Renewable Energy Curtailment Research Articles

Quantifying the challenge of reaching a 100% renewable energy power system for the United States

Quantifying the challenge of reaching a 100% renewable energy power system for the United States

Thermodynamic Analysis of a Hybrid Electrical Energy Storage System Integrating High‐Temperature Thermal Energy Storage and Compressed Air Energy Storage for Mitigating Renewable Energy Curtailment

Compressed air energy storage (CAES) system can smooth out the fluctuated power from renewable energy and allow it to meet electricity demands reliably. It further enables the mitigation of renewable energy curtailment. A hybrid energy storage system integrating high‐temperature thermal energy storage (HTTES) and CAES is proposed. In the energy charging process, the high‐ and low‐quality power from renewable energy are stored separately in the air storage reservoir (ASR) and HTTES system. In the energy discharging process, the compressed air is heated to high temperature in the HTTES system and finally expands in air turbines for electricity generation. Thermodynamic analysis reveals that a round trip efficiency of 64.36% with an energy storage density of 5.38 kWh m−3 can be achieved. It is found that the proposed hybrid system has the beneficial effect of improving the system performance. The largest exergy destruction takes place in the HTTES system. The round trip efficiency is mostly sensitive to the output temperature of HTTES, the isentropic efficiency of compressors and turbines, and the maximum and minimum operating pressures of ASR.

A novel cluster-based spinning reserve dynamic model for wind and PV power reinforcement

The share of low-carbon energy in the electricity-production industry is increasing, creating reliability disturbances in modern power systems. Globally, the various renewable resources are distinguished by their origin into firm, variable and uncertain. To cope with the impact of variable and uncertain renewables on residual load, system operators need to plan-ahead adequate spinning reserves. In this work, we introduce a new paradigm for addressing the dynamic spinning reserve formulation, that is capable of accounting for the largely unaddressed challenge of the volatile behavior of different power inputs in the presence of storage. Based on realistic models and spinning reserve clusters, our solution leverages widely adopted robust approaches in the field, providing optimum cost/risk trade-off without deteriorating the computational burden. The proposed framework relies on a hybrid optimization mechanism to enable the effective unit commitment and allow for the minimization of spinning reserve deficits, renewable energy curtailment and load shedding. In the presence of storage, our formulation improves not only the annual total cost, but also allows for renewable generation enhancement at the maximum reliability level. The annual improvement accounts for 1.18% increases in renewable penetration, reduced costs in the range of €9M-€27 M and 3.75–9.45 GWh of services that are not withheld.

Hosting Capacity Maximization of Wind and Solar DGs in Distribution Networks Using Demand Response and Renewables Curtailment

The wind and solar Distributed Generations (DGs) are currently the most used Renewable Energy Sources (RES) based DGs worldwide. The integration of RES in distribution networks has attracted great interest for several objectives; one of the main objectives is to maximize the RES hosting capacity of distribution networks. The wind speed and solar irradiance along with their associated generated power are stochastic in nature and uncertain, and thus their uncertainty should be considered. In this study, a general frame work is presented for the integration of renewable wind and solar DGs, Demand Response (DR), and renewable energy curtailment for hosting capacity maximization of distribution networks, considering renewables uncertainty. The proposed framework is implemented and tested on a standard IEEE 33-radial bus system. The obtained results demonstrate that using different types of renewables is more effective than using only one type for hosting capacity maximization of distribution networks. Moreover, using DR and renewable energy curtailment have proved their effectiveness as active network management (ANM) tools for enhancing the hosting capacity by controlling the load variation and renewables generation, respectively.

