Following Electrical Load Research Articles

Multi-energy synergistic planning of distributed energy supply system: Wind-solar-hydrogen coupling energy supply

This study is to improve the efficiency of energy utilization with the continuous growth of global energy demand and the increasingly severe environmental problem. A hydrogen-containing distributed energy supply system is proposed, which includes a hydrogen energy subsystem. The main driver of the system is renewable energy, while hydrogen energy is used as a carrier to assist the flow of energy. This study proposes an improved following electric load (FEL) strategy based on a comprehensive consideration of energy interactions within the system, and designs an optimal configuration model aimed at improving its economic, environmental and energy benefits. In addition, an improved rime algorithm (IRIME) is proposed, whose convergence performance and solution stability are greatly improved. A multi-objective optimization algorithm with better convergence performance, multi-objective improved rime algorithm (MO-IRIME), is proposed for solving the optimal configuration model to obtain the optimal capacity of the equipment inside hydrogen-containing distributed energy supply system. The total annual cost is reduced by 44.80 %, the primary energy consumption by 68.47 % and the pollutant gas emissions by 75.79 % compared to the reference system. In addition, the way of interaction and coordination of multiple energy sources in the daily cycle is analyzed.

Comparative study on the improvement of a distributed energy system performance by optimized operation strategy from design to operation

The operation strategy directly affects the optimal design and operation performance of distributed energy systems (DESs). Following electrical load (FEL) and following thermal load (FTL) strategies, for example, cannot achieve the flexible scheduling of DESs. As a result, this paper proposes an optimized operation strategy with the optimization objectives of minimizing operating costs and reducing carbon emissions. A multi-objective system optimization model with a minimum total cost and a minimum fossil energy consumption as optimization objectives are established based on the optimized operation strategy. The design and operation of the proposed DES are optimized according to loads of a public building in Changsha, and the results are compared with those under the FEL and FTL strategies. The study demonstrates that the optimized operation strategy can avoid using the gas boiler under the design conditions, which improves the system’s operating efficiency and lowers the total system cost and fossil energy consumption. Compared to the FEL and FTL strategies, the total cost reduction rate of the system under the optimized operation strategy is 1.44% and 1.69%, respectively, and the fossil energy saving rate is 3.25% and 2.3%. Different from the design condition is that the optimized operation strategy under winter and summer operating conditions can not only improve the operating efficiency but also avoid the waste of waste heat from CHP units and reduce the grid power consumption, which makes the total system cost and fossil energy consumption under the optimized operation strategy significantly smaller than those under the FEL and FTL strategies, especially than the FEL strategy. Under the summer operation condition, the optimized operation strategy’s fossil energy saving rate and total cost reduction rate are 6.76% and 12.01%, while the rates are 22.38% and 36.20% in winter. Even if the energy price fluctuates, the total system cost and fossil energy consumption under the optimized operation strategy are less than those under the FEL and FTL strategies. Therefore, the proposed optimized operation strategy can improve the system’s energy efficiency and reduce total cost under the design and operation conditions.

Techno-economic-environmental assessment and performance comparison of a building distributed multi-energy system under various operation strategies

The distributed energy system (DES) is a promising technology that could enable decarbonization in the building sector. Comprehensive DES system assessment from a holistic perspective is crucial for system design, operation strategy selection, and performance optimization. This paper proposes a techno-economic-environmental integrated assessment model for comprehensive system evaluation. The DES configuration mainly includes a photovoltaic panel, ground source heat pump, gas turbine, absorption heat pump, and thermal storage tank. The system is simulated under three operation strategies with MATLAB/Simulink, which are following thermal load (FTL), following electric load (FEL), and following electric load with thermal storage (FELTS). Entropy-TOPSIS method is used to evaluate the DES's techno-economic-environmental performance under various operation strategies. The results indicate that the DES' primary energy efficiency ratio under the three operation strategies of FTL, FEL and FELTS are 51.49%, 86.78%, and 125.69%, respectively. The dynamic annual values are 1.05×106 CNY, 7.23×105 CNY, and 5.94×105 CNY, respectively. The total greenhouse gas emissions are 36.2 kgCO2eq/(m2∙a), 22.8 kgCO2eq/(m2∙a), and 16.4 kgCO2eq/(m2∙a), respectively. The entropy-TOPSIS analysis results showed that under FELTS operation strategy, DES performs the best; it has the best indicators for technical and environmental evaluation.

