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A bidirectional impulse turbine is a self-rectifying air turbine used in an oscillating water column wave energy converters. Most of the study on bidirectional impulse turbines involves steady-state performance analysis; however, the performance under oscillating airflow conditions is necessary to understand its behavior. The objective of this study is to experimentally analyze an optimized and numerically investigated bidirectional impulse turbine with fixed guide vane subjected to oscillating airflow conditions. A bidirectional airflow test facility developed at Indian Institute of Technology Madras, Chennai, India is employed to determine the aerodynamic characterization of the turbine and the dynamics involved in each of the coupling stages. The test rig consists of a piston chamber assembly, which provides different airflow rates by varying the stroke length (SL) and cycle time. Emphasis is made on the pressure and flow rate coefficients of the turbine, turbine-generator coupling, and power developed for different input conditions. The operating range of the turbine is mapped for four different frequencies and three SLs. Different electrical loading and the power output were analyzed for accelerations and decelerations of inflow and outflow. The preliminary dynamic characterization of the turbine with respect to nondimentionalized pressure coefficient and flow coefficient was determined for inflow and outflow. The power output is found to be in strong correlation with the flow rate and angular rotation of the rotor. The turbine analyzed in the experimental test rig will be proceeded with real sea testing on the Indian coast by the National Institute of Ocean Technology, Chennai, India.

In India, the navigational buoy is a standalone system to guide the ship in the navigational channel of the port. Conventional navigational buoy is usually powered by solar energy and the continuous operation of the buoy may be affected during prolonged rainy weather and cloud cover. The indigenously developed wave powered navigational buoy produces electrical power from ocean wave and the same is utilised to electric power up in situ components as marker lamp, oceanographic sensors and its data logger along with a wireless communication system.Based on the results of experimental studies conducted and results obtained during open sea trials, this paper elaborately describes about power take-off system and power assessment of power module which includes sizing of battery, integrated sensor and power circuit, power mangement etc., In this paper elaborated about energy generated during open sea trials in the year 2019 (June-Novemebr). This buoy generated electricity which is self sutatined for power requirement of the buoy.This standalone wave powered navigational buoy is successfully demonstrated for longer periods at all weather conditions in Kamarajar Port limited, chennai. It may be useful product for ports and harbours in India as a stand alonewave power device.

A floating wave power device called backward bent ducted buoy (BBDB) which was developed by National Institute of Ocean Technology works on oscillating water column (OWC) principle. The power module on BBDB consists of a unidirectional impulse (UDI) turbine and a permanent magnet direct current generator (PMDC). It underwent open sea trials several times for studying performance characteristics and improvising the power module from year 2011 to 2015. These trials were carried out off the Chennai coast near the south breakwater of Kamarajar Port Limited (KPL). BBDB was deployed and monitored over several weeks and it generated electric power. During the trials the buoy also withstood the strong winds and large waves during Cyclone Thane in December 2011. Though BBDB produced power, it was felt it needed improvement on wave to wire energy conversion. For any OWC-based wave energy device, it is necessary that the power module provides appropriate damping to oscillating water column in order to achieve efficient wave to wire energy conversion. Damping provided by the turbine depends on the relation between pressure drop across a turbine and volumetric flow rate. For a geometric similar construction, turbines with different diameters provide different levels of damping and it became necessary to study the performance of turbines with different diameters. Thus, two major areas were earmarked for optimization studies, namely, wave to pneumatic energy conversion (energy capture by buoy) and pneumatic to mechanical power conversion (turbine performance). In situ pneumatic performance of BBDB was evaluated using orifices with different pressure drop—flow characteristics. The orifice providing optimum damping was chosen and a turbine with similar pressure drop—flow rate characteristics were fabricated. This turbine with polycarbonate stator guide vanes and rotor made using an additive manufacturing technique was extensively tested in oscillating airflow test rig. After this, an open sea trial of BBDB with this new turbine and four-point mooring was carried out in 2015 and it was observed during the trials that there was a significant improvement in overall performance of BBDB. This article gives a detailed account of turbine-OWC matching exercise, including all sea trials. For the entire duration of this long exercise, a comprehensive instrumentation plan was devised and implemented in order to record performance data for assessing the BBDB’s performance. This article gives details of the instrumentation and data acquisition system and its transmission to the shore station inside port premises. This exercise has paved way for developing OWC-based BBDB for producing larger power outputs.

