Hybrid power plants could increase grid congestion – study

New research shows that hybrid power plants that combine solar or wind with energy storage only reduce congestion in areas with large amounts of variable renewable energy resources under specific circumstances, depending on the plant configuration, operation, and technology.

The research, from the Lawrence Berkeley National Laboratory, found that the impact a hybrid power plant has on congestion depends not only on its precise location, but also on how a plant’s operation is constrained by limits on battery cycling. 

It also found that the ability to charge the battery from the grid (not only from on-site solar or wind generators) is an important factor in determining the ability of a hybrid plant to reduce grid congestion.

Development of new wind and solar plants has outpaced development of new transmission, the report said. Transmission is important because it allows load centers to access electricity generated from low-cost resources in other areas. Congestion occurs when transmission limits are reached and it may prevent low-cost wind and solar resources from being fully utilized, limiting their market value. 

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Energy storage, which can often be built more quickly than new transmission, can help ease transmission congestion by shifting both generation and load over time. In locations with a high concentration of wind or solar power plants (variable renewable energy rich areas, or VRE-rich areas), development of hybrid solar+battery and wind+battery power plants is growing, partly motivated by the desire to avoid selling energy during congested, low price hours. 

The report said that in solar-rich and wind-rich areas, new hybrids which charge from the grid and can cycle their battery frequently typically decrease congestion, though the effect is small. 

New hybrids in other configurations (for example, with a more conservative cycling requirement that only charges from the paired renewable generator result) increase congestion, the research found. However, these resources result in less congestion than by building a stand-alone solar or wind plant. This final point indicates, the researcher said, that adding batteries to an existing stand-alone wind or solar plant “will almost always reduce congestion.”

The study focused on 23 locations in the U.S. bulk power system that experience significant congestion today and already have a stand-alone solar or wind plant. The locations were selected as offering examples of conditions that may emerge broadly in systems with a high VRE penetration. 

Study results were published in the journal Advances in Applied Energy. The research said that more frequent cycling and lower-cost batteries can help reduce congestion-related impacts of hybrid plants. It also highlights the need to develop more sophisticated cost-benefit trade-offs between the battery degradation costs of various types of cycling and the associated arbitrage opportunity. 

And, the research suggests a possible link between battery warranty policies and grid congestion. It suggested that changes to manufacturing warranties could help to modestly reduce congestion.

The study said the benefits of hybrid plant grid charging for reducing congestion point to the importance of plant design choices that provide this capability and also the role of flexibility in incentive programs. The Inflation Reduction Act, for example, provides incentives for hybrids that charge from the grid, facilitating these hybrids to reduce congestion more easily. In contrast, previous incentive programs focused on hybrids with storage that charged only from the attached solar or wind generator. 

The study also considers how transmission expansion might financially affect projects in congested regions. Here, it found that in VRE-rich areas wind plants see similarly large revenue opportunities from local transmission expansion and hybridizing by adding battery storage. Solar plants also benefit from transmission expansion, but the value is small compared both to wind plants and to adding storage. 

Originally published on renewableenergyworld.com