Assessment of wave and solar energy potential along Western coast of India

 

Prerna Goswami¹, Dr. S.P. Deshmukh²

¹Assistant Professor, Department of General Engineering, Institute of Chemical Technology,

Nathalal Parekh Marg, Matunga, Mumbai, Maharashtra, India -400019

²Associate Professor, Department of General Engineering, Institute of Chemical Technology,

Nathalal Parekh Marg, Matunga, Mumbai, Maharashtra, India -400019

 

ABSTRACT:

Renewable energy is the need of the day to address energy crisis in the world. Renewable energy share in India is nearly 14% of the total installed capacity. Ocean energy does not contribute to this share at all. With a long coast line ocean energy has enormous potential of electricity generation in India especially for remote coastal areas which are still deprived of electricity. Although India is blessed with large amount of solar power, but during south west monsoon months, western coast of India experiences rainy season for around three to four months i.e. from June to September. Wave energy potential increases during monsoon months, which is evident from considerable increase in significant wave height and mean wave period. A hybrid arrangement with wave energy and solar energy generation using stand alone micro-grids can solve the problem of energy deficit and can also supply households of remote coastal areas of India that have no electricity.

This paper describes potential of wave energy along western coast of India. With significant wave height and mean wave period data obtained from wave rider buoys and moored buoys installed along various locations of western coast of India, an assessment of wave energy has been obtained. With solar irradiation data along the coast it is established that solar and wave energy hybrid system can be an answer to the problem of remote coastal areas deprived of grid connection.

 

 

 

1. INTRODUCTION:

Renewable energy share in India is nearly 14% of the total installed capacity [1]. India has a long coast line of around 7500 km, but ocean energy does not contribute to this share at all. According to a report prepared by CRISIL Risk and Infrastructure Solutions Limited, Agence française de development (AFD) & Indian renewable energy development agency limited (IREDA) and Indian Institute of Technology Madras [2] on assessment of tidal and wave energy along Indian coast line suggests that India has total wave energy potential of 41 GW and tidal energy potential of around 12 GW.

 

Ocean energy has different forms e.g. tidal energy, wave energy, ocean thermal energy and osmotic energy [3]. Tidal energy is obtained from tides resulting from gravitational force between earth and moon and between earth and sun. Wave energy is the kinetic energy in the waves generated in the sea resulting from winds. Ocean thermal energy is the result of temperature difference and osmotic energy is due to salinity difference between two locations in the sea.

 

Tidal energy is the most exploited form of ocean energy which is harnessed at various locations around the world. Prominent locations of tidal generation plants include

1.      240 MW La Rance-River Tidal power station in France

2.      254 MW Sihwa Lake Tidal Power station in South Korea

3.      20 MW Annapolis Royal Generating Station in Canada

 

Tidal energy can be extracted either by building tidal barrages or dam or by installing turbines activated by tidal flow. This requires large tidal range and large area for reservoir.

 

Ocean thermal energy converters and osmotic energy conerters are at a very early stage of development.

There have been a very few wave energy plants in operation in the world, some of them being

1.      500 KW station at sland of Islay, Scotland,

2.      300 KW break water wave plant at Mutriku, Spain and

3.      200 KW Azura wave power device at United states.

 

The world’s first commercial wave energy power station has started working in February 2015 after being connected successfully to Western Australia’s electricity grid. The station will provide electricity and desalinated water for Australia’s biggest naval base. Gibraltar's wave power station installed [4] on Ammunition Jetty of British territory also started operating from May 2016.

 

Electricity generation from Wave power is also in research and experimentation stage. It is also obvious that due to variability of wave environment wave energy converters are more suitable for small ratings feeding to stand alone micro-grids.

 

An oscillating water column based wave energy converter was installed in 1999 in India at Vizinzham, Kerala. The plant with generating capacity 150 KW was earlier feeding to the state Grid. The plant generated around 75 KW during April to November but only 25 KW from December to March. Its maximum output came during monsoon months due to high significant wave height and large wave period. The plant was decommissioned in 2011. For a sustained supply to the stand alone microgrid it is therefore desirable that wave energy generation is combined with solar generation so that they can supplement each other throughout the year.

