In this study, prototype electrodynamic dust shield (EDS) devices large enough to cover commercial photovoltaic (PV) modules were fabricated and tested in the lab and in the field. The EDS device consisted a polyethylene terephthalate (PET) substrate with screen-printed silver electrodes, and a PET cover sheet that bonded to the substrate using a synthetic rubber adhesive. The voltage-current characteristics of the EDS device was measured while square wave high voltage was applied to the device, so as to determine the power consumption of the EDS device. The EDS device was also tested in the field to determine its effectiveness in soiling mitigation. Measurements showed that the EDS capacitance varied from approximately 600 pF in the air-conditioned lab to 2 nF in the field when the EDS device temperature reached 45 °C. The variation of the capacitance has significant relevance to the capacity requirements for the high voltage sources needed to energize the EDS device and its power consumption. Under laboratory conditions, the EDS power consumption was found to be 0.3 W m −2 at 6 kV p-p and 1 Hz, and roughly proportional to the voltage squared. In the field test electrode damage was observed, due to electrical discharge at the electrode lines. As a result, the EDS operation did not show significant effect of soiling mitigation. The results of this study are useful for designing high voltage sources for EDS operation, and for modifying the design and fabrication methods in order to produce EDS devices that can effectively repel dust in the field.

Supercritical carbon dioxide (sCO2) Brayton power cycles have the potential to significantly improve the economic viability of concentrating solar power (CSP) plants by increasing the thermal to electric conversion efficiency from around 35% using high-temperature steam Rankine systems to above 45% depending on the cycle configuration. These systems are the most likely path toward achieving the Department of Energy’s (DOE) Office of Energy Efficiency and Renewable Energy (EERE) SunShot targets for CSP tower thermal to electric conversion efficiency above 50% with dry cooling to air at 40 °C and a power block cost of less than 900 $/kWe. Many studies have been conducted to optimize the performance of various sCO2 Brayton cycle configurations in order to achieve high efficiency, and a few have accounted for drivers of cost such as equipment size in the optimization, but complete techno-economic optimization has not been feasible because there are no validated models relating component performance and cost. Reasonably accurate component cost models exist from several sources for conventional equipment including turbines, compressors, and heat exchangers for use in rough order of magnitude cost estimates when assembling a system of conventional equipment. However, cost data from fabricated equipment relevant to sCO2 Brayton cycles is very limited in terms of both supplier variety and performance level with most existing data in the range of 1 MWe power cycles or smaller systems, a single completed system around 7 MWe by Echogen Power Systems, and numerous ROM estimates based on preliminary designs of equipment for 10 MWe systems. This data is highly proprietary as the publication of individual data by any single supplier would damage their market position by potentially allowing other vendors to undercut their stated price rather than competing on reduced manufacturing costs. This paper describes one approach to develop component cost models in order to enable the techno-economic optimization activities needed to guide further research and development while protecting commercially proprietary information from individual vendors. Existing cost models were taken from literature for each major component used in different sCO2 Brayton cycle configurations and adjusted for their magnitude to fit the limited vendor cost data and estimates available. A mean fit curve was developed for each component and used to calculate updated cost comparisons between previously-reviewed sCO2 Brayton cycle configurations for CSP applications including simple recuperated, recompression, cascaded, and mixed-gas combined bifurcation with intercooling cycles. These fitting curves represent an average of the assembled vendor data without revealing any individual vendor cost, and maintain the scaling behavior with performance expected from similar equipment found in literature.

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.

When a coal-fired power plant is considered for closure, arguments are commonly made about the loss of jobs and unrealized investments. Facing this pressure, governments are reluctant to enact enforceable emission standards, and these plants continue to emit pollutants into the atmosphere. As the equipment ages, the plants may retire, but in their lifetime they will cause irreversible environmental damage. This report presents a method to mediate this damage, create jobs, maintain the efficiency of the turbine, and maintain or increase the capacity factor of the plant. Solar parabolic troughs using molten salt technology are scalable and can meet the steam conditions of a standard Rankine cycle coal-fired power plant. A marriage of these technologies allows the parabolic trough field to be installed without new power generation equipment. The turbine, generator, and transmission equipment are already in place, and when compared to a standalone concentrated solar power (CSP) plant, can be amortized over a greater number of operational hours without the use of very large amounts of thermal storage. That allows for a reduction in capital investment compared to a greenfield CSP plant, and reduces the levelized cost of energy (LCOE) from the solar contribution to well below current US Department of Energy SunShot targets. Coal-fired plant operators note that they typically cannot operate at partial power output without reducing the efficiency of their turbine accordingly. So, while a photovoltaic hybridization can take advantage of existing transmission infrastructure, it will require that the coal-fired system reduces its output and will consequently reduce the efficiency of the coal cycle. If we have to burn coal, we should do it in the most efficient way possible. Hybridizing with a molten salt parabolic trough installation makes use of the same turbine as the coal-fired system, which maintains the overall efficiency of the turbine at its design point and optimal load. With this model, the coal plant can operate at full power, reduce overall usage of coal while maintaining or even increasing employment opportunities, and reduce CO2 emissions.

