The electricity grid is changing, and the pace of change will likely pick up, particularly as more renewable energy sources deliver power to it. Another huge driver of change are efforts to improve the resilience of the power grid. Some solutions can effectively serve both needs.
In this blog I’ll examine how electricity storage can be implemented at the utility scale and how some new storage technologies are also enhancing grid stability and resilience.
Background on the electricity grid
Our electricity grid is a complex and hard-to-manage system. The amount of power (electricity) being generated has to be closely balanced with the amount of power being consumed (demand). Fluctuations in demand occur all the time. In the morning hours between 6 and 8 am, for example, a lot of people get up, turn on lights, shower, operate their coffee makers, and turn up the heat (or air conditioning); electricity demand rises significantly.
One of the big challenges in managing this fluctuating demand is that most generators can’t be turned on and off quickly. You can’t just throw a switch and expect a several-hundred-megawatt generator start cranking out electricity—though gas-fired generators can be fired up more quickly than coal or nuclear plants.
Storing electricity behind dams
Utility companies have long been attracted to power sources that can provide for storage and whose output can be quickly ramped up and down. That’s one of the beauties of hydropower. When more power is called for, the water flow through turbines can be increased, and when less power is needed that flow can be reduced—which then may raise the water level of a reservoir.
Most hydropower facilities operate on a daily cycle, with less electricity generation at night and the potential to generate power being banked in a rising reservoir level, and then increased generation during the daytime, when electrical demand is greater. The turbines can ramp up or down quickly to adjust to fluctuations.
A somewhat involved approach with hydropower is to use electricity during off-peak periods—when base-load coal and nuclear power plants are generating more electricity than is needed—to pump water uphill to a pumped storage reservoir. There’s a pumped storage facility just south of us in Northfield, Massachusetts that I’ve visited. At that facility, water is pumped several hundred feet uphill to a reservoir at night and during off-peak periods, and then the water is allowed to flow back down those large-diameter pipes to generate power during peak periods.
But places where pumped-storage facilities can be built are few and far between. What are the other options?
The emergence of microgrids
With more intense storms, wildfires, terrorist actions, and other events causing widespread power outages—and likely to cause increasingly common outages in the future, according to many experts—there is growing demand for creating islandable “microgrids.”
Microgrids are small to moderate-size power grids, often serving university or medical campuses, that have the capability to be isolated from the regional power grid in the event of a widespread outage. Such systems must have their own generation capacity along with sophisticated electricity management systems. If the power quality of microgrids isn’t managed properly, there is risk of crashing the microgrid, the larger grid, one or both. Bobby Magill posted an excellent article on microgrids on Climate Central this past September.
More than fifty military bases have created, or are in the process of creating, microgrids. Military facilities have to maintain operability, even if widespread outages occur, so they are a natural for microgrids. Some universities and hospital complexes have also created microgrids, and the State of Connecticut, heavily hit by Superstorm Sandy, Tropical Storm Irene, and a freak October snowstorm in 2011, has passed legislation to create demonstration microgrids in eight cities.
Another advantage of microgrids is that the small-scale power generation needed for such systems takes place close to where the power is being used, so if there is waste heat created in the generation process (as occurs with reciprocating-engine generators, steam turbines, microturbines, and fuel cells), that heat can be captured and productively used. This is referred to as cogeneration or combined heat and power (CHP), and it can improve the economics for microgrids.
How a small amount of electricity storage can boost grid resilience
With renewable energy power-generation systems—particularly wind and solar—fluctuations in output provide another complication. When the wind stops blowing the output from a wind farm ceases, and when clouds obscure the sun the output of PV systems drops dramatically.
Batteries and some other technologies allow electricity to be stored when more is being generated than consumed, and it allows electricity to be pulled out of storage when demand exceeds supply. Some of these storage options can allow a critical loads in microgrid to remain powered when the regional grid goes down—until back-up generation can be brought online. This role of electrical storage in managing the output from wind and solar systems is important and will grow in significance as the percentage of our electricity supplied by renewables grows.
Lithium-ion battery storage
Solar Grid Storage, LLC, based at the Philadelphia Navy Yard, is at the forefront of efforts to use renewable energy to create a more resilient utility grid. In a recent BuildingGreen blog, I reported on The Navy Yard in Philadelphia, a remarkable 1,200-acre business campus with 300 companies employing 10,000 people—with as many as 35,000 employees projected eventually. I visited there, while I was in town for a conference, to learn about an innovative demonstration that’s been launched showing how solar-electric (PV) systems with battery back-up and smart controls can be employed to create a more resilient power grid.
