**1. Introduction**

With the development of the economy, fossil energy is decreasing and environmental pollution is increasing day by day. In order to alleviate the pressure of energy shortages and environmental deterioration, various countries are committed to the development and utilization of clean energy. The proposal of the carbon peaking and carbon neutrality goals demonstrates China's determination to actively respond to climate change and achieve high-quality economic development. To further accelerate the development and utilization of non-fossil energy, especially new energy represented by wind and solar energy, is an important measure to achieve the arduous task of the carbon peaking and carbon neutrality goals.

Compared with other clean energy sources, wind power has greater development advantages and competitive potential. In the last 10 years, global onshore wind power has achieved rapid development, and the development of onshore wind power in some countries has become saturated. At present, there is an urgent demand for offshore wind power development and application all over the world [1]. China's offshore wind power has great development potential and good development prospects. To develop a high-quality offshore wind power industry and accelerate the development of offshore wind power from near-sea to deep-sea to far-sea, promoting the large-scale, intensive and sustainable development of offshore wind power is an important support to promote the adjustment of China's energy structure and achieve the carbon peaking and carbon neutrality goals [2]. Compared with onshore wind power, offshore wind power has three outstanding characteristics: (1) The offshore wind energy resources in the southeast coastal areas of China are

**Citation:** Yu, H.; Yang, X.; Chen, H.; Lou, S.; Lin, Y. Energy Storage Capacity Planning Method for Improving Offshore Wind Power Consumption. *Sustainability* **2022**, *14*, 14589. https://doi.org/10.3390/ su142114589

Academic Editors: Luis Hernández-Callejo, Jesús Armando Aguilar Jiménez and Carlos Meza Benavides

Received: 7 October 2022 Accepted: 4 November 2022 Published: 6 November 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

abundant and close to the power load center, which is convenient for the consumption and utilization of the power grid. However, transmission cables need to be configured; (2) The overall output level of offshore wind farms is higher, with higher annual power generation utilization hours; (3) The transmission mode of offshore wind power is more flexible and does not need to occupy land resources.

The cost of transmission cable is high, and it is often difficult to send it complete. On the one hand, offshore wind power connected to the grid for operation will cause abandoned wind due to transmission congestion in part of the overall output. On the other hand, it will bring severe challenges to the peak regulation of the power grid. The lack of peak regulation capacity of the power grid leads to abandoned wind. The installation of an energy storage system is flexible, and the configuration of energy storage for an offshore wind power station can promote it to become a high-quality power supply. The source-side energy storage mainly works out a charge and discharge scheme to stabilize the fluctuation of its output power to achieve a higher proportion of offshore wind power consumption. However, there are some problems, such as the high cost of the energy storage configuration, the mismatch between energy storage technology and offshore applications, and so on. The improper use of energy storage equipment limits the appropriate absorption of wind power and increases the cost. The optimal allocation of energy storage capacity has always attracted much attention, and domestic and foreign researchers have carried out a lot of research on this issue.

The current research is mainly focused on energy storage capacity planning [3–6] and wind–storage operation optimization [7–10], and there is little research in [11,12] considering the interaction between the energy storage system planning and operation at the same time; a two-layer collaborative optimization model for energy storage capacity planning and operation is proposed. Starting from the wind power delivery channel, based on multi-stage stochastic programming and sequential Monte Carlo simulation, an optimal energy storage allocation method for wind farm stations considering energy storage life loss and delivery channels is proposed in [13]. Based on the characteristics of the wind farm, references [14–16] determined the energy storage allocation method based on a wind power prediction error, wind farm generation curve deviation correction, and wind farm output smoothing, respectively, but the work done in these references does not take into account the influence of the power grid peak regulation capacity. References [17–19] put forward the optimal allocation method of energy storage from the point of view of the influence of insufficient peak regulation capacity of grid-connected wind power, so that the power grid has a more downward regulation capacity to accept wind power, but only the performance of thermal power peak regulation is considered. The work done in these references does not consider the comprehensive effects of many types of power sources.

