bluuebunny/crossref_metadata_2025 huggingface dataset:
Design and Performance of a Photobioreactor Utilizing Spatial Light Dilution
Authors: Dye Dan , Muhs Jeff , Wood Byard , Sims Ron
Published: January 2011

A photobioreactor with an optical system that spatially dilutes solar photosynthetic active radiation has been designed, built, and tested at the Utah State University Biofuels Center. This photobioreactor could be used to produce microalgal biomass for a number of purposes, such as feedstock for an energy conversion process or high-value products such as pharmaceuticals and nutraceuticals. In addition, the reactor could be used to perform services such as removing nitrates, phosphates, and other contaminants from waste water, as well as scrubbing toxic gases and carbon dioxide from flue gas. Preliminary tests were performed that compared growth and productivity kinetics of this reactor with that of a control reactor simulating a pond. Tests indicated higher specific growth rates and higher areal and volumetric yields compared with the control reactor. The maximum specific growth rate, volumetric yield, and areal yield were 0.21 day−1, 0.059 gm L−1 day−1, and 15 gm m−2 day−1, respectively. Over 10 days of sequential-batch operation, the prototype photobioreactor converted direct-normal solar energy to energy stored in biomass at an average efficiency of 1%. The areal productivity, as mass per aperture per time, was three times higher than that of the control reactor, indicating the photobioreactor design investigated holds promise.
Radiative Cooling in Northern Europe Using a Roof Window
Authors: Fa¨lt Martin , Zevenhoven Ron
Published: January 2011

The design and performance of a triple glass window used as a roof component was analyzed in this paper. A mathematical model was set up for the component and weather data for the Finnish city Helsinki was used to assess its performance. This roof component would act as a passive radiative cooler during the summer and as a thermal insulator during the rest of the year. This versatile usage of the window component would thus decrease the need for traditional air-conditioning during summer and hence save electricity. The triple glass window would consist of one normal silica window and of two High Density Polyethylene (HPDE) windows. The space between the three windows would contain a (pressurized) greenhouse gas that would act as the heat carrier in this system. The heat would be transferred in to the system to the gas by heat radiation, conduction and natural convection through the window facing the room. This heated gas would then rise to the upper vacant space due to a decrease in the gases density caused by the heating. In the upper vacant part, the gas would then be cooled by radiative cooling through the HDPE, and the atmospheric window with colder air masses in the upper atmosphere. When, the greenhouse gas would have cooled down its density would increase and the gas would drop to the lower part of the window component. During times when no cooling would be needed the connection between the two vacant spaces would be cut, thus changing the roof components’ task from a passive radiative cooler to a thermal insulator. The heating of the space due to sunshine is of course evident and lower temperatures would be achieved if no window at all be used, but for places were roof windows are built this component would offer a viable alternative. This paper is a continuation to the paper by Zevenhoven and Fa¨lt submitted to this conference (1).
Performance-Cost Analysis of Solar Combined Heat and Power Systems
Authors: Norwood Zack , Pepe Stephen , Romanin Vincent , Kammen Daniel
Published: January 2011

Solar combined heat and power (CHP) systems can compete or exceed solar photovoltaics (PV) — which is often used as the benchmark in terms of efficiency, performance, and cost — in a range of distributed generation applications, and across a range of specific technology platforms. A common metric to evaluate the cost of photovoltaics is a cost per peak power output or “dollars per watt” metric. For the purpose of comparison, we develop a new analytic methodology to evaluate the cost of the electricity generated from a solar CHP system. The electricity generation and thermal subsystems of a solar CHP system are energetically intertwined, yet by comparing thermal and electrical outputs a sensible cost division can be determined. This method is then used to compare the cost of stationary PV and solar Rankine CHP systems with tracking and stationary collectors. The capacity factors of electricity generation for each system is found in simulation using NREL TMY3 climatic data for 1020 sites in the United States. The solar Rankine system with stationary collectors outperforms the PV system in warmer and sunnier climates relative to its rated “dollar per watt” output, while PV outperforms solar Rankine in cooler climates. With tracking concentrating collectors, the solar Rankine system outperforms PV systems in the vast majority of US sites at an estimated cost of $4/W and a collector high temperature of 250°C. In conclusion, a PV system and solar Rankine CHP system, sized equally in terms of peak power output, will produce comparable amounts of electricity (+/− 10% on average), however the solar Rankine CHP system will additionally provide 4 to 6 units of useful heat energy for every one unit of electricity generated.
Renewable Powered Desalination in the Coastal Mekong Delta
Authors: Nguyen Ha T. , Pearce Joshua M.
Published: January 2011