This paper presents an optimization procedure which integrates lightning strike analysis into design reliable and economical composite wind turbine blades. A high-fidelity 5-MW composite wind turbine blade is applied into the lightning strike analysis and the optimization procedure under four different lightning severity levels. The lightning-strike-induced electric field along the wind turbine blade at the top vertical position is calculated using finite element analysis. The dielectric breakdown strength of the composite wind turbine blade is considered as a function of laminate thickness. The lightning safety ratio is then calculated as the ratio between the dielectric breakdown strength and the magnitude of the lightning-strike-induced electric field. Subjected to the lightning constraints and fatigue constraints, the optimization procedure minimizes the total composite material cost by fine-tuning the laminate thickness design variables of the blade model. Both the lightning strike analysis and the optimization results indicate that the blade tip is the most vulnerable region against lightning strike damage. The obtained optimum designs under the four lightning severity levels increase the lightning safety ratio by 36% – 45% and increase the fatigue life more than 15 times compared with the initial blade design.

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.

The rise of energy prices, concerns over climate change and geopolitical issues have brought special attention to renewable sources of energy and wind energy in particular. Based on NREL projections, the United States has more than 32,000 TWh of onshore and 17,000 TWh of offshore potential for wind power generation, which is far beyond its 11,000 TWh of current annual electricity consumption. However, there are a number of efficiency challenges that must be overcome in order to turn this potential into actual production. One area that can potentially improve the energy production of wind turbines is the correction of yaw error. Yaw error (also referred to as yaw angle or yaw misalignment) is the angle between the turbine’s rotor and the wind direction. A yaw error reduces turbine’s power production at wind speeds below the rated speed. Besides impacting the power producing ability of a turbine, yaw error also affects the reliability of critical subsystems in wind turbines. Variation in yaw error (at any wind speed and not only below the rated speed) affects the loads on the components and the subsequent mechanical stresses. These mechanical stresses change the damage accumulation for components and sub-assemblies, which ultimately affects their reliability. About 17 to 28% of wind project costs attribute to O&M costs, which are directly affected by the reliability. In this study, we investigate the effects of yaw error on the reliability of blades by performing load and stress analysis for various yaw errors. We then use the results of these analyses to adjust the Weibull parameters used for predicting the failure time of blades. Finally, we will use a stochastic cost model to show how correcting the yaw error can avoid maintenance costs in wind farms.

Closed-loop super-critical carbon dioxide (sCO 2 ) Brayton cycles are being evaluated in combination with concentrating solar power to provide higher thermal-to-electric conversion efficiencies relative to conventional steam Rankine cycles. However, high temperatures (650–700°C) and pressures (20–25 MPa) are required in the solar receiver. In this study, an extensive material review was performed along with a tube size optimization following the ASME Boiler and Pressure Vessel Code and B31.1 and B313.3 codes respectively. Subsequently, a thermal-structural model was developed using ANSYS Fluent and Structural to design and analyze the tubular receiver that could provide the heat input for a ∼2 MW th plant. The receiver will be required to provide an outlet temperature of 650°C (at 25 MPa) or 700°C (at 20 MPa). The induced thermal stresses were applied using a temperature gradient throughout the tube while a constant pressure load was applied on the inner wall. The resulting stresses have been validated analytically using constant surface temperatures. The cyclic loading analysis was performed using the Larson-Miller creep model in nCode Design Life to define the structural integrity of the receiver over the desired lifetime of ∼10,000 cycles. The results have shown that the stresses induced by the thermal and pressure load can be withstood by the tubes selected. The creep-fatigue analysis displayed the damage accumulation due to the cycling and the permanent deformation of the tubes. Nonetheless, they are able to support the required lifetime. As a result, a complete model to verify the structural integrity and thermal performance of a high temperature and pressure receiver has been developed. This work will serve as reference for future design and evaluation of future direct and indirect tubular receivers.

