P.I.: c/o Luis A. Vega, Ph.D.
Latest Information from OES AnnexIV of the International Energy Agency (IEA) on the effects of marine renewable energy devices on the marine environment was published February 2016 ( Executive-Summary_Effects of marine renewable energy devices in the marine environment ).
Previously, HINMREC tried working in coordination with federal regulatory agencies (FERC, BOEM, and NOAA) to define differences between ocean energy systems and already established regulated industrial activities. HINMREC concluded that: (i) Discharge of deep seawater below the photic zone is the OTEC differentiator; and, (ii) The effect of arrays/farms over large coastal regions (spacing and quantity) the WEC differentiator.
The OTEC environmental baseline database, for a potential site off Kahe Point in Oahu, has been documented and is available upon request ( Environmental Assessment of OTEC in Hawaii.) Key oceanographic parameters to be considered in assessing the OTEC environmental impact have been identified and can be grouped as follows:
Nutrients and Biological
– Chlorophyll a
– Dissolved Oxygen
– Dissolved inorganic carbon
The primary indicators of impact during plant operations are: Chlorophyll a; CDT Data; and, pH. These should be monitored at the discharged plume Neutral-Buoyancy-Depth as well as the Far-Field and compared to baseline conditions.
Generalities: Wave Energy Devices Among the various possible impacts to be considered for each specific device are: electromagnetic effects on sharks, acoustic effects on whales, bird-strikes, entanglement, benthic effects of anchors, and aggregation of animals. Objects placed in the ocean often become powerful fish aggregators. The depths proposed for wave energy conversion (WEC) devices are less than 80m. In Hawai’i, these water depths are not major habitats for the commercial pelagic fishes such as tunas. There is a network of Fish Aggregation Devices (FADs) in Hawaiian waters than are installed for the purpose of aggregating tunas and other commercial species, and these FADS are in waters much deeper than 100m (http://www.hawaii.edu/HIMB/FADS/). The WECs under consideration may aggregate small schooling fishes such as opelu. The opelu is one of the main bait fishes used in fisheries for larger species such as tunas. Therefore, fishermen may be attracted to these shallow water facilities to catch bait.
Generalities: OTEC Operations Deep seawater used in OTEC operation contains elevated levels of dissolved inorganic nutrients, primarily phosphate, nitrate and silicate, which could be expected to promote blooms of photosynthetic organisms if and only if the seawater is discharged and contained within the upper ocean or in coastal waters. However, the density of the deep seawater is higher than that of surface waters, and thus deep seawater discharged above the thermocline would sink, mitigating this effect. Deep seawater also contains elevated levels of dissolved carbon dioxide, which would lead to the release of carbon dioxide to the atmosphere if and only if discharged water was allowed to come in contact with the atmosphere.
Two additional points are worth noting: (i) discharges of deep seawater within the photic zone of the ocean, but below the surface mixed layer, should result in photosynthetic production that would remove both the dissolved nutrients and the dissolved carbon dioxide at approximately the same stoichiometric ratio as they are elevated in deep seawater; thus, the only large-scale environmental impact would involve the fate of the resulting photosynthetically produced organic matter; and, (ii) the reduction in pressure of deep seawater as it is brought to the surface will lead to an increase in its pH, offering some relief to the acidification of seawater due to global increases in atmospheric carbon dioxide.
Modeling work by Makai Ocean Engineering: A report describing the modeling work by Makai Ocean Engineering, Inc. to simulate the biochemical effects of the nutrient-enhanced seawater plumes that are discharged by one or several 100 MW OTEC plants is available at: http://www.osti.gov/scitech/servlets/purl/1055480
The modeling is needed to properly design OTEC plants that can operate sustainably with acceptably low biological impact. The report shows that the biochemical response of OTEC discharges can be modeled, quantified, and dynamically visualized for OTEC plants having different discharge configurations. In all cases modeled (discharge at 70 meters depth or more), no perturbation occurs in the upper 40 meters of the ocean’s surface. The picoplankton response in the 110 – 70 meter depth layer is approximately a 10-25% increase, which is well within naturally occurring variability. The nanoplankton response is negligible. The enhanced productivity of diatoms (microplankton) is small, but this additional “standing stock” may potentially enhance growth if the plume water subsequently advects into nearshore water.
The model does not attempt to calculate the higher order trophic levels where fauna consume the phytoplankton, but these results could be readily extended to this purpose. The subtle phytoplankton increase in their baseline design suggests that higher-order effects will be very small.