Reference [20] studies the feasibility and rationality of wind–storage combined power generation under current market conditions from the point of view of a technical and economic evaluation, which provides a reference for an optimal allocation in a wind– storage combined power generation system. References [21,22] fully consider the operation characteristics of the energy storage system and determine the energy storage allocation method based on the dynamic adjustment of charge state and a variable life model. The joint planning model of energy storage and the transmission network for improving the receptive capacity of wind power is established in [23], but the focus is on the power capacity of the energy storage, and the energy capacity is not mentioned. Based on the characteristics of offshore wind power, an optimal scheduling method for the joint operation of offshore wind power and seawater-pumped storage power stations is proposed in [24], but the work done in the reference only mentions optimization and does not involve the optimal allocation of offshore energy storage units. There is little research on offshore wind power and energy storage. A physical model combining offshore wind power generation with an underwater compressed air energy storage system was established in [25]. In [26], an optimal energy storage allocation model was constructed based on the improved scene clustering algorithm under the application scenario of smoothing the offshore wind power

output fluctuation. A new multi-objective programming framework is proposed in [27] to determine the optimal capacity of battery energy storage systems in the cooperative operation of large offshore wind farms and battery energy storage systems. The cited references present the different technologies of energy storage. Their characteristics are shown in Table 1.


**Table 1.** The characteristics of common energy storage types.

Pumped hydro storage is the most reliable, economical, large capacity and most mature energy storage device in the power system. It has the advantages of flexible startup, fast climbing speed, peak cutting and valley filling, and it is an important part of the development of new energy. However, it depends on geographical conditions and needs high hydropower stations. It has a great impact on geography and terrain, and the construction cost is high. Large-scale battery energy storage systems can be used for power grid energy management and peak regulation, and the technology is quite mature. Moreover, it has a fast load response and daily regulation ability, so it is suitable for large-scale wind power generation.

This paper presents two innovative points: based on the idea of combining planning and operation through operation simulation, an optimization model of offshore wind energy storage capacity planning is established, which aims to minimize the total national economic expenditure of the system. It considers the offshore wind power transmission channel constraint and uses the abandoned wind rate below a certain level as a strict constraint. Further, based on 24 scenarios for the optimization model and the contour line of annual cost and the contour line of abandoned wind rate, an energy storage capacity planning method for improving offshore wind power consumption is proposed, which can obtain a reasonable economic and optimal energy storage configuration scheme quickly.

The rest of the paper is organized as follows. The optimization model of offshore wind energy storage capacity planning is established and the principal block diagram of the planning and optimization process is shown in Section 2. The case study and data analysis for the optimization model for offshore wind energy storage capacity planning are carried out and an energy storage capacity planning method for improving offshore wind power consumption is proposed in Section 3. Finally, Section 4 concludes the paper.

#### **2. Model and Methods**

At present, electrochemical energy storage systems are the most widely used technology on the source side of offshore wind farms. Small-scale battery storage systems are generally used in ships and offshore platforms, while large-scale battery storage systems are mainly used in islands and coastal areas. This paper takes electrochemical energy storage systems as an example to conduct relevant research on the energy storage technology of offshore wind farms [28–33].

The electrochemical energy storage for offshore wind farms is required to meet the applicable conditions of environmental temperature; it is not easy to maintain the working temperature of high-temperature sodium-sulfur batteries and liquid metal batteries in the sea environment. It is required that the mechanical moving parts of the energy storage device should be as few as possible, so as not to be damaged by corrosion or wave impact in the marine environment. The liquid flow battery should not be adopted because of its electrode characteristics with many such parts. It is required that the leakage of battery materials has no obvious harm to prevent pollution of the marine environment, so lead–acid batteries, lithium-ion batteries, seawater batteries and silver–zinc batteries can be used for offshore wind farms [34]. Offshore energy storage needs to be resistant to wind and wave impact, seawater immersion, seawater corrosion, and so on. Therefore, developing offshore energy storage systems tends to be more costly than developing onshore energy storage systems. It is necessary to configure suitable offshore energy storage capacities for offshore wind power to avoid excessive costs.
