When wind farm developers lined up at a grid operator's or utility's door a few years ago, plans to add a new project didn't cause undue concern. After all, 10 megawatts here, 50 megawatts there, weren't going to significantly change the scheduling. Now that wind projects are measuring in the hundreds of megawatts in recent years, they are not only creating interconnection issues on their own, but are also occupying a more prominent place in the overall resource mix in large or multi-state regions. And while utilities are still adding smaller projects, they present their own challenges as many are even smaller than the original wind projects, like solar PV installations on a warehouse roof or hundreds of individual homes. While wind can't be expected to provide on-demand or base-load power, a larger share of generation is being counted on in the states and by an expected federal mandate for renewal energy over the coming decade. However, with many states mandating increased use of renewable energy, wind generation is often given priority when it is available and traditional forms of power sources have to be backed off to accommodate it.
Various Scenarios
Various scenarios have been created by wind energy advocates and the U.S. Department of Energy under which up to 20 percent of U.S. electric generation could be supplied by wind by 2030, so this is no longer just an academic exercise. Texas is the national leader in wind nameplate capacity, by far, with more than 7,000 megawatts, with another 52,000 megawatts under review. The grid operator for most of the state, the ERCOT or Electric Reliability Corporation of Texas, manages the flow of electricity from the sparsely populated West Texas wind region to the populated load centers of Dallas and other eastern cities. The state has recently adopted a transmission development plan with a funding mechanism, competitive renewable energy zones, with a $5 billion price tag that will accommodate up to 18,000 megawatts of wind when it is completed. A similar plan to create National Renewable Energy Zones was introduced into Congress last year. Bonneville Power Administration in the Pacific Northwest states also has an exploding growth curve, with 1,600 megawatts of wind currently it its territory, with the potential for 10,000 megawatts by 2016, counting projects under development or in the transmission interconnection queue. Never was the need for plans for integrating large quantities of wind more evident than on Feb. 26, 2008, when dying wind caused a sudden drop-off in generation and forced ERCOT to use its plans for interruptible customers to balance the system during the event. The grid operator blamed inaccurate wind forecasts and a fast ramp-up in demand for the shortage.
Confronting Issues
What the event did was expedite work already started by ERCOT to more smoothly integrate large quantities of wind generation, said Dottie Roark, ERCOT's communication manager.
"There is a stakeholders' committee with ERCOT reviewing protocol changes that would involve all the participants."
These initiatives include developing more forecasting tools with a wind assessment company, improving control room operator awareness through automated tools and developing a risk based management program. The BPA has different issues to confront, with Oregon and Washington State among the national leaders in wind capacity. While seemingly blessed with copious amounts of hydropower that can supplement wind, nuclear and fossil fuel generation sources when needed, there are limitations. While true, the process isn't always as simple as ramping up hydro assets as soon as wind speeds appear to be declining.
"An example is when we need generation it's not just a matter of spilling runoff because there are fish management issues, especially during spawning season."
Solar power presents its own set of challenges, not only by its smaller scale than most commercial operations, but because of the more gradual appearance and retreat it makes on the power grid. But the challenges solar power presents no less daunting, as many commercial sites may generate one to two megawatts at peak, while home systems are measured in a few kilowatts.
"When you're thinking about a landfill topped with a solar array, that's quite a different scenario from a homeowner's roof. There's a whole different loading considerations, instrumentation, and there's a different sort of marketing issues."
The state is now expanding eligibility for net metering that allows such users to sell back into the grid. Dan Zaweski, assistant vice president for energy efficiency and distributed generation at the LIPA or Long Island Power Authority, said the home- and business-based generation systems do not yet create operational challenges for the public utility that serves Long Island, N.Y. There are about 1,600 residential solar systems out of a customer base of about 990,000, and 83 commercial customers out of a base of 1.1 million. For a utility that operates with megawatts as its crucial unit measure, smaller generating stations present new issues. Its operations strategy is running one to two megawatts on a distribution feeder.
"An average homeowner with a solar PV system might generate six kilowatts at peak, so there has to be 333 of them operating before you really see any grid impact."
Business operations are also impacted on Long Island, as elsewhere, when smaller renewable energy systems are added. Utility systems are geared toward the amount of revenue gathered from retail sales, but savings from reduced demand don't create income for the utility. Billing is the most obvious area affected both in terms of the potential impact on the utility's bottom line, but also the upfront costs of meters and any other operational expenses and customer care processes needed to accommodate these energy sources.
