Concentrating Solar Power (CSP) plants have the potential to provide dispatchable renewable power generation to support the baseload need currently supplied primarily by coal and nuclear plants and peaking power capability to reduce the use of natural gas for load following. However, these plants have had difficulty achieving widespread use due to the low cost of combined photovoltaic and battery systems capable of providing similar services to the electricity grid. A new generation of CSP technologies must be developed to reduce the levelized cost of electricity (LCOE) to 6 cents/kWh by leveraging heat transfer fluids (HTF) capable of operation at higher temperatures and coupling with higher efficiency power conversion cycles. Three promising pathways for Generation 3 CSP (Gen3CSP) technology development have been funded by the U.S. Department of Energy (DOE) leveraging solid, liquid, and gaseous HTFs to transfer heat to a supercritical carbon dioxide (sCO2) Brayton cycle. The primary heat exchangers (PHX) necessary to couple these high-temperature HTFs to sCO 2 are an essential new technology that must be demonstrated at a scale relevant to commercial CSP to validate design expectations for performance, lifetime, and operability. The demonstration of these PHXs need a reliable 1 MWth-scale sCO 2 test system that can provide sCO 2 coolant to the PHX in a compact package suitable for installation near any Gen3CSP thermal storage system. This paper outlines the final design of such a system including the expected operating range and off-design capabilities. The system uses a dense-phase high pressure canned motor pump as the sCO 2 circulator and ambient air as the ultimate heat sink operating at pressures up to 250 bar and temperatures up to 715 °C with capability to supply up to 5.3 kg/s of sCO 2 flow to the primary heat exchanger. Key component requirements for this system have been frozen and procurement is underway. The expected completion date for heated acceptance testing of this system is September of 2020. This system is also capable of being upgraded through the addition of a turbo-compressor and turbo-generator to operate as a complete sCO 2 Brayton cycle with power generation in order to demonstrate an integrated solar to sCO 2 power pilot plant and understand transient interactions between the thermal storage system, sCO 2 turbomachinery, and ambient air temperature. In addition, this upgrade would provide experience with plant operating considerations including balancing charging the thermal storage system with generating and dispatching power to the electrical grid. A roadmap for this upgrade will be discussed including limitations and requirements for the necessary turbomachinery.

The following paper aims to explore a heat pump’s (HP) as well as an organic Rankine cycle’s (ORC) novel combination for the development of both an efficient and low-emissions heating and cooling systems. This latest review examines both benefits and possibilities of a combined HP-ORC system. Previously, studies have explored several different combinations, such as directly-coupled and reversible combination units as well as parallel configurations units in addition to indirectly-coupled ones. Following defining aforementioned configurations, a discussion on their performance is carried out in detail. Considerations for the optimisation of the architecture, overall of such hybrid systems via utilising the same sources while also discussing heat source, sink selection and operating temperatures as well as thermal energy storage, expander/compressor units, control strategies in addition to working fluids’ selection and managing seasonal temperatures that are increasingly variable, have been identified. Additionally, the experimental studies that have been performed reveal increasingly practical obstacles as well as other areas that require more research while serving to shed light on experimental techniques, which can be applicable to this research’s area. Based upon research, it has been revealed that regional conditions including temperatures and annual weather as well as the cost of energy produce a colossal effect on such systems’ economic feasibility framework as well as partially dictating the overall system configuration’s selection. Additionally, the review disclosed how important the following elements are: 1) a greater temperature differential amid the source of heat and heat sink; 2) proper source of heat and sink selection; 3) working fluid selection; and 4) thermal storage for the maintenance of the difference. Comparatively, from the research works from the past, additional optimisation based on individual component level as well as through control strategies of either an advanced or predictive method, these produce a smaller effect and are worth performing an evaluation on economically due to them not being feasible for the current system. Lastly, based on investigated research, there are certain areas for which recommendation have been provided with regard to future research and this includes a technology configurations’ comparison for understanding different regions’ optimal system, a sensitivity analysis for understanding key system elements for both optimisation as well as design, both an investigation as well as testing carried out for available units and applicable systems that are presently available, and identifying novel use cases.