Chance-Constrained Economic Dispatch Considering Curtailment Strategy of Renewable Energy

Chance-constrained economic dispatch (CCED) is widely used to cope with uncertainties brought by renewable energy sources. In CCED, security of power system is guaranteed by restricting risks under permitted level. As the penetration rate of renewable energy increases rapidly, the CCED model may be infeasible because of inadequate system reserve and/or transmission congestion under certain circumstances. Therefore, the curtailment of renewable energy is indispensable to guarantee security in some scenarios for power systems with high penetration of renewable energy. To address this crucial issue, this paper proposes a novel CCED model, where generation of conventional units and curtailment strategies of renewable energy are co-optimized to minimize total operational cost and restrict operational risks. An efficient solution method is developed to schedule generation and curtailment sequentially, in which tractable optimization models are formulated for each step. Numerical tests demonstrate that the proposed model can significantly reduce the probability of emergency control of curtailment compared with conventional CCED models. Furthermore, this solution method also outperforms scenario-based method with significantly improved computational efficiency and higher-quality solution.

Artificial intelligent based energy scheduling of steel mill gas utilization system towards carbon neutrality

Steel industry contributes significantly to the world economy, but is highly energy intensive and CO2 intensive since the coal-based blast furnace route is dominant in steelmaking. Besides efficient utilization of the steel mill gases for power and heat supply, deploying technologies of carbon capture, utilization and renewable power is in urgent need for the transition of the steel industry towards carbon neutrality. To attain this goal, this paper develops a low-carbon steel mill gas utilization system with the integration of solvent-based carbon capture, methanol production based carbon utilization and renewable power. An artificial intelligent based optimal scheduling is then proposed to coordinate the interactions among gas, heat, electricity and carbon under variant weather and load conditions. Gradient boosted regression trees with Bayesian optimization is exploited to identify efficient surrogate models for the complex devices within the system. Heuristic search algorithm of particle swarm optimization is applied to find the low-carbon and economical scheduling within the entire scheduling period. Case studies show that the optimal scheduling can unlock complementary advantages among renewable energy, carbon capture and utilization, leading to 97% renewable energy curtailment reduction, 62% CO2 emission reduction and 126 tons of methanol production in 24 h. Sensitivity analyses are carried out to investigate the effects of additional coal consumption, renewable power installed capacity, CO2 emission penalty coefficient and CO2 capture constraint mode, providing broader insight into the operation of the steel mill gas utilization system towards carbon neutrality.

The curtailment paradox in the transition to high solar power systems

Summary 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.

Enhancing the self‐resilience of high‐ renewable energy sources, interconnected islanding areas through innovative energy production, storage, and management technologies: Grid simulations and energy assessment

Electrification of heating and transportation can be greatly combined with excess energy production from variable renewable energy sources that exist in many geographical islands. Grid interconnections, where available, play a vital role in the energy system as provide the required balance between energy consumption and demand but many limitations emerge due to cable capacity and other technical constraints, which in many cases, lead to curtailment events. With the minimization of the energy exchange through the cable between islands and the mainland, the islands' self-resilience is enhanced. The islands of Samsø and Orkney are used as the case studies where, among others, the specific technical solutions of (a) heat pump districting heating with heat storage, (b) electrolyzer for hydrogen production, and (c) electrical vehicles are examined. The proposed technical solutions are enhanced by Demand Side Management actions utilizing high renewable energy sources availability and curtailment events. The solutions are examined and compared with a reference/current status scenario for each island. This work is based on a detailed model representation, using Modelica language, of the transfer and distribution grid assets, allowing the estimation of the impact of the proposed electrification solutions to the grid level as well as the island level. Simulation results revealed that with the proposed actions in Orkney, annual energy export is reduced by 24 GWh but the corresponding energy imports are slightly increased by 13 GWh, reducing curtailment by 1.4 GWh (77%). As for Samsø, the energy imports are reduced by 5 GWh, while the energy imports increase by 2.0 GWh. Grid losses remain at the same level as before at around 2%, but some distribution lines have significantly lower energy traffic due to higher renewables self-consumption.

Exploring the Role and Value of Grid-Scale Energy Storage in Deep Decarbonisation: Synergies with CCS?

