Batteries

Saving for a Sunny Day: Shaving Peak Demand with Utility-Scale Energy Storage

Boothbay, Maine is the kind of town that still has general stores. And not any ordinary general stores-general stores with screen doors, and front porches, and rocking chairs. 

By Tim Miser, Associate Editor

Eos’ Znyth battery technology is designed for stationary, utility-scale storage. With a volume price of $160/kWh and a 15-yr life, the Eos Aurora® 1000│4000 DC battery system enables turnkey energy storage solutions with a levelized cost of storage of $0.07/kWh. The 4-hour battery is designed as a locational capacity product that reduces peak demand and debottlenecks congested nodes on the grid.

Image Courtesy: Eos Energy Storage

Boothbay, Maine is the kind of town that still has general stores. And not any ordinary general stores-general stores with screen doors, and front porches, and rocking chairs. It’s the kind of place where old men drink Coke from glass bottles, where evergreen trees cling to craggy islands just offshore, where fishing trawlers are as common as automobiles. If you’re lucky and keep a close eye out, you might see a whale breach out past the breakers. And check out those wooden buoys hanging on the outside of that clapboard barn over there, or the lobster traps piled up against that dock house. If the wind blows in the right direction, you can even hear the clinking of the schooners hoisting their sails on the bay and smell the barnacles and other marine detritus collecting in the tidal pools. Can you hear the terns navigating the salt air?

Yes, Boothbay is a midsummer vacation heaven, so it’s no wonder that tourists flock to the area. The 2010 census puts Boothbay’s population at just 3,120 people, and that’s including the surrounding villages. But the area lies at ground zero of the vacation onslaught, so in the warm months those numbers soar. “Summer people”, they’re called, and if the four-season veterans like to complain about them, they become rather quiet when the dollar bills begin to change hands. Whether the tourists are walking the pre-colonial streets adrift in picaresque fantasy or lounging in Adirondacks on the waterfront like Kennedys, people love this town, and that love translates to real money.

But what most tourists don’t think about as they tuck into lobsters or peruse the shops for souvenirs for the grandkids is just how tricky their presence makes it to plan for electric service. Any time a population varies so dynamically from season to season, capacity planning at local utilities is bound to take on the aspect of a migraine. Just how do you ensure enough power in the summer without also having massive oversupply when the tourists are at the beach and not using hotel amenities, or when the winter surf turns gray and they go home altogether?

The short answer is, sometimes you don’t. Striking such a balance can indeed be a tricky business. In the past, utilities have struggled to walk this wire and have occasionally missed their marks, turning up with supply-demand incongruences.

“The electricity system is built for the peak minute, of the peak hour, of the peak day, of the peak week, month, year, and 10-year horizon,” says Johannes Rittershausen, CEO of Convergent Energy + Power. “Often another 15 percent is added on top of this for buffer.” He explains that planning like this ensures that utilities are prepared to meet customers’ electricity needs even at times of peak demand. But though this kind of capacity planning is standard and has worked out well traditionally, it results in a massively overbuilt infrastructure that goes underutilized in times of lower demand.

That’s why when greater capacity and reliability were required during the summer vacation season in coastal Maine, Central Maine Power (CMP) chose to explore Non-Transmission Alternatives (NTA) to shore up supply, rather than build an $18 million transmission line that would have otherwise been required. CMP called on Convergent Energy + Power, an energy storage asset developer that serves as a liaison between utilities and large users of electricity, original equipment manufacturers (OEM), and financing resources, to provide a solution that would “shave the peak”, allowing the utility to provide electrical power when and where it was required while better spending capital investment dollars in capacity infrastructure.

Convergent installed chemical batteries integrated by the OEM Lockheed Martin Energy Storage that allow the utility to generate power during times of low demand, and store it away to provide a multi-hour energy boost when demand once again peaks in the late afternoon. It’s like saving for a rainy day, only in this case the summer days in Maine are decidedly sunny and clear. Convergent retained ownership and operational responsibility of the energy storage project, and was able to provide CMP with a solution that addressed the utility’s infrastructure needs at less than 50 percent the cost of a traditional line upgrade. The Boothbay project went online April 1, 2015 and for two successful summers has helped support Maine tourists as they run their air conditioners and plasma screen televisions.

Like Your Computer’s UPS, Only Bigger…MUCH bigger!

Energy storage has been used on a small scale for years. The battery in the uninterruptable power supply (UPS) that you plug your computer into relies on technology not so dissimilar to larger energy storage applications, and big manufacturing and healthcare facilities have long relied on energy storage to support operations at the building or campus level.

While energy storage projects at utility scale are also not new, they do retain something of that new smell. In many cases, utilities lack the knowledge or experience to feel comfortable implementing such technologies on their own. “Utilities are interested in technologies like grid-scale energy storage,” says Rittershausen, “but they don’t always want to bear a long-term risk on new technology. Because of this, they often prefer to have a developer like Convergent step in and build a project, taking the construction and operational risk.”

Rittershausen explains that energy storage projects serve a variety of needs and, as such, take on different scopes. By and large, the energy storage industry breaks down into two categories: fast-response and long-duration applications. “There are technologies that are optimized for shorter charge/discharge cycles,” he says, “and technologies that are optimized for longer cycles.” Rittershausen cautions that talking about technologies without also discussing the problems they solve can be misleading. “It’s hard, for instance, to compare a flywheel and a six-hour battery,” he says. “No one would ever ask if they need to buy a racecar or a tractor. They’re both forms of transportation technologies, but they don’t equate in a side-by-side comparison of things like horsepower or zero-to-60 times.” The only relevant comparisons are made between technologies that solve similar problems under similar constraints.

Fast-Response Energy Storage

Some projects require fast-response energy storage, so they demand very fast charge/discharge horizons that occur several times a day, or even several times a minute.

Fast-response energy storage is mostly used for frequency regulation, voltage control, and power quality enhancement. In cases such as these, flywheels can be preferable to chemical batteries. Because flywheel systems are entirely mechanical, relying on heavy underground wheels that spin in vacuums to harness momentum for power generation, they do not suffer performance degradation at the end of their service lives. As long as flywheels are maintained and their worn components repaired, they are not vulnerable to the explicit lifespan limitations incumbent in battery chemistries, whose useful lifetimes are influenced by factors like charge rates, cycle numbers, and operating temperatures.

Convergent Energy + Power worked with Central Maine Power to install a 3-MWh battery asset engineered by Lockheed Martin. Shown here on the interior of the battery’s ISO shipping container, the energy storage installation was designed to reduce summer peak loading on existing transmission & distribution infrastructure cause by the tourist season in Boothbay, Maine. Image Courtesy: Convergent Energy + Power

However, flywheels are generally more expensive than chemical batteries and so make greater financial sense if the infrastructure is meant to serve needs that span decades. Owing to this, says Rittershausen, the vast percentage of fast-response energy storage solutions currently rely on lithium-ion battery technologies.

Long-Duration Energy Storage

Rather than regulate frequency and improve power quality as fast-response systems do, long-duration energy storage solutions are meant to shave 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.

Philippe Bouchard is Vice President of Business Development at Eos Energy Storage, which has worked closely with Convergent on past projects. Eos manufactures a proprietary battery technology called Znyth.

“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,” says Bouchard. “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.”

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.

“Our manufacturing facility ships a roughly 42-kW, 167-kWh energy stack that’s 5-feet square and about 11 feet high,” says Bouchard. 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. “It’s plug-and-play,” says Bouchard. “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.”

 

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