J. G. McGowan

Lead acid battery storage model for hybrid energy systems

This paper describes a new battery model developed for use in time series performance models of hybrid energy systems. The model is intended to overcome some of the difficulties associated with currently used methods. It is based on the approach of chemical kinetics. This model, which can be used for charging and discharging, is specifically concerned with the apparent change in capacity as a function of charge and discharge rates. It assumes that the charge can be stored in two ways, either as immediately available or as chemically bound. As described in this paper, it requires the determination of as few as three constants. Examples of the deviation of the battery model constants and comparisons of the new model with those used previously are given. Based on the success of the new model, it has been incorporated into the latest versions of the University of Massachusettss wind/diesel simulation codes.

Condition monitoring and prognosis of utility scale wind turbines

Abstract The state of the art in condition monitoring in wind turbines, and related technologies currently applied in practice and under development for aerospace applications, are reviewed. Condition monitoring systems estimate the current condition of a machine from sensor measurements, whereas prognosis systems give a probabilistic forecast of the future condition of the machine under the projected usage conditions. Current condition monitoring practice in wind turbine rotors involves tracking rotor imbalance, aerodynamic asymmetry, surface roughness and overall performance and offline and online measurements of stress and strain. Related technologies for monitoring of load history and fatigue crack growth in aircraft structures are evaluated for their applicability to wind turbine blades. Similarly, condition monitoring practice in wind turbines is compared with monitoring and prognosis in helicopter gearboxes. The state of the art in condition monitoring of electronic controls, power electronics and towers is also evaluated and compared with the state of the art in aerospace. Based on these comparisons, technology needs and future challenges for the development of condition monitoring and prognosis for large wind machines, both onshore and offshore, are summarised.

HYBRID WIND/PV/DIESEL SYSTEM EXPERIENCES

The past ten years have seen significant developments in the design, analysis and installation of hybrid (wind/PV/diesel) power systems. This paper presents a summary of recent progress on this subject in the United States with emphasis on the analytical and experimental work carried out at the University of Massachusetts. Topics discussed here include: 1) System configuration and hardware, 2) Modeling and design tools, and 3) Recent applications.

Hybrid wind/PV/diesel hybrid power systems modeling and South American applications

This paper presents an applications case study and comparison of performance results between two computational models for simulating the performance of hybrid power systems. The first model, HYBRID2, was developed at the University of Massachusetts under National Renewable Energy Laboratory (NREL) sponsorship. The second model, SOMES, was developed at Utrecht University in the Netherlands. Both models have been designed to predict the technical and economical (life cycle cost) performance of hybrid power plants that typically might be comprised of renewable energy sources, a battery bank, and a diesel generator. A South American (Brazil) based hybrid power system used to power a remote telecommunications system was used for the applications case study. A final system configuration be used as a basis for model prediction comparison was established as a result of HYBRID2 parametric evaluation. Both codes yielded similar performance results, and this work points out that the predicted performance discrepancies are due basically to different subcomponent models and differences in control strategy. The generalized nature of this work is intended to be of interest to engineers involved with the design and analysis of hybrid power systems.

An Investigation of Wind-Shear Models and Experimental Data Trends for Different Terrains

The importance of characterizing the wind-shear at a given site for a utility-scale wind turbine cannot be overemphasized. Such characterization is needed for an accurate prediction of its power output. Thus, the objective of this work based on the use of several US tall tower wind data sets was to determine the accuracies of different wind-shear enumeration methods, especially when used at sites having hills and/or forests. In addition, average wind-shear variations with respect seasonal and annual effects and data length are presented for various long data sets, recorded to between 1995 and 2005. Wind direction and atmospheric stability were not a factor in the analysis. At some of the sites the greatest average wind-shear was found during the summer. For the site with the most complex terrain, the average annual all-direction wind-shear varied by up to 7% between different years; this was partly due to year-to-year variations of the direction distribution. There was found to be no significant difference between the performance of the log and power laws; using either may give inaccurate predictions of hub-height mean wind speeds.