The hydrokinetic energy potential of at Indian oceans remains largely untapped. The attempts toward utilizing this resource have made recently in India. However, those were mostly limited to academic studies. The current speeds along the Indian coastline are lesser as compared to other locations in the world. However, few places in India like the Gulf of Khambhat, Sundarbans, and Andaman and Nicobar Islands have currents due to tides. To initiate technology development to develop the hydrokinetic turbines and electric generator suitable for Indian sea climate, surveying of such location is essential. Early in 2008, when NIOT was executing the freshwater transportation project between islands, the current was visibly observed at Macpherson Strait in Andaman Island. Hence, the detailed current measurement exercise was carried out at the nearby Viper Island and Macpherson Strait. Even though the surface current was high on Viper Island, the current measured at 1–2 m below the sea water level was as low as 0.5 m/s (since it is a closed channel), whereas in Macpherson Strait it was observed as high as 2 m/s. In this location, the in-house developed prototype of ϕ 0.8 × 1 m straight bladed turbine was tested in floating configuration. In this trial, the current measurement was carried out over a period of time. The occurrences of current were plotted from these measured current data. From these occurrence data, the maximum available annual hydrokinetic energy is in the order of 4.8 MWh/m2 at this location. This paper focuses the suitable locations for ocean current turbine installations and current availability on Viper Island and Macpherson Strait of Andaman, India.

In India we have twelve major ports and two hundred minor and intermediate ports. All the port deploy several conventional navigation buoys with marker lamps in the navigational channel for guiding the ships entry into the port. Generally, these marker lamps are powered by batteries using the photovoltaic power module. The efficiency of PV modules mostly affected by waves and weather and it demands regular maintenance. In order to replace the PV modules, National Institute of Ocean Technology (NIOT) has indigenously developed wave powered navigational buoy similar to the existing buoys and the major advantage of this wave powered buoys is, the power will be extracted throughout the day. This power module is such as designed, it will generate power in low wave conditions. Since the waves are very random in nature, the extraction of maximum power is a challenge. The objective of this paper is to discuss about the development of the power takeoff system (PTO), which includes the selection of generator, design of charging circuit and sizing of the battery bank to catch the power at maximum efficiency. A range of combinations of chosen power modules is tested under various input frequencies in the oscillatory airflow test rig at the ocean engineering department of IIT Madras. To validate the design of the power takeoff system, NIOT has successfully filled out open sea trial at off Ennore, Chennai and generated power under various input wave conditions also presented in this paper.

Permanent Magnet Synchronous Generator (PMSG) is a type of electric generator where external excitation source is not required to produce a magnetic field because of which it suits underwater electricity generation using Ocean Current Turbines (OCT). Due to the slow speed nature of the OCT, mechanical transmission systems such as gear box, belt drives usually being used to fit the torque — speed characteristics of OCTS with the high speed PMSGs. This results in high starting torque in addition to the transmission losses. To avoid these issues, low speed PMSGs are required to be designed for the speed-torque characteristics of the OCT. This paper briefs the novel methodology to design the low speed PMSGs for the OCT applications and in-house fabrication of a low speed PMSG using the same methodology.

The ocean current energy is one of the clean forms of available renewable energy sources. Based on the topography of the islands, the subsea current is comparatively more than the mainland. Most of the islands are not having self-sustained power sources due to the limitations of infrastructure even though the power requirement is less. The National Institute of Ocean Technology (NIOT) of Ministry of Earth Sciences has undertaken the research and development of an ocean current power module for such islands. The first prototype ocean current turbine (OCT) power module was tested at Macpherson Strait in the Andaman open sea. The subsea power module of the system comprises of the turbine, transmission system, generator and the associated power and instrumentation systems. The development and implementation of electrical and instrumentation system for an underwater OCT power module are one of the challenging task, hence the entire system required to be designed for in-situ conditions. This paper aims to describe the design of Power take off (PTO) system, data acquisition, and wireless communication of prototype ocean current power module trials in open sea conditions.

A major attraction of a floating wave power plant as opposed to a fixed Oscillating water column (OWC) plant is in the cost of construction. The price paid is in the lower efficiency of conversion in the hydrodynamic stage. This puts onus on the subsequent power module stage in achieving an efficiency that is necessary for a commercial plant. A new backward bent ducted buoy (BBDB) was designed in which the power module is a twin unidirectional turbine. Basic experimentation on the power module is done on a turbine with 165 mm diameter and characterized with bidirectional flow with widely varying flow rates. The efficiency is shown to be better than 68% over the expected working range. The details of a plant producing 50 kW for Indian conditions is described. The range of powers over which a BBDB structure compares with a fixed OWC is highlighted.