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Integration of renewable generation in California: Coordination challenges in time and space
Abstract
The successful integration of intermittent and distributed electric generation from renewable resources can be viewed as a coordination problem at multiple scales in both space and time. This paper presents an overview of coordination issues relative to the goals for renewable integration in California.
... The renewable energy industry may also substitute 'variability' as a generic term for the irregular power fluctuations derived from intermittent meteorological phenomena. von Meier (2011) posed that the interesting question in distributed generation of renewable energy is how to address intermittency/variability for many time scales, using current and emerging technologies and techniques. Systematic coordination challenges will span orders of magnitude in spatial and temporal scales, highlighting the importance of successful planning and adaptation to future integration of intermittent renewable energy sources. ...
... Systematic coordination challenges will span orders of magnitude in spatial and temporal scales, highlighting the importance of successful planning and adaptation to future integration of intermittent renewable energy sources. In order to maximize benefits for the emerging renewable energy resources, one must be cognizant of both finer spatio-temporal scales and large-scale strategic planning and contracting that consider the systematic properties of the regional power grids (von Meier, 2011). Solar power generation must be considered in conjunction with challenges to management for power regulation and transmission, and with challenges for electricity markets and long term contracts. ...
... In Table 2 we consider solar power generation in conjunction with three challenges identified by von Meier (2011) as cases for evaluation: day-ahead markets, service and restoration power management time scales, and hour-ahead markets. We refer back to Fig. 1 to compare a b c d Fig. 6. ...
Understanding fluctuations of irradiance across spatio-temporal scales is crucial for improving solar resource forecasting and evaluating co-production strategies for solar-fossil power technologies. We show that irradiance can be coupled across spatial and temporal coordinates, for regional analyses of short-term (less than 12 h) and long-term (intra-seasonal) variability as well as inter-site regional coherency and phase behavior. Downwelling shortwave solar irradiance data (DWS; 3-min averaging) is used for a three-year period from 2007 to 2009. Six USA sites are selected from the Integrated Surface Irradiance Study (ISIS) and Surface Radiation (SURFRAD) budget network. Power spectral density is used to analyze the short term and long term variations in DWS. To assess the long-term variations, the data is analyzed in seasonal periods: winter, spring, summer, and fall. Additionally, the cospectra are evaluated to compare the regional variation between sites. The inter-site coherency and phase analysis allows geographic correlation of the solar resource variability to be evaluated. The three pairs of locations include a mid-continent region: Fort Peck, MT with Bismarck, ND; a mid-Atlantic region: Rock Springs, PA with Sterling, VA; and a southwest region: Desert Rock, NV with Hanford, CA. Results indicate that understanding long-term aperiodic oscillations are useful to optimize the co-production of solar/fossil power technologies via slow ramping solutions. Seasonal analysis of short term variations (<12 h) suggests that the ability of a regionally dispersed network of PV to dampen the high variability of solar power production is dependent upon the climatic regime (both location and season-dependent), resulting in a variable decreased demand for fast-ramping fossil technologies.
... Privatization and deregulation are posing lots of challenges on the electrical power system. This makes the grid to be loaded up to its stability limits and wide-area power trading with quick varying load patterns will add to increasing transmission congestion [8]. There are lots of challenges before the electricity distribution system in responding to the increasing demand of customer for electricity in the modern world [9]. ...
... It contributes to solve technical problems in the interconnected grid. FACTS can be utilized in parallel {static VAR compensator (SVC), static synchronous compensator (STATCOM)} or series {fixed series compensation (FSC), thyristor controlled/protected series compensation (TCSC/TPSC), solid-state series compensation (SSSC)} or in conjunction of both {unified power flow controller (UPFC), convertible static compensator (CSC)} for load flow control and dynamic conditions improvement [8]. GPFC is a special DC back-to-back (B2B) link, which is made for fast voltage and power control at both terminals. ...
... SVCs can have a maximum rating of 800MVAr, and series FACTS devices can be utilized on 550kV and 735kV level to improve the transmission line capacity up to many GW. Through DC and AC Ultra High Power transmission technologies, the smart grid will be smarter for a secure and sustainably made available to large renewable energy resources [8]. ...
The increasing complexity of the conventional grid due to population growth, advancement in technology, and infrastructures are the factors that contribute immensely to instability, insecurity, and inefficiency of the use of electrical energy. To overcome the problems, the environmental energy sustainability calls for the use of renewable energy for sustainability of power supply. Intermittency and fluctuation of the renewable energy is a great challenge on the smart grid. This paper reveal the potential challenges of renewable energy on the smart grid and proffer solution with the application of high voltage DC (HVDC) and Flexible AC transmission system (FACTS) devices. The functions and advantages of FACTS devices are presented in this paper. Voltage control and stability control with FACTS application are also discussed because FACTS has fast controllability and capability to exchange active and reactive power independently.
