Large-Format Lithium Ion Batteries Provide Enhanced Energy Storage for Solar Generated Power

John Battaglini, Vice President, International Battery, Inc.

President Obama’s “Clean Energy Standard for America” seeks to achieve 80 percent of electricity to come from renewables and other clean energy sources by 2035. It’s an ambitious goal, however one that can be met through the help of new innovations in grid technologies. Certainly, the quest for more reliable, cleaner alternatives to fossil fuels is driving technological advancement in the smart grid. According Greentech Media research, “6.5 gigawatts of solar demand will be reached by 2015, with a 2009 to 2015 CAGR of 109 percent and a total market value of $13.0 billion. In 2009, the entire US photovoltaic (PV) market received an estimated $2.4 billion in total project investment, a number that will be exceeded as early as 2011 in the utility market alone.” Managing and storing solar energy is the Holy Grail of success for not only utilities, but for consumers as well. Secretary John Hanger of the Pennsylvania Department of Environmental Protection said, “Renewable energy is booming, gaining an ever larger share of our electricity generation mix. To take it to the next level, though, we must improve our ability to store energy in large amounts.”

The integration of intermittent renewable energy sources into the smart grid has presented challenges due to the inconsistent nature of the energy source. While solar power can provide a clean alternative to fossil fuels, the energy produced is difficult to store and utilize during the off-peak hours, which include cloud cover and night time. Difficulties in load leveling, back-up power, grid regulation and line efficiencies have created the need for enhanced energy storage systems. The ability to have energy stored and prepared to return to the grid during peak demand has inspired developments in both lead-acid and lithium ion batteries to satisfy growing energy storage needs. Just as smaller, longer-lasting lithium batteries became the standard energy storage format utilized by laptops and cell phones, solar integrators are applying battery systems with advanced chemistries and larger formats to fill the needs of the growing renewable energy storage requirements.

Energy Storage System Formats
Solar integrators are employing several different battery technologies including: lead-acid, lithium ion, ultracapictors, sodium sulfur, vanadium redox, flywheels, compressed air, fuel cells and pumped hydro. With so many choices, system designers and integrators need to consider the following:
• Weight- effecting mounting, installation, maintenance and mobility issues
• Footprint/Location- volume reduction, when space matters
• Modularity/Scalability/Mobility- ease of system expansion and relocation
• Cycle Life- evaluate length of life and capacity, e.g. high C rates
• Service/Maintenance- projected life for specific operating temperatures
• Charge Times- will be different for various battery chemistries
• Capacity loss at high rates of discharge- evaluate and compare

Premium Performance Provided by Large-Format Lithium Ion Batteries
Due to lack of options in the past, the lead-acid battery has been one of the earliest formats to be applied to solar energy storage applications. Though lead-acid has a loyal following due to the initial purchase price, their limits are being recognized and replaced by lithium ion for demanding solar and other high energy density storage systems. The lithium ion battery as a supplement to the lead-acid type of battery offers many advantages as they are better at moving large amounts of energy into the battery without overheating and offer much higher round trip efficiency top-off charging of the fully depleted batteries by stationary charges can be accomplished in just two or three hours with lithium, versus a six-to eight hour charge time required by lead-acid batteries. The advantages of lithium over lead-acid also include:
• Dramatic weight reduction, up to 80 percent in high C-Rate applications
• Footprint/volume reduction, up to 65 percent in high C-Rate applications
• Dramatically longer cycle-life
• Use 100 percent of capacity of lithium battery without shortening rated cycle life, verses 40 to 60 percent of capacity for lead acid
• No service for the lifetime of the battery
• Shorter charge times (1.5 to two hours verses five to eight for lead-acid)
• Lithium has lower effective capacity loss at high rates of discharge

International Battery, Inc. is one such company manufacturing these new types of large-format lithium cells. The company’s current generation of large-format cells is up to 70 times the capacity of the prior generation of cylindrical lithium cells. Large-format cells offer much lower system integration costs when aggregated into large battery packs.

Having an order of magnitude reduction in the number of cells also enables reduced number of battery interconnections, further improving the reliability of the battery pack and providing for a much higher value proposition. Individual cell monitoring with the use of a battery management system is a key to success with these systems.

Energy Storage at Work
To further revolutionize the integration of renewable energy into the smart grid in the US, several pilot demonstration programs have been launched to prove the practicality of energy storage and its potential to impact the grid. Besides grid stabilization and load leveling, the inclusion of storage systems can potentially provide back-up power to thousands of residential and commercial customers, especially when renewable energy is not available.

Large-format lithium ion cells are being utilized by Sunverge Energy. Sunverge’s turnkey Solar Integration System (SIS) is currently being demonstrated as part of a micro grid project at the Philadelphia Navy Yard’s Energy Innovation Hub. The Hub is a national center for research, education and the commercialization of energy-related technologies, combining efforts of researchers from academia, the private sector and national research laboratories to save energy, reduce carbon emissions and position the US as a leader in renewable energy resources. The Navy Yard Campus in Philadelphia encompasses 1,200 acres, more than seven miles of waterfront, a workforce of 8,000 in more than 100 companies, 5.5 million square feet of facilities and more than $500 million of private investment. Within the Energy Innovation Hub includes a live demonstration of a micro grid with a 2,700 square foot net-zero energy home. Sunverge’s efficiently designed, integrated system includes an inverter, gateway interoperability and lithium ion energy storage technology, making it a unique and comprehensive solution. The Sunverge SIS captures solar energy at its most plentiful and stores it for use during peak demand hours, when cost to produce and deliver electricity is at its highest. The Navy Yard project showcases the next-generation zero-energy home and the importance of managing, distributing and storing energy within the smart grid.

Large-format lithium ion cells have also been adapted by Princeton Power, who is developing a $1.5 million solar generation system with a 200-kilowatt solar array and energy storage system that will be connected to the grid. The project funded in part by the State of New Jersey’s Clean Energy Manufacturing Fund, will demonstrate advanced smart grid functionality including micro grid operation, demand response, time shifting, frequency regulation and power dispatch. Princeton Power’s inverter and International Battery’s energy storage system will be housed in a mobile shipping container that is expandable to include one mega-watt-hour of storage.

As the Smart Grid continues to develop and integrates more renewable energy sources, energy storage will represent a key value proposition for the electricity grid of the future. Solar and wind will certainly pose challenges to the grid as more of these intermittent energy sources come online. Moreover, with the future adoption of plug-in vehicles, smart energy management will be needed to assure the quality and reliability of the grid. To this end, energy storage systems will serve as a key foundation technology that will advance the grid to its full potential.

Contact International Battery, Inc. at

This article was printed in the May/June 2011 issue of Battery Power magazine.

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