Solar Thermal Storage System Research Articles

Designing Efficient Solar-Thermal Fuels with [n.n](9,10)Anthracene Cyclophanes: A Theoretical Perspective.

Molecular solar thermal storage (MOST) systems have been largely limited to three classes of molecular motifs: azo-benzene, norbornadiene, and transition metal based fulvalene-tetracarbonyl systems. Photodimerization of anthracene has been known for a century; however, this photoprocess has not been successfully exploited for MOST purposes due to its poor energy storage. Using well-calibrated theoretical methods on a series of [n.n](9,10)bis-anthracene cyclophanes, we have exposed that they can store solar energy into chemical bonds and can release in the form of heat energy on demand under mild conditions. The storage is mainly attributed to the strain in the rings formed by the alkyl linkers upon photoexcitation. Our results demonstrate that the gravimetric energy storage density for longer alkyl-chain linkers (n > 3) are comparable to those for the best-known candidates; however, it lacks some of the deleterious attributes of known systems, thus making the proposed molecules desirable targets for MOST applications.

Optimal design and operation of CHPs and energy hub with multi objectives for a local energy system

This study presents a multi-objective optimization process to determine the optimal operations of combined heat and power (CHP) units and energy hub according to present value and carbon emissions. Mixed integer linear programming (MILP) model is applied to a local energy system including both electricity and gas to achieve multi objectives (energy costs versus carbon emissions). The optimization problem is formulated on the coupling electricity load and gas load with an energy hub and CHP model for optimal design and operation. The components of the energy hub includes solar thermal system, heat pump, battery, photovoltaics (PV), CHPs and thermal storage system. The results show a set of optimal design solutions of each component including their half-hourly operations and trade-off between them to achieve multi-objectives. The total cost including energy cost, carbon emission and investment with energy hub will be 112 million pound lower compared to that without energy hub system in a 20 year time frame.

Seasonal Solar Thermal Energy Sand-Bed Storage in a Region with Extended Freezing Periods: Part I Experimental Investigation

We present the first experimental study of sand-bed thermal energy storage conducted in a region with extended freezing period. The study was carried out on a home situated in Palmer, Alaska, 61.6° N, and 149.1° W. The home is equipped with evacuated tube solar thermal collectors that are connected to a seasonal sand-bed solar thermal energy storage system. Fourteen weeks of data was collected from a period of 28 January 2017 through 7 May 2017. Results suggest that seasonal sand-bed solar thermal storage systems are an excellent option for storing heat for climates in regions with long periods of freezing temperatures. The present study shows a proof of concept of a sand-bed seasonal solar thermal storage that needs additional controls for residential heating application. The system could also be used to provide heat for unoccupied spaces such as garages and greenhouses.

Seasonal sand-bed solar thermal energy storage in a region with extended freezing periods: Experimentally verified numerical simulation

In this paper, we report the comparison of the experimental results with numerical simulation. The numerical simulation was performed using TRNSYS. Fourteen weeks of data (January 28 to May 7) were collected and compared against numerical simulation results obtained using TRNSYS. For the 14-week period, the results showed that there was close agreement between the experimental measurement and the numerical simulation. The measured average temperature was 8.1 °C compared to the simulated average temperature of 8.6 °C. The measured maximum and minimum temperatures were 21 °C and −7.8 °C, respectively, while the numerical simulation maximum and minimum temperatures were 17.8 °C and −7.5 °C, respectively. For the five-year seasonal simulation, the system became fully charged by June 14. The maximum temperature the sand-bed achieved annually was 24.83 °C, occurring approximately on July 10, with a minimum of 11.1 °C occurring on January 24. The results demonstrate that sand-bed solar thermal storage systems are suitable for climates in regions with long periods of freezing temperatures which can contribute towards the net-zero energy status of a residential home. We reported the first experimental study, to the authors' knowledge, of sand-bed solar thermal storage conducted in a region with an extended freezing period carried out on a home situated in Palmer, Alaska, 61.6°N, 149.1°W [see G. Hailu et al., Energies 10, 1873 (2017)].

High temperature solar receiver and thermal storage systems

For concentrating solar power (CSP) plants to become cost competitive, it is necessary to design systems with significantly higher cycle efficiencies and to innovate cost-effective storage systems and materials. Higher cycle efficiency demands higher operating temperature, which implies that the optical system for the solar receiver needs to be designed for higher concentration ratio. This paper reviews the present technologies for high temperature solar receivers associated with power dish and power tower systems. Significant research and development work required for high temperature storage systems and materials is also discussed. Recently, the supercritical carbon dioxide (s-CO2) Brayton cycle is identified as a potential candidate to realize significantly higher thermal efficiency at high operating temperature and pressure. Recent developments and challenges involved in development of solar receivers and thermal storage systems for such applications are also presented.