... Remark 5: It is important to realize that fluctuations of renewable energy sources occur on time scales that are large compared to the intrinsic time scales of the power system [20]. As a matter of fact, time scales in the synchronous grid of continental Europe have been found to satisfy γ −1 2.5s and λ D α −1 0.5s [19]. ...
... means that we take the average over all nodes in the grid. It is commonly accepted that power fluctuations from renewable energy sources such as wind turbines or photovoltaic panels fluctuate on time scales that are larger than both time scales in Eq. (13) [20]. Therefore, the asymptotic limit of large noise correlation time, corresponding to Eq. (11) applies, and we expect that the primary control effort as measured by Eq. (7) is influenced only by damping, and not by inertia. ...
Many recent works in control of electric power systems have investigated their synchronization through global performance metrics under external disturbances. The approach is motivated by fundamental changes in the operation of power grids, in particular by the substitution of conventional power plants with new renewable sources of electrical energy. This substitution will simultaneously increase fluctuations in power generation and reduce the available mechanical inertia. It is crucial to understand how strongly these two evolutions will impact grid stability. With very few, mostly numerical exceptions, earlier works on performance metrics had to rely on unrealistic assumptions of grid homogeneity. Here we show that a modified spectral decomposition can tackle that issue in inhomogeneous power grids in cases where disturbances occur on time scales that are long compared to the intrinsic time scales of the grid. We find in particular that the magnitude of the transient excursion generated by disturbances with long characteristic times does not depend on inertia. For continental-size, high-voltage power grids, this corresponds to power fluctuations that are correlated on time scales of few seconds or more. We conclude that power fluctuations arising from new renewables will not require per se the deployment of additional rotational inertia. We numerically illustrate our results on the IEEE 118-Bus test case and a model of the synchronous grid of continental Europe.
... -8 - Table 3 Challenges of VRE integration. [4,5,11,12,[14][15][16][17][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42] Category Challenge Description Source ...
... The location dependency of VRE generation requires increasingly long transmission distances between generation and consumption locations leading to higher transmission losses. [5,23] ...
Variable renewables such as solar photovoltaics and wind power are key technologies for achieving the decarbonization of the power sector. However, they differ significantly from conventional power generation sources. As the share of variable renewables increases, these differences lead to numerous challenges in power systems. Failure to deal with these challenges may jeopardize power system reliability or the achievement of decarbonization targets. Various solution technologies are available to mitigate these challenges. The extant literature, however, lacks clarity on the scope of the challenges and the solution technologies to address them. This study provides a comprehensive overview of challenges and solution technologies among all domains of the power system. The interrelation matrix of challenges and solution technologies developed in this study provides important insights: First, solution technologies vary significantly in their potential to solve certain challenges. The solution potential of different technologies can therefore help prioritize solution technologies in addition to focusing on cost-effective options. Second, it is possible to identify groups of solution technologies that can help mitigate certain challenge groups. The categorization developed in this paper helps to better specify the need for specific solution technologies and enhances transparency of the complex process of renewable energy integration.
... Time and length scales relevant to ancillary services (highlighted with red circles), adapted from[10]...................................................................................................................... Sequential actions of primary, secondary and tertiary frequency controls following sudden loss of generation and their impacts on system frequency, adopted from [16]. ........... Power triangle showing the relationship between real, reactive and apparent power component of an AC supply. ...
... Time and length scales relevant to ancillary services (highlighted with red circles), adapted from[10]. ...
This report reviews a set of electric grid ancillary services and analyzes the technical potential for residential devices to provide those services. A set of common residential devices are evaluated against six indicators of capability: flexibility, availability, fast response, reserves, reactive power, and power level. Based on these indicators of capability, three scores are developed to express the potential of a device to provide frequency response, reserves and reactive power services. These scores are additionally used to estimate how many of each device might be required, in aggregation, to provide a meaningful level of each of these three ancillary services to the grid. This report also provides a review of some existing programs and pilot efforts where residential devices are being used to provide ancillary services. Lastly, the report provides insights on a continued path to increased integration of residential devices for ancillary services provision.
