Novel Batteries for Bulk Storage of Energy
Finding effective means for harnessing power from energy sources has become a hot research area in recent years, spurred by the nation’s ever-increasing demand for more power and the need to reduce consumption and reliance on fossil fuels. Renewable energy sources, such as solar and wind, could help reduce the carbon footprint. For centuries, hydropower has been the most productive form of renewable energy and geothermal power has also been tapped to generate electricity to help meet consumer demand.
Unfortunately, hydro and geothermal sources are not always located in areas that make it easy to integrate them into the electric grid. Solar and wind power, on the other hand, may increase the possible locations where energy might be produced, but their energy production is intermittent—not always available or predictable. This quality makes it difficult for utility companies to effectively rely on these sources. In fact, utility companies need to provide an equal amount of backup power, often not from renewable sources, to ensure energy availability.
Storing energy from wind, solar, and conventional sources when conditions are favorable, so that it can then be used at a later time, such as when demand is high, may be the answer to this grid-integration problem. A novel electromechanical battery (EMB) designed by Livermore has the potential to provide maximum bulk storage of energy produced from a variety of sources with minimal energy loss. As part of a Cooperative Research and Development Agreement (CRADA), laboratory scientists are working with EMB Energy Corp., which has engaged several other commercial partners, including Arnold Magnetics Technologies Corporation, to build large, modular EMB storage systems capable of addressing the huge power-leveling requirements of the grid.
Livermore has had several decades of experience developing EMBs. Initial systems were designed for specialized, high-power applications where pulses of electricity were needed to ride through short interruptions in electrical power. “This technology was beneficial for facilities such as hospitals that cannot afford downtime in their power supply,” says physicist Richard Post, who has led EMB research efforts. “However, previous versions of the technology had energy losses that were too great for the device to be sufficient for energy storage applications, where the required storage time is many hours.”
With several innovative technologies integrated into one, the newest EMB iteration is predicted to store energy for 6 to 8 hours, while releasing it over periods of 1 to 4 hours. In addition, unlike previous EMBs, which can waste 20 to 30 percent of their energy through internal losses, the newest EMBs have only a projected 5-percent energy loss.
The commercialization of the EMB technology is being facilitated through a CRADA between Livermore and EMB Energy Corp., one of the Oklahoma-based Keogh Group companies that will incorporate exclusive licensing agreements toward bringing EMB-based bulk energy storage systems to large-scale utility, various-scale industrial, renewable energy and other distributed applications.
Working closely with Livermore, EMB Energy is in the process of building its first prototype devices for initial field testing and data collection in partnership with a regional public utility company in the western United States. These tests will ultimately lead to installation and trial of a 250-kilowatt-hour EMB system sometime in 2012, followed by EMB Energy beginning full-scale marketing and manufacturing of its bulk energy storage systems at facilities tentatively slated to be located in Utah and Oklahoma.
Pending further design plans, the company anticipates that a typical large-scale installation will be made up of several hundred batteries, which, because they don’t require any type of cooling system, will be configured in an underground array to capture, store and dispatch energy gathered from various energy sources, including solar and wind.
Energy on the Fly
During Richard Post’s nearly 60-year career at Livermore, he has been the mastermind behind many inventions, including three distinct devices that have come together to create the bulk storage EMBs. A flywheel made from low-density, high-strength composite materials stores rotational energy for the system. A novel electrostatic generator–motor both powers up and discharges energy from the EMB system with the proverbial flip of a switch. And, tapping into his expertise in magnetic fusion, Post developed “passive” magnetic bearings that stabilize the EMB system with no mechanical friction energy losses. All the components are encased in a sealed, cylindrical vacuum vessel, where they work in concert to store and extract electricity with high efficiency.
In the 1970s, Post was one of the first to point out that a material’s strength per unit weight is what dictates its kinetic energy storage capacity. “The idea for using high-strength, low-density composite materials instead of high-density metals to create flywheels grew out of working with my son Steve on an EMB for electric vehicles,” says Post. Together, they wrote an article entitled “Flywheels” for Scientific American that discussed approaches to designing flywheels using high-strength composites. At that time, flywheels were typically fabricated from metals such as steel because at a given rotational speed the more mass a material has, the more kinetic energy it can store. However, in the article, they showed that a high-strength, lower density material could be rotated at a much faster rate than steel, enabling the lighter weight flywheel to store more kinetic energy.
Over the last decade, composite materials have greatly advanced. They are not only stronger but also easier to manufacture, which substantially reduces their cost. A team led by Livermore engineer and composite materials expert Scott Groves has developed a high-strength, low-density carbon-fiber composite perfectly suited for EMBs. The next step is to determine the right material combinations for fabricating the flywheel and integrating it into the device.
Inside the vacuum vessel, the flywheel is an essential part of the rotor for the electrostatic generator–motor, and the two components are integrated into the same piece of hardware. To charge the EMB, the generator–motor feeds energy to the rotor–flywheel assembly, causing it to spin until it eventually reaches a maximum speed of tens of thousands of revolutions per minute. The device is then discharged by using the generator–motor to slow the rotor–flywheel assembly, thus drawing out the kinetically stored energy. Unlike the more common flywheel-battery storage systems that use electromagnetic generator–motors, the electrostatic version has virtually no internal losses. Also, instead of using so-called “active” magnetic bearings that require electrical power, permanent “passive” magnetic bearings are used to dynamically stabilize the system without the need for complicated sensors, control circuits, and electromagnets.
Placed in a configuration known as a Halbach array, invented by the late Klaus Halbach of Lawrence Berkeley National Laboratory, the magnets are arranged to create a periodic magnetic field that is alternately vertical and horizontal. This arrangement concentrates the field on one side, while canceling it on the other. The passive magnetic bearings have very low losses, allowing the rotor–flywheel to continuously spin with minimal energy loss.
All together, the passive magnetic bearings, electrostatic generator–motor, and composite flywheel make up a system that suffers far less energy loss and provides greater storage-time capability compared to standard EMB systems that contain electromagnetic or mechanical bearings and magnetostatic generator–motors.
Livermore researchers demonstrated prototypes of the electrostatic generator–motor and the passive magnetic bearings. Ultimately, the team will design several EMB prototypes, each serving as a springboard to the next, with the first one scheduled for completion this summer. Bob Yamamoto, the project’s principal investigator, says, “The initial proof-of-concept will be a 5-kilowatt-hour battery about the size of a coffee urn that will demonstrate all the disparate parts fully integrated into a single homogeneous operational unit.”
A 25-kilowatt-hour battery built in collaboration with Livermore’s industrial partners will