The Trombe wall [1], named from the French engineer who popularized it, is a (semi-)passive solar heat storage device consisting of a internal wall behind south-facing windows. The wall absorbs sunlight during the day and radiates heat during the night.

The main disadvantage is the blocking of sunlight from entering the room, requiring a source of light from another wall or artificial means. Water can store heat while letting most sunlight pass through, but a way to convert visible light into infrared is needed. These two designs use a selective surface (finely powered charcoal in a epoxy binder, for example) to realize this conversion. The vertical Venetian blinds are a bit more complex, but can be built by hand [2].

[1] https://www.appropedia.org/Trombe_walls
[2] https://ibuildit.ca/projects/making.....rtical-blinds/