... Both the CAISO and the CPUC have initiated proceedings to develop more robust estimates to guide utility and CAISO procurement of flexible capacity. Integration studies for California find that key characteristics of firming resources include not only their total capacity, but response times, ramp rates and flexible operating range [17]. With aggressive RPS goals driving increased penetration of intermittent renewable generation, planned retirements of fossil generation with once-through cooling (OTC) and the permanent closure of the 2,350 MW San Onofre Nuclear Generating Station (SONGS), California is a leading case study on the need for new methods to evaluate and procure flexible capacity. ...
... However, the value of storage as a flexible resource is not well represented in existing markets or modeling tools [12]. Von Meier [17] states that "in the face of substantial costs, a key implementation challenge for storage lies in the definition of the value proposition -that is, the valuation of diverse services offered to the grid by a given storage resource -and the design of appropriate incentive mechanisms that account for risk and reward sharing among utilities, consumers, and third parties." Prior studies have found that bulk energy storage can provide system benefits that are not captured in energy markets alone [18] and that market structure and ownership can have significant impacts on break-even costs [19]. ...
... This in turn, leads to cascading journeys, breaches of regulations on dynamic stability or an accumulation of incidents of stability. [27,103,127] Diminishing reserves of frequency control ...
Wind power, solar power and water power are technologies that can be used as the main sources of renewable energy so that the target of decarbonisation in the energy sector can be achieved. However, when compared with conventional power plants, they have a significant difference. The share of renewable energy has made a difference and posed various challenges, especially in the power generation system. The reliability of the power system can achieve the decarbonization target but this objective often collides with several challenges and failures, such that they make achievement of the target very vulnerable, Even so, the challenges and technological solutions are still very rarely discussed in the literature. This study carried out specific investigations on various technological solutions and challenges, especially in the power system domain. The results of the review of the solution matrix and the interrelated technological challenges are the most important parts to be developed in the future. Developing a matrix with various renewable technology solutions can help solve RE challenges. The potential of the developed technological solutions is expected to be able to help and prioritize them especially cost-effective energy. In addition, technology solutions that are identified in groups can help reduce certain challenges. The categories developed in this study are used to assist in determining the specific needs and increasing transparency of the renewable energy integration process in the future.
... Whereas data used to be collected on the level of daily or hourly means, now data is collected and even used in real time [5,6]. Since household load and renewable generation are known to fluctuate on the level of minutes or even seconds [7], fine grained data collection could be relevant to provide an accurate picture of energy use and generation. Indeed these new possibilities are embraced by researchers who are formulating increasingly precise energy profiles [8,9,10,11]. ...
Research regarding the optimal planning of distributed generation is often based on coarse energy use and generation data, which does not accurately reflect real variations in energy profiles. This paper investigates the impact of this inaccuracy on the optimal planning of distributed generation. The problem of loss minimization in the residential setting is used as a guideline. The outcomes of a stochastic optimization model for energy profiles defined on different time aggregation levels are compared. At first glance, modeling on a finer time scale seems to affect optimal planning solutions, with a shift from variable stochastic sources to sources that provide constant generation. However, it turns out that the gains of using these new optimal solutions in terms of reducing energy losses are limited. The results suggest that for optimization purposes it is not necessary to use data at a resolution smaller than hourly time steps. If energy profiles are defined on time steps smaller than one hour it is important that the full range of the stochastic fluctuations is taken into account, rather than evaluating a couple of scenarios.
... As a result, traditionally structured power systems must adjust to accommodate these new resources. Intermittent resources increase both the forecast error and the variability in net loads across multiple time scales [1]. This presents a challenge to system planners tasked with deciding which new resources to build, subject to forecasted trends in load growth and future renewable development. ...
As intermittent energy resources become more significant in power production, traditional capacity planning may be insufficient to ensure reliable system operation. A system planner must ensure that flexibility solutions are available to respond to large and uncertain ramping events. These solutions may be operational, such as improved unit commitment and dispatch, curtailment of renewables, or demand response; procurement based, such as new fast ramping resources or batteries; or involve market reform. This paper outlines a new methodology for modeling the economic tradeoffs in implementing flexibility solutions for integrating renewables. The proposed model includes both a stochastic treatment of system states to account for a wide range of operating conditions and an adapted production simulation methodology that weighs the cost of reliability and subhourly flexibility violations against the cost of the operational flexibility solutions available to mitigate them. The model's functionality is demonstrated with a case study of California at a 50% RPS in 2030. The model tests the value of 1088 MW of generic flexible units, relative to the same capacity of must-run resources, finding an expected annual value of million/yr. Potential applications of the model for resource planning and procurement are also discussed.
