Power density capacity of tidal stream turbine arrays with horizontal and vertical axis turbines

Abstract

Tidal and wind energy projects almost exclusively adopt horizontal axis turbines (HATs) due to their maturity. In contrast, vertical axis turbines (VATs) have received limited consideration for large-scale deployment, partly because of their earlier technology readiness level. This paper analyses the power density of turbine arrays comprising aligned and staggered configurations with decreasing turbine spacing of HATs and VATs with height-to-diameter aspect ratios from one to four at three real tidal sites. The VAT rotor has vertical blades extending over a portion of the water depth on a circular frame. Equivalent diameter is defined as $$D_0$$ D 0 = $$\sqrt{A}$$ A based on the projected rotor area for both VATs and HATs. The three-dimensional velocity field is computed using analytical wake models that capture cumulative wake effects. At highly energetic sites, e.g. Ramsey Sound (UK), HATs are the most suitable technology attaining power densities beyond 100 W m$$^{-2}$$ - 2 , whilst VATs provide higher power densities than HATs at those sites with low-to-medium velocities, e.g. Ría de Vigo (Spain) and Kobe Strait (Japan). At the latter site, VATs provided up to 35% larger energy yield than HATs over a 14-day tidal cycle. Our results show that VATs with height-to-diameter aspect ratios larger than three notably reduce wake effects even when deployed with a normalised turbine spacing of two $$D_0$$ D 0 , reaching an average power density capacity of 40.7 W m$$^{-2}$$ - 2 compared to HATs that attain 49.3 W m$$^{-2}$$ - 2 . This study outlines the higher efficiency of tidal stream energy compared to other renewable energy resources, e.g. offshore wind farms, reaching power densities at least one order of magnitude larger, and that VATs counterbalance their smaller individual performance with improved array synergy as wake effects are limited.

A Probabilistic Methodology for Determining Collision Risk of Marine Animals with Tidal Energy Turbines

“…Tidal turbines are designed to begin rotating when the flow rate reaches a speed at which power generation becomes viable; often referred to as the 'cut in' speed of the device. The cut in speed will vary with the particular turbine design, but for turbines that can generate utility scale energy, is unlikely to be less than 1.0-1.5 m/s [93,94]. If marine animals are present in the immediate vicinity of the device, or within the turbine swept area, they are not at risk of collision when tidal flows are less than the cut in speed of the turbine.…”

Evaluating Mechanical Strength in Vertical-Axis Tidal Turbines: A Comparative Study of Internal Blade Structure and Material Selection through CFD Simulation

“…This paper centers its attention on the examination of small-scale vertical-axis tidal turbines intended for deployment in regions characterized by low-to-moderate flow velocities. VATTs deliver better power densities than Horizontal Axis Tidal turbine (HATTs) in areas with low-to-moderate speeds (4). Furthermore, in a remote area there will be limited regional infrastructure for turbine assembly, and limited supporting equipment facilities (cranes, barges, etc.)…”

Design of Ocean Current Blade Turbine 100 kW using Hydrodynamics Simulation Approach

“…Changes in flow velocity of ocean water due to the ups and downs of ocean water could be used as the primary energy to drive turbines and generate electricity [4]. There are two types of ocean current turbines, namely Horizontal Axis Turbines (HAT) and Vertical Axis Turbines (VAT) [5,6]. HAT blade was designed as counter ocean current flow, that had kinetic energy from blade spinning by ocean current velocity (Figure 1(a)).…”