(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.
the gap with demand and supply responses, or where even greater effective availability is needed, backup generation can help system operators further optimize wind capacity.
“There can be a very rapid change in the wind as fronts move through,” says Frank Donnelly, president of Wartsila North America, which builds reciprocating engine-based power plants. “That adds to the known variability and creates the need for a certain type of generation product to cope with it. Our plants happen to match those characteristics quite well.”
Specifically, the company’s plant designs can be started remotely, many times a day. They ramp up to full output quickly—to 25 percent of rated capacity in 100 seconds, and full capacity in 8 minutes or less. Plus, the typical reciprocating engine plant consists of multiple engines running in parallel, which allows for partial operation with minimal loss of efficiency or environmental performance.
Additionally, gas-fired reciprocating engines bring the benefit of siting flexibility. They don’t need high gas pressure and they present a small footprint, making them easier to locate than some generating technologies. This can be helpful when generating capacity is needed in remote locations with weak transmission grids, where variable loading or supply can threaten stability.
“Some utilities are using our equipment for wind firming and generally as a stability product,” Donnelly says. Such applications might increase in the future as wind capacity expands and reserve margins shrink—particularly in systems with limited generation resources.
“If there’s overcapacity you’re probably OK, but once you get large quantities of renewable energy it will become more difficult,” he says. “That’s why we’re seeing a lot of RFPs from utilities for quick-start, variable-load and load-shaping capacity. They don’t call it wind enabling, but it has the same definition as what’s needed to enable wind and other renewables, and for that matter to address other types of grid stability issues.”
And some RFPs are specifying wind-firming services. For example, in Snohomish County (Wash.) Public Utility District (PUD), a recent RFP for 100 MW of renewable power starting in 2008 noted: “The PUD does not have other resources under its control that can respond to [windpower’s] variable and changing output in order to balance our resources to our load and reduce the potential for scheduling error and cost. At a minimum, the PUD desires to receive wind resource pro- posals that are coupled with a wind firming product that provides for a firm day-ahead hourly schedule of energy deliveries to the PUD.”
As a result of forecasting, integrated system operations and backup capacity, windpower is gradually shedding its reputation as an intermittent and unreliable energy source. And as power grids become more intelligent and operate on a broader geographic basis, wind’s value and cost characteristics will improve.
Depending on how long-term trends develop, wind’s variability eventually could become a non-issue, even at large penetration rates. Most notably, plug-in vehicles might form a remarkable synergy with windpower—charging when the wind is blowing and providing distributed electricity storage capacity when it isn’t.
Some studies suggest vehicle-to-grid (V2G) technology could provide enough storage to completely