The thermal performance of a candidate next-generation falling particle receiver (FPR) is analyzed subject to various expected operating conditions. This receiver design was created from the result of an extensive optimization study and developed to support the Generation 3 Particle Pilot Plant (G3P3) project. Previous analysis demonstrated high thermal efficiencies for the receiver at nominal quiescent conditions, but further analysis was required to demonstrate that the receiver could maintain that thermal performance in a wide range of anticipated environments. In this study, the thermal efficiency was numerically evaluated using a CFD model for different wind conditions and shown to maintain a thermal efficiency above 83% for considered wind conditions. Moreover, the effect of radiative spillage from the incoming concentrated solar beam on the receiver exterior was investigated using ray tracing and CFD models. The exterior wall material temperature limits were not exceeded for the anticipated design power from the heliostats. Additional features were numerically explored including the addition of a chimney to capture particle fines and waste heat and a multi-stage concept to maximize curtain opacity. Particle fines of 10 μm were shown to preferentially flow into this chimney rather than out of the aperture, and the multi-stage design decreased radiative losses and minimized wall temperatures behind the particle curtain.

Falling particle receivers (FPRs) are an important component of future falling particle concentrating solar power plants to enable next-generation energy generation. High thermal efficiencies in a FPR are required to high thermodynamic efficiencies of the system. External winds can significantly impact the thermal performance of cavity-type FPRs primarily through changing the air flow in and out of the aperture. A numerical parametric study is performed in this paper to quantify the effect of wind on the thermal performance of a FPR. Wind direction was found to be a significant parameter that can affect the receiver thermal efficiency. The particle mass flow rate did not significantly change the overall effect of wind on the receiver. The receiver efficiency was strong function of the particle diameter, but this was primarily a result of varying curtain opacity with different diameters and not from varying effects with wind. Finally, the model was used to demonstrate that receiver efficiencies of 90% were achievable under the assumption that the effect of wind/advective losses were mitigated.

The design of, and preliminary on-sun tests on, an 8 cm × 8 cm microchannel supercritical carbon dioxide (sCO 2 ) receiver is presented. The receiver has a laminated design, wherein sheets of Haynes 230 nickel superalloy are patterned and diffusion bonded to form microscale flow passages. The microscale pattern is in the form of square pins with width and height of 500 μm and 200 μm respectively. The pins are arranged in an in-line pattern with respect to the flow direction. The longitudinal and transverse pitch ratios of the micro pin fins are identical and equal to two times the side width of the pillar. A sCO 2 test facility is developed with the ability to supply sCO 2 at 200 bar pressure and at temperatures between 300–500°C to the receiver inlet. The sCO 2 facility is coupled to a seven meter diameter parabolic dish with a 25 kW rating and a concentration ratio of about 800. On-sun tests are performed at a receiver inlet pressure of 150 bar and a receiver inlet temperature between 110–130°C. Receiver and thermal efficiencies in excess of 0.91 and 0.96 respectively for the incident heat flux ranging from 8 to 80 W/cm 2 , and average surface temperatures ranging from 150–550°C are obtained in these experiments.

Falling particle receivers are an emerging technology for use in concentrating solar power systems. In this work, quartz tubes cut in half to form tube shells (referred to as quartz half-shells) are investigated for use as a full or partial aperture cover to reduce radiative and advective losses from the receiver. A receiver subdomain and surrounding air volume are modeled using ANSYS ® Fluent ® . The model is used to simulate fluid dynamics and heat transfer for the following cases: (1) open aperture, (2) aperture fully covered by quartz half-shells, and (3) aperture partially covered by quartz half-shells. We compare the percentage of total incident solar power lost due to conduction through the receiver walls, advective losses through the aperture, and radiation exiting out of the aperture. Contrary to expected outcomes, simulation results using the simplified receiver subdomain show that quartz aperture covers can increase radiative losses and, in the partially covered case, also increase advective losses. These increased heat losses are driven by elevated quartz half-shell temperatures and have the potential to be mitigated by active cooling and/or material selection.

Prior research at Sandia National Laboratories showed the potential advantages of using light-trapping features which are not currently used in direct tubular receivers. A horizontal bladed receiver arrangement showed the best potential for increasing the effective solar absorptance by increasing the ratio of effective surface area to the aperture footprint. Previous test results and models of the bladed receiver showed a receiver efficiency increase over a flat receiver panel of ∼ 5–7% over a range of average irradiances, while showing that the receiver tubes can withstand temperatures > 800 °C with no issues. The bladed receiver is being tested at various peak heat fluxes ranging 75–150 kW/m 2 under transient conditions using Air as a heat transfer fluid at inlet pressure ∼250 kPa (∼36 psi) using a regulating flow loop. The flow loop was designed and tested to maintain a steady mass flow rate for ∼15 minutes using pressurized bottles as gas supply. Due to the limited flow-time available, a novel transient methodology to evaluate the thermal efficiencies is presented in this work. Computational fluid dynamics (CFD) models are used to predict the temperature distribution and the resulting transient receiver efficiencies. The CFD simulations results using air as heat transfer fluid have been validated experimentally at the National Solar Thermal Test Facility in Sandia National Labs.

