Curtailment Rate Research Articles

Demand side industrial load control for local utilization of wind power in isolated grids

Lack of flexible power source results in the high wind curtailment rate in northern and western China. Meanwhile, many energy-intensive industrial loads such as the polysilicon production enterprises went bankrupt because of the high costs of huge electricity consumption. Constructing the high electricity consumption enterprises for local utilization of wind power is effective to alleviate the wind power curtailment problem, and the high cost of the electricity consumption for the industrial load production can be reduced correspondingly. Thus, a new wind power local utilization way that an isolated power grid driven by coal and wind power for polysilicon production is presented. However, without the power support from the bulk power system, frequency stability issue is critical for the industrial isolated power system. Based on the actual production process, a polysilicon load control method by adjusting the pieced voltage value and voltage piecing time is proposed for supplementary frequency regulation. The detailed polysilicon load characteristic model is established considering the constraints of cooling water flow rate and temperature so that the polysilicon production quality is not impacted by the load control. An actual isolated power grid with high wind power penetration is studied as the example case to verify the effectiveness of the proposed control strategy under different working conditions.

Reflection on opportunities for high penetration of renewable energy in China

Increasing penetration of renewable energy (RE) is expected to be an essential component for China to achieve goals in mitigating global climate change and domestic air pollution. Although China has experienced rapid growth of RE over the past two decades, problems restricting further development of RE occur, among which high curtailment rate of wind and solar power raises great attention. This paper reflects on the challenges and opportunities of high penetration of RE from both technical and market perspectives in China based on literature review. In particular, it emphasizes technical options to address the inherent variability of RE from three layers, namely using interconnected geographically dispersed sources to reduce random variance, increasing storage capacity to deal with minute‐to‐day imbalance, and applying backup capacity for seasonally mismatch. From the market perspective, the paper analyzes the needs of shifting from central planning to market‐based dispatch, introducing markets for ancillary services, and having a larger and more precise market. Meanwhile, our paper further points out that opportunities for high RE integration may rely on deep electrification of transportation and building sectors, which are also the foci for future air pollution control in China. It is feasible for China to achieve a high if not 100% RE system, but first these technical and market challenges have to be addressed in the process of adjusting its energy structure.This article is categorized under: Energy Systems Analysis > Climate and Environment Energy and Climate > Climate and Environment

Research on renewable energy accommodation in Henan Province during the 13th five-year plan

As the government is promoting the development of distributed renewable energy (Renewable energy in this paper refers to wind power and solar power) in central and eastern China, the renewable energy generation in Henan Province will develop rapidly during the 13th Five-Year Plan period. In order to avoid the serious wind and solar power curtailment, this paper established an assessment model of renewable energy accommodation of Henan Province, and estimated renewable energy accommodation in Henan. Through time-sequential power system production simulation, this study drew the following conclusions: if the renewable energy installation capacity and distribution are as planned, the renewable energy curtailment rate of Henan would be 2.2% ∼ 3.6% in 2020; if the distribution can be adjusted, more renewable energy will be consumed in Henan with no renewable energy curtailment.

Demand for flexibility improvement of thermal power units and accommodation of wind power under the situation of high-proportion renewable integration-taking North Hebei as an example.

As much wind power is connected to the power system, the accommodation of the wind power in the power grids becomes a huge challenge to the operation model of China's power system. Releasing and improving the flexibility of the power system will be necessary and important to enable the accommodation of power generated with renewable energy sources, which is connected to the power grids on a large scale and accounts for a high proportion. The paper, with North Hebei as an example, discusses the relationship between the demand for the flexibility of thermal power units and the accommodation of wind power. This paper further analyzes the demand for peak load regulation in North Hebei at both the present and the future as well as the characteristics of power sources in the power grids of North Hebei and the technical potential of power generation. It also compares the quantity of curtailed power before and after the flexibility-oriented transformation of thermal power units in North Hebei and calculates the minimum technical output of thermal power under different levels of accommodation of wind power. The research shows that the peak load regulating resources in the power grids of North Hebei boast huge potential, but in the long term, to achieve the objective of a 10% curtailment rate of power generated with renewable energy sources, the minimum technical output of condensing units must be lower than the internationally advanced level of 25%. So, it is difficult to fulfill the said objective solely relying on the strengthened transformation of generating units. To reach the level of 5% curtailment rate of power generated with renewable energy sources, the minimum technical output must achieve breakthrough improvement, which requires continuous technological innovation and power flexibility in close coordination.

