Energy storage systems (ESSs) are enabling technologies for well-established and new applications such as power peak shaving, electric vehicles, integration of renewable energies, etc. This paper presents a review of ESSs for transport and grid applications, covering several aspects as the storage technology, the main applications, and the power converters used to operate some of the energy storage technologies. Special attention is given to the different applications, providing a deep description of the system and addressing the most suitable storage technology. The main objective of this paper is to introduce the subject and to give an updated reference to nonspecialist, academic, and engineers in the field of power electronics.

Energy Storage Systems for Transport and Grid Applications

Energy storage for mitigating the variability of renewable electricity sources: An updated review

Energy storage: Applications and challenges

Vehicle-to-grid (V2G) has been proposed as a way to increase the adoption rate of electric vehicles (EVs). Unidirectional V2G is especially attractive because it requires little if any additional infrastructure other than communication between the EV and an aggregator. The aggregator in turn combines the capacity of many EVs to bid into energy markets. In this work an algorithm for unidirectional regulation is developed for use by an aggregator. Several smart charging algorithms are used to set the point about which the rate of charge varies while performing regulation. An aggregator profit maximization algorithm is formulated with optional system load and price constraints analogous to the smart charging algorithms. Simulations on a hypothetical group of 10 000 commuter EVs in the Pacific Northwest verify that the optimal algorithms increase aggregator profits while reducing system load impacts and customer costs.

Optimal Charging Strategies for Unidirectional Vehicle-to-Grid

The paper analyzes the impact of integrating wind generation on the regulation and load following requirements of the California Independent System Operator (CAISO). These requirements are simulated and compared for the study cases with and without wind generation impacts included into the study for the years 2006 and 2010. Regulation and load following models were built based on hour-ahead and five-minute ahead load and wind generation forecasts. In 2006, the CAISO system peaked at 50 270 MW. Wind generation (at the installed capacity of 2600 MW) had limited impact on the requirement of load following and regulation in the CAISO Balancing Authority. However, in 2010 (with an expected installed capacity of approximately 6700 MW), this impact will significantly increase. The results provide very useful information for the CAISO to adjust its scheduling and real-time dispatch systems to reliably accommodate future wind generation additions within the CAISO Balancing Authority.

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Operational Impacts of Wind Generation on California Power Systems

Energy produced by intermittent renewable resources is sharply increasing in the United States. At high penetration levels, volatility of wind power production could cause additional problems for the power system balancing functions such as regulation. This paper reports some partial results of a project work, recently conducted by the Pacific Northwest National Laboratory (PNNL) for Bonneville Power Administration (BPA). The project proposes to mitigate additional intermittency with the help of Wide Area Energy Management System (WAEMS) that would provide a two-way simultaneous regulation service for the BPA and California ISO systems by using a large energy storage facility. The paper evaluates several utility-scale energy storage technology options for their usage as regulation resources. The regulation service requires a participating resource to quickly vary its power output following the rapidly and frequently changing regulation signal. Several energy storage options have been analyzed based on thirteen selection criteria. The evaluation process resulted in the selection of flywheels, pumped hydro electric power (or conventional hydro electric power) plant and sodium sulfur or nickel cadmium batteries as candidate technologies for the WAEMS project. A cost benefit analysis should be conducted to narrow the choice to one technology.

On the use of energy storage technologies for regulation services in electric power systems with significant penetration of wind energy

Wind power is growing in a very fast pace as an alternative generating resource. As the ratio of wind power over total system capacity increases, the impact of wind on various system aspects becomes significant. This paper presents a methodology to study the future impact of wind on BPA power system ancillary services including load following and regulation. Existing approaches for similar analysis include dispatch model simulation and standard deviation evaluation. The methodology proposed in this paper uses historical data and stochastic processes to simulate the load balancing processes in BPA power system. Then capacity, ramp rate and ramp duration characteristics are extracted from the simulation results, and load following and regulation requirements are calculated accordingly. It mimics the actual power system operations therefore the results can be more realistic yet the approach is convenient to perform. Further, the ramp rate and ramp duration data obtained from the analysis can be used to evaluate generator response or maneuverability and energy requirement, respectively, additional to the capacity requirement.

