Development of an approach to compare the ‘value’ of electrical and thermal output from a domestic PV/thermal system

When considering the design of a PV/thermal system, determination of the ratio of the values of the electrical and thermal output from the system allows a rational approach to design optimisation via the minimization of ‘equivalent electrical levelised energy cost’. This paper focuses on methods that can be employed to develop a ratio between electrical and thermal output from a domestic style PV/thermal system. Methods discussed include thermodynamic analysis using exergy; market analysis for both an open market and a renewable energy market; and environmental analysis using avoided greenhouse gas emissions. Ratios are developed for each method based on real data. It is concluded that a renewable energy market approach seems most logical for such a system, and an indicative value of 4.24 is obtained. An example is given comparing a PV/thermal system that uses amorphous silicon cells with one that uses crystalline silicon cells. Levelised energy cost is plotted against the energy value ratio to show that there is a critical electrical-to-thermal energy value ratio below which a collector with a-Si cells is more cost effective than one with c-Si cells.     

Holographic diffraction‐through‐aperture spectrum splitting for increased hybrid solar energy conversion efficiency

A holographic module is designed to split light into two spectral bands for hybrid solar energy conversion. Incoming light is either transmitted to a large subsystem receiver or diffracted through an aperture in this receiver toward a second subsystem receiver. The holographic element is simulated using rigorous diffraction and ray‐tracing methods. Two applications of the design are described and simulated. A photovoltaic/thermal system with 93% optical efficiency and adjustable subsystem power output ratio is designed to address solar intermittency and provide energy storage. A photovoltaic system added to an alga biofuel operation significantly increases energy output while maintaining 92% of the original algae yield. The energy return on investment of this photovoltaic/biofuel system is 2.4× greater than that of the biofuel system alone, leading to economically viable operation. Modifications to the standard holographic lens provide additional increases in spectrum‐splitting capability, optical efficiency, and energy conversion efficiency. The diffraction‐through‐aperture concept is demonstrated as a successful approach to spectrum splitting for hybrid solar applications. Copyright © 2014 John Wiley & Sons, Ltd.     

The dynamics of integrated compressed air renewable energy systems

An integrated compressed air renewable energy system is defined here as one which harvests renewable energy directly in the form of compressed air and later converts that to the form of electrical power for transmission. There are two main motivations for considering such systems: firstly the lifetime cost per kW h exported has the potential to be substantially lower than the lifetime cost per kW h of a system generating electricity directly. Secondly these systems offer the intrinsic capability to store large amounts of energy in a very cost effective way. The only marginal costs associated with energy storage are those connected with providing some means for storing the compressed air and some means for managing heat. This paper describes an approach to simulating the performance of such systems including a controller to determine how much power to generate at a given time and it explains an appropriate rationale for the design of that controller. The simulations conducted indicate three remarkable performance measures. Specifically: (a) the marginal loss of energy associated with passing some energy through storage may be below 15% even with energy residency times in the order of months, (b) the marginal increase in total output electrical energy arising from integrating some solar heat capture can be as high as 60% of the captured solar heat for solar heat inputs up to 5% of total mechanical power and (c) the average value of the total power output may easily be raised by over 30% if power values continue to fluctuate at rates exhibited today and if the capacity for expansion-generation matches the peak input power of the primary (mechanical) energy harvesters.     

A method for evaluating the influence of wiring on the performance of components in a photovoltaic system design

This paper presents a simple method for evaluating the influence of wiring on the operating conditions of the direct current components in a photovoltaic system design. This method uses electrical circuit theory, electrical resistance modeling, and an iterative calculation approach to address the causality dilemma that exists when estimating voltage reductions in the wires that connect photovoltaic modules to power inverters. This method can be used to estimate the voltage, current output, and power output of each photovoltaic module in a system, and the corresponding total power available at the inverter, given current–voltage (I–V) models for the photovoltaic modules, and the lengths and thicknesses of the corresponding interconnection wiring. This paper uses this method to illustrate the influence that wiring can have on the direct current operating voltage that is needed at the power inverter to achieve maximum power performance for the system. The goal is that this method would be incorporated into software that analyzes the power performance and energy output of photovoltaic systems.     