To reduce the dependency on fossil-based energy resources, the utilization of renewable fuels in unmodified diesel engines is gaining more emphasis from researchers in the recent years. The aim of the current study is to take part in the efforts being made to this regard by experimentally investigating a compression ignition engine fueled with different fuels ((diesel, diesel-biodiesel (B20), and diesel-biodiesel-butanol (BU20)) for their performance and emissions comparison. The experimental study was conducted in a water cooled single-cylinder direct injection (DI) diesel engine. It was operated at a constant engine operation speed of 1800 rpm and under varied engine load conditions. It is found that BU20 shows promising results in terms of performance and emissions characteristics as compared to using B20 and D100. Butanol addition to diesel-biodiesel blends is considered as an appropriate solution of higher density and viscosity the blend and thus for the sustainable usability of biodiesel. Maximum thermal efficiency improvement of 3.18% was observed at an engine load of 75%. The NO x emission was improved with BU20 as compared to the conventional diesel fuel (D100) at most of the engine loads. As an improvement on the engine performance and emissions is reported from the current study, the BU20 fuel blends can be used in similar engines with no further engine retrofitting. This blend can be a good environmental friendly fuel that can serve in the reduction of fossil-based diesel fuels. A further study on diesel engine tribology is required.

Novel particle release patterns have been proposed as a means to increase the thermal efficiency of high-temperature falling particle receivers. Innovative release patterns offer the ability to utilize light-trapping and volumetric heating effects as a means to increase particle temperatures over a conventional straight-line particle release pattern. The particle release patterns explored in this work include wave-like patterns and a series of parallel curtains normal to the incident irradiation that have shown favorable results in previous numerical studies at lower particle temperatures. A numerical model has recently been developed of an existing falling particle receiver at the National Solar Thermal Test Facility at Sandia National Laboratories to evaluate these patterns at elevated temperatures necessary to evaluate radiative and convective losses. This model has demonstrated that thermal efficiency gains of 2.5–4.6% could be realized using these patterns compared to the conventional planar release depending on the particle mass flow rate. Increasing the number of parallel curtains, increasing the spacing between curtains, and shifting the particle mass flow rate deeper in the receiver cavity was also found to increase the thermal efficiency. These effects became less significant as the particle mass flow rate increased.

Solid particles can operate at higher temperature than current molten salt or oil, and they can be a heat-transfer and storage medium in a concentrating solar power (CSP) system. By using inexpensive solid particles and containment material for thermal energy storage (TES), the particle-TES cost can be significantly lower than other TES methods such as a nitrate-salt system. The particle-TES system can hold hot particles at more than 800°C with high thermal performance. The high particle temperatures increase the temperature difference between the hot and cold particles, and they improve the TES capacity. The particle-based CSP system is able to support high-efficiency power generation, such as the supercritical carbon-dioxide Brayton power cycle, to achieve >50% thermal-electric conversion efficiency. This paper describes a solid particle-TES system that integrates into a CSP plant. The hot particles discharge to a heat exchanger to drive the power cycle. The returning cold particles circulate through a particle receiver to absorb solar heat and charge the TES. This paper shows the design of a particle-TES system including containment silos, foundation, silo insulation, and particle materials. The analysis provides results for four TES capacities and two silo configurations. The design analysis indicates that the system can achieve high thermal efficiency, storage effectiveness (i.e., percentage usage of the hot particles), and exergetic efficiency. An insulation method for the hot silo was considered. The particle-TES system can achieve high performance and low cost, and it holds potential for next-generation CSP technology.

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.

This study focuses on the power cycles such as organic Rankine cycle (ORC) and combined regenerative Brayton/ORC. The selection of working fluids and power cycles is traditionally conducted by trial and error method and performing a large number of parametric calculations over a range of operating conditions. A methodology for selection of optimal working fluid based on the cycle operating conditions and thermophysical properties of the working fluids was developed in this study. Thermodynamic performance (thermal efficiency and net power output) of a simple subcritical and supercritical ORC was analyzed over a range of operating conditions for a number of working fluids to determine the effect of operating parameters on cycle performance and select the best working fluid. New expressions for thermal efficiency of a simple ORC are proposed. In case of a regenerative Brayton/ORC, the results show that CO 2 is the best working fluid for the topping cycle. Depending on the exhaust temperature of the topping cycle, Isobutane, R11 and Ethanol are the preferred working fluids for the bottoming (ORC) cycle, resulting in highest efficiency of the combined cycle. Finally, a performance map is presented as guidance for selection of the best working fluid for specific cycle operating conditions.

