• Energy Research

Abstract Availability of long term solar data and the quality of available data is usually an obstacle to the development of proposals for new concentrating solar power plants. Typical or representative meteorological years using hourly solar and weather data that has been selected to match long-term averages are often used to perform the preliminary design and performance assessment of solar power plants. Although the use of this data is convenient due to the reduced computational requirements in plant optimization, it may result in a simplistic prediction of plant operations that does not reflect the real plant performance by neglecting the impact of short-term variability in solar irradiance and the variations in weather and available solar energy for different years. This study conducts a systematic analysis of the influence of multi-year data sets with a range of different time step sizes (5, 15, 30 and 60 min) and thermal storage capacities (4, 8 and 12 h) using the physical parabolic trough with molten salt storage model in NREL’s System Advisor Model. Results indicate that the appropriateness of different step sizes is likely to vary depending on the purpose of the modelling; however, sensitivity to step size is reduced for larger storage capacities.

Abstract Availability of long term solar data and the quality of available data is usually an obstacle to the development of proposals for new concentrating solar power plants. Typical or representative meteorological years using hourly solar and weather data that has been selected to match long-term averages are often used to perform the preliminary design and performance assessment of solar power plants. Although the use of this data is convenient due to the reduced computational requirements in plant optimization, it may result in a simplistic prediction of plant operations that does not reflect the real plant performance by neglecting the impact of short-term variability in solar irradiance and the variations in weather and available solar energy for different years. This study conducts a systematic analysis of the influence of multi-year data sets with a range of different time step sizes (5, 15, 30 and 60 min) and thermal storage capacities (4, 8 and 12 h) using the physical parabolic trough with molten salt storage model in NREL’s System Advisor Model. Results indicate that the appropriateness of different step sizes is likely to vary depending on the purpose of the modelling; however, sensitivity to step size is reduced for larger storage capacities.

There is an increasing trend in using heat pumps in air conditioning (heating/cooling) systems of residential and commercial buildings. The required power to drive the compressor of vapor compression heat pump cycles may be provided by either an electrical motor or an internal combustion engine. In this paper thermal modeling and economic analysis of gas engine heat pumps (GEHPs) are presented based on energy and mass balance equations as well as the gas engine operating parameters (such as thermal efficiency, fuel consumption and fuel mass flow rate) and heat pump operating parameters (such as evaporator and condenser capacity and compressor input power). Based on the modeling results and with estimating GEHP fuel consumption, the economic analysis of using gas engine heat pumps (in comparison with the electrical heat pumps) at various climate regions of Iran, for both residential and commercial (office) buildings, and for both cooling and heating modes, was performed. Appropriate cost functions for predicting GEHP capital investment were proposed. Three approaches including equivalent uniform annual cost (EUAC), the annual cost of energy consumption, and payback period were applied in the economic analysis.

There is an increasing trend in using heat pumps in air conditioning (heating/cooling) systems of residential and commercial buildings. The required power to drive the compressor of vapor compression heat pump cycles may be provided by either an electrical motor or an internal combustion engine. In this paper thermal modeling and economic analysis of gas engine heat pumps (GEHPs) are presented based on energy and mass balance equations as well as the gas engine operating parameters (such as thermal efficiency, fuel consumption and fuel mass flow rate) and heat pump operating parameters (such as evaporator and condenser capacity and compressor input power). Based on the modeling results and with estimating GEHP fuel consumption, the economic analysis of using gas engine heat pumps (in comparison with the electrical heat pumps) at various climate regions of Iran, for both residential and commercial (office) buildings, and for both cooling and heating modes, was performed. Appropriate cost functions for predicting GEHP capital investment were proposed. Three approaches including equivalent uniform annual cost (EUAC), the annual cost of energy consumption, and payback period were applied in the economic analysis.

Hybrid power generation systems that combine more than one renewable resource type are a potential option to improve the capability of renewable power generation systems to meet network demands reliably. This increases the system complexity and cost, so this must be compensated by achieving correspondingly higher capacity factors to achieve similar financial performance to simpler systems. In the analysis undertaken, the hybrid systems developed were limited to combinations of biomass combustion and concentrated solar thermal technology for production of steam to feed a Rankine cycle turbine system. To ensure that resource availability was realistic in the study, biomass availability was based on 5 years of historical data for an existing biomass power generation site in Australia that currently has limited seasonal operations and matching solar data for the same location. A technoeconomic assessment was undertaken in parallel with optimization of plant configurations by inclusion of additional plant components and varying sizing. This included plant designs with different storage capacities, both thermal storage for solar energy and torrefaction char from short-term surpluses of biomass. Several system options were identified where financial performance matched the simple biomass combustion system, but with significant increases in capacity factor through hybridization.

