Long-term Storage Of Solar Energy Research Articles

Solar Hydrogen Production by Artificial Photosynthesis in Photoreactor for Sustainable Mobility

The thermo-industrial human society is mainly based on fuels. Currently, societies are fully dependent on fossil fuels which cause climate change that threaten human race. Solar fuels are well suited technologies to face these challenges. Long-term solar energy storage based on chemical fuel production from water (and potentially CO2) has a significant importance to decarbonize our societies. Artificial photosynthesis is especially adapted to produce solar fuels, such as hydrogen, methane, ethanol, etc. This study focuses on hydrogen production. Water splitting with photolysis reaction is possible thanks to photocatalysts that absorb light and produce hydrogen. Modeling the hydrogen production is based on 3 main physics fields because the process is limited and controlled by radiative transfer. Electromagnetism is used to determine radiative properties. Then, radiative transfer allows to calculate photon absorption rates. Finally, the thermokinetic coupling law establishes a relation between photon absorption rate and hydrogen production rate. Experimentally, hydrogen production is operated in a dedi-cated laboratory-scale benchmark photoreactor. Photon flux density is controlled by a LED panel and hydrogen pressure variation is monitored with a pressure sensor. It is then possible to calculate experimental hydrogen production rates. The model predicts a non-linear thermo-kinetic coupling law, which fits well experimental results. Consequently, we demonstrated that the concept of incident solar flux density dilution is an important feature for process optimiza-tion. Several dilution technologies from TRL 3 to 5 are implemented in our laboratory thanks to the new PAVIN solar platform. They aim to validate high-efficiency technologies thanks to solar flux dilution.

Understanding Wavelength-Dependent Synergies between Morphology and Photonic Design in TiO2-Based Solar Powered Redox Cells.

Solar powered redox cells (SPRCs) are promising for large-scale and long-term storage of solar-energy, particularly when coupled with redox flow batteries (RFBs). While efforts have primarily focused on heterostructure engineering, the potential of synergistic morphology and photonic design has not been carefully studied. Here, we investigate the wavelength-dependent effects of light-absorption and charge transfer characteristics on the performance of gold decorated TiO2-based SPRC photoanodes operating with RFB-compatible redox couples. Through an in-depth optical and photoelectrochemical characterization of three complementary TiO2 microstructures, namely nanotubes, honeycombs, and nanoparticles, we elucidate the combined effects of nanometer-scale semiconductor morphology and plasmonic design across the visible spectrum. In particular, thin-walled TiO2 nanotubes exhibit a ∼ 50% increase in solar-to-chemical efficiency (STC) compared to thick-walled TiO2 honeycombs thanks to improved charge transfer. Au nanoparticles both increase generation and interfacial charge transfer (above bandgap) and promote hot carrier injection (below bandgap) leading to a further 25% increase in STC. Overall, Au/TiO2 nanotubes achieve a high photocurrent at 0.098 mA/cm2 and an excellent STC of 0.06%, among the highest with respect to the theoretical limit. The incident photon to current efficiency and internal quantum efficiency are also superior to those of bare TiO2 showing maximum values of 54.7% and 67%, respectively. Overall, nanophotonic engineering that synergistically combines morphology optimization and plasmonic sensitization schemes offer new avenues for improving rechargeable solar-energy technologies such as solar redox flow batteries.

Evaluation of a high-performance evaporative cooler-assisted open three-phase absorption thermal energy storage cycle for cooling

Absorption thermal energy storage is promising for long-term storage of solar energy with both cooling and heating output purposes. Recently, the three-phase absorption thermal energy storage attracts significant attention due to its high energy storage density. However, its operation suffers from the vacuum operation and crystals blockage of piping systems, especially for the cooling output scenario. To resolve these issues, a three-phase absorption thermal energy storage in humid air for cooling is proposed, in which the dehumidification via three-phase absorption drives the evaporative cooling. Airflow is used for heat and mass transfer, which avoids vacuum operation and crystal blockage simultaneously. Comprehensive analysis considering the thermodynamic status of both working pair and humid air is carried out, with LiCl-H2O, LiBr-H2O, and CaCl2-H2O. Results showed that high ESD (energy storage density) of 563 kWh/m3 and COP (coefficient of performance) of 1.22 can be achieved under typical summer operating conditions, which are 3.2 and 2.1 times higher than that of the conventional cycle, respectively. Such simultaneous enhancement in ESD and COP has not been achieved by low-grade energy-driven sorption thermal storage yet, showing its great potential in real applications.