Grid-scale inter-seasonal energy storage and its ability to balance power demand and the supply of renewable energy may prove vital to decarbonise the broader energy system. Whilst there is a focus on techno-economic analysis and battery storage, there is a relative paucity of work on grid-scale energy storage on the system level with the required temporal resolution. Here, we evaluate the potential of a power-to-gas-to-power as inter-seasonal energy storage technology. Our results suggest that inter-seasonal energy storage can reduce curtailment of renewable energy, and overcapacity of intermittent renewable power. Importantly, grid scale energy storage assumes a critical role especially when the technology options for dispatchable power are limited. It appears that neither high CAPEX nor low round-trip efficiency preclude the value of the technology per se, however the rate of charge and discharge of the technology emerges as key technical characteristic. This study emphasises the rising importance of balancing seasonality in energy systems characterised by a high penetration of renewable energy, and prompts questions regarding sector integration and resilient decision-making toward a zero-carbon economy.

Enhancing the power grid flexibility with battery energy storage transportation and transmission switching

The penetration of large-scale renewable energy puts an urgent demand on increasing power grid flexibility. From the power grid perspective, transmission congestion has become one of the bottle-neck factors limiting renewable energy integration. In the tradition, transmission topology is regarded to be unadjustable, and energy storage only plays an important role in the local area where it locates. To enhance the transmission system flexibility and relieve transmission congestion, this paper proposes a network-constraint unit commitment (NCUC) model considering battery energy storage transportation (BEST) and transmission switching (TS). This model is integrated with a novel indicator based BEST model and a TS model to minimize the overall operating cost. The benefits of BEST mobility and TS flexibility are quantitatively evaluated through compared with the traditional NCUC model. Based on the difference between the overall operating cost of unit commitment (UC) and NCUC, we quantitatively evaluated the flexibility provided by BEST and TS by the overall operating cost reduction. A case study on a modified IEEE RTS-79 system is provided to validate the effectiveness of the proposed model. The results show that the BEST and TS have a synergistic effect on enhancing power grid flexibility, which reflects in this study as the power grid operating economics improvement and renewable energy curtailment reduction. Besides, though the BEST and TS bring transmission system more losses, applying them into the system could relieve transmission congestion, which makes them valuable technologies to improve power system security.

Distributed model predictive control for joint coordination of demand response and optimal power flow with renewables in smart grid

Demand response is an emerging application of smart grid in exploiting timely interactions between utilities and their customers to improve the reliability and sustainability of power networks. This paper investigates the joint coordination of demand response and AC optimal power flow with curtailment of renewable energy resources to not only save the total amount of power generation costs, renewable energy curtailment costs and price-elastic demand costs but also manage the fluctuation of the overall power load under various types of demand response constraints and grid operational constraints. Its online implementation is very challenging since the future power demand is unpredictable with unknown statistics. Centralized and distributed model predictive control (CMPC and DMPC)-based methods are respectively proposed for the centralized and distributed computation of the online scheduling problem. The CMPC can provide a baseline solution for the DMPC. The DMPC is quite challenging that invokes distributed computation of a nonconvex optimization problem at each time slot. A novel alternating direction method of multipliers (ADMM)-based DMPC algorithm is proposed for this challenging DMPC. It involves an iterative subroutine computation during the update procedure of primal variables that can efficiently handle the difficult nonconvex constraints. Comprehensive experiments have been conducted to test the proposed methods. Simulation results show that the gap in objective values between the DMPC and its baseline counterpart (CMPC) are all within 1%, further verifying the effectiveness of the proposed ADMM-based DMPC algorithm.

Analysis of Methanation Path Based on Power-to-X Technology——Taking China as an Example

In order to accelerate the realization of the “Paris Agreement” global warming temperature control goals and to achieve carbon emission reduction and green sustainable energy development, countries around the world are actively exploring and developing new energy utilization technologies. This paper takes China as an example to study and analyze the methanation path based on Power-to-X technology. The results show that:①China’s potential for hydrogen production from renewable energy in the future, as well as the introduction of CO2 capture technology for thermal power plants and other sectors for carbon emission reduction and resource utilization, all have good potential, and both can provide sufficient raw materials for the methanation process;②Methanation production by providing green hydrogen and capturing and recovering carbon dioxide is in line with the goals and requirements of the new generation of energy systems for sustainable development. This technological path is actually helpful for delaying global warming and realizing the reduction and resource utilization of renewable energy curtailment in CO2. At the same time, in the future, relying on the synergy of technology and policy to continuously increase the scale of the system to reduce the overall cost, it is expected to achieve large-scale applications.