Energy, exergy, energy-saving, economic and environmental analysis of a micro-gas turbine-PV/T combined cooling, heating and power (CCHP) system under different operation strategies: Transient simulation

A micro-gas turbine (MGT) combined cooling, heating and power system coupled with low concentrating photovoltaic/thermal-heat hump (LCPV/T-HP) and absorption chiller is proposed in this study. LCPV/T is used as the heat source of HP to realize mutual promotion. The performance of CCHP system under different operation strategies is dynamically simulated and analyzed by TRNSYS software from energy, exergy, energy-saving, economy and environment. The results demonstrate that both high temperature water source heat pump (HWHP) and low temperature water source heat pump (LWHP) achieved better COP in following electric load (FEL) mode. The average COP of HWHP and LWHP are 22.69% and 4.75% higher than the rated COP, respectively. Annual total cost per unit building area (ATCUBA) and carbon dioxide emissions per unit building area (CDEUBA) are also more advantageous in FEL mode, while primary energy consumption per unit building area (PECUBA), ATCUBA and CDEUBA seems less preferable in following thermal load (FTL) mode. The exergy efficiency and energy efficiency of the system in FEL mode are 19.96% and 41.90% in summer, and 25.13% and 59.36% in winter. Additionally, the equipment with higher exergy loss is mainly LCPV/T, gas-fired boiler, absorption refrigeration unit, MGT and hot water generator under the three operation strategies.

Energy, exergy and exergoeconomic optimization of a proposed CCHP configuration under two different operating scenarios in a data center: Case study

Due to high demand for power and cooling in the data centers, employing combined cooling, heating and power (CCHP) systems could be an effective solution. The use of an operationally optimized CCHP system plays an important role in improvement of data center's performance. In this study, at first, based on energy, exergy and exergoeconomic analysis, an ICE-driven CCHP system following electrical load (FEL) is proposed to meet the power and cooling energy requirements of a data center as a case study. Then, the performance of CCHP system under two different operating scenarios are compared to introduce the optimal energy supply design. Finally, the optimal energy supply design is employed to optimize the performance of the selected CCHP system through a parametric study. In the first scenario, the water flow is applied for cooling of the ORC condenser while in the second scenario, the refrigerant of absorption chiller is considered as cooling source for the ORC condenser. Results of energetic and exergetic analysis show that using the second scenario, the cooling capacity, energy efficiency and exergy efficiency of the CCHP system are higher than the first scenario by 30.66%, 14.18% and 13.48%, respectively. In addition, exergoeconomic analysis results show that the total cost rate associated with fuel and product in the CCHP system under second operating scenario are lower than first one by 38.9% and 31.58%, respectively.

Economic, energetic and environmental optimization of hybrid biomass gasification-based combined cooling, heating and power system based on an improved operating strategy

The multi-objective optimization of the hybrid biomass gasification-based combined cooling, heating and power (BGBCCHP) system with respects to economy, energy and environment were realized. A feasibility study of adding the electric chiller (EC) and heat storage tank (HST) to the system was performed. An improved following hybrid electric-thermal load (IFHL) strategy was proposed. Three operating strategies (following thermal load (FTL), following electric load (FEL) and IFHL) and four kinds of biomass raw materials (corn straw (CS), wood pellet (WP), wheat straw (WS) and rice straw (RS)) were used in the optimization. Results show that CS is more conducive to improving economic, environmental and comprehensive performance, while WP is more conducive to improving energetic performance. The capacity of the EC of the system optimized from energetic perspective is larger than that of the system optimized from other perspectives. HST is recommended to add to the system under FEL. IFHL and FEL yield the best and worst system performance, respectively. Sensitivity analysis indicates that gasification efficiency has the greatest impact on system performance. As for the feed-in tariff policy, the equipment capacity and economic performance of the system are not affected by incentive coefficient.