The Design of Solar Thermal Storage System Used to Improve the Ramp Rate of Coal-fired Units

The Design of Solar Thermal Storage System Used to Improve the Ramp Rate of Coal-fired Units

Two-Phase Anaerobic Digester Combined with Solar Thermal and Phase Change Thermal Storage System in Winter

Using solar energy as the heat source for biogas improvement of the anaerobic digester is an effective method. However, intermittent solar radiation and low ambient temperature in the winter make it difficult to maintain a steady fermentation temperature. In this study, a pilot-scale two-phase anaerobic digester combined with solar thermal and phase change thermal storage (PCTS) system has been constructed. A set of comparative field studies were carried out during the winter in Maanshan City, Anhui Province, China; these periods of study included no heating mode (P1), heated with solar thermal and PCTS system (P2), and conventional solar heating mode (P3). The comparison shows that methane yields and the energy conversion rate of the substrates of P2 were 12.33 m3 and 48.6%, respectively, both of which increased by 5.65 and 1.01 times, compared with that of P1 and P3, respectively. The statistical coefficients of variation for the fermentation temperature were 2.5% in P2 and 6.6% in P3, which means that ...

Model predictive control of solar thermal system with borehole seasonal storage

Abstract This work addresses the model predictive controller design for a complex solar boreal thermal storage system which models a real Drake Landing Solar Commercial Community. The overall discrete system is obtained from a coupled finite and infinite dimensional subsystems of solar collector, heat exchanger, hot tank and gas boilers without any spatial approximation or model reduction. The novel model predictive control addresses a house heat regulation by constrained optimization problem with the manipulation constraints, and accounts for possible unstable system dynamics and disturbances arising from solar and geothermal radiations. The realistic output regulation is considered by the inclusion of an observer which constructs finite and infinite dimensional states. The proposed model development and control regulation can successfully account for the long range variability in environmental and/or economic conditions associated with the overall operational costs of the large scale solar energy community. Finally, the controller performance is assessed by numerical simulations.

Improvement of collection efficiency and solar fraction in solar thermal storage system using a 3-way valve and a 2-stage flowrate control

In the present study, we investigated the effects of a combined system-control method in a solar thermal system; specifically, prevention of temperature reversal plus a reduced circulation rate. A 3-way valve is adopted as a remedy of the temperature reversal in the water storage tank and a 2-stage flowrate is implemented as the flowrate control strategy. To evaluate the effects, we perform five experiments and TRNSYS based simulations with a carefully developed system-control algorithm. As the main result, we experimentally validated that a 3-way valve is effective for the prevention of temperature reversal and a 2-stage flowrate extends the solar energy collection time. Annual simulation results show that the proposed combined method improves the system performances (1.9%p increase of collector efficiency, 2.2%p increase of solar fraction, and 5.3% additional collected energy) compared to the conventional forced circulation system. Our results should be applied to the water storage tank proposed in this study.

Modelling and control of solar thermal system with borehole seasonal storage

The paper addresses the problem of controlling a solar thermal storage system with the purpose of achieving a desired thermal comfort level and energy savings. A solar thermal power plant is used for heating district houses with borehole seasonal energy storage. As the energy output from the solar thermal plant with borehole seasonal storage varies, the control system maintains the thermal comfort by using a servo controller. In this work, the modelling of the solar thermal system with borehole seasonal storage is inspired by the Drake Landing Solar Community in Okotoks, Alberta, Canada [1]. The discrete model of the integrated energy system is obtained by using energy preserving Cayley-Tustin discretization. A simple and easily realizable servo control algorithm is designed to regulate the system operating at desired thermal comfort level despite disturbances from the solar thermal plant system, the borehole geo-thermal energy storage system and/or the district heating loop system. Finally, the performance of the servo controller and frequency analysis of the plant is given in simulation results section.

Optimization of Norbornadiene Compounds for Solar Thermal Storage by First-Principles Calculations.

Molecular photoswitches capable of storing solar energy are interesting candidates for future renewable energy applications. Here, using quantum mechanical calculations, we carry out a systematic screening of crucial optical (solar spectrum match) and thermal (storage energy density) properties of 64 such compounds based on the norbornadiene-quadricyclane system. Whereas a substantial number of these molecules reach the theoretical maximum solar power conversion efficiency, this requires a strong red-shift of the absorption spectrum, which causes undesirable absorption by the photoisomer as well as reduced thermal stability. These compounds typically also have a large molecular mass, leading to low storage densities. By contrast, single-substituted systems achieve a good compromise between efficiency and storage density, while avoiding competing absorption by the photo-isomer. This establishes guiding principles for the future development of molecular solar thermal storage systems.

