1. Introduction
Energy is a very important factor in ensuring economic and social growth. Resources and the environment are becoming more significant constraints on energy generation as fossil fuels deplete and the threat of climate change intensifies. The major problems that the globe faces today are environmental security, energy resource conservation, and sustainable energy production. Because of population growth and industrialization, power consumption is continually increasing [
1,
2]. The only solution to this catastrophe, to develop sustainable energy, is all over the world [
3]. Wind energy has grown rapidly during the previous two decades, with a global total installed wind power capacity surpassing 733 GW in 2021 [
4]. Because of the unpredictable and stochastic nature of wind, the vast quantity of wind power generation poses significant problems to the steady functioning of power networks. Many hurdles face the integration of LSWF into national transmission systems in many countries, including technical, economic, and environmental considerations [
5,
6].
In 1978, Denmark erected the first onshore multi-megawatt wind turbines [
7], which were largely erected on farmland, allowing for cost-effective joint-use projects near the sea to take benefit of higher coastal wind profiles [
8]. Offshore wind has the potential to be a significant technology because of its greater capacity factors [
9]. Recent advancements in offshore foundations have enabled the deployment of wind turbines in deeper seas, increasing the worldwide offshore wind potential [
10]. At the end of 2019, Germany had the most onshore wind capacity in Europe, with 54 GW, while the UK had the most offshore wind capacity, with 11 GW, followed by Germany (7.6 GW) at the end of 2020 [
11,
12]. After years of study and development, emerging nations have devised novel solutions and improved their grid codes and infrastructure to account for wind risks [
13]. Developing nations, on the other hand, continue to suffer from insufficient grid infrastructure, particularly in terms of LSWF integration.
Resource integration, power quality (PQ) as per grid codes, and reactive power correction, as well as forecasting and the wake effect, have all been investigated as technical, economic, and environmental elements of wind farms (WFs) integration. Such improvements in power would not only improve the financial payback on the development of wind farms but would also improve the competitive pricing of wind power usage [
14]. Repowering a wind farm entails either changing the existing turbines with brand new and more competent ones towards the end of their mean life cycle or installing new, more efficient (20 years) turbines [
15] or the midlife restoration of current degraded turbines [
16] to enhance their energy-generating capacity. Changing the heights of hub-impacted turbines might thus be a potential choice for improving energy production [
17]. Inter-farm wake impact has been studied from a variety of angles, including the distance between WTs and the decrease in wind speed caused by upstream WTs, the proportion of generation deficiency, as well as the overall efficiency of the LSWF [
18,
19,
20,
21]. Additionally, it is confirmed that a rise in overall power production and a reduction in turbulence can be achieved with different hub heights.
To maintain voltage levels under acceptable ranges, severe wind speed changes were resolved in [
22], utilizing active (P) and reactive (Q) power-coordinated controllers established on multi-scale model predictive control theory. Wake effect and wind intermittency amplify PQ concerns in LSWF, resulting in variable output power that affects voltage stability [
23,
24], frequency stability [
24], harmonics [
23], fault ride-through [
25], and power factor [
26]. The incorporation of the LSWF into transmission grids raises the risk of Q compensation issues, which have been studied in a variety of situations for a variety of applications, most notably in FACTS. Reactive power compensators such as capacitor banks and reactor banks are often employed to maintain voltage and PF; however, they emit high-frequency harmonics and severe switching transients [
27]. SVCs provide for real-time Q-control as well as grid voltage and PF stabilization; they lack dampening mechanisms. As a consequence, voltage overshoots may cause a cascade of WTs to trip [
28]. The static synchronous compensator (STATCOM) incorporates a damping mechanism that solves the concerns of SVC, resulting in improved power quality and stability [
29]. UPFC can manage both active and reactive power flows, increasing the system’s stability rapidly and constantly [
30]. Furthermore, in different evaluation scenarios, the static synchronous series compensator (SSSC), UPFC, and STATCOM all result in enhanced Q compensations and have a positive impact on voltage profiles and load flows [
25,
31].
The WTG is created on types such as the doubly-fed induction generator (DFIG), squirrel-cage induction generator (SCIG), and wound rotor synchronous generator (WRSG) [
6,
26,
32]. Because of its low cost and high performance, the DFIG is frequently employed in wind farms [
33,
34]. Wind-based renewable energy sources (RESs) have been increasingly integrated into the national grid and used in the energy market in recent decades [
35]. However, their naturally intermittent nature can pose problems for grid operators in terms of forecasting and meeting load [
36,
37]. Energy storage devices established on hydrogen for WF are one of the alternatives proposed throughout the years to alleviate such issues (ESSs) [
38,
39,
40].
