Keywords

1 Introduction

Offshore wind integration plays a crucial role to determine technical boundaries and preliminary economic assessment of integration options [1]. Due to the variability and intermittency of this renewable source, several aspects including the possibility to ensure generation capacity, and stable system operation need to be analyzed thoroughly.

This study aims to explore the potential of offshore wind generation in Vietnam and to provide a preliminary assessment on system adequacy with the given power development plan to help policymakers sharping a roadmap for offshore wind development. In particular, this study investigates the penetration levels of offshore wind capacity while addressing wind integration aspects including generation adequacy and transmission adequacy. A focus will be on the period from now till 2030 to provide an insight into how much offshore wind capacity the grid can accommodate based on the current development of the infrastructure.

2 Methods and Models

2.1 Offshore Wind Potential

Elements for preliminary assessment of strategic zones for offshore wind development are based on the UK methodology [2] and recent research about potential offshore wind resources in Vietnam [3], which assessed the technical resource based on wind speed and variation, ports, and synchronous power plants. This assessment considers oil and gas infrastructures, shipping routes, and Particularly Sensitive Sea Areas to be excluded from the technical resources areas. The spatial distribution of the annual mean wind power density at 100 m height and capacity factor was obtained by using numerical simulations with Weather Research and Forecasting (WRF) model at a 10-km resolution for 10 years (2006–2015) and validated with two observational data sets [4]: (i) wind data observed for 10 years 2006–2015 at six ground-based weather stations located in islands off the coast of Vietnam and run by the Vietnam Center of Hydro-Meteorological Data; and (ii) the QuikSCAT (Quick Scatterometer) data. QuikSCAT is NASA’s Earth observation satellite carrying the sea winds scatterometer [5, 6]. The reference turbine is Vestas V164-8.0 with a rated power of 8 MW, a blade length of 80 m, and an approximate hub height of 105 m [4].

2.2 Grid Integration Assessment

The method used in this study refers to the recommended practices from the International Energy Agency (IEA) – Wind expert group [1] with an adaptation suit the scope of the study. The load demand is adopted from the demand scenarios developed in the Power Development Plan 7 Revised (PDPR7), recently updated directives (58/BC-BCT in 2019, and 724/BCT-DL in 2020), as well as other studies like the one published by the World Bank [7]. The transmission expansion plan module includes mainly 500 and 220 kV transmission lines and substations. The offshore wind generation module includes offshore wind capacity fitting into the national energy mix scenarios and associated transmission possibilities to connect to the (nearest) onshore substations.

To analyze generation adequacy with various penetration levels of offshore wind, this study developed energy mix models for Vietnam’s power system in 2025 and 2030 accordingly, including information reported in PDPR7 and document No. 2491/BCT-DL. DIgSILENT PowerFactory is used as the simulation platform that can integrate the energy mix model along with stochastic wind models to analyze the impact of offshore wind uncertainty in terms of Loss of Load Probability (LOLP). With the same simulation platform, this study developed further a network model simulating current Vietnam’s 500 kV and 220 kV grids and its expansion planned in 2025 and 2030 according to PDPR7 and critical update from Document No. 1968/TTr-BCT (2020) and 2491/BCT-DL (2020) to accommodate the high renewable installed capacity recently, i.e. transmission adequacy.

To support future integration of offshore wind, some assumptions have been made:

  • Network models: Integrating a complete 500 kV grid model and some important 220 kV grids.

  • Generation models are based on the high generation mix scenario from the PDPR7 with the recent update regarding the commissioning progresses of some important power plants.

    • Integrating detailed models of important conventional generators (>600 MW) and large-scale solar PV and onshore wind installations (>100 MW);

    • Aggregating smaller renewable resources in provinces to the equivalent models;

    • Simulating offshore wind farms (OWFs) with the standard platform of 600 MW for the simulation with various transmission options in different voltage levels, i.e. 220 kV or 500 kV, and transmission technologies, i.e. High-Voltage Alternative Current (HVAC) or High-Voltage Direct Current (HVDC).

  • Load models: Scaling load demand in the North, Central, and South based on given scenarios developed from PDPR7 with the recent update from Ministry of Industry and Trade (MOIT) as in Table 1.

  • Simulation cases:

    • Simulating the “worst-case” scenarios only (Pmax scenario at the end of the dry season when the demand of the South is at peak and electricity generation from main hydropower plants in the North is limited).

    • Not taking voltage violations as the limit of calculation.

    • Not taking contingency study (n − 1) into account.

