A Case Study of Wind Farm Re-Powering ^†

Abstract

The Jhongtun wind farm in the area of Penghu Archipelago is studied. The first part of the Jhongtun wind farm has been operated for 19 years, and the second part has been operated for 15 years. It is about time to evaluate the feasibility of this wind farm’s re-powering process to promote its power production. The evaluated AEPs are 82.65 GWh/year and 107.32 GWh/year. With the current deployment, roughly 12% of the power is provided by the wind farm with a 600 kW wind turbine, and its AEP is 11.46 GWh/year. The newly proposed 3 MW wind turbine has the potential to provide 100% of the power needed for the entire Penghu Archipelago.

1. Introduction

The research related to the exploitation of renewable energy (mainly wind and solar power) has been important in recent years. The traditional way of power production (mainly via fossil fuel) is not attractive due to its impact on the environment and the possibility of losing it entirely in the future. The goal of net zero emission and limiting the temperature change to 1.5 °C was declared in the Conference of the Parties 26 (COP26), who are also promoting the development of renewable energy.

Most of the onshore wind farms are developed by the Taiwan Power Company (TPC) and WPD [1]. The operation of TPC’s wind farms has been ongoing for over 10 years. It is worth to conduct a comprehensive assessment on the benefit/cost of prolonging, decommissioning, and re-powering operational wind farms.

Besides the main island of Taiwan, the wind resources in the Penghu Archipelago are sufficient. About 10−12% of the needed energy was generated by wind turbine systems in the Penghu Archipelago in recent years. Capital investment is largely conducted in the Penghu Archipelago with the goal of 100% green energy. As the wind turbine systems have also been operating for more than 10 years in the Penghu Archipelago, re-powering to upgrade the power generation capacity is beneficial to meet the proposed goal.

The pre-process of a wind resources assessment (WRA) is an important step in acquiring wind power. Besides the technical consideration, the profitability of evaluating wind farms is vital for risk assessment planning. In recent years, larger wind turbines have been proposed, and the effects of complex terrain have to be considered for potential applications.

Wu et al. [2] evaluated the power generated in a wind farm with different heights and layouts by using the LES (large-eddy simulation) model. Eight layouts of turbine arrays were considered with 120 turbines in 30 rows. The aligned and staggered configurations were employed along the wake direction. Results showed that an obvious power reduction (45−65%) was observed for the first 12 turbines. More power was produced for the laterally staggered wind farm due to its better adaptability in the first 6 turbine rows. Meanwhile, the reduction of velocity and turbulence intensity of wake flow was observed for the vertically staggered wind farm configuration.

2. Method and Analysis

The effects of the characteristics of the targeted wind farm, compatibility with the considered wind turbines, price, and reliability of manufacturers need to be considered. The selection of wind turbines is based on the wind condition of the investigated wind farm. The effects of average wind speed and turbulence intensity (TI) must be considered in the assessment. For an area with a higher TI, a wind turbine with stronger robustness and a lower capacity factor is superior. In general, the same type of wind turbine is employed for an entire wind farm. In special cases, two or more different wind turbines are deployed in a wind farm with different hub heights for a maximum power output. It is also suggested that different wind turbines should belong to the same series and be made by the same manufacturer to be considerate of integration and management.

An onsite investigation must be conducted to assess the characteristics of a wind farm. The procedure of micro-siting is indicated in Figure 1. The feasibility of the selected wind turbine on a planned wind farm is evaluated. An adjustment is made for an optimization if needed. With the calculated net annual electricity production (AEP) and load on a wind turbine, the finalized plan of micro-siting can be proposed.

In this study, the evaluation model is developed by the software Wind Atlas Analysis and Application Program (WAsP) [3]. The data from the published wind atlas [4,5] are introduced for a comparison. The calculated AEP is then compared with the experimental value for validation of the proposed WAsP model. With the verified model, several scenarios are considered as possible deployments in the future for wind farm re-powering.