Wind turbines are typically intended to have a 20–25-year service life; several studies have looked at the techno-economic viability of WF, but only a few have gone into the end of their mean life scenarios in-depth [
41,
42,
43]. During the lifespan of the system, the NPV idea is used to correspond to the total present value of cash flow, which includes the initial expense of all components, replacement costs, maintenance expenses, investment costs, and discount costs [
44]. The LCOE is a widely used economic measure for comparing various energy technologies [
45]. The LCOE displays the price of generated energy rather than estimating the prospective profit of an investment, which may be evaluated using other economic measures such as return on investment and internal rate of return (IRR) [
46].
Global warming and climate change have been driven by a rise in the concentration of CO
2 during the previous few years, posing a danger to environmental sustainability [
47]. According to research from the European Commission’s Joint Research Centre (JRC), the burning of fossil fuels accounts for around 90% of total world CO
2 emissions [
48]. Following these matters, governments adopted the Kyoto and Paris climate contracts to limit greenhouse gas production. Pakistan ratified the Paris Agreement on 11 November 2016, nearly precisely one year after submitting its climate pledge, or “nationally determined contribution” (NDC), to the Paris climate summit. Pakistan’s 2025 vision climate and energy framework established objectives for improving at least 32% of renewable energy proportion and improving at least 32.5% of energy efficiency [
49]. Technological innovation helps stabilize the economy and pushes countries to embrace contemporary development plans that reduce CO
2 emissions [
50,
51]. Researchers have assessed the greenhouse gas emissions of wind-generating plants in the United States [
52], Mexico [
53], Jordan [
54], Brazil [
55], Turkey [
56], Japan [
57], and Libya [
58].
By 2020, each member state of the European Union (EU) is expected to have a required 20% renewable energy contribution in their overall energy consumption [
59]. The study in [
24] explored increasing wind penetration in the power pool grid of the southwestern United States to address stability concerns such as constant voltage profiles, under-voltage ride-through capabilities with capacitors banks, and SVC as Q compensators [
60]. According to estimates of industry, about 8 GW of capacity will be built by 2016 and over 18 GW by 2020, supplying around 20% of the UK’s annual power consumption [
61].
There is a significant study vacuum in the examined literature on the effects of growing wind penetration into Pakistan’s wind corridor’s transmission network as well as the related technological, economic, and environmental impact. Pakistan is an interesting case study since it is one of the few countries that has been battling a serious energy problem while only producing modest amounts of electricity. In the next five years, this deficit is expected to worsen, with a 7.5% annual growth rate. Only 34% of the rural residents and the country’s overall residents (63%) have access to electricity [
62,
63]. The energy shortfall caused a 2% drop in GDP. The country’s power consumption is 18,000 MW, whereas the supply is 11,500 MW. The demand and supply disparity is estimated to be approximately 6500 MW [
64]. The purpose of this article is to assess the efficacy of these approaches for suggested WFs in Pakistan in meeting the Grid Codes standards specified by NEPRA. This paper involves creating test systems in MATLAB/Simulink for a 155.4 MW wind farm. The actual characteristics given by the local electric company, Hyderabad Electric Supply Company (HESCO), are used to construct a genuine Pakistani power system. The primary objective of this study is to analyze the technological, economic, and environmental implications of a projected 50 MW WFs on the external grid of Pakistan. The study includes the midlife refurbishment of existing degraded turbines. Furthermore, the comparative research in [
21] was restricted to power quality and compensation concerns using FACTS devices (i.e., capacitor bank, STATCOM, SVC, SSSC, and UPFC). These FACTS devices will need to be evaluated further in terms of their technological, economic, and environmental applications in LSWF in various circumstances.
Due to an uncoordinated design, previous onshore LSWF grid integration studies failed to account for the collective implications of inter-and intra-farm wake effects. Wake effects, wind intermittency, PQ, and Q compensation are all addressed in this study, which gives a technical and cost-effective guideline for FACTS devices. Capacitor banks and FACTS devices such as SVC, STATCOM, SSSC, and UPFC were used with and without renovating HUB height in the second part of their service life to increase power system stability and PQ through improved reactive power regulation with a relative efficiency evaluation. This study considers the wake effect, which occurs when wind speeds drop as it passes from one wind farm to another owing to the energy extracted from the wind. As a result of this occurrence, the energy production of subsequent wind farms drops, simulating a real-time scenario. This study looks at the reduction in carbon footprints after wind turbines have been refurbished and reach the second half of their operational life. The core contributions of the proposed paper are as follows:
LSWF integration in a deficient transmission grid, using Pakistan as a case study.