Global climate destabilization is exacerbating water problems in Vietnam, most acutely in the South and Central regions where most of the inhabited area lies in the low elevation coastal zone. Using a geographical information system (GIS) platform, a wind resources atlas developed by the Asia Sustainable and Alternative Energy Program and the projected rural population available from Columbia University’s Center for International Earth Science Information Network, this paper explores the potential for off-grid medium to small-scale reverse osmosis desalination powered by small wind turbines for the coastal fringe of Vietnam’s Mekong Delta. The analysis estimated that in the absence of all other water supply facilities, off-grid wind desalination could provide clean water to 5.4 million rural residents living in 18.9 thousand km2 of the Mekong Delta coastal provinces at the rate of 60 liters per capita per day. In addition to providing clean water, the use of wind powered desalination in the region would have educational benefits, combat poverty and unemployment, ease water-related conflicts, and has been shown to be improve environmental and agricultural sustainability. Thus this technology was found to represent a decentralized and community-based method to adapt to and mitigate climate change in the coastal fringe of the Mekong Delta.
Thermodynamic Cycles for a Small Particle Heat Exchange Receiver Used in Concentrating Solar Power Plants
Authors: Kitzmiller Kyle , Miller Fletcher
Published: January 2011

Gas-cooled solar receivers for concentrating solar power plants are capable of providing high temperature, pressurized gas for electrical power generation via a Brayton cycle. This can be accomplished by expanding hot, pressurized gas directly through a turbine, or through using a heat exchanger to indirectly heat pressurized air. Gas-cooled receivers can be divided into two basic technologies. In tube based solar receivers, thermal energy is transferred to air through convection with the heated tube wall. This limits receiver efficiency since the tube wall needs to be substantially hotter than the gas inside due to the relatively poor gas heat transfer coefficient. In volumetric receivers, solar energy is absorbed within a volume, rather than on a surface. The absorption volume can be filled with ceramic foam, wires, or particles to act as the absorbing medium. In a small particle heat exchange receiver, for example, sub-micron sized particles absorb solar radiation, and transfer this energy as heat to a surrounding fluid. This effectively eliminates any thermal resistance, allowing for higher receiver efficiencies. However, mechanical considerations limit the size of volumetric, pressurized gas-cooled receivers. In order to solve this problem, several thermodynamic cycles have been investigated, each of which is motivated by key physical considerations in volumetric receivers. The cyclic efficiencies are determined by a new MATLAB code based on previous Brayton cycle modeling conducted by Sandia National Laboratories. The modeling accounts for pressure drops and temperature losses in various components, and parameters such as the turbine inlet temperature and pressure ratio are easily modified to run parametric cases. The performance of a gas-cooled solar receiver is largely a function of its ability to provide process gas at a consistent temperature or pressure, regardless of variations in solar flux, which can vary due to cloud transients or apparent sun motion throughout the day. Consistent output can be ensured by combusting fuel within the cycle, effectively making a solar/fossil fuel hybrid system. Several schemes for hybridization with natural gas are considered here, including externally fired concepts and combined receiver/combustor units. Because the efficiency of hybridized cycles is a function of the solar thermal input, the part load behavior of the recuperated cycle is examined in depth. Finally, a brief report of economic costs inherent to solar powered gas turbine engines is given. Possibilities for the future of solar power gas turbine power plants are discussed, with key issues regarding thermal storage techniques.
Exergetic Analysis of a Solar-Heated Fuel Cell System Fed by Methanol
Authors: Hotz Nico , Lee Ming-Tsang , Grigoropoulos Costas P. , Zimmerman Raul , Rosengarten Gary , Poulikakos Dimos
Published: January 2011

The present study proposes a combination of solar-powered components (two heaters, an evaporator, and a steam-reformer) with a Proton Exchange Membrane fuel cell to form a powerplant that converts methanol to electricity. The solar radiation heats up the mass flows of methanol-water mixture and air and sustains the endothermic methanol steam-reformer at a sufficient reaction temperature (typically between 220 and 300°C). In order to compare the different types of energy (thermal, chemical, and electrical), an exergetic analysis is applied to the entire system, considering only the useful part of energy that can be converted to work. The effect of the solar radiation intensity and of different operational and geometrical parameters like the total inlet flow rate of methanol-water mixture and the size of the fuel cell on the performance of the entire system is investigated. The results of the exergetic analysis prove that the proposed solar methanol fuel cell system has the potential to be operated with a high efficiency and power density by combining methanol steam-reforming and a PEM fuel cell with solar-powered heating. The chemical exergetic efficiency can be increased by a factor of around 1.6 (e.g. from 36% to 60% for the 1000 W m−2 incoming solar heat flux) by using solar radiation as a heat source instead of any other source (e.g. by burning a chemical fuel). This enhancement of effective exergetic efficiency by using solar power for heating the system amounts to even much higher values of up to above 10 for lower solar heat fluxes and very low flow rates of inlet fuel. The effective exergetic efficiency for the herein presented solar-powered system is significantly higher than any non-solar fuel cell system fed by hydrocarbon or alcoholic fuels. At the same time, an electrical power density per irradiated area of more than 986 W m−2 is obtained for a solar heat flux of 1000 W m−2. Comparable photovoltaic systems would need excessive sunlight-to-electricity efficiencies of more than 98%. Even for decreased intensities of solar radiation as low as 300 W m−2, the system achieves very satisfactory results regarding the solar power density (89.3 W m−2) and the chemical exergetic efficiency (61%). Therefore, the combination of exergy input in form of chemical fuel and solar radiation can be promising to achieve both, a high exergetic efficiency and a high power density per area irradiated by sunlight.
Exergetic Analysis of Solar-Powered Hybrid Energy Conversion and Storage Scenarios for Stationary Applications
Authors: Hotz Nico , Pan Heng , Grigoropoulos Costas P. , Ko Seung H.
Published: January 2011

