Distributed power control
Results from distributed power control include integrating power users with power suppliers with Smart Grid technologies and storing energy for peak load shifting, and evening the load from renewable (non-baseload) power sources.
Peak-load shifting mitigates the effects of large energy load blocks during a period of time by advancing or delaying their effects until the power supply system can readily accept additional load. If loads cannot be regulated, then energy storage systems (ESSs), which often charge in off-peak times, can shift the load profile. Load shifting has been implemented successfully by end users in industrial and large-scale commercial facilities to decrease electrical peak demand and associated energy costs, although it is receiving noteworthy attention, and for different reasons than in the past. Peak shaving or peak smoothing can mitigate utility bills. It also effectively shifts the impact of the load on the system, minimizing the generation capacity required.
Renewable energy sources—specifically wind and photovoltaics (PV), which have seen exponential growth recently—provide irregular power due to meteorological and atmospheric conditions. As these power sources come to provide an increasingly significant contribution to the load flow in the electrical grid, their effects become more pronounced on the power quality of that grid. The erratic fluctuations in power generated by these renewables can be detrimental to maintaining transient and dynamic stability in the system. Renewable energy power quality concerns include voltage transients, frequency deviation, and harmonics.
An ESS can turn the intermittent source into one with a relatively uniform and consistent output. As such, the large-scale deployment of renewable energy sources coupled with the Smart Grid relies greatly on energy storage systems for maximum effectiveness and optimization.
ESS benefits can vary with the price of peak electricity. For example, consider that ERCOT's pricing on June 27, 2014, varied from approximately $35/MWh ($0.035/kWh) to approximately $1,000/MWh ($1.00/kWh) between 1 and 4 p.m. Each MWh consumed to charge batteries in off hours would save $965, to be discharged during peak hours. For large energy users, this could result in thousands of dollars in savings per day.
Power quality, measurement, control
An ESS can increase the quality of power to a facility by maintaining nominal voltage and frequency values. Fast-acting energy storage devices, such as batteries or ultra-capacitors, can absorb or discharge power to account for transient fluctuations in the utility power to help accomplish this.
Renewable generation controls
As renewable energy expands, it becomes increasingly necessary to convert the variable and intermittent power output into a more steady and reliable source.
As PV power is generated intermittently between sunrise and sunset, it is possible that generation does not coincide with a grid's peak power demands, necessitating that the utility have access to generation assets to supply high demand when cloud coverage restricts PV generation. As PV power grows to represent increased contribution to the grid, reliability issues could emerge, similar to the impact of wind power in states where wind has had much greater penetration.
ESS holds the promise of supporting end users in reducing their costs and allows generators access to a higher value of dispatchable generation through generation shifting.
Local energy storage can mitigate fluctuations in renewable generation output power by regulating ramp-up controls, absorbing power spikes, and responding to sudden sags by injecting power. This smoothing of the generation curve provides a more stable power source and reliable distribution grid. Some utility companies have requirements for grid connected generation, regulating power production waveforms by means of energy storage.
Utility ESS use
ESS use helps utilities to postpone major baseload power plant upgrades or additions that could be exponentially more costly.
A wide variety of methods for storing energy are implemented today, depending on the specific application and nature of the system requiring it. Energy can be stored using electrical, mechanical, thermal, and chemical storage systems, each with benefits and appropriate applications. Electrical storage systems are the most ubiquitous, typically in the form of batteries or capacitors. These can range from small watch batteries, to data center storage with emerging lithium-variant batteries, to utility-scale storage systems.
Battery energy storage systems have a response time that permits load flow and dynamic contribution for voltage control and frequency regulation, a critical element in coupling energy storage with renewable generation and maintaining grid stability.
For ESS, in contrast to lead-acid batteries, Li-ion batteries provide increased energy density and efficiency, and have more than double the life span of a typical lead-acid system. Li-ion battery systems require a management system to monitor the batteries for proper charging, discharging, and internal voltage regulation. Thermally unstable electrodes in the battery could undergo thermal runaway.
Smart Grid monitoring, controls
The Smart Grid is considered by many to be the future of the power grid, and energy storage plays an essential role in generation, transmission, and distribution systems. As demand for energy increases, constraints can exist in each system. Smart Grid methodologies and approaches can complement existing systems to improve the reliability and operation of the overall grid while meeting growth expectations.
The Smart Grid can help supplement centralized resources with decentralized options. The Smart Grid supports the central power plant configuration with the integration of renewable energy sources in the power network, from utility scale generation that can occupy hundreds of acres to small residential power sources. A control and automation center monitors and reacts to system events, from regulating generation and load flow to isolating power outages.
To create the Smart Grid, utility and renewable generators require flexible technologies that can quickly respond to transient and dynamic power fluctuations. Consumers also are likely to be encouraged to have an ESS to shift peak loads and mitigate demand fluctuations to the grid, requiring additional monitoring, controls, and integration.
As the Smart Grid develops and renewables increase in the percentage of generation, the use of energy storage system technology will mature to accommodate these demands. As battery and other energy shifting technology systems improve the quality and efficiency of our distribution systems, users will experience greater reliability and superior voltage and frequency stability, at lower costs.
- Robert C. Corson, PE, is a senior electrical engineer at Triad Consulting Engineers Inc. and an adjunct professor at New York University. Ronald R. Regan, PE, and Scott C. Carlson are staff engineers, both at Triad Consulting Engineers Inc. Edited from a peer-reviewed article in the Winter 2014 issue of Pure Power, a supplement to Consulting-Specifying Engineer by Mark T. Hoske, content manager, Control Engineering, firstname.lastname@example.org.
Integrating commercial buildings, utilities with the Smart Grid (includes more questions and answers about Smart Grid, lighting controls, building automation systems, codes and standards, financial incentives, and building system integration)
Implementing energy storage for peak-load shifting (includes recommended codes and standards for ESS from National Electric Code and from IEEE and other information)
- Control and monitoring technologies are helping with distributed power and Smart Grid technology implementations.
- Energy storage systems (ESSs), which often charge in off-peak times, can shift the load profile, saving costs.
- Smart Grid technologies will continue to advance electrical generation, transmission, and distribution.
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