Economic dispatch of multi-energy system considering seasonal variation based on hybrid operation strategy

A modeling framework of a multi-energy system (MES) with coordinated supply of combined cooling, heating and power using solar energy is established in this research. A new operation strategy named following operation cost (FOC) is proposed to compare with traditional operational modes which are following electric load (FEL) and following thermal load (FTL). The results indicate that the strategy of FOC has the advantage in saving operation cost. The study analyzes the three operation strategies from three criteria including the operation cost (OC), the carbon dioxide emission (CDE), and the primary energy consumption ratio (PER) in each season to find the most suitable hybrid operation strategy in the MES. For the MES of this paper, we choose the FEL strategy in winter, the FOC strategy in summer, spring, and autumn. The hybrid operation strategy is selected to make the MES have higher PER, lower CDE, and lower OC. The hybrid operation strategy has better comprehensive performance than the single operation strategy. It provides a reference for the operation mode of other MESs.

Multi-objective optimization and evaluation of hybrid CCHP systems for different building types

The hybridization between renewable energy and fossil energy in energy supply system is a feasible solution to reduce the fossil energy consumption and CO2 emission. The hybrid CCHP systems that can include gas turbine (GT), absorption unit (ABS), ground source heat pump (GSHP), photovoltaic panels (PV), solar thermal collectors (ST), photovoltaic thermal solar collectors (PVT), battery, water storage tank (WST), are proposed in this study. Two different systems to use solar energy are evaluated: in system A, solar energy is converted into thermal and electric energy by ST and PV, respectively; while in system B, solar energy is converted into thermal and electric energy by PVT. The NSGA-II algorithm is employed to search the Pareto frontier solutions of the multi-objective optimization model that considers economy, energy and environment performances. The TOPSIS method is used as decision making tool for ideal configuration selection. The hybrid CCHP systems for three buildings (hotel, office, market) are optimized and compared under different operation strategies. The results reveal that the system A operating in following electric load (FEL) strategy achieves more benefits for three buildings. Besides, the system configuration and component size are closely related to the building type.

System Design and Optimisation Study on a Novel CCHP System Integrated with a Hybrid Energy Storage System and an ORC

For achieving higher energy transferring efficiency from the resources to the load, the Combined Cooling, Heating, and Power (CCHP) systems have been widely researched and applied as an efficient approach. The key idea of this study is designing a novel structure of a hybrid CCHP system and evaluating its performance. In this research, there is a hybrid energy storage unit enhancing the whole system’s operation flexibility while supplying cooling, heating, and power. An ORC system is integrated into the CCHP system which takes responsibility of absorbing the low-temperature heat source for electricity generation. There are a few research studies focusing on the CCHP systems’ performance with this structure. In order to evaluate the integrated system’s performance, investigation and optimisation work has been conducted with the approaches of experimental studies and modelling simulation. The integrated system’s configuration, the model building process of several key components, the optimisation method, and the case studies are discussed and analysed in this study. The design of the integrated system and the control strategy are displayed in detail. Several sets of dynamic energy demand profiles are selected to evaluate the performance of the integrated system. The simulation study of the system supplying selected scenarios of loads is conducted. A comprehensive evaluation report indicates that the system’s efficiency during each study process differs while supplying different loads. The results include the power supplied by each component, the energy consumed by each type of load, and the efficiency improvements. It is found that the integrated system fully satisfies the selected domestic loads and various selected scenarios of loads with high efficiency. Compared to conventional power plants or CHP systems, the system efficiency enhancement comes from higher amount of recovery waste heat. Especially, the ORC system can absorb the low-temperature heat source for electricity generation. Compared to the original following electrical load (FEL) control strategy, the optimisation process brings overall efficiency improvements. The system’s overall efficiency was increased by from 3%, 3.18%, 2.85%, 17.11%, 8.89%, and 21.7% in the second case studies. Through the whole study, the main challenge lies within the design and the energy management of the integrated system.