The idea of this study is to investigate possibilities to use sunlight as the main energy source to generate and store electrical energy via different methods and technologies. Several systems consisting of photovoltaics, photoelectrolytic converters and solarthermal reformers in combination with fuel cells have been investigated in terms of efficiency and costs. A simple energetic approach would not account for these different kinds of energy and their differing availabilities (radiant, thermal, chemical, and electrical energy). To consider different forms of energy and compare them in a fair manner, exergy as the useful part of energy (the part that can theoretically be completely converted to work) provides a perfect instrument for dealing with complex energy conversion systems. In this study, four different scenarios have been investigated: Scenario A describes the direct conversion of sunlight to electricity by photovoltaics. The electric power is used in a Polymer Electrolyte Membrane (PEM) electrolyzer to split water to hydrogen which is stored in a pressure tank. A PEM fuel cell converts hydrogen to electricity on demand. Scenario B deals with a photoelectrolytic cell splitting water to hydrogen by solar irradiation combined with a storage tank and a fuel cell. In Scenario C, solar radiation is converted by photovoltaic cells to electricity which is stored in different types of batteries. Scenario D combines a methanol steam reformer heated by solar power with a PEM fuel cell to generate electricity. The reformate gas mixture can be stored at elevated pressure in a gas tank. In contrast to routes A–C, scenario D has two exergy inputs: Solar radiation and chemical exergy in form of methanol as fuel. All systems are analyzed for an average day in July and February in Central California, including a storage device sufficient to store the energy for one week. Scenario D reaches an overall exergetic efficiency of more than 25% in summer at the expense of an additional exergy input in the form of methanol. The exergetic efficiency of scenario C amounts to 10–17% in summer (4–6% in winter) depending on the battery type and scenarios A and B achieve less than 10% efficiency even in summer. The systems of scenarios A and C would cost around $20k–$45k per 1 kW average electricity generation during the day in July. Scenario D leads to significantly lower costs and scenario B is the most expensive design due to the current immaturity of photoelectrolytic devices.
Implementation of an Integrated Solar Combined Cycle on an Existing Coal Fired Power Plant
Authors: Reitze Eric , Price Hank
Published: January 2011

This paper presents the implementation of an integrated solar combined cycle (ISCC) on the existing 44 MW Cameo Power Generating Station, located in Palisade, Colorado. The plant was originally built in 1957 as a coal fired power plant, to serve the Grand Junction community. This plant has been chosen to demonstrate the viability of the ISCC because of its time line to decommissioning and the availability of additional power from nearby stations to fulfill the community’s needs. The solar system at Cameo utilizes 8 aluminum parabolic trough collectors arranged in 4 loops. Each of these collectors is approximately 150 meters long and 5.77 meters wide. The hot heat transfer fluid used in the solar field is sent to a solar feed water heater, located in between two of the existing feed water heaters, to supplement the thermal energy required by the steam cycle. At design conditions, the solar field will provide 4 MW of thermal energy to the power plant. The development of this ISCC has faced several design and construction challenges not common in traditional power plant and solar power plant design. When first constructed, the Cameo station had no provisions made regarding solar field location, heat transfer fluid piping runs, heat transfer fluid pumping station, thermal expansion vessels, the addition of solar thermal energy to the feed water system, and the integration of a solar field control system into the existing plant distributed control system. Also unaccounted for are the affects the integration of a solar feed water heater has on the thermodynamic efficiency of the steam cycle. This paper discusses these challenges, as well as their resolution, as seen during the engineering, procurement, construction, and commissioning phases of this project. The Cameo Power Generating Station is located in the DeBeque Canyon, 4 miles east of Palisade, Colorado along the Colorado River and Interstate 70. The solar feed water heating demonstration will be in operation for 1 to 2 years, at the discretion of Xcel Energy, to test and develop operating and maintenance methods for large scale application. After such time, both the plant and the solar field will be decommissioned. After decommissioning all applicable solar field equipment shall be refurbished and utilized at additional testing facilities.
Sustainable Communities Case Study: Energy Management Using Demand Response Methods
Authors: Palacio Santiago Naranjo , Zhang K. Max , Patel Disha , Basu Megha , Trager Jason
Published: January 2011

