A Hydrogen Storage System for Efficient Ocean Energy Harvesting by Hydrokinetic Turbines

The paper presents result from an NSF funded project on the design and development of control systems for ocean power plants involving moored hydrokinetic turbines. The envisioned hydrokinetic turbines are flying tethered and submerged in ocean currents. Effective energy harvesting requires active control of heading, attitude, and other operational parameters of the turbine(s).Underwater or tidal turbines are nowadays a cutting-edge technology in terms of energy harvesting. Kinetic energy of moving water masses is been transformed in electricity following basic principles of power generation. A novel approach towards a more efficient energy management, dictates the usage of electrolyzing units in order to store hydrogen and oxygen rather than the direct supply of cable connected loads. The electrolysis products when present in the correct amounts can serve external users and at the same time activate fuel cells in order to sustain autonomous operations of the power architecture. This paper presents a model and simulation of a hybrid system coupling the tidal turbines, a regenerative fuel cell and an electrolyzer. A simple electrolysis model, utilizing the power generated by the turbines and capable of providing the input parameters to the fuel cell system is been developed in this regard. Main objective of the fuel cell is to provide enough energy to the architecture to guarantee autonomous operations. A model devoted to the fuel cell operation is been implemented. The model is capable to capture both the steady state and dynamic behavior of the cell. Dynamic behaviors are of particular interest since loads can exhibit significant variations, reflected then in large fluctuations of the cell output, thus in fuel consumption. The two systems are then interconnected by means of a controller. The abundance of fuel in the storage tanks must be managed in such way that is always available to the user and the power system. Larger demand on the turbines side will activate generation on the fuel cell side, thus hydrogen and oxygen consumption. On the other hand small demand will result in a higher fuel stock inside the tanks. Thus the energy flow is regulated to guarantee optimal fuel reserve inside the tanks at all times by means of availability to the user and the system itself. The simulation results show the viability of the power architecture in terms of requirements. The output of the cell can be adapted to the demand taking into account at all times the availability of the electrolysis products.