•On-grid photovoltaic/battery/fuel cell system is considered as hybrid system.•Thermal and electrical operation of hybrid energy system is studied.•Hybrid energy system is used to reduce dependency ...on upstream grid for load serving.•Demand response program is proposed to manage the electrical load.•Demand response program is proposed to reduce hybrid energy system’s operation cost.
In this paper, cost-efficient operation problem of photovoltaic/battery/fuel cell hybrid energy system has been evaluated in the presence of demand response program. Each load curve has off-peak, mid and peak time periods in which the energy prices are different. Demand response program transfers some amount of load from peak periods to other periods to flatten the load curve and minimize total cost. So, the main goal is to meet the energy demand and propose a cost-efficient approach to minimize system’s total cost including system’s electrical cost and thermal cost and the revenue from exporting power to the upstream grid. A battery has been utilized as an electrical energy storage system and a heat storage tank is used as a thermal energy storage system to save energy in off-peak and mid-peak hours and then supply load in peak hours which leads to reduction of cost. The proposed cost-efficient operation problem of photovoltaic/battery/fuel cell hybrid energy system is modeled by a mixed-integer linear program and solved by General algebraic modeling system optimization software under CPLEX solver. Two case studies are investigated to show the effects of demand response program on reduction of total cost.
The operation of a combined heat and power (CHP) plant coupled with a heat storage tank (HST) can decouple heat–power constraints and improve the flexibility of unit operations during the heating ...season. A capacity optimization model is developed to solve the problem of HST capacity selection for deep peak shaving based on the heat–power decoupling principle of HST and peak shaving compensation policy in northeast China, taking a power plant as an example. The model takes the net present value of environmental benefits as the main optimization target function, and the particle swarm optimization (PSO) algorithm is used for optimization. The results show that the optimal HST capacity based on environmental benefits is smaller than the optimal HST capacity considering operating income. The heat load significantly impacts the configuration of the CHP system's optimal HST capacity, and the area corresponding to the optimal capacity is not the area where the maximum increment of deep peak shaving is located. The optimal HST capacity configured for the CHP plant is 170 MWh based on the characteristic daily load data of months. With the configured HST, the CHP plant can provide 8147.95 MW capacity for new energy grid-connected power generation every year during the heating season, eliminating 1692.33 tons of CO2, 41.68 tons of SO2, and 39.4 tons of NOx emissions. This study provides a HST capacity configuration method for CHP plant to improve the peak shaving ability and realize the sustainable development of society.
•Peak shaving principle of heat storage tank (HST) for CHP units is analyzed in detail.•A HST capacity optimization model embedded operation optimization is proposed.•The capacity optimization model considers the peak shaving compensation policy.•The heat load significantly impacts than power load for the optimal HST capacity.
The article concerns a theoretical investigation on the ground thermal energy storage (GTES) applied to a low-temperature district heating (LTDH) distribution network. A general formula describing ...the time-dependent GTES temperature variation was introduced. The highest values of the GTES operating parameters were obtained for the second model. The ground temperature of a varying liquid fraction content (0, 0.1, 0.2) reached a value of 33.42 °C, 33.29 °C and 33.07 °C, respectively. After the GTES was applied, the heat flux transferred to the end-users increased by 14.5 kW. Deactivation of the GTES caused that the heat flux transferred to the consumers had a constant value of 149.5 kW. The LTDH heat supplier was able to provide the heat flux which decreased in time by 8.26% when the GTES was activated. The impact of the GTES insulation on the ground temperature was studied. The results have shown that reducing the insulation by 1/3 results in the GTES temperature decrease by about 3%. It was also found out that inappropriate GTES operation mode may cause larger thermal depletion of the GTES.
•A general formula allowing the GTES mean temperature calculation is introduced.•The GTES in the LTDH increases the heat flux transferred to the consumers.•The GTES in the LTDH increases water's outlet temperature of the supply pipe.•Random charging/discharging duration time of the GTES causes its thermal depletion.•1/3 insulation reduction translates to 2.93% decrease in the GTES temperature.
•Optimum performance of PV/battery/fuel cell/grid hybrid system under load uncertainty.•Employing information gap decision theory (IGDT) to model the load uncertainty.•Robustness and opportunity ...functions of IGDT are modeled for risk-averse and risk-taker.•Robust strategy of hybrid system's operation obtained from robustness function.•Opportunistic strategy of hybrid system's operation obtained from opportunity function.
Nowadays with the speed that electrical loads are growing, system operators are challenged to manage the sources they use to supply loads which means that that besides upstream grid as the main sources of electric power, they can utilize renewable and non-renewable energy sources to meet the energy demand. In the proposed paper, a photovoltaic (PV)/fuel cell/battery hybrid system along with upstream grid has been utilized to supply two different types of loads: electrical load and thermal load. Operators should have to consider load uncertainty to manage the strategies they employ to supply load. In other words, operators have to evaluate how load variation would affect their energy procurement strategies. Therefore, information gap decision theory (IGDT) technique has been proposed to model the uncertainty of electrical load. Utilizing IGDT approach, robustness and opportunity functions are achieved which can be used by system operator to take the appropriate strategy. The uncertainty modeling of load enables operator to make appropriate decisions to optimize the system’s operation against possible changes in load. A case study has been simulated to validate the effects of proposed technique.
