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Marine & Hydrokinetic Technology Readiness Initiative
TIDAL ENERGY SYSTEM FOR ON-SHORE POWER GENERATION
A. Executive Summary
Addressing the urgent need to develop LCOE competitive renewable energy solutions for
US energy security and to replace fossil-fuel generation with the associated benefits to
environment impacts including a reduction in C02 emissions, this Project focused on the
advantages of using hydraulic energy transfer (HET) in large-scale Marine Hydrokinetic
(MHK) systems for harvesting off-shore tidal energy in US waters. A recent DOE resource
assessment, identifies water power resources have a potential to meet 15% of the US
electric supply by 2030, with MHK technologies being a major component. [1]
The work covered a TRL-4 laboratory proof-in-concept demonstration plus modeling of a
15MW full scale system based on an approach patented by NASA-JPL, in which
submerged high-ratio gearboxes and electrical generators in conventional MHK turbine
systems are replaced by a submerged hydraulic radial pump coupled to on-shore
hydraulic motors driving a generator. The advantages are; first, the mean-time-between-
failure (MTBF), or maintenance, can be extended from approximately 1 to 5 years and
second, the range of tidal flow speeds which can be efficiently harvested can be extended
beyond that of a conventional submerged generator. The approach uses scalable,
commercial-off-the-shelf (COTS) components, facilitating scale-up and commercialization.
All the objectives of the Project have been successfully met
1) A TRL4 system was designed, constructed and tested. It simulates a tidal energy
turbine, with a 2-m diameter blade in up to a 2.9 m/sec flow. The system consists of a
drive motor assembly providing appropriate torque and RPM, attached to a radial
piston pump. The pump circulates pressurized, environmentally-friendly, HEES
hydraulic fluid in a closed loop to an axial piston motor which drives an electrical
generator, with a resistive load. The performance of the components, subsystems and
system were evaluated during simulated tidal cycles. The pump is contained in a tank
for immersion testing. The COTS pump and motor were selected to scale to MW size
and were oversized for the TRL-4 demonstration, operating at only 1-6% of rated
values. Nevertheless, in for 2-18 kW drive power, in agreement with manufacturer
performance data, we measured efficiencies of 85-90% and 75-80% for the pump and
motor, respectively. These efficiencies being 95-96% at higher operating powers.
2) Two follow-on paths were identified. In both cases conventional turbine systems can
be modified by replacing the existing gear box and generator with a hydraulic pump
and on-shore components. On the conventional path, a TRL5/6 15kW turbine system
can be engineered and tested on a barge at Project partner TEDEC, facilities in
Maine. Alternatively, on an accelerated path, a TRL-8 100kW system can be
Sunlight Photonics Inc. 1 DE-EE0003636
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Bruce, Allan J. Tidal Energy System for On-Shore Power Generation, report, June 26, 2012; United States. (https://digital.library.unt.edu/ark:/67531/metadc828949/m1/3/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.