A scheme to streamline the electric power generation profile of concentrating solar power plants of the parabolic trough collector type is suggested. The scheme seeks to even out heat transfer rates from the solar field to the power block by splitting the typical heat transfer fluid loop into two loops using an extra vessel and an extra pump. In the first loop, cold heat transfer fluid is pumped by the cold pump from the cold vessel to the solar field to collect heat before accumulating in the newly introduced hot vessel. In the second loop, hot heat transfer fluid is pumped by the hot pump from the hot vessel to a heat exchanger train to supply the power block with its heat load before accumulating in the cold vessel. The new scheme moderately decouples heat supply from heat sink allowing for more control of heat delivery rates thereby evening out power generation.

Electric vehicles (EVs) are receiving more attention these days because they are environmentally friendly (no emissions) and are much quieter than internal combustion engine vehicles with rapidly decreasing prices. One of the serious limitations of EVs is the limited driving range. When conventional heating and air conditioning systems are used in winter and summer, the driving range is reduced further because they consume a lot of electric energy stored in the batteries. A thermoelectric cooling system integrated with thermal energy storage has been identified as an attractive alternative to traditional air conditioning in electric vehicles. The main goal of such a system is to minimize the amount of electricity that is drawn for air-conditioning from the electric battery of the vehicle, thus eliminating further reduction in driving range. Not only is the alternative more light weight than the conventional vapor compression based air-conditioning system, it also reduces the amount of electricity drawn from the battery. The proposed system is comprised of thermal energy storage (TES) employing phase change materials (PCMs), thermoelectric electric modules, and a fan. The TES, also referred to as a thermal battery here, can be charged before at home or at a charging station before driving like the electric battery, and is discharged when used in driving. This study involved the design and development of a TES for EVs employing computational fluid dynamics and heat transfer analyses. The model includes all the key components such as thermoelectric (Peltier) modules, heat sinks and the PCM. Various simulations for thermal battery charging and discharging have been conducted to demonstrate the feasibility of incorporating TES coupled with thermoelectric modules.

In this study, an efficient cooling technique for concentrator photovoltaic (CPV) cells is proposed to enhance the system electrical efficiency and extend its lifetime. To do this, a comprehensive three-dimensional conjugate heat transfer model of CPV cells layers coupled with the heat transfer and fluid flow model inside jet impingement heat sink is developed. Four different jet impingement designs are compared. The investigated designs are (A) central inlet jet, (B) Hypotenuse inlet jet, (C) staggered inlet jet, and (D) conventional jet impingement design with side drainage. The effect of coolant flowrate on the CPV/T system performance is investigated. The model is numerically simulated and validated using the available experiments. The performance of CPV system is investigated at solar concentration ratios of 20 and coolant flowrate up to 6000g/min. It is found that increasing the flowrate from 60 g/min to 600 g/min decrease the maximum cell temperature by 31°C for the configuration D while increasing the flowrate from 600 g/min to 6000 g/min reduce the cell temperature by 20.2°C. It is also concluded that at a higher flowrate of 6000g/min, all the investigated configurations relatively achieve better temperature uniformity with maximum temperature differences of 0.9 °C, 2.1 °C, 3.6 °C, and 3.9 °C for configurations A, B, C, and D respectively.

To achieve reliable and efficient operation of generic polycrystalline silicon solar cell under concentrated sunlight, a novel structure of the cell layers is proposed along with effective cooling technique using microchannel heat sink (MCHS). In the novel structure, Boron Nitride with the volume fraction of 20%, 40%, and 60% as a filler is incorporated in the Ethylene Vinyl Acetate (EVA) matrix to form a new composite. The new composite is used instead of the conventional EVA layer in the solar cell. Various solar cell structures integrated with MCHS are studied and compared with the conventional structure. To determine the performance of the developed concentrated photovoltaic thermal (CPVT) system, a comprehensive three-dimensional model of the solar cell with heat sink is developed. The model is numerically simulated and validated. Based on the validated results, it is found that the novel structure with EVA-60% BN composite along with aluminum foil back sheet attains 30% increase in the gained solar cell electric power with 10.9 % reduction in the cell temperature compared with the conventional solar cell structure at the same cooling mass flow rate of 50 g/min and concentration ratio of 20. However at CR = 20, V w = 1m/s and T a = 30°C a significant damage of the conventional solar cell structure will occurs if no effective cooling technique is used. Moreover, the developed design of solar cell achieves a higher CPVT-system thermal efficiency compared with the conventional one.