Application of Heat Storage in Heating Network for Surplus Wind Power Consumption

Among northern China, CHP is the main electric and heating source to provide electricity and heat. While, with the increasing integration of wind power, the peak regulation capacity is lacking. Wind power curtailment occurs frequently because of the contradiction between heating and electric load. District heating system plays the majority role in heating supply because of its efficiency and cleanness. There are enormous heat storage capacity contained in district heating system, if the stored heat energy could be utilized efficiently the contradiction between heating and electric load could be relieved and the wind power curtailment ld be avoided considerably. This study presents an approach that takes advantage of the heat in the primary heating circuit to absorb surplus wind power. The expressions of the components in heating system are given to establish the mathematical model. Followed, the thermodynamic properties of heating pipelines are analyzed, the heat storage capacity and heat transmit delay characters are studied. Then, the consumption capacity of surplus wind power is discussed, and the temperature changes are also be considered. Finally, a case study are undertook to prove the effectiveness. The results show that by utilizing the heat in heating network, the wind power curtailment rate could be reduce by 20.6% which means about 219.4MWh surplus wind energy could be consumed during a valley electric load period.

A multi-objective optimization model of hybrid energy storage system for non-grid-connected wind power: A case study in China

In recent years, the wind curtailment has become a serious problem in China and the government are actively seeking solutions to deal with this energy loss. Therefore, the use of non-grid-connected wind power has received great attention since it can be supplied to local end users equipped with energy storage and then mitigate wind curtailment. Since the non-grid-connected wind power and local power load have to confront dramatic power fluctuations, a hybrid energy storage system (HESS) including batteries and supercapacitors is applied. This paper proposes a multi-objective optimization model of HESS configuration in non-grid-connected wind power/energy storage/local user system. In this model, two decision variables, numbers of batteries and supercapacitors, are determined based on the objective of annual profit maximization and wind curtailment rate minimization. To solve this model, a non-dominated sorting genetic algorithm II (NSGA-II) is employed to obtain Pareto front and VIKOR (VlseKriterijumska Optimizacija I Kompromisno Resenje) technique is applied to select the optimal solution from Pareto solutions. Finally, a wind farm in Hebei province is studied and discussed. A scenario analysis, a sensitivity analysis and a comparative analysis are performed to show the advantages of the proposed model.

Can carbon pricing support onshore wind power development in China? An assessment based on a large sample project dataset

Abstract There is much discussion about whether the rapid expansion of onshore wind power in China is sustainable, given the decrease in feed-in tariffs (FIT). It is unclear whether the recently launched nationwide carbon pricing system, which will include 1700 power companies, can compensate for decreasing FITs and possibly provide new incentives for wind power developments. This paper investigates the ability of carbon pricing policies to compensate for declining FITs in support of onshore wind power investment in China. First, we constructed a dataset of 2059 onshore wind power projects from China’s thirty provinces between 2006 and 2015 to estimate the levelized costs of electricity (LCOE). This dataset was used to assess the profitability of each wind project for different carbon prices, varying levels of FITs, curtailment rate, and discount rate. Our findings suggest that the carbon price can compensate partially for the revenue loss caused by declining FITs as well as improving the profitability of projects. However, current carbon prices in China’s carbon emission trading pilots are not sufficiently high to compensate for the revenue losses, especially under the grid parity scenario. Consequently, without FITs, the sustainable development of onshore wind power in China is uncertain. A sensitivity analysis of the effect of the carbon pricing policy demonstrates that in the case of higher investment risk and more serious curtailment, the effect of carbon pricing policy on promoting the wind power investment seems to be more significant.

A Framework to Split the Benefits of DR Between Wind Integration and Network Management

In power systems today, considerable developments are being made in the energy transition from centralized fossil fuels to renewable distributed generation (DG) sources. However, this ongoing progress has presented several challenges to the operation and planning of distribution systems due to the variability of intermittent renewable generation. Demand response (DR) is widely regarded as a feasible tool to provide a seamless transition by altering the load profiles according to the intermittent generation profile. However, the resultant volatile power flows can be taxing for network capacity. This paper offers a framework from the distribution system operator's perspective for the optimal utilization of DR between DG curtailment mitigation and network management. The application of the developed framework to a generic Finnish distribution system demonstrates that the benefits of DR should be envisioned for network management as long as the wind curtailment rate is below a certain level. This means that, beyond the threshold energy curtailment rate, the distribution system operator would be more economically efficient by making network reinforcements.

