Ocean wave is a rich source of renewable energy with much higher power density than winds. Various WEC technologies have been proposed or are under development. In this study, we developed a 2-dimensional (2D) model and analyzed the rotational motion of the lift-type rotor’s blade under steady flow and unsteady flow. The numerical model was validated by experiments under steady flow. Fast Fourier Transform (FFT) analysis was performed to identify the major contribution of frequency in terms of vortexes generated in the flow field. A comparative study was also performed by comparing all the cases in terms of energy conversion efficiency under different wave conditions. It turns out that the efficiency of energy conversion has a maximum value in the steady flow, while the efficiency for unsteady flow keeps decreasing, therefore this is highly due to the increased dissipation because of the oscillating. When the flow is oscillating, the rotational speed of the rotor under periodic condition is lower than the rotational velocity with steady flow, and a curve fitting was performed in this study to predict the periodic average rotational speed. We conclude that for oscillating flow a minimum of 1.6% energy conversion efficiency can be expected, but it may vary for the actual ocean waves. It is expected the current 2D simulation results can contribute to the wave energy community, especially when the rotor design and optimization is required.

This paper is an ASHRAE Level 3 study of the energy audit process carried out in an institutional building, The Umm Shaif Building, of The Petroleum Institute, Abu Dhabi, UAE. It undertakes the study by collecting data and conditional surveys. The energy loss locations are highlighted through psychrometric and infrared camera analysis. The detailed dynamic model has been simulated using the EnergyPlus ® simulation engine. The details of the building envelope, and fenestration, the occupancy schedules, the equipment energy consumption and HVAC details are presented. The detailed building model is used to allocate the energy usage and identify key energy consumers. The main results are reported using monthly total energy consumption. The validation and calibration are performed through different statistical metrics including Coefficient of Determination (R 2 ), Root Mean Square Error (RMSE) and Coefficient of Variance Root Mean Square Error (CVRMSE). Finally, energy conservation measures are suggested with the energy and cost savings.

In this contribution we introduced an integrated energy system consists of thermal power plants, combined heat-power (CHP) plants and wind power plants, and aimed to supply electricity and heat to users simultaneously. A large-scale battery, a TES device and heat transfer devices are included also. During the operation time of the battery, the TES device stores the generated heat and meanwhile supplies heat to users. Applying the power flow method, the electro-thermal analogy and the entransy dissipation-based thermal resistance method, we constructed the power flow model of the system. Besides, we optimized the system aimed to minimize wind curtailments. Optimization results presented for a typical day the system reduces wind curtailment percentage from 40.63 % to 13.70 % and supply 5% heat load. Besides, the operation strategy of the battery is to charge at night and discharge in the day.

The present study introduces fundamental aspects of a novel concentrated photovoltaics (CPV) technology. The technology is based on combining CPV/T receiver along with a solar thermal receiver. The combination is referred to as a High Concentrated Photovoltaic/Thermal - Combined receiver or HCPV/T-CT. The receiver is allocated in lieu of the conventional solar thermal receivers in the solar tower power plant schemes. The plant is designed to generate electricity and thermal energy simultaneously prior to integration with the conventional water desalination plant. The centralized generation in the CPV/T-CT receiver will remarkably simplify the complexity of the conventional solar power plants, and eliminate the piping networks’ energy losses in the CPV/T Dish tracking plants. The viability of the HCPV/T-CT power tower plant has also been investigated by; firstly, designing and simulating the plant performance using the System advisor model (SAM) software, and secondly, designing a prototype receiver and then deriving a mathematical model. The Levelised Cost Of Electricity/Energy (LCOE) was found to be 0.119 $/kWhe and 0.021 $/kWhe for electricity and energy generation, respectively, while the photovoltaic cells temperature maintained below the 90 °C.

Intermittency of sustainable energy or waste heat availability calls for energy storage systems such as thermal batteries. Thermo-chemical batteries are particularly appealing for energy storage applications due to their high energy densities and ability to store thermal energy as chemical energy for long periods of time without any energy loss. Thermo-chemical batteries based on a reversible solid-gas (MgCl 2 - NH 3 ) reactions and NH 3 liquid-gas phase change are of specific interest since the kinetics of absorption are fast and the heat transfer rates for liquid — vapor phase change are high. Thus, a thermo-chemical battery based on reversible reaction between magnesium chloride and ammonia was studied. Experimental studies were conducted on a reactor in which temperature profiles within the solid matrix and pressure and flow rates of gas were obtained during charging processes. A numerical model based on heat and mass transfer within the salt and salt-gas reactions was developed to simulate the absorption processes within the solid matrix and the results were compared with experimental data. The studies were used to determine dominant heat and mass transfer processes within the salt. It is shown that for high permeability materials, heat transfer is the dominant factor in determining reaction rates. However increasing thermal conductivity might decrease permeability and reduce reaction rates. The effect of constraining mass flow rate on the temperature and reaction propagation is also studied. These results show that optimized heat and mass transfer within the solid-gas reactor will lead to improved performance for heating and air conditioning applications.