The photovoltaic output power is directly proportional to the solar radiation and inversely with the cell temperature. The higher the photovoltaic temperature is, the lower the electrical efficiency is with possible damage to the cell. To improve the electrical efficiency and to avoid the possible damage, a concentrating PV system associated with an effective cooling technique is of great importance. In the present study, a new cooling technique for concentrated photovoltaic (CPV) systems was introduced using various designs of micro-channel heat sinks. The suggested configurations included parallel flow, counter flow single and double layer micro-channels, and single layer flat micro-channel integrated with CPV system. A comprehensive three-dimensional thermo-fluid model for photovoltaic layers integrated with microchannel heat sink was developed. The model was simulated numerically to estimate the solar cell temperature. The numerical results were validated with the available experimental and numerical results. In the meantime, the effects of different operational parameters were investigated such as solar concentration ratio and cooling mass flow rate. Performance analysis of CPV using different microchannel configurations was implemented to determine the average and local solar cell temperature, pumping power, and temperature uniformity. Results indicated that the use of microchannel heat sink was a very effective cooling technique which highly attained temperature uniformity, viz., eliminated the hot spots formation with a significant reduction in the average temperature of CPV. The single layer parallel flow achieved the minimum solar cell temperature while the counter flow attained the most uniform temperature distribution compared with other configurations. Furthermore, the double layer parallel flow microchannel attained the minimum pumping power for a given cooling mass flow rate.

Germany’s current energy policy is focused on the replacement of the conventional powered electrical energy supply system by renewable sources. This leads to increasing requirements on the flexibility for the conventional thermal power plants. Larger differences between energy supply from renewable energy sources and energy demand in the grid lead to high dynamic requirements with respect to the load change transients. Furthermore, a reduction of the required minimum load of existing thermal power plants is necessary. The existing power plants are indispensable for securing the network stability of the power grid. Accordingly, activities to improve the flexibility of existing power plants are required. By the use of thermal energy storage (TES) it is possible to increase the load change transient. Furthermore, it is possible to temporarily provide an increased generator power and reduce the minimum technical load of the unit. Currently, there is no closed methodical approach for the load profile-dependent and location-based dimensioning and integration of TES into thermal power plants. The aim is to generate contributions for the development of a universal design method. This requires the provision of characteristics for dimensioning and integration of TES into thermal processes. For this purpose, it is necessary to derive quantifiable information on the required capacity, performance and stationary and dynamic operating conditions. Starting from analyzing the anticipated, site-specific load profiles the derivation of concepts for technical implementation, feedback on the process and cost of the thermal storage unit takes place. In order to investigate the technical feasibility, the implementation of storage and the associated control concepts as well as to validate the developed design models, the test facility THERESA has been built at the University of Applied Sciences in Zittau (Germany). The acronym THERESA is the abbreviation for thermal energy storage facility. This test facility includes a reconstructed thermal water-steam process, similar to a power plant with integrated TES. The test facility is unique in Germany and enables the delivery of saturated steam up to 160 bars at 347 ° and superheated steam up to 60 bars at 350 °C with an overall thermal power of 640 kW. The design, planning and construction of the facility took 3 years and required an investment volume of 3 mill. Euro. The facility includes two preheater stages, steam generator, super heater, direct TES with mixing preheater and a heat sink. The TES with a volume of 600 L as well as the mixing preheater are prototypes which developed for the special requirements of the facility. Based on this facility, it is possible to investigate methods for the flexibilization of thermal power plants with TES under realistic parameters. Furthermore, the test facility allows the development of control and regulatory approaches as well as the validation of simulation models for process expansion of thermal power plants. Initial investigations show the impact of a simulated load reduction at the heat sink on the system behavior. Here, the load reduction takes place from the heat sink in the storage without changing the steam production. The development and construction of the test facility were funded by the Free State of Saxony and the European Union. The further work on the development of the integration methods are funded by the European Social Fund ESF.

