Solar Hot Water Heater Basics

If you are considering a solar hot water heater, you’ll be happy with recent innovations in design and function. There are some basic considerations to keep in mind.

Basic Designs
Over the past 30 years, there have been dozens of solar hot water heater designs. Today there are five basic designs sold in two basic categories. The categories are “active” that use moving parts like pumps and valves to move the water, and there are “passive” that use no mechanical parts – nothing that moves.

Solar Batch Heaters
These simple water heaters collect and store hot water in one unit. Cold water is piped into the bottom of the tank and hot is taken off the top. It is an open-loop, passive system with the water heated directly.

Thermosyphon Systems
Another simple, passive system, the thermosyphon is used around the world. The tank must be located directly above the solar collector, and it works on the principle of rising heat.

Open Loop Direct
These systems run tubing back and forth through collectors to heat the water, then the water is stored in an insulated tank.

Pressurized Glycol Systems
Incoming water is pumped into the storage tank, but it never actually goes into the collector. Instead, a  mix of water and antifreeze runs through the collectors, then goes through the coil in the water tank to warm the water.

Closed Loop Drainback
This system requires the least maintenance of any active system. The fluid used for heat transfer is distilled water, which rarely needs to be changed. The pump moves the distilled water through the collector, then into the heat exchanger, heating the water in the tank.