Tidal-range and tidal-stream energy characterisation in the Gulf of California, Mexico

Abstract

In the last two decades, there has been a growing interest in tidal energy, which is a predictable source of renewable energy driven by astronomical forces. To date, no dedicated assessments of the available tidal-stream energy resource have been carried out for the Gulf of California, México (hereafter GC) and only two limited studies of tidal-range have been undertaken in this region. The
northern part of the GC has a relatively large mean tidal-range (up to 5 m). Furthermore, tidal flows of over 1.5 m/s have been recorded on spring tides in between the Midriff Islands in the central part of the GC. Hence, this region has the potential for tidal energy exploitation. However, locations like the GC, with a strong diurnal tidal influence and less energetic tidal currents, but in deeper waters, have often been overlooked. The aim of this thesis is therefore to
quantify the theoretical tidal-range and tidal-stream energy characterisation within the GC.
The first objective is to quantify the theoretical tidal-range energy resource. This was done using tidal level predictions from a depth-averaged barotropic hydrodynamic model, extensively validated against tide gauge and current observations. A 0-D modelling approach was then used to determine
the power that can be technically exploited at four key sites in the northern regions of the GC. The results indicate that the annual energy yield ranges from 20 to 50 kWh/m2 while the maximum values are between 45 and 50 kWh/m2 in the vicinity of the Gulf of Santa Clara. This site was the best performing in regard to tidal-range energy potential, delivering a technical annual energy
output of 125 GWh (ebb-only), 159 GWh (two-way) and 174 GWh (two-way with pumping), assuming an impound area of 10 km2.
The second objective is to determine the present day theoretical tidal-stream energy resource available in the GC. This was done by utilising tidal current predictions from the hydrodynamic model. The highest current speeds of 2.4 m/s were found to occur in the channel between San Lorenzo and San Esteban Island (hereafter San Lorenzo Passage), and three lower-velocity potential
sites were identified in the channels between: (1) Baja California Peninsula and San Lorenzo Island; (2) San Esteban and Tiburon Islands and (3) Baja California Peninsula and Angel de la Guarda Island. Although peak kinetic power density (hereafter KPD) in these regions is found to be relatively low (~ 3 to 6 kW/m2), the large water depth (100 to 500 m) results in an undisturbed theoretical annual mean power of between 100 to 200 MW. Technical power was estimated for four device types, first assuming just an array of devices near the surface, and second an array of devices down through the water depth. The estimated total annual mean technical power varied between 251 and 460 MW, considering just a near surface area, and between 304 and 1030 MW if the
full water column was utilised. Results of the hydrodynamic model, based on localised refined bathymetry datasets, highlighted that global and freely available bathymetry data products under-resolve the energy resource by up to 75%. Findings also suggesting that diurnal and higher order harmonic constituents are important for accurate resource assessments in this region. A detailed analysis of the 3D characteristics of tidal currents in the central Gulf was undertaken, using predictions from a HAMSOM model, developed previously. This analysis has shown that current velocities varying considerably with depth, and the vertical profile varies depending on site. At the four sites, considered here, the current speeds are fastest in the upper water column. A novel
analysis was also undertaken assessing whether knowledge of the phase relationship between tidal energy sites be exploited by aggregating the electricity generated by a number of geographically distributed sites. The results highlight that if one considers tidal- range and tidal-stream schemes separately, it is not possible to generate a form power supply through a day from the four
tidal-range and four tidal-stream sites identified. However, if one considers tidal-range and tidal-stream sites together, it is possible to generate a more consistent supply, with short periods of zero electricity generation.
In conclusion, the northern part of the GC contains several promising locations for a tidal-range energy extraction, with a two-way and pumping scheme option appearing viable for these sites. The tidal-stream resource was found to be large at four main areas in the central region of the GC, but new turbine technologies would be required to exploit these ‘next generation’ resource regions.
This study highlights that regions like the GC, with a strong diurnal tidal influence and less energetic tidal-ranges and currents, but in deeper waters, should not be overlooked when considering sites around the world suitable for tidal energy exploitation.

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ORCID for Ivan Haigh: orcid.org/0000-0002-9722-3061

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