 

2. An overview of Wave energy converters:

Wave energy converters [5-14] capture mechanical energy of waves which can be converted into electricity using hydraulic or pneumatic turbines.

Some of the important wave energy converters are

·        Attenuators

·        Point absorbers

·        Overtopping devices and

·        Oscillating water columns

 

2.1 Attenuators:

Attenuators are long floating devices made up of many segments joined together as shown in fig.1. They float in parallel with the wave. The wave causes flexing of joints which are connected to hydraulic pumps or other converters to generate electricity.

 

Its examples are Pelamis and wave star.

 

Fig.1 Attenuators

 

2.2  Point absorbers:

Point absorbers (fig 2) are moored buoys which move perpendicular to the direction of wave. They move up and down with the movement of wave and their movement is captured by power take off devices for conversion to electricity. Examples: Aqua buoy and Power buoy.

 

Fig.2 Point absorber (http://www.waterpowermagazine.com/)

 

2.3  Over topping device:

This device as shown in fig.3 works on the principle similar to hydro electric power plant. Incoming wave fills the reservoir. The water then flows back to the sea from high head. Its kinetic energy is then used to drive turbine and the generator to generate electricity. Example of commercial overtopping device is Wave dragon.

 

Fıg. 3. Overtopping device

 

2.4  Oscillating Water Column (OWC):

Oscillating water column [15-18] is a concrete column as shown in fig.4 installed near shore with opening in the direction of incoming wave. As the wave strikes the water in the column rises and falls as the wave recedes. The water colums oscillates like a piston and causes the air trapped inside to rotate the pnumatic turbine which is coupled with a generator for electricity generation.

 

The turbine used is normally wells turbine which rotate in the same direction irrespective of the water column moving up or down. Impulse turbines for higher efficiency are also used and in this case the direction of air is monitored to make the turbine rotate in the same direction. Examples of commercial oscillating water colums are Wave-gen or Ocenlinx.

 

Fig.4 Oscillating Water Column

 

3. Wave energy potential in India:

India has total wave energy potential of 41 GW, but due to natural conditions and constraints such as water depth this full potential cannot be realized and a realistic estimate of each site is required. Kudal in Maharashtra and Trivandrum in Kerala are suggested as more than 2000 MW wave power locations where the wave energy can be harnessed with oscillating water columns. Entire western coast has potential for harnessing wave energy using OWC technology. The sites in east coast are suitable for hybrid wind and wave energy.

 

4. Wave power calculations:

Wave power [19-23] per unit width of wave front considering a sinusoidal wave and water depth more than 0.5 λ is given by

 KW/m             (1)

Where

ρ= density of sea water=1024 Kg/m² (approximately with slight variation with location)

g= Acceleration due to gravity = 9.8m/s²

H= wave height (vertical distance between trough to crest)

T= wave period

 

The equation indicates that the wave power is directly proportional to the square of the wave height H and wave period T.

 

To represent irregular waves, two quantities i.e. significant wave height H_s and mean wave period T_Z are defined.

·        Significant wave height H_s is defined as the mean height of the largest 33% waves of the wave spectrum.

·        T_J is taken as 1.2 times T_Z, where T_Z is the time period between two successive crossings of mean water level. T_J is said to be the period of energy transport.

For irregular waves α_J= α/2,

Where constant α= ρ g²/32π = 978.25 W/m²

               KW/m                             (2)

 

5. Wave energy Estimate of Western coast of India:

Wave energy estimate was obtained using month-wise data from four locations of India. The month-wise data was collected for Significant wave height and Mean wave period from wave rider buoys at locations, Ratnagiri in Maharashtra, Karwad in Karnataka and Kozhikode and Kollam in Kerala from ESSO- INCOIS [24], [Earth System Science Organization (ESSO)-Indian National Centre for Ocean Information Systems(INCOIS)].

 

Fig.5. Rise in significant wave height during south west monsoon in western coast of India

 

Fig 5 shows rise in significant wave height during south west monsoon in western coast of India. The collected data of wave period and significant wave height is shown in figure 6 for Ratnagiri, Figure 7 for Karwad, Figure 8 for Kozhikode and figure 9 for Kollam. During southwest monsoon i.e. from mid June to mid September, western coast of India receives heavy rains. The sky is mostly covered with thick clouds therefore the region receives very little solar irradiation. On the other hand there is rise in the wave heights favoring increase in wave energy output which is directly proportional to the product of square of the significant wave height and the mean period. Wave energy can easily offset the deficit in solar energy input during monsoon months. Therefore a hybrid microgrid supplied by solar PV and wave energy generation can give relatively stable output to the region throughout the year.

