Energy Storage 101: Key to a Flexible Utility System

In order for your lights to turn on when you flip a switch at the end of a long day, electricity needs to flow into your home at a moment’s notice. To respond to this need, and to the litany of energy needs on an electric utility’s system in a given day, a utility must constantly seek to balance its power supply with the demand on its system. Utilities serve consumers and balance their systems in a variety of different ways: by dispatching quick-ramping generation plants to meet peak needs, by purchasing energy on open markets, and by fluctuating the generating capacity of large generating plants, among others. What if energy didn’t need to be generated in real time to meet consumer demand?

In fact, it doesn’t have to be. Energy storage—the capture of energy produced for later use—has been around for quite some time. With advances in technology, the benefits that energy storage can provide, from system balancing, to avoided transmission and generation curtailment costs, to integrating intermittent renewable resources, are realized on a larger and larger scale every day.

Pumped hydroelectric storage was developed over a century ago, and most of it was built in the 1960s and 1970s. This type of storage uses energy from other generating plants when demand for electricity is low to pump water into reservoirs at a higher elevation. This water can then be released through turbines for later using during peak energy demand. While these pumped hydro plants are great for bulk storage to help adjust to small changes in demand or supply, the more advanced technologies now emerging will enable storage of energy generated from wind, solar, and other intermittent renewable resources on shorter time frames.

As of late 2017, approximately 800 MW of advanced energy storage technologies have been deployed in the United States, with nearly all of that capacity coming online in the last decade. The deployment of energy storage systems is expected to grow exponentially in the coming decades, either in stand-alone facilities, or co-located with renewable resources to provide more consistent or on-demand power output. Storage can be incredibly flexible: it can be installed at varying levels from residential to utility scale, can perform either as generation or load, can provide several market products, and can be used to defer massive investments in transmission and distribution infrastructure. Energy storage technologies contribute to electricity stability by working at various stages of the grid, from generation to consumer end-use. The following is a high level overview of some of the most common forms of storage technologies.

Batteries
Battery energy storage technologies involve electrochemical processes that convert stored chemical energy into electrical energy. These processes generally fall into one of two categories: solid-state batteries and flow batteries. Throughout the first half of 2017, lithium-ion (Li-Ion) solid-state batteries made up nearly the entire market share for advanced energy storage. These batteries are used in most electric vehicles as well. Since batteries can be located anywhere, they are often used as storage for distribution, such as when a battery facility is located near consumers to provide power stability. They also provide end-use applications, such as in electric vehicles or behind-the- meter home energy storage.

Flywheels
Flywheel storage technologies convert the energy of a rotating mechanical device into electrical energy. Flywheels use electrical energy to drive a motor that spins a mechanical device to increase its rotational speed, effectively storing electrical energy in the form of kinetic energy, which can then be called on in an instant to discharge from the spinning rotational device as electricity. They are well-suited to provide power quality and reliability services as well as fast regulation and frequency response, although their ability to provide larger capacity services is currently limited.

Compressed Air Energy Storage (CAES)
CAES facilities compress ambient air and store it under pressure. When the CAES facility is needed to supply electricity, the pressurized air is heated and expanded to power turbines. CAES is similar to pumped energy storage in terms of its broad range of potential applications. However, CAES is still in the early stages of technological development, with less than a handful of large-scale projects currently in operation around the world.

Thermal
Thermal energy storage can be realized through a wide variety of technologies using resources that temporarily store energy in the form of heat or cold. For example, one type of thermal energy technology uses solar radiation to heat molten salt to store energy in the form of heat, which can then be used later to produce steam to power a turbine and generate electricity. Plants like these are currently operating or proposed in California, Arizona, and Nevada. Thermal storage technologies can vary widely in storage media, facility size, progress of technological development, and cost.

More and more energy storage applications, projects, and emerging technologies are appearing throughout the country and world, spurred by a variety of different laws, regulations, incentives, and mandates. Enacted in 2015, Oregon’s House Bill (HB) 2193 directed Portland General Electric and PacifiCorp respectively to procure one or more qualifying energy storage systems that have the capacity to store at least five megawatt hours (MWh) of energy. The legislation gave a deadline of January 1, 2020. Both utilities have now filed energy storage proposals, which are currently being examined by stakeholders and Oregon PUC Staff. Stay tuned to the CUB blog for a follow-up post that details the storage proposals of each utility.

Sources:

https://www.ucsusa.org/clean-energy/how-energy-storage-works#.WoTQmK6nGUk

K&L Gates, Energy Storage Handbook, Oct. 2017. http://klgates.com/ePubs/Energy-Storage-Handbook-October2017/

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