Decomposing driving factors for wind curtailment under economic new normal in China

China’s energy transition, from a coal-dominated system to one with the world largest deployment of wind power, is facing major challenge as China entered the economic “New Normal” in recent years. A key phenomenon is serious wind curtailment, where potential clean wind power is abandoned and the associated environmental and climate benefits could not be fulfilled. Multiple causes have been identified to explain the serious wind curtailment in China; but few studies provide explanations for the patterns of wind curtailment and quantify the relative contributions of the underlying factors. We develop a flexible analytical framework and adapted the logarithmic mean Divisia index method to quantify the contributions of key factors in the change of wind curtailment rate. While the early stage of wind curtailment was constrained by limited transmission capacity, recent wind curtailment is primarily driven by the deceleration of the overall economic growth, which resulted in a slowdown of electricity demand and low willingness-to-accept imported power across provinces. The current economic transition has induced an oversupply of power in general and wind power in particular, especially in wind rich provinces. This seems to be hindering further energy transition. With greater political will and better policy design, the oversupply of power could be an opportunity to speed up substitution of coal with wind and to expedite the de-carbonization of the economy.

Why the Wind Curtailment of Northwest China Remains High

The total grid-connected installed capacity of wind power in northwest China has grown from 16,260 MW in 2013 to 43,290 MW in 2016; an increase of 88.7% each year. However, this region has suffered from increasingly serious wind curtailment since 2014, and the wind curtailment amount accounts for nearly a half of China’s total. The wind curtailment rate of Gansu Province, Xinjiang Uygur Autonomous Region and Ningxia Hui Autonomous Region in this area has increased and remains high. This paper constructs an analytical model to explore the reasons of the high wind curtailment of these three provinces from the four aspects of the wind power supply capacity, demand, grid transmission capacity, power system flexibility and market mechanism and laws. The results show that the relationship between the wind energy distribution and supply and the local load is incompatible, which is the source causing the high wind curtailment in northwest China. On the one hand, the game between the local government and developers has driven the development of wind power bases. On the other hand, the electricity sector is growing slowly and oversupply of electricity is seen in many areas of China. The wind power grid of northwest China not only faces limit of grid transmission capacity, but also constraint of insufficient flexibility of the electricity system. Presently, China has not set up a market mechanism and subsidy mechanism for the peak load adjustment, thus the thermal power companies lack motivation to voluntarily adjust the peak load. Moreover, the regional segregation and market barriers are also obstacles for the wind power outward transmission.

Operation optimization strategy for wind-concentrated solar power hybrid power generation system

This paper presents a new hybrid system to reduce wind curtailment and improve scheduling flexibility. This hybrid system includes a wind farm, a concentrated solar power plant with thermal energy storage, and an electric heater. The major role of the electric heater is to convert the redundant wind power into thermal energy, and the thermal energy is stored in the thermal energy storage of the concentrated solar power plant. The optimal scheduling of this hybrid system is formulated as a mixed-integer linear programming problem to maximize the profit subjected to technical constraints. The effects of the electric heater on the system are studied under different weather conditions. The test results show that the electric heater is helpful for reduction of the both deviation from generation plan and wind curtailment. The maximum relative deviation falls from 5.15% to 0% during the clear sky day, and 47.49% to 31.74% during the partial cloudy day. The wind curtailment rate decreases by 52.59% and 100% for clear and partial cloudy days, respectively. An annual simulation for the system shows that the overall daily cumulative deviations of the new system are significantly decreased, and the wind curtailment can be reduced by greater than 90% for 151 days, validating the effectiveness of the proposed system.

Study on reasonable curtailment rate of large scale renewable energy

Energy curtailment rate of renewable energy generation is an important indicator to measure renewable energy consumption, it is also an important parameters to determine the other power sources and grids arrangement in the planning stage. In general, to consume the spike power of the renewable energy which is just a small proportion, it is necessary to dispatch a large number of peaking resources, which will reduce the safety and stability of the system. In planning aspect, if it is allowed to give up a certain amount of renewable energy, overall peaking demand of the system will be reduced, the peak power supply construction can be put off to avoid the expensive cost of marginal absorption. In this paper, we introduce the reasonable energy curtailment rate into the power system planning, and use the GESP power planning software, conclude that the reasonable energy curtailment rate of the regional grids in China is 3% -10% in 2020.

