Level Of Curtailment Research Articles

Solidarity measures: Assessment of strategic gas storage on EU regional risk groups natural gas supply resilience

This paper focuses on strategic storage as a solidarity measure in response to short-term “high-impact, low-probability” (HILP) disruptions in the European Union (EU) gas supply from major suppliers (i.e., Ukraine, Russia, Norway, and North Africa), assuming its implementation in selected Member States. A two-stage stochastic cost minimization gas transport model is used to evaluate the impact of HILP events on the level of demand curtailment, survival time, and the natural gas supply mix of EU regional risk group. Results show that geographic proximity alone, without solidarity measures, is inadequate in providing system resilience. In contrast, solidarity measures lead to a longer survival time for regional risk groups (14 days) and to a reduction in system (15%) and LNG (70%) costs relative to a base scenario with no strategic storage. The analysis stresses the value of the coordinated use of strategic storage in balancing the natural gas network during emergencies, and provides further evidence supporting the EU legislative path towards an Energy Union.

North Sea region energy system towards 2050: integrated offshore grid and sector coupling drive offshore wind power installations

Abstract. This paper analyses several energy system scenarios towards 2050 for the North Sea region. With a focus on offshore wind power, the impacts of meshed offshore grid and sector coupling are studied. First, a project-based scenario, where each offshore wind power plant is connected individually to the onshore power system, is compared to a meshed grid scenario. Both the amount of offshore wind power installed and the level of curtailment are assessed. Then, these results are compared to a scenario with sector coupling included. The results show that while the introduction of a meshed grid can increase the amount of offshore wind power installed towards 2050, sector coupling is expected to be a more important driver for increasing offshore wind power installations. In addition, sector coupling can significantly decrease the level of offshore wind curtailment.

A techno-economic comparison of traditional upgrades, volt-var controls, and coordinated distributed energy resource management systems for integration of distributed photovoltaic resources

In some cases, increased deployment of distributed photovoltaic (PV) systems can impact the distribution grid, including causing steady-state voltages and thermal loading of lines and equipment to deviate from operational limits. We present techno-economic analysis of three possible solutions for mitigating these effects on two real feeders: traditional infrastructure upgrades, autonomous volt-var controls, and a distributed energy management system (DERMS). We focus on issues arising in aggregate from residential and small commercial PV systems at different penetration levels and use a bottom-up approach that couples cost modeling with sequential hosting capacity analysis and quasi-static time-series simulation. We compare trade-offs for each solution in terms of effectiveness, upfront capital costs, operating costs, PV output curtailment, and distribution system losses. We find that volt-var controls offer the lowest cost option for hosting capacity expansion but cannot mitigate all violations at high penetration levels. For the feeders studied, the range of upfront cost for the DERMS and traditional upgrades is similar, but the DERMS results in a greater expansion of the hosting capacity. However, unlike traditional solutions, DERMS also involves higher level of PV curtailment than is observed with autonomous volt-var controls.

The Economics of Explicit Demand-Side Flexibility in Distribution Grids: The Case of Mandatory Curtailment for a Fixed Level of Compensation

Demand-side flexibility can be incentivised to reduce the need for investment in distribution grids either implicitly or explicitly. Implicit demand-side flexibility is when prosumers react to price signals triggered by network tariffs. Explicit demand-side flexibility is when the DSO can contract flexibility. In this paper, we focus on one contractual arrangement: mandatory curtailment by the DSO for a fixed level of compensation. We develop a long-term bi-level equilibrium model. The upper level (UL) is a regulated DSO deciding on the network investment and/or curtailing consumers for a fixed level of compensation. The lower level (LL) consists of consumers, which can be prosumers or passive consumers. Prosumers can invest in solar PV and battery systems. They react to the network tariffs and to the compensation provided by the DSO for curtailing them. The regulated DSO anticipates the reaction of the consumers when investing in the network and when setting the level of curtailment. Network tariffs are set to recover the network costs and the payments made to consumers that have been curtailed. We find that the economics of explicit demand-side flexibility in distribution grids are positive, and they are more positive when tariffs are cost-reflective. This implies that we cannot avoid redesigning tariffs by using explicit demand flexibility. We also find that setting an appropriate level of compensation is difficult in the presence of prosumers and passive consumers. A level of compensation that is high enough for passive consumers will be gamed by prosumers.

