This work investigates desalination salt thermal energy storage (TES) using a benchtop air-to-salt module and a complementary CFD study of an electro-thermal concept with embedded electrical heaters. Experiments were conducted at inlet air temperatures of 200, 300, and 400 °C for charging, storage, and discharge performance of the TES module. Dimensionless analysis using the Fourier number captured consistent charge-discharge behavior across setpoints. CFD simulations (ANSYS Fluent) of an electro-thermal TES system with desalination salt investigated corner vs. center heater placement at two heat generation rates for 110 V and a 220 V setups. The collected data for temperature gradients, heat flux, and heat transfer coefficient demonstrate technical feasibility, identify loss mechanisms at lab scale, and outline design levers–heater layout, flow rate, geometry, and insulation–for scalable desalination salt-based TES systems.

The feasibility of using desalination salt for sensible thermal energy storage (TES) has been demonstrated at a laboratory scale. This study leverages Computational Fluid Dynamics (CFD) simulations to enhance the performance and design of TES systems operating within a temperature range of 100 degrees C to 400 degrees C. Key considerations include dynamic charging and discharging behavior, the influence of axial conduction during discharge, and establishing heat rate limits to safeguard system integrity. Various TES configurations - shell-and-tube, concentric tube, and composite designs - were evaluated for thermal stability, energy transfer efficiency, and loss minimization. The integration of resistive heaters directly within the salt medium offers a streamlined charging mechanism but introduces challenges such as localized overheating and uneven heat distribution. CFD analyses were instrumental in optimizing heater placement and developing robust thermal management strategies to ensure uniform energy transfer and system reliability. The results indicate that axial conduction significantly impacts discharge performance by moderating temperature gradients and energy recovery efficiency. Among the designs, the shell-and-tube configuration demonstrated superior thermal stability, while the concentric tube excelled in heat transfer rates. Composite designs provided a balance between retention and transfer but required enhanced management near heat sources. Compared to traditional TES materials, desalination salt emerges as a cost-effective, sustainable option with high energy density, suitable for industrial applications and renewable energy integration.

Renewable energy sources, such as solar and wind, hold immense potential in transitioning towards a sustainable energy future. However, their intermittent nature poses challenges to grid stability. Energy storage solutions, particularly Thermal Energy Storage (TES) systems, have emerged as a promising approach to address this issue and enhance the integration of renewables. This study delves into the development of a TES system that utilizes repurposed minerals as storage material, integrated with a low-temperature zero liquid discharge thermal desalination system. The integration of TES with desalination processes holds significant promise in mitigating the economic and environmental consequences of ocean or brackish water desalination. By employing TES, the study aims to improve the overall efficiency of the integrated system, contributing to the sustainability of both energy generation and water production. This research employs a comprehensive thermodynamic analysis, encompassing optimization and sensitivity analyses of the TES system utilizing only sensible heat. A detailed MATLAB model relying on the first law of thermodynamics provides valuable insights into the transient behavior of a 4,000-15,000 kg storage system under various charge and discharge scenarios.

Thermal energy storage (TES) plays a crucial role in energy sustainability, enabling the efficient storage and utilization of thermal energy from various sources. In this paper, we propose a novel TES system that utilizes reclaimed minerals as the heat storage medium. The system comprises a tightly packed bed of processed minerals enclosing a circular pathway for heat transfer fluid (HTF). To achieve optimal performance, we develop a computational method and algorithm to estimate the required pipe length for efficient charge and discharge cycles. The analysis encompasses various factors, including pipe length, storage material thickness, tube material, schedule, and contact resistance. Through a systematic examination of these parameters, we propose an algorithmic design for an effective pipe length tailored to the specific requirements of diverse applications in heat storage systems. A significant aspect of the proposed system is its adaptability. The system parameters, such as the temperature and mass flow rate of the HTF, can be modified based on the established effective length of the pipe. This adaptability contributes not only to increased cost-effectiveness but also to diminished energy loss in the overall energy storage system. This research employs Computational Fluid Dynamics (CFD) modeling to simulate charge and discharge cycles, incorporating varying scenarios of pipe lengths and system parameters. By evaluating the exit temperatures of the HTF and the average temperature of the storage material at different stages, the study identifies a suitable pipe length that ensures adequate discharge time for the storage material once the cutoff temperature is achieved. This tailored approach aligns with the specific demands of diverse applications, ranging from solar power plants to industrial processes, showcasing the versatility and practicality of the proposed methodology.

