Our simplest and oldest use of solar  Energy Cube System energy is passive hear absorption, using natural materials or absorptive structures with no moving parts to simply gather and hold heat. For thousands of years, people have built thick-walled stone and adobe dwellings that slowly collect heat during the day and gradually release that heat at night. After cooling at night, these massive building materials maintain a comfortable daytime temperature within the house, even as they absorb external warmth.A modern adaptation of this principle is a glass-walled “sun space” or greenhouse on the south side of a building. Incorporating massive energy-storing materials, such as brick walls, stone floors, or barrels of heat-absorbing water into buildings also collects heat to be released slowly at night. An interior, heat-absorbing wall called a Trombe wall is an effective passive heat collector. Some trombe walls are built of glass blocks enclosing a water-filled space or water-filled circulations tubes so heat from solar rays can be absorbed and stored, while light passes through to inside rooms.Active solar system generally pump a heat absorbing, fluid medium through a relatively small collector, rather than passively collecting heat in a stationary medium like masonry.