Energy sharing in microgrids can benefit all parties involved — including utilities — but establishing successful sharing projects can be difficult because of regulatory, policy and technical hurdles.
What’s more, it’s not easy deciding how to allocate payment for the energy among the energy users.
Some of the few energy-sharing efforts in the US include a project in Chicago between Commonwealth Edison’s (ComEd) Bronzeville microgrid and a microgrid at the Illinois Institute of Technology (IIT), and another with the microgrid system at the Daughters of Mary of the Immaculate Conception, which includes four separate microgrids in Connecticut.
“Energy sharing is a great goal and difficult to do. Challenges are not so much technically, as the battles are with regulation and policy,” said Don Wingate, vice president of sales, microgrid and utility solutions for Schneider Electric, which was involved in the Daughters of Mary project.
In Europe, energy sharing in “energy communities” is much easier, thanks in part to incentives from utilities, said Michael Stadler, chief technology officer at Xendee, which provides microgrid controls. Stadler initiated an energy-sharing test bed, the Microgrid Lab Wieselburg in Austria, along with Bioenergy and Sustainable Technologies, which designed the test bed. It includes an office building and fire station that are expected to share heat and electricity.
4 in 1 microgrid
The Daughters of Mary system from Schneider Electric and Citizens Energy can run on 100% renewable energy around the clock while in island mode.
The microgrid system includes four separate microgrids and each can share energy with any of the other microgrids, said Jana Gerber, president of microgrids North America at Schneider Electric. Instead of curtailing excess solar or other generation, the system can share that excess energy. And it’s possible to charge an energy storage system in one microgrid with another microgrid if there’s excess energy. That means a separate microgrid can be used to fill a storage system that is not at a maximum state of charge, extending the off-grid operation time, she said.
During grid-connected mode, however, the four microgrids can’t share electrons. Under an agreement with utility Eversource, they have to remain physically isolated from each other. Because the four microgrid “nodes” are fed from different utility substations, connecting the buildings could cause problems if the different feeders aren’t at the same frequency, Gerber explained.
Each building has solar photovoltaic (PV) arrays and energy storage controlled by a Schneider Electric Energy Control Center.
The system islands by opening the switches or breakers connected to the utility. The controls can close the breakers as needed. That’s possible because of auxiliary feeders — or extra cables — installed between the breakers, she said. Often, these extra cables have to cross a right of way, which is not legal in most states. But Connecticut passed a law to allow this under certain circumstances after Hurricane Irene and an ice storm, both in 2011, left many in the state without power for nearly two weeks.
“This made microgrids more valuable for resilience,” Gerber added.
The benefits of energy sharing include serving more loads across more buildings, allowing greater renewable energy penetration when islanded, reducing load shedding requirements and their costs, enabling longer islanding duration times and enabling battery charging in the system by separate microgrids, she said.
“Working with multiple stakeholders and applying proven technology is the key,” said Wingate. Schneider Electric designed and built a similar energy-sharing microgrid for the city of Fairfield, Connecticut’s public safety department. The microgrid connects the city’s fire and police stations and a homeless shelter when the grid is down using auxiliary cables under the street that operate during island mode. This was made possible by the changes in right-of-way restrictions made by the state’s Department of Energy and Environmental Preservation after Hurricane Irene, said Wingate.
Sharing energy in Chicago
In Chicago, ComEd’s Bronzeville Community Microgrid, a much-watched project, will share energy with the neighboring IIT microgrid. The Bronzeville Community Microgrid, which will serve 1,000 residents, businesses and public service buildings, is expected to be up and running in late 2023. This is a demonstration project, and both microgrids are built to serve the needs of their own customers, said Paul Pabst, senior manager of smart grid and innovation for ComEd.
The microgrids will share energy when they are merged, he said. For now, they will only share energy when they are in testing mode. One of the biggest technical challenges is ensuring the microgrids have the same technical specifications, he said. Utility customers building microgrids might not think of this issue, which can create electrical and physical challenges when connecting two microgrids.
If a major outage occurred in the area, ComEd could depend on its own microgrid, and IIT could depend on its microgrid. If IIT had a high peak load that couldn’t be met, ComEd could share energy — and vice versa, he said.
Another benefit is the stability energy sharing provides. “Because we have more spinning reserves and generation online we will have a more stable grid,” said Pabst. Each microgrid benefits the other by providing stability.
Mohammad Shahidehpour, chairman of the electrical and computer engineering department at IIT, said IIT and ComEd are working closely with the Bronzeville community and community developers to determine how clustering the two microgrids can enhance the socioeconomic status of the neighborhood. In addition, IIT will expand its engagement with the Bronzeville community to study equity in microgrid design and planning among potential stakeholders.
Who pays what?
Pabst added that IIT and ComEd are building a transactional model for determining who pays what for the energy when it’s shared.
“We are very interested in the technical and the business side and creating a financial model that makes sense. If we are asking for 100 kW for an hour, how is IIT compensated? What’s that worth?” he said.
Easier rules in Austria
In Austria, the test bed project that Stadler initiated aims to share biomass-powered heat from an office building with a fire station, and electricity from the fire station with the office building. In Europe, this is called an energy community. The project includes solar PV and energy storage in addition to the heat powered by biomass.
The buildings are connected through a utility distribution system. In Europe, it’s cheaper to share energy so there’s a law that requires utilities to allow energy sharing entities to use the distribution system. The energy sharing entities also receive discounts on their utility bills.
As part of the project, Stadler and his associates are gathering data that informs issues such as load forecasting. “The problem is complex; you need to forecast how much output you need for the next couple of hours,” he said. The data collected will help Stadler’s company, Xendee, develop algorithms that may be used in other parts of Europe or the US, he said. These algorithms will make setting up microgrids faster.
Interfaces and communication protocols
Michael Zellinger, area manager for the test bed, stressed that a key factor impacting the success of such projects will be open interfaces and communication protocols.
“Here it is essential to create standards to ensure that different technologies and platforms can communicate with each other,” Zellinger said. The researchers are developing standardized interfaces between open-source building management systems. This would connect different technologies using simple hardware gateways, he said.
“The concept will allow electric vehicles, stationary electric storage, photovoltaics, biomass and other decentralized energy technologies for electricity, heating and cooling to be easily integrated into the microgrid or energy community,” Zellinger said.
If all goes as planned, all parties in an energy-sharing community benefit from working together, said Stadler.
“This creates a win-win situation for everyone,” he added.
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