Storage of sun´s heat by using modified carbon nanotubes

Broadly speaking, there have been two approaches to capturing the sun´s energy: photovoltaics, which turn the sunlight into electricity, or solar-thermal systems, which concentrate the sun´s heat and use it to boil water to turn a turbine, or use the heat directly for hot water or home heating. But there is another approach whose potential was seen decades ago, but which was sidelined because nobody found a way to harness it in a practical and economical way. This is the thermochemical approach, in which solar energy is captured in the configuration of certain molecules which can then release the energy on demand to produce usable heat. And unlike conventional solar-thermal systems, which require very effective insulation and even then gradually let the heat leak away, the heat-storing chemicals can remain stable for years. A novel application of carbon nanotubes shows promise as an innovative approach to storing solar energy for use whenever it´s needed. Storing the sun´s heat in chemical form rather than converting it to electricity or storing the heat itself in a heavily insulated container has significant advantages, since in principle the chemical material can be stored for long periods of time without losing any of its stored energy. The problem with that approach has been that until now the chemicals needed to perform this conversion and storage either degraded within a few cycles, or included the element ruthenium, which is rare and expensive. Thus the molecule called fulvalene diruthenium known as the best chemical for reversibly storing solar energy, since it did not degrade was able to accomplish this feat. By better understanding this process could make it easier to search for other compounds, made of abundant and inexpensive materials, which could be used in the same way. The new material is made using carbon nanotubes, tiny tubular structures of pure carbon, in combination with a compound called azobenzene. The resulting molecules, produced using nanoscale templates to shape and constrain their physical structure, gain "new properties that aren´t available" in the separate materials. Not only is this new chemical system less expensive than the earlier rutheniumcontaining compound, but it also is vastly more efficient at storing energy in a given amount of space about 10,000 times higher in volumetric energy density and also making its energy density comparable to lithium-ion batteries. By using nanofabrication methods, you can control the molecules interactions, increasing the amount of energy they can store and the length of time for which they can store it and most importantly, you can control both independently. Thermochemical storage of solar energy uses a molecule whose structure changes when exposed to sunlight, and can remain stable in that form indefinitely. Then, when nudged by a stimulus - a catalyst, a small temperature change, a flash of light - it can quickly snap back to its other form, releasing its stored energy in a burst of heat. So that we could create a rechargeable heat battery with a long shelf life, like a conventional battery. One of the great advantages of the new approach to harnessing solar energy is that it simplifies the process by combining energy harvesting and storage into a single step. You´ve got a material that both converts and stores energy. "It´s robust, it doesn´t degrade, and it´s cheap." One limitation, however, is that while this process is useful for heating applications, to produce electricity would require another conversion step, using thermoelectric devices or producing steam to run a generator. Compared to other approaches to solar energy, it has many of the advantages of solar-thermal energy, but stores the heat in the form of a fuel. It´s reversible, and it´s stable over a long term. You can use it where you want, on demand. You could put the fuel in the sun, charge it up, then use the heat, and place the same fuel back in the sun to recharge.