That’s a fascinating and increasingly relevant area of materials science! The inspiration drawn from sunburn for developing molecular heat storage systems comes from understanding how certain molecules react to energy absorption, specifically by undergoing a structural change that traps that energy.
Here’s a breakdown of the connection:
### The Sunburn Analogy: How Skin “Stores” UV Energy
1. **Energy Input (UV Light):** When your skin is exposed to ultraviolet (UV) radiation from the sun, the DNA within your skin cells absorbs this high-energy light.
2. **Molecular Transformation:** This absorbed UV energy causes a chemical change in the DNA structure. Specifically, neighboring pyrimidine bases (like thymine) on the same DNA strand can bond together, forming what are called “pyrimidine dimers.” This is a change in the molecule’s shape and bonding.
3. **Energy Trapping:** The pyrimidine dimer is a *higher-energy* state than the original, un-dimerized DNA bases. The UV energy has been used to create a less stable, but structurally distinct, form of the molecule.
4. **Reversion and Release (or Damage):** Your body has repair mechanisms (enzymes) that can detect these dimers. These enzymes essentially “break” the dimer bonds, allowing the DNA to revert to its original, lower-energy state. In this process, the stored energy is released, typically as a small amount of heat, but more importantly, the DNA’s correct structure is restored. If the damage is too extensive or not repaired efficiently, it leads to cell damage, mutations, and the visible signs of sunburn.
The key takeaway for the analogy is: **A molecule absorbs energy, changes its shape into a higher-energy configuration, and can then revert to its original shape, releasing that stored energy.**
### Sunburn-Inspired Energy Storage Molecules (MOST & TES)
Scientists are developing “Molecular Solar Thermal (MOST)” or “Thermal Energy Storage (TES)” systems that mimic this principle, but with molecules designed to absorb and store *heat* or *visible light* efficiently and reversibly.
Here’s how they work:
1. **Molecular Design:** Researchers engineer specific molecules (often organic compounds like derivatives of azobenzene, norbornadiene, or spiropyran) that have two stable structural forms, called *isomers*.
* **Isomer A:** The lower-energy “charging” state.
* **Isomer B:** The higher-energy “storage” state.
2. **Energy Input (Charging):**
* When Isomer A is exposed to heat (or sometimes visible light, depending on the molecule), it absorbs that energy.
* This absorbed energy causes the molecule to undergo a precise structural rearrangement (an *isomerization*) from Isomer A to Isomer B.
* **Crucial difference from sunburn:** These engineered molecules are designed so that Isomer B is *thermodynamically meta-stable*. This means it can remain in its high-energy state (Isomer B) for long periods without spontaneously reverting, even at ambient temperatures. It essentially “locks in” the absorbed energy.
3. **Energy Storage:** The heat energy (or light energy that converted to heat) is now stored chemically within the bonds and structure of Isomer B. This storage is highly efficient, with little to no heat loss, unlike traditional hot water tanks or molten salt systems.
4. **Energy Release (Discharging):**
* When heat is needed, a specific trigger is applied. This could be a catalyst, a slight temperature increase, or even light of a different wavelength.
* The trigger causes Isomer B to rapidly revert back to its original, lower-energy Isomer A.
* This reversion releases the stored chemical energy *as heat*, often at a higher temperature than it was originally absorbed.
### Why this is a “New Way to Store Energy” and its Decarbonization Potential:
* **Long-Term, Lossless Storage:** Unlike traditional thermal storage (like water tanks) which constantly lose heat, these molecules can store energy indefinitely at room temperature with virtually no loss.
* **High Energy Density:** A small volume of these molecules can store a large amount of energy, making them efficient for transport.
* **On-Demand Release:** Heat can be released precisely when and where it’s needed, simply by applying the trigger.
* **Decarbonizing Heating:**
* **Seasonal Storage:** Imagine capturing solar heat in the summer and storing it in these molecules to release for heating homes in the winter, eliminating the need for fossil fuels.
* **Remote Heating:** Stored energy can be transported in liquid form to remote locations or buildings without direct access to renewable energy sources, and then released as heat on-site.
* **Industrial Processes:** Many industrial processes require significant heat. These molecules could provide a way to integrate renewable energy into these processes.
By understanding the fundamental molecular dance that occurs during sunburn – absorbing energy, changing shape, storing that energy, and then releasing it – scientists have gained valuable insights into designing artificial molecular systems for a truly transformative energy storage future.
