As with most clean-energy markets, activity in the energy-storage segment is directly tied to government policies. According to Navigant Research, energy storage is used to fix existing problems in energy systems, so it stands to reason that the technologies that solve the largest, oldest and most pressing problems will win the most market share.


Wind, solar and other grid applications use an array of energy-storage technologies, including lithium-ion ­(Li-ion), lead–acid and flow batteries; kinetic flywheels; thermal systems; and, to a lesser degree, hydrogen fuel cells.


“In the direct electrical-storage segment of the industry, the most prevalent technology in use is still lead-acid batteries,” said Ralph Muehleisen, principal building scientist at Argonne National Laboratory, Argonne, Ill. 


Lead-acid batteries are able to discharge a lot of power for their physical size, and they have low self-discharge rates. However, they don’t store much energy for their weight (low-energy density) and they have short cycle lives and safety issues, such as hydrogen buildup.


Li-ion batteries, with countless uses including cell phones and laptops to tools and car batteries, are also becoming common in energy-storage applications. They have five times the energy density of lead-acid batteries and a much longer cycle life, according to Muehleisen.


“The primary safety hazard of Li-ion is the risk of overheating and, depending upon the design, fire or explosion risks,” he said.


Although not widespread, other battery technologies are also being installed in some projects.


“New, advanced, carbon-enhanced lead-acid batteries that will increase cycle life by an order of magnitude are now starting to come to market, and new flow batteries [such as iron chrome, vanadium redox and zinc bromine] have been developed,” said Dan Borneo, engineering program/project lead in Sandia National Laboratories’ Energy Storage Technology and Systems Department, Albuquerque, N.M.


Innovation


According to Borneo, the path forward for successful energy-storage innovations includes research and development of storage technologies, power electronics that connect energy-storage systems to the grid, and controllers that operate, control and optimize energy storage to solve grid problems.


“Control-optimization software advances are key to making energy storage more cost-effective,” he said.


Sandia Labs is developing novel algorithms and processes to optimize and manage several integrated “systems of systems,” and the engineers and technologists are involved in improving software with predictive analytics to manage energy storage’s critical attributes of ramping up and down as well as recovery.


On the technology side, the next generation of Li-ion batteries will have higher storage density, longer cycle life and improved safety.


“Argonne is looking for the next chemical that is not ion, such as magnesium, to use in energy-storage batteries, with the goal of delivering five times the energy density at five times lower cost,” Muehleisen said.


Supercapacitors, which store energy in an electromagnetic field rather than electrochemically, also are under investigation. 


“Right now, the cost is too high for real-life application,” Muehleisen said. “But, as the technology matures, the goal is to achieve higher energy density, lower self-­discharge and an almost infinite lifetime.”


In addition, the development of two-way power-flow systems will make it easier to connect storage systems to renewable-energy systems and the grid.


“Affordable systems will allow buildings to interact directly with the grid and create power flow in both directions,” Muehleisen said.


With federal clear air policies and, as more states enact standards requiring utilities to increase the amount of renewables in their generation mix, there has been an influx of photovoltaics (PV) and wind on the national grid. These renewables are intermittent by nature. If the penetration is large enough—research has indicated more than 20 percent of total generation on any particular grid node—the grid may face stability problems.


According to Borneo, energy storage can help mitigate these problems.


Energy storage has also been proven to provide the grid with other services, such as deferring transmission-system upgrades, energy arbitrage, power quality and congestion relief.


“The cost and reliability of battery systems are of concern, and there is presently no clear winning technology for the many applications where energy storage can provide a value,” Borneo said. 


In addition, there are limitations to the battery chemistry and to creating designs that are of lower cost with less energy loss.


Even so, it is possible that energy storage is nearing the point of critical mass, where increased market applications will push further innovation. This will, in turn, make systems more reliable, cost effective and eventually ubiquitous.