Politicians, activists, business-leaders and engineers alike all agree that future societal progress depends heavily on the development of sustainable cities and communities designed to achieve long-term environmental, social, and economic viability. A key factor that must be considered when planning for sustainable communities is the desirability for living and the productivity potential for industry and research. At the foundation of both is energy — from generation through transmission to consumption. Innovations and novel designs at all levels within a community — from individual buildings to system-wide infrastructure — will allow homes and offices to operate without noticeable sacrifice of comfort and convenience. An interdisciplinary team of professors and graduate students at Cornell University has formed to address the energy challenges of transforming Cornell University campus into a sustainable community. Cornell University’s main campus in Ithaca, NY is uniquely situated to serve as a model for validation and implementation of an advanced electricity infrastructure, commonly known as a Smart Grid. The campus owns and operates its electricity infrastructure powered by a combination of renewable energy, coal production and other electricity purchased from independent providers. In addition, similar to other communities, Cornell has a variety of building types, each having its unique energy consumption profile and thus providing great opportunities for interaction between buildings. This can prove to be very beneficial in our validation as all communities have variable load profiles. With new capital expenditures for new infrastructure, we expect to see a great reduction in energy costs and lowered operation costs resulting from the implementation of smart-grid in the present electric grid. Moreover, introducing demand response schemes, one of the major components of a smart-grid, would allow the community to incorporate more renewable energy sources into its energy mix, increase energy efficiency, and achieve significant monetary savings.
A TRNSYS Simulation and Experimental Comparison of the Thermal Behavior of a Building Located in Desert Climate
Authors: A´lvarez G. , Chagolla M. A. , Xama´n J. P. , Jime´nez M. J. , Sua´rez S. , Heras M. R.
Published: January 2011

This paper describes a TRNSYS simulation of a space of an office building in dessert climate. The space simulated by TRNSYS represents a meeting room which is placed in one of the high mass buildings of the Plataforma Solar of Almeria located in the desert of Tabernas, Spain. The meeting room was selected because hygrothermal variables are being measured. The simulation results are compared with experimental data of the meeting room. The main goal is to describe the thermal behavior of the meeting room of this high mass building in free evolution and verify its thermal performance with the measured data. Climate input variables to the simulation were solar radiation, dry bulb temperature, relative humidity and wind velocity recorded by a meteorological station installed on top of the building. As a first approach coolest winter day and hottest summer day were analyzed. The comparison results between the TRNSYS simulation results and measured ones show a maximum percentage difference of 4.51% (0.60 °C).
Enhanced Sensible Heat Capacity of Molten Salt and Conventional Heat Transfer Fluid Based Nanofluid for Solar Thermal Energy Storage Application
Authors: Kwak Hyun-eun , Shin Donghyun , Banerjee Debjyoti
Published: January 2011

In concentrating solar power (CSP) systems, the thermo-physical properties of the heat transfer fluid (HTF) are key parameters for enhancing the overall system efficiencies. Molten salts, such as alkali nitrates, chlorides or carbonates, and their eutectics, are considered as alternatives to conventional HTF (such as water or oil) to extend the operational capabilities of CSPS. However, the usage of the molten salt as the HTF is limited, since the heat capacity of the molten salt is relatively lower than that of conventional HTF. Nanofluid is a mixture of a fluid and nanoparticles. Well dispersed nanoparticles can be used to enhance the thermo-physical properties of HTF. In this study, silicon dioxide nanoparticles were dispersed into a molten salt and into a conventional HTF (Therminol VP-1, Solutia Inc). The specific heat enhancement of each nanofluid was studied and the applicability of such nanofluid materials for solar thermal storage applications was explored.
Design and Analysis of a Continuous Operating Solar Absorption Cooling System
Authors: Patil Samved , Zhang K. Max , Sahasrabuddhe Aditya , Padhye Shrewans
Published: January 2011

