Coal

Pumping Up Might Offer New DG Approach

Issue 9 and Volume 109.

Pumped storage is hardly a new idea. About 18,000 MW of hydro pumped storage is installed in the United States, whereby water is pumped uphill during off-peak periods and allowed to return downstream on-peak to generate power. A very small amount of compressed air storage also exists, by which air is pumped into underground formations off-peak and released on-peak to produce power. But a former power industry executive has come up with a new approach to pumped energy storage.

As former head of RJM Corp.’s Combustion and Environmental Division and, prior to that, president and CEO of DB Riley Consolidated, John Halloran has spent much of his professional career developing emission control technologies for coal-fired power plants. Now, Halloran has come up with a concept that could allow pumped storage to be introduced into urban and suburban electricity markets in a unique manner, by way of small-scale units that fit with the distributed generation approach. He believes the concept would allow sustained growth in those markets without the need for new, large central station generating plants. Presumably, it would also delay the need for upgrading wires in the local area.

Instead of the fluid head created by a large water reservoir above a turbine/pump prime mover, his concept – Potential Energy Storage System (PESS) – would use the weight of a commercial structure exerting force on hydraulic fluid. The support steel of the structure would be designed so that the support columns would be vertically movable by hydraulic cylinders working from a common fluid header system. A reversible pump/turbine driven by an engine/generator using off-peak power (during night hours) would provide the fluid pressure required to lift the structure as much as 10 feet from its “at rest” elevation. The weight of the structure would then provide the pressure head at the turbine inlet to generate power on demand during the daylight hours, gradually decreasing its elevation by approximately 1 ft/hour.

“Although specially designed vertical guides for the building columns will be incorporated into the structure and external vertical support guides are provided at the corners of the structure, a controlled, very small horizontal relative movement between the building and its foundation can be accommodated,” says Halloran (see figure). He explains that this feature provides an advantage in earthquake-prone zones. “All system equipment, as well as the hydraulic fluid reservoir, is mounted on the basement floor of the building and thus would not change elevation during the pumping or generation cycles.”

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Halloran believes the concept could lessen the need for new, central generation plants; reduce the need for upgraded transmission infrastructure and associated permitting; increase capacity factor for existing generation assets; and provide reliable, uninterruptible, predictable-cost power for the PESS user/owner. He also notes such facilities would be zero-discharge DG units that would be available at the load demand sites, providing higher relative percentages of green power for use during peak demand hours.

The first systems would likely be in the 250 to 500 kW size range, with the generated power sold in the cogeneration mode or utilized to supply the internal electricity demand of the structure itself. “Depending on the structure’s footprint, it would probably not exceed four to six floors in height in order to eliminate any potential problems related to vertical stability,” he says.

The PESS concept received a patent in March. Halloran is now in the process of considering alternative approaches leading to the first commercial installation of a PESS. A pilot-scale test model design is being prepared in conjunction with a major test laboratory for use as a “proof-of-concept” demonstration if required prior to inclusion into an actual construction project. He is also seeking public sector development funding and is also interested in potential sponsorship by hydraulic system suppliers, generating companies, architect/designers and commercial project developers/owners.

“There’s no rocket science needed here,” says Halloran. “PESS technology can be commercialized in a relatively short time span. What is needed is a new heavy structure construction project into which the system can be installed and demonstrated.” He notes that a municipal parking garage would be one of the most ideal structures, because it would have much less weight at night, when the structure was being elevated, and be much heavier during the day, as the structure descends and produces power.