Design optimization under uncertainty of hybrid fuel cell energy systems for power generation and cooling purposes

Reliance on point estimates when developing hybrid energy systems can over/underestimate system performance. Analyzing the sensitivity and uncertainty of large-scale hybrid systems can be a challenging task due to the large number of design parameters to be explored. In this work, a comprehensive and efficient sensitivity/uncertainty methodology is applied on two fuel cell hybrid systems to help analysts to investigate hybrid systems more efficiently. This methodology also includes a step-by-step approach to perform design optimization under uncertainty of energy systems. The two hybrid systems are: molten carbonate fuel cell with thermoelectric generator (MCFC-TEG) and phosphoric acid fuel cell with refrigerator (PAFC-REF). Various sensitivity and uncertainty methods are utilized to analyze the design parameters and their effect on the performance of these two systems. These methods perform local and regression-based sensitivity analysis, Monte Carlo uncertainty propagation, parameter screening, and variance decomposition. Detailed approach is adopted to identify and rank the influential design parameters for each system. Results demonstrate that the optimum power output of the MCFC-TEG has 10% uncertainty, driven mainly by the operating temperature, cahtode activation energy, TEG figure of merit, and TEG thermal conductivity. However, PAFC-REF is more reliable with larger power output and 1.4% uncertainty, driven by the charge transfer coefficient, heat transfer in the refrigeration cycle, cold reservoir temperature, and operating temperature. Based on this identification, design optimization under uncertainty is performed using these sensitive parameters to improve the system performance through increasing the power output and reducing its uncertainty.     

Framework design of a hybrid energy system by combining wind farm with small gas turbine power plants

Owing to the stochastic characteristic of natural wind speed, the output fluctuation of wind farm has a negative impact on power grid when a large-scale wind farm is connected to a power grid. It is very difficult to overcome this impact only by wind farm itself. A novel power system called wind-gas turbine hybrid energy system was discussed, and the framework design of this hybrid energy system was presented in detail in this paper. The hybrid energy system combines wind farm with several small gas turbine power plants to form an integrated power station to provide a relatively firm output power. The small gas turbine power plant has such special advantages as fast start-up, shutdown, and quick load regulation to fit the requirement of the hybrid energy system. Therefore, the hybrid energy system uses the output from the small gas turbine power plants to compensate for the output fluctuation from the wind farm for the firm output from the whole power system. To put this hybrid energy system into practice, the framework must be designed first. The capacity of the wind farm is chosen according to the capacity and units of small gas turbine power plants, load requirement from power grid, and local wind energy resource distribution. Finally, a framework design case of hybrid energy system was suggested according to typical wind energy resource in Xinjiang Autonomous Region in China.     

Framework design of a hybrid energy system by combining wind farm with small gas turbine power plants

Owing to the stochastic characteristic of natural wind speed, the output fluctuation of wind farm has a negative impact on power grid when a large-scale wind farm is connected to a power grid. It is very difficult to overcome this impact only by wind farm itself. A novel power system called wind-gas turbine hybrid energy system was discussed, and the framework design of this hybrid energy system was presented in detail in this paper. The hybrid energy system combines wind farm with several small gas turbine power plants to form an integrated power station to provide a relatively firm output power. The small gas turbine power plant has such special advantages as fast start-up, shutdown, and quick load regulation to fit the requirement of the hybrid energy system. Therefore, the hybrid energy system uses the output from the small gas turbine power plants to compensate for the output fluctuation from the wind farm for the firm output from the whole power system. To put this hybrid energy system into practice, the framework must be designed first. The capacity of the wind farm is chosen according to the capacity and units of small gas turbine power plants, load requirement from power grid, and local wind energy resource distribution. Finally, a framework design case of hybrid energy system was suggested according to typical wind energy resource in Xinjiang Autonomous Region in China.     

