Alex Yokochi

Optimal Energy Storage Sizing and Control for Wind Power Applications

The variable output of a large wind farm presents many integration challenges, especially at high levels of penetration. The uncertainty in the output of a large wind plant can be covered by using fast-acting dispatchable sources, such as natural gas turbines or hydro generators. However, using dispatchable sources on short notice to smooth the variability of wind power can increase the cost of large-scale wind power integration. To remedy this, the inclusion of large-scale energy storage at the wind farm output can be used to improve the predictability of wind power and reduce the need for load following and regulation hydro or fossil-fuel reserve generation. This paper presents sizing and control methodologies for a zinc-bromine flow battery-based energy storage system. The results show that the power flow control strategy does have a significant impact on proper sizing of the rated power and energy of the system. In particular, artificial neural network control strategies resulted in significantly lower cost energy storage systems than simplified controllers. The results show that through more effective control and coordination of energy storage systems, the predictability of wind plant outputs can be increased and the cost of integration associated with reserve requirements can be decreased.

Comparison of Direct-Drive Power Takeoff Systems for Ocean Wave Energy Applications

This paper presents a comprehensive power takeoff (PTO) analysis program conducted as a collaborative research effort between Columbia Power Technologies, Inc., Oregon State University (OSU), and the U.S. Navy. Eighteen different direct-drive technologies were evaluated analytically and down-selected to five promising designs. Each of the five prototypes was simulated, modeled in SolidWorks, and built at the 200-W peak level and tested on OSUs wave energy linear test bed. The simulations were validated with the 200-W experimental results and then scaled up to 100 kW, with full 100-kW designs including costs, maintenance, operations, etc., to estimate the cost of energy (COE) for each PTO buoy system at utility scale.

X‐ray diffractometric study of microcrystallite size of naturally colored cottons

Cellulose crystallite sizes of naturally green and brown cottons as well as of white undyed and dyed cotton were studied by using X-ray diffractometry. Data were analyzed both by a peak stripping method using the program WinFit and by whole profile matching using the FullProf program. The fit obtained with WinFit agreed with the results from the FullProf except for a small difference centered on the 002 reflection. Crystallite sizes of white and colored cottons were estimated by the full-width-at- half-minimum (FWHM) method, and the results showed that compared to the white cotton, the crystallite sizes of green and brown cottons based on the 101 and 002 reflections were found to be comparable, whereas smaller 101¯ crystallite sizes were observed. After dyeing, the crystallite size of dyed brown cotton displayed a slight increase in the 002 crystallite size compared to that of the undyed white cottons. The average crystallite size of 101, 101¯, and 002 for each cotton determined by the WinFit program was comparable to that estimated by the FullProf program.

Supercapacitor energy storage for wind energy integration

The fast growth of wind energy utilization has necessitated research on wind energy integration. Due to the variable nature of wind and the forecasting challenges, it is desirable to utilize wind energy alongside energy storage sources for reliable wind energy integration. This paper details the design of a supercapacitor storage system that is integrated into an in-lab grid that was developed to research methods aimed at optimizing energy production while increasing the predictability of wind farm outputs. The in-lab grid features the emulation of several high-power grid sources and loads including a wind farm, energy storage systems and hydro resources. Results include the storage system simulations generated from a variety of AGC algorithms run on a dSPACE rapid prototyping machine. In addition, this paper presents a model for a supercapacitor developed to be used in characterization and lifetime tests. These tests are useful in predicting performance of the system for purposes of ensuring its efficient and safe use. Results validating the model and estimating the expected performance of the system are presented.

Advancing the Wave Energy Industry

An extremely abundant and promising source of energy exists in the worlds oceans. Ocean energy exists in the forms of wave, tidal, marine currents, thermal (temperature gradient), and salinity. Among these forms, opportunities and benefits have been identified in the area of ocean wave energy extraction, i.e., using wave energy converters (WECs) to harness the motion of waves and converting that motion into electrical energy. Ocean wave power exhibits several advantageous characteristics including high power density, low variability, and excellent forecastability. The United States is estimated to have 260 TWh of potential wave energy off its coasts, which is approximately 6% of its annual electrical load (comparable to the current traditional hydro power contribution). Ocean waves have well-defined geographical attributes, where the wave power tends to be stronger on the western coasts of land masses and also stronger moving north and south away from the equator. This is due to the global wind cells, primarily the Westerlies, which tend to cause eastwardly moving waves.

