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Case Study: Testing Wave Energy
Converters Offshore
CASE STUDY – TESTING WAVE ENERGY CONVERTERS OFFSHORE
Case Study: Testing Wave Energy Converters Offshore
Northwest National Marine Renewable Energy Center – Oregon State University
Company Profile
The Northwest National Marine Renewable Energy Center (NNMREC) is one of three U.S. Department of
Energy-funded centers charged with facilitating the development of marine renewable energy
technology via research, education, and outreach. Established in 2008, NNMREC is a partnership
between Oregon State University (OSU) and the University of Washington (UW). While OSU focuses on
wave energy and offshore wind energy, UW’s emphasis is tidal energy. NNMREC was developed to
facilitate wave and offshore wind energy development by bringing science to bear on the technical,
environmental, and social dimensions of these ocean energy technologies.
Business Situation
Can wave energy meet our needs? Are wave energy conversion devices capable of generating sufficient
energy to be connected to the grid? How can they be tested in the real world so we can quickly
understand their performance and make improvements?
Ocean wave energy is an area of increased interest, with over 100 conceptual wave energy converter
(WEC) designs developed worldwide. Of these only a few have been built as full-scale prototypes and
tested in open ocean.
In order to help Oregon state reach its renewable energy power goals, NNMREC was tasked with
developing a method to test WEC devices to determine their power output, their survivability in harsh
marine conditions, and what type of wave situation would be ideal for the type of wave energy
technology used.
Ocean testing facilities are essential to enable wave energy developers to demonstrate performance and
survivability, and to optimize devices. Currently, the U.S. marine energy industry is challenged by the
lack of proper and standardized infrastructure to deploy and test devices in the marine environment. In
addition, many WEC technologies are ready for field trials, but are not sufficiently mature to be
connected to the electrical grid for commercial power production.
A mobile wave energy test facility could be used by many companies and academic researchers in the
quest to develop wave energy technology, measure and understand the wave resource, and study the
energy output.
Requirements for the primary functions of a mobile wave energy test facility are as follows:
1. Provide stand-alone electrical loading and power conversion for the WEC under test.
2. Measure and record WEC power output.
3. Configurable for different types of WECs.
4. Collect and store data transmitted from a wave measuring buoy moored nearby.
5. Transmit collected data to a shore station via a wireless telemetry system.
6. Conduct environmental monitoring.
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CASE STUDY – TESTING WAVE ENERGY CONVERTERS OFFSHORE
Technical Situation
OSU’s current ocean testing facilities include the Wallace Energy Systems & Renewables Facility (WESRF)
and the O.H. Hinsdale Wave Research Laboratory.
The WESRF is home to the Linear Test Bed – an instrument that creates the relative motion between a
spar and heaving buoy to simulate wave action. Eleven wave energy device prototypes have been tested
on the Linear Test Bed.
The Hinsdale Wave Research Laboratory is a leading center for research and education in coastal
engineering and nearshore science with facilities that include a Large Wave Flume (104m long), Tsunami
Wave Basin with multi-directional wavemaker, and control room for on-site researchers. The Large
Wave Flume is the largest of its kind in North America.
While these facilities provide state-of-the-art simulations, NNMREC required a way for new technologies
to be tested in a real environment – offshore in the ocean.
Solution
To help NNMREC reach their goal of an offshore mobile wave energy testing facility, AXYS partnered
with them to design a new buoy – the Ocean Sentinel Instrumentation buoy.
AXYS engineers worked with NNMREC staff to develop this custom buoy system that interfaces with
numerous custom control and monitoring devices, as well as basic meteorological and oceanographic
parameters. The system also provides real time communications that monitor all aspects of the system
performance. The Ocean Sentinel platform is based on a proven NOMAD (Navy Oceanographic
Meteorological Automatic Device) 6m hull design with 4 large watertight compartments able to
withstand the most severe oceanic weather. The base design allows for a high degree of flexibility and
expansion capacity in system architecture and to allow incorporation of a variety of hybrid power
solutions.
Data from the buoys are collected by AXYS' proprietary onboard WatchMan500™ data acquisition
system and transmitted to a shore station by satellite and cell phone telemetry. In addition, this buoy
also has an Automatic Information System (AIS) transmitter which transmits buoy position and
environmental data to passing ships. Authorized users can access buoy status and environmental data
from their remotely located base station. The AXYS' Data Management System (DMS) permits remote
control and configuration for the entire buoy network, down to the individual sensor.
A TRIAXYS™ directional wave buoy will be deployed separately from the Ocean Sentinel and will provide
precision wave measurements to quantify the wave resources in the test facility local. These wave
measurements are also transmitted to the Ocean Sentinel.
AXYS also designed and provided a custom 3 point mooring and deployment procedures for the Ocean
Sentinel.
WECs under test are moored approximately 125 meters from the instrumentation buoy and connected
by an umbilical cable. Power generated by the WEC is controlled by switchgear and power conversion
equipment located on-board the instrumentation buoy and dissipated in an on-board load bank.
The Ocean Sentinel power conversion and load bank system provides a stand-alone load for the WEC
under test. This system provides generator control for WECs in early stages of development that do not
include onboard generator power conversion. A switchgear enclosure that includes the contactors along
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CASE STUDY – TESTING WAVE ENERGY CONVERTERS OFFSHORE
with an electrical disconnect, current and voltage sensors, and fuses is installed below deck in the
forward compartment of the Ocean Sentinel, together with the power converter. Two 50 kW, air-cooled
load banks are installed above deck. This system is controlled by a National Instruments CompactRIO
based data acquisition system developed by NNMREC, which is also used to record WEC power and
measured wave data.