Thermochemical performance assessment of solar continuous methane-driven ZnO reduction for co-production of pure zinc and hydrogen-rich syngas

Converting renewable solar energy to dispatchable chemical products via solar-driven thermochemical processes is one of the best solutions for long-term solar energy storage and renewable fuel production. This study addresses the performance assessment of continuous methane-driven ZnO reduction, fully powered by renewable solar heat, for co-production of hydrogen-rich syngas and metallic Zn in a solar prototype consuming-bed chemical reactor. On-sun experiments were conducted under continuous ZnO and CH4 co-feeding to assess the effect of key parameters (inlet CH4/ZnO molar ratio: 1–1.5, temperature: 900–1000 °C, and ZnO feeding rate: 0.5–1.5 g/min) in order to maximize syngas and Zn yields, and reactor performance metrics. As a result, a rise in either the CH4/ZnO molar ratio or temperature enhanced the reaction extent but favored solid carbon formation, which downgraded syngas products quality, and consumed more solar energy input. Increasing ZnO feeding rate under a constant ZnO/CH4 molar ratio significantly promoted ZnO + CH4 reaction performance thanks to both hastened ZnO consumption rate (boosting products yield) and reduced solar energy consumption (improving solar conversion efficiency). However, excessively high ZnO feeding rate caused temporal ZnO accumulation in the reactor. Optimal operating conditions for on-sun continuous methane-driven ZnO reduction were identified (at ZnO feeding rate = 1.2 g/min, CH4/ZnO molar ratio = 1.5, and temperature = 950 °C), yielding total syngas yield of 12.3 mmol/gZnO, solid carbon formation down to 0.58 mmol/gZnO, ZnO conversion of 63.0%, methane conversion of 10.6%, energy upgrade factor of 1.08, and solar-to-fuel energy conversion efficiency of 5.3%. High-purity Zn particles with hexagonal morphologies were generated in continuous mode, demonstrating the proposed approach feasibility and reliability for simultaneous methane conversion to syngas and metallic Zn production in a single process.

Performance analysis of seasonal soil heat storage system based on numerical simulation and experimental investigation

Renewable energy has become very prominent these days because of its sustainable and environment-friendly nature. The soil heat storage system plays an important role in the long-term storage of solar energy to ensure a consistent power supply. The experimental analysis and practical implementation of soil heat storage system are very difficult due to its large size and the simulation-based calculation is also very complex for the entire storage system. In order to reduce the system from the perspective of space and time, this paper has applied a similar function relationship for soil heat storage system and develops the traditional CFD simulation model and similar model. According to the dimensions of similar model, the corresponding experimental setup is constructed and the experimental results of long-term heat storage in the soil are compared with the calculation results of a CFD similar model. The relative error of inlet and outlet temperature difference is measured 10% and the error for soil temperature rise is below 1 °C. The proposed method has reduced the simulation and experimental workload for soil heat storage using similarity theory. Hence, the proposed method has great significance in the research domain of soil heat storage and the application of similarity theory.

Long-Term Solar Energy Storage under Ambient Conditions in a MOF-Based Solid–Solid Phase-Change Material

This paper demonstrates a metal−organic framework (MOF) containing photoswitches within the pores as a hybrid solar thermal fuel (STF) and solid−solid phase-change material (ss-PCM). A series of azobenzene-loaded MOFs were synthesized with the general formula Zn2(BDC)2(DABCO)(AB)x (BDC = 1,4-benzenedicarboxylate, DABCO = 1,4- diazabicyclo[2.2.2]octane, AB = azobenzene, where x = 1.0, 0.9, 0.5, 0.3), herein named 1⊃AB1.0, 1⊃AB0.9, 1⊃AB0.5, and 1⊃AB0.3 respectively. X-ray powder diffraction, solid-state NMR, and density functional theory calculations were used to explore in detail the structural changes of the host framework that take place upon loading with the AB guest molecules. Differential scanning calorimetry measurements reveal a reversible phase change, which is absent from the evacuated framework. Upon irradiation with 365 nm light, 40% of the AB guests converted from the trans to the higher-energy cis isomeric form in 1⊃AB1.0. The energy stored within the metastable cis isomers is released upon heating and balances the endotherm associated with the phase transition. However, the exotherm associated with the phase transition is retained upon cooling, resulting in a net energy release over a full heating−cooling cycle. The maximum energy density is observed for the fully loaded composite 1⊃AB1.0, which releases 28.9 J g−1. In addition, the cis-AB guests in this composite showed negligible thermal reconversion during 4 months at ambient temperature, with an estimated energy storage half-life of 4.5 years. Further development of MOF-based STF-ss-PCMs could lead to applications for solar energy conversion and storage, and thermal management.