Performance and cost–benefit analysis of various FACTS devices as a problem-solving solution.
Scenario-based approach for dealing with PQ and Q compensation by appropriate and cost-effective FACTS devices as well as recovering power shortfalls by raising hub height with and without FACTS devices.
A complete techno-economic impact evaluation of LSWF integration in terms of the environment.
2. Energy Analysis
To assess the available wind sources on the location, examining the density of wind energy helps determine how much energy is accessible in the area to transform wind energy into electricity. The formula may be used to calculate the wind energy per unit area (A) in W/m
2.
The wind power can be computed using the Weibull probability density function [
65].
where
is the air density at sea level at 15 °C and 1.225 kg/m
3 atmospheric pressure, f(v) is the probability of wind speed, v is the wind velocity, and
k is the shape and scale parameters.
is the gamma function.
The following formula is used to get the adjusted monthly air density (kg/m
3):
where
is the monthly average temperature of air in (K°),
is the monthly average pressure in Pascals, and
represents dry air gas constant. The density of the air will decrease as height and temperature increase [
66].
By using (2) and (3) the wind energy density
E for a given time
T may be computed using (4).
The following formula may be used to assess the annual generation of a wind power system:
P(x) is the probability of a wind speed of (m/s) occurring each year, as defined by
where
denotes the form factor defined by local meteorological circumstances, and
denotes the scale factor defined by wind speed.
Temperature, pressure, and other losses are considered when calculating the restructured yearly generation
(kWh).
where
is the air pressure (kPa) of the wind turbine at the location,
is the standard atmospheric pressure (101.3 kPa),
is the temperature (K) of the wind turbine at the location, and
is the standard absolute temperature (288.1 K),
represents the array loss factor (valued at 3%),
represents the airfoil loss factor (valued at 2%),
represents the miscellaneous loss factor (valued at 2%), and
represents the downtime loss factor (valued at 2%).
6. Methodology
The proposed methodology seeks to fill in the gaps in prior research on onshore LSWF grid integration studies. In recent research [
21], a noteworthy attempt was made to handle PQ and Q compensation difficulties with capacitor banks and different (FACTS) devices for a specific WF. However, the research did not consider the LSWF’s techno-economic analysis or environmental effect. The objective of the comparative performance evaluation is to address LSWF repowering owing to wake effects as well as a cost–benefit analysis of PQ improving system stability using capacitor banks and FACTS devices such as SVC, STATCOM, SSSC, and UPFC. On a technological level, the approach is expected to give a beneficial midterm solution for expensive long-term TN reinforcements. The suggested technique is depicted in
Figure 5 is a flow chart with three cases and with respective scenarios.
The test case (FFCEL) in this study was initiated in 2013 and has a project life of 20 years. A project’s first half-life is likely to finish in 2023. In this work, a detailed techno-economic analysis of the first half-life is performed to evaluate the economic losses caused by a deficiency in PQ due to the wake effect. After the refurbishment due to wake, a techno-economic study of the second half-life is performed for a more comprehensive evaluation designed to improve power quality and reactive power compensation difficulties related to LSWF integration in poor transmission networks. The capacity of the compensating device is set to 30 MVAR for the MATLAB simulation and cost assessment, as stated in [
80]. The SAM is utilized in this research to examine the economic aspects. The SAM needed data on wind speed, temperature, and the atmospheric pressure of the precise site where the WF is placed for a complete analysis. These data were gathered from a meteorological station in Jhampir City.
6.1. Case-1: Base Case Scenarios Assessment
Case-1 comprised scenarios with and without wake effects. The created base scenario (Case-1) was simulated to examine the impact of LSWF integration on TN across key PQ measures. Case-1 with scenario 2 did not involve any Q compensation device integrated into the system.
Scenario 1: Techno-economic impact analysis of the ideal base without wake effects and seasonal fluctuations. This scenario discusses the documentation FFCEL has submitted to NEPRA.
Scenario 2: Techno-economic impact analysis of the base scenario with wake effects and no compensation device. This scenario discusses the penalty incurred for failing to adhere to grid codes.
6.2. Case-2: VAR Device-Based Scenario Assessment
Case-2 assesses the Q/VAR compensation device assessment and is comprised of five scenarios, as follows:
Scenario 3: Techno-economic impact analysis considering SVC integration with inter-farm wake effects. This scenario discusses SVCs installed throughout the duration of the plant’s useful life (20 years).
