(May 2008) Senators were voting on legislation to extend the renewable production tax credit (PTC) as this issue of Fortnightly went to press. But with federal tax support for...
Taming the Wind
Modern approaches to system operations and forecasting make the most of variable energy sources.
integrate wind up to even 30 percent of your supply—if you have the right tools to give you a reasonable knowledge of what’s going to happen.”
Forecasting also helps reduce windpower costs. Armed with knowledge about wind resources on a forward basis, portfolio managers will better understand changing conditions in the power market. This helps minimize the amount of capacity and energy utilities need to buy to pick up the slack when the wind dies down. “To the degree we can forecast output from wind turbines, the more valuable that output becomes,” Ahlstrom says. “And the easier it is to integrate, the less costly it is.”
In locations where wind turbines begin generating a large share of the power supply, variability becomes an increasingly important issue—and a dilemma. Utilities need windpower’s climate-friendly energy, but as the power system becomes more reliant on windpower, its variability will bring greater reliability concerns.
The primary and most effective way to address the issue is for system operators to manage variable energy supplies the same way they manage variable load—by dispatching different resources to keep the system stable. “The power system can do this most efficiently as an integrated pool with a system operator at the controls, balancing needs up and down,” Gramlich says. “The dichotomy between base load and peaking isn’t appropriate anymore.”
Historically, demand-side resources have been a fairly limited tool in the system-operator’s kit, so they’ve relied on dispatchable power plants to satisfy peak demand. But this is changing with trends toward a smart grid and more active and aggressive load-management practices.
The idea of matching demand to available supply, rather than the reverse, has emerged as an actual product in electricity markets. And service providers are finding new ways to provide that product. For example, Site Controls, an energy management company based in Austin, Texas, has demonstrated the ability to ramp up and down commercial and industrial load in concert with wind availability.
“We’ve used off-peak energy from wind farms from 2 a.m. to 6 a.m. to pre-cool a bunch of retail facilities, effectively absorbing that energy when there was nowhere else to put it,” says Chris Hickman, president of the energy services division of Site Controls. “If demand-side management can act as both a ‘call’ option and a ‘put’ option in the market, we can balance renewables and make them a solution instead of a problem.”
Further, by managing resources across a large and diverse pool, system operators can reduce the effect of wind’s variability. Some studies suggest an interconnected grid can count on much greater than 10 percent of wind capacity, if system operators manage the output of several facilities together rather than separately. “While wind speed could be calm at a given location, it will be non-calm elsewhere in the aggregate array,” stated the authors of a recent Stanford University research study. “An average of 33 percent and a maximum of 47 percent of yearly averaged wind power from interconnected farms can be used as reliable, baseload electric power.” 2
In small systems that can’t fill in