A batch solar heater is a passive solar system that heats potable water directly in insulated tanks exposed to sunlight, with no moving parts or controls required. Water enters and leaves through thermosiphon circulation, where heated water naturally rises while cooler water sinks, eliminating pump requirements.
Construction and Performance
Batch heaters consist of one or more water-filled tanks painted matte black, enclosed in an insulated box with transparent glazing. Typical systems contain 30-50 gallons and can raise water temperatures from 50°F to 130°F on sunny days. They provide 5,000-15,000 BTU of energy per square foot per day depending on solar irradiance and ambient temperature.
Operating Principles
Water circulates through natural convection; no electricity or controls required. The system self-regulates through thermosiphon flow, reducing circulation during cold weather. Nighttime losses occur through the transparent cover, reducing stored heat by 20-40% after sunset.
Climate Suitability
Batch heaters perform well in mild climates with regular sunny days. They require freeze protection in freezing climates through drain-back or antifreeze systems. These systems suit remote locations or applications where pump failure risk must be minimized.