Levelized cost of solar photovoltaics and wind supported by storage technologies to supply firm electricity

Abstract Energy storage technologies can assist intermittent solar and wind power to supply firm electricity by forming flexible hybrid systems. However, evaluating these hybrid systems has proved to be a major challenge, since their techno-economic performance depends on a large number of parameters, including the renewable energy generation profile, operational parameters of storage technologies and their associated costs. In this study, we develop a method to simulate the performance and determine the levelized cost of hybrid systems to provide firm electricity supply under various supply strategies such as peak demand and baseload at three different scales (representative sizes). The methodology is implemented for Switzerland, however, it can also be replicated for other geographies. Our results show that the optimal choice for a hybrid system depends on the scale rather than the supply mode strategy. We find that solar photovoltaics in combination with lithium-ion battery at the residential (0.39 to 0.77 EUR/kWh) and utility scale (0.17 to 0.36 EUR/kWh) as well as with pumped hydro storage at the bulk scale (0.13 to 0.18 EUR/kWh) offer the lowest levelized costs. Reducing the cost of both renewable and storage technologies as well as the storage size by allowing some level of curtailment or distortion in the firm supply profile improves the cost-competitiveness of hybrid systems.

Electricity Storage as a Matching Tool Between Variable Renewable Energy and Load

The transition to low carbon emitting solutions imposes new challenges to the power sector to accommodate a large penetration of intermittent renewables. It goes beyond the cheapest symmetrical reduction of fossil thermal generation that is being avoided. Storage is seen as the solution and also the option for batteries, but using a Discrete Fourier Transform and real hourly data it is shown that storage acts as an integral function, attenuating the “daily” and “weekly” harmonics of the charging / discharging function and leaving the “yearly” cycle as the main component to set the storage capacity needed. Export / import with neighbour systems shall be seen as a competitor with storage, but it poses mutual dependency and shared security issues. The renewable generation cost reduction in the “learning curve”, achieving a levelized cost below the variable cost of a CCGT is a milestone and it allows accepting a certain level of curtailment as an alternative to reduce the investment in storage. Batteries do not solve the long-term storage problem but today its use begins to be competitive in the “daily” cycle, replacing peaking gas plants and reinforcing the concept that the cost of storage can be seen as an equivalent thermal power plant. Better than assuming a fraction of renewable energy curtailment, it might be the development of Power-To-X solutions (hydrogen, synthetic gas, etc.) or even investing in nuclear power plants and limiting intermittent renewables penetration accordingly. Both solutions represent indirect electricity storage – fuel has a low storage cost - and it can solve the renewable surplus seasonal transfer problem, recovering synchronous generators for providing dispatchable flexibility, inertia to the system and serving as backup for periods with low renewable generation.

Assessing the Potential Benefits and Limits of Electric Storage Heaters for Wind Curtailment Mitigation: A Finnish Case Study

Driven by policy changes and technological advancement, wind power installations are booming as compared to any other types of power generation. However, the increased penetration of renewable generation in the power systems has resulted in high level of curtailment. Advanced energy storage technologies have been increasingly scrutinized as a feasible mitigation option in smart grids. This paper investigates the potential of mitigating wind generation curtailment via aggregating the domestic electric storage heaters. The key findings show that aggregating domestic thermal storages is a viable option for curtailment mitigation, but with the indispensable caution that mitigation potential significantly saturates as the share of wind generation escalates beyond a certain limit.

