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Rooftop solar needs better communication between transmission, distribution

Q2: U.S. Solar and Wind Power by the Numbers

Essential Energy Insights - September 17, 2020

Essential Energy Insights September 2020

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Rooftop solar needs better communication between transmission, distribution

There needs to be more interaction between transmission anddistribution system operators to increase rooftop solar and distributedgeneration resources onto the grid, a PJMInterconnection LLC panel said.

Grid modernization was a key topic at PJM's Focus onDistributed Energy Resources symposium held on Sept. 21 in Chicago. As moredistributed generation resources, such as energy storage and rooftop solar, getdeployed, the National Renewable Energy Laboratory, or NREL, expects changes inhow transmission and distributing operating systems interact.

A rooftop solar resource interconnects and provides data tothe distribution system operator that may not get communicated up totransmission system operators.

"[A]s soon as we get significant amounts of thesetechnologies deployed, they can help the big bulk transmission-leveloperations, but the interconnections between distribution and transmissionoperations to really enable that full capability have not really been developedand operated in a way," NREL's Ben Kroposki, director of NREL's PowerSystems Engineering Center, said during the second panel of the symposium.

The laboratory, which is funded by the U.S. Department ofEnergy, is studying various architectures of what the grid could look like, sothat the bulk power transmission system, the distribution system andcustomer-sited resources can be integrated in a few months, Kroposki added.NREL is working on projects to link transmission and distribution operations.Linking the systems would help share grid-level information about reliabilityand any market and pricing signals, Kroposki said.

The information is valuable for companies that need to makestrategic investment decisions in distributed generation projects over a longertime horizon, PJM's Denise Foster, who is vice president of state and memberservices, said while moderating the panel.

Part of the reason for the disconnect between thetransmission and distribution systems is because of fundamental differences.

"At the bulk-power level, the transmission systemoperator owns no assets. They own computers and so forth, but they do not ownany wires or power supply. At the distribution level, the utility owns wiresand — those that are not in regional and RTO markets — they own wires and powersupply," David Owens, executive vice president of business operations andregulatory affairs at the Edison Electric Institute, said on the panel.

There is also a difference in the market structure with somedistribution companies employing mesh networks, with power lines connected tomultiple power sources, while others use radial networks, a simple type of gridconnected to single power source, Owens said.

Owens suggested that moving toward "transactionalenergy," which involves peer-to-peer transactions, can help develop amarket for distributed resources, but "there has to be an integratedcommunication system and data exchange platform" first, which is notavailable right now. "We have a long way to go," he said.

Consumer advocacy groups are wary about the potential coststo ratepayers from modernizing the grid. "The one thing I know is thatutility [information technology] systems are very cumbersome and closed andexpensive to adapt," Citizens Utility Board Deputy Director Kristin Munschsaid. Munsch, who represents the ratepayers of Illinois, said the growth ofdistributed resources will require distributed system operators to manage a lotof data.

PJM, which manages the demand and supply of power crossing13 states and the District of Columbia, generated less than 1% of itsgeneration through July from solar power including distributed photovoltaicpower, according to data from PJM's Generation Attribute Tracking System, orGATS. The largest renewable resource in the region, in terms of generation,comes from wind, which produced about 2.3% of PJM's power in the first sevenmonths of this year. Though distributed generation has made a minor imprint onPJM's system mix, distributed generation has increased penetration in certainpockets of the U.S. such as in California, which legislation to advance energystorage and distributed generation.