Evolution and Innovation in Large-Scale Renewables — Finding a Way Forward

By Jennifer Delony

Renewable energy stakeholders on Tuesday gathered at Power Generation Week in Orlando to consider the place for large-scale renewables on the grid, their role in markets and how they can be used to reduce greenhouse gas emissions.

During a session on evolution and innovation in large-scale renewables, Paul Denholm, principle energy analyst with the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) discussed the findings of a study on flexibility options for integration of solar energy in California that were part of a larger study released today by NREL. He said that the study identified the changes that can be made in the way the grid is operated to provide an increase in the value of renewable energy by recognizing the inherent capabilities of renewables, understanding our ability to forecast renewables, and understanding the ability of renewables to provide services. These resources are no longer considered “must-take,” he said.

According to Denholm, the goal of the study was to examine the issues surrounding grid flexibility, and understand the challenges with grid integration and the role of flexibility incorporating variable generation.

The study looked at the economic cost benefit of renewables being placed on the grid, comparing, using cost-benefit matrix, the point at which we should be putting renewables on the grid or doing something else to enable integration of renewables.

“There’s a point at which the value per megawatt-hour for renewables drops below the cost of renewables per megawatt-hour,” he said, “and it probably doesn't make sense to continue putting more renewables on the grid, unless you make some changes.”

According to Denholm, there are two things you can do to address that value issue — reduce the cost of renewables, or change the value by changing the way you operate the grid.

At around 10 or 15 percent penetration on an energy basis, solar no longer has capacity credit, and the value of PV shifts entirely to its energy value with the ability to offset fuel.

NREL’s study asked what would happen if the flexibility of the California grid could be increased with existing options.

“We focused on things that we think are going to happen between now and 2020 – essentially these are things that the California grid operator is already doing, including allowing distributed generation to provide reserves,” he said.

Other options include demand response, distributed energy plus energy storage, standalone energy storage and energy exports.

“By allowing some curtailed energy to provide reserves, and relying on improved forecasting, you can have PV when you want it or need it —you can decrease the curtailment by a substantial amount,” Denholm said.

Other Insights

Raymond Schauer, director of engineering and public works, Solid Waste Authority of Palm Beach County, discussed during the session the ability of large-scale waste-to-energy technology to be a significant player in reducing greenhouse gas emissions.

Waste-to-energy doesn’t “get the same respect as wind or solar,” Schauer said. He outlined the benefits to Palm Beach County that have come with the development of a 96-MW waste-to-energy facility that reduces waste landfill for the county by 90 percent and extends landfill life 20 years.

Landfill waste generates methane and carbon dioxide, all of which, at some point, goes into the atmosphere. If that waste is processed in a waste-to-energy facility, the production of that greenhouse gas goes away.

Ashraf Ul Haque, supervising engineer at Teshmont Consultants, also discussed the role of wind energy in Alberta, Canada’s ancillary services market. According to Haque, existing coal generation in Alberta will be retired by 2030, and two-thirds of the coal-generating capacity will be replaced with renewables — mainly wind — with one-third replaced by natural gas.

“The ancillary services market will need to be redesigned,” to accommodate that shift, Haque said. Parameters that must be addressed, he said, are available transfer capacity, frequency response, and technological compatibility.

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