'Microgrids' fed from renewables could help stabilise power supplies

The benefit of microgrids is that they can disconnect from larger utility grids and continue to provide power locally.

“If the microgrid is always connected to the main grid, what’s the point?” says US Department of Energy and Oak Ridge National Laboratory (ORNL) researcher, Yan Xu. “If something goes wrong with the main grid, like a dramatic drop in voltage, for example, you may want to disconnect.”

Microgrids are designed to not only continue to power local units such as neighbourhoods, hospitals or industrial parks, but also improve energy efficiency and reduce cost when connected to the main grid. Researchers predict an energy future more like a marketplace in which utility customers with access to solar panels, battery packs, plug-in vehicles and other sources of distributed energy can compare energy prices, switch on the best deals and even sell back unused power to utility companies.

However, before interested consumers can plug into their own energy islands, researchers at facilities such as ORNL’s Distributed Energy Control and Communication (DECC) lab need to develop tools for controlling a reliable, safe and efficient microgrid.

To simulate real scenarios where energy would be used on a microgrid, DECC houses a functional microgrid with a total generation capacity of approximately 250kW that seamlessly switches on and off the main grid.

This grid includes an energy storage system that generates 25kW of power and uses 50kWh of energy built from second-use electric vehicle batteries, a 50kW- and a 13.5kW-solar system and two smart inverters that serve as the grid interfaces for the distributed energy emulators. Programmable load banks that mimic equipment consuming energy on the grid can provide sudden large load changes and second-by-second energy profiles.

“A microgrid should run an automated optimisation frequently - about every five to ten minutes,” Xu says.

To optimise grid operations, microgrid generators, power flow controllers, switches and loads must be outfitted with sensors and communication links that can provide real-time information to a central communications control.

“Microgrids are not widely deployed yet," says Xu. "Today, functional microgrids are in the R&D phase, and their communications are not standardised. We want to standardise microgrid communications and systems so they are compatible with the main grid and each other.”

Now two years into the inception of ORNL’s microgrid project, dubbed: Complete System-Level Efficient and Interoperable Solution for Microgrid Integrated Controls (CSEISMIC), the microgrid test bed at DECC is functional and employs an algorithm developed at ORNL that directs automatic transition on and off ORNL’s main grid.

Xu says the next year will focus on getting the energy management system (EMS) running. The EMS will drive optimisation by allowing microgrid components to fluctuate operation based on parameters such as demand and cost.

The CSEISMIC team has long-term goals of partnering with industries to conduct field demonstrations of standardized grid prototypes. Xu believes that as soon as microgrids are standardised and easy to integrate into the main grid, they will begin to be implemented in areas with a high penetration of renewables and high energy prices.