Microgrids are transforming the energy landscape in the United States and Canada. Powered by a variety of sources, such as solar arrays, wind turbines and diesel and natural gas generators, they provide the commercial markets, industrial markets and oil and gas markets with some or all of the electricity they require to operate.

Microgrids are often designed and deployed as a supplemental source of power during peak usage periods when traditional utility grids are at full capacity. They can assist organizations that want to move toward renewable energy and/or reduce their traditional utility consumption and cost. Microgrids also supply electricity to remote areas when traditional power grids are not reliable or not in place.

Should a microgrid fail while in operation, the consequences are serious. Backup generators keep the microgrid operating, but it’s essential to ensure that the transition from the microgrid to the backup generator is efficient and smooth.

To back up its permanent sewage plant generators, a municipal wastewater treatment plant in the Northeast relies on a microgrid powered by four United Rentals diesel generators and high voltage electrical distribution system. If one of the plant-owned generators were out of service for maintenance or repair, the plant would not have enough capacity to handle the load, which would result in a critical situation potentially involving the discharge of raw sewage.

“We came in and offered them a solution where we can have our generators run the microgrid in parallel with their permanent generators,” said Wayne Davis, a senior electrical engineer with United Rentals. Davis helps design customized microgrid solutions for the company’s customers.

“Once the rental generators are in place and able to carry the entire load, they can take their permanent generators offline. After they perform whatever maintenance is needed, we could bring their generators back online while our rental generators are still on the microgrid so there’s no interruption in power,” Davis explained.

What makes United Rentals’ backup solution unique is the fact that all of its Cummins generator sets, with their Power Command Controllers, can be run in parallel with a variety of power sources, including utility grids, solar voltaic panels, wind turbines and other generators.

“We offer microgrid owners an engineered solution that provides a seamless transition between their generators or other power source and our temporary generators,” Davis added. “Plus, they have the ability to do that without having expensive switch gear or even transfer switches. They don’t have to go to outside vendors.”

Backup planning

Davis said one of the biggest mistakes microgrid owners make when planning for a backup generator system is judging the generator power they’ll need. “If they have a 200-amp breaker, they may think they need a 200 kva generator. That usually means they end up oversizing their generator and paying more than they need to. It’s better to know the true load so they can accommodate that,” he explained.

United Rentals helps companies by engineering the microgrid system, evaluating the operating parameters and limitations and determining appropriate microgrid capacity. In addition, United Rentals provides arc flash analysis and engineered drawings as part of a complete engineered solution.

Davis noted that almost all of the generators United Rentals supplies for microgrid backups are outfitted with telematics that provide full monitoring capability. If anything happens to a United Rentals backup generator when it’s running, both the customer and United Rentals will be notified so they can address the problem quickly and keep the microgrid operating.

Relying on a microgrid for electrical power makes good sense in many situations. So does having a backup generator system to take the load in an emergency so the power keeps flowing.

Freelance writer Mary Lou Jay writes about business and technical developments in a variety of industries. She has been covering residential and commercial construction for more than 25 years.