Curtailment in a Highly Renewable Power System and Its Effect on Capacity Factors

The capacity factor of a power plant is the ratio of generation over its potential generation. It is an important measure to describe wind and solar resources. However, the fluctuating nature of renewable power generation makes it difficult to integrate all generation at times. Whenever generation exceeds the load, curtailment or storage of energy is required. With increasing renewable shares in the power system, the level of curtailment will further increase. In this work, the influence of the curtailment on the capacity factors for a highly renewable German power system is studied. An effective capacity factor is introduced, and the implications for the distribution of renewable power plants are discussed. Three years of highly-resolved weather data were used to model wind and solar power generation. Together with historical load data and a transmission model, a possible future German power system was simulated. It is shown that effective capacity factors for unlimited transmission are strongly reduced by up to 60% (wind) and 70% (photovoltaics) and therefore of limited value in a highly renewable power system. Furthermore, the results demonstrate that wind power benefits more strongly from a reinforced transmission grid than photovoltaics (PV) does.

Optimal Sizing and Control of Energy Storage in Wind Power-Rich Distribution Networks

This paper presents a planning framework to find the minimum storage sizes (power and energy) at multiple locations in distribution networks to reduce curtailment from renewable distributed generation (DG), specifically wind farms, while managing congestion and voltages. A two-stage iterative process is adopted in this framework. The first stage uses a multi-period AC optimal power flow (OPF) across the studied horizon to obtain initial storage sizes considering hourly wind and load profiles. The second stage adopts a high granularity minute-by-minute control driven by a mono-period bi-level AC OPF to tune the first-stage storage sizes according to the actual curtailment. Congestion and voltages are managed through the optimal control of storage (active and reactive power), on-load tap changers (OLTCs), DG power factor, and DG curtailment as last resort. The proposed storage planning framework is applied to a real 33-kV network from the North West of England over one week. The results highlight that by embedding high granularity control aspects into planning, it is possible to more accurately size storage facilities. Moreover, intelligent management of further flexibility (i.e., OLTCs, storage, and DG power factor control) can lead to much smaller storage capacities. This, however, depends on the required level of curtailment.

Economic curtailment of intermittent renewable energy sources

In a power system featuring a large share of intermittent renewables and inflexible thermal generators, efficiency gains could be achieved by curtailing the production of renewables. However, as renewables feature very low variable production costs, over-curtailment can be costly. In this article, we use a stylised analytical model to assess this trade-off. We show that while curtailing renewables when their variability is high and the system flexibility is low can reduce generation costs, the different stakeholders will not necessarily benefit from such measures. As a consequence, leaving this decision to generators will lead to a sub-optimal level of curtailment. Either incentives to provide accurate RES availability forecasts or alternatively centralised forecasting should be put into place to solve the resulting problem of asymmetry of information.

Quantifying the value of improved wind energy forecasts in a pool-based electricity market

This work illustrates the influence of wind forecast errors on system costs, wind curtailment and generator dispatch in a system with high wind penetration. Realistic wind forecasts of different specified accuracy levels are created using an auto-regressive moving average model and these are then used in the creation of day-ahead unit commitment schedules. The schedules are generated for a model of the 2020 Irish electricity system with 33% wind penetration using both stochastic and deterministic approaches. Improvements in wind forecast accuracy are demonstrated to deliver: (i) clear savings in total system costs for deterministic and, to a lesser extent, stochastic scheduling; (ii) a decrease in the level of wind curtailment, with close agreement between stochastic and deterministic scheduling; and (iii) a decrease in the dispatch of open cycle gas turbine generation, evident with deterministic, and to a lesser extent, with stochastic scheduling.

