The new advancements in grid technologies as well as the quest for cleaner, longer-lasting alternatives to fossil fuels are driving technological advances for the smart grid. The ongoing challenge of integrating and balancing intermittent renewable energy sources including load leveling, back-up power, grid regulation, and line efficiencies, have created the need for innovation in energy storage. As more renewable energy sources are integrated into the smart grid, managing and storing energy is essential, in particular, large-scale diurnal storage. State and Federal laws, policies, incentives and higher energy rates have spurred new interest in energy generation and storage.
Besides grid stabilization and load leveling, storage systems can potentially provide back-up power
Veteran solar photovoltaic (PV) integrators have considered batteries for energy storage as long as they have installed PV. Having power ready to return to the grid during peak demand has spurred development in both lead-acid battery technology and lithium-ion batteries to fill growing storage needs. In the same way longer lasting, smaller lithium batteries became a staple to the energy storage of laptops and cell phones, battery manufacturers and integrators are now developing battery packs with more complex chemistries and larger formats to fill the needs of the growing renewable energy storage requirements.
Energy Storage System Considerations:
While there are several choices for energy storage (figure 1), including lead-acid, lithium-ion, sodium sulfur, vanadium redox, ultracapacitors, flywheels, compressed air, pumped hydro, fuel cells - 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
Figure 1 Battery Technology Comparisons
Courtesy of the Electricity Storage Association (ESA)
Large Format Lithium Ion Batteries
The lead-acid battery, long one of the few options for solar energy storage applications, has limits. While lead-acid have a loyal following due to lower cost, their ubiquity is starting to be replaced by lithium-ion for demanding solar and other high energy density storage applications. The lithium-ion battery as a replacement to the lead acid type of battery offers many advantages as they are much better at moving large amounts of energy into the battery without overheating and offering much higher round trip efficiency. Top-off charging of the fully depleted batteries by stationary chargers can be accomplished in just two or three hours with lithium, versus a six- to eight-hour charge time required by lead-acid batteries.
International Battery Inc. is one such company manufacturing these new types of large format lithium cells. The companys 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 (BMS) Battery Management Systems (software and hardware) is a key to success with these systems.
Putting Energy Storage to the Test
Recently, utilities and system integrators in the US have initiated several demonstration pilot programs to prove the viability of energy storage (evaluating chemistries of all types) and its potential impact on the grid. Besides grid stabilization and load leveling, storage systems can potentially provide back-up power to thousands of residential and commercial customers, especially when solar or wind is not available.
To this point, an interesting project using energy storage has been deployed in Maui, Hawaii. With electricity rates the highest in the country, the Maui Economic Development Board wanted to assess the effectiveness of storing solar energy using efficient battery technology. The renewable energy system is comprised of sixty 224-Watt PV panels, a bi-directional 3-phase inverter system and a state-of-the-art charge-controller network provided by HNU Energy in Maui. A 48V, 16.4kWh lithium-ion based energy storage system was integrated complete with battery management and controls to store the energy generated from the solar array.
The energy storage system includes four battery modules; totaling 32 160Ah lithium iron phosphate (LFP) cells and a battery management system (BMS) that is integrated into a standard 19 portable rack mount chassis and enclosure. The large-format lithium ion batteries were chosen because of their proven high-energy density, robust thermal and cycling performance as well as easy system expandability.
Large format lithium-ion cells (figure 2) also have the attention of Princeton Power, which is developing a $1.5M solar generation system with a 200-kW solar array and energy storage system that will be connected to the grid. The project funded in part by the State of New Jerseys Clean Energy Manufacturers Fund, will demonstrate advanced smart grid functionality including microgrid operation, demand response, time shifting, frequency regulation and power dispatch. Princeton Powers inverter and International Batterys energy storage system will be housed in a mobile shipping container that is expandable to include 1MW/h of storage. (1)
As the integration of renewable sources continues to evolve, the role and significance of energy storage in a smart electric network significantly increases. And, while there are different storage solutions, large-format lithium ion cells are leading the way in many high-energy applications because of their near 100% efficiency, modular and scalable architecture and versatility.
(1) See "Princeton Power Chooses Large-Format Lithium Ion Batteries for Solar Generation System" for more details on the Princeton Power system.
About the Author
John Battaglini is Vice President of International Battery, Inc., an Allentown, Pennsylvania company that manufactures large-format, rechargeable, lithium-ion batteries. He holds an MBA from Villanova University, an MS in Electrical Engineering from Clemson University, a BS in Electrical Engineering from Drexel University and he has over 20 years of sales and marketing experience in high technology companies.