Numerical and Experimental Modeling of Direct-Drive Wave Energy Extraction Devices

The solutions to today’s energy challenges need to be explored through alternative, renewable and clean energy sources to enable a diverse national energy resource plan. An extremely abundant and promising source of energy exists in the world’s oceans in the forms of wave, tidal, marine current, thermal (temperature gradient) and salinity. Among these forms, significant opportunities and benefits have been identified in the area of wave energy extraction. Waves have several advantages over other forms of renewable energy such as wind and solar, in that the waves are more available (seasonal, but more constant) and more predictable, thus enabling more straightforward and reliable integration into the electric utility grid. Wave energy also offers higher energy densities, enabling devices to extract more power from a smaller volume at consequent lower costs. However, many engineering challenges need to be overcome to ensure wave energy device survivability, reliability and maintainability, in addition to efficient and high quality power take-off systems. Optimizing wave energy technologies requires a multi-disciplinary team from areas such as Electrical, Chemical, Ocean, Civil and Mechanical Engineering, to enable innovative systems-level research and development. This paper presents some recent research developments on experimental and numerical modeling on direct-drive approaches and the associated devices designed to convert the motion of the ocean waves into electrical energy using point absorber wave energy converters. This research is focused on a simplification of processes, i.e., replacing systems using intermediate hydraulics or pneumatics with direct-drive approaches to allow generators to respond directly to the movement of the ocean by employing magnetic fields for contact-less mechanical energy transmission, and power electronics for efficient electrical energy extraction. The term “direct” drive describes the direct coupling of the buoy’s velocity and force to the generator without the use of hydraulic fluid or air. The wave energy buoy and spar are designed to efficiently capture ocean wave energy and transfer it to the generator. These buoys have been tested at the Oregon State University O.H. Hinsdale Wave Research Laboratory, with planned testing off the coast of Oregon. The paper will examine several direct-drive approaches, including electrical and mechanical design characteristics, describe the numerical modeling of the associated conceptual devices, prototype testing, and some ongoing research on the dynamics of buoy generator systems for design optimization.Copyright

Research and ocean testing solutions to advance the wave energy industry

This paper presents the wave energy research thrusts as well as the development of novel scaled and full-scale ocean testing solutions through the Northwest National Marine Renewable Energy Center (NNMREC) headquartered at Oregon State University (OSU). NNMREC performs fundamental technological, social, and environmental research, in addition to providing unique testing facilities. Testing resources include a wave energy linear test bed, 2D and 3D wave tanks, an Ocean Sentinel instrumentation buoy to facilitate open-ocean testing without a cable-to-shore grid connection, as well as developing cable-to-shore grid emulator and grid-connect facilities. All of NNMRECs marine energy converter testing facilities are being branded as the Pacific Marine Energy Center (PMEC), including the scaled lab testing facilities and intermediate and full-scale open water testing facilities. This paper includes an overview of ongoing NNMREC research and advancing ocean testing solutions as well as the 2012 and 2013 Ocean Sentinel deployments, along with the associated testing of materials and technologies for biofouling resistant surfaces.

Rapid bidirectional power flow of supercapacitor energy storage systems through grid-tied inverters for improved renewables integration

The variable output of renewables presents integration challenges, especially at high levels of penetration. The coordination of multiple energy storage solutions can provide an effective approach to integrate these variable resources. Since supercapacitor energy storage systems (SESS) are designed to meet fast response energy demands, examination of the effect of frequency of power flow reversal on system operation is crucial, as is development of suitable SESS control algorithms. This paper presents experimental and modeling work carried out using a SESS integrated in a research scale lab grid through a high frequency grid-tied inverter. Operation of the SESS at high frequencies shows poor performance, with effective SESS energy rating significantly decreased for power flow reversals faster than 0.3Hz. Two approaches to control power flow from a SESS are developed and tested, with one aimed at power smoothing and the other aimed at limiting ramp rates. Both effectively reduce the time the system spends in a ramp failure, with the ramp rate algorithm most effective at reducing the time spent in a ramp failure state.

Advancing wave energy converter array-to-grid transmission systems

The Northwest National Marine Renewable Energy Center (NNMREC), a US Department of Energy (USDOE) Center headquartered at Oregon State University (OSU), seeks to facilitate the integration of marine renewables onto the utility grid. This paper presents NNMRECs approach to streamlining the research, development and testing process to enable wave energy converter (WEC) array-to-grid transmission systems. The WEC development process tools and facilities are presented, including modeling, scaled laboratory and wave tank testing as well as field testing. The NNMREC ocean testing solutions include scaled non-grid connected facilities as well as developing utility-scale cable-to-shore grid emulator and grid-connect facilities. This paper concludes with the NNMREC cable-to-shore site grid integration configuration along with a high-level array-to-grid transmission system simulation.