Solar Cell gets Married with Redox Battery to Provide Nightly Power
Solar cells are now becoming more efficient and more abundant, thus producing more and more solar energy. It is hoped that solar power will become a significant contributor to grid power. However solar power produced beyond daytime need is useless if we cannot store it for nighttime use. In fact, it is said that further solar installations may have to be halted in certain regions if better storage devices do not become available.
Where efforts are on to improve the performance of photovoltaic converters, serious efforts have also been going on for producing inexpensive large scale batteries. As performance of solar cells improves the quest for better storage is picking pace. But this has been a rather tough knot until now. Lead acid batteries have been the workhorse of charge storage, but not good enough. Lithium ion batteries are more costly per watt-hour. And the interface circuitry also causes complexity and losses.
Now a new scheme with multiple advantages over the conventional ‘panel-controller-battery’ has been proposed. It has come not from electrical engineers, but from a professor of chemistry, Song Jin, at the University of Wisconsin-Madison. His idea: integrate the solar cell with Redox Battery ( a large-capacity battery). He, along with his colleagues including those at King Abdullah University of Science and Technology in Saudi Arabia has actually demonstrated an integrated single device that incorporates the cell and the storage eliminating the usual intermediate step of making electricity and charging.
In their device, the cell is mounted onto the reaction chamber, and directly charges the electrolyte of the Redox Flow Battery (RFB). The RFB stores chemical energy in liquid electrolyte.
A special feature is that the charged electrolyte is pumped out continuously to be stored in a large reservoir. The reservoir can be as large as you want it. When you want to use the stored energy at night simply pass the charged electrolyte through the device. It is relatively cheap and can be scaled up for as much storage as you need. Redox batteries have been on the market, and already been used to store solar energy. But Professor Jin has simply married the two to make a single integrated device, improving efficiency, storage capacity, and cost.
Charging and discharging can be repeated for many cycles without any significant loss of efficiency.
A word of caution: There is many a slip between the cup and the lip. The team is trying to remove certain snags like finding an electrolyte with ionizing potential better matching the cell voltage for better efficiency.
Wenjie Li, Hui-Chun Fu, Linsen Li, Miguel Cabán-Acevedo, Jr-Hau He, Song Jin. Integrated Photoelectrochemical Solar Energy Conversion and Organic Redox Flow Battery Devices. Angewandte Chemie International Edition, 2016; DOI: 10.1002/anie.201606986