Grid Integration

The US has been presented with a credible scenario to achieve 20% of its energy needs from clean, secure wind generation, in a report prepared by the US DOE. [1] The report concludes that this level of wind penetration is possible without new technologies by expanding load balancing areas, creating more flexible electric transmission and using natural gas combustion turbine generators to balance the remaining variability.  However, there are multiple barriers to this approach, including: regulatory hurdles to expanding load balance areas; financial, permitting and public opinion barriers to expanding the transmission grid; and long-term risk associated with supply and regulation of fossil fuels such as natural gas.

Researchers at Boise State believe that grid integration is one of the key obstacles to achieving 20% of electric generating capacity from wind by 2030.  To facilitate integrating high penetration levels onto the nation’s electric grids, our research foci are:

• improved energy forecasting
• distributed energy storage
• greater utilization of deferrable loads

Energy Forecasting
Wind energy forecasting has seen many improvements recently, but many grid operators remain skeptical of such forecasts.  Some industry partners have indicated that grid operators simply assume that the net energy contributions from wind generation facilities will be zero – regardless of the current state of generation or the forecasts they are receiving.  Until forecasts become reliable to grid operators, the nation will continue wasting other energy sources, such as natural gas, in spinning reserves.  Further, ramp events must be accurately forecast to prevent imbalance between load and generation.  Such events have recently occurred on both the BPA and ERCOT transmission grids.  Therefore, we recommend increased research in the area of wind forecasting –and not just by national labs, universities and forecasting companies.  Rather, we believe the grid operators – such as our industry partners at Idaho Power and Bonneville Power Administration – must collaborate and actively participate in efforts to improve wind energy forecasting methods.

Boise State University is the lead institution on a research project titled “Forecasting for Wind Energy Grid Integration”; funding (50%) is provided by the Bonneville Power Administration; the project is attempting to forecast power (MW) output from a 42 MW wind energy facility in time increments 5-minutes, one-hour and 24-hours ahead by coupling mesoscale weather forecasts with Computational Fluid Dynamics to forecast wind speeds at each turbine and incorporating SCADA system information for turbine availability; project collaborators include Idaho National Lab, Idaho Power Company, John Deere Renewable Energy (facility  owner/operator) and Renaissance Engineering and Design. 

Energy Storage
Energy Storage provides many benefits to both grid operators and distributed power providers.  The primary benefits are ancillary services provided to the grid.  Applications include: peak shaving; spinning reserve; VAR support; and arbitrage.  Independent power providers benefit because the energy from a variety of sources (including wind, solar and the grid itself) can be temporarily stored to be recovered at a later time, presumably when it is more needed and, perhaps, more valuable. 

The advantages of energy storage are particularly compelling when coupled with an intermittent source such as wind energy.  For example, a wind farm or solar power plant coupled with onsite energy storage could conceivably be used by utilities to supplement base loads or meet hourly load variations and peaks.

During wind ramp events, as discussed above, energy can be stored in bulk systems (on the order of several hours) and delivered to the grid when it is needed; storage can “firm” energy delivery to the grid; and response systems (on the order of milliseconds to minutes) can reduce the need for ancillary services.  Many types of energy storage have seen increases in research and development, including compressed air, hydrogen, pumped hydro, utility scale flywheel facilities, and trailer based batteries.  Likewise, there has been much popular discussion of plug-in electric hybrid vehicles providing grid support.  However, none of these systems has yet gained broad market acceptance.  More research is required to develop energy storage systems which are: low-cost; carbon-neutral; and non-site-specific. 

Mechanical engineering researchers at Boise State have made significant progress towards an energy storage system that mitigates some of the grid-integration challenges posed by intermittent electric generators, such as wind turbines.  Our research on Carbon-Free, Site Independent Energy Storage will be summarized at the 2009 AWEA Windpower Conference and Exhibition in Chicago. The approach is similar to existing Compressed Air Energy Storage but with two key differences: it avoids the requirement of natural gas combustion that is mandatory in the traditional compressed air energy storage systems and is not site specific. The proposed approach incorporates the most attractive attributes from traditional CAES and pumped hydro energy storage systems and eliminates some of their shortcomings.  The cycle starts with a storage tank partially filled with water.  Energy from the wind is used to compress air over the water, where it is stored until needed.  When the grid operators need energy, a valve is opened and the air pushes the water through a hydro turbine, creating on-demand electricity.  This system has the potential to be very efficient. 

Please see our Resource Library, which contains an Overview of Compressed Air Storage as well as conceptual sketches of novel energy storage systems.

Deferrable Loads
Much attention has been paid to demand-side-management and smart-grid applications.  In practice these efforts have been limited in scope – such as allowing grid operators some control over residential air-conditioning loads, irrigation pumping and occasionally the ability to curtail large industrial users.  We believe that by making more loads “deferrable” across user-classes (residential, commercial, industrial & irrigators) the nation can significantly decrease both peak-demand and overall demand, thereby reducing necessary increases in both transmission and generation.  Thus, we are beginning research into the role that deferrable loads may play in conjunction with smart grids.

1) 20% Wind Energy by 2030, US Department of Energy Office of Energy Efficiency and Renewable Energy (DOE-EERE) Wind and Hydropower Technologies Program (WHTP), July 2008

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