It has been estimated that approximately 15% of electricity produced in the whole world is utilized for refrigeration and air-conditioning applications. Increased use of air conditioning and related appliances during hot summer days leads to high electricity demands in metropolitan areas, which have to be met, in part, by generations from expensive and polluting peaking units. Thus solar cooling has great potential in reducing peaking electricity demands and the overall energy demands. We first compared the overall efficiencies of two solar cooling systems, i.e., vapor compression powered by electricity generated from photovoltaics, and vapor absorption using solar heating. Both systems matched evenly when the coefficients of performance (COP) were compared. But the payback time for vapor compression was five times longer than that for vapor absorption. Then we designed a novel solar cooling system by combining vapor absorption refrigeration (NH3-H2O absorption cycle), concentrated solar and thermal storage. The system is capable of operating autonomously at nights or two days without adequate sunlight. Heating oil is heated by a parabolic trough collector and is then stored in an insulated tank. The oil is then used to heat the refrigerants (i.e., NH3). Oil flows in two loops, one from parabolic collector to tank using thermo-syphon action and other from the tank to refrigerator using a small pump. Next, we created a model to calculate the volume of storage tank, area of solar collector for a given longitude and latitude and application. A micro-processor controlled program can be then be developed in future to control mass flow of oil in the second loop to control the output temperature.
Modeling of Vortex-Flow Solar Reactor via Ideal Reactors in Series Approach
Authors: Ozalp Nesrin , Shilapuram Vidyasagar , Jayakrishna D.
Published: January 2011

In this work, we present a thorough reaction engineering analysis on the modeling of a vortex-flow reactor to show that commonly practiced one-plug reactor approach is not sufficient to explain the flow behavior inside the reactor. Our study shows that N-plug flow reactors in series is the best approach in predicting the flow dynamics based on the computational fluid dynamics (CFD) simulations. We have studied the residence time distribution using CFD by two different methods. The residence time distribution characteristics are calculated by approximating the real reactor as N-ideal reactors in series, and then estimated the number of ideal reactors in series for the model. We have validated our CFD model by comparing the simulation results with experimental results. Finally, we have done a parametric study with a different sweeping gas to identify the best screening gas to avoid carbon deposition inside the vortex-flow reactor. Our results have shown that hydrogen is a better screening gas than argon.
Research Development and Application of Solar Thermal Storage With Phase Change Materials
Authors: Liu Fang , Liang Hao , Yu Hang , Tang Xiaomei
Published: January 2011

Research on efficient and economical thermal storage technology becomes common issue to the scholars. Especially research on PCMs becomes hot spot these years. In view of the discontinuity and instability of solar energy, efficient and economic research on energy storage technology occupies a very important position. This article summarizes and evaluates the research development and applications of solar thermal storage technology with PCMs both in China and the other countries. Including four parts: A review on preparation of new composite phase change materials and its thermophysical properties was carried out. Various heat transfer enhancement technology was overviewed. Including adding metal fill, adding graphite, capsule package, plus fins, adding carbon fiber and composite phase change materials, etc. Mathematical modeling of a latent heat thermal energy storage system (LHTES) was reviewed in recent years which is used for the optimum material selection and to assist in the optimal designing of the systems. The important characteristics of different models and their assumptions used are presented and discussed, the experimental validation of some models are also presented. The applications and prospects of PCMs used in the different fields were summarized, such as industry, agriculture, construction, textiles, electronic products, medicine, transportation etc. Finally, conclusions and perspectives were drawed. Hope to provide references to the other researchers in this field.
SIHG Testing and Analysis
Authors: Bredariol Gregory , Garnier Aaron , Stevens Kevin , Foley Andrew
Published: January 2011

This paper describes the Sailboat Integrated Hydroelectric Generator (SIHG). This turbine is intended to be fixed to the transom of a 30–40 foot sailing vessel to produce green power for the vessel’s electrical systems. The design goal for the SIHG was the generation of a minimum of 225 watts at 6 knots and an ideal output of 400 watts at 6 knots. Power is generated by the SIHG when water moving over five turbine blades creates rotational motion, which is transferred through a gear box to a three-phase electrical generator. The three-phase electrical output is then rectified and used to recharge the boat’s battery. Presently, most sailboats of this size run their engines in order to recharge their batteries. The SIHG produces no emissions and has no operating costs. Extensive testing in the Thames River at the U.S. Coast Guard Academy in New London Connecticut produced data that was then used to determine the power output and efficiency of the SIHG at various speeds through the water. The turbine was fixed to the transom of a dinghy which was then towed behind a rigid hulled inflatable vessel to simulate a sailboat under wind power. Novel data collection methods and instrumentation were then used to gather power and drag data for the turbine at various speeds. Power output plots and efficiency curves were calculated from this data and are represented in this paper. Actual performance shows that the SIHG is capable of producing 275 watts at 6 knots and 400 watts at 8 knots. The maximum efficiency of the SIHG is calculated to be 37% and occurs when traveling through the water at a speed of 5 knots. Due to the substantial power generation at relatively low speeds, tidal applications are discussed.
The Design of a Low Speed Water Turbine
Authors: Foley Andrew C.
Published: January 2011

This paper describes a method for the design of a low r.p.m water turbine designed for an operating point of 5 knots that would be suitable for use as a generator on a recreational sailboat. The low flow speed also means that this design process is also suitable for the hydraulic design of stationary tidal or current generators. The turbine example described in this pare has subsequently been manufactured and successfully tested with a hydraulic efficiency of 13%. Details of the testing are described in a separate paper. (Bredariol et al (2010)).
Evaluation of Measurement and Verification Procedures for Retrofit Savings Using Calibrated Energy Building Models
Authors: Kalinic Niko , Krarti Moncef
Published: January 2011