Previous research at Sandia National Laboratories showed the potential advantages of using light-trapping features which are not currently used in direct tubular receivers. A horizontal bladed receiver arrangement showed the best potential for increasing the effective solar absorptance by increasing the ratio of effective surface area to the aperture footprint. Ray-tracing analyses using SolTrace were performed to understand the light-trapping effects of the bladed receivers, which enable re-reflections between the fins that enhance the effective solar absorptance. A parametric optimization study was performed to determine the best possible configuration with a fixed intrinsic absorptivity of 0.9 and exposed surface area of 1 m 2 . The resulting design consisted of three vertical panels 0.584 m long and 0.508 m wide and 3 blades 0.508 m long and 0.229 m wide with a downward tilt of 50 degrees from the horizontal. Each blade consisted of two panels which were placed in front of the three vertical panels. The receiver was tested at the National Solar Thermal Test Facility using pressurized air. However, the receiver was designed to operate using supercritical carbon dioxide (sCO 2 ) at 650 °C and 15 MPa for 100,000 hours following the ASME Boiler and Pressure Vessel Code Section VIII Division 1 . The air flowed through the leading panel of the blade first, and then recirculated toward the back panel of the blade before flowing through one of the vertical back panels. The test results of the bladed receiver design showed a receiver efficiency increase over a flat receiver panel of ∼5 – 7% (from ∼80% to ∼86%) over a range of average irradiances, while showing that the receiver tubes can withstand temperatures > 800 °C with no issues. Computational fluid dynamics (CFD) modeling using the Discrete Ordinates (DO) radiation model was used to predict the temperature distribution and the resulting receiver efficiencies. The predicted thermal efficiency and surface temperature values correspond to the measured efficiencies and surface temperatures within one standard deviation. In the near future, an sCO 2 flow system will be built to expose the receiver to higher pressure and fluid temperatures which could yield higher efficiencies.

Direct solar power receivers consist of tubular arrays, or panels, which are typically tubes arranged side by side and connected to an inlet and outlet manifold. The tubes absorb the heat incident on the surface and transfer it to the fluid contained inside them. To increase the solar absorptance, high temperature black paint or a solar selective coating is applied to the surface of the tubes. However, current solar selective coatings degrade over the lifetime of the receiver and must be reapplied, which reduces the receiver thermal efficiency and increases the maintenance costs. This work presents an evaluation of several novel receiver shapes which have been denominated as fractal like geometries (FLGs). The FLGs are geometries that create a light-trapping effect, thus, increasing the effective solar absorptance and potentially increasing the thermal efficiency of the receiver. Five FLG prototypes were fabricated out of Inconel 718 and tested in Sandia’s solar furnace at two irradiance levels of ∼15 and 30 W/cm 2 and two fluid flow rates. Photographic methods were used to capture the irradiance distribution on the receiver surfaces and compared to results from ray-tracing models. This methods provided the irradiance distribution and the thermal input on the FLGs. Air at nearly atmospheric pressure was used as heat transfer fluid. The air inlet and outlet temperatures were recorded, using a data acquisition system, until steady state was achieved. Computational fluid dynamics (CFD) models, using the Discrete Ordinates (DO) radiation and the k-ω Shear Stress Transport (SST) equations, were developed and calibrated, using the test data, to predict the performance of the five FLGs at different air flow rates and irradiance levels. The results showed that relative to a flat plate (base case), the new FLGs exhibited an increase in the effective solar absorptance from 0.86 to 0.92 for an intrinsic material absorptance of 0.86. Peak surface temperatures of ∼1000°C and maximum air temperature increases of ∼200°C were observed. Compared to the base case, the new FLGs showed a clear air outlet temperature increase. Thermal efficiency increases of ∼15%, with respect to the base case, were observed. Several tests, in different days, were performed to assess the repeatability of the results. The results obtained, so far, are very encouraging and display a very strong potential for incorporation in future solar power receivers.