With the advent of a new Precision Time Protocol specification, new opportunities abound for clock synchronization possibilities within power grid control systems. The third iteration of the Institute of Electrical and Electronics Engineers Standard 1588 specification provides several new features specifically aimed at complex, wide-area deployments in which situational awareness and control require precise time agreement. This paper describes the challenges faced by existing technology, introduces the new time distribution specification, and provides examples to explain how it represents a game-changing innovation.
Australia is one of the leading countries in energy transition, and its largest power system is intended to securely operate with up to 75% of variable renewable generation by 2025. High-inertia synchronous condensers, battery energy storage systems, and grid-forming converters are some of the technologies supporting this transformation while facilitating the secure operation of the grid. Synchronous condensers have enabled 2500 MW of solar and wind generation in the state of South Australia, reaching minimum operational demands of ≈100 MW. Grid-scale battery energy storage systems have demonstrated not only market benefits by cutting costs to consumers but also essential grid services during contingencies. Fast frequency response, synthetic inertia, and high fault currents are some of the grid-supporting capabilities provided by new developments that strengthen the grid while facilitating the integration of new renewable energy hubs. This manuscript provides a comprehensive overview, based on the Australian experience, of how power systems are overcoming expected challenges while continuing to integrate secure, low cost, and clean energy.
This paper discusses the need for data-driven tools to manage modern electric grids, where planning and operational decisions increasingly require empirical data on various time scales. The advancement of such tools will hinge on deploying instrumentation to collect faster and more localized measurements, capitalizing on state-of-the-art software solutions to facilitate big-data workflows, and enabling open exchange of data and information with research collaborators.
System operators face significant evolving conditions in power systems with the increasing penetration of RES, the growing competitiveness of the free electricity market, the integration of new technologies and the need to increase flexibility and control capabilities into the operational framework. Operational processes in today’s power system are still primarily based on the availability of sufficient conventional synchronous generation. Operation of the future power system, however, will be characterised by time instances with few to no conventional synchronous generation in operation, urging operators to adapt their knowledge and skills, methods, tools and processes accordingly. This chapter describes the current practices and provides insight into the expected operational challenges inherent to the future power system. To cope with these challenges, ongoing developments of innovative technological- and market-based solutions are presented. Finally, the need for more integration and coordination, and the role of sector coupling in the future power system are highlighted.
This chapter gives comprehensive overviews of the social context of energy in Japan and underscores the pressing need for economically efficient energy management systems. Next, because the aim is to overcome emerging worldwide issues, this chapter surveys past, present, and future academic research trends and their contributions to the study of power, economics, control, and system architecture. This chapter also provides a detailed outline of the book.
The global energy landscape is witnessing a concerted effort toward grid modernization. Motivated by sustainability, skyrocketing demand for electricity, and the inability of a legacy infrastructure to accommodate distributed and intermittent resources, a cyber-physical infrastructure is emerging to embrace zero-emission energy assets such as wind and solar generation and results in a smart grid that delivers green, reliable, and affordable power. A key ingredient of this infrastructure is electricity markets, the first layer of decision-making in a smart grid. This chapter provides an overview of electricity markets which can be viewed as the backdrop for their emerging role in a modernized, cyber-enabled grid. Starting from a brief history of the electricity markets in the United States, the article proceeds to delineate the current market structure, and closes with a description of current trends and emerging directions.
The intermittency of solar power production is dependent on the evolution and advection of the nearby cloud field. A key problem related to solar energy integration is the improvement of 1-h-ahead forecasts to reduce the impact of intermittency on power systems operations. Many solar forecasts explicitly or implicitly assume Taylor's hypothesis. While such advection-only forecasts can be presumed to be valid across sufficiently short time scales, it is not clear how rapidly the skill of such a forecast decays with increased lead time. As the goal is to improve the quality of 1-h-ahead forecasts, this work focuses on quantifying the skill of cloud-track wind-based cumulus-dominated cloud field forecasts with respect to lead time. No explicit connection is drawn to the quality of solar forecasts because of the importance of separating two potential sources of error: cloud field forecasting and radiative transfer estimation. It is found that the cumulus field forecast skill begins to asymptotically approach a minimum at lead times of beyond 30 min, suggesting that advection-only forecasts in a cumulus-dominated environment should not be relied upon for 1-h-ahead point forecasts used by radiative transfer methods to estimate solar power production. A first attempt at forming a probabilistic forecast that can quantify this increasing uncertainty when using advection-only methods is presented.