Floods are among the most common natural hazards in Florida. They are threatening the safety and economic welfare of Floridians. Every year Florida spends millions of dollar to mitigate direct flood damages. Amongst the effective solutions to these flood damages is the control of urban drainage in school buildings and nearby grounds to conserve and preserve natural resources and to promote sustainable thinking. This paper discusses how public schools in Florida can benefit from sustainable techniques by applying the sustainable urban drainage system (SUDS) to school designs. The article also illustrates how Florida can use school sites as double functions to provide an active educational environment and to manage storm water runoff at the same time. Construction costs estimation for sustainable techniques is calculated based on data available for the year 2011 and compared with the conventional construction methods for schools. The result indicates a high initial cost that can easily be offset by considering the cost of conventional drainage structure, conserved storm water, flooding impact, storm water sewage disposal, and other measures.

Contemporary biomass-burning power systems face a number of economic constraints that have historically limited their broad adoption. Foremost among these is the cost of transporting the biomass fuel within the collection radius required to sustain the system. Many systems capable of using raw feedstocks incorporate Rankine power cycles, which are not economical in plants below 50 MW e . At this scale the collection radius becomes prohibitively large with respect to transportation costs. An alternative solution has been to transport feedstock to a processing facility where the fuel can be densified into a bio-oil. The high capital and labor costs associated with the processing facility make the fuel cost too high for electric power production. The solution presented here is a Brayton cycle system that incorporates several innovations to address the historical limitations to biomass energy production, while retaining the traditional advantages. These advantages include low operating and maintenance (O&M) costs, autonomous operation, portability, and fast starting. The relatively small size of the 1 MW e engine reduces the required feedstock collection radius to a range that is economical and practical. The engine incorporates a novel compact solid-fuel-burning combustor that is designed to emulate traditional gas-turbine can-type combustor behavior and performance, enabling the use of a broad range of biomass feedstocks. Integrated on-demand fuel processing eliminates the need for an expensive central facility and serves to dry, densify, and pulverize the feedstock for direct injection into the cycle. Additionally, bound nitrogen within the fuel is driven off as stable elemental nitrogen during the integrated fuel-processing, allowing combustion to occur with characteristically low emissions. The engine itself is designed for maximum efficiency in a back-heated configuration, wherein the cycle heat addition takes place downstream of the turbine. This arrangement protects the turbomachinery and bearings from the risk of foreign object damage (FOD) or contamination that might potentially be introduced by the variable feedstock. An overview of the full design is presented, including thermodynamic cycle models and conversion efficiencies. An operational profile is provided, including the collection radius and transportation costs associated with the solution. Test data for a scale solid biomass combustor, including emissions results, is presented.

A major challenge for solar water heaters is to provide heat at a cost comparable to or lower than conventional fuels. Since the price of a passive integral-collector-storage (ICS) solar water heater has historically been less than that for active systems with freeze protection, they can potentially heat water at a lower cost. However, ICS panels are subject to freeze damage, as the collector generally has metal tubes carrying pressurized water that can freeze and burst. In order to delineate the geographical areas where ICS panels can be deployed safely, it is necessary to experimentally characterize the conditions causing freeze damage, to develop a model relating the freeze behavior to climatic conditions, to validate that model with experimental data, and to run the model against long-term weather data across the U.S. Two variations of an ICS panel and/or their bare tubes were tested in a walk in freezer and subjected to freezing conditions until freeze damage occurred. The units tested include both a single and double glazed tubular ICS panel. Key data includes the volume expansion of the tube(s) at burst and the collector loss coefficient near 0 degrees C. Under freezing conditions the insulated supply/return lines would freeze solid initiating a pressure-buildup and eventual burst in the collector tubes due to further internal freezing. An additional test on the single glazed unit was also conducted in which heat tape was installed on the inlet and outlet pipes to prevent them from freezing, which increases the freeze tolerance of the panel by forcing small internal interconnection pipes to freeze solid before damage occurs. Existing models for ICS thermal performance were modified to incorporate the freezing process, and have been validated with the experimental data. The validated models were used to predict regions of the country that are safe for installing the ICS panels. Simulations were run using 30 years of weather data available for all TMY2 sites, and maps were created to illustrate regions of safe installation throughout the US for both the with and without heat tape scenarios for the two ICS models. A correlation using record minimum temperature was developed to generalize the maps to any location for which the record minimum is known. The maps show quantitatively the expected conclusions: 1) that double glazing and higher insulation will extend the safe region; and 2) that the use of heat tape on the inlet and outlet pipes significantly increases the region in which ICS panels can be safely installed in the US.

