Techno-Economic Feasibility of Harnessing Offshore Wind, Wave and Combined Offshore Wind-Wave Energy in the Indian Exclusive Economic Zone

Abstract

Over the past few years, power generation using renewable energy sources has grown rapidly to mitigate climate change and improve energy security. Recently, marine renewable energy is emerging as one of the potential alternatives to conventional energy sources for coastal countries. Despite having an extensive coastline, offshore wind and wave energy sources are yet to be developed in India. The lack of detailed resource analysis of these sources is one of the major challenges for development. In view of this, the main objectives of this study are to evaluate offshore wind, wave and combined wind-wave resource potential, identify the potential sites and assess the technical and economic feasibility of harnessing these resources in the exclusive economic zone of India. At the beginning of this research, an assessment of offshore wind resources for the Indian coast was performed using the latest ERA5 near hub height (100 m) wind products and real air density data for the period of nineteen years (2000-2019). While estimating wind power density (WPD) and actual power generation using the specifications of two latest offshore wind turbines (WTs) (9MW V164/9500 and 8MW SG8.0-167 DD), air density variation was taken into account. The results show that consideration of standard air density overestimates WPD and turbine output by 5-7.5% and 2.5-5.1%, respectively as compared to real air density data. The peak value of mean wind speed (7-10 m/s) and WPD (0.5-0.65 kW/m2 ) are found along the southern coast. A new index, the optimum hotspot index for wind (OHIwind), is developed to identify potential sites. The technical potential of selected sites combined with economic analysis has been performed. The application of SG8.0-167 DD and V164/9500 turbines contributes the lowest Levelised Cost of Energy (LCOE) of 94.7 €/MWh (7.8 ₹/kWh) and 107.1 €/MWh (8.8 ₹/kWh) respectively at the location near the south coast. Economic sensitivity analysis is also carried out to evaluate the effect of changes in six cost parameters on LCOE. Interest rate is found as the most influencing (±6-14 €/MWh), and WT cost is the least influencing (±0.7-1.5 €/MWh) parameter among all. In the subsequent part of this study, an exhaustive investigation of the feasibility of wave energy exploitation is conducted using 19-year high-resolution hindcast wave data generated by the spectral wave model WAVEWATCH-III (WWIII). Peak wave energy flux (WEF) (9-12 kW/m) is concentrated in the offshore region of the west coast. Three hotspots are determined based on local maxima of OHIwave value within the 100 m depth region of the eligible area. The technical potential and cost of electricity generation at hotspot locations are estimated and compared using four different wave energy converters (WECs): Wavedragon, Pelamis, Oceantec, and Aquabuoy. Oceantec generates maximum power (40-57 GWh) among all WECs and attains maximum capacity factor (22- 31%) at all the hotspots. Moreover, Oceantec is the most cost-effective WEC with the lowest LCOE ranging from 354 to 505 €/MWh (29 to 41 ₹/kWh) at all hotspots. The LCOE of wave power is most and least influenced by interest rate and OPEX, respectively. In the final part of this work, a detailed combined offshore wind and wave resources assessment is performed using ERA5 wind data and WWIII model wave data. A spatial map of the instantaneous correlation is developed to analyze the synergy between wind and wave resources. The lowest cross-correlation (<0.2) factor is observed along the southern coast. The co-location feasibility index (CLF) is used to locate the most favorable sites for combined wind and wave power generation. A maximum CLF value of up to 0.7 is observed in the southern coastal region. At identified sites based on CLF index and depth constraint, actual power generation of combined farms was estimated by considering eleven combinations (C1-C11) of SG8.0-167 DD (8 MW) (WT) and Oceantec (0.5 MW) (WEC) for an 80 MW farm. Even though combined farms are found to produce lower power outputs than stand-alone wind and wave farms at hotspots, the duration of zero power and power output fluctuations was reduced. At a hotspot near the south coast, power generation using combined farms is more cost-effective than standalone wave farms (321 €/MWh equivalent to 26 ₹/kWh). Still, it is relatively more expensive than wind farms (108 €/MWh equivalent to 8.8 ₹/kWh). According to the present analysis, it was found that offshore wind, wave and co-located offshore wind-wave energy is expensive relative to other renewable energy sources. However, future technological advances can contribute to their cost reduction, which will enhance the share of these marine energy sources for electricity generation in the near future.