Comparative Ab-Initio Study of Substituted Norbornadiene-Quadricyclane Compounds for Solar Thermal Storage.

Molecular photoswitches that are capable of storing solar energy, so-called molecular solar thermal storage systems, are interesting candidates for future renewable energy applications. In this context, substituted norbornadiene-quadricyclane systems have received renewed interest due to recent advances in their synthesis. The optical, thermodynamic, and kinetic properties of these systems can vary dramatically depending on the chosen substituents. The molecular design of optimal compounds therefore requires a detailed understanding of the effect of individual substituents as well as their interplay. Here, we model absorption spectra, potential energy storage, and thermal barriers for back-conversion of several substituted systems using both single-reference (density functional theory using PBE, B3LYP, CAM-B3LYP, M06, M06-2x, and M06-L functionals as well as MP2 calculations) and multireference methods (complete active space techniques). Already the diaryl substituted compound displays a strong red-shift compared to the unsubstituted system, which is shown to result from the extension of the conjugated π-system upon substitution. Using specific donor/acceptor groups gives rise to a further albeit relatively smaller red-shift. The calculated storage energy is found to be rather insensitive to the specific substituents, although solvent effects are likely to be important and require further study. The barrier for thermal back-conversion exhibits strong multireference character and as a result is noticeably correlated with the red-shift. Two possible reaction paths for the thermal back-conversion of diaryl substituted quadricyclane are identified and it is shown that among the compounds considered the path via the acceptor side is systematically favored. Finally, the present study establishes the basis for high-throughput screening of norbornadiene-quadricyclane compounds as it provides guidelines for the level of accuracy that can be expected for key properties from several different techniques.

Orchestration of Renewable Generation in Low Energy Buildings and Districts Using Energy Storage and Load Shaping

There is increasing penetration of renewable generation in buildings and districts. There are challenges in making the effective use of this generation. The objective of the ORIGIN project (Orchestration of Renewable Integrated Generation In Neighborhoods) is to shape loads so that the fraction of energy consumed that is from local renewable generation is maximized, and energy imported from outside sources is minimized. This paper presents the overall approach taken in the ORIGIN project and explores building physics aspects of solar thermal storage system orchestration. The case study districts are briefly introduced and characteristics of their generation, buildings, districts and shiftable loads described. The orchestration approach taken in ORIGIN is then presented. At the core of the ORIGIN system is the orchestration algorithm which generates informational and control outputs to shape future loads to best meet the objectives. The model based approach used to quantify thermal and electrical load shifting opportunities for pre-charging, coasting or avoiding loads, while meeting thermal comfort and other demands, is described using a solar thermal storage system as an example. The future steps for the ORIGIN project; retrofit of the ORIGIN system into existing districts and potential for other future applications is briefly discussed.

Renewable Energy Devices and Systems – State-of-the-Art Technology, Research and Development, Challenges and Future Trends

In this paper, essential statistics demonstrating the increasing role of renewable energy generation are firstly discussed. A state of the art review section covers fundamentals of wind turbines and PV systems. Included are schematic diagrams illustrating the main components and system topologies and the fundamental and increasing role of power electronics as an enabler for renewable energy integration, and for the future power system and smart grid. Recent examples of research and development, including new devices and system installations for utility power plants, as well for as residential and commercial applications are provided. Fuel cells, solar thermal, wave generators, and energy storage systems are also briefly presented and illustrated. Challenges and future trends for 2025 are summarized in a table for on-shore and off-shore wind energy, solar power, including photovoltaic and concentering, wave energy, fuel cells, and storage with batteries and hydrogen, respectively. Recommended further readings on topics of electric power engineering for renewable energy are included in a final section. This paper also represents an editorial introduction for two special issues of the Electric Power Component and Systems Journal, 43(8–10) and 43(12), respectively.

Solar Thermal Energy Storage in Power Generation Using Phase Change Material with Heat Pipes and Fins to Enhance Heat Transfer

Phase change materials absorb or otherwise release heat at close to a constant temperature during its melting and solidification phases. This is a very sought after property in power generation, where a high temperature heat source is required within a narrow temperature range as heat input for the turbine. Solar tower technology provides a high temperature heat source, but unfortunately it is time dependent. A sufficient amount of this heat may be stored in a phase change storage system which can deliver dispatchable heat. In such a storage system the phase change material needs to be exposed to a sufficient heat transfer area to melt or solidify at sufficient rates. In this study this is achieved with heat pipes with metallic fins. The analysis of this design included testing an experimental module during heat absorption and heat removal cycles, as well as a numerical analysis to model the storage module. To determine the parameters for a specific phase change storage system in a high temperature solar tower application the validated numerical thermal response simulation is incorporated. Certain solar input conditions and load cases are applied to the phase change storage system model and the size and geometry of the solar thermal storage system are determined from this analysis.

