Saving for a Sunny Day with Stored Energy

Instead of regulating frequency and improve power quality as fast-response systems do, long-duration energy storage solutions are meant to cut the peak in times of high demand. They provide a power boost when a generation asset or transmission line would otherwise be overloaded in times of heavy use. They are generally called on for one to six hours of dispatchable power at a time, frequently on late summer afternoons when the weather is at its hottest.

Vice President of Business Development at Eos Energy Storage, Philippe Bouchard said “its’ an aqueous zinc battery that relies on a zinc hybrid cathode chemistry and is optimized for the stationary, utility-scale, grid-connected energy storage market.”

“So our product meets the needs of a very specific business case. We’re able to provide four to six hours of continuous discharge to reduce system peak demand,” Bouchard added.

Eos’ Aurora 1000/4000 product is a 1-MW, 4-MWh DC system. It’s comprised of Znyth chemical batteries, which are sealed, static-cell sub-modules that are slightly larger than a shoe box. Each battery stores about 4 kWh of energy. Eos strings these together in series and in parallel, and packages them in an outdoor-rated module called an energy stack.

Bouchard also said, “our manufacturing facility ships a roughly 42-kW, 167-kWh energy stack that’s 5-feet square and about 11 feet high. These energy stacks are delivered to the site via flatbed truck, where the EPC contractor can place it onto an integrated skid and simply plug it in. “its plug-and-play. You don’t even need an electrician to install it.”

Six of these modular energy stacks can be aggregated into 250-kW, 1-MWh subsystems, which can themselves be aggregated into the full-sized 1-MW, 4-MWh product. This parallel aggregation creates in-built redundancies. “There’s no single common point of failure,” says Bouchard, “so issues can be isolated at the energy stack level.” Additionally, he explains, parts of the battery can be kept operational while other parts are isolated for maintenance.

The resulting product has a broad operating temperature range, and since it relies on a water-based chemistry, is not at risk of thermal propagation or runaway. Because of this, Bouchard says, the batteries do not require dedicated heating or cooling. They also don’t create any onsite emissions. Additionally, their small footprint ensures their ability to target capacity needs at the grid’s most congested nodes and load centers. They fit where they’re needed.

The Role of Energy Storage in the Larger Generation Ecosystem

While energy storage is often thought of as a way to smooth over intermittency issues inherent in renewable generation sources like wind and solar power, Rittershausen disagrees that this is the technology’s primary value in the current generation ecosystem. “So far, the intermittency issues associated with renewable energy resources have impacted the reliability of the grid almost not at all,” he says. “Once renewables reach a certain level of penetration, the grid may begin to lose stability and make energy storage solutions that much more important. So far though, that hasn’t happened in most places.”

Some studies suggest that a grid would need to reach 50-percent renewable penetration before reliability suffers in a way that energy storage could mitigate. Because of this, energy storage is currently more applicable for peak shaving than it is for combatting intermittencies in non-fossil generation. “Long-duration energy storage technologies are really designed to help utilities avoid the need to upgrade capacity to meet increased peak demand,” Rittershausen says.

Cost-effective batteries have begun to make capacity planning more flexible via the use of reliable, dispatchable, location-targeted battery solutions that avoid an overbuilt electrical system. Batteries make capacity additions possible on an incremental level. So if an existing facility is approaching a level of unreliable performance on particularly hot days, batteries can very quickly extend the life of that facility a little at a time, and in as little as six months from the contracting date, helping to ensure that loads don’t creep too high, and postponing the day on which more expensive capacity additions must be undertaken.

Rittershausen puts it like this: “Now that we have increasingly cost-effective energy storage solutions, it may not be good planning to build an entire electrical system for a resort town that is designed to support the few weekends in a summer when most tourists visit the area. Non-invasive batteries solve this problem much more efficiently and elegantly.”