storage per liter is only about 80% more than water at 60C differential (useful for hydronic floor heating), but per square meter of panel in sun only gains 2wh/hour, whereas water could gain close to 1000wh/hour. A bit complex to extract the heat as well.

For anyone with an interest in chemistry, I recommend the scientific paper.

https://www.science.org/doi/10.1126/science.aec6413

Trying to think of critiques:

• the wavelength of light necessary to "charge up" pyrimidone is fairly short (300 nm, UVB ultraviolet light)

• the quantity of UVB light on Earth's surface is limited (it is mostly absorbed by the ozone layer)

• however, one can artificially produce ultraviolet light from solar electrical power, or figure out molecules that charge with UVA or even blue light, which would be perfect

Positive aspects:

• pyrimidone looks simple, synthesis probably is not hard
• it is solid at room temperature
• it lasts long when charged
• it is compatible with a water environment when energy needs releasing

Addition of hydrochloric acid (HCl) to Dewar pyrimidone (107 mg in 0.46 ml of water) increased the solution temperature to 100°C and induced boiling within 1 s, demonstrating rapid macroscopic heat transfer to an environmentally benign medium under ambient conditions.

Subsequently, the solution can be neutralized with an alkaline chemical, pyrimidone can be "recharged" and the cycle repeated. The summary of the article does not mention how many cycles it endures. I would be good to know that.

That's great in concept. How large would you have to scale up to power turbines to light up a city. This doesn't seem feasible in practical applications like cell phone batteries, since you are transferring thermal heat, rather than electrons through a redox reaction.

Furthermore, the release of that stored solar heat requires catalysis by acid. Sort of reminds me of a glow stick, where you have to crack the internal container containing a secondary chemical to create a reaction to generate light. It's a 1x use product, it isn't reversible. On a larger scale, how to you recapture the pyrimidone, and acid and convert the pyrimidone back to it's dewar form? You have to irradiate the pyrimidone with UV light to break its aromaticity and create a strained bicyclic structure - which means you have to put energy back into the system.

Is the cycle have the UV light/sun create the dewar form, then throw some acid in to generate heat, put the pyrimodone back in the sun and repeat? Mirrors and Solar panels don't produce acid waste while they operate. (Manufacturing might be a different issue.)