In Hawai’i, OTEC electricity generators, fueled with near shore ocean thermal resources, can supply all electricity consumed throughout the year and at all times of the day. With the development of electric vehicles, OTEC could also supply all electricity required to support land transportation. All domestic water needs can also be satisfied with desalinated water produced with OTEC systems. This renewable ocean resource is vast enough to met additional electricity demand equivalent to several times present consumption (e.g., see Ocean Thermal Resource offshore Hawaiian Islands). Further information is given in the OTEC Thermal Resource and the OTEC References pages.
In an annual basis, wave energy conversion (WEC) devices could generate more than 30% of the electricity presently consumed in the State (e.g., see Wave Resource Report October 11 2010 with an updated version using thirty-four (34) years long wind records as input to the wave numerical models Hawaii Wave Energy Resources from 34 Year Hindcast .
P.I.: Assoc. Prof. Gerard Nihous, Department of Ocean and Resources Engineering
Objective: (i) Document the ocean thermal resource; and (ii) Analyze potential OTEC worldwide sustainable energy production.
One might ask: is OTEC renewable energy? The simple answer is that as long as the sun shines and, if and only if, deep-ocean cold water is provided by the thermohaline circulation the ocean thermal resource is renewable. A pertinent question, however, is: what is the worldwide power resource that could be extracted with OTEC plants without affecting the thermohaline ocean circulation? Our estimate is that the maximum steady-state OTEC electrical power is about 14 TW (Terawatts) corresponding to 250,000 plants of the kind described in the “OTEC Power Production” link below. These would be deployed throughout the OTEC region in the exclusive economic zone (EEZ) of ninety-eight nations. This power rating corresponds to 77% of the current worldwide annual energy consumption (Global OTEC Resources_2013).
Please use Google Chrome or Safari to view the links given below because Internet Explorer does not provide the display we intended.
Ocean Thermal Resource.- The temperature difference between 20 m and 1000 m water depths gives a good indication of available OTEC resources across tropical oceans. For example, values less than 18°C may not be economically viable for OTEC power generation. The NOAA National Ocean Data Center’s World Ocean Atlas (WOA) database (2005 version) was used to construct the link given below which shows the annual and monthly averages of the temperature difference (between 20 m and 1000 m depths) across the world oceans on a quarter-degree horizontal grid. The link TemperatureDifferentialWOA2005 provides the user with a color coded world map of the annual average temperature difference. The user can choose any region of interest defined by specific latitude and longitude ranges to view color-coded data of the annual average temperature difference as a function of latitude and longitude. Further, clicking on any location gives a plot of monthly averages of the temperature difference there.
OTEC Power Production.- An estimate of OTEC power production capabilities can be made with the temperature difference data available from the WOA database. The link PowerMaps gives annual and monthly averages of the power that would be produced by a single generic OTEC plant rated at 100 MW in standard conditions (seawater temperature difference of 20°C between 20 m and 1000 m depths, and seawater temperature of 300 K at 20 m depth). The standard conditions, along with other realistic assumptions are found in: OTEC Summary Aug 2012. The display is limited to a latitude band between 30°S and 30°N. The link provides the user with a color-coded distribution of OTEC power production from the generic 100 MW plant, in GWh per year. The user can choose any region of interest between 30°S and 30°N to view detailed values of annual average power. Further, clicking on any location provides the user with a plot of the monthly averages of net power there, in GWh per month.
P.I.: Prof. Lloyd Hihara, Department of Mechanical Engineering
Objectives: Investigate corrosion of Aluminum Alloys in the splash-spray zone, surface waters, and deep ocean water. Examine novel corrosion-resistant ceramic-polymer hybrid coating developed in the Hawai’i Corrosion Laboratory (HCL) of the University of Hawai’i.
Presently: The viability of ocean power generating technologies will be affected by their ability to resist corrosion in the harsh marine environment. It has been shown that aluminum can be used in the manufacturing of Heat Exchangers (HXs) for closed cycle OTEC systems and that properly chosen alloys could achieve a life expectancy of 30-years.
Project: Building upon seminal work performed by researchers of the Argonne National Laboratory in the 1980’s (Acceptability of Aluminum Alloys for OTEC Heat Exchangers) corrosion studies of Aluminum Alloys were undertaken at the HCL. Standard sample coupons with and without coatings were prepared and tested. The exposed samples were analyzed in the laboratory to determine corrosion mechanisms. Novel corrosion-resistant ceramic-polymer hybrid coatings developed in the HCL were studied (Corrosion of Aluminum Alloys in Seawater _ Progress Report). Work at HCL was discontinued due to NEPA Compliance requirements and information was incorporated into ongoing work by Makai Ocean Engineering at the OTEC Test Site. The latest progress report is: OTEC Heat Exchanger Project_Aluminum Corrosion
P.I.: Assoc. Prof. Guangyi Wang, Department of Oceanography
Biocorrosion and Biofouling of Aluminum Alloys using molecular methods to identify the composition of fouling communities.
