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Wind and Solar Curtailment
Abstract and Figures
High penetrations of wind and solar generation on power systems are resulting in increasing curtailment. Wind and solar integration studies also predict increased curtailment as penetration levels grow. This paper examines experiences with curtailment on the bulk power system in countries around the world. It discusses how much curtailment is occurring, how it is occurring, why it is occurring and what is being done to reduce curtailment. This summary is produced as part of the International Energy Agency Wind Task 25 on Design and Operation of Power Systems with Large Amounts of Wind Power.
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... It can also be used to allow PV systems to generate at reduced levels so that it can ramp up quickly to balance the system [4]. The amount of curtailed power, duration, and method of curtailment are discussed through examples of several countries that apply this process in different manners [5]. Power curtailment is crucial for the installation of different scales of PV systems. ...
Active power control of the photovoltaic (PV) power generation system is a promising solution to regulate frequency fluctuation in a power system with high penetration of renewable energy. This paper proposes an autonomous active power control of a small-scale PV system for supporting the inertial response of synchronous generators and power-frequency control. In the proposed control approach, an effective grid frequency regulation scheme is realized using slow- and fast-frequency responses. A low-pass filter based frequency measurement is used for slow-frequency response, while direct frequency measurement is used for fast-frequency response. The designed dual droop characteristic-based control is shaped to achieve a smooth transition between slow- and fast-frequency responses. The performance of the proposed control approach is demonstrated for serious disturbance scenarios, i. e., considerable power-load imbalance and generation trip. In the power-load imbalance test scenario, the proposed control approach works properly within the normal frequency deviation region even when the frequency deviation exceeds that region occasionally. In the generation trip test, the frequency deviation is mitigated quickly, and the employed droop control is smoothly transferred from the slow- to fast-frequency responses.
... 3,5,9 Curtailment of renewables results from oversupply and a lack of system flexibility, which can include transmission congestion, minimum generation levels of thermal generators or hydropower, or back-feeding in the distribution system. [10][11][12][13][14] The large quantity of economic curtailment that is observed in grid integration studies with very high VRE penetration levels and is also suggested by empirical evidence reflects a possible paradigm shift in how future power systems will operate. Curtailment might be a ''new normal'' for everyday operations, 4,15 as the ability to curtail output from VRE sources is an important source of flexibility by helping to maintain supply-and-demand balance and system frequency. ...
Rising penetrations of variable renewable energy (VRE) in power systems are expected to increase the curtailment of these resources because of oversupply and operational constraints. We evaluate the effect on curtailment from various flexibility approaches, including storage, thermal generator flexibility, operating reserve eligibility rules, transmission constraints, and temporal resolution, by using a highly resolved realistic system. Results reveal two aspects of a curtailment paradox as the system evolves to higher solar penetration levels. First, thermal generator parameters, especially in restricting minimum operating levels and ramp rates, affect VRE curtailment more in mid-PV penetration levels (∼25%–40%) but much less at lower (∼20%) or higher (∼45%) PV penetration levels. Second, although allowing VRE and storage to provide operating reserve results in significant operating costs and curtailment benefits, the price suppression effect from these resources reduces incentives for PV to provide operating reserves with curtailed energy.
... Additionally, increasing penetration levels of VRE can lead power systems to encounter operational constraints, resulting in system operators accepting less VRE than is available [10]. Thus, high penetrations of VRE sources on power systems result in increasing VRE curtailment, and infrastructure and operational changes to power systems may be required [11]. VRE curtailment is therefore defined as the act of reducing the supply from VRE sources to the power grid. ...
