“Zombie” Solar Energy Storage System From 1980s Revived By Science

It’s been a long time coming, but vintage solar energy storage research dating back to the 1980s (and beyond) is finally bearing fruit. In the latest development, scientists at the University of Houston in Texas have demonstrated proof of life for a hybrid device that collects and stores sunlight in the form of heat for 24/7 use. Nope, it’s not a concentrating solar system and it doesn’t rely on molten salt or specialized oils. It involves norbornadiene-quadricyclane, something fairly new on the CleanTechnica radar.

This hybrid solar thermal energy storage device “consists of a molecular storage material (MSM) and a localized phase-change material (L-PCM), separated by a silica aerogel to maintain the necessary temperature difference.” (via University of Houston)

Energy Storage With Norbornadiene-Quadricyclane

Norbornadiene-quadricyclane has been studied for solar energy storage since at least 1983, when the American Chemical Society published a paper aptly titled, “Norbornadiene-quadricyclane system in the photochemical conversion and storage of solar energy” in the journal Industrial & Engineering Chemistry Process Design and Development.

The research toddled along slowly until a veritable volcano of new papers erupted in recent years. A 2016 study by a team of researchers in Sweden nails down the reason for the fresh burst of activity (emphasis added):

“Molecular photoswitches that are capable of storing solar energy, so-called molecular solar thermal storage systems, are interesting candidates for future renewable energy applications. In this context, substituted norbornadiene-quadricyclane systems have received renewed interest due to recent advances in their synthesis.“

Wait, What Is Norbornadiene-Quadricyclane?

Got all that? Compared to the olden days, nowadays a norbornadiene-quadricyclane system can be tailored more precisely for peak performance.

As for what norbornadiene-quadricyclane is, that’s the easy part. It’s a compound of two hydrocarbons (aka organic molecules), norbornadiene and quadricyclane.

And now for the super interesting part. Remember back in high school when isomers were a thing? In chemistry, isomers are two or more chemical compounds that have the same kind and number of atoms. The atoms are configured differently in each isomer, meaning that each isomer has different properties.

Using solar energy in the form of heat to “flip” one isomer to another is the heart of a norbornadiene-quadricyclane energy storage system.

Sunlight creates a reaction in norbornadiene, transforming it into quadricyclane. The switch from one to the other is also a switch from low energy state to a high energy state, which is where the energy storage angle comes in.

Solar Energy Storage Breakthrough, Texas Edition

The potential for high energy density in a norbornadiene-quadricyclane storage system is coming to light, which explains all the interest from renewable energy researchers.

That finally brings us to the University of Houston in Texas. Last fall a team of scientists at the school cooked up a new norbornadiene-quadricyclane solar energy storage device that solves a number of problems that have been blocking the way to commercial development.

By combining solar energy harvesting with energy storage in a single hybrid system, the new device avoids losses that occurs when energy is transferred from a collection device to a storage platform.

The result is a high-density system that can can convert solar energy for immediate use and store the excess, as the researchers describe in the journal Joule:

“Here, we combine the physics of molecular energy and latent heat storage to introduce an integrated, simultaneous harvesting and storage hybrid paradigm for potential 24/7 energy delivery. The hybrid paradigm utilizes heat localization during the day to provide a harvesting efficiency of 73% at small scale and ∼90% at large scale.”

That’s just for starters. The team also writes that “remarkably, at night, the stored energy by the hybrid system is recovered with an efficiency of 80% and at a higher temperature than that of the day, in contrast to all of the state-of-the-art systems.”

If that sounds a little on the high side, consider that conventional solar cells only capture part of the light spectrum. In contrast, the new system can collect the entire spectrum.

So, what are the next steps? It might involve applying the hybrid setup to different compounds, with an eye toward optimizing performance and scaling up. CleanTechnica is reaching out to the researchers for an update, so stay tuned for more on that.

Meanwhile, it will be a long time before the new system challenges concentrating solar power for a place on the bulk solar thermal storage shelf. Here in the US, the Department of Energy is still banking on concentrating solar as part of a scheme to put conventional power plants in mothballs.

Hybrid wind-solar farms with storage are also emerging as a force to be reckoned with for 24/7 electricity generation from renewables. Coal is already on the way out for power generation in the US, and it’s only a matter of time before renewables give natural gas the boot, too.

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Image: Via University of Houston, “The hybrid device consists of a molecular storage material (MSM) and a localized phase-change material (L-PCM), separated by a silica aerogel to maintain the necessary temperature difference.”