Table 1. Load demand scenarios in regions
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Table 2. Estimation of residual capacity for the onshore transmission to OW resource zones
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The residual capacity of the onshore grid is estimated to determine which resource zones might be exploited first (Table 2). The residual capacity is based on the maximum loading of the existing near 500 kV substations to the resource zones and the grid expansion capacity reflected by new planned 500 kV substations in the region. The estimation is based on the thermal rating of the grid assets, i.e. transformer rating, according to the PDPR7. The contingency calculation (n − 1) and stability analysis, which are not taken into account in this study, might lead to lower levels of the residual capacity.

3 Result and Discussions

3.1 Offshore Wind Zonation

The Energy Sector Management Assistance Program (ESMAP) [8] estimates the country’s total technical potential within 200 km from the shoreline is 261 GW for fixed wind and 214 GW for floating wind. The offshore wind potential and distribution in the ESMAP report agree well with those in [4] that verify the potential of offshore wind in Vietnam.

Based on the potential and variation of offshore wind energy in [4] and [8], and consultations with experts, the offshore wind resource in Vietnam is proposed to be divided into four zones as in Fig. 1 [3].

Fig. 1.
figure 1

Location of major ports and container terminals and proposed four zones for evaluation of offshore wind technical resources in Vietnam.

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Zone 1 is the region with the coldest winter and consisting of eight provincial sea areas from Quang Ninh to Ha Tinh. In the northern area of this Zone (in the Gulf of Tonkin), there is a sizeable area with a technical potential for fixed foundation wind of 88 GW and an area with a technical potential of 39 GW for floating foundation [8]. Zone 2, where the winter is moderately cold, has a sea area of seven coastal provinces from Quang Binh to Binh Dinh and marginal potential for offshore wind. Zone 3, comprising of five provincial seas from Phu Yen to Ba Ria – Vung Tau, is less affected by the winter monsoon. Zone 4 is the sea region from Ho Chi Minh city to Kien Giang, least affected by the winter [3]. Off the coast of Binh Thuan and Ninh Thuan, the mean wind speeds exceed 10 m/s. This area then extends south and, with average wind speeds falling to 7 m/s the area extends up to 125 km from shore and covers both Zones 3 and 4. In water depths, less than 50 m, this area alone has a technical potential for 165 GW of fixed offshore wind [8]. Outside there is a very large area below 1,000 m water depth and running from the South to the Central region (south of Hue), covering a part of Zone 2, Zone 3, and Zone 4, with a technical potential of 175 GW for floating foundation [8].

The major seaports and container terminals with channel depths greater than 10 m and maximum vessel size acceptable of 30,000 Dead Weight Tonnage (DWT) all located in Zone 1, the southern of Zone 2, 3 and 4 [3]. Three container ports in Vietnam: Hai Phong and Dinh Vu in Zone 1, and Tan Cang Sai Gon in Zone 4 are listed in the top 20 of Southeast Asia [9]. Especially, the Van Phong International Transshipment Terminal is being developed in Van Phong Bay, Khanh Hoa of Zone 3, which has a depth range of 15–20 m, a large area, and expects to accept the maximum vessel size of 9,000 TEUs (Twenty-foot Equivalent Units) or approximately 120,000 DWT. Considering the important information including draft/channel depth, vessel accepted and the available area, the port facilities in Zone 3 are most favorable to offshore wind farm development. Those in Zone 1 and 4 are also in good capacity.

3.2 Generation Adequacy – Loss of Load Probability

LOLP Calculation

Within the scope of our study, we took certain assumptions from the PDPR7 and calculate the LOLP values without having complete data (even the historical data for dispatchable generation units is needed to develop the stochastic models). It is assumed that the additional offshore wind capacity aims to cover 10% of the thermal plant capacity to be added in the corresponding period 2020–2025 and 2025–2030. The generation adequacy analysis considers the fixed demand level according to the load scenarios presented in Table 2 for the stochastic assessment. To calculate the above LOLP results, a Monte Carlo simulation is conducted, taking the stochastic wind models into account. The wind penetration levels were added to Vietnam’s generation mix in 2025 and 2030 scenarios.

Fig. 2.
figure 2

Impact of offshore wind capacity on the Loss of Load Probability.

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Figure 2 shows the results of LOLPs according to the increase in offshore wind penetration levels in 2025 and 2030. This study takes the import capacity for the generation mix high case scenario reported in document No. 2491/BCT-DL as the indication of the expected LOLP value. It was planned that the import capacity is set at the levels of 2.9% in 2025 and 3.4% in 2030 accordingly. As it can be seen from the calculation results, a penetration level of above 3 GW offshore wind can secure the 2.9% level of LOLP in 2025. To retain LOLP at the level of 3.4% in 2030, the offshore wind capacity is expected to be above 10,5 GW. In addition, the spatial diversity of wind resource zones would likely have higher effects on securing power supply, i.e. decreasing LOLP levels.