Assessing the Economic Benefits of Compressed Air Energy Storage for Mitigating Wind Curtailment

Renewable energy generation in the All-Island of Ireland (AII) is set to increase by 2020 due to binding renewable energy targets. To achieve these targets, there will be periods of time when 75% of electricity will be generated mainly from onshore wind. Currently, the AII system can accommodate a 50% maximum permissible instantaneous level of wind generation. The system operators must make system-wide wind curtailment decisions to ensure that this level is not breached. Subsequently, the ability to limit wind curtailment using large-scale energy storage such as pumped hydroelectric energy storage and compressed air energy storage (CAES) is increasingly being scrutinized as a viable option. Thus, the aims of this paper are to estimate the level of wind curtailment on the 2020 AII system for various scenarios including with and without CAES, and assess and quantify the revenue loss due to wind curtailment using power systems simulation software PLEXOS.

Economic Curtailment of Intermittent Renewable Energy Sources

In a power system featuring a large share of intermittent renewable energy sources (RES) and inflexible thermal generators, efficiency gains on generation costs could be achieved by curtailing the production of RES. However, as RES feature very low variable production costs, over-curtailment can be costly. In this article, we use a stylised analytical model to assess this trade-off. We show that while curtailing RES when their variability is high and the system flexibility is low can reduce generation costs, the different stakeholders (consumers, dispatchable generators, RES) will not necessarily benefit from such measures. As a consequence, generators will opt for a sub-optimal level of curtailment, and this level of curtailment should rather be set by the TSO. Either incentive to provide the TSO with accurate forecasts of RES availability, or alternatively centralised forecasting by the TSO, should then be put into place to solve the resulting problem of asymmetry of information.

Optimum Level of Shear Wall Curtailment in Wall-Frame Buildings: The Continuum Model Revisited

AbstractThe continuum model constitutes a simple and efficient tool to analyze high-rise wall-frame buildings. It has been commonly used in recent decades to analyze the behavior of these structures. The related equations are revisited to study the effect of the calculation precision on the determination of the optimum level of wall curtailment. The results obtained illustrate the influence of calculation precision in specifying the optimum level of wall curtailment. The relationship between the curtailment level and the resulting internal forces is investigated. The level of curtailment which results in the minimum top deflection of the structure eliminates, at the same time, the negative moments and negative shear forces in the wall.

How much wind energy will be curtailed on the 2020 Irish power system?

This paper describes a model of the 2020 Irish electricity system which was developed and solved in a mixed integer programming, unit commitment and economic dispatch tool called PLEXOS®. The model includes all generators on the island of Ireland, a simplified representation of the neighbouring British system including proposed wind capacity and interconnectors between the two systems. The level of wind curtailment is determined under varying levels of three influencing factors. The first factor is the amount of offshore wind, the second is the allowed limit of system non-synchronous penetration (SNSP) and the third is inclusion or exclusion of transmission constraints. A binding constraint, resulting from the 2020 EU renewable energy targets, is that 37% of generation comes from wind. When the SNSP limit was increased from 60% to 75% there was a reduction in wind curtailment from 14% to 7%, with a further reduction when the proportion of wind capacity installed offshore was increased. Wind curtailment in the range of SNSP limit of 70–100% is influenced primarily by the inclusion of transmission constraints. Large changes in the dispatch of conventional generators were also evident due to the imposition of SNSP limits and transmission constraints.

Behavior of Curtailed Wall‐Frame Structures

The lateral load resistance of tall wall‐frame building structures comprising a combination of moment‐resisting frames and shear walls that are reduced in size or terminated entirely at intermediate heights is investigated. A generalized theory for the deflection of such structures is developed on the basis of a continuum model, to show that curtailment of the walls is not necessarily detrimental to the performance of the structure. Indeed, if the walls are curtailed within a certain height region the forces in the upper part of the frame are reduced while the top deflection is negligibly affected. An expression for the deflection of curtailed uniform wall‐frame structures is minimized to provide guidance for the optimum level of wall curtailment to cause a minimum increase in the top deflection. Guidance on the level of curtailment without detriment to the structure's performance for practical nonuniform wall‐frame structures is given.