Reciprocating-piston compressors and expanders are promising solutions to achieve higher overall efficiencies in various energy storage solutions. This article presents an experimental study of the exergetic losses in a gas spring. Considering a valveless piston-cylinder system allows us to focus on the thermodynamic losses due to thermal-energy exchange processes in reciprocating components. To differentiate this latter loss mechanism from mass leakages or frictional dissipation, three bulk parameters are measured. Pressure and volume are respectively measured with a pressure transducer and a rotary sensor. The gas temperature is estimated by measuring the Time-Of-Flight (TOF) of an ultrasonic pulse signal across the gas chamber. This technique has the advantage of being fast and non-invasive. The measurement of three bulk parameters allows us to calculate the work as well as the heat losses throughout a cycle. The thermodynamic loss is also measured for different rotational speeds. The results are in good agreement with previous experimental studies and can be employed to validate CFD or analytical studies currently under development.

Open expansion tanks are applied vastly in central heating and air-conditioning systems. Central heating systems are subjected to great deals of energy losses, owing to the lack of proper design. In this paper, the structure of Open Expansion Tanks is revised and some modifications for reducing energy and heat loss are made to their elements. Moreover, some common designs available in the market are studied in order to better recognize their defects and capabilities. To reach an efficient design, several scenarios are tested using Computational methods (CFD based). In order to validate the new design, an experimental model was created and heat and energy survey operations were performed. The results of energy auditing were analyzed to show the convergence of numerical and experimental models. Additionally, the proposed model was economically evaluated. The final presented model named “Optimized OET with twin containers” is capable of reducing the energy loss by 85 to 95 percent.

Wind energy has been identified as an important source of renewable energy. In this study, several wind turbine designs have been analyzed and optimized designs have been proposed for low wind speed areas around the world mainly for domestic energy consumption. The wind speed range of 4–12 mph is considered, which is selected based on the average wind speeds in the Atlanta, GA and surrounding areas. These areas have relatively low average wind speeds compared to various other parts of the United States. Traditionally wind energy utilization is limited to areas with higher wind speeds. In reality a lot of areas in the world have low average wind speeds and demand high energy consumption. In most cases, wind turbines are installed in remote offshore or away from habitat high wind locations, causing heavy investment in installation and maintenance, and loss of energy transfer over long distance. A few more advantages of small scale wind turbines include reduced visibility, less noise and reduced detrimental environmental effects such as killing of birds, when compared to traditional large turbines. With the latest development in wind turbine technology it is now possible to employ small scale wind turbines that have much smaller foot print and can generate enough energy for small businesses or residential applications. The low speed wind turbines are typically located near residential areas, and are much smaller in sizes compared to the large out of habitat wind turbines. In this study, several designs of vertical and horizontal axes wind turbines are modeled using SolidWorks e.g. no-airfoil theme, airfoil blade, Savonius rotor etc. Virtual aerodynamic analysis is performed using SolidWorks Flow simulation software, and then optimization of the designs is performed based on maximizing the starting rotational torque and ultimate power generation capacity. From flow simulations, forces on the wind turbine blades and structures are calculated, and used in subsequent stress analysis to confirm structural integrity. Critical insight into low wind speed turbines is obtained using various configurations, and optimized designs have been proposed. The study will help in the practical and effective utilization of wind energy for the areas around the globe having low average wind speeds.

The Riyadh Techno Valley Solar Tower, an innovative type of concentrator solar power plant, is being developed by King Saud University (KSU) and Georgia Tech (GT). The facility is being constructed at the Riyadh Techno Valley development near the KSU campus and will store thermal energy collected from the sun in solid particles, which can be heated to higher temperatures than is currently possible using molten salts. The particles must be well insulated to stop energy loss to the environment. Hence, GT and KSU have incorporated an insulated storage bin into the plant design. The bin will be constructed in several layers: an inner layer of firebrick, which can endure direct exposure to the heated particles; a specially prepared refractory insulating concrete, which maintains good insulating value at high temperatures; and a conventional structural concrete shell surrounding the entire bin. This paper presents a thermal analysis of this storage device and discusses structural analyses. Simplified analytical solutions are compared with the finite element results from a 3D ANSYS model of the entire bin. A temperature distribution is obtained, and heat loss through the bin is also evaluated. Modeling of rebar and concrete cracking are described, and methods of reducing stress on the outer concrete shell are considered. Structural support for an access tunnel into the bin is also explored. The current tunnel design involves a material with a relatively high thermal conductivity, necessitating modifications to the bin. Finally, material selection is considered, particularly with regard to the insulating concrete layer. Limitations on the use of Portland cement based insulating concretes are discussed, and alternative base materials are evaluated.