Thermal energy is a leading topic of discussion in energy conservation and environmental fields. Specifically for large-scale applications solar energy and concentrated solar power (CSP) systems use techniques that include thermal energy storage systems and phase change materials to harvest energy. However, on the smaller centimeter scale, there have been historically fewer investigations of these same techniques. The main goal of this paper is to investigate thermal energy storage (TES) as applied to a small scale system for thermal energy capture. Typical large-scale TES consists of a phase change material that usually employs a wax or oil medium held within a conductive container. The system stores the energy when the wax medium undergoes a phase change. In typical applications like buildings, the system absorbs and stores incoming thermal energy during the day, and releases it back to the surrounding environment as temperatures cool at night. This paper presents a new TES unit designed to integrate with a thermoelectric for energy harvesting application in small, cm-scale applications. In this manner, the TES serves as a thermal battery and source for the thermoelectric, even when originating power supply is interrupted. A unique feature of this TES is the inclusion of internal heat pipes. These heat pipes are fabricated from copper tubing and filled with working fluid, mounted vertically, and immersed in the wax medium of the TES. This transfers heat to the wax by means of thermal conductivity enhancement as an element of the heat pipe operation. This represents a first of its kind in this small-scale, thermal harvesting application. As tested, the TES rests atop a low temperature (60 °C) heat source with a heat sink as the final setup component. The heat sink serves to simulate thermal energy rejection to a future thermoelectric device. To measure the temperature change of the device, thermocouples are placed on either side of the TES, and a third placed on the heat source to ensure that the energy input is appropriate and constant. Heat flux sensors (HFS) are placed between the heat source and the TES and between the TES and heat sink to monitor heat transferred to and from the device. The TES is tested in a variety constructions as part of this effort. Basic design of the storage volume as well as fluid fill levels within the heat pipes are considered. Varying thermal energy inputs are also studied. Temperature and heat flux data are compared to show the thermal absorption capability and operating average thermal conductivities of the TES units. The baseline average thermal conductivity of the TES is approximately 0.5 W/mK. This represents the TES with wax alone filling the internal volume. Results indicate a fully functional, heat pipe TES capable of 8.23 W/mK.

To experiment 20kW OTEC, the closed-cycle type of OTEC (Ocean Thermal Energy Conversion) was designed and manufactured. R32 (Difluoromethane, CH2F2) was used as the working fluid and a temperature of heat source and heat sink is 26°C, 5°C, respectively. The semi-welded type heat exchanger is applied for the evaporator and condenser and the cycle was designed for the gross power of 20kW. In the plate arrangement of the semi-welded type heat exchanger, one channel for working fluid is welded, and another channel for seawater is sealed by gasket. In this paper, various performance evaluations and experiments were carried out as constructing subminiature pilot plant of the OTEC and compared with the results of cycle analysis. In results, gross power of the turbine shows 20.1kW and cycle efficiency is 1.91% when heat source and heat sink is 26°C, 5°C. For the variation of temperature difference between the heat source and heat sink, when the temperature difference was 21°C, the gross power increased by about 33.3% from that when the temperature difference was 19 °C.

Internal combustion (IC) engines typically have an efficiency of less than 35%. This is largely due to the fact that much of the energy dissipates into waste heat. However, the waste heat may be converted into electricity by using energy conversion modules made from bismuth telluride. In this work, it is demonstrated that electricity can be generated from waste heat due to the difference in temperatures. The thermal to electrical energy conversion is achieved by using a self-assembled thermoelectric generator (TEG). The TEG (thermoelectric generator) uses two different types of metallic compound semiconductors, known as n-typed and p-typed, to create voltage when the junctions are held at different temperatures. The work mechanism is based on the Seebeck effect. In this study, the TEGs are made from bismuth telluride (Bi-Te) with relatively high energy conversion efficiencies. In addition, it is readily available. The installation location of the TEG is studied. For testing purposes and convenience, the top of the radiator of a 1990 Mazda Miata car was chosen. The TEG and an aluminum finned heat sink were placed in order on the top of the radiator. Thermal paste was applied to both surfaces and secured with zip ties. A vent was cut on the hood of the car to promote airflow between the fins. Appropriate electrical wiring allowed the unit to output to a digital multi-meter which was located within the car for operator to take data. It is found from the measured results that 0.948 V is the maximum output and the average voltage is 0.751 V. The highest voltage came from driving mountain paths due to the heat sink and coolant temperature being higher than nominal. We estimate that placing an insulator between the heat sink and TEG would push the maximum voltage over 1.0 V. During the cool down phase, the TEG produced electricity continuously with a maximum voltage of 0.9 V right after engine cutoff. The voltage decreased to about 0.6 V within 40 minutes. It is found that the relationship between the temperature difference and output voltage is linear.

