The U.S. Department of Energy has made the research and development (R&D) of long-duration energy storage at fossil fuel generating stations a priority to keep reliable and affordable supplies of electricity flowing to American homes, businesses, and industries while reducing greenhouse gas emissions.

As part of its new Advanced Energy Storage Program, the Department of Energy’s (DOE’s) Office of Fossil Energy (FE) recently released a funding opportunity announcement (FOA) for technologies that are nearly ready for implementation, as well as innovative concepts with game-changing potential that can be integrated with fossil assets. Benefits of hybridizing energy storage with fossil assets include improved asset utilization, grid reliability, and environmental performance.

The National Energy Technology Laboratory (NETL), which is managing the program for FE, has requested research organizations, universities, and industry to provide proposals for funding the advancement of integrating energy storage technologies with a range of fossil asset types. Per an earlier FE-sponsored request for information (RFI), it is anticipated that proposals focusing on chemical, thermal, mechanical, and flow battery storage technologies capable of medium- and long-duration storage are most likely to be submitted. This initiative supports the broader DOE-wide Energy Storage Grand Challenge, which was announced by U.S. Energy Secretary Dan Brouillette in January to position the U.S. as a world leader in energy storage by the end of the decade.

Energy storage is not new. Pumped-storage hydropower, for instance, has been around since the 1920s, and other technologies that involve capturing energy produced and storing it for later use remain part of the equation. Therefore, the obvious question is: Why has FE established a new energy storage program?

The issue driving the initiative is the need to protect the modern grid and ensure it can supply the electricity America requires as more variable renewable forms of energy, such as solar and wind power, are added. Integrating energy storage systems with coal- and natural gas-fired power plants provides an economical and environmentally responsible solution to meet that need and strengthen the grid’s resiliency in the event of natural disasters or cyberattacks that disrupt service.

Fossil fuel-fired plants are designed to generate power while operating at continuous maximum capacity and efficiency. However, with more renewables on the grid, these conventional fossil energy plants are required to operate at minimum loads for longer periods of time. Such deviations from maximum efficiency increase fuel consumption and emissions. Additionally, reduced downturn of fossil energy plants causes stress and wear to steam-raising equipment.

FE maintains that energy storage combined with fossil energy assets offers a suite of benefits to the environment, asset owners, the electricity grid, and consumers. Here are several examples:

    ■ Consumers can rest easy. Energy storage at fossil fuel-fired plants will play a tremendous role in meeting electricity demand during peak times, including those sweltering summer days when air conditioners run at full blast. In the evenings, energy storage will help provide electricity during usage spikes when households turn on their lights and families power up an increasing number of home electronics.
    ■ Resource planners and power plant operators will find that hybridizing energy storage with fossil assets offers a strategy to support the grid with firm dispatching capability, improved asset flexibility, and overall system efficiency. During off-peak hours, plants will continue to operate at full load and redirect steam from the steam cycle to an on-site storage system. During peak hours, or when renewables are offline, the stored energy could be discharged back to the plant to raise additional steam for electricity generation.
    ■ Fossil fuel-powered plants running at high efficiency produce lower emissions of carbon dioxide, a greenhouse gas. And if such a plant were to add a carbon capture system to its operations, the prospect of a zero-level emissions, fossil fuel-based generating station could become a reality. The energy storage capability also supports renewable capacity expansions in regions that evolve consistent with various market and regulator drivers.

Today’s fleet of existing coal-fired plants is operating at approximately 50% of capacity. These generating stations and many natural gas-fired combined cycle (NGCC) plants, single-cycle combustion turbines, and reciprocating engines operate in a load-following or peaking manner. Operating these cycling assets in a more predictable manner, leveraging the additional flexibility afforded by energy storage, offers a large potential business opportunity through asset life extension, reduced fuel costs, dispatch capture, and other benefits. The opportunity before us is clear. Using energy storage is a business strategy to operate these assets with greater efficiency to generate cleaner electricity that can be sold when it is needed.

Energy storage systems will permit utilities that burn coal or natural gas to run at high efficiency during down times and save the energy they produce for rainy or windless days when renewable forms of energy are unavailable. Clearly, fossil fuel-based electricity, coupled with on-site energy storage, can help supply the U.S. with the reliable, cleaner power it needs to prosper in an evolving energy landscape.

Sparks of Strong Interest

On April 22, 2020, the 50th anniversary of Earth Day, more than 300 government policymakers, utility operators, researchers, and others took part in a U.S. Energy Association webinar to hear FE and NETL officials discuss their plans for the energy storage program.