Solar Grid Storage offers a modular system for managing the output of PV arrays (and other renewable energy systems) and storing power to better balance the output and power availability from large, grid-connected PV systems.
Advanced, lithium-ion batteries are used in this system. This technology avoids the use of heavy metals like lead and cadmium that are used in other batteries. The technology also allows deep discharge without wearing out the batteries and very rapid recharging—though cost is an issue.
The business model for Solar Grid Storage is that the owner of a large PV array would own just the actual array, and Solar Grid Storage would own the inverter, battery system, and other equipment needed to manage the system. These components come packaged in a 30-foot container, which the company (confusingly) refers to as PowerFactor.
The battery bank and controls allow the system to take over instantaneously in the event of a regional power outage.
One of the first four of these systems has been installed at The Navy Yard, and my colleagues and I got a chance to tour this facility. This PowerFactor250 system includes a 250 kW inverter and has 125 kWh of battery storage. Being modular, it is shipped directly to the site and can be hooked up quickly.
Another, larger PowerFactor system was installed in October, 2013 in Laurel, Maryland for the real estate developer Konterra. That PowerFactor500 system manages power from a 402 kW solar array that is integrated with parking lot canopies, and it includes 300 kWh of battery storage (though 250 kWh would be more typical with the 500 kW inverter). It includes critical loads power that can provide 50 kW of electricity for just over four hours.
Using flywheels to store electricity
A very different approach for storing electricity involves flywheels. At BuildingGreen we’ve written in the past about flywheel electrical storage for use in data centers to provide instantaneous back-up power that can last for a few minutes until back-up generators can be started up. But I had not been aware of utility-scale projects that were in operation.
The idea with a flywheel for power storage is that a small amount of electricity is used to keep a heavy mass rotating at a very high speed—10,000 revolutions per minute (rpm) or faster. Then when power interruptions happen or some extra power is needed to stabilize the grid, that flywheel generates power, gradually slowing down in the process.
Those of us who read Popular Science have been hearing about the potential of flywheel energy storage for decades; for me, it has been one of those technologies that has been perpetually “just a few years away from commercialization.”
Beacon Power, located in Tyngsboro, Massachusetts (near Lowell), has been a technology leader with utility-scale flywheel power storage since its founding in 1997. The company installed its first 20 megawatt (MW) system in Stephentown, New York in June, 2011, and that system has been working well.
Following a reorganization after financial troubles and the acquisition by Rockland Capital (which I described in more detail a couple weeks ago in this blog), Beacon Power has a new manufacturing facility in place, and in September 2013 the company put online the first 4 MW of a planned 20 MW flywheel energy storage facility in Hazle Township, Pennsylvania. The full system should be completed in the second quarter of 2014.
The Stephentown and Hazle Township flywheel energy storage facilities can almost instantly (in less than one second) begin injecting significant amounts of electricity into the grid. This helps stabilize the utility grid—the operation of which is a constant balancing act between supply and demand. Adding this capability—whether with a flywheel or a more conventional chemical battery—makes the grid less prone to blackouts and, thus, more resilient.
The flywheel system is modular, comprised of many of Beacon Power’s Smart Energy 25 flywheels, each of which can deliver up to 25 kilowatt-hours (kWh) of electricity. When delivering power at a capacity of 100 kW, full discharge takes about 15 minutes. When providing 150 kW (heavier power draw), full discharge occurs in 5 minutes with only 12.5 kWh delivered.
The flywheel itself, according to the Beacon Power website, has a rotating carbon-fiber composite rim, levitated on magnetic bearings so that it operates in a near-frictionless, vacuum-sealed environment. It rotates at 16,000 rpm and is designed for a 20-year life with 100,000 full-discharge cycles.
According to Beacon Power, the company’s flywheel power storage system “corrects imbalances more than twice as efficiently as traditional generators while consuming no new fuel, producing no emissions, and using no hazardous materials or water.”
The power grid of the future
Pumped hydro, Solar Grid Storage’s Li-Ion battery systems, and Beacon Power’s flywheel systems are examples of a variety of new energy storage technologies that promise to make tomorrow’s electric grid quite different from what we have today.
As a higher percentage of renewable energy sources, such as wind and solar, feed power into the grid, it will become more and more important to have systems like these that can store power when there is excess available and deliver that power when needed. (Smart meters will also play an important role in management of the grid, with utility companies able to turn off non-critical loads of customers for which “dispatchable loads” have been negotiated.)
Solar Grid Storage CEO Tom Leyden told me that his company is “proud to be part of what we believe will help usher in the grid of the future.”
I believe that such innovations will demonstrate very effective synergies between solar energy (and other renewables), the goals of resilience, and the efficient operation of the power grid. It should be fun to watch!