrogen-based technologies is investigated. For the hydrogen-based storage system, a variable efficiency and fixed efficiency representation of the electrolysis and fuel cell systems are used. Results using these two models show the importance of considering the changing performance of hydrogen systems for sizing algorithms.

Sensitivity Analysis of Occupant Preferences on Energy Usage in Residential Buildings

Residential buildings, accounting for 37% of the total electricity consumption in the United States, are suitable for demand response (DR) programs to support effective and economical operation of the power system. A home energy management system (HEMS) enables residential buildings to participate in such programs, but it is also important for HEMS to account for occupant preferences to ensure occupant satisfaction. For example, people who prefer a higher thermal comfort level are likely to consume more energy. In this study, we used foresee™, a HEMS developed by the National Renewable Energy Lab (NREL), to perform a sensitivity analysis of occupant preferences with the following objectives: minimize utility cost, minimize carbon footprint, and maximize thermal comfort. To incorporate the preferences into the HEMS, the SMARTER method was used to derive a set of weighting factors for each objective. We performed week-long building energy simulations using a model of a home in Fort Collins, Colorado, where there is mandatory time-of-use electricity rate structure. The foresee™ HEMS was used to control the home with six different sets of occupant preferences. The study shows that occupant preferences can have a significant impact on energy consumption and is important to consider when modeling residential buildings. Results show that the HEMS could achieve energy reduction ranging from 3% to 21%, cost savings ranging from 5% to 24%, and carbon emission reduction ranging from 3% to 21%, while also maintaining a low thermal discomfort level ranging from 0.78 K-hour to 6.47 K-hour in a one-week period during winter. These outcomes quantify the impact of varying occupant preferences and will be useful in controlling the electrical grid and developing HEMS solutions.