Hybrid power generation systems that combine more than one renewable resource type are a potential option to improve the capability of renewable power generation systems to meet network demands reliably. This increases the system complexity and cost, so this must be compensated by achieving correspondingly higher capacity factors to achieve similar financial performance to simpler systems. In the analysis undertaken, the hybrid systems developed were limited to combinations of biomass combustion and concentrated solar thermal technology for production of steam to feed a Rankine cycle turbine system. To ensure that resource availability was realistic in the study, biomass availability was based on 5 years of historical data for an existing biomass power generation site in Australia that currently has limited seasonal operations and matching solar data for the same location. A technoeconomic assessment was undertaken in parallel with optimization of plant configurations by inclusion of additional plant components and varying sizing. This included plant designs with different storage capacities, both thermal storage for solar energy and torrefaction char from short-term surpluses of biomass. Several system options were identified where financial performance matched the simple biomass combustion system, but with significant increases in capacity factor through hybridization.

Abstract Combined heat and power (CHP) systems due to their high efficiency compared to the conventional power generation systems have received considerable attention as they have less harmful impact on the environment. Recently, the serious concern with reducing the greenhouse gas emissions has focussed the attention on the possibility of a carbon tax in some countries. Here, we address the impact of such tax on the sizing and economics of a CHP system. Optimum sizing of CHP systems is of great importance to maximize the benefits of these systems. To select the optimum prime mover of a CHP system, performance characteristics of engine as well as economic parameters should be taken into consideration. A general thermo-economic approach to optimum sizing of internal combustion engines as the prime movers (any type and size) of a medium scale CHP system (500–5000 kW) and planning their operational strategy is developed. Net Annual Cost (NAC) as the criterion for making decision is introduced and appropriate equations for estimating thermodynamic and economic parameters as well as greenhouse gas emissions are presented. We consider three modes of operation: one-way connection (OWC) mode, two-way connection (TWC) mode, and heat demand following (HDF) mode. The proposed method has been used for a case study where data is available in the literature and the optimum nominal powers using gas engines are 3.3 MW, 3.2 MW, and 1.2 MW and in the case of using diesel engines are 3.4 MW, 3.4 MW, and 1.4 MW for TWC, OWC, and HDF modes, respectively. To determine the sensitivity of results to input parameters (e.g. electricity price) a comprehensive parametric study was conducted.

Abstract Combined heat and power (CHP) systems due to their high efficiency compared to the conventional power generation systems have received considerable attention as they have less harmful impact on the environment. Recently, the serious concern with reducing the greenhouse gas emissions has focussed the attention on the possibility of a carbon tax in some countries. Here, we address the impact of such tax on the sizing and economics of a CHP system. Optimum sizing of CHP systems is of great importance to maximize the benefits of these systems. To select the optimum prime mover of a CHP system, performance characteristics of engine as well as economic parameters should be taken into consideration. A general thermo-economic approach to optimum sizing of internal combustion engines as the prime movers (any type and size) of a medium scale CHP system (500–5000 kW) and planning their operational strategy is developed. Net Annual Cost (NAC) as the criterion for making decision is introduced and appropriate equations for estimating thermodynamic and economic parameters as well as greenhouse gas emissions are presented. We consider three modes of operation: one-way connection (OWC) mode, two-way connection (TWC) mode, and heat demand following (HDF) mode. The proposed method has been used for a case study where data is available in the literature and the optimum nominal powers using gas engines are 3.3 MW, 3.2 MW, and 1.2 MW and in the case of using diesel engines are 3.4 MW, 3.4 MW, and 1.4 MW for TWC, OWC, and HDF modes, respectively. To determine the sensitivity of results to input parameters (e.g. electricity price) a comprehensive parametric study was conducted.

Abstract Flexibility in connection methods as well as the capability to be stacked in parallel in order to reliably supply larger demands are amongst the significant features which have attracted considerable interest in microturbines for distributed generation applications. One of the leading applications of microturbines is operating as the prime mover of a Combined Heat and Power (CHP) system. There is an increasing trend towards CHP systems due to their high fuel consumption efficiency as a result of simultaneous production of heat and power. These systems deal more effectively with the environmental issues, since they emit less pollution in comparison with a separate production of the same amount of electricity and heat. In order to optimally benefit from combined heat and power generation, the proper sizing of prime movers is of paramount importance. We have developed a technical-economic approach to selecting the optimum arrangement of microturbines (i.e. number of units and nominal power) and planning its operational strategy in small scale combined heat and power systems (capacities up to 500 kW) for three modes of operation: one-way connection (OWC) mode, two-way connection (TWC) mode, and heat demand following (HDF) mode. The economic decision making is based on Net Present Worth (NPW) method. In addition to the common practice of using identical models, a novel method for stacking microturbines is studied and the results are compared. Performance characteristics of microturbines as well as economic parameters play a crucial role in the proposed sizing procedure; hence appropriate relations are presented to estimate the technical and economic parameters of the system and a detailed sensitivity analysis is conducted. A carbon tax legislation is being considered now in Australia and we have also included in our analysis the impact of this on the economics of the system.