Because NNMREC anticipates testing WECs with different power outputs and generator configurations,
the Ocean Sentinel loading system has been designed for a high degree of flexibility and is
reconfigurable via terminations in the switchgear enclosure. The air cooled load bank can be
reconnected for different voltage and power levels, and can be controlled by either contactor switching,
converter control, or a combination of the two. WECs with output current to 125 A continuous can be
accommodated, for a power capability of 100 kW at 460 V or 50 kW at 230 V.
The on-board power system developed by AXYS can supply up to 400W of 24 Vdc and 120 Vac power to
the instrumentation and power conversion equipment installed on the Ocean Sentinel, and to the WEC
via the umbilical. Primary power is provided by 40x sealed lead acid batteries (2000 Amp-hours at 24V),
which are maintained through the use of a 1 kW wind generator, 2x 210 W solar panels and a 3.2 kW
standby diesel generator. The system can provide 400 W throughout a 3 month deployment period
without refueling. This power system is controlled and monitored by the WatchMan500 data acquisition
and control system.
Two independent cellular telemetry systems are used between the Ocean Sentinel and shore, one for
the WatchMan500 that controls and monitors the power system, and the other for the CompactRIO
system that provides control and data acquisition for WEC testing.
The Ocean Sentinel provides a standardized, accurate system to compare various wave energy
technologies.
The Ocean Sentinel instrumentation buoy facilitates open-ocean, stand-alone testing of WECs with
average power outputs of up to 100 kW. Deployment is at a NNMREC test site that is approximately 2.5
nautical miles offshore from Yaquina Head, north of Newport, Oregon.
NNMREC will operate the facility which is a one-square-mile site located about two miles northwest of
Yaquina Head Oregon in open Pacific Northwest Waters carefully studied, both for its physical and
biological characteristics.
Deployment
In late July 2012, AXYS technicians and engineers provided NNMREC personnel with the initial dockside
system commissioning and training. The Ocean Sentinel was deployed in August 2012 for the first
testing of a WEC. The Ocean Sentinel and WEC were moored at NNMREC’s open-ocean test site north of
Newport, Oregon for a six week period while the testing was performed. The Ocean Sentinel power
converter was used to control the electrical generator on board the WEC device via the umbilical cable
throughout these tests. This allowed WEC performance to be characterized while operating in several
different control regimes and under a variety of sea conditions. A final paper will detail the deployment,
testing and data analysis process.
Benefits
1. Validate the performance of WEC devices in a real-world testing environment.
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CASE STUDY – TESTING WAVE ENERGY CONVERTERS OFFSHORE
2. Understand how each WEC device performs in varying types of wave environments. Some WEC
devices will operate better in low wave settings while others will have better performance with
a more powerful wave resource. The Ocean Sentinel measures wave amplitude, device energy
output, ocean currents, wind speeds, extremes of wave height and other data.
3. Gain a better understanding of the surrounding environment.
4. The creation of the Pacific Marine Energy Center (PMEC) as an expansion and continuation of
the work started with the Ocean Sentinel. PMEC will be the first utility-scale, grid-connected
wave energy test site in the United States. Subsea cables will transmit energy from the wave
energy devices to the local power grid, and data to scientists and engineers at on-shore
facilities. PMEC will have four “test berths,” open spaces of water dedicated to testing individual
devices or small arrays of devices, each of which will be connected to the community’s electrical
grid. It will also collect data associated with environmental and human dimension impacts. The
development and operation of this facility will provide jobs and other economic development as
it attracts researchers and device developers to the Oregon coast from around the world.
.
References
von Jouanne, A., Brekken, T., Lettenmaier, T., Amon, E., and Phillips, R. “A Novel Ocean Sentinel
Instrumentation Buoy for Wave Energy Testing.” In Power and Energy Society (PES) Conference, 2012.
Amon, E., Brekken, T.K.A., and von Jouanne, A. 2011. A power analysis and data acquisition system for
ocean wave energy device testing. Renewable Energy: An International Journal, vol. 36, pp. 1922-1930.
Leijon, M., Waters, R., Rahm, M., Svennson, O., Bostrom, C., Stromstedt, E., Engstrom, J., Tyrberg, S.,
Savin, A., Gravrakmo, H., Bernhoff, H., Sundberg, J., Isberg, J., Agren, O., Danielsson, O., Eriksson, M.,
Lejerskog, E., Bolund, B., Gustafsson, S., and Thorburn, K. 2009. Catch the wave to electricity. IEEE Power
and Energy Magazine, January/February 2009.
Le-Ngoc, L., Gardiner, A.I., Stuart, R.J., Caughley, A.J., Huckerby, J.A. 2010. Progress in the development
of a multi-mode self-reacting wave energy converter. In: OCEANS 2010 IEEE – Sydney. pp. 1-7. Institute
of Electrical and Electronic Engineers.
Pitt, Edward. Assessment of performance of wave energy conversion systems: marine renewable energy
guides. [London]; Orkney: Dept. of Energy and Climate Change; European Marine Energy Centre, 2009.
Stauth, David. Public wave energy test facility begins operation in Oregon. Oregon State University –
News & Research Communications, 2012. Web. 8 July 2013.
Testing Facilities and Facilities Partners. Oregon State University – Northwest National Marine
Renewable Energy Center, 2013. Web. 8 July 2013.
Batten, Belinda. Newport selected as home of Pacific Marine Energy Center. Oregon State University –
News & Research Communications, 2013. 8 July 2013.
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