Can Evacuated Tube Collectors Store Heat Overnight?

Thermal Storage and Phase Change Materials

Evacuated tube collectors can store heat for extended periods using a combination of thermal storage tanks and phase change materials. A thermal storage tank is typically a large insulated tank filled with water or a mixture of water and antifreeze. The tank is heated during the day by the evacuated tube collector and can store heat for 8-12 hours, depending on the tank size and insulation quality. Phase change materials (PCMs) can also be used to store heat in the tank. PCMs change state from solid to liquid as they absorb heat, releasing it as they solidify. This process can occur at a consistent temperature, allowing for a more stable water temperature throughout the night.

Design Considerations for Nighttime Heat Storage

Designing an evacuated tube collector system for nighttime heat storage requires careful consideration of several factors, including tank size, insulation quality, and collector performance. A larger tank can store more heat, but may also increase the cost and space requirements. Insulation quality is critical to prevent heat loss from the tank, and collectors with a higher efficiency rating can produce more heat during the day. In general, a tank size of 1-2 cubic meters is recommended for small to medium-sized homes, depending on the hot water demand.

System Configuration and Operation

The system configuration and operation of evacuated tube collectors for nighttime heat storage typically involves a controller and a pump. The controller monitors the temperature of the thermal storage tank and the collector, and activates the pump to circulate water through the collector during the day. During the night, the pump circulates water from the tank to the point of use, releasing the stored heat as required. This allows for a consistent hot water supply throughout the night, even in areas with limited sunlight.