Infrastructural coupling of the electricity and gas distribution grid to reduce renewable energy curtailment

Following the European Union’s emission reduction goals, the expansion of intermittent renewable energy sources is being pursued by numerous member states. This poses challenges especially to low-voltage electricity grids that are not designed for the volatile and unpredictable feed-in from renewable generation capacity. In addition to the expansion of renewable capacity, further measures, including the decarbonization of the transport, heating and industrial sectors are needed to achieve the environmental targets. Sector coupling refers to the electrification of end-user energy demand as well as the coupling of different energy infrastructures such as the electricity and gas networks through Power-to-Gas technology. In this paper, we address these issues by developing a methodology that enables distribution system operators to identify future grid constraints in advance and to address them using Power-to-Gas technology using geographical information systems. In further detail, we present a novel approach to identify sections of the distribution network that are likely to be congested in the future in order to locate congestion-induced potential sites for Power-to-Gas plants. We show the applicability of our approach in a case study for a municipality in the German state of Baden-Wurttemberg. We show the economic feasibility of a medium-sized Power-to-Gas plant that couples the gas and electricity distribution networks. Our findings offer insights into the possibility to use the existing gas infrastructure in order to integrate surplus electricity generation, avoid electricity grid congestion and to further decarbonize energy demand.

Evaluating the ancillary services market for large-scale renewable energy integration in China's northeastern power grid

The installed renewable energy capacity in China is the largest in the world. However, the curtailment of renewable energy remains problematic. To alleviate this problem, a pilot for integrating the ancillary service market for renewable energy in China's northeastern power grid began in 2017. Before this time, a compensatory ancillary service cost mechanism was implemented, in which thermal plants not providing ancillary service paid the costs of the thermal plants providing ancillary service under government supervision. The pilot ancillary service market allowed thermal plants providing ancillary service to make independent quotes. Renewable energy plants were included in those paying the ancillary service costs. We examine the effects of the ancillary service market in the context of large-scale renewable energy integration. The results show that this market has given rise to competing interests between renewable energy and thermal plants. Therefore, measures must be taken to improve the ancillary service market, including eliminating the ancillary service bidding limits, establishing a renewable auction mechanism, and transforming the spot market.

The investigation of the optimization based on market mechanism to the operation of a thermal‐wind‐photovoltaic hybrid generation system

The renewable energy hybrid generation system in the area with renewable energy and land source plays a key role in improving the application of the renewable energy in China, with the rapid development of the extra high voltage (EHV) and ultra-high voltage (UHV) grids to transmit the electricity. The suitable plan and decision-making mechanism has a significant influence on the utilization of the renewable energy. The output of thermal power, wind power and photovoltaic are respectively simulated in the plan period of a hybrid generation system, and then all the output are comprehensively studied with the consideration of some constrains. However, the experience of the applications of the renewable energy hybrid generation system with thermal power revealed an obvious disadvantage that to maintain the competitiveness of the power output without the guidance of the price signals in the electricity market is difficult. The dispersed areal distribution and discontinuous power output of the renewable energy may be responsible for this disadvantage. The investigation to improve the consumption of the renewable energy hybrid generation system is meaningful to solve the renewable energy curtailment problems. In the present study, the investigation to the operation of a thermal-wind-photovoltaic hybrid generation system with market mechanism was conducted to optimize the consumption of the renewable energy. These results are beneficial to the operations of the similar hybrid generation systems.