A new approach to exergoeconomic analysis and design of variable demand energy systems

Exergoeconomics is an attractive research field regarding the optimisation of design and operability where complex energy systems are concerned. The different approaches to thermoeconomics can easily achieve optimal or near-optimal solutions for the design of energy systems in industrial applications, characterised by regular energy demand profiles; for applications in buildings, however, the great number of components operating at unsteady conditions due to the demand variability make these methodologies hard to use. Furthermore, in project phases of complex plants such as Combined Heat and Power (CHP) or Combined Heat Cooling and Power (CHCP), energy demand can be satisfied with different output shares among the various components. In this paper, a simplified exergo-economic methodology is presented, which is based on aggregate consumption data and on a case-oriented procedure for analysis simplification. A technique to internalise exergy flows between the considered energy system and other external systems is also introduced. The proposed approach was applied to a trigeneration plant serving a 300-bed hospital situated in a Mediterranean area; the obtained results were finally compared with the optimal solution previously determined by means of demand cumulative curves and plant running simulations.     

Design and optimization of radioisotope sources for betavoltaic batteries

A Monte Carlo source model using PENELOPE was developed to investigate different tritiated metals in order to design a better radioisotope source for betavoltaic batteries. The source model takes into account the self‐absorption of beta particles in the source which is a major factor for an efficient source design. The average beta energy, beta flux, source power output, and source efficiency were estimated for various source thicknesses. The simulated results for titanium tritide with 0° and 90° angular distributions of beta particles were validated with experimental results. The importance of the backscattering effect due to isotropic particle emission was analyzed. The results showed that the normalized average beta energy increases with the source thickness, and it reaches peak energy depending on the density and the specific activity of the source. The beta flux and power output also increase with increasing source thickness. However, the incremental increase in beta flux and power output becomes minimal for higher thicknesses, as the source efficiency decreases significantly at higher thicknesses due to the self‐absorption effect. Thus, a saturation threshold is reached. A low‐density source material such as beryllium tritide provided a higher power output with higher efficiency. A maximum power output of approximately 4 mW/cm³ was obtained for beryllium tritide with SiC. A form factor approach was used to estimate the optimum source thickness. The optimum source thickness was found near the thickness where the peak beta particle average energy occurs.     

“Key” sectors in final energy consumption: an input–output application to the Spanish case

In this paper we analyze the determination of “key” sectors in the final energy consumption. We approach this issue from an input–output perspective and we design a methodology based on the elasticities of the demands of final energy consumption. As an exercise, we apply the proposed methodology to the Spanish economy. The analysis allows us to indicate the greater or lesser relevance of the different sectors in the consumption of final energy, pointing out which sectors deserve greater attention in the Spanish case and showing the implications for energy policy.     

Modeling and optimization of a typical fuel cell–heat engine hybrid system and its parametric design criteria

A theoretical modeling approach is presented, which describes the behavior of a typical fuel cell–heat engine hybrid system in steady-state operating condition based on an existing solid oxide fuel cell model, to provide useful fundamental design characteristics as well as potential critical problems. The different sources of irreversible losses, such as the electrochemical reaction, electric resistances, finite-rate heat transfer between the fuel cell and the heat engine, and heat-leak from the fuel cell to the environment are specified and investigated. Energy and entropy analyses are used to indicate the multi-irreversible losses and to assess the work potentials of the hybrid system. Expressions for the power output and efficiency of the hybrid system are derived and the performance characteristics of the system are presented and discussed in detail. The effects of the design parameters and operating conditions on the system performance are studied numerically. It is found that there exist certain optimum criteria for some important parameters. The results obtained here may provide a theoretical basis for both the optimal design and operation of real fuel cell–heat engine hybrid systems. This new approach can be easily extended to other fuel cell hybrid systems to develop irreversible models suitable for the investigation and optimization of similar energy conversion settings and electrochemistry systems.     

