By all outward appearances, the transmission grid and distribution network have not changed much over the last 100 years. The conductor is still strung from structure to structure and pole to pole, but these are only surface characteristics and looks can be deceiving. Look a little deeper, and it is easy to see the transformation taking place: Renewable generation is becoming more economical than fossil-fuel-based generation. Customers are now prosumers, capable of producing megawatts of power from their side of the meter, which has turned the grid into a bidirectional power pipeline. Distributed energy resources have started the decentralization process that has been talked about for years.
The edge of the grid is being redefined with power generated where it is consumed. Microgrids are changing the dynamics of grid resiliency. However, the real game-changer has been the addition of energy storage to the grid. The technology is being deployed throughout the delivery system to balance power fluctuations, manage peak demand, make wind and solar dispatchable, and reduce carbon emissions. It is a different grid than ever before, and energy storage is only a small part of the transformation.
Fuel Cells and Flow Batteries
Li-ion batteries are the workhorse technology in today’s energy storage systems, but another energy storage player is making waves: the reduction-oxidation (redox) flow battery. Simply stated, the redox flow battery is a regenerative fuel cell. The electrolyte is stored in external tanks and flows through a membrane. An ion exchange takes place at the membrane, which causes electric current to flow.
Multiple types of flow batteries are available, but vanadium, iron, bromine and sodium are the most popular commercial batteries right now. The technology is ideal for utility-scale batteries, because the available power is determined by the size of the electrochemical cell and the energy is proportional to the size of the electrolyte storage tanks. Flow batteries have a long cycle life and provide fast response times. One of the most positive features of the flow battery is they do not wear out.
VRB Energy announced the first phase of China’s Hubei Zaoyang storage integration demonstration project was commissioned in January 2019. This phase is a 3-MW/12-MWh vanadium redox flow battery storage system, which will have an overall rating of 40 MWh. VRB said the pilot project is being used to demonstrate the use of flow battery storage systems. In addition, a 200-MW/800-MWh vanadium energy storage project is underway in Dalian, China. It is being manufactured by Rongke Power Co. Ltd. and UniEnergy Technologies (UET).
Modular energy storage systems such as this 24.5 MW PowerStore were designed to allow storage to be integrated into the grid where needed.
San Diego Gas & Electric Co. (SDG&E) announced the Bonita vanadium redox flow battery storage pilot project in coordination with Sumitomo Electric Industries Ltd. The 2-MW/8-MWh flow battery pilot project is slated to run for four years. SDG&E plans to test the vanadium redox battery for providing voltage frequency, power outage support and shifting energy demand.
Another 2-MW/8-MWh vanadium flow battery was installed on Snohomish County Public Utility District’s network. UET built and installed the battery as well as its control system in 20 connected shipping containers using a molecular breakthrough developed by the Pacific Northwest National Laboratory (PNNL). PNNL found adding hydrochloric acid to the electrolyte solution almost doubled the energy storage capacity and increased its operational temperature range, which reduced the need to maintain temperature control.
Flow batteries also found their way into microgrids, which makes sense because today’s microgrids need longer-duration energy storage. CMI Group announced it had installed an industrial microgrid that integrates a 4.2-MWh energy storage system containing a Li-ion battery and two flow batteries with a 2-MW rooftop photovoltaic system in Seraing, Belgium. BYD Co. Ltd. supplied the Li-ion battery, VIZn Energy Systems supplied a 0.4-MW/1.2-MWh flow battery and Sumitomo supplied a 0.5-MW/1.75-MWh flow battery. Keep watching the flow battery technology. Their prices are coming down, and they typically have a 6-hr to 10-hr capacity compared to a typical Li-ion battery’s 2-hr to 4-hr capacity.
Energy Storage 2.0
Energy storage technology has become critical to the evolution of the grid as the electric utility industry transitions into the 21st century power delivery system. When more renewable resources are added, energy storage is necessary to balance the supply and demand. With the decentralization of the power supply, energy storage improves distributed generation systems. Making the grid more resilient to outside forces requires energy storage to prevent blackouts and reduce outages, but — as more grid applications are explored — there are many expectations about the next big push. Two topics gaining interest are long-duration storage and energy storage as a service (ESaaS).
With all the emphasis on taming wind and solar generation, long-term energy storage is natural. Studies have shown Li-ion battery projects with durations longer than four hours are pushing the technology. Longer-duration technology is available, and the DOE is funding research projects with storage capacities up to 100 days.
Another trend emerging is providing ESaaS, which makes perfect sense with the costs associated with energy storage. In the U.K., Solo Energy Ltd. launched a range of home energy services, including ESaaS. Aggreko has started an ESaaS group to rent energy storage systems with two-year to four-year rental contracts. According to the company, its ESaaS is available globally.
In the utility realm, Green Mountain Power is offering customers a Tesla Powerwall for a small monthly fee. It is reasonable to expect others will follow Green Mountain’s lead.
There is a great deal of speculation as to what energy storage technology will look like in the next five to 10 years. Given what has happened in the past two years to three years, it is impossible to predict, but one thing is for sure: Energy storage 2.0 will be exciting.