Professor to Create an All-day Solar Cell

09/05/2018
By Edwin L. Aguirre

Solar energy is the cleanest, safest and most abundant renewable source of energy available. And solar cells, also called photovoltaic (PV) cells, can convert this free and unlimited radiant energy from the sun directly into electricity to power our lights, electronics and household appliances.

But how do you harness solar energy at night or when it’s cloudy? The most common solution is to store the electricity generated by the solar cells in rechargeable batteries for later use.

Mechanical engineering Assoc. Prof. Fuqiang Liu thinks he can make solar energy more attractive to homeowners and businesses by simplifying the energy generation/storage process, improving its efficiency and reducing cost. His solution? An all-day solar cell that generates and stores electricity simultaneously during the day. This allows it to power lights for up to five hours at night, without the need for an external storage battery.

“Our portable, compact all-day solar cell relies on a dual-function electrode that generates and stores electricity at the same time,” says Liu. “This eliminates the need for expensive rechargeable batteries used in conventional PV systems, which steeply increase the dollar-per-watt price of the electricity produced. Our proposed solution will significantly reduce both the capital and operating costs as well as improve the system’s safety and reliability.”

To provide electricity under darkness for longer than five hours, more materials (i.e., larger PV panels) can be used with the solar cell, he says.

Because of the cell’s unique electron-storage mechanism, the electrons’ storage (charge) and release (discharge) can be automatically triggered by ambient light condition.

“Under darkness or low-intensity light conditions, discharge occurs automatically without the need for smart switches or controllers, as one sees in conventional PV systems,” notes Liu. “This maintenance-free feature of the all-day solar cell would be useful in the electrification of remote rural areas.”

Liu anticipates a 50 percent reduction in cost compared to traditional PV systems. For example, for a 5-kilowatt solar system, he estimates that a homeowner will save more than $9,000 in installation with the all-day solar cell system compared to a traditional PV system. If successful, he plans to collaborate with public agencies and private industry to expand and scale up the capability of the technology and bring it to market.

Liu’s work is funded with a five-year, $416,000 “CAREER” grant from the National Science Foundation (NSF). This highly competitive annual program recognizes the nation’s best young university faculty-scholars “who most effectively integrate research and education within the context of the mission of their organization.”

Liu also received a one-year, $50,000 grant from the NSF to explore the commercial potential of his new solar cell.

In 2017, the Massachusetts Clean Energy Center awarded Liu $65,000 through its Catalyst Program, which enables early-stage researchers to develop promising products and technologies in the fields of clean energy and clean water, and help bring them to the marketplace.

“Our efforts to reduce Massachusetts’ greenhouse gas emissions are reliant upon the technology advancements and hard work of our entrepreneurs,” says state Energy and Environmental Affairs Secretary Matthew Beaton. “This funding provides crucial resources to young companies and promising ideas, supporting clean-tech innovation and job creation in the commonwealth.”

Round-the-Clock Energy

Liu calls his all-day solar cell an “all-vanadium photo-electrochemical storage cell.”

“Unlike conventional rechargeable batteries, which convert solar energy first into electricity and then stores this electricity into chemical energy for later use, our all-vanadium photo-electrochemical storage cell stores solar energy directly in the form of chemical energy, increasing its efficiency and capacity,” he says. “At night, the stored energy is converted to electricity using a flow battery.”

Liu’s findings have been published in peer-reviewed publications, including ACS Catalysis, Scientific Reports, Electrochimica Acta, Journal of Materials Chemistry A, Journal of Power Sources, Materials Research Bulletin, Nano Energy and Electrochemistry Communications.

Assisting him with the lab research are postdoctoral associate Zi Wei and Ph.D. students Husain Almakrami and Guanzhou Lin. Liu is also collaborating with UMass Lowell mechanical engineering Asst. Prof. Ertan Agar as well as Prof. Krishnan Rajeshwar of the University of Texas at Arlington.

“As renewable energy sources become more prevalent, the ability to store solar energy can provide a sustainable solution to the world’s growing energy shortage. Our research, if successful, can effectively change the way we utilize the inexhaustible energy from the sun,” says Liu.