In this techno-economic analysis, a thermal energy storage system that repurposes desalination salt as a storage medium is investigated. The proposed system meets the Department of Energy’s SunShot Initiative goal of $15/kWhth for thermal energy storage (TES). A sensitivity analysis was performed on significant cost factors to determine how to meet this goal while considering a positive financial gain from obtaining the salt from desalination facilities. Based on a previous TEA study, adjustments were made to the costs of labor and material to account for inflation. Nanoparticle additives are considered to enhance thermal conductivity and improve system efficiency. Furthermore, desalination concentrates with lower total dissolved solids (TDS) tends to provide lower TES cost. A ZLD (Zero Liquid Discharge) process was considered to extract the total dissolved solids from the desalination brine and provide an additional gain from the potable water sale. The overall $/kwh results show that the SunShot goal is met using a desalination salt that exhibits solid-to-liquid phase change.

The by- product of desalination processes can potentially be repurposed as a thermal energy storage medium while simultaneously preventing the discharge of this waste into the environment. This study presents a lab-scale demonstration of repurposing desalination waste salt as a Thermal Energy Storage (TES) medium. The design is based on a shell and tube heat exchanger to simulate the charge (heating), storage, and discharge (cooling) of a thermal energy storage tank that is charged and discharged by a heat transfer fluid. The thermal cycling experiments were executed at three temperatures, 200 degrees C, 300 degrees C, and 400 degrees C. Compressed air as the heat transfer fluid was heated by an electric heater and was routed in the shell side and provided the heat for the heat storage medium, i.e., processed desalination salt. In the storage cycle. The thermal energy is recovered by flowing low-temperature heat transfer fluid to the storage tank. The results of this study show the feasibility of storing thermal energy in desalination waste salt on a laboratory scale.

Membrane processes are used for water treatment techniques to desalinate seawater and surface water into potable water. The undesired byproduct of these processes is a high concentrate salt. In this project, the repurposed concentrate salt was studied as a storage medium for grid-scale Thermal Energy Storage (TES). The Department of Energy’s (DOE) goal is to reduce the Levelized Cost of Energy of TES for concentrated solar power to be under 15 $/kWh by 2030. In this work, a techno-economic assessment was performed to estimate the cost of TES using concentrate salt. The total cost of TES was estimated by considering costs associated with transportation of brine, evaporation of remaining water, grinding the salt content, additives added, and containment costs while considering a positive financial gain from obtaining the concentrate from water treatment facilities. It was observed that the concentrate salt that went through solid to liquid phase change provides an increase in energy density and a reduction in TES cost. The results show a financial benefit using concentrate salt as a storage medium for heat making it a feasible material to meet the Sunshot Initiative goals for TES. Depending on the source of the brine, zero liquid discharge method, and operating temperature we can observe costs as low as (−$11.10), i.e., positive revenue. The occurrence of phase change within the operating temperature of the application significantly increases the energy storage density and reduces the cost of the TES which is seen in the results for the melting scenarios.

Inorganic salts (e.g., chloride salts) have gained attention in the energy field as a new thermal energy storage medium. Low cost, high melting temperature and high heat capacity of inorganic salts make them attractive in utility-scale thermal storage applications as higher energy storage temperatures lead to higher efficiency in power generation. There is a potential to use the dry byproduct of water desalination, i.e., Reverse Osmosis Concentrate (ROC) as a thermal storage medium. Using ROC as a thermal energy storage medium would prevent a harmful waste to be released to the environment while introducing a novel and low-cost alternative for thermal energy storage medium. In this study, heat transfer behavior of an ROC-based thermal energy storage system is studied using CFD. A computational model is developed, verified, and validated to simulate the phase change process and buoyancy-driven flow in a square ROC-based thermal energy storage element. The computational results provide a predictive model for charge and discharge cycles of an ROC-based thermal energy storage system.