The present work proposes a stand-alone process for brackish water thermal desalination for the Brazilian semi-arid (BSA) region. The Multi-Effect Distillation (MED) is coupled with solar collectors, ...a thermal energy storage (TES) system, a biodigester for electricity generation and a brine reject valorization scheme. The TES provides the continuous production of freshwater using solar energy alone, unlike other studies in the literature. The brine recycling affords lower amounts of brine reject than that reported in the literature for MED plants. A detailed cash-flow analysis estimates the economic feasibility of the plant and a water sales price of US$ 4.95/m³ for a plant with a capacity of 72 m3/day. The results indicate that thermal desalination is a cost-effective and sustainable alternative to mitigate the water shortage in the BSA region.
•Stand-alone MED plant coupled with thermosolar energy in Brazilian semi-arid.•Thermal energy storage system affords freshwater supply over the whole year.•Economic feasibility analysis estimates freshwater sales price at 4.95 US$/m3.•Brine recycling affords a reject of only 13% of the brackish water inlet.•Brine valorization scheme further provides biomass for electricity generation.
•A 3D transient water tank model is created and validated by experimental measurements.•Thermal stratification of the water tank with PCM units under dynamic operating conditions was ...investigated.•Multiple thermal stratification evaluation parameters are applied.•The transient simulation results were used to visualize the generation mechanism of thermal stratification inside the DHW tank during the heat storage process.
Among the various ways to improve energy storage and utilization in solar thermal energy storage systems, the water tank is often considered as an effective heat storage utilization. In this study, sodium acetate trihydrate (SAT) is coupled with a solar domestic hot water (DHW) storage tank as a phase change material (PCM). The thermal stratification of latent heat storage water tanks with different locations of PCM units and inlet flows was researched experimentally and numerically. The results show that in the charging process, as the inlet flow increases, the thickness of the thermocline gradually increases, with the degree of mixing in the tank aggravation. The Richardson number gradually increases as the PCM units are moved closer to the inlet. The RMSE between the experimental and simulated values reached the minimum at a flow rate of 3 L/min. The system has taken as the optimal working condition with better thermal stratification when the PCM units are placed at PCM1, and the flow rate is 3 L/min. This study provides theoretical and experimental guidance for the optimal design of DHW storage systems.
•Designed the thermal stratification optimization scheme of heat storage tank by RSM.•Established the quadratic regression model of the performance indices.•Analyzed influences of the interactive ...factors on evaluation indices.•Obtained the optimal parameter combination of single-objective optimization.
The aim of this study was to analyze the thermal stratification characteristics affected by the central hole-type baffle plate in heat storage tank. The response surface method was used to optimize the structure parameters. Experiments were conducted to investigate the thermal stratification characteristics of a hot water storage tank with a baffle plate during the charging process. The temperature field and flow field inside the storage tank were calculated by numerical simulation, and the effects of different structural parameters on the mixing number, stratification number, and the Richardson number were analyzed. The results showed that the three evaluation indices correspond to different optimal parameter combinations. The interaction factors that have a crucial influence on the three evaluation indices are baffle aperture and inlet velocity, baffle position and inlet velocity, and baffle position and baffle aperture. Taking the Richardson number with the highest precision of the regression model as the optimization objective, the optimal parameter combination optimized by the expected function is a baffle position of 0.79, aperture of 0.80, and inlet velocity of 0.2 m/s.
An effective heat storage system was achieved by fabricating a 400-L cylindrical thermal energy storage (TES) tank equipped with 9 conical frustum containers. These conical frustum containers with ...PCM (CFC-PCM) contain paraffin wax in the upper third of the tank and water as the heat transfer fluid (HTF) in the circulation process. The TES tank was integrated with a 40 kW diesel generator, and experiments were conducted by operating the engine at six different loads. During the charging process, heat was recovered from the engine exhaust gases and jacket cooling water. The performance parameters were evaluated and reported based on the transient behavior of a hybrid sensible/latent TES tank under the charging process. The results showed that at 72.55% of the engine peak load, the energy utilization factor (EUF) and the exergy efficiency of the system were 91.17% and 81.22%, respectively. Although adding PCM to water only resulted in a 3% enhancement in heat storage capacity, it improved the durability of heat charging by providing thermal stratification and increasing charging efficiency compared to the reference state in some of the studied cases.
Liquid metals are good potential heat transfer materials for thermoclinic heat storage (THS) systems and will play an important role in the next generation solar thermal power system with higher ...operating temperature. This paper presents a comparative research work on the charging, discharging and mechanical performances of THS tanks based on four different liquid metal materials, which are lead (Pb), lead-bismuth alloy (PbBi), sodium (Na) and sodium-potassium alloy (NaK). The analysis results indicate that for both the charging and discharging processes, the lead-based THS tank can have the shortest operating duration, largest charging and discharging quantities (9.78 × 109 J and 9.21 × 109 J) as well as the highest discharging efficiency (94.17%), revealing its best operating performance. Relatively acceptable operating performances of lead-bismuth-based and sodium-based THS tanks are also demonstrated. Furthermore, in contrast with other three liquid metals, the lead-based THS tank also has the best mechanical performance. It has the smallest peak maximum mechanical stress of the steel wall (58.6 MPa). In summary, the lead-based THS tank has both the best heat storage and mechanical performances.