Figure 1. Procedure of micro-siting for a wind farm [6].

Figure 1. Procedure of micro-siting for a wind farm [6].

3. Results and Discussion

In this study, the Jhongtun wind farm is analyzed, as shown in Figure 2 and Figure 3. The Jhongtun wind farm is the second wind farm in Taiwan produced by the TPC. There are eight wind turbines in the Jhongtun wind farm, and their generated power is integrated into the electricity network, providing 12% of the total demand of the Penghu Archipelago.

The first part of the Jhongtun wind farm was developed from May 2000 to December 2011 with four wind turbines produced by Enercon. The second part was developed from January 2004 to April 2005 with the same four wind turbines produced by Enercon. Their total capacity is 4.8 MW. The surrounding area of the Jhongtun wind farm was refurbished into a wind farm by the local government.

The hub height of the wind turbine installed in Jhongtun is 46 m. The statistical performance of the Jhongtun wind farm is shown in Figure 4.

As shown in Figure 4, the overall availability is higher than 85% (except in the case of 2016), with the AEP being larger than 15 GWh/year. Compared to the other operating wind farms produced by the TPC, the performance of the Jhongtun wind farm has recently been good. However, the first part of the Jhongtun wind farm has been operated for 19 years, and the second for 15 years. It is necessary to evaluate the feasibility of the wind farm re-powering process to promote the power production of the Jhongtun wind farm.

The wind resources near the Jhongtun wind farm are the main topic of this study. The wind atlas with a high resolution is evaluated with the proposed WAsP model.

The statistical treatment result of hourly weather data is shown in Figure 5. The annual wind speed at the site is about 8.03 m/s. The contour plot assessed with the proposed WAsP model is shown in Figure 6. The calculated annual wind speed at the height of 80 m is about 9 m/s, and it is comparable with the data from reference [5].

On the website of ref. [5], a simple and quick evaluation can be conducted. Results are shown in

Table 1. Summary of wind farm re-powering.

Specification	Vestas V60	Vestas V90	Vestas V80	Enercon E-70
V_hub (m/s)	7.7	8.1	7.85	7.79
Capacity (kW)	850	1800	2000	2300
Hub height (m)	60	80	67	64
AEP (kWh/y)	3,293,760	7,717,560	6,508,680	6,675,120
CF (%)	44.24	48.94	37.15	33.13
AEPX8(GWh/y)	26.4	61.7	52.1	53.4

with four sets of wind turbines. With the assumption that the new installation of the upgraded wind turbines have the same localization, the gross AEP is obtained by timing the AEP of a single wind turbine, as indicated in the last row of Table 1. The capacity of the considered wind turbines ranges from 850 to 2300 kW. The corresponding AEP of the re-powered wind farm ranged from 26 to 53 GWh/year. The effects of wake flow are not considered in such a simplified evaluation. For the scenario with different positions, heights, and numbers, the performance is evaluated with the proposed WAsP model.

The most feasible plan is to install a new and upgraded wind turbines at the Jhongtun wind farm in the same area via a preliminary discussion with the operator of the plant. The capacities of the considered wind turbine are 2 and 3 MW. The turbine characteristics are introduced into the WAsP model, and the results are shown in Figure 7.

As shown in Figure 7, the effects of wake flow on the Jhongtun wind farm are insignificant. This also indicates that the original design of this wind farm is well organized with regard to the orientation and distance between turbines. Thus, installing a new and upgraded wind turbine in the same position of an existing one would also lead to good results. It is also expected that such a plan leads to a minimal impact on residents. The AEPs are re-calculated with new wind turbines via the proposed WAsP model, and the results are shown in

Table 2. Summary of wind farm re-powering.

Turbine Capacity	Model	Hub Height (m)	AEP (GWh)
600 kW	Enercon E-40	46	11.46 (WAsP) 10.99 (Real, 2016)
2.0 MW	Vestas V90	80	82.65
3.0 MW	Vestas V90	80	107.32

.