In this paper, Computational Fluid Dynamics (CFD) is employed to investigate the heat transfer characteristics of Reverse Osmosis Concentrate (ROC) as an alternative, low-cost thermal energy storage medium. Thermal energy storage is a critical component for increasing efficiency and dispatchability of solar thermal and combined heat and power plants. The byproduct of water desalination, ROC, is classified as an industrial waste by the U.S. Environmental Protection Agency as it has negative effects on vegetation and sea-life. Currently, ROC disposal includes deep-well injection, surface discharge to rivers, discharge to the ocean, and evaporation ponds. The composition and thermal properties of ROC salt vary depending on the original source of feedwater. Transient models are utilized to understand the heat transfer between the heat transfer fluid and storage fluid (i.e., ROC) over time. This simulation also provides valuable information in determining the optimal operating conditions of the thermal energy storage system. This information will be used in conjunction with a cost analysis, focused on the transportation, processing and containment cost of the energy storage, that aims to determine the economic feasibility of ROC technology in large scale, commercial applications.

This special issue of Symposium Dedicated to Renewable Energy and Sustainable Technologies is devoted to the ASME 13th International Conference on Energy Sustainability held in Bellevue, WA, June 15–17, 2019. For more than 10 years, the conference has been a venue for researchers from all over the world and for industry leaders from important sectors of energy production and management to share their innovative ideas and research progress. The conference in 2020 was sponsored by the Advanced Energy System Division and the Solar Energy Division. The ES Conference included 15 parallel tracks on the broad topic of renewable/sustainable energy, including, but not limited to, Sustainable Buildings, Sustainable Infrastructure and Transportation, Conversion and Processing of Biofuel and Alternative Fuel, Distributed Energy Systems, Concentrating Solar Power, Ocean and Hydropower Technologies, Photovoltaics, Wind Energy, and Emerging Technologies. In order to highlight innovative research outcomes and enhance public visibility, we have invited high-quality papers among 166 presentations, to be included in this special issue. Conference chairs from the Advanced Energy Division and Solar Energy Division, as well as experts from around the world, organized this issue as guest editors. We greatly appreciate your interest in this special issue, and we take this opportunity to thank the authors and reviewers for their outstanding contributions. We would also like to express our deep gratitude for the editor-in-chief of the journal, Dr. Hameed Metghalchi, for his guidance and support.

The reject of the reverse osmosis water treatment process (aka brine, concentrate, ROC) is a mixture of salts that are dissolved in high salinity water. The ROC is classified as an industrial waste by the U.S. Environmental Protection Agency and can face regulatory limitations on disposal. State-of-the-art of ROC disposal includes deep-well injection, surface discharge to rivers, discharge to the ocean, and evaporation ponds. In this study, the feasibility of using Reverse Osmosis Concentrate as a low-cost Thermal Energy Storage (TES) medium is explored by a techno-economic analysis. The normalized cost of TES (cost per unit volume of stored thermal energy) is estimated through a series of cost analyses and is compared to the cost targets of the U.S. Department of Energy for low-cost thermal energy storage. It was shown that the normalized cost of TES using ROC salt content is in the range of $6.11 to $8.73 depending on ROC processing methods.

Power overgeneration by renewable sources combined with less dispatchable conventional power plants introduces the power grid to a new challenge, i. e., instability. The stability of the power grid requires constant balance between generation and demand. A well-known solution to power overgeneration is grid-scale energy storage. Compressed air energy storage (CAES) has been utilized for grid-scale energy storage for a few decades. However, conventional diabatic CAES systems are difficult and expensive to construct and maintain due to their high-pressure operating condition. Hybrid compressed air energy storage (HCAES) systems are introduced as a new variant of old CAES technology to reduce the cost of energy storage using compressed air. The HCAES system split the received power from the grid into two subsystems. A portion of the power is used to compress air, as done in conventional CAES systems. The rest of the electric power is converted to heat in a high-temperature thermal energy storage (TES) component using Joule heating. A computational approach was adopted to investigate the performance of the proposed TES system during a full charge/storage/discharge cycle. It was shown that the proposed design can be used to receive 200 kW of power from the grid for 6 h without overheating the resistive heaters. The discharge computations show that the proposed geometry of the TES, along with a control strategy for the flow rate, can provide a 74-kW microturbine of the HCAES with the minimum required temperature, i. e., 1144K at 0.6 kg/s of air flow rate for 6 h.

