Residential solar thermal installations fall into two groups: passive (sometimes called “compact”) and active (sometimes called “pumped”) systems. Both typically include an auxiliary energy source (electric heating element ) that is activated when the water in the tank falls below a minimum temperature setting, ensuring that hot water is always available. The combination of solar water heating and back-up heat can enable a hot water system to work all year round in cooler climates. Residential Solar Water Heater Product Range: