Renewable Storage

Jeff Brunings explains the challenges of mitigating the unpredictable and rapid changes of renewable generation.

Energy storage isn’t just about storage capacity. It’s about power. And a new breed of fast response, high-power energy storage systems, like those introduced by energy and power management company Altairnano, is helping solve some tough challenges.

Take the renewable portfolio standards for example. 29 states, including the District of Columbia, have adopted aggressive mandates for integrating renewable generation. Illinois, Minnesota, Nevada, Ohio and Oregon, each with relatively low levels of renewable generation, are all shooting to have 25 percent renewable integration with the grid by 2025.

Those are aggressive goals, especially when considering that renewable generation currently represents a little more than two percent of total US electricity generation.

As the penetration of wind and solar generation deepens, energy storage systems like the Altairnano Energy Storage System (ALTI-ESS) will be needed to help stabilize the electric grid and mitigate the unpredictability associated with renewable generation.

In the US today, the relatively small amount of non-dispatchable energy in a balancing area rarely has significant impact on system operations. This is because the natural variability of the load is still greater than the uncertainty of utility-connected renewable energy resources. But this is changing, and it’s changing fast.

In fact, FERC recently announced a $500,000 study to determine whether the existing US power grid can handle the addition of substantial amounts of renewable resources by 2012. Results are expected to be released in late 2009. And the California Independent System Operator (CAISO) anticipates by 2012 regulation capacity could increase by 250 MW for up regulation and up to 500 MW for down regulation for a total of 750 MW.

Of all renewable generation resources, wind and photovoltaic solar are most likely to contribute to grid instability. In a report published in April 2009, NERC predicted “at higher levels of variable generation, the operation and characteristics of the [system] can be significantly altered.” The study cites the potential for wind generation to increase ramping requirements of conventional generation as much as 45 percent to maintain grid stability.

Utility-scale PV systems have experienced substantial ramps, as well. According to the NERC study, PV systems may experience variations in output of +/- 50 percent in a 30 to 90 second timeframe and +/- 70 percent in a five to ten minute time frame.

The problem with conventional generation is that it can not dispatch in the time required to respond to sudden variations in renewable generation output. Ramp rates for diesel engines require up to three minutes for achieving full power. Gas engines require up to seven minutes. Industrial gas turbines may take up to 20 minutes. The ALTI-ESS achieves full power in milliseconds.
 
Based on advanced lithium-titanate technologies, ALTI-ESS responds to these fluctuations by releasing or absorbing power from the electricity grid. This helps improve equipment and capacity utilization, strengthen operational efficiencies and reduce carbon emissions. Current solutions in commercial operation include a 1 MW/250 kWh system at the PJM Interconnection, which runs nearly continuous operation throughout the day for The AES Corporation.

The ALTI-ESS features a power module and power control system module. The power module has a 1 MW lithium titanate battery stack and a battery management system. Power modules can be added for multiple MW configurations. The power control system module features necessary electronics to convert from DC to AC and communications software required for receiving and responding to grid signals, including PLC, SCADA, and data service unit.

Additionally, the ALTI-ESS is transportable, scalable to multi-megawatt configurations, achieves greater than 90 percent roundtrip efficiency and has an expected calendar life exceeding 20 years. A basic configuration is a 1 MW/250kWh system, but it’s capable of supplying different power and energy requirements depending on system.

As states move toward achieving renewable portfolio standards no one knows the increased costs utilities will incur for managing grid stability. No one really knows the full mega-watt potential for fast response, energy storage systems, either. But, if California is any indication, with an anticipated increase of 750 MW total regulation capacity required by 2012, both the cost and opportunity are significant.

Jeff Brunings serves as director, strategic marketing for Altairnano, a leading provider of energy storage systems for clean, efficient power and energy management.