This special issue of the ASME Journal of Energy Resources Technology is devoted to the ASME 12th International Conference on Energy Sustainability held in Lake Buena Vista, FL, June 24–28, 2018. For more than 10 years, the conference has been a place for researchers all over the world and from various sectors to share their innovative ideas and research progress. The conference in 2018 was sponsored by the Advanced Energy System Division and the Solar Energy Division, and co-located with the ASME Power Conference as well as the ASME Nuclear Forum. The conference included 14 parallel tracks on the broad topic of renewable/sustainable energy, including Nexus: Energy/Water/Climate/Food (new); Smart & Cyber-Physical Systems (new); Geothermal Technologies; Conversion and Processing of Biofuel and Alternative Fuel; Distributed Energy Systems; Sustainability and Society (new); Thermal and Mechanical Energy Storage; Sustainable Building Energy Systems; Photovoltaics; and Wind Energy Systems and Technologies. We are particularly excited to introduce the three new tracks, which have not received enough attention or did not have a proper place for presentation in the research community. In order to highlight innovative research outcomes and enhance public visibility, we have invited high quality papers out of 187 presentations to be included in this special issue. The conference chairs from the Advanced Energy Division as well as experts from around the world organized this issue as guest editors. We greatly appreciate your interest in this special issue and we take this opportunity to thank the authors and reviewers for their outstanding contributions. We would also like to express our deep gratitude for the editor-in-chief of the journal, Dr. Hameed Metghalchi, for his guidance and support.

The decline of surface water sources along with periodic droughts has introduced new challenges for the state of California. In order to keep up with the increasing demand for water, the state is heavily relying on imported water from the north to Southern California as well as importing water from the Colorado River. The imported water has a large carbon footprint due to using grid power for water transport. Water reuse (reclaimed) is considered as one of the solutions to reduce the dependency of state on imported water. The research team at Cal Poly Pomona, is developing an off-grid solar-powered greywater treatment system for non-potable use in single households. Greywater is the drained water from bathroom sinks, showers, tubs, and washing machines; not including wastewater from toilets or kitchen sinks. Treating greywater on-site can provide significant water savings, and can reduce the carbon footprint of desalination using solar panels. The developed system is comprised of a three-stage treatment train: micro-filtration, solar-driven reverse osmosis, and ultraviolet disinfection. The end product of the project is capable of reclaiming 90–100 gallons of water per day which is about 60% of residential greywater waste. The system removes large suspended particles (particles of dirt, food, etc.) as well as organic and inorganic dissolved contaminants. It is demonstrated that the system can provide a permeate quality that agrees with recommended guidelines for reclaimed water. The system has a recovery rate of up to 62%.

The growth in renewable energy generation highlights a demand for an effective energy storage system for future power grid. Energy storage systems have a crucial role in balancing the power grid and compensating for intermittency of renewable energy sources. The state-of-the-art of grid-scale energy storage technologies (e.g., pumped-hydro and conventional compressed air energy storage) require special topological considerations; however, thermal energy storage remains as a scalable technology for storing the energy from solar thermal plans and the power grid. In this paper elemental sulfur is further investigated as a storage medium for its driving low cost and high energy storage density capabilities. Presented work numerically investigates the heat transfer behavior between elemental sulfur and an internal heat source that is placed within the thermal energy storage element. The heat transfer from the internal heat source to the thermal storage medium (elemental sulfur) is investigated computationally to understand the heat transfer behavior during charge cycle. The computations were performed with a commercial CFD package (ANSYS FLUENT) using variable properties for the storage medium. A comprehensive grid refinement study was performed to ensure the accuracy of the computational results. The results of this study show that buoyancy-driven flow induced by the internal heat source forms a rising jet toward the top of the thermal energy storage element and enhances the mixing of the boundary layer leading to enhanced heat transfer from the internal heat source.

Decentralized water treatment consists of a variety of water treatment techniques for dwellings, industrial facilities, homes, and businesses independent of the power grid. According to the United States Geological Survey, brackish groundwater is abundant in the southwestern states including California; hence it can potentially be considered a new source for California’s water portfolio. Most of membrane-based desalination technologies (e.g. reverse osmosis) have high energy demand and cost. Using renewable energy (mostly solar photovoltaics) in concert with membrane-based water desalination can be utilized to develop decentralized and off-grid brackish water desalination systems especially for remote and rural regions. In this paper, the results of a case study on decentralized off-grid brackish water system have been presented and discussed. The system utilizes a high pressure pump that can provide a feed flow rate of 2.2 gpm of at 140 psi. The system is run by solar photovoltaic panels through a battery bank. The results of the study show that the system is capable of treating brackish water at a salt rejection rate of more than 97.5% and a recovery rate up to 80%.