A novel economic analyzing method for CCHP systems based on energy cascade utilization

Abstract A novel economic analyzing method was proposed to evaluate the combined cooling, heating and power (CCHP) system based on energy cascade utilization and the current feed-in tariff policy in China. Natural gas consumption rates were chosen as the economic criteria to evaluate operation costs of cooling, heating and electricity of an office building in Changchun, Jilin of China. Based on the building’s energy consumption and current energy price structures, the following electric load (FEL) operation strategy was used to achieve a more profitable performance from the CCHP system. Because of the deficiency in economic performance, no excess electricity was generated or sold to the grid, even though selling electricity to the grid was allowed when certain restrictions were satisfied. Meanwhile, the power generation unit size was optimized according to the basic electric requirement of the building. Additionally, a water storage tank was used because it could improve the primary energy consumption ratio and the profitability of the CCHP system.

Multi-objective optimization of a solar hybrid CCHP system based on different operation modes

Abstract This paper carries out a multi-objective optimization of a solar hybrid combined cooling, heating and power (CCHP) system, based on the objective functions of annual cost saving ratio (CSR) and primary energy saving ratio (PESR). The system is modeled in three modes: 1) following electrical load (FEL); 2) following thermal load (FTL) and 3) following thermal load and selling power to grid (FTL-S). Non-dominated Sort Genetic Algorithm- II (NSGA-II) is adopted to find the Pareto front solutions of the potentially optimal configuration and corresponding criteria. The results show a conflict between cost saving and fuel saving. By selecting the compromised optimal point, the CSR increases to 25.04% and the PESR increases to 37.86% on average. The system in FEL mode performs best in energy saving and the system in FTL-S mode performs best in economy. The solar hybrid CCHP system is also compared with other three systems: 1) conventional CCHP system; 2) CCHP system with photovoltaic assisted only and 3) CCHP system with solar collector assisted only. In the end, the sensitivity analysis is implemented and the results present that energy prices and the efficiency of major equipment have varying degrees of impact on system performance.

Developing an equipotential line method for the optimal design of an energy station location in a district heating system

The district heating system with distributed variable-frequency speed pumps (DVFSP) can provide substantial energy savings. Moreover, the energy station location has a great impact on the capital expenditure of heating system. Therefore, to determine the optimal energy station location in DVFSP system, this paper initially built a theoretical model of a DVFSP district heating system based on a cost-oriented index. Subsequently, an equipotential line method was illustrated and applied to a case study. This novel method can intuitively present the district distribution of the relative cost (RCnetwork) of DVFSP district heating system, which can conveniently determine the optimal location of an energy station. In the case study, six oval equipotential RCnetwork lines were described. The maximum RCnetwork reached 137.04% in the E4 location, and the minimum RCnetwork was 89.22% in the E11 location. The results showed that the optimal energy station location was near the district load center and biased to the side with higher building loads. Finally, a new energy utilization mode that coupled a combined cooling, heating and power (CCHP) system and a DVFSP district heating system was proposed. Economic analyses were carried out for the coupled system based on the following electric load (FEL) strategy and the following thermal load (FTL) strategy. The results confirmed that, in terms of the payback period and partial load rate (PLR) of the prime mover, the FEL strategy was more suitable for the coupled system. These results can provide guidance for district heating system design and management.

Thermo-ecological cost assessment and optimization for a hybrid combined cooling, heating and power system coupled with compound parabolic concentrated-photovoltaic thermal solar collectors

The aim of this work is to optimize and minimize the thermo-ecological cost (TEC) of a novel hybrid combined cooling heating and power (CCHP) system integrated with solar energy. A basic natural gas CCHP system based on internal combustion engine (ICE) is coupled with compound parabolic concentrated-photovoltaic thermal (CPC-PVT) collectors to construct a novel hybrid CCHP system. To minimize the TEC, an optimization methodology was proposed to optimize the configurations and installations of ICE and CPC-PVT, as well as the operation strategies. The TECs of multi-products of the CCHP system were assessed and compared in the following electrical load (FEL) and following thermal load (FTL) modes. The impacts of key parameters on TEC were analyzed and discussed. The results of a case study indicated that the system integrated with 100% photovoltaic covered ratio and 400 kW ICE gets the lowest TEC of 2.36 J/J in the FTL mode. The TECs of electricity decline 28.8% and 17.0% in the FEL and FTL modes, respectively when the photovoltaic covered ratio increases from 0 to 1.0. The increasing heat storage ratio leads to the increase of TEC of heat exergy carried by water due to the heat loss.

