Solar Heat Storage (Thermal Mass): The SunCatcher is a highly insulated structure that captures sunlight and converts most of that light to heat. The heat is stored in the SunCatcher’s thermal mass. The most efficient forms of thermal mass for absorbing and storing solar heat are water-filled metal containers or phase change materials (PCM). During a sunny day, the thermal mass prevents the SunCatcher from overheating by absorbing most of the heat while venting excess heat and moisture.
During the night or cloudy days, when the interior temperature drops, the thermal mass radiates this heat and helps maintain a suitable plant environment inside the SunCatcher. The thermal energy stored in the SunCatcher’s thermal mass keeps the interior temperature well above the outdoor (ambient) temperature. This thermal mass reduces temperature fluctuations inside the SunCatcher, greatly reducing the need for daytime venting and nighttime heating.
The phase change material (shown here prior to the walls being finished) stores heat directly into the SunCatcher’s walls. The PCM absorbs a major portion of its heat between the high 60s o F and low 80s o F. In the evening when the SunCatcher cools down the PCM provides heat, much like an extra heater coming on when it is needed most.
Water filled metal containers of various sizes can be added throughout the space to provide more thermal mass once you set up the growing area. Integrating more thermal mass in your SunCatcher will reduce the temperature swings and increase stored heat for night and cloudy days. Smaller containers will absorb and release heat faster than larger ones. Larger containers store more heat for longer periods. In addition, the soil and plants themselves act as thermal mass.