As the population grows, one issue that is continually being addressed is the lack of clean water resources. In order to explore viable solutions, rapid experimentation and research has been underway to alleviate the water crisis. With the addition of new emerging technology, the development, improvement, and understanding of various techniques used to treat non-potable water has expanded. One subcategory of water filtration in particular that has seen rapid growth is Membrane Distillation (MD). MD is a filtration process that utilizes thermal energy to desalinate and decontaminate water. Compared to current industry leading techniques such as reverse osmosis, MD does not require such large operating pressures, leading to less power consumption. MD is accomplished primarily by flowing contaminated feed water at elevated temperatures across semi-permeable membranes. The membranes used are made to allow water vapors to penetrate through and separate from the contaminated liquid portion. By maintaining a temperature difference across the membrane, a pressure gradient is created, which drives the vapor of feed water through the pores in the membrane. Once the vapor passes through the membrane, it condenses through various methods and is collected. Air Gap Membrane Distillation (AGMD) has shown significant ability to desalinate water effectively in small scales. The air gap between the membrane and condensation plate minimizes heat loss through conduction, making AGMD a more attractive option for upscaling. In this project a laboratory-scale test cell was developed to test AGMD using different membranes, and operational parameters. In order to test such parameters, a unique design with baffled channels to induce turbulence was designed and manufactured. Feed water and coolant temperature differences, flow rates, membrane porosity, and air gap thickness are among the parameters that has been studied in this research. Temperatures of the hot feed were varied from 40°C to 80°C while the cold feed temperature was kept at a near constant temperature of 0°C. Flow rates of feed water and coolant water range from 1 to 3 L/Min. It was observed that the permeate flux is an increasing function of feed water temperature and membrane porosity. The air gap thickness plays a major role in permeate flux and energy consumption of the system.

Thermal energy storage with elemental sulfur is a low-cost alternative to molten salts for many medium to high temperature energy applications (200-600 degrees C). In this effort, by examining elemental sulfur stored isochorically inside isolated pipes, we find that sulfur provides attractive charge/discharge performance since it operates in the liquid-vapor regime at the temperatures relevant to many important applications, such as combined heat and power (CHP) plants and concentrating solar power (CSP) plants with advanced power cycle systems. The isolated pipe configuration is relevant to shell-and-tube thermal battery applications where the heat transfer fluid flows over the storage pipes through the shell. We analyze the transient charge and discharge behavior of sulfur inside the pipes using detailed computational modeling of the complex conjugate heat transfer and fluid flow phenomena. The computational model is validated against experiments of a single tube with well-defined temperature boundary conditions and internal temperature measurements. The model results evaluate the influence of pipe diameter on charge and discharge times, heat transfer rate, and Nusselt number due to buoyancy driven convection currents. Depending on the Rayleigh number (pipe diameter), the average Nusselt number obtained for discharge is 3-14 times higher than proposed solid-liquid phase change technologies based on molten salt, which are limited in their performance due to conduction based solidification and low thermal conductivity. The results show competing trade-offs between increase in heat transfer coefficient, thermal energy stored in sulfur, and increase in charge and discharge time with increase in pipe diameter. A preferred pipe diameter can be determined for target applications based on their requirements and these competing trade-offs. A validated fundamental correlation for Nusselt number as a function of Rayleigh number for charge and discharge is developed that can be used to design the sulfur-based thermal storage system for transient operation.

In this study, turbulent natural convection heat transfer during the charge cycle of an isochoric vertically oriented thermal energy storage (TES) tube is studied computationally and analytically. The storage fluids considered in this study (supercritical CO2 and liquid toluene) cover a wide range of Rayleigh numbers. The volume of the storage tube is constant and the thermal storage happens in an isochoric process. A computational model was utilized to study turbulent natural convection during the charge cycle. The computational results were further utilized to develop a conceptual and dimensionless model that views the thermal storage process as a hot boundary layer that rises along the tube wall and falls in the center to replace the cold fluid in the core. The dimensionless model predicts that the dimensionless mean temperature of the storage fluid and average Nusselt number of natural convection are functions of L/D ratio, Rayleigh number, and Fourier number that are combined to form a buoyancy-Fourier number.