Day of smart grid nears

Major electricity blackouts such as the one that crippled the northeastern United States and parts of Canada in 2003 could be prevented in the future with energy-storage systems based on high-voltage lithium batteries. The Engineer reports that high-tech battery developer Saft and power specialist ABB recently unveiled what they claim is the world’s first high-voltage Li-ion system that can connect to the grid, without a transformer, and immediately turn on if there is a disruption in power. The technology combines a 5.2kV battery, provided by Saft, and a voltage-control system from ABB. The battery system hooks together 1,456 battery cells in series to deliver as much as 200kW for an hour and 600kW for 15 minutes.

Jim McDowall, Saft project manager for the Li-ion battery system project, said these fifteen minutes would have provided power grid operators in the 2003 blackout enough time to respond to disruptions and isolate trouble areas. “It would have given them enough time to match power generation with power consumption,” he said. McDowall added that currently available back-up generators have the ability to provide large blocks of energy, but it takes minutes for them to produce full-power output. Meanwhile, people across the country are turning on lights, using electricity and putting new loads on the grid. “A fast-acting battery storage would buffer the system and respond instantly to new loads and bring up power generation to match the consumption,” he said.

Li-ion batteries have become more popular over the years because of their light weight, charge-holding capacity, and the ability to handle hundreds of charge/discharge cycles. The batteries are used commercially in many applications such as mobile phones and iPods but this is the first time they have been developed for a power grid’s energy-storage system.

The technological breakthrough, McDowall said, can be attributed in great part to ABB’s dynamic voltage-control system, called SVC (Static Var Compensation) Light technology. “The technical challenge in developing such a high-voltage lithium-ion battery system is you are monitoring a whole lot of cells together and obviously there is a large voltage difference between the first and last cell in the series,” added McDowall.

While all the cells may start out with the same capacity, aging, manufacturing variations, and the temperature differences between all the cells can cause their state of charge to drift apart. One cell will always be the most discharged, but to completely charge it will require overcharging all the cells in the series that were not discharged. Overcharging conditions are hazardous and best avoided so therefore the ABB system works to balance the cell voltages and ensure all the cells are functionally matched to each other.

McDowall said the system uses a controlled-area network, or a CAN-bus, similar to the one used in electric vehicles to monitor the battery and communicate with the system controller. All of which ensures the battery is operated within safe parameters at all times. The CAN-bus in a car, however, works only at 300V, much lower than a power grid’s needs. So the developers of this new system needed a central electronic brain that could work as a more distributed management system. “We were able to distribute the brains of the battery in eight separate units or sub-brains,” said McDowall. “These separate sub-brains monitor all the cell voltages, temperatures and current. They then run algorithms and tell the system controller how much charge or discharge current can be driven through the battery.”

McDowall says these sort of intelligent systems fit perfectly into the U.S. and EU’s vision for “smart” power grids. U.S. and European governments have announced in the past couple of years efforts to modernize their grids. The EU’s SmartGrid Technology platform, which commenced in 2005, aims to develop an electricity network that can intelligently integrate the actions of generators and consumers in a way that makes electricity supplies more sustainable, economic and secure.

The initial scope of the platform also aims to remove obstacles that stand in the way of integrating distributed and renewable energy sources. Modernizing an entire grid will take some time, but the Saft/ABB technology is ready to go. The companies are marketing their technology through ABB for potential applications such as industries with high short-term power demands and utility grids with a high percentage of variable renewable energy sources such as wind power.

McDowall said the Saft and ABB’s pilot system is going to a utility customer next year but he is unable to name the customer at this time. He added that ABB’s SVC Light technology has already been in widespread use to help support voltage typically on the grid. “This is an add-on capability that ABB will be marketing to its customers to make the grid much stronger and more resilient,” said McDowall.