Calibrated energy simulations are often used to predict savings from energy conservation measures with little information about their associated prediction uncertainties. In this paper, the savings predicted by calibrated simulation models are compared to actual savings obtained through monitoring energy use before and after implementing selected energy conservation measures for three residential buildings. Both building envelope and HVAC system related energy conservation measures are considered in the study. Through case studies, this validity of using calibrated energy models for the estimation and verification of savings associated with energy conservation measures is thoroughly evaluated. Moreover, the paper provides useful guidelines for using calibrated models for measurement and verification energy savings from various weatherization programs specific to residential buildings.
Projections of Levelized Cost Benefit of Grid-Scale Energy Storage Options
Authors: Doty Glenn N. , McCree David L. , Doty F. David
Published: January 2011

The levelized costs of delivered energy from the leading technologies for grid-scale energy storage are calculated using a model that considers likely number of cycles per year, application-specific expected lifetime, discount rate, duty cycle, and likely trends in the markets. The expected capital costs of the various options evaluated — pumped hydrostorage, underground pumped hydrostorage (UPHS), hydrogen fuel cells, carbon-lead-acid batteries, advanced adiabatic compressed air energy storage (AA-CAES), lead-acid batteries, lithium-ion batteries, flywheels, sodium sulfur batteries, ultra capacitors, and superconducting magnetic energy storage (SMES) — are based on recent installation cost data to the extent possible. The marginal value of the delivered stored energy is analyzed using recent grid-energy prices from regions of high wind-energy penetration. Grid-scale energy storage is expected to lead to significant reductions in greenhouse gas (GHG) emissions only in regions where the off-peak energy is very clean. These areas will be characterized by a high level of wind energy with cheap off-peak and peak prices. At the expected price differentials, the only conventional options expected to be commercially viable in most cases are hydro storage, especially via dam up-rating, and UPHS. The market value of energy storage for short periods of time (under a few hours) is expected to be minimal for grid-scale purposes. Only low-cost daily storage is easily justified both from an economic and environmental perspective.
A Methodology for Comprehensive Characterization of Errors in Wind Power Forecasting
Authors: Bielecki Mark F. , Kemper Jason J. , Acker Thomas L.
Published: January 2011

Wind power forecasting will play a more important role in electrical system planning with the greater wind penetrations of the coming decades. Wind will most likely comprise a larger percentage of the generation mix, and as a result forecasting errors may have more significant effects on balancing operations. The natural uncertainties associated with wind along with limitations in numerical weather prediction (NWP) models lead to these forecasting errors, which play a considerable role in the impacts and costs of utility-scale wind integration. The premise of this project was to examine errors between the actual and commercially forecasted power production data from a typical wind power plant in the Northwestern United States. An exhaustive statistical characterization of the forecast behavior and error trends was undertaken, which allowed the most important metrics for describing wind power forecast errors to be identified. This paper presents only the metrics considered by the authors to be most significant. While basic information about wind forecast accuracy such as the mean absolute error (MAE) is valuable, a more detailed description is useful for system operators or in wind integration studies. System planners have expressed major concern in the area of forecast performance during large wind ramping events. For such reasons, this methodology included the development of a comprehensive ramp identification algorithm to select significant ramp events from the data record, and particular attention was paid to the error analysis during these events. The algorithm allows user input to select ramps of any desired magnitude, and also performs correlation analysis between forecasted ramp events and actual ramp events that coincide within a desired timing window. From this procedure, an investigation of the magnitude and phase of forecast errors was conducted for various forecast horizons. The metrics found to be of most importance for error characterization were selected based on overall impacts, and were ranked in a rudimentary (and perhaps subjective) order of significance. These metrics included: mean absolute error, root mean square error, average magnitude of step changes, standard deviation of step changes, mean bias levels, correlation coefficient of power values, mean temporal bias of ramp events, and others. While these metrics were selected and the methodology was developed for a single dataset, the entire process can be applied generally to any wind power and forecast time series. The implications for such a process include use for generating a synthetic wind power forecast for wind integration studies that will reproduce the same error trends as those found in a real forecast.
A Numerical Model for Off-Design Performance Calculation of Parabolic Trough Based Solar Power Plants
Authors: Giostri Andrea , Saccilotto Claudio , Silva Paolo , Macchi Ennio , Manzolini Giampaolo
Published: January 2011

