Solar Energy Even in the Dark

solar energy

A team of researchers from MIT have been working on a way to take some molecules and have them absorb solar energy which would be retrievable at any time of day or night. The energy retrieval would not be contingent upon the current sun conditions. Once the energy is stored in the molecules, regaining the energy would only require a small catalyst in the form of a bit of electricity, heat, or light. When the catalyst is applied, the end result would be the ability to have solar energy, even in the dark.

This can all be possible because scientists have discovered that by utilizing the photoswitching properties of a molecule, in this case azobenzene, and attaching them to nanotubes, they can effectively store and release the energy from the sun. The trial the engineers face is to pack enough azobenzene close together enough to make the output amounts usable. When running the initial trials, the engineers were not able to put the amount of molecules they wished onto the carbon nanotubes. They actually only managed to use less than 50 percent of the number for which they were aiming. They projected that given the amount of molecules they managed that they would see an energy density increase of approximately 30 percent. What actually happened was that they gained an energy density increase of about 200 percent, far more than they were expecting. The output was in close correlation to that of the energy density of Li-ion batteries. When the initial research was done, the models were only based on singular nanotubes but the actual experiment used multiple nanotubes which interacted in an unexpected manner.

In order to achieve the goal of obtaining solar energy no matter whether it is cloudy or even if it is dark outside, the key may lie in what is known as a photoswitch. This is a molecule, like the azobenzene used in the experiment, which has the ability to exist in more than one configuration. When a photoswitch absorbs the solar energy, it exists in a strained configuration which stores the energy until such time as another event triggers the release of that stored energy. When a trigger occurs, the molecule goes back into its beginning state while releasing the energy at the same time. The molecule can then again store more energy for another future release without degrading the molecule in any way. Theoretically, the molecule can continue this pattern an infinite number of times.

The MIT team of chemical engineers that has been conducting experiments on this has been doing studies for several years. They have concluded that a thermal battery would be possible by attaching the photoswitch molecule azobenzene to carbon nanotubes. Additionally, when more than one nanotube is used, the molecules interlocked with each other and the adjacent nanotubes. While this created the mass necessary to get a usable amount of energy the current method used to store and release thermal energy is inefficient. More research will be required in order to refine the ability of the molecules to give up the thermal energy but the first steps have been taken. The research already done indicates that the process could be used infinitely once the system is set up as the azobenzene molecules appear to be able to cycle through the energy storage and release process without breaking down. This process would provide solar energy to the end user regardless of the hour or exterior conditions and would even be usable to release the stored energy in the dark.

By Dee Mueller
on twitter @TuesdayDG

The Atlantic
The Christian Science Monitor

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