Thermal energy is stored within mass, either in a heat sink of rubble or gravel, or by installation of thermal batteries, like dark barrels of water. These thermal batteries store heat during the day by absorbing thermal energy from the sun and ambient temperature. At night, the air cools, and the thermal batteries adjust to match the ambient temperature, releasing heat.
Dark barrels of water are popular choices for 'thermal batteries'. In the daytime, the barrels absorb ambient warmth, and release it in the coolor nighttime. These barrels are cheap, and can serve many purposes for water storage within a greenhouse.