Maximising the energy output of a PVT air system

Simultaneously generating both electricity and low grade heat, photovoltaic thermal (PVT) systems maximise the solar energy extracted per unit of collector area and have the added benefit of increasing the photovoltaic (PV) electrical output by reducing the PV operating temperature. A graphical representation of the temperature rise and rate of heat output as a function of the number of transfer units NTUs illustrates the influence of fundamental parameter values on the thermal performance of the PVT collector. With the aim of maximising the electrical and thermal energy outputs, a whole of system approach was used to design an experimental, unglazed, single pass, open loop PVT air system in Sydney. The PVT collector is oriented towards the north with a tilt angle of 34°, and used six 110 Wp frameless PV modules. A unique result was achieved whereby the additional electrical PV output was in excess of the fan energy requirement for air mass flow rates in the range of 0.03–0.05 kg/s m². This was made possible through energy efficient hydraulic design using large ducts to minimise the pressure loss and selection of a fan that produces high air mass flow rates (0.02–0.1 kg/s m²) at a low input power (4–85 W). The experimental PVT air system demonstrated increasing thermal and electrical PV efficiencies with increasing air mass flow rate, with thermal efficiencies in the range of 28–55% and electrical PV efficiencies between 10.6% and 12.2% at midday.     

Evaluation of methods for estimating energy performance of biogas production

This study focused on identifying various system boundaries and evaluating methods of estimating energy performance of biogas production. First, the output–input ratio method used for evaluating energy performance from the system boundaries was reviewed. Secondly, ways to assess the efficiency of biogas use and parasitic energy demand were investigated. Thirdly, an approach for comparing biogas production to other energy production methods was evaluated. Data from an existing biogas plant, located in Finland, was used for the evaluation of the methods. The results indicate that calculating and comparing the output–input ratios (R_pr1, R_pr2, R_ut, R_pl and R_sy) can be used in evaluating the performance of biogas production system. In addition, the parasitic energy demand calculations (w) and the efficiency of utilizing produced biogas (η) provide detailed information on energy performance of the biogas plant. Furthermore, R_f and energy output in relation to total solid mass of feedstock (F_O/TS) are useful in comparing biogas production with other energy recovery technologies. As a conclusion it is essential for the comparability of biogas plants that their energy performance would be calculated in a more consistent manner in the future.     

Integrated solar pump design incorporating a brushless DC motor for use in a solar heating system

Most solar thermal hot water heating systems utilize a pump for circulation of the working fluid. An elegant approach to powering the pump is via solar energy. A “solar pump” employs a photovoltaic module, electric motor, and pump to collect and convert solar energy to circulate the working fluid. This article presents an experimental investigation of a new integrated solar pump design that employs the stator of a brushless DC motor and a magnetically coupled pump that has no dynamic seal. This design significantly reduces total volume and mass, and eliminates redundant components.The integrated design meets a hydraulic load of 1.7 bar and 1.4 litres per minute, equal to 4.0 watts, at a rotational speed of 500 revolutions per minute. The brushless DC motor and positive displacement pump achieve efficiencies of 62% and 52%, respectively, resulting in an electric to hydraulic efficiency of 32%. Thus, a readily available photovoltaic module rated 15 watts output is suitable to power the system.A variety of design variations were tested to determine the impact of the armature winding, pump size, pulse width modulation frequency, seal can material, etcetera. The physical and magnetic design was found to dominate efficiency. The efficiency characteristics of a photovoltaic module are such that over-sizing is wasteful.The integrated design presents a robust, efficient package for use as a solar pump. Although focus has been placed on application to a solar thermal collector system, variations of the design are suitable for a wide variety of applications such as remote location water pumping.     