Concentrated solar radiation can be utilized to generate electrical power from photovoltaic cells, but it increases the photovoltaic cell temperature. This can lead to a degradation of the cell efficiency and too high of a temperature can damage the cell integrity. This is particularly important in dish and tower systems where a maximum uniform flux may be difficult to achieve. While a variety of approaches have been used to the keep the cells cool, most are based upon removal of heat from the back (opposite to the incident flux) of the cell. This paper reports on an immersion cooling technique for the cells, where a coolant is circulated over the complete cell including the front surface. An analysis is given where the cells are placed in a cylindrical glass tube where a liquid is circulated. The impacts of the various thermal processes that result from this approach are described here. A comparison is made to limited experimental data.

Energy generation with fossil fuels produces emissions of greenhouse gases into the atmosphere and releases toxic chemicals into the environment. Greenhouse gases produce global warming which can cause climate change and costly human displacements. Toxic chemicals released into the environment produce health problems and damage the ecosystems. With fossil fuels providing today over 85% of energy needs and the Earth’s population projected to increase by several billion people and energy needs projected to double by the middle of this century, considerable pressure exists to develop sustainable energy supply services. This poses an enormous challenge to engineers, economists, and policy makers. The energy mix required to produce energy for humanity depends on the availability of energy resources, security of energy supply, climate change requirements, technological breakthroughs, financial conditions, and public acceptance. Population, standard of living, toxic and greenhouse gas emissions, thermodynamic limits imposed on biophysical processes, and economics and ethics of resource utilization produce some key sustainability indicators or attributes that need to be employed for guiding our path toward a sustainable energy future. Following a general discussion of indicators and frameworks of indicators, a small number of energy supply values or objectives are presented for the purpose of developing attributes that can measure the degree of accomplishment of these objectives. A systems approach is then employed to define indicators for generic energy supply services and a risk-based multi-criteria decision making procedure is presented for deciding which energy supply service option is most sustainable. The methodology can be applied locally, regionally, and globally, by both the energy services providers and energy policy makers.

With growing numbers of concentrating solar power systems being designed and developed, glint and glare from concentrating solar collectors and receivers is receiving increased attention as a potential hazard or distraction for motorists, pilots, and pedestrians. This paper provides analytical methods to evaluate the irradiance originating from specularly and diffusely reflecting sources as a function of distance and characteristics of the source. Sample problems are provided for both specular and diffuse sources, and validation of the models is performed via testing. In addition, a summary of safety metrics is compiled from the literature to evaluate the potential hazards of calculated irradiances from glint and glare. Previous safety metrics have focused on prevention of permanent eye damage (e.g., retinal burn). New metrics used in this paper account for temporary flash blindness, which can occur at irradiance values several orders of magnitude lower than the irradiance values required for irreversible eye damage.

In this paper, we explore a reduced-order framework to predict the sustainability of a given system. The approach combines concepts from economic theory, thermodynamics, and the environmental sciences into a simple scheme that allows evaluation of system sustainability in terms of a small number of variables. The underlying hypothesis behind the work is that sustainability can be correlated to reversibility, and therefore should bear a relationship with transitions from an initial benign state. We propose evaluation along three dimensions: (i) physical; (ii) economic; and (iii) social. The measure of physical damage follows from the second law of thermodynamics, and specifically we show when and how second-law derived metrics (such as lifetime exergy consumption) can be extended to capture additional impacts. The measure of economic impact is derived by correlating physical transformations of objects with their relative economic value, specifically through use of input-output models that have been previously published in the literature. Lastly, we explore capturing social value through a proxy of indexed measures that correlate to the notion of a ‘social entropy’, which is suggested as an approximation for the deviation of society from a general state of well-being. We propose unifying all three of these approaches through a generalized framework, and thus suggest a simple but broad ‘sustainability performance’ metric. The paper concludes by discussing the challenges associated with widespread implementation, validation, and completeness of such a framework.

Dish concentrators can produce highly concentrated flux for the operation of an engine, a chemical process, or other energy converter. The high concentration allows a small aperture to control thermal losses, and permits high temperature processes at the focal point. A variety of optical errors can influence the flux pattern both at the aperture and at the absorber surface. Impacts of these errors can be lost energy (intercept losses), aperture compromise (increased size to accommodate flux), high peak fluxes (leading to part failure or life reduction), and improperly positioned flux also leading to component failure. Optical errors can include small scale facet errors (“waviness”), facet shape errors, alignment (facet pointing) errors, structural deflections, and tracking errors. The errors may be random in nature, or may be systematic. The various sources of errors are often combined in a “root-mean-squared” process to present a single number as an “error budget”. However, this approach ignores the fact that various errors can influence the performance in different ways, and can mislead the designer, leading to component damage in a system or poor system performance. In this paper, we model a hypothetical radial gore dish system using Sandia’s CIRCE2 optical code. We evaluate the peak flux and incident power through the aperture and onto various parts of the receiver cavity. We explore the impact of different error sources on the character of the flux pattern, and demonstrate the limitations of lumping all of the errors into a single error budget.

