Final Report: Harnessing Ocean Wave Energy to Generate ElectricityEPA Grant Number: SU833157
Title: Harnessing Ocean Wave Energy to Generate Electricity
Investigators: Blumberg, Alan , Raftery, Michael , Reid, Marshall , Sednov, Nikolay , Stolkin, Rustam , Tsionskiy, Mikhail , Wainer, Tamara
Institution: Stevens Institute of Technology
EPA Project Officer: Nolt-Helms, Cynthia
Project Period: September 30, 2006 through August 31, 2007
Project Amount: $10,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2006) RFA Text | Recipients Lists
Research Category: Nanotechnology , P3 Challenge Area - Energy , Pollution Prevention/Sustainable Development , P3 Awards , Sustainability
Our research is focused on the development of a device to harness ocean surface waves to generate electricity. The wave energy harnessing device (WEHD) consists of an electricity generating dynamo anchored to the sea floor, driven by a rotating cablereel connected to a surface buoy. As waves move the buoy up and down, the cable extends and retracts, rotating the reel and thus the input shaft to the dynamo (figure 1).
Our phase one objective is to provide a proofofconcept, scale model device which can achieve 50W rms power output in tests with 10in, waves with period 3.5 seconds or less, in a laboratory wave tank. Using dimensionless scaling, we estimate that a full size prototype, 8 times larger than a 50W scale model, will equate to over 72kW rms power output per unit in ocean wave heights of 80 inches (6.7 feet or 2 meters).
Figure1. Fundamental concept of a buoy/cablereel wave energy harnessing system
Phase I has developed a scale model WEHD device and a comprehensive instrumentation test bed for wave energy research in wave tanks. Figures 2 and 3 show the mechanical components of the WEHD. In these figures, energy is transferred from left to right. As a wave passes over the device, the buoy rises and pulls up on the cable (figure 4), thus rotating the reel and drive shaft. The drive shaft engages the 1st clutch turning the input shaft to the gearbox. The gearbox amplifies drive shaft speed, to turn the 2nd clutch 25 times faster than the 1st clutch. The 2nd clutch turns the shaft for the flywheels. The flywheel shaft is connected to the alternator, so the alternator turns with the flywheels, generating electricity. As the buoy passes over the wave crest and begins to descend, the spring reel rewinds the cable and the drive shaft free spins in the 1st clutch, disengaging from the gearbox. While the cable is rewinding, the 2nd clutch also decouples the flywheel shaft from the gearbox, allowing the energy stored in the flywheels (during the buoy’s up stroke) to carry on turning the alternator during the buoy’s down stroke.
Figure 2. Scale Model Wave Energy Harnessing Device (WEHD)
Figure 3. WEHD with watertight pressure housing prepared for wave tank testing.
Figure 4. The buoy pulls on the cable which turns the reel and input shaft.
In addition to a prototype WEHD device, an instrumentation testbed apparatus has been developed, consisting of a comprehensive range of sensors interfaced to a PC and software for automated data logging (figure 5). This instrumentation enables automatic recording, throughout wave tank experiments, of wave motion, buoy motion, drive shaft speed, flywheel/alternator shaft speed as well as the electrical current, voltage and power output by the device. All sensors are input to specially designed software, which automatically stores and timestamps the data as well as plotting data as a series of graphs. This comprehensive instrumentation testbed enables a large number of experiments to be attempted to discover optimal values of key parameters such as gear ratio, flywheel inertia, electrical load and buoy geometry, over a range of input wave conditions (heights and periods).
Initial tests have already yielded invaluable information and lessons and have also served to demonstrate the successful design and functionality of the instrumentation and data logging test bed. The planned series of wave tank experiments has been somewhat hampered by delays during the extensive rebuilding and renovation of the SIT wave tank over the past 21 months. Despite these setbacks, Raftery has already managed some preliminary tank testing and will be able to complete a comprehensive series of tank tests and modifications of his design over the final two months of the Phase I funding cycle (April and May 2007). Some important lessons learned from initial tank tests include:
- Buoy motion during the test was different from the orbital wave motion expected. Rather than moving up and down with the wave peak, the buoy switched rapidly between positions in wave troughs to either side of the wave peak, see figure 6. This sidetoside motion reduces power generation.
- Buoy geometry may be to blame for this inefficient buoy motion. The initial buoy design was a wide, flat sheet (figure 7). More efficient buoy motion may result from redesigning the buoy to be tall and thin.