Optimal design and performance analysis of solar hybrid CCHP system considering influence of building type and climate condition

Abstract Incorporating solar energy technologies to the conventional combined cooling, heating and power (CCHP) system has been considered as an effective solution to mitigate the looming energy and environmental challenges. The mathematical model of a conventional CCHP system hybridized with photovoltaic (PV) panels and solar thermal collectors is built in this study. The particle swarm optimization (PSO) algorithm is employed to find the optimal size of key components of the solar hybrid CCHP system. The simulation work of solar hybrid CCHP systems in three building prototypes across seven climate zones is carried out to find appropriate design schemes of these cases. Besides, some guiding principles of the design of the solar hybrid CCHP system in early stage are summarized. The results show that the system under the following thermal load (FTL) strategy is the first choice in most cases of hospitals and hotels, except for the systems of hotels in the cold and very cold zones. On the contrary, the systems in offices perform better in the following electric load (FEL) mode in the majority of climate zones except for the hot-humid zone. Generally, the average optimal integrated performance (S) values of hospitals, hotels and offices can reach 28.95%, 28.20% and 22.69%, respectively.

A rolling prediction optimization strategy for the optimal design of grid connected integrated CCHP system with renewable energy and energy storage

Integrated Combined Cooling Heating and Power (CCHP) system with renewable energy (RE) and energy storage (ES), short as RE-CCHP-ES, is the distributed power station supply electricity, heating, cooling, and hot water by solar, wind power, and natural gas for a specific customer, such as campus, hospital, or commercial palace. Following electric load (FEL) and following the thermal load (FTL) are the traditional operation strategies for CCHP system. But for the system with gas boiler and electricity storage, their performances are not satisfied. Therefore, FLB-RPO operation strategy is designed and contracted with FEL-ECR, and FLB. The result of case study shows that the system designed under FLB-RPO strategy reducing more carbon emission, energy consumption, and system cost than the systems designed under other operation strategy or power supply.

Energy assessment of PEMFC based MCCHP with absorption chiller for small scale French residential application

In this paper, a novel micro combined cooling, heating, and power (MCCHP) system based on Proton Exchange (PEM) fuel cell and single-effect lithium LiBrH2O absorption machine, was designed and studied. PEMFC exhaust gas is used for heating the building and combustor exhaust gas energy is provided to absorption chiller for house cooling. A developed mathematical model is used to predict the MCCHP unit annual energy performance and saving. The study is focused on the MCCHP unit integrated on a single-family house located into eight different French climatic cities (Trappes, Rennes, Nantes, Strasbourg, Clermont-Ferrand, Bordeaux, Orange, and Marseille). Three operational strategies: following electric load (FEL), following thermal load (FTL) and following thermal and cold loads (FTCL) are investigated. The advantage of each strategy is analysed basing on different operational parameters such as electrical, thermal and total efficiencies of the combined PEMFC-absorption chiller, hydrogen consumption, and self-consumption ratios. The proposed MCCHP has been compared with the conventional separated energy systems using the fuel energy saving ratio as a performance index. The results show that the MCCHP unit saves energy during the whole year respecting the French climatic constraints and the house energy need. The best operational strategy is for MCCHP respecting electricity demand where the yearly average fuel energy saving ratio is about 35%. Furthermore, the analyses show that the maximum Fuel Energy Saving Ratio is about 35%, obtained for a single-family house located at Marseille, while the minimum Fuel Energy Saving Ratio, about 32%, is reached for a house situated at Rennes.

Optimal integration of renewable energy sources for autonomous tri-generation combined cooling, heating and power system based on evolutionary particle swarm optimization algorithm

Renewable energy (RE) sources can be integrated to serve autonomous tri-generation combined cooling, heating and power (CCHP) systems, so that the advantages of zero environmental emissions as well as higher energy efficiencies in generation and consumption are realized simultaneously. However, to override the inherent intermittent availability of RE sources and to enhance the performance of RE-CCHP systems, it is necessary to include thermal and electrical storage mechanisms. The objective of this study is to develop a simulation model for optimization of different configuration alternatives of autonomous RE-CCHP system for meeting cooling, heating and electrical loads, based on photovoltaic-thermal (PVT) panel, wind turbine (WT), thermal energy storage (TES), electrical energy storage (EES), absorption chiller (CHABS), electric chiller (CHELEC) and electric heater (EH). For operation of autonomous RE-CCHP system, two operational strategies, namely, following electric load (FEL) and following thermal load (FTL), are used. For optimization, a newly developed evolutionary particle swarm optimization (E-PSO) algorithm is examined and validated. It is demonstrated that the most cost effective configuration alternative of the autonomous RE-CCHP system is PVT+WT+EES+TES+CHABS+EH operating based on FTL operational strategy, where utilization of CHELEC is not needed.

