Chemically Storing Solar Energy Indefinitely

Solar power is a method of energy generation that is gaining more and more use because it draws power from the sun, a source of seemingly unlimited energy. Converting the sun’s rays into usable energy is very appealing to those interested in renewability and sustainability. A barrier preventing solar power from seeing more use is the immediacy with which its energy must be used; the energy generated by solar panels must be converted directly into electricity. There are a few means of storing and transporting energy produced from solar panels but they are somewhat crude. One such method is to use the energy to charge batteries. These batteries can be transported and used in other areas. However, battery energy dissipates over time, making it unreliable for long-term storage of energy.  

Azobenzene-functionalized carbon nanotube structureScientists have been looking into thermo-chemical storage as a more viable means of storing solar power energy. The goal behind thermo-chemical storage is creating a low-energy molecule that will change conformity and achieve a stable higher-energy state when exposed to the energy of. Upon being exposed to a catalyst such as a change in temperature, the molecule will revert to its old low-energy form, releasing all the energy it had stored. Once the molecule has returned to its low-energy state, the entire process can be repeated once again. In addition to being cheap and robust, this method would also combine energy harvesting and storage into one step. A slight limitation is that taking the heat generated from releasing energy in the molecules and converting it into electricity would require an additional step.  

The difficulty in making this reality was in finding a chemical compound that didn’t degrade or wasn’t too expensive. Chemicals that have been previous candidates for thermo-chemical storage either degraded over a few storage cycles or utilized the rare and expensive element ruthenium. Researchers at MIT got close when they discovered fulvalene diruthenium last year. It worked very well as a storage medium and held energy indefinitely, but required needed ruthenium. The same researchers may have gotten it right earlier this year by using nanotechnology and nanofabrication techniques to synthesize a chemical cheaper and more efficient than fulvalene diruthenium; azobenzene-functionalized carbon nanotubes. Carbon nanotubes have been seeing lots of use in science, especially nanotechnology, recently because of their versatility in fabrication of new materials. In this case, nanofabrication methods have modified the molecular interactions of the carbon nanotubes in a way that allows this material to have 10,000 times higher volumetric energy density than fulvalene diruthenium, meaning that it can hold much more energy in a given amount of space.

If azobenzene-functionalized carbon nanotubes work as well as reported, it will be very exciting for the solar power industry. A material that can efficiently store large amounts of solar energy indefinitely greatly eliminate the storage weakness of solar power. Extra power stored during the day could power houses at night while large solar power plants could reliably store generated power and transport it to nearby cities without losing any energy during transportation time. The MIT research was recently published in the journal Nano Letters and can be found here.

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