Scenario 4: Techno-economic impact analysis considering capacitor bank integration with inter-farm wake effects. This scenario discusses SVCs installed for the first 10 years, and a capacitor bank is replaced beyond the half-life.
Scenario 5: Techno-economic impact analysis considering STATCOM integration with inter-farm wake effects. This scenario discusses SVCs installed for the first 10 years, and a STATCOM is replaced beyond the half-life.
Scenario 6: Techno-economic impact analysis considering SSSC integration with inter-farm wake effects. This scenario discusses SVCs installed for the first 10 years, and an SSSC is replaced beyond the half-life.
Scenario 7: Techno-economic impact analysis considering UPFC integration with inter-farm wake effects. This scenario discusses SVCs installed for the first 10 years, and a UPFC is replaced beyond the half-life.
6.3. Case-3: VAR Devices and Heightening the Hubs-Based Scenario Assessment
Case-3 assesses the Q/VAR compensation device assessment with and increasing the height of the HUB and is comprised of five scenarios, as follows:
Scenario 8: Techno-economic impact analysis considering SVC integration with the heightening effects of the hub. This scenario discusses the SVCs installed throughout the duration of the plant’s useful life (20 years) and increasing the height of the HUB beyond the half-life.
Scenario 9: Techno-economic impact analysis considering capacitor bank integration with the heightening effects of the hub. This scenario discusses the SVCs installed for the first 10 years, a capacitor bank being replaced, and increasing the height of the HUB beyond the half-life.
Scenario 10: Techno-economic impact analysis considering STATCOM integration with the heightening effects of the hub. This scenario discusses the SVCs installed for the first 10 years, a STATCOM being replaced, and increasing the height of the HUB beyond the half-life.
Scenario 11: Techno-economic impact analysis considering SSSC integration with the heightening effects of the hub. This scenario discusses the SVCs installed for the first 10 years, an SSSC being replaced, and increasing the height of the HUB beyond the half-life.
Scenario 12: Techno-economic impact analysis considering UPFC integration with the heightening effects of the hub. This scenario discusses the SVCs installed for the first 10 years, a UPFC being replaced, and increasing the height of the HUB beyond the half-life.
6.4. Environmental Analysis
The environmental analysis considers all scenarios to determine the most efficient scenario in terms of environmental and GHG emission reduction.
9. Conclusions
MATLAB and SAM software is used to perform a comparative study of the concerns linked to LSWFs in a larger context for Pakistan. A complete technical, economic, and environmental study has been determined based on the energy deficit created by the wake effect power pumped into the grid, which is evaluated to imitate real-time circumstances, payback period, and GHG emission reduction. The wake causes a considerable active power loss as well as enhanced Q absorption. For a maximum wake of 32%, FFCEL had a P deficit of 10.65 MW and a Q deficit of +0.174 MVAR owing to wake impact. Furthermore, confirmation of the simulation findings with real FFCEL to NEPRA determinations reveals that the actual data closely match the simulation results.
A specific case study was conducted in which ideal scenario 1 was compared to both Case-2 and Case-3 eventualities. We conducted a performance investigation with several compensation devices to determine the optimal compensation device for enhancing PQ and PS parameters with and without repowering the WF during the wake while raising the WT hub height from 80 to 100 m. A significant quantity of P repowering was found at the highest recuperation of deficiencies, owing to a wake of up to 48%. Our primary goal was to create a device that aids in Q repowering while maintaining V, F, Z, and PF at PCC at the closest nominal number. It is determined that among the compensating devices considered, the UPFC is the most cost-effective and optimal for Q repowering while retaining PS parameters at PCC. As a result, the UPFC kept V up to 1.002 pu, suppressing frequency transients in the 49.88–50.17 Hz region and preventing any resonance while keeping the power factor within acceptable limits.
According to our research, scenario 12 has the largest yearly generation after repowering and the shortest payback time, followed by scenarios 10 and 7. In contrast, scenario 6 has the worst performance, with the lowest yearly generation and the longest payback time after repowering. The study results demonstrate that the proposed scenarios for the renovation of wake-affected WFs linked to a weak grid are possible. Furthermore, repowering a planned system results in a large decrease in CO2 emissions, which contributes to a greener environment. The research described in this paper will aid policymakers and financiers in finding appropriate repowering approaches for maximizing the return on investment in large-scale projects in Pakistan’s industrial sector.