Several studies predict an economic benefit of using nitrate-based salts instead of the current synthetic oil within a solar parabolic trough field. However, the expected economic benefit can only be realized if the reliability and optical performance of the salt trough system is comparable to today’s oil trough. Of primary concern is whether a salt-freeze accident and subsequent thaw will lead to damage of the heat collection elements (HCEs). This topic was investigated by experiments and analytical analysis. Results to date suggest that damage will not occur if the HCEs are not completely filled with salt. However, if the HCE is completely filled at the time of the freeze, the subsequent thaw can lead to plastic deformation and significant bending of the absorber tube.

Wind Turbine blade failures can occur in several modes, which may depend on the type of construction and load history. Cracking and delamination are two typical modes of blade failure (Fig. 1). A structural health monitoring (SHM) system can help to better understand warranty costs and warranty periods for the blades in wind turbines and predict imminent failure before it occurs. Currently, industry best practices are to increase the number of physical inspections when blades are approaching the end of their fatigue lives. Implementation of an in situ monitoring system would eliminate or greatly reduce the need for such physical inspections. Another benefit of such a monitoring system is that the life of any given component could be extended since real conditions would be monitored. The SHM system is designed to operate while the wind turbine is in service. This means that wireless communication options will be implemented. Because blade failures occur due to cyclic stresses in the blade material, the sensing system will focus on monitoring strain at various points. This paper describes a design and implementation scheme for a real time structural health monitoring system in order to better understand when blade replacement is necessary. Although not described in this research, the same concepts can also be applied to gearbox damage detection.

Measurements of the electric output of wind turbines have shown power oscillations with a 3p frequency which are caused by the interaction of the rotor with the supporting structure (tower). Potentially more troublesome than the power variations are the load pulses acting on the blades, the main shaft, the support bearings, the power transmission system, and the tower. These pulses are one factor among many causing the complex state of loading to which a wind energy converter is subjected. Simple aerodynamic modelling of this interaction is not capable of capturing all the effects present such as tower wake meandering, stall delay on the blades, lateral tower loads, and break-up of the rotor wake and trailing tip vorticity. This paper shows a method for estimating the magnitude of these effects based on fully turbulent CFD computations and discusses their importance for the design of structural components. Several turbulence models are used and their advantages and drawbacks are discussed. A better understanding of the aerodynamic and aeroelastic interaction between the rotor and the tower influences design parameters such as the tilt and overhang of the main shaft and should also be considered in the selection of the gear box and in possible modelling of blade damage. It is also shown that the near wake aerodynamics of the rotor has an influence on the far wake behavior making this an important factor for wind park simulations.

Structural testing of wind turbine blades is required for designing reliable, structurally efficient blades. Full-scale blade fatigue testing conducted at the National Renewable Energy Laboratory’s (NREL) National Wind Technology Center (NWTC) provides blade manufacturers quantitative information on design details including design assessment, manufacturing quality, and design durability. Blade tests can be conducted as a single axis test (flapwise or lead-lag) or a dual-axis test (flapwise and lead-lag simultaneously). Dual-axis testing is generally the preferred full-scale test method as it simulates to a greater extent the characteristic loading the blade is subjected to in the field. Historically, wind turbine blade fatigue testing has been performed through forced displacement methods using hydraulic systems which directly apply load to the blade. More efficient methods of fatigue testing are being developed at the NWTC that employ resonant excitation systems to reduce hydraulic supply requirements, increase the test speed, and improve distributed load matching. In the case of a dual-axis resonant test, the blade is excited through multiple actuators at two distinct frequencies corresponding to the flapwise and lead-lag frequencies. A primary objective of a dual-axis test is to test the blade to equivalent damage moments in multiple axes. A code was developed to simulate the performance of the dual-axis resonant test system, comparing the predictions to actual test results. Modeling of this test system was performed using a MATLAB script that integrates the NREL FAST code with a commercial dynamic simulator package ADAMS. This code has the advantage over existing methods to more accurately simulate the coupled response between the flapwise and lead-lag directions. In summary, this paper will provide information on the modeling of wind turbine blade dual-axis resonant test systems.