Solar

Energy Storage and the Smart Grid

Issue 7 and Volume 16.

By David J. McShane, International Battery

As the electrical grid is integrated with more renewable energy sources, energy storage will be instrumental for microgrids and smart grids.

Energy storage systems (ESS) combine energy-dense batteries with bidirectional, grid-tied inverters and communication systems to allow interface with the electric grid, provide valuable services and are programmable to run in various grid-support modes.

Grid-support services enable further penetration of intermittent resources such as solar.

Recently, U.S. utilities and system integrators have initiated several demonstration pilot programs to prove energy storage viability and its potential impact on the grid.

Also, organizations such as the Electric Power Research Institute (EPRI) are evaluating the efficiency and cycling performance capabilities of energy storage batteries.

Besides grid stabilization and load leveling, storage systems potentially can provide backup power to thousands of residential and commercial customers, especially when solar or wind is not available.

The Right Tools for the Right Job

Peak energy use is not going away soon, even with more consumer education and efforts to use less energy. Home energy monitors, along with unplugging appliances and turning off lights, won’t negate that most families need electrical power during peak times.

Energy use is on the rise with more computers, home entertainment systems, computer-based appliances and electronics stressing the already maxed-out grid. And then there are plug-in vehicles.

The grid must be intelligent to deliver reliable power when and where consumers need it.

Integrating renewable energy sources with smart energy storage will help mitigate grid overload, shift power loads and help reduce our carbon footprint. Discerning between available and viable storage technologies, however, means old technologies will compete for a position in a clean energy future.

Advances are being made in this market, but facts must be considered.

Several energy storage (see table) choices exist, including lead-acid, lithium-ion, sodium sulfur, vanadium redox, ultracapacitors, flywheels, compressed-air, pumped-hydro and fuel cells. System designers and integrators must consider:

  • Weight
  • Footprint and location
  • Modularity, scalability and mobility
  • Cycle life
  • Service and maintenance
  • Charge times, and
  • Effective capacity.

Optimum Performance

The lead-acid battery, previously one of the few options for energy storage applications, has limits. Lead-acid batteries have a loyal following because of their lower cost, but their ubiquity is starting to be diminished by lithium-ion in demanding, energy-dense storage applications.

The lithium-ion battery chemistry as a replacement to the lead-acid battery offers many advantages. It is much better at moving large amounts of energy into the battery without overheating and offers much higher round-trip efficiency. Top-off charging of the fully depleted batteries by stationary chargers can be accomplished in two or three hours with lithium, versus a six- to eight-hour charge time required by lead-acid batteries.

The lithium-based, large-format cells on the market are proving themselves in pilot programs, offering up to 70 times the capacity of prior generation of cylindrical lithium cells and have much lower system integration costs when aggregated into large battery packs. Having an order of magnitude reduction in the number of cells also enables fewer 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 battery management systems (BMS) is important with these systems.

The key to success is reliability. To meet sustainability initiatives, utilities are being pressed to adhere to strict quotas for renewable energy integration in the next decade and beyond. According to the Department of Energy (DOE), as of May 2009, 24 states plus the District of Columbia had renewable portfolio standard (RPS) policies. Together these states account for more than half of U.S. electricity sales. Maine has an aggressive 40 percent goal by 2017. California wants to reach 33 percent by 2020, and many states want to reach between 15 and 20 percent in the next five years. Beyond mandates, some companies are incorporating alternative power sources on their own and testing the viability of long-term success.

Energy Storage for Grid Applications

Lithium-ion batteries are the energy storage component of Sunverge Energy’s solar integration system (SIS) deployed in a net-zero home energy demonstration project at the Philadelphia Navy Yard’s Clean Energy Innovation Hub.

The hub includes a live demonstration of a microgrid with a 2,700-square-foot, net-zero energy home. Sunverge has incorporated an 8.2 kilowatt-hour lithium iron phosphate battery pack for use in the residential SIS system.

American Electric Power Co. Inc. (AEP) also is deploying grid-scale energy storage as part of the utility’s gridSMART demonstration project.

This project, funded in part by $75 million DOE stimulus funding, is being deployed to 110,000 AEP customers in northeastern central Ohio. [Editor’s note: See Page 18 for more on AEP’s energy storage options.]

As part of this project, AEP and system integrator S&C Electric Co. are using large-format, lithium-ion batteries.

Different from their smaller counterparts used in flashlights and iPods, large-format, lithium-ion prismatic batteries provide the right-size building blocks to deliver more energy and can scale up as energy demands increase.

Controlling and understanding the state of the batteries is vital, and that’s where highly intelligent battery management comes in to play. Advanced battery-monitoring systems can tell users the exact state of the battery, state of health, charging status and temperature.

Another project using energy storage has been deployed in Maui, Hawaii. With the highest electricity rates in the U.S., the Maui Economic Development Board wanted to assess the effectiveness of storing solar energy using efficient battery technology.

The renewable energy system is composed of photovoltaic panels, a bidirectional three-phase inverter system and a charge-controller network provided by HNU Energy in Maui. A lithium-ion-based energy storage system was integrated, complete with battery management and controls, to store the energy generated from the solar array.

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 also have the attention of Princeton Power Systems, which is developing a $1.5 million solar generation system with a 200-KW solar array and energy storage system that will be connected to the utility grid.

The project, funded in part by New Jersey’s Clean Energy Manufacturers Fund, will demonstrate advanced smart grid functionality including microgrid operation, demand response, time shifting, frequency regulation and power dispatch.

Princeton Power’s grid-tied inverter and the lithium-ion energy storage system will be housed in a ISO shipping container that is expandable to include 1 megawatt-hour of storage. Princeton Power Systems anticipates for the next-generation system to be fully operational by November.

As the smart grid transforms associated industries, the role and significance of energy storage will continue to increase.

There are storage solutions such as flywheels, compressed-air and hydro, as well as battery technologies, but large-format, lithium-ion cells are leading in many high-energy applications because of their nearly 100 percent efficiency, scalability and versatility.

Advances in battery technology, combined with superior methods of monitoring and managing batteries, take energy storage to a much higher level of integration in smart energy applications.

From an economic and environmentally sustainable perspective, high-density energy storage methods will prevail.

David J. McShane joined International Battery as executive vice president of business development and engineering in 2010. McShane brings more than 20 years of experience in the commercialization of early-stage technology companies.

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