The use of solid particles as a heat transfer and thermal energy storage (TES) medium in central receiver systems has received renewed attention in recent years due to the ability of achieving high temperatures and the potential reduction in receiver and TES costs. Performance of TES systems is primarily characterized by the percentage of heat loss they allow over a prescribed period of time. Accurate estimation of this parameter requires special attention to the transient nature of the process of charging the TES bin during solar field operation and discharging during nighttime or at periods where solar field operation is interrupted. In this study, a numerical model is built to simulate the charge-discharge cycle of a small cylindrical-shaped TES bin that is currently under construction. This bin is integrated into the tower of an experimental 300-kW (thermal) central receiver field being built in Riyadh, Saudi Arabia, for solid particle receiver research, most notably on-sun testing of the falling particle receiver concept within the context of a SunShot project. The model utilizes a type of wall construction that had been previously identified as showing favorable structural characteristics and being able to withstand high temperatures. The model takes into account the anticipated charge-discharge particle flow rates, and includes an insulating layer at the ceiling of the bin to minimize heat loss by convection and radiation to the receiver cavity located immediately over the TES bin. Results show that energy loss during the full charge-discharge cycle is 4.9% and 5.9% for a 5-hour and 17-hour discharge period, respectively. While large, these energy loss values are primarily due to the high surface-to-volume ratio of the small TES bin being investigated. Preliminary analysis shows that a utility-scale TES bin using the same concept will have an energy loss of less than 1%.

Concentrated Solar Power (CSP) systems used for photothermal conversion of solar energy to electricity are capable of meeting a large fraction of the global energy requirements. CSP plants are inherently robust with respect to the availability of materials, technology, and energy storage. However, dust depositions on solar collectors cause energy yield loss annually, ranging from 10 to 50% depending upon their location in the semi-arid and desert lands. Mitigation of energy loss requires manual cleaning of solar mirrors with water. A brief review of the soiling related losses in energy yield of the CSP plants is presented, which shows that cleaning of the CSP mirrors and receivers using water and detergent is an expensive and time-consuming process at best and is often impractical for large-scale installations where water is scarce. We report here our research effort in developing an electrodynamic dust removal technology that can be used for keeping the solar collectors clean continuously without requiring water and manual labor. Transparent electrodynamic screens (EDS), consisting of rows of transparent parallel electrodes embedded within a transparent dielectric film can be integrated on the front surface of the mirrors and on the receivers for dust removal for their application as self-cleaning solar collectors. When the electrodes are activated, over 90% of the deposited dust is removed. A summary of the current state of prototype development and evaluation of EDS integrated solar mirrors and experimental data on the removal of desert dust samples are presented. A brief analysis of cost-to-benefit ratio of EDS implementation for automated dust removal from large-scale solar collectors is included.

In order to reduce the consumption of energy and material, the optimization design of the refrigeration systems, especially the minimization for the total area of the heat exchangers, has been an attractive but tough issue in both research and engineering fields. Therefore, the entransy dissipation theory is introduced in this article to analyze the refrigeration systems. The systems are analyzed through the entransy dissipation analysis for the irreversible heat transfer processes in the heat exchangers and the thermodynamic analysis for the compressors and expanders, which are combined to deduce the mathematical relation between the known conditions, i.e. inlet temperatures of fluids, the heat absorbed from the cold end of the systems, and the design parameters, i.e. the heat conductances of heat exchangers and heat capacity rates of working fluids. Based on the relation, the optimization design for the refrigeration systems is converted to the conditional extremum problem that offers the optimization equations group. Solving the equations yields the optimal configuration of all the design parameters. Then a typical refrigeration system is numerically optimized to obtain the optimal configuration, optimal compression ratio and the minimum for the total area of heat exchangers, which is proved to be the least through the comparison with other configuration of the design parameters.

Lithium-ion (Li-ion) batteries are favored in hybrid-electric vehicles and electric vehicles for their outstanding power characteristics. In this paper the energy loss due to electrical contact resistance (ECR) at the interface of electrodes and current-collector bars in Li-ion battery assemblies is investigated for the first time. ECR is a direct result of contact surface imperfections and acts as an ohmic resistance at the electrode-collector joints. ECR is measured at electrode connections of a sample Li-ion battery, and a straightforward analysis is presented to evaluate the relevant energy loss. Through the experiments, it is observed that ECR is an important issue in energy management of Li-ion batteries. Effects of surface imperfection, contact pressure, joint type, collector bar material, and interfacial materials on ECR are highlighted. The obtained data show that in the considered battery, the energy loss due to ECR can be as high as 20% of the total energy flow in and out of the battery under normal operating conditions. However, ECR loss can be reduced to 6% when proper joint pressure and/or surface treatment are used. A poor connection at the electrode-collector interface can lead to a significant battery energy loss as heat generated at the interface. At sever conditions, heat generation due to ECR might cause serious safety issues, thermal runaway, sparks, and even melting of the electrodes.

