Perovskite solar cell combines with flow battery for integrated power system
Researchers in the US have combined a solar cell and a flow battery to create an integrated power system.
The team at the University of Wisconsin–Madison developed a low cost halide perovskite tandem solar cell as the source of the energy. These are shwong efficiencies of 24 to 27 percent by usng a perovskite layer on top of a standard silicon solar cell. The energy from this tandem cell was then stored in a flow battery developed with two organic chemicals optimised for the cell voltage. This produced an overall energy efficiency of 20.1 percent from source to output.
“Our motivation for the design of the solar cell was to combine these two materials together so we have both high efficiency and good stability,” said Wenjie Li, one of the researchers.
Professor Anita Ho-Baillie and postdoctoral researcher Jianghui Zheng in Australia fabricated the perovskite-silicon solar cells with an additional protection layer on the silicon surface. They shipped the solar cells to Wisconsin for testing.
To predict the ideal voltage that the flow batteries should run at, Li developed a new theoretical modelling method. This allowed the selection of a pair of chemicals in the flow based on the characteristics of the solar cell, maximizing efficiency. The chemicals are organic compounds rather than metals such as vanadium or zinc as in traditional flow batteries, and are dissolved in a solution of salt rather than strong acids.
Utah State University chemistry professor T. Leo Liu and his graduate students provided the key matching chemicals, a BTMAP-Vi/NMe-TEMPO redox combination.
This combination maintained the high efficiency over hundreds of hours and hundreds of charge-discharge cycles while retaining most of the capacity of the integrated power system. That lifespan was several times longer than earlier devices developed in the same lab. This is key as the stability of aqeuous organic salts over time in flow batteries is a key concern. However this can be easily overcome by topping up the battery cells as the materials are low cost and non-toxic.
“That’s 20 percent efficiency any time you like,” said Prof Song Jin who runs the laboratory. “You can use the solar electricity right away during the day and get 20 percent, or you can use it in the evening from storage and get 20 percent.”
Increasing the size and scale of the current small integrated power system in the research lab is one challenge. And even though the researchers created a relatively long-lasting battery, real-world applications demand still greater robustness. The Jin lab is continuing to develop even more efficient solar flow batteries while also experimenting with practical trade-offs to reduce the cost of the devices.
“Our eventual goal, if we can make this practical, is to target solar home systems,” said Li. “People who don’t have electrical grid access could use this device to have reliable electricity.”
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