Quantification of the tidal stream exergy in the ría de Vigo (NW Spain)

Abstract

Abstract:The exergy of the tidal currents in the ría de Vigo area (NW Spain) is quantified using the results of a 28-day long simulation of the tidal flows. The results show that the northernmost strait connecting the ría with the Atlantic Ocean is a promising site for tidal energy tapping, in contrast with the energetically weaker estuary. On the basis of the average power density (APD), a 7.5 km 2 region is identified in this strait as the most advantageous area to install tidal energy converters (TECs), with a total annual exergy of around 2 M. Mestres et al.3865 MWh/m 2 . Similar analyses using only 14-day simulations change this value in 16%, depending on whether the tidal cycle considered is apogean or perigean. The study contributes to enlarge the inventory of sites along the NW Spanish coast at which tidal stream energy can be potentially extracted.

Modelling assessment of the tidal stream resource in the Ria of Ferrol (NW Spain) using a year-long simulation

“…As expected, the mid-ebb power for this spring tide is larger than the mid-flood power (0.45 kW/m 2 vs. 0.40 kW/m 2 ). In both cases, the power density values are considerably smaller than those found in other Galician rías: Vigo (7.5 and 5.6 kW/m 2 , for the mid-flood and mid-ebb, respectively [7]), Muros (5 -2 kW/m 2 [31]), or Ortigueira (8-6 kW/m 2 [6]).…”

“…By using a long time series, it is expected to smooth out and quantify the variations in the tidal resource assessment that arise when shorter representative time windows (e.g., 14-day tidal cycles, or 28-day lunar months) are adopted. Previous studies comparing these shorter time periods [7,28] have shown that the potential tidal stream energy in an area can be under-or overestimated by as much as 16%, depending on whether the considered tidal cycle corresponded to a perigean or an apogean tide.…”

“…In addition, the depletion of fossil fuel reserves [2] and the rising awareness of the impact of fossil fuels on climate change [3] have increased the interest for the exploitation of renewable energy sources [4]. Amongst them, tidal current energy is one of the most promising [2,5,6] due to several advantages with respect to other renewable energy sources: a) the high predictability of tidal currents when compared to atmospheric flows, b) the higher density of seawater (over 800 times that of air) assuring much larger energy available for a tidal energy converter (TEC) than for a wind turbine under similar conditions [7], c) the minimum environmental impact compared to tidal barrage facilities [6] and d) the absence of extreme flow velocities that might damage the equipment or complicate its maintenance [6], although this depends strongly on the flow profiles induced by the local bathymetry near the TEC deployment site [8]. As a negative aspect, the extraction of tidal energy reduces flow speed [9] and can lead to modifications in the dispersion and transport patterns and, therefore, changes in the local water quality [10], sediment patterns [11] or even in the wave energy regime, depending on the particular wave-current interaction [12].…”

“…In the particular case of Spain, renewable sources account for 17.3% of the gross consumption, more than doubling the percentage in 2004 (8.5%, [14]). About 90% of the green electricity generated is provided by wind, hydraulic and solar sources [7]. Nevertheless, in the last few years the interest in marine energies has increased considerably due to their large potential as well as being seen as an opportunity for helping to achieve the EU directive goals.…”

“…produce electric power. For these reasons, several studies have assessed the tidal resource at different locations in this region [6,7,31,32].…”