Small scale Distributed Generation with waste heat recovery (<50 kW power output, micro-DG/CHP) is an expanding market supporting the widespread deployment of on-site generation to much larger numbers of facilities. The benefits of increased overall thermal efficiency, reduced pollutant emissions, and grid/microgrid support provided by DG/CHP can be maximized with greater quantities of smaller systems that better match the electric and thermal on-site loads. The 3-year CEC funded program to develop a natural gas fueled automotive based rotary engine for micro-DG/CHP, capitalizing upon the unique attributes engine configuration will be presented including initial performance results and plans for the balance of the program.

Multiple receiver designs have been evaluated for improved optics and efficiency gains including flat panel, vertical-finned flat panel, horizontal-finned flat panel, and radially finned. Ray tracing using SolTrace was performed to understand the light-trapping effects of the finned receivers. Re-reflections of the fins to other fins on the receiver were captured to give an overall effective solar absorptance. The ray tracing, finite element analysis, and previous computational fluid dynamics showed that the horizontal-finned flat panel produced the most efficient receiver with increased light-trapping and lower overall heat loss. The effective solar absorptance was shown to increase from an intrinsic absorptance of 0.86 to 0.96 with ray trace models. The predicted thermal efficiency was shown in CFD models to be over 95%. The horizontal panels produce a re-circulating hot zone between the panel fins reducing convective loss resulting in a more efficient receiver. The analysis and design of these panels are described with additional engineering details on testing a flat panel receiver and the horizontal-finned receiver at the National Solar Thermal Test Facility. Design considerations include the structure for receiver testing, tube sizing, surrounding heat shielding, and machinery for cooling the receiver tubes.

The main focus area of this research paper to efficiently remove the heat generated during conversion of solar energy into electricity using photovoltaic (PV) module. The photovoltaic conversion efficiency of commercial available PV module varies in the range of 8%–20% depending on the type of solar cell materials used for the module construction, e.g. crystalline silicon, thin film, CIGS, organic, etc. During the conversion process, only a small fraction of the incident solar radiation is utilize by PV cells to produce electricity and the remaining is converted into waste heat in the module which causes the PV cell temperature to increase and its efficiency to drop. This thermal energy could be extract using air or water as a heat removal fluid to utilize in heating applications. The purpose of a solar photovoltaic module is to convert solar energy into electricity. The hybrid combination of photovoltaic module and thermal collector called Photovoltaic-thermal (PVT) module. Such PVT module combines a PV, which converts electromagnetic radiation (photons) into electricity, with a solar thermal module, which captures the remaining energy and removes waste heat from the PV module. Cooling of cells either by natural or forced circulation can reduce the PV cell temperature. The simultaneous cooling of the PV cells maintains their PV efficiency at a satisfactory level and offers a better way of utilizing solar energy by generating thermal energy as well. PVT system has higher overall efficiency as compared to separate PV and thermal collector. The heat output of a PVT module can be used for space heating or production of domestic hot water. This paper presents an innovative design of top cooling Thermal Photovoltaic (T-PV) module and its performance under outdoor weather condition of Singapore. T-PV collector is designed to flow fluid over the top of PV panel through a very narrow gap between the solar lens. This process improves heat removal process from PV panel, and hence, improves the electrical output of PV panel as compared to other PVT collector available in the market. By flowing the water from top of the PV panel will also provide better thermal efficiency. A T-PV collector system with storage tank, sensors, pump, flow meters, data logger and controls, have been installed at test-site located in Ngee Ann Polytechnic, Singapore. Performance analysis of T-PV collector system has been evaluated under the tropical climatic conditions of Singapore. It was found that T-PV module could produce additional electrical power as compared to standard PV panel of same capacity by operating at lower temperature. In addition to electricity, T-PV panel also generate the hot water up to 60 deg C at an average thermal efficiency of 41% for usage in residential and commercial buildings. The average thermal energy output was 3.1 kWh/day on typical day’s basis.

This paper evaluates novel particle release patterns for high-temperature falling particle receivers. Spatial release patterns resembling triangular and square waves are investigated and compared to the conventional straight-line particle release. A design of experiments was developed, and a simulation matrix was developed that investigated three two-level factors: amplitude, wavelength, and wave type. Results show that the wave-like patterns increased both the particle temperature rise and thermal efficiency of the receiver relative to the straight-line particle release. Larger amplitudes and smaller wavelengths increased the performance by creating a volumetric heating effect that increased light absorption and reduced heat loss. Experiments are also being designed to investigate the hydraulic and thermal performance of these new particle release configurations.

