USF Sows the SEEDS of Renewable Energy Storage

Electricity storage is fast becoming the holy grail of sustainable energy. The performance of solar panels is intermittent, with panels functioning optimally on sunny days, marginally when it is overcast, and not at all when it is dark. Similarly, wind turbines produce electricity only when the wind blows above a certain speed. Even conventional sources of electricity, such as nuclear or coal-fired plants, operate less efficiently during hours of peak consumption. Current technology provides no large-scale means of capturing and storing excess energy that is not being consumed, but researchers at the University of South Florida, St. Petersburg, believe they have come one step closer to a solution.

A public-private partnership with the city of St. Petersburg, Progress Energy Florida, USF-St. Petersburg, and the Florida High-Tech Corridor Council has sponsored a demonstration-scale project of the Sustainable Electric Energy Delivery System (SEEDS) on the USF campus. Another SEEDS project, developed by the same partnership, exists in nearby Albert Whitted Park.

Each SEEDS project consists of an array of photovoltaic panels, an advanced energy storage system, and monitoring controls. During the day, the panels capture sunlight and convert it to electricity, which charges two vanadium redox battery systems, or VRBs, each with a capacity of 5 kilowatts x 4 hours. This means that, when fully charged, each VRB can discharge 5 kilowatts of energy every hour for up to 4 hours.

credit: University of South Florida

Peter Lilienthal, Senior Economist of International Programs at the National Renewable Energy Laboratory, seems enthusiastic about VRB technology. He noted that one appealing characteristic of the VRB is its ability to be charged and discharged repeatedly without losing its power. “The Achilles heel of most batteries,” he said, “is that there are only so many kilowatt-hours you can cycle through. Every time you use the batteries, you’re wearing them out. With vanadium, however, you can use it as hard as you want. When you do, you’re not reducing the life of the battery.”

Also of note is vanadium’s relatively benign nature when compared to elements such as lead and cadmium, elemental metals that are used in other battery systems and are known to have toxic effects on both humans and wildlife. Because the vanadium electrolyte solution has an indefinite lifespan, there is less concern over disposal or contamination than with other battery systems. (Note: Theoretically, the vanadium solution never has to be replaced–only the membrane separating the two tanks would, every 10 to 12 years. All new technology has the potential for nasty surprises down the road, but the fact that this solution may be reused indefinitely, and can simultaneously charge and discharge, sets it apart from other systems. –Ed.)

Mr. Arif Islam, Assistant Director of the Power Center for Utility Explorations at USF – St. Pete, said that this is the first time that such a technology has been demonstrated. “The two sites are extended laboratories for students and researchers at PCUE,” he said, noting the educational value of the project.

The SEEDS are also connected to the community power grid. If the photovoltaic panels do not fully charge the vanadium storage system—such as may occur on an overcast day—the system receives off-peak electricity from the grid, which can then be released during times of peak energy consumption. Energy from the photovoltaic panels will feed directly into the grid if the storage system is fully charged.

Currently, the SEEDS solar panels can generate about 5.5 megawatt-hours of energy per year, which offsets approximately 3.5 metric tons of CO2. This amount is eclipsed by the campus’s annual electricity consumption of nearly 17 gigawatt-hours, or 17,000 megawatt-hours, which cost the university 1.5 million dollars in the last fiscal year and resulted in the release of 10,500 metric tons of CO­­2.

Dr. Christopher D’Elia, professor of Environmental Science and Policy and associate Vice Chancellor of Academic Affairs at USF-St.Pete, hopes that the SEEDS project, once taken to a larger scale, will yield appreciable economic savings in addition to the environmental benefits. “We’re looking for solutions, and our budgets are extremely tight, and anything we can do to reduce power costs would be very, very helpful,” he said. At the moment, however, the project is in a small-scale, demonstration phase and should not yet be viewed as a solution to the campus’s energy needs.

Mr. Islam would like to see the SEEDS technology eventually reproduced on a larger scale and become an integral part of a smart grid system. As opposed to today’s energy grids, which usually consist of single-source energy producers and multiple-source consumers, a smart grid is decentralized, consisting of diverse energy producers (such as utility-scale wind farms and residential solar systems) that feed electricity into a grid system capable of storing power and delivering it during times of peak usage.

“We would like to scale [the SEEDS] up in megawatts to make it an adaptable technology for our industry partner and to make it more beneficial to the community,” Mr. Islam said, referring to Progress Energy, which supplies electricity to the city of St. Petersburg and USF itself.

For now, however, researchers at USF-St. Pete are pleased with the small step their campus is making to reduce its carbon footprint, and its value to students and other researchers.

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