April 02, 2010
In his days as a control room operator more than a decade ago, John Pespisa remembers working intermittent renewable energy resources like wind into the system. The footprint may have been small, but the resource had to be dispatched. "Sometimes at 3 a.m., you'd wonder where the wind went," he said.
No longer. With more advanced forecasting tools and improved monitoring of generation sites and communication with grid operators, controllers are better able to anticipate the fluctuations of what were once a few MWs of generation. Now, with renewables measured in the hundreds of MWs, better tools are available. And even more important than that, ambitious goals to incorporate renewable energy into California's resource mix have put added pressure on utilities to get it right. Instead of a goal to get wind, solar and geothermal power into the system, it's a mandate. Accurate forecasts and dispatch are imperative.
Nowhere is this more acute than in California, and specifically, at Southern California Edison (SCE). California has the most aggressive renewable energy portfolio standard in the country -- by far. An executive order signed by Governor Arnold Schwarzenegger last September requires 33 percent of the state's energy to come from renewable resources by 2020. In the meantime, the state's investor-owned utilities are mandated to procure 20 percent of their electricity from renewable resources by 2012. Utilities are scrambling to acquire generation assets, either from their own plants or through power purchasing agreements, and are sometimes looking beyond the state's borders to find it.
SCE is well on its way, and closer than many, with 16 percent of its electricity from renewables. With nearly 2,800 MW of wind, solar and geothermal and other generation assets, SCE controls the largest portfolio of renewable generation resources in the United States. And this past November, it started to roll out a Web portal for its generation portfolio for enhanced communication of availability and dispatch.
The company is a large user of renewable energy, with 12.6 billion kWh of renewable energy sold in 2008. In terms of the installed capacity, SCE has 1,137 MW of wind generation, 906 MW of geothermal and 356 MW of solar. It also acquires energy from hydropower and biomass generation. Geothermal is more of a base-load asset, depending on the production of the wells and any maintenance issues that could be faced, as is the case in any other power plant. In fact, it produces about 62 percent of SCE's total renewable generation.
SCE says it will meet its 20 percent goal. The company will even be importing 2 billion kWh of wind energy from Puget Sound Energy in Washington State over the next two years. And likewise, it's got more experience in integrating renewable energy into its system.
It is using digital technologies on its own and in conjunction with the vendors it employs for its site monitoring.
For assets like those inside and outside of California to be fully integrated into the system, site monitoring is crucial. That's where the meteorological towers come into play. "We're moving into an area where we think the technical advances of forecasting and managing that data are improving," Pespisa said. "We are able to share data that is more accurate in generating forecasts for forward markets."
Timelier Reporting
But the forecasting vendors are moving closer to refining the hourly forecasts so that there is more confidence built into the models that influence generation dispatch and utility bids that set power prices.
A second area is sharing the available information from the generation site. "Wind or solar is only as good as the capacity to determine the availability of each site," Pespisa said. For that, the utility uses a direct supervisory control and data acquisition (SCADA) system with each plant connected to the control area and the integration more automated through a series of nodes. That creates both operational challenges and cost issues.
For example, a single power plant, or perhaps a large solar array, might have its own SCADA system reporting its generating capacity and output to the independent system operator (ISO). But if there are perhaps hundreds of rooftop sites in a relatively small area all reporting similar data to the same central monitoring site, there are potentially thousands of pieces of data being generated. As commercial and industrial locations become part of the rooftop solar programs, there are also potentially thousands of sites instead of a few data collection sites.
The potential is not only duplication of the information generated, but also the real possibility of creating unnecessary costs. CAISO is developing a model to provide for both information and cost sharing. State regulators are developing plans to address the cost-sharing issue.
Another effort this November was the unveiling of a Web portal, part of the program to deploy digital technology through telemetry to monitor plant availability and production and even assist in outage management. The rollout is taking place over three months to all cell plant operations. Real-time availability is thus communicated.
A telemetry regime is also being rolled out with SCE and the ISO implementing technical requirements and standards for generating units and load participants. This effort is to establish and maintain a data processing gateway between the plants and CAISO's energy management system. This telemetry offers a gateway into the network of generation plants and transmission and distribution networks.
"This is better at data collection and it's timelier in its reporting," Pespisa said.
For dispatching generation assets, especially renewables, it is important to understand not just what a site is producing at a given moment, but that the amount produced by a renewable resource at a given moment matches the capacity expected.
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Bill Opalka Editor-in-Chief Energy Central
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