Storing heat for months is more effective than you might think. There are systems across northern Europe where insulation is used to store excess heat from summer for winter use. This approach is theoretically simpler. It does away with the need for insulation. In this case, pyrimidone, a molecule related to DNA, changes molecular structure. Solar energy provides the energy to do it, and it’s being undone, releases energy.

But there are still problems commercializing this for home use. In particular, the chemical reactions to change the pyrimidone depend on other chemicals, are multi-step, and relatively inefficient. Still, the promise is there. Combining this tech, heat pumps, and insulation means we should have future buildings that need little or no external energy for seasonal heating & cooling.

A fluid can store solar energy and then release it as heat months later - Sunlight can cause a molecule to change structure, and then release heat later