500 GW of solar could interconnect at existing fossil-fired generators

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About 500 GW of economically viable solar could be sited within six miles of a fossil generator in the U.S. and share that generator’s grid interconnection, reports a working paper by four researchers at the University of California, Berkeley.

The simplicity of the concept is shown in the diagram below. At any given time, the combined output of the two generators could not exceed the capacity of the point of interconnection.

The idea of interconnection sharing has been discussed for years, the authors say, but falling costs for renewables and recent policy developments “have sparked new commercial interest, particularly in integrating solar at existing fossil power plants.”

The working paper also considered the potential for wind power to share interconnection at fossil generators, and found that the shared interconnection potential for solar and wind capacity combined is more than 800 GW.

The paper counts renewables that share interconnection as economically viable only at sites where the “levelized cost” of solar or wind generation is less than the fossil plant’s variable cost, which consists of fuel costs plus variable operation and maintenance costs. That criterion for economic viability was met at more than 75% of fossil generators. Storage could also be added at those sites.

dashboard referenced in the paper shows the 1400 fossil generators in the U.S. and the potential for shared interconnection capacity at each one. The dashboard also permits a user to apply filters to the entire data set and view the resulting aggregated potential.

Interconnection sharing is also known as surplus interconnection. The Federal Energy Regulatory Commission’s Order 845 requires transmission providers to establish an expedited process for interconnection customers to utilize or transfer what FERC calls “Surplus Interconnection Service.”

To accelerate renewables deployment at existing points of interconnection, the working paper provides three pages of policy recommendations that could be implemented by FERC, grid operators, public utility commissions and other entities.

The nonprofit consultancy GridLab has published a “surplus interconnection policy explainer” in coordination with the release of the working paper.

The working paper says that from a power system perspective, integrating additional renewables while retaining conventional fossil assets “ensures the availability of sufficient generation capacity to serve rapid load growth, supporting grid reliability.”

There is a “significant opportunity” for interconnection sharing in the U.S. grid regions known as PJM and MISO, the paper says. “The opportunity in PJM is particularly acute” given PJM’s “significant challenges in maintaining resource adequacy due to surging electricity demand.”

Noting that U.S. coal-fired and oil-fired generating units are on average over 40 years old, the paper says “this aging infrastructure monopolizes increasingly valuable interconnection points at a time when new renewable generators face significant challenges securing timely grid access.”

The working paper also notes the opportunity for existing renewable generators, which have a combined capacity of 250 GW, to share their interconnection capacity with 250 GW of additional storage, “thereby adding significant new firm capacity to the U.S. grid while creating opportunities for an additional 250-500 GW of renewables deployment that can share the same interconnection.” The authors say that several renewables projects are already adopting such strategies.

The authors, pointing to their previous research showing that reconductoring transmission lines with advanced conductors could double U.S. transmission capacity, said that “combining a focus on renewables, surplus interconnection, and reconductoring can pave the way for low-cost, clean energy abundance.”

The working paper is titled “Existing fossil fuel plants sharing grid access with renewables can rapidly and cost-effectively double U.S. generation capacity.”

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