# Optimal Operation Strategy for Wind–Hydrogen–Water Power Grids Facing Offshore Wind Power Accommodation

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## Abstract

**:**

^{4}, and the strategy and model have good economic benefits and practical significance.

## 1. Introduction

- (1)
- Considering both the energy accommodation and freshwater input for electrolyzation, which are regarded as the energy input and raw material input of the system, this paper formulates a joint-operation power control strategy, establishing a wind–hydrogen–water power grid system to improve offshore wind power accommodation rate, freshwater production, and energy utilization rate;
- (2)
- The electrolyzer variable efficiency model is introduced to make full use of the flexible adjustment characteristics of the electrolyzer as a kind of detailed controllable load to match wind power fluctuations and to improve the system economy and reality;
- (3)
- In view of the problem of operation restriction arising from the direct connection between desalination and electrolysis, reservoir regulation is considered to reveal the uncertainty impacts of the reservoir capacity.

## 2. WHW-PGS Architecture and Mathematical Model

#### 2.1. HES Mathematical Model

#### 2.2. Desalination Mathematical Model

## 3. Optimal Operation Strategy of HES and Desalination

#### 3.1. Operation Rules

#### 3.2. Operation Strategy

## 4. Optimal Operation Model of WHW-HS

#### 4.1. Objective Function

#### 4.2. Constraints

## 5. Case Studies

^{4}tons. According to the parameter changes in the area, the simulation step is defined as 1h and the period is 24 h, which is solved by the CPLEX solver in MATLAB. The algorithm is the default interior point method, and the operation time is 2.84 s. The processor of the computer is Intel(R) Core(TM) i5-10210U CPU at 1.60 GHz 2.11 GHz and RAM is 8 G.

#### 5.1. Analysis of the Impact of Different Operation Modes on the Plan

^{4}× USD/h, which is not meaningful compared to the economic benefits under the operating strategy proposed in this paper, Thus this part will not be discussed. The income from the water sales of A3 increased by 3.2% compared with that of A1, and the income from electricity sales of A3 decreased by about 3 times. The main reason is that when the desalination system is operating alone, and redundant wind energy is not fully accommodated. A3’s hydrogen sales revenue is lower than that of A2. Although it improves the economics of the system’s green and low-carbon operation, the lack of freshwater revenue leads to a decrease in the total system’s energy revenue.

#### 5.2. Analysis of the Influence of Changes in the Efficiency of Electrolyzer

#### 5.3. Analysis of Uncertainty Influence of Reservoir Capacity

## 6. Conclusions

- (1)
- Introducing the “Coastal multi-energy complementation” optimal operation strategy (JO-PCS), which can flexibly adjust and match wind power fluctuations, achieving peak shaving and valley filling, greatly reduces interactions with the public grid and reduces the average daily operating cost of the system.
- (2)
- Aiming at the efficiency-power characteristics of the electrolyzer, the variable efficiency model of the electrolytic cell is introduced to improve the operation strategy, which can make the system more economic and practical and avoid resource loss caused by the improper use of system equipment.
- (3)
- When the reservoir drops, the emergency freshwater supply of the system is insufficient, resulting in an increase in the number of desalination devices. Although energy consumption increases, the cost also increases.

- (1)
- With the increase in OWP offshore deep-sea HVDC transmission projects and the reduction in the investment cost of HES, it can effectively increase the utilization rate of renewable energy and promote the prosperity and development of coastal microgrids.
- (2)
- The double objective optimization operation, which considers the relationship between operation cost and the overall system’s energy efficiency as well as the impact of hydrogen storage on the system, will be a part of future studies.