Integrated Natural Gas, Heat, and Power Dispatch Considering Wind Power and Power-to-Gas

A large amount of wind power has to be curtailed due to the inflexibility of the combined heat and power (CHP) system in the heating season in northern China. The power-to-gas (P2G) technology, which uses electricity to produce hydrogen or synthetic natural gas, has become a promising energy conversion option for the utilization of surplus power energy. In this paper, an integrated natural gas, heat, and power dispatch (INGHPD) model which balances natural gas, heat, and power demand considering wind power and a P2G unit, is proposed. A natural gas network and P2G are modeled and integrated into the dispatch model. To demonstrate the effectiveness of the proposed model, an integrated energy system consisting of a six-bus power system, a six-node natural gas system, and a district heating system is simulated. The benefits of P2G are investigated in terms of reducing wind power curtailment, as well as system operation cost and CO2 emissions. The results in the deterministic model show that with the introduction of 40 MW P2G, the wind power curtailment rate decreases from 24.0% to 9.7%. The daily wind power energy consumed by P2G reaches 256 MWh and the daily CO2 emissions reduction reaches 46,080 kg. Additionally, the impact of the power and heat demand on the gas production of P2G and of the P2G capacity on the wind power curtailment are also investigated. P2G tends to generate more natural gas when the power demand is low and the heat demand is high.

Optimal sizing of utility-scale photovoltaic power generation complementarily operating with hydropower: A case study of the world’s largest hydro-photovoltaic plant

The high variability of solar energy makes utility-scale photovoltaic power generation confront huge challenges to penetrate into power system. In this paper, the complementary hydro-photovoltaic operation is explored, aiming at improving the power quality of photovoltaic and promoting the integration of photovoltaic into the system. First, solar-rich and hydro-rich regions across the world are revealed, which are suitable for implementing the complementary hydro-photovoltaic operation. Then, three practical scenarios of the novel operation mode are proposed for better satisfying different types of load demand. Moreover, a method for optimal sizing of a photovoltaic plant integrated into a hydropower plant is developed by maximizing the net revenue during lifetime. Longyangxia complementary hydro-photovoltaic project, the current world’s largest hydro-photovoltaic power plant, is selected as a case study and its optimal photovoltaic capacities of different scenarios are calculated. Results indicate that hydropower installed capacity and annual solar curtailment rate play crucial roles in the size optimization of a photovoltaic plant and complementary hydro-photovoltaic operation exerts little adverse effect upon the water resources allocation of Longyangxia reservoir. The novel operation mode not only improves the penetration of utility-scale photovoltaic power generation but also can provide a valuable reference for the large-scale utilization of other kinds of renewable energy worldwide.

出力予測を考慮した発電機起動停止計画モデルによる太陽光発電出力制御必要量の分析

High penetration of variable renewable energy (VRE) systems will impact power system operations because generation of VRE systems depends on weather conditions. We analyzed the operational situation and photovoltaic power yield curtailment for the Tokyo Electric Power Company area in 2030 using day-ahead unit commitment (UC) model when a high penetration of VRE systems is expected. At first, we updated our UC model to optimize PV curtailment keeping power system's security (load frequency control reserve) and minimizing operational cost. Using the updated model, we found that in case of 53GW and 100GW of PV penetration, around 0.34% and 4.83% of PV curtailment would be required throughout the year. High curtailment rate would be required only in spring and autumn seasons when power demand is small and PV yield is large. Regarding the other seasons, high curtailment rate would not be needed in any of the high PV penetration scenarios.

Integrated Energy Systems for Higher Wind Penetration in China: Formulation, Implementation and Impacts

With the largest installed capacity in the world, wind power in China is experiencing a ∼20% curtailment. The inflexible combined heat and power (CHP) has been recognized as the major barrier for integrating the wind source. The approach to reconcile the conflict between inflexible CHP units and variable wind power in Chinese energy system is yet unclear. This paper explores the technical and economic feasibility of deploying the heat storage tanks and electric boilers under typical power grids and practical operational regulations. A mixed integer linear optimization model is proposed to simulate an integrated power and heating energy systems, including a CHP model capable of accounting for the commitment decisions and nonconvex energy generation constraints. The model is applied to simulate a regional energy system (Jing–Jin–Tang) covering 100-million population, with hourly resolution over a year, incorporating actual data, and operational regulations. The results project an accelerating increase in wind curtailment rate at elevated wind penetration. Investment for wind breaks even at 14% wind penetration. At such penetration, the electric boiler (with heat storage) is effective in reducing wind curtailment. The investment in electric boilers is justified on a social economic basis, but the revenues for different stakeholders are not distributed evenly.