Jeju Island announced the “Carbon Free Island (CFI) Plan by 2030” in 2012. This plan aims to replace conventional generators with distributed energy resources (DERs) up to a level of 70% by 2030. Akin to Jeju Island, as DERs have been expanded in islanded power systems, variable renewable energy (VRE) has become a significant component of DERs. However, VRE curtailment can occur to meet power balance, and VRE curtailment generally causes energy waste and low efficiency, so it should be minimized. This paper first presents a systematic procedure for estimating the annual VRE curtailment for the stable operation of the islanded power systems. In this procedure, the VRE curtailment is estimated based on the power demand, the grid interconnection, the capacity factor of VRE, and conventional generators in the base year. Next, through the analysis of the hourly net load profile for the year in which the VRE curtailment is expected to occur, a procedure was proposed to find the season and hour when VRE curtailment occurs the most. It could be applied to revised Time-of-Use (ToU) tariff rates as the most cost-effective mitigation method of VRE curtailment on the retail market-side. Finally, price elasticity of electricity demand was presented for applying the revised ToU tariff rate scenarios in a specific season and hour, which found that VRE curtailment occurred the most. Considering self- and cross-price elasticity of electricity, revised ToU tariff rate scenarios were used in a case study on Jeju Island. Eventually, it was confirmed that VRE curtailment could be mitigated when the revised ToU tariff rates were applied, considering the price elasticity of demand.
... It provides an energy arbitrage opportunity as well as a hedge against the intermittency of the renewable energy generation. It also helps achieve a more effective utilization of the renewable sources by reducing the amount of curtailment (i.e., the difference between the potentially available energy and the actually generated energy) (Lew et al. 2013 andWu andKapuscinski 2013). ...
We study the energy generation and storage problem for a hybrid energy system that includes a wind farm and a pumped hydro energy storage (PHES) facility with two connected reservoirs. The operator decides in real-time how much water to pump or release in the PHES facility, how much energy to generate in the wind farm, and how much energy to buy or sell. We model this problem as a Markov decision process (MDP) under uncertainty in streamflow rate, wind speed, and electricity price. We establish the optimality of a state-dependent threshold policy under positive prices: The state space of the problem can be partitioned into several disjoint domains, each associated with a different action type, such that it is optimal to bring the water level of the upper reservoir to a different state-dependent target level in each domain. Once the optimal amount of water that should be pumped or released is found, we can immediately derive the optimal amount of wind energy that should be generated. Leveraging our structural results, we construct and test three heuristic solution methods for data-calibrated instances in which the price can also be negative: policy-approximation, profit-approximation, and problem-approximation methods. While the policy-approximation method provides virtually optimal solutions about four times faster than the standard dynamic programming algorithm, the problem-approximation method yields instantaneous solutions with an average optimality gap of 3.35%. The existence of natural inflow in the upper reservoir - the major source of structural complexity - improves the profits by 19.9% on average.
In this paper, an hourly dispatch model was developed to analyze the system balancing and wind power curtailment challenges in the future of the Ethiopian electric power grid system. The developed model was validated using historical data and was used for the analysis of the grid system in 2030 with different scenarios. The model was used to examine the impacts of transmission capacity, regulation reserve requirement, and daily minimum generation of hydropower for irrigation with three cases of wind annual energy share of 14.5%, 17.8%, and 25.2%. Thus, the curtailment was found to be below 0.2%, 1.1%, and 9.8% for each case, respectively. The cost of wind energy increases in proportion to the percentage of curtailment and the increase in transmission line capacity. Reducing the minimum hydropower generation results in smaller wind power curtailment and better generation–consumption balancing.
As the share of VRE (variable renewable energy) has grown rapidly, curtailment issues have arisen worldwide. This paper evaluates and compares curtailment situations in selected countries using an objective and quantitative evaluation tool named the “C-E map” (curtailment-energy share map). The C-E map is a correlation map between curtailment ratios that mean curtailed wind (or solar) energy per available energy and energy shares of wind (or solar). The C-E map can draw a historical trend curve in a given country/area, as an at-a-glance tool to enable historical and/or international comparison. The C-E map also can classify the given countries/areas into several categories, according to the current levels of curtailment ratio and historical trends. The C-E map helps institutional and objective understanding of curtailment for non-experts including policy makers.