 

 

Fig.6 Mean period and significant wave height data of Ratnagiri wave rider buoy

 

Fig.7 Mean period and significant wave height data of Karwad wave rider buoy

 

Fig.8          Mean period and significant wave height data of Kozhikode wave rider buoy

 

Fig.9          Mean period and significant wave height data of Kollam wave rider buoy

 

 

6. Solar Energy Estimate of Western Coast of India:

India receives good amount of sunshine throughout the year. But during Monsoon months i.e. from mid June to mid September western coast of India receives heavy rains and the sky is mostly covered with cloudsSolar power can be converted into electricity using solar PV technology. Solar irradiation data was collected [25, 26] for the same locations from Solar Energy Centre Ministry of New and Renewable Energy, Government of India, solar resource maps data. Table 1 shows the Global horizontal irradiation (GHI) falling on various locations of western coast of India.

 

Table 1: Monthly variation in GHI of four locations of western coast of India

 

Fig.10  Monthwise Solar and wave energy potential at Ratnagiri

 

7. Nature balances itself: Solar and wave energy compensates each other:

During monsoon months the solar irradiations decrease drastically but at the same time wave energy potential increases substantially due to rise in significant wave height and mean wave period as recorded by wave rider buoys at Ratnagiri, Karwad, Kozhikode and Kollam. This wave energy can be harnessed using oscillating water columns for generation of electricity. Table 2 shows month-wise variation in wave energy estimates along western coast of India.

 

Table 2. Wave energy potential for various locations in western coast of India

 

Fig. 11 Monthwise Solar and wave energy potential at Karwar

 

Fig. 12 Monthwise Solar and wave energy potential at Kozhikode

 

Fig. 13 Monthwise Solar and wave energy potential at Kollam

 

Fig.14 Wave Energy Generation System

 

Fig. 10, 11, 12 and 13 show month wise solar and wave energy potential along western coast of India. Fig. 14 shows the block diagram of wave energy generation system. Output of Permanent Magnet Synchronous Generator is converted into DC and fed to the stand alone DC microgrid. For feeding to AC loads DC to AC conversion is done through inverters.

 

Fig. 15 shows working of an oscillating water column for generation of electricity.  Incoming and outgoing wave causes rise and fall in the water column height in the Oscillating water column as shown in Fig.13. It acts like a piston and air inside the column is compressed or decompressed. Air is forced out or sucked into Wells turbine. Wells turbine being rectifying pneumatic turbine rotates in the same direction irrespective of the direction of air. The rotation of the turbine causes the generator to rotate giving rise to generation of electricity. There have been many developments in turbine technology to increase efficiency of turbines to harness wave energy through oscillating water columns [27-34].

 

Fig. 15 Working of Oscillating water column

 

Fig. 16 shows block diagram of a hybrid stand alone micro-grid fed by solar and wave energy. This wave –solar hybrid can be used to generate electricity to supply remote areas using stand alone micro-grids. This potential can also be exploited to reduce carbon foot prints caused by thermal generation of electricity.

 

Fig.16        A hybrid stand alone DC microgrid arrangement for remote coastal areas

 

 

CONCLUSION:

Nature balances itself. It is evident from the solar insolation data and significant wave height and wave period data along western coast of India. Vizhinjam wave energy plant of India generated its maximum during monsoon months. Solar energy estimate show a dip in solar energy output from June to September due to the sky covered with thick clouds. On the other hand the wave energy estimate shows a rise during these months due to rise in significant wave height and wave period. Stand alone microgrids fed by hybrid solar and wave energy can prove as a boon for the remote coastal areas of India which are either not connected to the grid or do not get continuous supply of electricity. The Availability of electricity can result in overall growth and development in western coast of India. It can also help to enhance tourism in the naturally beautiful coastal areas of India.

 

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Received on 28.05.2017                             Accepted on 14.07.2017

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