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

## Nomenclature

OWP | Offshore wind power |

WHW-PGS | Wind–hydrogen–water power grid system |

JO-PCS | Joint operation power control strategy |

EVEM | Electrolyzer variable efficiency model |

EHP | Electrolytic hydrogen production |

HES | Hydrogen energy system |

HST | Hydrogen storage tank |

USE-WU | User satisfaction evaluation of water use |

$\gamma $ | Performance parameter |

k | Impurities |

SOC | State of charge |

O | Rated capacity |

Load | Conventional power consumption |

a | Net |

ov | Redundancy |

sh | Defect |

C_{f} | The average daily operating cost |

C_{u} | Daily energy accommodation revenue |

C_{m} | Daily average operation and maintenance cost |

u | Unit price (accommodation) |

m | Unit price (benefit) |

∆P | The climbing power |

E | Battery capacity |

$\delta $ | Self-discharge coefficient |

S | User water satisfaction |

$\alpha $ | Curtailment rate |

HHV | Calorific value of hydrogen |

Q_{1} | External heat required for the electrolysis reaction |

Q_{2} | Heat water to meet reaction heat |

P | Electric power (MW) |

W | Fresh water load in the reservoir (t) |

N | Desalination’s Number |

G | Freshwater production(t) |

Y | Pressure |

(t) | At time t |

ez | Electrolyzer |

fc | Full cell |

x/w | Desalination |

sw | Offshore wind power |

e | Grid (1—forward, 2—opposite) |

max | Upper limit |

min | Lower limit |

H_{2}/H | Hydrogen |

V | Certain voltage (Volt) |

A | Whether the electrolytic cell is opened, run to take 1; otherwise take 0. |

i | Electrolyzer’s number |

F | Faraday constant |

${\eta}_{f}$ | Faraday efficiency |

$\eta $ | Efficiency |

T | Adiabatic temperature (K) |

M | Quality of hydrogen (kg) |

V | Volume (m^{3}) |

n | Moles of hydrogen |

H_{2in} | Input of hydrogen load |

H_{2out} | Output of hydrogen load |

uw | Electrolytic water accommodation related to power accommodation |

T_{1} | Temperature of the heated substance |

T_{0} | Ambient temperature |

user | Use |

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Class | P (MPa) | T (°C) | Cost (CNY/kW) | Efficiency (%) |
---|---|---|---|---|

ALK | 0.1~3 | 60~80 | 410~1030 | 63~70 |

PEM | 3~8 | 50~80 | 280 | 56~67 |

SOEC | 0 | 650~1000 | 560 | 74~81 |

Layer 1 Control Strategy | Layer 2 Control Strategy | ||||
---|---|---|---|---|---|

No. | Condition | Strategy | No. | Condition | Strategy |

Strategy1 | ${P}_{x-\mathrm{min}}(t)<{P}_{a}(t)<{P}_{x-\mathrm{max}}(t)$ | Desalination start Electrolyzer start | Strategy1 | ${P}_{ov}(t)<{P}_{c-\mathrm{max}}(t)$ $\mathrm{or}{P}_{sh}(t)\le {P}_{d-\mathrm{max}}(t)$ | No interaction with power grid |

Strategy2 | $0<{P}_{a}(t)\le {P}_{x-\mathrm{min}}(t)$ | Desalination start Fuel cell start | Strategy2 | ${P}_{ov}(t)\ge {P}_{c-\mathrm{max}}(t)$ | Sell power |

Strategy3 | ${P}_{a}(t)\le {P}_{x-\mathrm{min}}(t)<0$ | Desalination close Fuel cell start | Strategy3 | ${P}_{sh}(t)>{P}_{d-\mathrm{max}}(t)$ √ | Power purchase |

Strategy4 | ${P}_{a}(t)\ge {P}_{x-\mathrm{max}}(t)$ | Desalination start Electrolyzer start | Strategy4 | ${P}_{sh}(t)>{P}_{d-\mathrm{max}}(t)$ × | Load shedding |

Class | Desalination | HES | JO-PCS |
---|---|---|---|

A1 | √ | ||

A2 | √ | ||

A3 | √ | √ | √ |

A4 | √ | √ |

Class (10^{4} × USD/h) | A1 | A2 | A3 |
---|---|---|---|

${C}_{u}$ | 59.2 | 0.6 | 60.4 |

${C}_{m}$ | 6.5 | 150.6 | 64.1 |

${C}_{f}$ | 52.1 | 150.1 | 3.9 |

Class | A1 | A2 | A3 | A4 |
---|---|---|---|---|

Accommodation | 94.4% | 89.2% | 98.2% | 95.2% |

Class (10^{4} × USD/h) | B2 | B3 | C1 | C2 | C3 |
---|---|---|---|---|---|

${C}_{u}$ | 0.58 | 60.7 | 63.5 | 57.9 | 55.5 |

${C}_{m}$ | 138.5 | 62.9 | 66.3 | 67.3 | 69.5 |

${C}_{f}$ | 137.9 | 2.17 | 2.8 | 9.4 | 14.1 |

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**MDPI and ACS Style**

Liu, Z.; Wang, H.; Zhou, B.; Yang, D.; Li, G.; Yang, B.; Xi, C.; Hu, B.
Optimal Operation Strategy for Wind–Hydrogen–Water Power Grids Facing Offshore Wind Power Accommodation. *Sustainability* **2022**, *14*, 6871.
https://doi.org/10.3390/su14116871

**AMA Style**

Liu Z, Wang H, Zhou B, Yang D, Li G, Yang B, Xi C, Hu B.
Optimal Operation Strategy for Wind–Hydrogen–Water Power Grids Facing Offshore Wind Power Accommodation. *Sustainability*. 2022; 14(11):6871.
https://doi.org/10.3390/su14116871

**Chicago/Turabian Style**

Liu, Zhen, He Wang, Bowen Zhou, Dongsheng Yang, Guangdi Li, Bo Yang, Chao Xi, and Bo Hu.
2022. "Optimal Operation Strategy for Wind–Hydrogen–Water Power Grids Facing Offshore Wind Power Accommodation" *Sustainability* 14, no. 11: 6871.
https://doi.org/10.3390/su14116871