Technology Battery Advances for Smart Grids
Energy storage systems are increasingly recognized as a key element for smart grids. It comes at a time where batteries in particular are already dominating the portable devices and transportation sectors. It is noteworthy to mention how both sectors are being influenced by their higher electrification, and the increased flexibility they offer to consumers. This enhanced flexibility is a key feature for smart grid applications, where storage systems can participate as distributed energy systems in microgrids, increase energy resiliency for consumers and also shift their role from passive consumers to active partners.
Energy storage is largely considered a key component of smart grids in its unique capability to adapt to renewable energy technologies and load variations. If one looks at the penetration of energy storage (mainly electrochemical batteries) in different sectors, an increasingly strong presence can be seen. And this is not a futuristic prediction, but evidence of how batteries have had the potential to disrupt the communication and transportation sectors since the end of the 19th Century through the telegraph and electric vehicle.
Batteries have transformed society toward higher connectivity and personal independence with their use for portable devices like cell phones, tablets and laptops. This has created a complete revolution of its own by supporting not only one-to-one communications through phone calls, but uninterrupted connection through social media. The role of consumers through this has changed from passivity to active involvement. It is in this way that smart grids align with this change in the consumer’s role. The capability of smart grids to communicate and integrate consumers in daily operations as partners and decision makers for their own energy use is a key feature for its success.
Energy storage holds a particular interest for smart grid applications. Its flexibility in supporting renewable energy, avoiding curtailment by storing energy and using it later for peak shaving, among other capabilities, give consumers the combination of increased energy resiliency, efficiency and economic benefit. It also can be used in concert with other energy storage devices available in the household, such as electric vehicles.
Currently, for new storage technologies, compressed air energy storage (CAES) dominates the sector, in terms of installed power. It is mainly focused on bulk energy management in roles comparable to pumped hydro. The rest of energy storage technologies, mainly batteries for the kW-MW applications, are dominated by sodium-sulfur (NaS), advanced lead-acid (Pb-acid), nickel-cadmium (NiCd), lithium-ion technologies (Li-ion), and flow batteries.
Even if lead- and nickel-based technologies have solid market share due to technology maturity and low costs, it is really lithium-based, sodium-based, and flow batteries technologies that are expected to dominate the market going forward. Liquid metal batteries, which present molten electrodes, have the potential to be a disruptive technology due to low materials cost and easy assembly. However, it still has to overcome slow starting times due to the need to operate at high temperature and its low voltage per cell. Trends for these technologies are focused on improving aspects that cover technical, economic, and environmental concerns.
Sodium-sulfur (NaS) batteries have had a wide acceptability for grid applications in different scenarios: support renewable energy, T&D investment deferral, etc. due to their excellent energy density, daily cycling capability and high round-trip efficiency. However, their high temperature operation (above 300ºC) and corrosive reactions pose a safety and environmental concern in the event of leakage and fire. Improvements have been made to the fail-safe design of the battery packs to further compartmentalize and protect in case of leakage.
Lithium-based technologies are expected to further dominate the grid application market as prodigious manufacturing reduces costs to a target of 100 $/kWh. in the next 20 years, with the expected impact in the U.S. of the Tesla Giga Factory agreement in Nevada. Other challenges Li-based technologies face include safety and their environmental impact. Lithium battery technologies have evolved from the more unstable and prone to thermal runway compositions, like LiCoO2, to safer technologies like LiFePO4. However, there are still challenges to not compromise energy density and ion conductivity when designing safer technologies. Lithium batteries are especially sensitive to temperatures above 60ºC, which must be carefully considered depending on the location and thermal management options. Major environmental activities are in setting up a more comprehensive recycling program for batteries that have reached their end-of-life. In this particular aspect, smart grids can actually be part of the recycling process for electric vehicle (EV) batteries. The reuse of EV batteries for grid applications is known as second life, and takes advantage of the remaining capacity in the battery; even if deemed inadequate for EVs, they can still be of use for stationary applications. For lithium technologies in particular, the use of rare-earth elements adds to the environmental toll and presents the difficulty of the supply being controlled in a large part by a single country (China). Therefore, research efforts are underway to eliminate the need of rare-earth metals.
Flow batteries, which take advantage of storing the reactants separately in tanks, present the unique quality of providing a decoupling of the power and energy, which is particularly interesting for grid applications. There has been an extensive development in the flow battery technologies and commercial availability. Traditional technologies, based on Vanadium, ZnBr, bromine polysulfide(BPS), etc. have seen increased commercial deployment. However, the main environmental concern is the hazardous disposal of the liquid electrolyte due to its corrosive nature. Newer developments like ZnFe present reduced costs, and non-hazardous alkaline electrolytes.
All these new advances in material design need to be matched by a stronger system level integration with the rest of smart grid elements, while keeping the needs of consumers in mind. This requires integral approaches that incorporate the energy storage design with the rest of the system, that is scalable and that generates a clear revenue path, while keeping in mind environmental and safety concerns.