In this paper, we present the results of the design, fabrication, installation, and operation of a 20-kW OTEC (ocean thermal energy conversion) pilot plant. The results can be used as basic data for the design of commercial plants with capacities in excess of 40 MW. To perform an experiment on the 20 kW OTEC, a closed OTEC cycle was designed and fabricated at the Ocean Water Plant Research Center. The cycle utilizes surface ocean water as its heat source and deep ocean water as its heat sink. R32 (Difluoromethane, CH2F2) was used as the working fluid, and the temperature of the heat source and heat sink were 26°C and 5°C, respectively. A semi-welded-type heat exchanger was used as the evaporator and condenser, and the OTEC cycle was designed for a gross power of 20 kW. The advantages of the semi-welded-type heat exchanger include easy maintenance of the gasket-type heat exchanger and the rare leakage of the welded-type heat exchanger. The plate arrangement of the semi-welded-type heat exchanger comprised one welded channel for the working fluid and another gasket-type channel. The gross power of the turbine was determined to be 20.49 kW. The evaporating capacity was calculated as 1,020 kW, and the cycle efficiency was determined to be about 2.00%.

Because of the performance of the power generation equipment is almost perfect, how to integrate the thermally-activated technologies and use the waste heat deeply are a critical issue for CCHP (Combined cooling heating and power) system. According to the characteristics of a typical end user’s demands, a CCHP system with the flue gas and geothermal energy is proposed. The system is composed of an internal combustion engine, a soil source absorption heat pump driven by the flue gas, and other assistant facilities, such as pumps, fans, and end user devices. In the winter, the flue gas is used to drive absorption heat pump to recover the waste heat of the soil source and the condensation heat of the flue gas simultaneously, and in the summer, the waste heat of the flue gas is used to drive absorption heat pump to cooling, and the heat sink is the soil. In the paper, the energy analysis of the system is done. Compared with the conventional CCHP system, the operation cost is lowered greatly and the increased investment could be returned within one year. It is show that the system is the efficient integration of clean energy, renewable energy, the discharge of the flue gas could be reduced to below 30°C, and the water steam could be catch to avoid the white smoke of the stack.

Heat pipes are widely used as a heat transporting device in a variety of applications. From space satellites, large industrial appliances to a heat sink for cooling electronic components and packages. Heat pipes are extremely efficient because of their high effective thermal conductivity, compactness, low cost and reliability. Therefore, the designers of heat sinks are often required to optimize the performance of the heat pipe itself in order to improve the overall thermal management system of any particular equipment. However, the detailed internal modeling of a heat pipe presents a challenging problem for an engineer. It is a multi physics problem including two phase flow within porous media and with conjugate heat transfer adding the solicited high capillary and surface tension effect. In this present study, detailed modeling of the heat pipe considering the mentioned effects is pursued. A basic review of the governing equations describing the complete heat pipe operation is given. The commercially available simulation tool Fluent 6.3 is used to describe and solve these equations in a coupled conjugate heat transfer set up. The geometry of heat pipe is divided in two different regions which solve simultaneously. The first region is core region where only vapor flow is assumed. The second region consists of wall and wick structure through which the mass transfer due to wettability and heat dissipates through conduction. Water was used as flowing fluids through wick porous structure. Previous experimental as well as numerical models regarding the heat pipes have been studied and used for the verification of the present model along with a standard grid convergence study. The effects of different heat pipe length, heat fluxes, wall thickness, wall material and porosity are investigated. The pressure drop and wall temperature increase with the value of heat flux. Similarly, porosity and wall material affect the wall temperature distribution. The effect of wall thickness and heat pipe length was not significant. In addition, a theoretical model is developed for the pressure drop across the heat pipe in vapor region and the respective output was used for the simulation. Finally, the temperature distribution in wall and wick is shown and discussed.

