The ability of substances to store energy from the sun has long been understood but has not been viable as a practical storage medium, so finding one that was viable would be quite valuable. The Sun pours so much energy onto the earth, that if all that fell in an hour could be captured it could supply the energy needs of the world for a year. So, the ability to capture and store in volume was of significant importance to the solar energy industry, because excess capacity on the brightest of days could be stored for use on the dull and wet.
At the “Center for Exploitation of Solar Energy” at University of Copenhagen, led by Professor Brøndsted, chemistry Master’s student Anders Bo Skov has published a paper co-authored by his supervisor, Professor Brøndsted, titled ”Towards Solar Energy Storage in the Photochromic Dihydroazulene-Vinylheptafulvene System”.
Professor Brøndsted’s team’s focus has been on developing molecules capable of capturing substantial amounts of solar energy, storing it for long periods of time, then releasing it when required. The compound used in the study stored its energy by changing the shape of the molecule, and then released that energy by reverting to its original shape, but, there seemed to be a chemical law that prevented any long term storage. This apparent block to the research seemed to be a law that said the greater the capacity of the molecules to store the energy, the less the time period it was able to be stored for. Conversely, if the storage period was increased the energy holding capacity decreased.
Anders’ brought his Bachelors project to the Center and was developing it further for his Masters degree when he made his breakthrough by doubling the amount of energy capable of being stored over long periods of time. Storage periods have moved from a few hours to up to around a hundred years, however, the next challenge is how to release the energy when needed.
As Mogens Brøndsted said; “Regardless of what we did to prevent it, the molecules would change their shape back and release the stored energy after just an hour or two. Anders’ achievement was that he managed to double the energy density in a molecule that can hold its shape for a hundred years. Our only problem now is how we get it to release the energy again. The molecule does not seem to want to change its shape back again“.
The compound that is being used is very environmentally friendly and produces no toxic waste either during the use or on its disposal, as Anders explains; “When it comes to storing solar power, our biggest competition comes from lithium ion batteries, and lithium is a poisonous metal. My molecule releases neither CO2, nor any other chemical compounds while working. It is “Sunlight in-power out”. And when the molecule wears out one day, it degrades to a colorant which is also found in chamomile flowers”.
Since the energy is released in the form of heat this can be used as pure heat energy, or by boiling water or a refrigerant could be converted to electricity. This breakthrough could have significant impact on the supply of energy to remote areas where the need is not when the sun is shining but when it is not. The ability to store usable amounts of solar energy and release it at night or other times when capacity is minimal will bring energy stability to many areas of the world.
Department of Chemistry, University of Copenhagen