Designing a micro Stirling engine for cleaner production of combined cooling heating and power in residential sector of different climates

In the present study the structure of an Alpha-type Stirling engine is designed which is capable of operating in reasonable operating condition ranges. The Alpha-type Stirling engine is simulated by GT-Suit program and the Solo V161 experimental data are used to validate the numerical model. The structure of the engine is kept constant and operating parameters such as, pressure, engine speed, temperature of the heater and working fluid are changed for using in a sample residential building in different climates. The engine is used for combined production of cooling, heating and power in micro scale (micro-CCHP). Three methods including following electrical load (FEL), following thermal load (FTL) and overall efficiency of the cycle are used for engine sizing. The maximum overall efficiency of the micro-CCHP ranges from 79% to 88% in different climates. The results show that both FEL and overall efficiency propose the same engine size and the highest overall efficiency for every climate. Furthermore, the reduction of environmental pollutants of CO2, CO, and NOx are calculated. The maximum CO2 reduction for every climate is more than 40%. In addition, leaking that usually occurs in this type of engine is lowered by operating at considerably lower pressure.

Solar assisted CCHP system, energetic, economic and environmental analysis, case study: Educational office buildings

Combined cooling, heating, and power (CCHP) systems have been attracted substantial interest during the last years due to their higher efficiency and their cost benefits while reducing greenhouse gases. With regard to the need for less pollutant and more efficient energy generation technologies, solar assisted combined cooling, heating and power (SCCHP) system in office buildings in Iran is studied. Four operational strategies, following electrical load (FEL), following thermal load (FTL), cooling demand hybrid supply and an optimization model are studied in order to find optimum equipment size. Results of hourly thermodynamic simulation, for one typical day in summer and one in winter show that overall system efficiency can reach up to 89% in summer considering FEL mode and CO2 emission production can be reduced by 2217kg/day in winter considering optimization model. The optimization model can reduce proposed system daily cost up to 69% in comparison to other strategies, but daily cost of the proposed system in all strategies is more than conventional system.

Modeling a novel CCHP system including solar and wind renewable energy resources and sizing by a CC-MOPSO algorithm

Due to problems, such as, heat losses of equipment, low energy efficiency, increasing pollution and the fossil fuels consumption, combined cooling, heating, and power (CCHP) systems have attracted lots of attention during the last decade. In this paper, for minimizing fossil fuel consumption and pollution, a novel CCHP system including photovoltaic (PV) modules, wind turbines, and solid oxide fuel cells (SOFC) as the prime movers is considered. Moreover, in order to minimize the excess electrical and heat energy production of the CCHP system and so reducing the need for the local power grid and any auxiliary heat production system, following electrical load (FEL) and following thermal load (FTL) operation strategies are considered, simultaneously. In order to determine the optimal number of each system component and also set the penalty factors in the used penalty function, a co-constrained multi objective particle swarm optimization (CC-MOPSO) algorithm is applied. Utilization of the renewable energy resources, the annual total cost (ATC) and the CCHP system area are considered as the objective functions. It also includes constraints such as, loss of power supply probability (LPSP), loss of heat supply probability (LHSP), state of battery charge (SOC), and the number of each CCHP component. A hypothetical hotel in Kermanshah, Iran is conducted to verify the feasibility of the proposed system. 10 wind turbines, 430 PV modules, 11 SOFCs, 106 batteries and 2 heat storage tanks (HST) are numerical results for the spring as the best season in terms of decreasing cost and fuel consumption. Comparing the results of the system with a common separated production (SP) system shows that the fossil fuels consumption and the pollution can be reduced up to 263 and 353 times, respectively.