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. 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.