- Gearbox design may also be to blame for the unusual buoy motion and lower than expected power output. The WEHD was designed for tests with 10in waves. Unfortunately, following rebuilding, our wave tank can only manage 8in waves. Our high gear ratio and gearbox friction are too much for these small waves to drive properly. The next tests will be performed with more efficient, lower ratio gearing.
Figure 5. Electrical system showing the alternator’s resistive load and the data acquisition electronics.
Figure 6. Unexpected side-to-side buoy oscillation.
Figure 7. Initial buoy design. Too wide and flat?
This project has inspired and brought together a highly interdisciplinary team of individuals with a broad range of expertise and interests. Prototype WEHD machinery has been designed, constructed and deployed in preliminary wave tank tests. Additionally, a comprehensive instrumentation and datalogging system has been developed which can automatically monitor and record the performance of the WEHD during wave tank testing. In parallel with the engineering innovation team, the technology management team is investigating business development models and forging industrial partnerships in order to develop a full scale prototype and bring the device to market.
The buoy/cable/reel WEHD design is highly innovative. Raftery has successfully presented his concept to the SIT patent committee, who filed a provisional patent with USPTO in March 2007. Substantial partnerships have been initiated with several industrial and academic partners, for the scale up efforts towards an industrial size device.
Critical barriers and impediments to our success have been the inability to produce the expected 10 inch waves in the Stevens wave tank following its reconstruction, also limited access to the wave tank facility due to delayed renovation works, and thus insufficient time to modify the design and test the modifications before the due date of this report. Preliminary tank tests have now been undertaken and a comprehensive series of test and modification iterations will be undertaken during the remaining two months (April and May 2007) during which we are optimistic of reaching or (hopefully) exceeding the original 50Watt objective for this prototype device. We also hope to test in the Texas A&M wave tanks which are capable of generating much larger waves.
Harnessing wave energy can substantially reduce humanities emissions and harmful environmental impact. Wave energy is the only clean renewable that can reliably, realistically, and economically replace all current fuel sources used by the people of this planet. Our research balances many elements of people, prosperity, and the planet. Our WEHD will not require use of additional land resources to provide an emissions free energy source. All people will prosper from wave energy because it is globally available in sufficient quantity to power all human energy consumption for the foreseeable future. The project can reduce environmental impact beginning with the first commercial production model and grow toward a global shift in human energy use.
Proposed Phase II Objectives and Strategies:
The objective of Phase II research is to learn lessons about optimal design using the Phase I apparatus, and then apply these lessons to developing a larger and more sophisticated WEHD device which can be deployed in a real, open water marine environment for an extended period of time. Phase II will transition from shortterm (minutes) laboratory testing to longterm (weeks) field testing.
Specifically, Phase II will install a prototype WEHD in open water, tethered to a data buoy that will continuously collect a variety of sensory data from the device, throughout its deployment, and transmit this data wirelessly back to a computerized data log in the laboratory (figure 8).
Scaleup of the Phase I device to Phase II will pose a considerable engineering challenge. More tests using Phase I apparatus must be performed to learn more about key design parameters. A new, robust housing and seals must be developed to withstand the greater depths and harsher conditions of the open water marine environment. A marine anchoring system must be developed with actuator and control systems such that the device’s depth can be varied and so that the buoy can be reeled in and submerged as desired. Intelligent feedback control mechanisms will also be explored for variable speed transmission control and automatic electrical load varying – different gear ratios and resistive loads are desirable for different speeds of buoy motion and sea states. New instrumentation must be developed, with additional sensors to monitor the device’s performance and also to detect problems (e.g. seal failure and flooding) and this instrumentation must be interfaced via wireless communications systems on data buoys to long term, automated datalogging computers. Importantly, all of this prototype machinery must be designed so that it can be quickly and conveniently varied and adapted. Many permutations of key design parameters must be tested (e.g. gear ratios, depths, inertias, loads) and these design parameters must be gradually adapted and optimized as lessons are learned during testing.
Figure 8. Phase II WEHD open water deployment setup.
Important, additional objectives of Phase II are to learn enough to finalize the key technological ingredients which will comprise a largescale commercial product; use this knowledge to define and pursue full patent applications; research appropriate business development models; negotiate partnerships with industry to manufacture a working product.
The Phase II project will also feature expanded educational impact. As well as enabling graduate level studies in both Ocean Engineering and Technology Management, Phase II will involve a number of undergraduate projects. The team will also create classroom activities based around wave energy engineering which will be contributed to SIT’s substantial outreach efforts, introducing engineering material to the middle and high school science curriculum.