Attendees learned that large-scale integration of energy storage at a fossil energy plant can improve reliability and resiliency as cleaner, renewable forms of energy become stronger components of the grid. Furthermore, it will provide a heightened level of energy security so that electricity can continue to flow to the grid during unplanned events such as disruptions in the natural gas supply chain.

A poll taken during the webinar showed that the strongest level of interest exists for integrating energy storage with NGCCs, followed by coal plants.

Attendees were also asked to rate the most important characteristic of an energy storage system when deciding to invest in one. More than 23% of attendees rated low capital cost as the top characteristic, followed by duration of storage (21.10%), and ease of deployment and integration (16.56%). Revenue increase was rated as the top characteristic by less than 10% of the webinar participants.

Return on investment for utility ownership cannot be overlooked. Fossil fuel-fired power plants are designed to generate power at maximum capacity all day long. However, with renewables on the grid, these conventional plants are required to operate in load-following mode. Because of the deviation of actual efficiency from the design value, there is monetary loss during power plant operation as fuel consumption increases and equipment is subjected to increased wear and tear. Energy storage enables such plants to run with greater efficiency, reduce some of their costs, and produce energy that will be used to generate electricity for eventual sale.

Reaching Beyond Batteries

The new FE program is seeking partners from industry, academia, and research organizations to develop affordable storage technologies beyond the scope of battery systems with limited storage capacity. These areas of research interest include:

    ■ Thermal Energy Storage. Some work has begun. NETL is currently supporting an Electric Power Research Institute project to design, construct, and test a pilot-scale concrete thermal energy storage system. As designed, high-pressure steam from a power plant would flow through tubes and heat concrete modules, which store the thermal energy until it is returned to the power plant to generate electricity. The project will test modules similar in size to those expected to be used in larger-scale commercial applications. A team at Lehigh University in Bethlehem, Pennsylvania, is also developing a thermal energy storage prototype with NETL support to improve plant flexibility and efficiency.
    ■ Mechanical Energy Storage. Compressed air energy storage is a prime example of mechanic energy storage. It uses off-peak electricity to compress air and store it in a pressurized storage reservoir. When electricity is needed at peak demand, the air is withdrawn to drive an electric generator. With this system, air can be preheated by recovering heat from the compressor train or by burning fuel such as natural gas to improve efficiency.
    ■ Chemical Energy Storage. This energy storage concept seeks to advance the use of fossil fuels in an environmentally responsible manner by generating hydrogen and other forms of chemical energy from coal or natural gas, which can be stored for long durations and used when needed to produce electricity and valuable products.
    ■ Hybrid Energy Storage. HES systems merge two or more energy storage technologies to achieve the desired performance by combining the appropriate features of different technologies.

Engaging Potential Partners

FE has taken a robust approach to solicit proposals and a broad range of concepts. Its FOA sought proposals to advance near-term, system-integrated, energy storage solutions toward commercial deployment with fossil assets; mature promising mid-technology-readiness-level (TRL), component-level energy storage solutions toward eventual system integration with fossil assets; and develop innovative, low-TRL concepts and technologies that offer game-changing benefits for fossil assets. Concept papers were received on June 17, 2020.

As part of this FOA, the formation of multidisciplinary teams that include technology developers and asset owners/operators was highly encouraged. To support this goal, a team partner list was included in the FOA, and interested entities could sign up to publicly share their interest in participating as team members on project applications.

Prior to issuing the FOA, FE sought input from those with experience, expertise, and interest in energy storage. These insights were gained by hosting webinars and workshops, and issuing an RFI to gather suggestions that could help utilities operate their plants at high efficiency while storing power until it is needed by the grid. Figure 1 summarizes the results of these efforts.

1. Selected technologies were proposed in response to a Department of Energy (DOE)-issued request for information and augmented with additional input accumulated through subsequent stakeholder engagements. The technology readiness level (TRL) scale ranges from 1 (basic principle observed) to 9 (total system used successfully in project operations). However, TRL is not an indication of the quality of technology implemented in designs.  Source: DOE

The insights, recommendations, and suggestions received were used to develop the FOA, which will award funding to proposals designed to mature and integrate energy storage technologies with fossil power plants to produce greener and abundant power for tomorrow.

NETL looks forward to working with partners who share its passion for energy storage and the important role it will play in achieving energy security for the nation. FE funds R&D projects to reduce the risk and cost of advanced fossil energy technologies and to further the sustainable use of the nation’s fossil resources. To learn more about FE programs, visit the FE website and sign up for related news announcements. More information about NETL is available on its website. ■

Briggs White, PhD is technology manager for High-Performance Materials, Water Management, and Energy Storage at the U.S. Department of Energy’s National Energy Technology Laboratory.