A microgrid is nothing but a very small grid. Microgrids have existed for a long time. Lately, they have attracted attention as a means of making the grid greener, more reliable, and more resilient.

We speak of the electric grid. A single grid with three “interconnects” powers all the US and Canada. It combines many sites that generate electricity with many users. It accomplishes the task with a lot of wires and a control system. But, of course, other countries have their own grids. So there are lots of grids worldwide.

Large national grids sometimes fail. If something happens in one location to cause a failure, it can cause failure in neighboring locations. Some spectacular failures have blacked out large regions for hours or even days at a time.

Hospitals and other institutions can continue to operate only if they have some kind of alternative power source. A hospital operating its own generator in a power failure is an example of a microgrid. So is a house with its own backup generator and transfer switch.

Some microgrids have no connection with the main grid. Some operate in remote areas where it’s too expensive to extend centralized power. Or people who want to be “off grid” can operate them.

That hospital with a diesel generator has a grid-connected microgrid. In the event of an outage, it makes itself an island that can operate until the main grid has been restored. It gives the hospital reliability that the grid itself lacks.

Microgrids have much greater potential than that. They can operate as part of the internet of things and the digital grid, or smart grid.

Basic microgrid principles

The US Department of Energy’s Microgrid Exchange Group offers this definition of a microgrid:

A microgrid is a group of interconnected loads and distributed energy resources within clearly defined electrical boundaries that acts as a single controllable entity with respect to the grid. A microgrid can connect and disconnect from the grid to enable it to operate in both grid-connected or island-mode.

This definition excludes specifying the source of electricity. It emphasizes that a microgrid is locally controlled and can be either connected to the central grid or operate as an island. Power can come from distributed energy resources or from burning fossil fuels. But microgrids can help integrate renewable energy into the electrical infrastructure.

Utilities have trouble dealing with solar panels on hundreds of individual rooftops. A microgrid collects their output and feeds it to the grid at a single point. It offers automatic switching technology to connect, disconnect, and reconnect to the grid without the utility having to devise a control system.

Microgrids can also incorporate “combined heat and power systems” (CHP). These systems use cogeneration to capture what would otherwise be waste heat and reuse it. When waste heat is circulated through a building, that building no longer needs to operate a furnace. When applied to an absorption chiller system, it provides air conditioning.

The definition of microgrids also excludes mention of storage. Most current microgrid design includes renewable energy. In that case, storage becomes an important component.

Advantages of microgrids

Microgrids offer several distinct advantages to utilities and their customers:

• improved energy efficiency.
• minimalization of energy consumption
• reduced environmental impact
• improved reliability of supply
• reduction of loss
• relief from network congestion
• voltage control
• enhanced security of supply
• less expensive replacement of infrastructure

The digital grid can become, among other things, a network of microgrids. Each one can aggregate distributed energy resources from small-scale resources. Some solar panels or wind turbines with battery storage may be the most familiar of these, but smart appliances and electric vehicles can play a role.

Not only can grid-tied microgrids detach in emergencies. They can also either supply power to the grid or store power from the grid. They can help balance fluctuating grid frequency or voltage.

Some examples of microgrids

New York University

New York University has produced its own power since 1960. In 1980, it installed an oil-fired cogeneration plant. When that facility reached the end of its useful life, the university replaced it with a natural gas CHP facility in 2011.

The new plant has twice the output capacity of the old one. It powers 22 campus buildings and heats 37. The university purchases electricity from Con Edison when demand exceeds its system’s capacity.

The old microgrid was also connected to Con Edison, but the new one can operate in island mode. During Hurricane Sandy, the university still had power when much of Con Edison’s distribution system was destroyed.

Hartley Bay, British Columbia

Many remote areas lack access to the electric grid. Canada alone has 292 such communities. They have traditionally relied on expensive and dirty diesel generators to supply electricity. One of them, Hartley Bay, British Columbia, is more than 400 miles northwest of Vancouver.

It has been participating in an energy management initiative since 2008. Three diesel generators still supply the village’s electricity, but its smart microgrid has used a demand response system to reduce electricity usage. It comprises 20 smart thermostats and 12 load controllers. The system allows real-time measurement of electricity usage, which identifies operational issues more efficiently than conventional system audits.

Stone Edge Farm

Stone Edge Farm, near Sonoma, California, is a demonstration organic farm. It displays aspects of conservation of soil, water, and energy.

Owners Leslie and Mac McQuown bought the property in 1995 and installed solar panels on a sunny corner of the farm.

Unfortunately, the greatest power need was in a shady corner. They had to buy electricity from the utility until they devised their microgrid to power the entire farm.

Besides the solar panels, it derives power from hydrogen fuel cell hives and a natural-gas-fired turbine. The McQuowns intend to convert the latter to hydrogen. Their microgrid has multiple storage technologies: a sodium ion battery, an iron flow battery, two zinc-bromide flow batteries, and three kinds of lithium batteries.

The farm has designed the microgrid to be open source. Anyone can use the technology without paying for the intellectual property

Borrego Springs, California

It has become apparent that power lines can start or worsen wildfires. For the sake of fire control, utilities need to de-energize them. As a result, whole communities can be without electricity for hours at best.

Without the grid, residents can’t cool their homes or their food. They can’t recharge phones. People who depend on electricity for some kind of life support technology will die. And if the fire continues despite the shutoff, it can further endanger first responders and hinder evacuation.

In response to recent wildfires, San Diego Gas & Electric Co. is building an advanced microgrid in Borrego Springs. Both solar panels and diesel generators will produce electricity. The system also includes storage from both batteries and an ultracapacitor.

Historically, most microgrids have relied on fossil fuels. So the use of solar panels in this one marks something of a departure. In the near future, most new microgrids will probably rely entirely on renewable energy.

California utilities have begun to urge state regulators to offer incentives to build microgrids. The technology hasn’t matured yet to where it can protect residents in the coming fire season. Regulators are not inclined to push for microgrids in the near future. The Borrego Springs experiment should help determine how quickly the technology can be ready for the problem.

These are just a few examples of the wide variety of microgrid projects worldwide. Look for microgrids to play a role in the transformation of the national grid.

Sources:

About microgrids / Berkeley Lab, [2010?]
California’s wildfire threat could be an opportunity for clean-energy microgrids / Sammy Roth, Los Angeles Times. March 14, 2019
Examples of microgrids
The first Canadian smart remote microgrid: Hartley Bay, BC / Natural Resources Canada. January 5, 2016 [Link no longer works.]
Meet the microgrid, the technology poised to transform electricity / David Roberts and Alvin Chang, Vox. May 24, 2018
Stone Edge Farm Microgrid
Why two grids can be better than one: how the CERTS microgrid evolved from concept to practice / Elizabeth McGowan, U.S. Department of Energy’s Office of Electricity Delivery and Energy Reliability [2010?]

Image credits:
Microgrid diagram. Public domain from Wikimedia Commons 
Solar farm. Public domain, US Air Force photo
Microgrid equipment. Public domain, National Renewable Energy Lab photo
Flow battery. Photo by UniEnergy Technologies. Public domain from Wikimedia Commons 
Solar inverter. Public domain from Wikimedia Commons