Heat pipe based cold energy storage systems for datacenter energy conservation

In the present paper, design and economics of the novel type of thermal control system for datacenter using heat pipe based cold energy storage has been proposed and discussed. Two types of cold energy storage system namely: ice storage system and cold water storage system are explained and sized for datacenter with heat output capacity of 8800 kW. Basically, the cold energy storage will help to reduce the chiller running time that will save electricity related cost and decrease greenhouse gas emissions resulting from the electricity generation from non-renewable sources. The proposed cold energy storage system can be retrofit or connected in the existing datacenter facilities without major design changes. Out of the two proposed systems, ice based cold energy storage system is mainly recommended for datacenters which are located in very cold locations and therefore can offer long term seasonal storage of cold energy within reasonable cost. One of the potential application domains for ice based cold energy storage system using heat pipes is the emergency backup system for datacenter. Water based cold energy storage system provides more compact size with short term storage (hours to days) and is potential for datacenters located in areas with yearly average temperature below the permissible cooling water temperature (∼25 °C). The aforesaid cold energy storage systems were sized on the basis of metrological conditions in Poughkeepsie, New York. As an outcome of the thermal and cost analysis, water based cold energy storage system with cooling capability to handle 60% of datacenter yearly heat load will provide an optimum system size with minimum payback period of 3.5 years. Water based cold energy storage system using heat pipes can be essentially used as precooler for chiller. Preliminary results obtained from the experimental system to test the capability of heat pipe based cold energy storage system have provided satisfactory outcomes and validated the proposed system concept.     

平抑风电功率波动的储能容量经济配置方法

以东北某风电场月出力实测数据为对象,通过分析该风电场的功率波动特性,提出了储能系统功率、容量配置方法。该方法以储能系统投资收益最大为目标,结合储能平滑风电出力效果,获取经济性最优的储能系统容量配置方案。结果表明,该优化配置方案在平滑风电功率的前提下,具有良好的经济效益,为风电场中配置储能系统、推进储能系统规模化应用提供了参考。     

A new approach of sizing battery energy storage system for smoothing the power fluctuations of a PV/wind hybrid system

In this paper, a new approach for optimally sizing the storage system employing the battery banks for the suppression of the output power fluctuations generated in the hybrid photovoltaic/wind hybrid energy system. At first, a novel multiple averaging technique has been used to find the smoothing power that has to be supplied by the batteries for the different levels of smoothing of output power. Then the battery energy storage system is optimally sized using particle swarm optimization according to the level of smoothing power requirement, with the constraints of maintaining the battery state of charge and keeping the energy loss within the acceptable limits. Two different case studies have been presented for different locations and different sizes of the hybrid systems in this work. The results of the simulation studies and detailed discussions are presented at the end to portrait the effectiveness of the proposed method for sizing of the battery energy storage system. Copyright © 2016 John Wiley & Sons, Ltd.     

能源需求与二氧化碳排放分析决策支持系统

本文将情景分析思想和投入产出方法相结合,提出并设计开发了基于投入产出的能源决策支持系统;阐述了其设计原理及结构组成;通过对该系统的开发和应用表明,将情景分析和投入产出相结合为能源需求和相应二氧化碳排放预测提供了一条有效的途径。     

Combining simulation techniques and design expertise in a renewable energy system design package, RESSAD

Computer simulation is an increasingly popular tool for determining the most suitable renewable energy system type, design and control for an isolated community or homestead. However for the user without any expertise in system design, the complicated process of system component and control selection using computer simulation takes on a trial and error approach. Our renewable energy system design package, RESSAD, has been developed to simulate a wide range of renewable power supply systems, and to go beyond system simulation, by combining design expertise with the simulation model. The knowledge of the system designer is incorporated into the package through a range of analysis tools that assist in the selection process, without removing or restricting individual choices. The system selection process is analysed from the early stages of renewable resource assessment to the final evaluation of the results from a simulation of the chosen system. The approach of the RESSAD package in this selection process is described and its use is illustrated by two case studies in Western Australia.     

Optimisation strategy for an operational planning of a large photovoltaic system with enhanced electrical vehicles

Photovoltaic (PV) systems are rapidly gaining acceptance as some of the best alternative energy sources. In the installation area of a large PV system, appropriate operation is required, for example, of a method considering power output fluctuation and solar radiation forecast errors. In addition, it is better to minimise the size of the battery and its capital cost. This paper proposes an optimisation approach to determine the operational planning of the power output for a large PV system. This approach includes the method of determination of the charge/discharge amount for the battery of an electric vehicle as a demand response. The method aims to obtain a more beneficial deal with the sale of electrical power. The optimisation method applies the genetic algorithm to smoothen the fluctuating power output due to the PV system, and also to determine the initial state of charge of the battery. The validity of the proposed method is confirmed by the simulation results.