We find out that 10.5 GW of offshore wind in 2030, spreading across four zones, makes an adequate reliable power source. More precisely, we simulated the LOLP to be 3.4%, which compares to the reliability level expected from imported electricity. To have more insight into the wind contribution to power demand adequacy, extensive measurement-based data crossing the wide geographic areas coupling with available flexibility resources is required [10].

3.3 Transmission Adequacy

This section takes a step further from the estimation of the onshore transmission residual capacity summarized in Table 2 to calculate possibilities for connecting around 10 GW offshore wind in 2030 as specified in the previous section. Based on the wind resource potential and transmission expansion plan, three main stages for offshore wind integration to reach 10 GW in 2030 are proposed, as follows:

  • Integrating the first 100 × 6 MW OWF from the southern part of Zone 3 (Binh Thuan sea) by 2023 (see Fig. 3 left frame);

  • Expanding six additional OWFs in the South (mainly Zone 3 and partially Zone 4) by 2025 with the first VSC-HVDC transmission line (see Fig. 3 middle frame);

  • Adding ten additional OWFs over the period 2025–2030, half of them in the North (Zone 1) connecting via the second VSC-HVDC transmission line (Fig. 3, right).

Based on the simulated results, the maximum offshore wind capacity that the grid can absorb is about 4.2 GW until 2025 (Table 3), coming mainly from Zone 3 and partially Zone 4. Besides the high potential of wind resources in these zones, the high load demand in the South urges for having higher regional wind penetration.

Figure 3 left and middle frames show snapshots of electricity flows between main regions in 2023 and 2025. The simulations are calculated with the worst-case scenario during peak periods in April-May when the demand from the South is max while having high production from renewable sources, including offshore wind generation. In 2023, the major part from 3 GW solar PV in Quy Nhon, Ninh Thuan, Binh Thuan together with the first OWF platform (100 × 6 MW) will be delivered to the central load in the South via 500 kV Song May and Tan Uyen substations. Another 1.5 GW flow comes from the Highland areas which have a high amount of small hydropower plants together with solar PV and onshore wind. By 2025, five additional OWF platforms can be added to ensure sufficient power supply for the South and Central areas. A significant surplus of electricity (especially from onshore wind collected from Quang Tri, Ha Tinh, and Nghe An) will be delivered back to the North that approaches the transmission limit.

The calculation shows that about 6 GW capacity of offshore wind can be integrated from mainly Zone 1 (3 GW) and partially Zone 3 (1.2 GW) and Zone 4 (1.8 GW) (Table 3) in the 2026–2030 period. This possible development plan considers the residual transmission capacity of the onshore grids and the urgency to meet the peak load demand in the regions concerned. After 2025, the peak load demand in the North will increase and the regional generation capacity will not be sufficient, especially if commissioning new thermal plants is delayed. As can be seen from Fig. 3 right frame, exploiting offshore wind resources from Zone 1 earlier in this period would contribute to reduce the risk of not having generation adequacy for the North and relieve the transmission stress of the Central – North interconnection. A total of 10.2 GW offshore wind capacity can be integrated from 2020–2030.

Fig. 3.
figure 3

Load flow snapshot in 2023, 2025, and 2030 (from left to right) - Cases of high renewable sources including max capacity from OWFs.

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Table 3. A possible development plan of offshore wind in the period 2023–2030
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4 Conclusions

This study explores the options for zonation and grid integration to 2030. Four offshore wind resource zones have been identified with the highest potential in the sea from Phu Yen to Ba Ria – Vung Tau.

The grid integration simulations shows that in the period 2023–2025, some first fixed-bottom OWFs could be developed in Binh Thuan, Ba Ria – Vung Tau, and Bac Lieu sea with a total capacity of 4.2 GW to meet the peak load demand in the South. In the period 2025–2030, the development of OWFs near the coastline in the North with a total capacity of 3 GW can play an important role to relieve inter-region transmission stress. This together with further development of OWFs along with the coastlines of the South Central and the South can add up to 10.2 GW. We find that 10.5 GW of offshore wind in 2030, spreading across four zones, makes an adequate reliable power source. We simulated the Loss of Load Probability to be 3.4%, which compares to the reliability level expected from imported electricity.

More analyses are needed to explore the robustness of alternative infrastructure plan, because this study’s result appears sensitive to yet-to-be-decided parameters, such as feed-in-tariffs (FITs) for solar PV and wind. Still, this study confirms that offshore wind can contribute to the energy transition in Vietnam. It is time to start including this technology in Vietnam’s power development plans.