Renewable Energy Device Efficiency, Maintenance and Power Output

Improving Efficiency, Maintenance and Power Output

The NC Renewable Ocean Energy Program is currently researching and testing ways to improve the current state renewable energy device technology.  The development of new technologies and methods that increase device efficiency, maintenance and power output is critical for the long term application of renewable energy for the state of North Carolina and beyond.  In an effort to improve these key components, the NC Renewable Ocean Energy program is currently focusing on two main areas, ocean compressed air energy storage systems and magnetic gearing technology.

Ocean Compressed Air Energy Storage

OCAES Storage Vessel

A subsea storage vessel.

Due to the somewhat unpredictable nature of renewable ocean energy sources (waves, currents, wind, etc.), the ability to store energy for use during peak demand times is critical for the long-term application of renewable power sources.  The Ocean Compressed Air Energy Storage (OCAES) research is focused on evaluating a new form of bulk energy storage.  North Carolina has approximately 300 miles of coastline with the opportunity for electric power generation from energy imparted by wind, waves, and gulf stream currents. Regardless of the mode of energy production, the storage of the generated power is one of the most challenging aspects in order to affect a dependable and economically viable feed to the power grid or in some non-grid discreet applications, such as remote locations, the user. These renewable sources of energy are, to varying degrees, intermittent in nature and are dependent on seasonal and climate factors. On the other hand, the demand of electricity is not balanced throughout the day and power grids regulate the amount of power being supplied at all times. Therefore the need for energy storage is critical key component for the success of the power generation from ocean energy.

OCAES_system

A centralized OCAES system could be used with a variety of renewable energy technologies.

Ocean Compressed Air Energy Storage  is an innovative concept that is based on converting the electrical energy generated from ocean energy devices into compressed air stored in an array of containers, located on the ocean floor.  OCAES takes advantage of the pressure gradient from the seafloor to the surface to store the energy potential in the form of compressed gas.  Scientists and engineers at UNC CSI and NCSU are developing OCAES systems that would be able to store large volumes of compressed gas in underwater vaults that are filled during times of renewable power generation. During peak demand times, or times when power is not being generated by renewable sources, the air would be released from the vaults, travel towards the surface and be used in a gas expander with a generator to feed electricity to the grid.  Because of the technology independent nature of Ocean Compressed Air Energy Storage systems, different renewable energy devices (wind, wave, current) could utilize centrally located OCAES systems for energy storage and distribution to the grid.

Magnetic Gearing Systems

Magnetic gear cross section

Cross section of a magnetic gear.

To generate electricity, the relatively low rotational speed of renewable energy sources has to be converted to the high rotational speed needed for power generation. Typically a mechanical, hydraulic or pneumatic gear system is used to increase the speed before being coupled to a traditional electromagnetic rotary generator.  The use of physical gears presents challenges in power loss, maintenance and overall life span in marine environments.  The magnetic gear research is focused on demonstrating a revolutionary new means of efficiently and reliably converting wave and ocean current energy into electricity. Magnetic gears replace mechanical gears as a means to increase or decrease rotational speed of a machine, such as an underwater turbine or a wave energy generator. In order for ocean power generation to be competitive with incumbent technologies the power conversion system must be low-cost while at the same time exceptionally reliable, efficient, robust and environmentally benign.

Scientists and engineers from UNC CSI and UNC Charlotte have been researching and developing magnetic power takeoff systems that use powerful magnets and their intrinsic attractive and repulsive forces to convert the low rotational speed of renewable sources to the high rotational speed needed for power generation.  The systems designed and constructed have near frictionless start up, with very low power loss and the same torque and power output of traditional systems.  In addition, their reliability is increased considerably and the maintenance required is reduced over the life of the device.

Magnetic Gearing Video