The paper deals with the development and testing of an innovative code for the performance prediction of solar trough based CSP plants in off-design conditions. The code is developed in MS Visual Basic 6.0 with Excel as user interface. The proposed code originates from a previously presented algorithm for on-design sizing and cost estimation of the solar field lay-out, as well as of the main components of the plant, including connecting piping and the steam cycle. Off-design calculation starts from data obtained through the on-design algorithm and considers steady-state situations. Both models are implemented in the same software, named PATTO (PArabolic Trough Thermodynamic Optimization), which is very flexible: the optical-thermal model of collectors can simulate different kinds of parabolic trough systems in commerce, including a combination of various mirrors, receivers and supports. The code is also flexible in terms of working fluid, temperature and pressure range, and can also simulate direct steam generation plants (DSG). Regarding the power block, a conventional steam cycle with super-heater, eventually a re-heater section, and up to seven regenerative bleedings is adopted. The off-design model calculates thermal performance of collectors taking into account proper correlations for convective heat transfer coefficients, considering also boiling regime in DSG configurations. Solar plant heat and mass balances and performances at off-design conditions are estimated by accounting for the constraints imposed by the available heat transfer areas in heat exchangers and condenser, as well as the characteristic curve of the steam turbine. The numerical model can be used for a single calculation in a specific off-design condition, as well as for a whole year estimation of energy balances with an hourly resolution. The model is tested towards real applications and reference values found in literature; in particular, focusing on SEGS VI plant in the USA and SAM® code. Annual energy balances with ambient condition taken from TMY3 database are obtained, showing good accuracy of predicted performances. The code potentiality in the design process reveals twofold: it can be used for plant optimization in feasibility studies; moreover it is useful to find the best control strategy of a plant, especially the mass flow of heat transfer fluid in each operating condition.
Exergy Analysis of PV-Water Cooling System and PV-SAHP System
Authors: Wei Bing , Ma Fei
Published: January 2011

With the increase of the energy crisis and environmental pollution, the solar energy as a clean and renewable energy is paid more attention. The photovoltaic cells are being widely used, and many researchers are studying the light and heat integration of photovoltaic systems (PV/T). PV-water cooling system and PV-SAHP system are all the integration of solar photovoltaic systems and thermal utilization system, which use the solar energy to supply the electric power and space heating or daily hot water. Due to the difference of the equipment installations and application conditions, two systems are different from their system efficiencies. To analyze the system exergy is of great significance, as the energy loss and utilization deficiency can be identified through the exergy analysis, and based on the analyzed results the system efficiency can be improved. Furthermore the system can be optimized by the exergy efficiency calculation. In this paper the exergy values of two systems are analyzed, the energy loss and utilization deficiency are analyzed, and the exergy efficiencies are obtained. The work will be good references for the application and optimization of solar photovoltaic systems and thermal utilization system.
Solar Thermal Closed-Helium Brayton Cycle With High Temperature Phase-Change Thermal Storage
Authors: Xu Xinhai , Valmiki M. M. , Pradhan Saurabh , Liu Hsinhung , Li Peiwen
Published: January 2011

A 1 MW closed helium Brayton cycle is proposed in this study to eliminate the use of water in solar thermal power plants in arid areas. The power system uses highly concentrated sunlight to generate heat at temperatures around 850 to 900 °C. The heat is used in a closed, helium Brayton cycle and is partly stored in a high temperature phase-change material to provide heat for nighttime use. The energy efficiency of the system is analyzed. Other technical issues are discussed.
The Thermodynamic Analysis and Experimental Investigation on Transcritical Carbon Dioxide Heat Pump System
Authors: Xie Yingbai , Liu Yingfu , Mai Yingcheng , Zong Luxiang
Published: January 2011

Synthetic refrigerants such as CFCs and HCFCs deplete ozone and cause greenhouse effect. CO2 as a natural working fluid has zero Ozone Depletion Potential and its Global Warming Potential is equal to 1, is receiving more and more attention in the refrigeration field. Because the critical temperature of CO2 is only 31.1°c, the trans-critical cycle can be used to improve the coefficient of performance of the system. The thermodynamic analysis and experimental investigation on trans-critical carbon dioxide heat pump system are carried out in this paper. It points out that there is an optimum operational pressure on trans-critical carbon dioxide heat pump cycle, when the outlet temperature of gas cooler is constant, the coefficient of performance increases with increasing evaporating temperature at the same conditions, and the operational efficiency increased with decrease of gas cooler exit temperature. So in order to obtain the optimum performance, the influence of evaporating temperature, gas cooler exit temperature, and the operational pressure should be considered during the designing and operating transcritical carbon dioxide heat pump system.
Modeling of Ocean Thermal Energy Conversion (OTEC) Plant in Reunion Island
Authors: Sinama Frantz , Lucas Franck , Garde Franc¸ois
Published: January 2011

