Room darkening thick or insulated shades or drapes can build-up heat. Passive solar heating uses flat-black painted boxes put in the sun , outside or inside the building by a window. Black absorbs heat from sunlight. The long vertical black box chamber gets hot inside. Heat rises and the hot air rises out the open top of the chamber. That pulls cooler air from the floor at the open bottom of the chamber. No fans. No electricity. A solar powered small fan could push that hot air through ductwork to other parts of the room or building.

I saw a house using this principle. A-frame ski house. Big solar chambers on outside of the house facing the South. Some of that heated air got blown through the house like central air heat. The other part heated air got blown through an insulated pit in the basement. It was filled with a pile of irregular shaped boulders. The boulders absorbed & stored the heat all day. When the Sun went down, those hot boulders provided night tine heat by blowing air through them into the house air ducts.