The National Renewable Energy Laboratory has found that the Eastern Interconnection, one of the largest power systems in the world, could accommodate a yearly average of 30 percent renewables, an additional 400 gigawatts, with the grid operating essentially as it does today.

Using a more detailed model than ever before, NREL researchers looked at 5-minute intervals for the power system that stretches from the Midwest through the entire eastern U.S.

The researchers modeled existing thermal and hydro capacity, along with four different scenarios of wind and solar power. One scenario was low renewable penetration (about 3 percent), another 10 percent, one at about 30 percent renewable penetration and one at 30 percent with six additional HVDC transmission lines. It took into account 60,000 miles of transmission and about 5,600 generation units. As much as possible, the study relied on how each grid is operated today.

“While this study does not capture all of the regional practices and individual resource parameters of the actual system,” the authors wrote, “these assumptions represent a reasonable approach to simulating operations which is consistent with actual practice in many regions.”

The study did not account for the cost of building out the additional renewable capacity, or the cost of using existing thermal generation in a less efficient manner. Coal- and gas-fired power plants would have to be ramped up and down more frequently, which makes them more expensive and less efficient.  

In a scenario of low renewables, about 7 percent of thermal generation would sit idle during peak demand, but that figure rises to 30 percent when 30 percent of generation on the system is wind and solar.

A large amount of renewables would also create something resembling a duck curve, but the need for curtailment is minimized in the scenario with additional transmission. “This is the first time anyone has seen a duck curve in the Eastern Interconnection,” said the lead author of the study, Aaron Bloom. In some regions, renewable generation could peak at 60 percent penetration on windy or sunny days.

The study is detailed, yet limited. It looks at the system as it is today, which doesn’t take into account advancements such as the falling cost of energy storage or enhancements for grid operators to better manage intermittent renewables. Just as important, it does not model for demand response, which study authors acknowledge makes this a particularly conservative approach.

Those limitations are significant, but they also highlight the capability of the grid to manage large amounts of wind and solar generation as it is now, absent major cost or technology breakthroughs.

With costs as they stand today, there would still be a considerable savings in the scenarios modeled by NREL, mostly from fuel costs, at a savings of $30 billion on the high end. By comparison, an NREL study published in 2013 on high renewable penetration in the Western Interconnection found avoided fuel cost savings of about $7 billion. 

Carbon dioxide emissions cuts are also significant under the high renewable scenario. Carbon emissions would be about 30 percent lower under the two more aggressive scenarios.

NREL admitted there is still much more work to be done, including incorporating demand response, electricity storage and operational practices. For now, NREL hopes that the industry and broader research community will adopt its research tools to push the research further, providing more insight into cost analysis and applying this research in the real world.