Research teams from the Ocean University of China and Yunnan Normal University developed a solar cell that is capable of generating electricity from both sunlight and rainfall. The solar cell prototypes are similar to conventional dye-sensitized solar cells but comprise an additional highly conductive graphene-oxide layer. Electrons flow freely in the graphene-enriched electrode and interact with the salt ions—such as sodium, calcium, and ammonium—present in rainwater, forming a pseudocapacitor. This solar cell is therefore capable of harvesting electricity from rainwater and from solar energy.

According to Qunwei Tang, materials scientist at Ocean University, "We would like to develop a solar cell that can be triggered by sun and rain.... Future solar cells may produce electricity in all weather." However, the researchers' laboratory tests revealed that the current energy-harvesting efficiency of the new solar-cell prototype is only 6.5%, in comparison with 22.5% for conventional photovoltaic cells.

Implications

Solar cells are becoming increasingly more efficient and affordable. Since 2008, demand for solar cells has been increasing, with the cost of producing photovoltaic cells on the industrial scale falling by 60% in 2015. One obvious primary drawback of conventional solar cells is that they require solar rays to produce electricity and generate only negligible levels of power during overcast days and overnight. Rainwater is particularly beneficial to solar cells by removing dirt from their surfaces. The rain also reduces the amount of sunlight reaching the photovoltaic cells, which would typically reduce the efficiency of the cells.

The researchers' new solar-cell technology could increase the energy input of the solar cell by adding an additional renewable-energy source in the form of rainfall. In addition, it could provide governments and private citizens—in particular, in countries with limited sunlight—incentive to increase their investments in solar-cell technologies. However, incorporating additional functionalities into the solar cells will result in higher production costs at the outset, which is not useful for an industry striving to compete with low-cost fossil fuels.

Impacts/Disruptions

The renewable-energy industry relies heavily on innovative research and design of materials to increase the productivity of energy-harvesting technologies. In particular, nanomaterials with oxide and hydroxide structures play a key role in pseudocapacitor applications for energy storage.

Energy harvesting has the potential to be a major market for smart materials such as piezoelectric materials that generate energy from the impact of rainwater—which could compete or combine with this solar-cell technology. However, at least ten years will most likely pass before these technologies are capable of reaching the high efficiency and low manufacturing costs necessary for their successful commercial release.