Zinc redox flow batteries could be a “viable substitute” for simple cycle peaking power plants in the US, especially as the increase of solar penetration adds concerns over grid stability, according to a new whitepaper.
The study, by grid-scale energy consultancy Energy Strategies Group (ESG) pitted flow batteries made by Montana-headquartered ViZn Energy against combined cycle gas turbines in terms of their ability to act as simple cycle peaking power plants, more commonly known as peaker plants. Peaker plants run to meet demand when it is at its highest, or peak level. Flow batteries, on the other hand, use tanks of electrolytes to store energy, meaning that in theory they can be scaled up to provide longer-duration storage than is typically found in other types of battery, such as lithium-ion. Typically, ViZn’s flow batteries provide up to about four hours of storage.
According to Chet Lyons of ESG, who authored the paper, ViZn Energy’s batteries are “an economically attractive substitute for many simple cycle gas-fired combustion turbine peaking plants, especially when deployed on a distributed basis and owned and operated by the electric utility”.
Lyons said that the retirement of 25% of the coal-fired plants traditionally used to provide peaking capacity in the US will lead to a requirement for substitutes. The coal plants are likely to be retired due to the impact of low cost natural gas, mercury and air toxics standards from the Environment Protection Agency (EPA) and proposed carbon dioxide reduction measures.
At present, Lyons explained in the white paper, “simple cycle CTs are so successful and well accepted that Public Utility Commissions (PUCs) rarely question a utility’s choice of the venerable CT as a preferred peaker solution”. However, Lyons argues, “the power grid’s long love affair with gas-fired CTs is being challenged by advanced energy storage”.
A former coal-fired plant in New Jersey, now operating as a gas-fired peaker plant. Image: wikimedia/jim.Henderson
As times and technologies change, Lyons says, distributed energy storage could be located at utility substations, owned, aggregated and controlled by utility companies. The use of the same storage asset to provide energy balancing services on two levels, transmission and distribution, “the locational value and capacity utilisation of storage can be much higher compared to combustion turbines interconnected at transmission voltage and operated as a central station resource”.
Storage could be especially useful – and suitable for monetisation – if located on distribution grids where PV penetration levels are high. In addition, Lyons argues that storage could provide maximum benefit in allowing deferment of distribution infrastructure upgrades. In a recent real-world example, utility ConEdison announced that it was seeking to prevent the need to invest US$1 billion in upgrades to one substation in New York State using measures that are expected to include storage.
Lyons echoed the sentiments of other recent commentators in saying that comparable to solar, storage is at the beginning of a stage of “disruptive decline in cost” over the next three to five years. Solar PV combined with storage is likely to replace conventional centralised generation, transmission and distribution assets on a large scale, while turning the centralised power grid model “inside out”. This predicted turnaround for the electricity industry, Lyons said, has already lead to a number of US utilities investing heavily in solar, while Arizona’s Public Utilities’ Commission is already looking at replacing 10% of the state’s simple cycle gas peaking plants with storage.
The white paper asserts that by 2018, ViZn’s flow batteries could cost essentially the same in terms of installed kilowatt-hours as the gas plants.
“By 2018 the CapEx of ViZn Energy’s four-hour flow battery storage solution, which ESG uses as a proxy for the lowest cost flow battery technologies now being commercialised, is projected to be US$974 per kW, or US$244 per (installed) kWh, essentially the same as a conventional simple cycle CT. Storage will be a disruptive winner against simple cycle gas-fired CTs at that point, assuming a typical mid-range cost for competing fossil-based CT generation resources,” Lyons said.