Presently: Marine installations are vulnerable to biocorrosion which is a serious problem for power generation facilities and the offshore oil and gas industry. Biocorrosion occurs when complex microbial consortia interact with metallic surfaces through the establishment of multispecies biofilms. Biofilms mediate interactions between metal surfaces and the liquid environment, leading to major modifications of the metal-solution interface by drastically changing the types and concentrations of ions, pH, and oxygen levels. The mechanism of biocorrosion is complex and insufficiently understood. While application of biocides and surfactants has been successful in mitigating biocorrosion these effects are generally temporary and may not be acceptable for use in sensitive marine
Project: Biocorrosion of sample coupons was explored using molecular methods to identify the composition of fouling communities. Innovative marine coatings, containing natural compounds extracted from algae and sponges and conductive polymers, were tested in the laboratory to determine if they are effective in providing protection from biocorrosion to ferrous and non-ferrous metals. A progress report is available (Biofouling and Biocorrosion _ Progress Report). Work was discontinued due to NEPA Compliance requirements and information was incorporated into ongoing work by Makai Ocean Engineering at the OTEC Test Site. The latest progress report from the ongoing Aluminum corrosion experiment is OTEC Heat Exchanger Project_Aluminum Corrosion
P.I.: Assoc. Prof. Michelle Teng, Department of Civil and Environmental Engineering
Objectives: (i) refinement of numerical simulation packages to predict dynamic loads on floating and submerged structures and assess the performance of single wave power devices and interacting arrays of these devices; and, (ii) scale tests in an UH wave tank of generic prototype devices.
Presently: Some wave-structure-interaction computer models are available. There are two Wave-Tanks available to test scale models of Wave-Power devices at the Department of Civil and Environmental Engineering: (i) 15.2 m (l) x 1.2 m (w) x 0.9 m (d) wave tank/wave generator equipped with a towing carriage; (ii) a longer 1.8 m deep wave flume and towing carriage is under construction.
Project: (i) Experiments were conducted under different wave conditions to examine single devices ( UH Wave Tank Experiments and MS Thesis R. Hager). However, due to the relatively small size of the UH wave tanks it was determined that testing of scale versions of prototype devices should be conducted at larger facilities like those found at Oregon State University and the US Naval Academy.
P.I.: Prof. Yi-Leng Chen, Department of Meteorology
Objective(s): To provide high-resolution wind data from advanced weather models as the input for the wave modeling and forecasting system developed by Prof. Kwok Fai Cheung. The goal of the wind-wave modeling system is to identify time windows and locations around the Hawaiian Islands that are most favorable for the operation of wave power systems through hindcasting and forecasting protocols and methods.
Presently: Prof. Chen has set up a high-resolution weather model wind forecast system using the WRF-ARW model (http://www.soest.hawaii.edu/MET/Faculty/wrf/arw/) which includes a 6-km resolution domain covering the entire State of Hawai’i; 1.5-km resolution domains for Oahu and Kauai; 3-km resolution domain for the island of Hawai’i (Big Island); and, a 2-km resolution domain covering both Maui and Oahu counties. Prof. Chen has also set up the WRF-ARW model for hindcasting and for the development of a Wave Atlas.
Project: Improve the accuracy of high resolution ocean surface winds simulations over the Hawaiian Islands for the purpose of improved forecasting. Generate long-term ocean surface wind data over the Hawaiian Islands through hindcasting. The long-term ocean surface wind data generated from these models will be used by Prof. Cheung (see Wave Forecasting project) for the development of a Wave Atlas of the Hawaiian Islands.
This project was completed and incorporated into the 34-year wave hindcast report and database (Hawaii Wave Energy Resources from 34 Year Hindcast).
P.I.: Prof. Kwok-Fai Cheung, Department of Ocean and Resources Engineering
Objective(s): Identify time windows and locations around the Hawaiian Islands that are most favorable for the operation of wave power systems through hindcasting and forecasting protocols and methods.
Presently: 7.5-day wave forecasts for the Hawaiian Islands at 6-km resolution and the individual islands at 600-m resolution using a suite of numerical models compiled by the Department of Ocean and Resources Engineering (ORE). http://oceanforecast.org
Project: Improve accuracy of the wave forecast using high-resolution wind data and develop a Wave Atlas of the Hawaiian Islands. Improved wave forecasting accuracy will aid the deployment and operation of test devices, while the Wave Atlas will offer detailed information about the wave energy resource for this and other applications. A report documenting the 34-Year wave hindcast has been completed: Hawaii Wave Energy Resources from 34 Year Hindcast