Paper title: thermochemical heat storage behavior of ZnSO4.7H2O under low-temperature

Thermochemical heat storage materials for space heating applications such as, ZnSO4 offer high energy storage density, low cost and clean mean of long-term solar energy storage. Herein, we studied the ZnSO4 hydrated salt as potential heat storage material at low temperature and furthermore observed the impact of temperature and concentration on the dehydration/hydration process and enthalpy. The thermal behavior of ZnSO4•7H2O was investigated by applying various dehydration temperatures. The results showed that 85% of water loosed at 100 °C temperature, which released 699 J/g (1.37 GJ/m3) in the dehydration process. The hydration process of ZnSO4.7H2O at 100 °C recovered 541 J/g enthalpies, which delivered 1.1 GJ/m3. Similarly, the dehydration result obtained at 150 °C was the same as showed at 100 °C. However, the enthalpy of hydration was 20% less than prior. The XRD result showed that at higher temperatures agglomeration appeared followed by Van der Waals forces which affect the hydration rate. The result of good cyclability and larger water sorption performance of ZnSO4 make them a promising and suitable for heat storage in space heating application, which can be used as thermochemical heat storage material for thermal storage devices.

Tuning the Properties of Benzothiadiazole Dyes for Efficient Visible Light-Driven Photocatalytic H2 Production under Different Conditions

Photocatalytic hydrogen production has recently emerged as a promising process for the long-term storage of solar energy. In this work, we studied the application of a series of heterogeneous photo...

Characterisation of magnesium, zinc and iron sulfates for thermochemical storage

Thermochemical heat-storage materials such as magnesium, zinc and iron sulfates offer high energy-storage densities and a reliable means of long-term storage of solar energy. In this research study, the dynamic properties of these three salts were investigated based on their hydration and dehydration characteristics. To investigate the effect of regeneration temperatures on the physio-chemical properties of the materials, four sets of temperatures were used. At 100°C, zinc sulfate showed a significant loss of water as compared to magnesium and iron salts, while in the hydration process at lower temperatures, zinc sulfate showed the highest sorption enthalpy and energy density. Furthermore, the crystallinity of salt hydrates was characterised using powder X-ray diffraction measurements, which revealed that dehydration of water molecules occurred only in magnesium sulfate, whereas partial distortion occurred in iron sulfate with a rise in temperature. Collating the results together indicated that zinc sulfate is more energy efficient than both magnesium and iron sulfate. With a calculated hydration energy density at 100°C of 1·26 GJ/m3, zinc sulfate is the best option among the three salts for its use as a thermochemical material.

Hydration performance and cycling stability of threeTCM:MgSO4,ZnSO4andFeSO4

Thermochemical heat storage materials offer high-energy storage densities and clean means of long-term solar energy storage. The aim of the study is to assess the potential heat storage efficiency of salt hydrates, based on sufficient hydration/dehydration performance, water sorption and cyclicability. MgSO4 7H2O, ZnSO4 7H2O and FeSO4 7H2O were evaluated based on preselected criteria. The main highlights of the dehydration result show that higher enthalpy was obtained for MgSO4 and ZnSO4, shows 2256 and 1731 J g−1 enthalpy, respectively. During hydration process, six water molecules were absorb by MgSO4 and ZnSO4 after pre-dehydrated temperature 150°C and 120°C, respectively. The cycle stability of MgSO4 and ZnSO4 showed better performance which give rise 1210 g−1 and 1155 J g−1 enthalpy, respectively. It was expected that FeSO4 would show higher cyclicability due to their higher enthalpy (1400 J g−1) in the first round; however, overhydration does not permit it to released larger energy. The impact of relative humidity on water sorption performance and rate of hydration were reported which showed that MgSO4 and ZnSO4 can uptake maximum water under 85% and 75% relative humidity. Ongoing studies and the booming progress of ZnSO4 7H2O illustrate that likewise MgSO4 7H2O, it is also the potential candidate and can be use in thermochemical heat storage devices. To bring zinc sulfate heptahydrate into market, more detail studies in fields of evaluation of advanced materials and development of efficient and compact prototypes are still required.

