When most utility industry people hear the words “energy storage,” their minds immediately jump to the lithium-ion or flow battery systems that store excess solar or wind energy for use when generation is lower.
Battery energy storage can be a great way to relieve congestion during peak usage periods, and it can bring consistency and reliability to a power grid that relies increasingly on intermittent renewables. But it is not the only way. Utilities may be able to achieve many of the same goals by using stored liquified natural gas (LNG). Natural gas that has been cooled to -260 degrees F becomes a liquid and takes up approximately 1/600th the volume as it does in gas form, making it easier to store in large volumes.
Think of an LNG tank as a giant battery that, when paired with a gas turbine generator or a reciprocating engine, can be used to meet base electric load and peak power demands. The potential applications are widespread. In fact, many places in which battery storage is an option, LNG storage might be a viable alternative.
For example, imagine a region in the midst of a polar vortex. A utility could use stored LNG to help fuel the existing gas-powered generation needed to heat homes during a three- or four-day period when temperatures grow brutally cold. Likewise, an island or remote military base that generates its own power might rely on stored LNG to fill the gap during peak times or when energy supply is unreliable or unavailable.
A logical choice for utilities that need to balance renewables, LNG storage could also be a cleaner-burning solution for coal- or gas-fired plants that currently rely on fuel oil as a backup source. Additionally, it could solve potential fuel oil-related maintenance issues because it does not degrade and “gum” up when it sits idle.
LNG Supply Alternatives
Utilities interested in LNG storage can choose between two basic approaches.
Islanded utilities, or those with limited space or resources, might consider transporting LNG by truck or rail to their site, where it can be held in storage tanks. For simple-cycle or combined-cycle plants, this approach likely would require the utility to add an LNG truck unloading station and a vaporizer that transforms the LNG back into vapor. While this option requires the least amount of infrastructure, space for the LNG storage tank (or bullets) must be available.
Rather than purchase LNG from third parties, natural gas utilities that own their pipelines might prefer to liquify their own gas and store it on-site. This approach requires more space and upfront investment in a liquefaction plant, if one is not already in place. Some utilities may just need to expand and upgrade existing LNG storage and production capacities. State and federal regulators are viewing these projects in a favorable light as their peak-shaving value is recognized.
Batteries vs. LNG
Stored LNG offers multiple possible advantages over other energy storage methods. For one thing, LNG is a mature, trusted fuel source with a long history of reliability. It can not only reduce a utility’s dependence on a single fuel or energy source, it may also offer safety advantages over lithium-ion batteries, whose use may require special permitting to meet local fire codes.
LNG offers greater flexibility when it comes to storage duration. While a typical lithium-ion battery is limited to eight hours or less of storage, LNG’s storage capacity is based on volume. The more LNG stored, the longer the time frame it can provide backup power. Users have a lot of options when it comes to choosing LNG storage volumes — there are small prefabricated vessels for short durations or large field-erected tanks that can hold several days’ worth of energy. An additional advantage of LNG is that unlike with lithium-ion batteries, there is no degradation of the stored LNG.
LNG storage isn’t a new concept. Given the ready availability of domestic natural gas supply and LNG storage and production infrastructure, it’s time to look at it in a fresh way and see it as a viable alternative to battery storage.
Identifying the right LNG storage container solution depends on careful evaluation of plot space, siting options, cost and schedule.