Solar Hot Water System Types

Five main types of solar water heating systems are sold today. These five are a distillation of dozens of types sold over the past 25 years. They are:

• Batch
• Thermosyphon
• Open-loop direct
• Pressurized glycol
• Closed-loop drainback

The proven winners are simple, reliable, and long lasting. Some systems are "open loop" (the domestic water itself is directly heated) and some are "closed loop" (a heat-transfer fluid is heated by the collector and the heat is passed on to the domestic hot water by means of a heat exchanger). Some systems are "active," using moving parts such as pumps and valves, and others are "passive," using no mechanical or moving parts.

There are many considerations in choosing the best system for a home, but the client and the situation will dictate the right system.

For instance, for a one- to two-person household in a temperate climate where hard freezes rarely occur, you might go with a batch heater, especially if the hot water will be used more at the end of the day rather than first thing in the morning. In a household with three or more people, where aesthetics and weight are not an issue, the thermosyphon system might fit the bill, especially if there´s no room for an additional tank near the existing water heater.

The drainback system, a personal favorite here in the Northwest, requires continuous drop between the solar collector and the solar storage tank. If continuous fall is not possible, there´s always the pressurized glycol system where piping can go up, down, over, and around without concern. Usually more than one option can work for any situation.

The number of people in the household will dictate how large the system will need to be, and which systems are even possible. Rebate and incentive programs may only qualify certain systems in a given area. Some systems are relatively easy to install for do-it-yourselfers, while others most laypeople shouldn´t attempt. See the comparative chart showing features of the different system types. Make your choice, and enjoy using solar energy to heat your water!