An interconnected electric power system is a complex system that must be operated within a safe frequency range in order to reliably maintain the instantaneous balance between generation and load. This is accomplished by ensuring that adequate resources are available to respond to expected and unexpected imbalances and restoring frequency to its scheduled value in order to ensure uninterrupted electric service to customers. Electrical systems must be flexible enough to reliably operate under a variety of"change" scenarios. System planners and operators must understand how other parts of the system change in response to the initial change, and need tools to manage such changes to ensure reliable operation within the scheduled frequency range. This report presents a systematic approach to identifying metrics that are useful for operating and planning a reliable system with increased amounts of variable renewable generation which builds on existing industry practices for frequency control after unexpected loss of a large amount of generation. The report introduces a set of metrics or tools for measuring the adequacy of frequency response within an interconnection. Based on the concept of the frequency nadir, these metrics take advantage of new information gathering and processing capabilities that system operators are developing for wide-area situational awareness. Primary frequency response is the leading metric that will be used by this report to assess the adequacy of primary frequency control reserves necessary to ensure reliable operation. It measures what is needed to arrest frequency decline (i.e., to establish frequency nadir) at a frequency higher than the highest set point for under-frequency load shedding within an interconnection. These metrics can be used to guide the reliable operation of an interconnection under changing circumstances.
The deployment of small ( < 1-2 MW ) clusters of generators, heat and electrical storage, efficiency investments, and combined heat and power (CHP) applications (particularly involving heat-activated cooling) in commercial buildings promises significant benefits but poses many technical and financial challenges, both in system choice and its operation; if successful, such systems may be precursors to widespread microgrid deployment. The presented optimization approach to choosing such systems and their operating schedules uses Berkeley Lab's Distributed Energy Resources Customer Adoption Model (DER-CAM), extended to incorporate electrical and thermal storage options. DER-CAM chooses annual energy bill minimizing systems in a fully technology-neutral manner. An illustrative example for a hypothetical San Francisco hotel is reported. The chosen system includes one large reciprocating engine and an absorption chiller providing an estimated 11% cost savings and 8% carbon emission reductions under idealized circumstances.
With the growing implementation of synchrophasors or PMUs across the power grid, it is now possible to observe and analyze system-wide dynamic phenomena in real-time. At Washington State University (WSU), we have been developing the framework of an Oscillation Monitoring System (OMS) for extracting the modal information of electromechanical oscillations from synchrophasors in real-time. A prototype version of OMS has already been implemented in real-time at Tennessee Valley Authority (TVA) and it is being tested and tuned. The paper summarizes the theory of OMS and highlights the implementation features at TVA.
The future power system integrated a large share of distributed generation (DG) may causes a reduction of the system rotational inertia, resulting in high frequency variations with any disturbances. An additional rotational inertia will be provided to the system if many DG units combined with relative small storage systems operate like virtual synchronous generators (VSG). This paper presents the demonstration approach for the VSGs in order to bring the VSG models developed in the laboratory into practice at two distribution test sites for both single- and three-phase applications. The results show promising results where changes in frequency and voltage are clearly counteracted by power flows from the VSG. In addition, VSG may provide a solution for hosting a large share of DG in future grids while maintaining system stability.
This paper develops new methods to model and control the aggregated power demand from a population of thermostatically controlled loads, with the goal of delivering services such as regulation and load following. Previous work on direct load control focuses primarily on peak load shaving by directly interrupting power to loads. In contrast, the emphasis of this paper is on controlling loads to produce relatively short time scale responses (hourly to sub-hourly), and the control signal is applied by manipulation of temperature set points, possibly via programmable communicating thermostats or advanced metering infrastructure. To this end, the methods developed here leverage the existence of system diversity and use physically-based load models to inform the development of a new theoretical model that accurately predicts – even when the system is not in equilibrium – changes in load resulting from changes in thermostat temperature set points. Insight into the transient dynamics that result from set point changes is developed by deriving a new exact solution to a well-known hybrid state aggregated load model. The eigenvalues of the solution, which depend only on the thermal time constant of the loads under control, are shown to have a strong effect on the accuracy of the model. The paper also shows that load heterogeneity – generally something that must be assumed away in direct load control models – actually has a positive effect on model accuracy. System identification techniques are brought to bear on the problem, and it is shown that identified models perform only marginally better than the theoretical model. The paper concludes by deriving a minimum variance control law, and demonstrates its effectiveness in simulations wherein a population of loads is made to follow the output of a wind plant with very small changes in the nominal thermostat temperature set points.
Transmission technology research for renewable integration
- M Brown
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Oscillation monitoring system using synchrophasors
- Guoping Liu
- V M Venkatasubramanian
- J R Carroll
Guoping Liu, VM Venkatasubramanian and JR Carroll, "Oscillation
monitoring system using synchrophasors," IEEE Power Engineering
Society General Meeting, July 2009.