New molecule to vastly amplify solar energy potential

Not only is the sun the most abundant source of energy known to man, it is infinitely renewable, so long as it is still there. It continues to generate astonishing amounts of energy on a daily basis, rain or shine. Solar energy can be collected and stored in many different ways, and the use of solar energy does not emit greenhouse gases, which may help reduce the impact of climate change. Because of these reasons, solar energy is becoming more widely selected as the primary source for renewable energy. It is only a matter of time until humanity finds ways to more efficiently utilize solar energy – such as the innovation described below.

Manipulating sunlight

There are two main types of solar energy: photovoltaics (PV), and concentrated solar power (CSP), also known as solar thermal power. Photovoltaics convert sunlight directly into electricity using solar cells in solar panels. Concentrated solar power uses sunlight to heat a fluid which generates steam and powers a turbine to create energy. PV currently comprises 98% of global solar energy, with CSP as the remaining 2%.

PV and CSP vary in the way they are used, the energy that is produced, and the materials that are used in their construction. The efficiency of the energy that is produced with PV stays constant with the size of the solar panel, meaning that using a smaller over a larger solar panel will not increase the rate of energy production. This is because of the Balance-of-System (BOS) components that are also used in solar panels, which includes the hardware, combiner boxes, and inverters.

With CSP, bigger is better. As it uses the heat from the sun’s rays, the more sunlight that can be collected the better. This system is very similar to the fossil fuel power plants in use today. The major difference being that CSP uses mirrors that reflect the heat from sunlight to heat fluids (instead of burning coal or natural gas), which generate steam to turn turbines. This also makes CSP well suited for hybrid plants, such as combined cycle gas turbine (CCGT), which use solar energy and natural gas to turn turbines, generating energy. With CSP, the energy output from incoming solar energy yields only 16% net electricity. CCGT energy output yields ~55% net electricity, much more than CSP alone.

From humble beginnings

Anders Bo Skov and Mogens Brøndsted Nielsen from the University of Copenhagen are attempting to develop a molecule that is capable of harvesting, storing, and releasing solar energy more efficiently than PV or CSP. Using the dihydroazulene/vinyl hepta fulvene system, DHA/VHF for short, the pair have made great strides in their research. One problem they encountered initially was that as the storage capacity of the DHA/VHF molecules increased, the capacity to hold the energy over an extended period of time decreased. Mogens Brøndsted Nielsen, a professor from the Department of Chemistry, 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.”

Since the new molecule’s shape is more stable it can hold the energy for longer, but it also makes it easier to work with. There is a theoretical limit to how much energy a set unit of molecules can hold, this is called energy density. Theoretically 1 kilogram (2.2 pounds) of a so-called “perfect molecule” can store 1 megajoule of energy, meaning it can hold the maximum amount of energy and release it as necessary. This is approximately enough energy to heat 3 litres (0.8 gallons) of water from room temperature to boiling. The same amount of Skov’s molecules can heat 750 milliliters (3.2 quarts) from room temperature to boiling in 3 minutes, or 15 litres (4 gallons) in one hour. While the DHA/VHF molecules cannot store as much energy as a “perfect molecule” can, it is a significant amount.

The science behind the molecule

The DHA/VHF system is composed of two molecules, DHA, and VHF. The DHA molecule is responsible for storing the solar energy, and VHF releases it. They do this by changing shape when introduced to external stimuli, in this case sunlight and heat. When DHA is exposed to sunlight it stores the solar energy, by doing so the molecule changes its shape to the VHF form. Over time, VHF collects heat, once it has collected enough it reverts back to its DHA form and releases the solar energy.

At the end of the day

Anders Bo Skov is rather excited about the new molecule, and with good reason. Even though it can’t release energy quite yet, Skov says “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.” Not only is the molecule used in a process that releases little to no greenhouse gases during its use, when it eventually degrades it does so into an inert chemical that is naturally found in the environment.