Optimal Offering Strategy for Concentrating Solar Power Plants in Joint Energy, Reserve and Regulation Markets

In addition to energy, a concentrating solar power (CSP) plant with thermal energy storage (TES) could also provide ancillary service (AS) in the reserve and regulation markets. On one hand, providing AS contributes to the flexibility of the power systems and increases the revenue of CSP plants. On the other hand, the flexibility of CSP plants to accommodate solar energy, which is of great uncertainty, might be significantly weakened by an inappropriate offering strategy, e.g., offering excessive AS. Insufficient flexibility might cause massive solar energy curtailment and reduce the potential revenue. This paper develops a general model framework on the optimal offering strategy for CSP plants in joint day-ahead energy, reserve and regulation markets, which is robust for solar energy uncertainty and stochastic for market price uncertainty. On this basis, given the optimal day-ahead offering strategy, the offering curves to provide incremental AS capacities in the supplemental AS markets are further derived considering the opportunity cost. A new index, the maximum acceptable curtailment rate, is introduced to formulate the tradeoff of CSP plants between supplying AS to the system and reserving the flexibility for solar energy accommodation. The case study results demonstrate the validity of the proposed model.

Efficiency assessment of wind farms in China using two-stage data envelopment analysis

China has been the world’s leader in wind power capacity due to the promotion of favorable policies. Given the rare research on the efficiency of China’s wind farms, this study analyzes the productive efficiency of 42 large-scale wind farms in China using a two-stage analysis. In the first stage, efficiency scores of wind farms are determined with data envelopment analysis and the sensitivity analysis is conducted to verify the robustness of efficiency calculation results. In the second stage, the Tobit regression is employed to explore the relationship between the efficiency scores and the environment variables that are beyond the control of wind farms. According to the results, all wind farms studied operate at an acceptable level. However, 50% of them overinvest in the installed capacity and about 48% have the electricity-saving potential. The most important factors affecting the efficiency of wind farms are the installed capacity and the wind power density. In addition, the age of the wind farm and the wind curtailment rate have a negative effect on productive efficiency, whereas the ownership of the wind farm has no significant effect. Findings from this study may be helpful for stakeholders in the wind industry to select wind power projects, optimize operational strategies and make related policies.

Interactions of rooftop PV deployment with the capacity expansion of the bulk power system

Distribution-sited solar photovoltaics (PV) economics (including rooftop PV) have improved significantly during the past several years, spurring increased installations, with over 2.2GW installed in 2014 in the United States. This increased deployment is largely projected to continue and has prompted additional interest in the interactions of rooftop PV deployment with the greater electricity system. In this paper we focus on one piece of this interface, namely the interaction between rooftop PV deployment and the evolution of the bulk power system. We develop a novel linkage between NREL’s bulk power capacity expansion model (the Renewable Energy Deployment System [ReEDS] model) and NREL’s rooftop PV adoption model (the dSolar model). We use these linked models to gain insights into the interactions of rooftop PV deployment with the bulk power system. We explore two sets of scenarios. In the first set we examine how different levels of rooftop PV deployment impact the generation mix on the bulk power system. In the second set we examine how the generation mix of the bulk power system impacts the deployment of rooftop PV by applying grid-wide curtailment rates to rooftop PV systems. In these sets of scenarios, we find that rooftop PV generation and utility PV generation have a nearly 1:1 substitution effect. We also find that curtailment rate feedback can have dramatic impacts on rooftop PV adoption, though the range of impacts is strongly dependent on the generation mix of the bulk power system and the amount of total PV generation in the system. For example, scenarios with more natural gas generation tended to have lower curtailment rates and thus more rooftop PV deployment.

Experiencing Commercialized Automated Demand Response Services with a Small Building Customer in Energy Market

An Automated Demand Response is the most fundamental energy service that contributes to balancing the power demand with the supply, in which it realizes extensive interoperations between the power consumers and the suppliers. The OpenADR specification has been developed to facilitate the service communications, and several facilities offer primitive forms of services in a retail market. However, few researches have reported the details of such a real-world service yet, and thus we are still unaware of how it works exactly. Instead, we rely on our textbooks to design next generations of the ADR service. To overcome the discrepancy of our understanding, this paper shares our hand-on experiences on the commercialized ADR service. In particular, we deploy smart submeters to manage energy loads and install an energy management system in a small commercial facility, helping the owner participate in the ADR service that a local utility offers. The building owner makes a service contract with a qualified load aggregator based on her curtailment rate, a reference point that decides the success of her load curtailment. With the rate, the customer facility participates in three DR events for tests that last for 2, 1, and 3 hours, respectively. Our experimental results are illustrated with discussions on various aspects of the service.