The future impact of wind on BPA power system ancillary services

Energy production must continuously match demand on the electric grid. A deficiency can lead to service disruptions, and a surplus can place tremendous stress on grid components, potentially causing major blackouts. To manage this balance, grid operators must increase or lower power generation, with only a few minutes to react. The grid balancing problem has also impeded the pace of integrating bountiful renewable resources (e.g., wind), whose generation is intermittent. An emerging plan to mitigate this problem is demand response, i.e., for grid operators to alter the electricity usage behavior of the masses through real-time price signals. But due to prohibitively high infrastructure costs and societal-scale adoption, tangible demand response mechanisms have so far been elusive.We believe that altering the usage patterns of a multitude of data centers can be a tangible, albeit initial, step towards affecting demand response. Growing in both density and size, today's data center designs are shaped by the increasing awareness of energy costs and carbon footprint. We posit that shifting computational workloads (and thus, demand) across geographic regions to match electricity supply may help balance the grid. In this paper we will first present a real grid balancing problem experienced in the Pacfic Northwest. We then propose a symbiotic relationship between data centers and grid operators by showing that mutual cost benefits can be accessible. Finally, we argue for a low cost workload migration mechanism, and pose overarching challenges in designing this framework.

Electric grid balancing through lowcost workload migration

The area control error (ACE) determines how much a balancing authority (BA) needs to move its regulating units to meet mandatory control performance standard requirements. Regulation is an expensive resource that could cost several hundred million dollars a year for a BA. The amount of regulation needed in a system is increasing with more intermittent generation resources added to the system. The ACE diversity interchange (ADI) program provides a tool for reducing the regulation requirement by combining ACEs from several participating BAs followed by sharing the total ACE among all participating balancing areas. The effect is achieved as a result of the low statistical correlation between the original ACEs of participating BAs. A rule-based ADI approach has already been put into practice in the US Western Interconnection. The degree of actual ACE sharing is artificially limited because of the unknown redistribution of power flows and possible system congestion (these factors are not monitored in the existing ADI). This paper proposes a two-step linear programming (LP) ADI approach that incorporates congestion constraints. In the first step of the proposed LP ADI, the line transmission limits are enforced by setting up corresponding constraints. In the second step, the business fairness is pursued. Simulation is performed to compare the properties of the proposed LP ADI and the existing rule-based ADI. Favorable features, such as avoiding line limit violations and increasing the degree of possible ACE sharing, are observed for the proposed LP ADI.

Improving area control error diversity interchange (ADI) program by incorporating congestion constraints

The variability and uncertainty of wind power production require increased flexibility in the power systems, or more operational reserves to maintain a satisfactory level of reliability. The incremental increase in reserve requirement caused by wind power is often studied separately from the effects of loads. Accordingly, the cost in procuring reserves is allocated based on this simplification rather than a fair and transparent calculation of the different resources' contribution to the reserve requirement. This work proposes a new allocation mechanism for variability and uncertainty of resources regardless of their type. It is based on a new formula called the grid-balancing metric (GBM). The proposed GBM has several distinct features: 1) it is directly linked to the control performance standard scores and interconnection frequency performance, 2) it provides scientifically defined allocation factors for individual resources, 3) the sum of allocation factors within any group of resources is equal to the groups' collective allocation factor (linearity), and 4) it distinguishes helpers and harmers. The paper illustrates and provides results of the new approach based on actual transmission system operator data.

Bart McManus

Papers

On the use of energy storage technologies for regulation services in electric power systems with significant penetration of wind energy

The future impact of wind on BPA power system ancillary services

Electric grid balancing through lowcost workload migration

Improving area control error diversity interchange (ADI) program by incorporating congestion constraints

Calculating Individual Resources Variability and Uncertainty Factors Based on Their Contributions to the Overall System Balancing Needs