As summarized in Table 2, the calculated AEP with the WAsP model is consistent with the true value of power production in 2016, validating the reliability of the proposed model. The wind turbines of Vestas V90 with a capacity of 2 and 3 MW are introduced into the evaluation. The hub heights for both wind turbines are the same and have different power curves. For a wind turbine of 3 MW, the rated power can be produced with the rated wind speed. The evaluated AEPs are 82.65 and 107.32 GWh/year, respectively.

When comparing the current deployment, roughly 12% of the area’s power is provided by the wind farm with a 600 kW wind turbine with an AEP of 11.46 GWh/year; the newly proposed 3 MW wind turbine has the potential to provide 100% of the power needed for the entire Penghu Archipelago considering the yearly average power requirement.

In this study, a numerical model is proposed for the evaluation of the performance of a wind farm. The results are compared with a reference value to validate the proposed model. The AEP of the newly designed wind farm, with different scenarios, is evaluated and discussed. In the future, the economic assessment of the designed wind farm plans can be conducted as a comprehensive evaluation for the re-powering of a wind farm in question.

4. Conclusions

The pre-process of an assessment of wind resources is important in the process of acquiring wind power. Besides technical considerations, the profitability of evaluating a wind farm is also vital for risk assessment planning. In this study, the software Wind Atlas Analysis and Application Program is employed to develop a wind atlas of the investigated wind farm. The calculated AEP is then compared with the experimental value for validation of the proposed WAsP model. With the verified model, several scenarios are considered as possible deployments in the future for wind farm re-powering. Suggestions are provided based on the calculated results.

The Jhongtun wind farm is analyzed in the area of Penghu Archipelago. The Jhongtun wind farm is the second wind farm developed in Taiwan by the TPC. There are eight wind turbines installed in the Jhongtun wind farm, and the generated power is integrated into the electricity network, providing 12% of the total demand of the Penghu Archipelago area.

The overall availability is higher than 85% (except for the case in 2016), with an AEP larger than 15 GWh/year. Compared to the other operating wind farms produced by the TPC, the performance of the Jhongtun wind farm in recent years is good. However, the first part of the Jhongtun wind farm has been operated for 19 years, and the second for 15 years. The evaluation of the feasibility of the wind farm is needed for the re-powering process to promote the power production of the Jhongtun wind farm. The calculated annual wind speed at the height of 80 m is about 9 m/s, which is comparable with the reference data.

The most feasible plan is to install new and upgraded wind turbines in the same positions in the Jhongtun wind farm via a preliminary discussion with the operator of the plant. The capacities of the considered wind turbines are 2 and 3 MW, respectively. Results show that the original design of this wind farm is well organized in terms of the orientation and distance between turbines. Thus, installing new and upgraded wind turbines in the same positions also leads to good results. Such a plan leads to a minimal impact on residents. The calculated AEP with the WAsP model is consistent with the true value of power production in 2016, validating the reliability of the proposed model. The wind turbines produced by Vestas V90 with the capacity of 2 and 3 MW are introduced. The hub heights for both wind turbines are the same, with a different power curve. The evaluated AEPs are 82.65 and 107.32 GWh/year, respectively. When comparing the current deployment, roughly 12% of the power is provided by the wind farm with a 600 kW wind turbine and an AEP of 11.46 GWh/year. The newly proposed 3 MW wind turbine has the potential to provide 100% of the power needed for the entire Penghu Archipelago considering the yearly average power requirement.

In this study, a numerical model is proposed for the evaluation of the performance of a wind farm. The results are compared with a reference value to validate the proposed model. The AEP of the newly designed wind farm, with different scenarios, is evaluated and discussed. In the future, the economic assessment of the designed wind farm plans can be conducted as a comprehensive evaluation for the re-powering of a wind farm in question.