An offshore wind resource assessment study for New England

This paper gives a summary of ongoing work on the assessment of the wind energy resource off the coast of southern New England in the United States. This project was carried out to determine the potential for the near-term development of offshore wind energy projects in that region. The work summarized here consists of four aspects: (1) a review of existing offshore wind data, (2) the measurement of new data at an offshore site, (3) correlation and prediction of long-term data at a new offshore site by reference to a longer-term island site and (4) assessment of the overall coastal resource through the use of the MesoMap software.

PERFORMANCE MODELING OF NON-METALLIC FLAT PLATE SOLAR COLLECTORS

Abstract This paper extends the current techniques used in the prediction of flat plate solar collector performance for use in the analysis of non-metallic collectors. An analytical model was developed to study the characteristics of these solar collctors which eliminate the need for metals, glass, and special coatings. Using this model, plate efficiency factors are presented for various common non-metallic absorber plate configurations. A parametric study was conducted with emphasis placed on collector plate thermal conductivity and partial transmittance of glazings to long-wave radiation. From the results of this study, it was shown that it is possible to meet or exceed performance levels of conventional metal tube and fin collectors through the use of non-metallic collectors in the low- to medium-temperature range.

Recent renewable energy driven desalination system research and development in North America

Abstract This paper summarizes the current status of renewable energy driven water desalination projects built or designed in North America. It considers both solar and wind energy as the energy sources. It discusses results of experimental projects and assessments that have been made of them. It also includes a discussion of advances in development of components that have been used in such systems. The following processes are considered: simple distillation, multistage flash distillation, freeze separation, vapor compression, electrodialysis, and reverse osmosis (RO). As indicated, the paper specifically addresses projects of North American origin. Among the most successful renewable energy driven plants to date have been those that use RO. Reverse osmosis is, in fact, the most commonly used method of conventionally powered desalination in the United States. For example, approximately 100 RO systems are known to be operating in Florida. For that reason a particular effort has been directed at describing those developments in RO technology in North America that can be applied in renewable energy driven applications. Similarly, advances in wind energy system design make wind turbines more readily usable for powering RO systems reliably and cost effectively than they could do so in the past. The paper discusses these advances in the context of desalination, and suggestions are made for future development which could further enhance wind energys potential for use in desalination.

ELECTRICAL MECHANICAL OPTIONS FOR VARIABLE SPEED WIND TURBINES

The use of variable speed wind turbines, especially in large-scale utility electricity generating systems, offers a potential improvement in the cost effectiveness of wind energy systems. This paper presents a review of the potential options (including mechanical, electrical/mechanical, electrical, and electrical/power electronic) open for variable speed wind turbine design and gives some of the advantages and disadvantages of these design options. As summarized, a major design problem is to build a system that will allow the rotor to turn at a variable speed, while the machine is feeding power of constant frequency to the load. Although many approaches have been suggested for variable speed operation, they can be grouped into two main classes: (i) discretely variable, and (ii) continuously variable. It is concluded that, based on the current state-of-the-art, the systems with the most promise appear to be those incorporating power electronics.

A review of materials degradation in utility scale wind turbines

Abstract This paper presents a comprehensive review of the state of knowledge of materials used in the major wind turbine components of both land based and offshore wind turbines. The paper is divided into the following seven major sections: utility scale wind turbine design overview; current state of wind turbine technology; review of degradation of materials used in wind turbines; a summary of materials degradation service experience; condition monitoring overview; review of materials based research and development for wind turbines; a summary of missing knowledge and future materials challenges. The review points out that the most important degradation mechanism is fatigue which limits the life, reliability and performance of current wind turbines. As even larger machines are built in the future, with pressures to cut weight and cost, continued materials research and development, as summarised in this paper, is warranted. This critical assessment and review of materials based degradation should be of interest to a wide range of technical energy specialists including those from manufacturers, research and development centres, end users (i.e. electric power generation companies) and financiers and insurers.