Improved Optimization Study of Integration Strategies in Solar Aided Coal-Fired Power Generation System

Solar aided coal-fired power generation system (SACFPGS) combines solar energy and traditional coal-fired units in a particular way. This study mainly improves the solar thermal storage system. Genetic algorithm is used to optimize the SACFPGS. The best integration approach of the system, the collector area, and the corresponding thermal storage capacity to replace each high-pressure extraction are obtained when the amount of coal saving in unit solar investment per hour is at its largest. System performance before and after the improvement is compared. Results show that the improvement of the thermal storage system effectively increases the economic benefit of the integrated system.

Corrosion Behaviors of Thermal Diffusion Coating on the Surface of Inconel625 Alloy in Chloride Molten Salts

In solar thermal storage system, the mixed chloride molten salt with the higher conversion efficiency than a single molten salt, but they are more corrosive than the often used nitride molten salts. In the presents work, aluminide and chromate coating were prepared on the surface of Inconel625 alloy by thermal packing method. The corrosion behaviors of thermal diffusion coating on the surface of Inconel625 alloy in mixed molten salts at 900°C were studied by using XRD and SEM equipped with EDS in the present work. The results showed that both of the two thermal diffusion coatings have sever corrosion in the mixed chloride molten salts, but thermal diffusion Al coating in the mixed chloride molten salt corrosion is more serious than thermal diffusion Cr coating, because Cr2O3is more easily dissolved in the molten salt than Al2O3.

Solar Driven Air Conditioning System Integrated With Latent Heat Thermal Energy Storage

This work is to investigate and validate of solar thermal storage system integrated with phase change material (PCM). The existing system is suggested to setup a Storage tank with phase change material (PCM), between the Solar concentrate dishes and Vapour absorption machine (VAM). The storage tank was used instead of an Electrical AC compressor, by which the renewable energy can be utilized to its full extent. Numerical Simulation is done and the Total Heat output, Temperature distribution along the bed, Pressure, charging time, discharging time, Mass flow rate are calculated. The storage system contains Erythritol as PCM in HDPE spherical capsule, having the storage capacity 345,121 KJ/hr (for the storage tank capacity) considering the latent heat and sensible heat of the Heat transfer fluid.

Solar Driven Air Conditioning System Integrated With Latent Heat Thermal Energy Storage

This work is to investigate and validate of solar thermal storage system integrated with phase change material (PCM). The existing system is suggested to setup a Storage tank with phase change material (PCM), between the Solar concentrate dishes and Vapour absorption machine (VAM). The storage tank was used instead of an Electrical AC compressor, by which the renewable energy can be utilized to its full extent. Numerical Simulation is done and the Total Heat output, Temperature distribution along the bed, Pressure, charging time, discharging time, Mass flow rate are calculated. The storage system contains Erythritol as PCM in HDPE spherical capsule, having the storage capacity 345,121 KJ/hr (for the storage tank capacity) considering the latent heat and sensible heat of the Heat transfer fluid. Solar Driven Air Conditioning System Integrated With Latent Heat Thermal Energy Storage A. Ponshanmugakumar1*, M. Sivashanmugam1 and S. Stephen Jayakumar2 1 AMET University,Chennai,India; shnmgkmr8@gmail.com 2 VOLTAS India Ltd, Chennai, India Keywords: Vapour Absorption Machine (VAM), Phase Change Materials (PCM), Erithritol, Storage Tank, Numerical Simulation.

A Review on Properties of Phase Change Material for Solar Thermal Storage System

Thermal energy could have several geneses but storage of solar thermal energy is one of the principal areas of investigation. The various conventional and unconventional materials are investigated for their capability to store thermal energy. These thermal energy storage devices (TESD) are selected on the basis of some essential properties like, thermal, physical, chemical properties and economic aspects. Melting point, heat of fusion, density, heat capacity, thermal conductivity, compatibility with container and cost of production are the chief parameters for selection of phase change material. Phase change materials (PCMs) have the capability of storing heat (latent heat storage units) and phase transition point to the environment of the operating temperature. This research paper focus on assessment of PCMs properties and economic aspect for rural and industrial applications. The design and development of thermal storage system depend on fundamentals of thermodynamic or heat transfer analysis