The value of battery systems in helping with grid frequency regulation is being put to the test this week in a project in Ohio, USA.
Renewable Energy Systems Americas (RES Americas), a North American renewable power project developer, announced Monday the start of its first energy storage plant, which is dedicated to providing frequency regulation to the US grid.
Located in Sunbury, Ohio, the plant is made up of two containers each holding a 20-ton lithium iron phosphate battery, said by RES Americas to be “an inherently safe variant of the lithium battery chemistry.”
These batteries provide plus or minus 4MW for a total frequency range of 8MW, with an output of 2.6MWh. A third container in the plant converts the direct current output of the system to alternating current for the grid.
BYD America supplied the equipment for the project, which is being used to stabilise grid operations at PJM Interconnection. PJM is the largest regional transmission organisation in the US, incorporating 830 companies and serving 60 million customers.
Interest in frequency regulation
The plant implementation comes amid growing interest in energy storage for frequency regulation.
Observers such as Hugues Chanoine at Clean Horizon Consulting in Paris, France, have pointed out that batteries and other energy storage systems, such as flywheels, might have significant advantages over existing frequency regulation methods.
“A gap between power generation and demand on the grid causes the grid frequency to move away from its nominal value,” Chanoine explained in a blog posting last year.
“This grid frequency is the same everywhere on an interconnected grid, for instance 50 Hz in Europe and 60 Hz in the USA, and must remain as close as possible from this value.”
When there is a mismatch between grid supply and demand, for example because of a power plant failure or a drop in consumption, the grid frequency changes.
Increasing likelihood of blackouts
A shift of more than around 0.5 Hz from the nominal value will cause rotating machines on the grid to disconnect as a safety precaution, increasing the likelihood of blackouts.
“To avoid this scenario, automatic regulation mechanisms have been created,” said Chanoine. “The network operator holds in store active power capacity made available by producers, which can be activated at any time to bring balance to the grid.”
Typically, fast-reacting primary reserve resources are brought online soonest to check any frequency imbalance.
Slower-responding secondary reserves, such as generators, then help bring the frequency back to normal, sometimes aided by a tertiary reserve if the imbalance is over a period of hours.
In general, however, having these ancillary services kick in as quickly as possible improves the level of grid stability and lowers the chances of a secondary reserve overcorrecting the original imbalance and needing further power to return to normality.
The business case for storage
Furthermore, since grid imbalances tend to happen on a timescale of seconds rather than hours, primary reserves are more valuable in maintaining grid safety. This where the business case for energy storage crops up.
Hydro, batteries and flywheels can react quickly enough to act as primary reserves and hence avoid the need for less efficient secondary response mechanisms.
In a 2008 study of the California grid, for example, the Pacific Northwest National Laboratory found that “the regulation system should be able to provide ramps of between 40 and 60MW per minute for a period up to six minutes.”
It concluded that the California Independent System Operator could save the amount of reserve needed for frequency regulation by 40% if it switched to faster-responding resources.
Recognising this, in 2011 the US Federal Energy Regulatory Commission introduced a pay-for-performance incentive that offers a premium to the fast-reacting primary reserves that do most of the work and deliver the greatest value in frequency regulation.
A growing need worldwide
The need for careful frequency regulation is growing worldwide as grids take on increasing levels of renewable energy. Wind and solar photovoltaic generation plants are both subject to abrupt changes in output depending on weather conditions.
As reported recently in Energy Storage Report, the industrial giant GE is already incorporating battery storage into its Brilliant turbine design in order to improve the machines’ ability to curtail frequency swings.
RES Americas is now taking the concept further with battery plants purely aimed at frequency regulation.
The company expects to deliver a second frequency regulation system, of 4MW, for the Independent Electricity System Operator in Ontario, Canada, this June.
In a press release, RES Americas added: “The company is currently marketing additional fully-developed frequency regulation projects in PJM. Frequency regulation represents a small fraction of the numerous services that energy storage can provide to the grid.”
Written by Jason Deign