Mixed Metal Oxide Systems Applied to Thermochemical Storage of Solar Energy: Benefits of Secondary Metal Addition in Co and Mn Oxides and Contribution of Thermodynamics

Thermochemical energy storage is promising for the long-term storage of solar energy via chemical bonds using reversible redox reactions. The development of thermally-stable and redox-active materials is needed, as single metal oxides (mainly Co and Mn oxides) show important shortcomings that may delay their large-scale implementation in solar power plants. Drawbacks associated with Co oxide concern chiefly cost and toxicity issues while Mn oxide suffers from slow oxidation kinetics and poor reversibility. Mixed metal oxide systems could alleviate the above-mentioned issues, thereby achieving improved materials characteristics. All binary oxide mixtures of the Mn-Co-Fe-Cu-O system are considered in this study, and their properties are evaluated by experimental measurements and/or thermodynamic calculations. The addition of Fe, Cu or Mn to cobalt oxide decreased both the oxygen storage capacity and energy storage density, thus adversely affecting the performance of Co3O4/CoO. Conversely, the addition of Fe, Co or Cu (with added amounts above 15, 40 and 30 mol%, respectively) improved the reversibility, re-oxidation rate and energy storage capacity of manganese oxide. Computational thermodynamics was applied to unravel the governing mechanisms and phase transitions responsible for the materials behavior, which represents a powerful tool for predicting the suitability of mixed oxide systems applied to thermochemical energy storage.

Zeolite–MgCl2 composites as potential long-term heat storage materials: Influence of zeolite properties on heats of water sorption

Thermochemical heat storage materials such as MgSO4 and MgCl2 offer high energy storage densities and an inexpensive and clean means of long-term solar energy storage. The aim of this paper is to investigate zeolite–MgCl2 composites as potential heat storage materials, studying the link between the composites physico-chemical properties and the heat of dehydration/hydration obtained. Four series of wide pore zeolite composites containing 5–15wt% MgCl2 have been prepared and characterized. Zeolites Na-X, Mordenite and Y (Na and H) were selected with the goal of impregnating the highest quantity of MgCl2, while achieving the highest heat release/store possible. Heats of water sorption/desorption studies of MgCl2 composites using thermogravimetry coupled to differential scanning calorimetry (TG–DSC) were recorded and compared with those of analogous MgSO4 composites. Both Na-Y and H-Y containing 15wt% MgCl2 achieved the highest heats of water sorption (1173 and 970Jg−1, respectively). BET surface area and pore volume measurements lead to clarification that a retention of the host zeolites large pore volume upon impregnation is essential to allow accessibility of water molecules to the dehydrated salt particles. It was shown that MgCl2 composites offered a far superior heat release upon hydration in comparison to that of MgSO4 composites, due to the higher energy density of MgCl2, but also due to the blocking of zeolite pores with MgSO4 particles.

Efficiency Limit of Molecular Solar Thermal Energy Collecting Devices

As a larger fraction of energy is based on solar energy and other renewable energy sources, technologies for energy storage and conversion is becoming increasingly important. Molecular solar thermal (MOST) is a concept for long-term storage of solar energy in molecules and release of the energy as heat with full regeneration of the initial materials. The process is inherently closed cycle and emission free. No assessment of the fundamental efficiency limits of the technology has been made. In this report, efficiency limits and fundamental factors for molecular design of molecular solar thermal systems are discussed. Maximum efficiencies and potential temperature gradients are estimated using a number of basic assumptions on desired storage lifetimes and energy losses. The predicted maximum solar energy conversion efficiency is 10.6% at a S1–S0 gap of 1.89 eV. At this S1–S0 gap, the stored energy is able to create temperature differences of ∼300 °C. Several existing systems have an energy storage density i...

Solar Heat for Corn Drying Under Ohio Conditions Part II Summer Storage of Solar Heat

ABSTRACT THE cost of storing and recovering heat for use in crop drying is presented as a function of storage temperature. At the level of 1980 fuel prices, the allowable cost for stored heat was calculated to be $2.50 to $3.00 per year per GJ. In addition, the costs of storing heat under Ohio weather conditions were estimated for systems using underground tanks or an above ground solar pond. The analysis included an investigation of the effect of storage temperature and tank insulation on energy storage cost. Results indicate that the overall energy efficiency from collection to utilization with long-term heat storage systems is 10 to 20 percent. Results also show that long-term solar energy storage, based upon high temperature water (above 55 C) for drying, is not economically feasible.

Long-term storage of solar energy in industrial process heat and electricity production: an analysis with reference to mediterranean weather

This paper describes how thermal processes, which use the integral over time of solar power, represent the best proposition for the long-term thermal storage of solar energy. Mediterranean weather was recorded for 638 consecutive days, starting on 21 October 1976. The performance of a solar power plant producing heat at a constant temperature level of 325°C was taken as a reference by simulating the operation of the plant under different weather conditions. The size of the storage and the maximum age of the heat required for efficient operation for 70% of the days of a year are obtained with reference to the Mediterranean weather. The analysis is then extended to electrical power generation and integrative as well as total solar electricity systems are analysed. Widespread use of solar power plants to produce electricity as integrative or autonomous generators can be accomplished with various efficiencies. With the present state of knowledge concerning the storage and transmission methods of electricity, the best performances are obtained when dynamic storage is used and direct storage is avoided.