The optimization of energy conversion systems is of great significance in the utilization of low-grade heat. This paper presents an analysis of 6 working fluids in 12 thermodynamic cycles to optimize the energy conversion systems. The optimal exergy efficiency of the system is dependent on the type of the thermodynamic cycle, the choice of appropriate working fluid, and the working conditions. A zeotropic mixture of R134a and R245fa shows advantages in energy conversion process, as well as its heat exchange with the heat source and heat sink. The exergy efficiency of a 0.5R134a/0.5R245fa-based supercritical Rankine cycle system is 0.643–0.689 for a turbine inlet temperature of 415–445K, which is about 30% improvement over the exergy efficiency of 0.491–0.521 for a pure R32-based organic Rankine cycle under the same temperature limits. Furthermore, the 0.5R134a/0.5R245fa mixture saves more than 60% of the cooling water during the condensation process than the pure R32, R134a and R245fa.

Thermal power plants provide the majority of electricity used around the world and will continue to do so for some time. The goal of this paper is to provide an understanding of technology and fuels used in thermal power plants and the byproducts they create. The emphasis is on magnitudes of fuels used, emissions created and the sustainability and practicality of methods of production and control. A basic thermal power plant burns fuel to produce steam, which turns a turbine generator to produce electricity. The basic elements of thermodynamics apply to all thermal power plants: a heat source, a heat engine and a heat sink. Heat sources for thermal power plants include boilers fueled by coal, natural gas and biomass; gas turbines fueled by natural gas; and nuclear reactors fueled by uranium. Topics of discussion include the logistics involved in supplying fuels and handling their byproducts, including carbon compounds; types of heat engines utilized; methods to improve efficiency to reduce the fuel consumed; byproducts generated; and the heat sink required. The focus is on Rankine (vapor) and Brayton (gas) cycles. Although not directly affecting carbon byproducts, the heat sink used affects the heat engine efficiency and the consumption of water, a valuable resource. The types of heat sinks discussed include open-cycle water cooling, closed-cycle water cooling and air cooling. Thermal power plants provide many benefits to the electrical power system. They provide power 24 hours a day and 365 days a year, regardless of the weather. They are relatively compact, making them easier to build, operate and maintain. They also can be located close to electrical load concentrations reducing the need for transmission lines that disrupt the environment. The technologies involved in thermal power plant operation are proven effective and in use today. The challenges are to manage the fuel supply and byproduct disposal in an environmentally acceptable manner.

An irreversible solar-driven Braysson heat engine system is put forward, in which finite rate heat transfer with the radiation-convection mode from the solar collector to the heat engine and the convection mode from the heat engine to the heat sink, the radiation-convection heat loss from the solar collector to the ambience, the internal irreversibility due to nonisentropic processes in the expander and compressor devices are taken into account. On the basis of thermodynamic analysis method, the analytic expression between the overall efficiency of the solar-driven Braysson heat engine system and the operating temperature of the solar collector is derived and the influences of different heat transfer mechanism, the internal irreversibility parameter, the isobaric temperature ratio, the ratio of heat-transfer coefficients on the optimal performance of the solar-driven Braysson heat engine system are evaluated and depicted quantificationally. The results obtained in the present paper are helpful to deeply reveal the effect of heat transfer mechanism and multi-irreversibilities on the performance of solar driven heat engines.

Since the first geothermal power plant was built at Larderello (Italy) in 1904, many attempts have been made to improve conversion efficiency. Among innovative technologies, using the Kalina cycle is considered as one of the most effective means of enhancing the thermodynamic performance for both high and low temperature heat source systems. Although initially used as the bottoming cycle of gas turbines and diesel engines, in the late 1980s the Kalina cycle was found to be attractive for geothermal power generation [1, 2, 3]. Different versions (KSC11, KSC12 and KSC13) were designated. Comparison between Kalina cycle and other power cycles can be found in later studies [4, 5, 6]. Here we examine KSC11, because it is specifically designed for geothermal power generation, with lower capital cost [3]. We compare this design with the existing Kawerau ORMAT binary plant in New Zealand. In addition, parametric sensitivity analysis of KCS11 has been carried out for the specific power output and net thermal efficiency by changing the temperatures of both heat source and heat sink for a given ammonia-water composition.

An exergy analysis was performed for flow boiling of R-123 in a hydrofoil-based micro pin fin heat sink. It was found that exergy efficiencies decreased with mass velocity at fixed heat input, pressure drop and pumping power under flow boiling conditions, and exergy efficiency could be better represented using the exit mass quality. The outcome of this study also proved noteworthy in view that exergy efficiency could be utilized to assess thermodynamic performance.