Solar Water Heater, A Homeowner's Guide
A solar water heater can provide from 50-100% of the home's hot water needs. That will save you money and help save the environment too. Some of the systems are sold as kits that can be added onto existing storage water heaters while others include a storage tank and in some cases a boiler for a backup heater.
The two main types of systems are active and passive systems.
In an active system, a pump is used to circulate water through a solar collector where the water is heated by the sun. The water is then pumped to the storage tank. The pump is usually controlled by a controller that senses the temperature in the collector as well as the storage tank. It compares the two temperatures and when the temperature of the water in the collector gets a certain amount higher than the temperature in the storage tank, the circulating pump is started.
In a passive system the water circulates by natural convection. This is a process where warm water rises and cold water falls. For that reason the storage tank must be mounted above the collector. These systems are sometimes referred to as thermosiphon systems or batch water heaters. The hot water is stored in the tank on the roof with the collector.
Active systems are used in moderate to cold climates. Passive systems are suitable for hotter climates where there is no danger of freezing.
In areas where the outside temperature drops below freezing, the collector is connected to an indirect fired water heater. This is a standard water tank with a heat exchanger inside. This is also referred to as a closed loop system.
The water in the solar water heater system has an antifreeze solution in it and circulates inside the heat exchanger. The heat exchanger transfers the heat from the solar system to the home's hot water system while keeping them separate.
Another option for cold climates is to drain the system during the cold months. Some systems automatically drain the water as required by the temperature and are referred to as auto drainback systems. In this case, the water that is normally inside the collectors drains down into the home and is stored in atank while the system is off.