Renewable Energy has a crucial interest for a remote area like Reunion Island. The supply of electricity based on renewable energy has many advantages but the major drawback is the production of electricity which varies highly according to the availability of the resource (wind, solar, wave, etc...). This causes a real problem for non interconnected electrical grid where intermittent renewable energies should be limited to a maximum of 30%. The ocean Thermal Energy Conversion (OTEC) provides an alternative of electricity production from the available energy of the oceans present all the time. By using surface hot water and deep cold water from the ocean, it is possible to operate a thermodynamics cycle, which will then generate electricity. In this article, in the first part a literary and technological review is carried out in two areas: electricity production and cooling of buildings with deep water. This study establishes a knowledge base on thermodynamic cycles consistent with the OTEC and on dimensional and functional parameters associated with this technology. Steady state simulations are presented to understand the operation of the system. Steady state models will evaluate the potential of the OTEC in distributing base electricity. These simulations will help evaluating the potential for new thermodynamic cycles such as the Kalina cycle. With these tools, a sensitivity study will evaluate the influence of different parameters on the cycle.
Economics of Wastewater Treatment Codigestion
Authors: Keleman Michael P.
Published: January 2011

Wastewater treatment is the method by which sewage of both residential and industrial sources is processed to promote public health and reduce environmental impacts on receiving waters. This physical and biological process generates sludge, which after being treated to reduce pathogens, is referred to as biosolids. In the US there are over 16,000 wastewater treatment plants (WWTP), and every year they produce approximately 7 million tons of biosolids according to the EPA.1 These biosolids are handled differently depending upon local conditions, but most are either buried in landfills, land applied for agriculture or incinerated. Reducing the volume of biosolids produced by each facility is desirable for improving operational efficiency since lower volumes are easier to manage and cheaper to handle and dispose. Most facilities utilize either aerobic digestion to process sludge into biosolids, but larger facilities use anaerobic digestion because this process reduces the overall volume of solids left for management. Anaerobic digestion is more complex and capital intensive, so typically only those facilities treating flows higher than 5 million gallons per day (MGD) use anaerobic digestion. Given current economic conditions and rising energy costs, however, anaerobic digestion is becoming more attractive to utility managers as they attempt to offset energy costs. The anaerobic process produces methane gas. Also called biogas, methane can be utilized not only to fire boilers for heating digesters and nearby buildings, but also to fuel internal combustion engines, microturbines or fuel cells to generate power for plant processes such as blowers in the aeration system. There is also the potential for WWTPs to obtain carbon credits for utilizing renewable energy, especially in those states with renewable portfolio standards. Because anaerobic digestion has limited application in the US, this study evaluated economic viability at plants with design flows less than 5 MGD by incorporating codigestion of food waste to improve the production of biogas for use as energy to reduce operational costs and recover capital costs.
Thermal Modelling and Simulation of Parabolic Trough Receiver Tubes
Authors: Eck Markus , Feldhoff Jan Fabian , Uhlig Ralf
Published: January 2011

Receiver tubes (or heat collecting elements — HCE) are a key component of parabolic trough solar thermal power plants. They are mounted in the focal line of the collectors, absorb the concentrated solar irradiance and transfer the absorbed energy to the heat transfer fluid flowing through them. During the design phase of the receiver tubes and for the performance prediction of solar thermal power plants it is helpful to derive their technical properties, like the thermal losses or the temperature field in the receiver tubes, from their physical and geometrical properties. For this purpose, several models have been developed in the past [1–3]. In this paper, the different existing models are presented, compared and assessed. It is found that a simple analytical model is a helpful tool for the fast prediction of the temperature distribution in the receiver tube. Furthermore, a 2-dimensional and a 3-dimensioanl model are compared regarding the heat losses of a HCE at different operation conditions. Both tools show a good agreement with available measurements. Finally with these tools the efficiency factor F′ is calculated that considers the heat losses of an irradiated receiver compared to that of an un-irradiated receiver. According to the performed calculations, the efficiency factor of parabolic trough receivers is higher than expected.
Performance Optimization and Parametric Analysis of a Class of Solar-Driven Heat Engines
Authors: Zhang Houcheng , Wu Lanmei , Lin Guoxing
Published: January 2011

A class of solar-driven heat engines is modeled as a combined system consisting of a solar collector and a unified heat engine, in which muti-irreversibilities including not only the finite rate heat transfer and the internal irreversibility, but also radiation-convection heat loss from the solar collector to the ambience are taken into account. The maximum overall efficiency of the system, the optimal operating temperature of the solar collector, the optimal temperatures of the working fluid and the optimal ratio of heat transfer areas are calculated by using numerical calculation method. The influences of radiation-convection heat loss of the collector and internal irreversibility on the cyclic performances of the solar-driven heat engine system are revealed. The results obtained in the present paper are more general than those in literature and the performance characteristics of several solar-driven heat engines such as Carnot, Brayton, Braysson and so on can be directly derived from them.