This paper evaluates the on-sun performance of a 1 MW falling particle receiver. Two particle receiver designs were investigated: obstructed flow particle receiver vs. free-falling particle receiver. The intent of the tests was to investigate the impact of particle mass flow rate, irradiance, and particle temperature on the particle temperature rise and thermal efficiency of the receiver for each design. Results indicate that the obstructed flow design increased the residence time of the particles in the concentrated flux, thereby increasing the particle temperature and thermal efficiency for a given mass flow rate. The obstructions, a staggered array of chevron-shaped mesh structures, also provided more stability to the falling particles, which were prone to instabilities caused by convective currents in the free-fall design. Challenges encountered during the tests included non-uniform mass flow rates, wind impacts, and oxidation/deterioration of the mesh structures. Alternative materials, designs, and methods are presented to overcome these challenges.

The massive use of fossil fuel has caused huge carbon emission and serious air pollution in China. Now all kinds of alternative energy technology are developing rapidly to solve such problem in China. Electricity produced by non-fossil fuel energy is continued to increase sharply in China. But it’s hard for regular alternative energy, such as wind power, solar power, hydroelectricity power, nuclear power and so on, to easily provide process heat for industry, especially high temperature steam. High temperature Gas-cooled Reactor (HTGR, sometimes also called HTR) is a kind of nuclear reactor, which are demonstrated very high efficiencies, safety and availability features by American and German power plant. HTR differs from water nuclear reactors by offering a high thermal efficiency for electricity generation and a high level of passive safety features. Now HTR-PM project is built in Shidao Bay of China. Moreover, HTR is the only nuclear reactor, which can provide high temperature steam comparing with other water nuclear reactors. So HTR can provide a versatile cogeneration solution for industry. In this paper, a case was studied, how to provide heat for a refinery and petro-chemical plant with HTR. Firstly, the energy need of a typical large chemical plant in china was investigated. Steam supply diagram of an oil refinery plant, which produced 10 million tons oil products and 1 million tons ethylene in China, was calculated. Secondly, technical feasibility of energy providing by HTR cogeneration plant was discussed. Extraction steam from HTR system was designed for the chemical plant. It would meet the requirement of steam supply for chemical plant and would replace the captive power plant, where coal was burning. The balance of steam, enthalpy and temperature was calculated. At last, economic evaluation for such cogeneration plants was carried out. The steam supply cost from captive coal power plant and HTR cogeneration plant was compared. Some economical conclusion was made from the discussion.

Concentrated Solar Power using supercritical CO 2 (S-CO 2 ) Brayton cycles offers advantages of similar and even higher overall thermal efficiencies compared to conventional Rankine cycles using superheated or supercritical steam. In this paper, a S-CO 2 Recompression Brayton cycle is integrated with a central receiver. The effect of pressure drops in heat exchangers and solar receiver surface temperature on the thermal and ex-ergetic performance of the recompression Brayton cycle with and without reheat condition is studied. Energy, exergy and mass balance are carried out for each component and first law and exergy destruction are calculated. In order to obtain optimal operating condition, optimum cycle pressure ratios are obtained by maximising the thermal efficiency. The results showed that under low solar receiver pressure drops and solar receiver temperature approach, the S-CO 2 Recompression Brayton cycle has more thermal and exergy efficiencies than the no reheat case. Pressure drop reduces the gap between reheat and no reheat case, and for pressure drops in the solar receiver of 2.5% or higher, reheat has significant impact on thermal and exergy performance of the cycle studied. The overall exergy efficiency showed a bell shaped, reaching a maximum value between 19.5–22.5% at turbine inlet temperatures in the range of 660–755 °C for solar receiver surface temperature approach among 100–200 °C.

The performance of CAES is evaluated for various configurations, with and without thermal energy storage. First, a conventional compressed air energy storage process is modeled using a time series iterative forward differencing method to simulate the round trip efficiency, exergy storage, cavern temperatures and pressures, and the gas expander exit temperature of a CAES plant. The computational model was validated experimentally by comparing trended data of the compression cycle of a 280 HP Gardener-Denver tandem horizontal two-stage compressor to computational results. It was found that the process of cooling the compressors resulted in a large exergy loss and the inefficiencies of the expanders lead to higher temperature gas being exhausted back to ambient pressures. Second, Advanced Adiabatic Compressed Air Energy Storage (AACAES) was simulated to study the effectiveness of storing the thermal energy removed from the compressors to be added to the compressed air as it enters the expanders at a later time. Third, the concept of increasing the capacity of the thermal energy storage systems to allow recharge with concentrated solar heat was explored. It was found that the thermal efficiency of converting the solar thermal energy to power would be high (> 60%). Further, the expander exhaust temperature and exergy are high (> 500 K), implying that additional waste heat energy recovery will be possible. Taken together, the results of this study show that an integrated, high efficiency, on-demand, water-free, solar energy delivery system is possible if combined with an AACAES system.