A thermal model was developed to estimate the energy losses from prototypical domestic hot water (DHW) distribution systems for homes. The developed model, using the TRNSYS simulation software, allows researchers and designers to better evaluate the performance of hot water distribution systems in homes. Modeling results were compared with past experimental study results and showed good agreement. The model was also compared with existing domestic hot water distribution system modeling software HWSIM for verification. The developed model has several capabilities that are not available in HWSIM, including the ability to integrate any new or existing types of water heater systems, the ability to handle several simultaneous draws to different end uses, and the ability to handle unique annual draw profiles instead of weekly draw profiles. It also allows for draw profiles and ambient conditions to be considered using any time resolution. To demonstrate the abilities of this new model, a series of sensitivity analyses were performed using a benchmark domestic hot water distribution system. The effects of adding insulation to the domestic hot water distribution system of homes with a gas water heater and a solar water heater were also examined.

Improving the efficiency of thermodynamic cycles plays a fundamental role in reducing the cost of solar power plants. These plants work normally with Rankine cycles which present some disadvantages due to the thermodynamic behavior of steam at low pressures. These disadvantages can be reduced by introducing alternatives such as combined cycles which combine the best features of each cycle. In this paper a combined Rankine-Goswami cycle (RGC) is proposed and a thermodynamic analysis is conducted. The Goswami cycle, used as a bottoming cycle, uses ammonia-water mixture as the working fluid and produces power and refrigeration while power is the primary goal. This bottoming cycle, reduces the energy losses in the traditional condenser and eliminates the high specific volume and poor vapor quality presented in the last stages of the lower pressure turbine in the Rankine cycle. In addition, the use of absorption condensation in the Goswami cycle, for regeneration of the strong solution, allows operating the low pressure side of the cycle above atmospheric pressure which eliminates the need for maintaining a vacuum pressure in the condenser. The performance of the proposed combined Rankine-Goswami cycle, under full load, was investigated for applications in parabolic trough solar thermal plants for a range from 40 to 50 MW sizes. A sensitivity analysis to study the effect of the ammonia concentration, condenser pressure and rectifier concentration on the cycle efficiency, network and cooling was performed. The results indicate that the proposed RGC provide a difference in net power output between 15.7 and 42.3% for condenser pressures between 1 to 9 bars. The maximum effective first law and exergy efficiencies for an ammonia mass fraction of 0.5 are calculated as 36.7% and 24.7% respectively for the base case (no superheater or rectifier process).

With the increase of the energy crisis and environmental pollution, the solar energy as a clean and renewable energy is paid more attention. The photovoltaic cells are being widely used, and many researchers are studying the light and heat integration of photovoltaic systems (PV/T). PV-water cooling system and PV-SAHP system are all the integration of solar photovoltaic systems and thermal utilization system, which use the solar energy to supply the electric power and space heating or daily hot water. Due to the difference of the equipment installations and application conditions, two systems are different from their system efficiencies. To analyze the system exergy is of great significance, as the energy loss and utilization deficiency can be identified through the exergy analysis, and based on the analyzed results the system efficiency can be improved. Furthermore the system can be optimized by the exergy efficiency calculation. In this paper the exergy values of two systems are analyzed, the energy loss and utilization deficiency are analyzed, and the exergy efficiencies are obtained. The work will be good references for the application and optimization of solar photovoltaic systems and thermal utilization system.

The work focused on the analysis of the connection between a photovoltaic (PV) plant and an electrolyzer for hydrogen production. On the basis of PV plant and electrolyzer experimental data, the effectiveness of the models adopted in the simulation program has been verified in order to choose the best model and, eventually, modify some parameters. By running the simulations, the procedure to optimize the PV plant and the electrolyzer combination has been established. In fact, the simulation results might be considered to size an electrolyzer as small as possible, which is able to exploit up to the maximum power actually produced by the PV plant during a working year. This criterion allows minimizing the overall plant costs. Furthermore, the possibility of deleting the Maximum Power Point Tracker (MPPT) and the DC/DC converter has been analyzed. On the basis of the obtained results, this opportunity is preferable to avoid the energy losses in the power control system; and it is convenient even from an economic point of view, considering that the electronic devices costs are comparable with the PV plant ones.