Power systems with a high share of variable renewable energy (VRE) represent a challenge to system operators because of the increased flexibility requirements and stability. This study analyses the performance of a real power grid with a high penetration of VRE (mainly wind and solar photovoltaic). A rule-based power model is developed to simulate the power system behaviour. One European country was selected (Spain), with limited international interconnections and well-established decarbonisation scenarios by national and European organisations. Flexibility requirements in the future power system were found through power plants' flexibility and stability constraints (i.e., inertia) and the expected changes in grid interconnection. The model results indicate that the ambitious targets for grid decarbonisation are not realistic because of these requirements. Considering the share of VRE for a sustainable transition (ST) scenario in 2030 (33% power generation) and in 2040 (35%), CO2-equivalent emissions will be reduced up to 157 and 159 kg CO2/MWh, respectively, which is well above Paris targets. Furthermore, no scenario allows meeting the expected environmental targets. Therefore, in power systems with more than 39% VRE, the results suggest that new technologies should be considered with emissions below ∼113 kgCO2/MWh, a maximum cost of ∼134 €/MWh, and an inertia constant above 5 s.
Carbon neutrality by 2060 is the recent expression of China’s international commitment to reduce its carbon dioxide emissions. Energy and chemical sectors, the two main contributors for carbon dioxide emissions in China, are the biggest bottlenecks for reaching the objective of carbon neutrality. Moreover, coal-to-ammonia and coal-to-methanol are the major CO2 emission process contributors in China’s coal chemical sector. Herein, a possible route to the carbon neutral target based on energy-chemical nexus for electricity generation as well as methanol and ammonia production is proposed in this study. The most cost-effective solution for meeting the commitment is identified by considering regional variations in renewable and non-renewable resources and adopting an optimized regional cooperation. According to the roadmap presented in this study, an optimized combination of fossil fuels and renewable energies forming “blue energy economy” is feasible and promising.
In this paper, the performance analysis of a 30 MW wind power plant is performed. The farm consists of fifteen (T1-T15) G9 7/2000/GAMESA 2 MW grid-connected turbines. The farm is in operation mode installed 28 km south of Nouakchott city in Mauritania. The analyzed data are monitored from July 1st, 2015 (the first operation day of the power plant) to December 31st, 2019. The parameters of performance evaluation are power generation, capacity factor, machine availability, grid availability, and system availability. It is observed from data analysis, the wind farm supplies a total energy of 507.39 GWh to the power grid and have a high average capacity factor of 42.55%. T1 produces the highest amount of electrical energy among the other turbines with a total energy output of 35.46 GWh, an average capacity factor of 44.97%, and operating hours of 33,814 hours. While T12 produced the minimum amount of energy in this period, the difference in energy compared to T1 is 4.563 GWh. It is observed that the availability of the network is unstable and needs improvement, varying between 90.86% in 2016 and 93.16% in 2018. In the first year of operation, 97.06% of the turbines were available. However, the average availability of the wind farm is approximately 94% during the total study period. Keywords: Capacity factor Machine Power grid Power system availability Wind power plant This is an open access article under the CC BY-SA license.
The amount of wind power and other time-variable non-dispatchable renewable energy sources (RES) is rapidly increasing in the world. A few power systems are already facing a very high penetration from variable renewables which can surpass the systems’ consumption during no-load periods, requiring the energy excess to be curtailed, exported or stored. The limitations for electric energy storage naturally lead to the selection of the well-known form of storing potential energy in reservoirs of reversible hydropower stations, although other technologies such as heat storage are also being used successfully. This paper reviews the storage technologies that are available and may be used on a power system scale and compares their advantages and disadvantages for the integration of fast-growing renewables, such as wind power, with a special focus on the role of pumped hydro storage.
The amount of wind power in the world is quickly increasing. The background for this development is improved technology, decreased costs for the units, and increased concern regarding environmental problems of competing technologies such as fossil fuels. Some areas are starting to experience very high penetration levels of wind and there have been many instances when wind power has exceeded 50% of the electrical energy production in some balancing areas. The aims of this paper are to show the increased need for balancing, caused by wind power in the minutes to hourly time scale, and to show how this balancing has been performed in some systems when the wind share was higher than 50%. Experience has shown that this is possible, but that there are some challenges that have to be solved as the amount of wind power increases.
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