PiggyBack Solar Hot Water System

The PiggyBackTM system is classified as a drain-back system. A standard water heater mounts on top of the non-pressurized solar storage tank. The storage tank contains 40 gallons of tap water initially filled from a garden hose. When the sun comes up, the solar electric panel receives sunlight. An electronic controller conditions the voltage and provides power to the dc pump for a soft start. The water in the storage tank gradually heats up as the water is circulated from the tank through the solar collector and back to the tank.

Heat is drawn out of the solar hot water tank when hot water is used from an appliance, sink or shower. The cold make up water draws heat from the solar heated water as it courses through the immersed stainless steel coil heat exchanger. The pre-heated potable pressurized water exits the heat exchanger and enters the water heater. Additional heating of the water may or may not be necessary depending on the heat generated by the day long's energy collection.

The water heater is also thermally coupled through the heat exchanger connections at locations at the P&T valve at the top side of the tank and check valve at bottom side of the water heater. The normal temperature of a water heater is set to 120°F. The hottest water rises to the top because it is less dense than the cold water at the bottom of the tank. We use this principle, called thermo-siphoning, to passively (without a pump) transfer the solar energy from the solar storage tank to the water heater once the temperature in the solar tank exceeds the water temperature at the bottom of the water heater tank.

Read more about the advantages of the PiggyBackTM Solar Hot Water System here.