# Study on Critical Factors Affecting Tidal Current Energy Exploitation in the Guishan Channel Area of Zhoushan

^{1}

^{2}

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## Abstract

**:**

^{2}, and the spatial distribution is uneven. The resource level in the central part is much higher than that at both ends of the waterway. Three sections, i.e., A-A′, B-B′, and C-C′, with different key influence factors are selected for specific analysis, and it is concluded that the tidal energy development conditions are relatively superior near the B-B’ section in the middle of the GCA, and the exploitable power calculated using the Flux method is about 24.19 MW. The discussion of the results provides a certain reference for the development of local tidal current energy. These key factors affecting tidal current energy development can also be applied to assess the suitability of tidal current energy resource development in other regions.

## 1. Introduction

^{6}kW, exceeding half of the total tidal energy resources in the country. The tidal current energy resources in the Zhoushan sea area account for more than 80% of the total resources in Zhejiang Province [6], with considerable development prospects.

## 2. Numerical Model and Regional Flow Field Analysis

#### 2.1. Regional Introduction

#### 2.2. Model Hydrodynamic Equations

^{2}; $\phi $ is the local latitude; $\rho $ is the density of water; ${\rho}_{0}$ is the relative density of seawater; ${\tau}_{sx},{\tau}_{sy}$ are the wind stress components; ${\tau}_{bx},{\tau}_{by}$ are the bottom stress components; ${p}_{a}$ is the local atmospheric pressure; $S$ is the source–sink term; ${T}_{xx},{T}_{xy},{T}_{yy}$ are the viscous force, turbulent stress, and horizontal convection terms, which are derived from the eddy viscosity equation based on the velocity gradient averaged along the water depth: ${T}_{xx}=2A\frac{\partial \overline{u}}{\partial x}$, ${T}_{xy}=A\left(\frac{\partial u}{\partial y}+\frac{\partial v}{\partial x}\right)$, and ${T}_{yy}=2A\frac{\partial v}{\partial y}$; and $A$ is the horizontal eddy viscosity coefficient.

#### 2.3. Model Setup

_{2}, O

_{1}, S

_{2}, K

_{2}, N

_{2}, K

_{1}, P

_{1}, Q

_{1}, M

_{f}, M

_{m}, and S

_{sa}for a total of 11 major divisions of the tide. The closed boundary has zero normal velocity. The horizontal turbulence diffusion coefficient is based on Smagorinsky’s formula, and the value of Cs is 0.28. Manning’s roughness coefficient was chosen for the effect of riverbed roughness and interpolated between 0.012 and 0.025 depending on the water depth. The simulation did not consider wind, waves, and storm surges or other complex ocean hydrographic conditions. The time step was set to 30 s, the simulation time was from 1 January 2022 0:00:00 to 31 December 2022 0:00:00, and the simulation results were output once every hour. Figure 2 shows the schematic diagram of the grid of the simulation area.

#### 2.4. Model Verification

#### 2.5. Flow Field Analysis

## 3. Analysis of Key Factors for Tidal Energy Exploitation

#### 3.1. Energy Flow Density

^{3}, and $V$ is the local tidal current velocity. In the actual calculation, since the tidal current velocity constantly changes with time and its magnitude and direction have instantaneous values, the average current velocity $\overline{V}$ over a period of time is often used to calculate the average energy density ${P}_{\mathrm{m}}$ over that period of time.

^{2}; meanwhile, it is relatively low at both ends of the waterway, with average annual energy flow densities at both ends of 300 to 500 W/m

^{2}, with a large difference in magnitude. The average energy density of the sea plane above 500 W/m

^{2}is about 10.88 square kilometers, and that of the sea plane above 1000 W/m

^{2}is about 7.1 square kilometers. In addition, an annual average energy density of more than 1500 W/m

^{2}is also found in the central part of the Gaoting Channel and Guanmenn Waterway in the north and south, but both the peak value and the area of high energy density are not as extensive as those of the GCA.

#### 3.2. Frequency of Flow Rate Occurrence

#### 3.3. Flow Rate Asymmetry

#### 3.4. Flow Direction Rotatability

#### 3.5. Available Flow Time for Exploitation

## 4. Evaluation of the Theoretical Exploitable Amount of Tidal Energy

^{2}were selected according to different key influence factors of tidal energy exploitation to discuss their respective theoretical exploitable amounts of tidal current energy. In order to facilitate a comparison and eliminate the differences caused by the different areas of developed sections, the length of all three sections is 1500 m, and the water depth is 25 m. The location of the sections is shown in Figure 14, and the parameters of each section are shown in Table 2.

^{2}, which corresponds to an average annual flow velocity of 1.63 m/s, while the highest-frequency flow velocity occurring in the section is 1.8 m/s, indicating that the flow velocity in the region is higher than the average annual flow velocity most of the time, so the actual developable power should be slightly higher than the theoretical developable power. The flow velocity asymmetry of the A-A′ section is 0.25, and the flow direction rotation is 6. The tidal energy will not have high technical exploitation difficulty. The annual effective flow time is 6800 h, and the theoretical developable volume is 12.38 MW. The exploitation potential is large in a comprehensive way. The average annual energy density of the B-B′ section is 4300 W/m

^{2}, and the daily flow velocity is around 2.4 m/s. It has the smallest flow velocity asymmetry and flow direction rotation. The annual effective flow hours for power generation total 7300 h, and the developable power is 24.19 MW. These exploitation conditions of tidal energy are the best among the three cross-sections. The annual average energy flow density of the C-C′ section is 860 W/m

^{2}, and the exploitable power is about 6.75 MW. Although the daily performance of the flow velocity is high, the resource is still relatively small, and the flow velocity asymmetry and flow direction rotation are high, at 0.38 and 11, respectively, which makes the actual exploitation of tidal energy more difficult. The annual average effective flow time is 6000 h, and the total exploitable power is relatively low.

## 5. Conclusions

^{2}, and the peak energy density is greater than 500 W/m

^{2}in the area, compared to the adjacent Gaoting Channel and Guanmen Waterway.

^{2}, the flow velocity distribution is mainly between 1.8 and 2.4 m/s, and the velocity asymmetry is only 0.1. The flow velocity is high and essentially unchanged. The rotation of the flow direction is about 2, showing a typical reciprocating flow, and the annual effective flow time exceeds 5500 h. By combining these key factors for the development of tidal current energy, there is an excellent development prospect here. The tidal current energy calculated using the Flux method can develop a power of about 24.19 MW.

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Conflicts of Interest

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Average Annual Flow Rate/m·s^{−1} | Average Annual Tide Level/m | Main Direction of High Tide/° | Main Direction of Low Tide/° | Highest Tide Level/m | Lowest Tide Level/m | Average Annual Tide Difference/m | Average Annual Low-Tide Duration/min | Average Annual High-Tide Duration/min | Differences in Average Annual High-Tide Duration and Low-Tide Duration/min |
---|---|---|---|---|---|---|---|---|---|

1.97 | 0.16 | 288 | 111 | 2.12 | −5.28 | 2.16 | 395 | 348 | 47 |

Cross-Section | Longitude and Latitude | Annual Average Energy Flow Density | The Flow Rate at Which the Highest Frequency Occurs | Flow Rate Asymmetry | Flow Direction Rotatability | Annual Available Hours | Theoretical Developable Power |
---|---|---|---|---|---|---|---|

A-A′ | 122°10′27.25″ E, 30°13′01.89″ N~122°10′07.97″ E, 30°12′15.72″ N | 2200 W/m^{2} | 1.8 m/s | 0.25 | 6 | 6800 h | 12.38 MW |

B-B′ | 122°11′03.72″ E, 30°12′51.00″ N~122°10′53.95″ E, 30°12′03.01″ N | 4300 W/m^{2} | 2.4 m/s | 0.1 | 1 | 7300 h | 24.19 MW |

C-C′ | 122°11′55.58″ E, 30°12′48.74″ N~122°11′35.57″ E, 30°12′02.87″ N | 1200 W/m^{2} | 1.9 m/s | 0.38 | 11 | 6000 h | 6.75 MW |

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**MDPI and ACS Style**

Ye, Z.; Gu, W.; Ji, Q.
Study on Critical Factors Affecting Tidal Current Energy Exploitation in the Guishan Channel Area of Zhoushan. *Sustainability* **2022**, *14*, 16820.
https://doi.org/10.3390/su142416820

**AMA Style**

Ye Z, Gu W, Ji Q.
Study on Critical Factors Affecting Tidal Current Energy Exploitation in the Guishan Channel Area of Zhoushan. *Sustainability*. 2022; 14(24):16820.
https://doi.org/10.3390/su142416820

**Chicago/Turabian Style**

Ye, Zhou, Wenwei Gu, and Qiyan Ji.
2022. "Study on Critical Factors Affecting Tidal Current Energy Exploitation in the Guishan Channel Area of Zhoushan" *Sustainability* 14, no. 24: 16820.
https://doi.org/10.3390/su142416820