Characterizing and Visualizing the Impact of Energy Storage on Renewable Energy Curtailment in Bulk Power Systems

The uncertain natures of renewable energy lead to its underutilization; energy storage unit (ESU) is expected to be one of the most promising solutions to this issue. This paper evaluates the impact of ESUs on renewable energy curtailment. For any fixed renewable power output, the evaluation model minimizes the total amount of curtailment and is formulated as a mixed integer linear program (MILP) with the complementarity constraints on the charging and discharging behaviors of ESUs; by treating the power and energy capacities of ESUs as parameters, the MILP is transformed into a multi-parametric MILP (mp-MILP), whose optimal value function (OVF) explicitly maps the parameters to the renewable energy curtailment. Further, given the inexactness of uncertainty’s probability distribution, a distributionally robust mp-MILP (DR-mp-MILP) is proposed that considers the worst distribution in a neighborhood of the empirical distribution built by the representative scenarios. The DR-mp-MILP has a max–min form and is reformed as a canonical mp-MILP by duality theory. The proposed method was validated on the modified IEEE nine-bus systems; the parameterized OVFs provide insightful suggestions on storage sizing.

A compact model to coordinate flexibility and efficiency for decomposed scheduling of integrated energy system

The conflict between inflexible operation of high-efficient cogeneration system and demand for flexibility in power grid has engendered severe renewable energy curtailment, which raises a requirement of multi-energy management. Nowadays, researchers have focused on flexibility improvement, but rarely considered energy conversion efficiency of cogeneration systems based on the 2nd law of thermodynamics. This paper establishes a compact model of cogeneration systems by taking nonlinear energy conversion and heat transfer constraints of combined heat and power units into account, and further proposes a two-stage heat and power dispatch procedure. The lower stage conducts plant-level operation optimization to obtain the compact model, i.e., quantitation of the best trade-off relations between energy supply flexibility and conversion efficiency as well as the power generation feasible region in each cogeneration system. The upper stage formulates a convex optimal power flow problem based on the compact model to achieve the global coordination between energy supply flexibility and conversion efficiency in integrated energy system. To apply the model, we introduce a multi-energy management system consisting of a central power-grid dispatch system and multiple distributed plant-level energy management systems. Optimization results reveal that the proposed method saves 11.65% heat consumption comparing with traditional method.

Impact of Revised Time of Use Tariff on Variable Renewable Energy Curtailment on Jeju Island

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.

Optimal Sizing of PV-Diesel-Battery System Using Different Inverter Types

Different inverters types have different technical specifications and costs which contribute to the changes of inverter type decisions. It is therefore important to know which inverter is more advantageous for certain criteria. In this paper, the central, string, multi-string, and AC module types of inverters were compared through optimally designing a DG-PV and DG-PV-battery system of an off-grid island using each type of inverter. The problem was solved as a multi-objective optimization considering cost and uncertainty. The results were compared in terms of cost, reliability, renewable energy penetration, renewable energy curtailment, and changes in battery cost. The optimization results showed that the string inverter is best in terms of cost and highly affected by the decrease of the battery cost, the AC module in terms of reliability and curtailment, and the multi-string for renewable energy penetration. Meanwhile, the central inverter can be the choice when a balance between cost and reliability is considered.

Optimal Operation of an Integrated Electricity-heat Energy System Considering Flexible Resources Dispatch for Renewable Integration

Large fluctuations may occur on the energy supply and the load sides when large-scale renewable energies are integrated, leading to great challenges in power systems. The renewable power curtailment is especially numerous in the integrated electricity-heat energy system (IEHES) on account of electricity-heat coupling. The flexible resources (FRs) on both the energy supply and load sides are introduced into the optimal dispatch of the IEHES and further modeled to alleviate the renewable fluctuations in this paper. On the energy supply side, three kinds of FRs based on electricity-heat coordination are modeled and discussed. On the load side, the shiftable electricity demand resource is characterized. On this basis, the solution for FRs participating in IEHES dispatch is given, with goals of maximizing the renewable penetration ratio and lowering operation costs. Two scenarios are performed, and the results indicate that the proposed optimal dispatch strategy can effectively reduce the renewable energy curtailment and improve the flexibility of the IEHES. The contribution degrees of different FRs for renewable integration are also explored.