The cold water supply is connected to the solar storage tank. Water to be heated circulates between the storage tank and the solar collectors. The output from the solar storage tank becomes the cold water connection to the conventional gas, electric or oil water heater. When a hot tap is opened, preheated water is drawn from storage into the conventional ("auxiliary") water heater. The burner or electric element turns on only if the temperature cannot be maintained by the solar heater. Most properly-designed solar water heaters will supply 70 per cent or more of all the energy needed for water heating.

Installation conditions for a Solar Water Heating System
To get the full benefits of a solar heater you must have an area for the solar collectors that is large enough and has the proper exposure to the sun. A flat roof is ideal because the collectors can usually be oriented to face the sun directly very easily. If you install the collectors on a pitched roof, the ideal direction the roof should face is south.

The facing direction ("orientation") may be any direction within 90 degrees of due south (in the northern hemisphere), but you will need more solar collectors as the angle from due south increases to near 90 degrees. If you cannot use an orientation within these limits, the solar heater will be useless. Solar panels need to face north in the southern hemisphere. Also, be sure that the collectors will not be shaded.

The collector area required will depend on the daily amount of hot water use, the type of collectors used, the orientation of the collectors and your geographic location. If you consider a standard "package", you should be sure it is sized appropriately for your specific installation.

If you choose a "Passive" solar water heater, the storage tank(s) will be on the roof. In this event, simple structural bracing may be required. Active solar systems do not normally require structural calculations or roof bracing, because the weight of the collectors is well within normal roof load limits.

An "Active" solar water heater uses a small pump for solar collector circulation, and does not require a tank on the roof. A "Passive" solar heater depends on thermosyphon action, so does not use a pump, but tanks(s) must be on the roof.

Operation and Maintenance
Your solar water heater should be supplied with operation and maintenance instructions. You will find that there is little, if anything, for you to do once the installer has started your system and checked its operation for the first time. Properly designed solar water heaters are completely automatic and are left in operation year-round. Active systems have a small electronic control with one or more indicator lights to let you know if there is a malfunction. Be sure the instructions specify how your system is protected from freezing!

Many systems are capable of furnishing all the hot water for six months or more, and have manual bypass valves that permit you to shut down your auxiliary water heater during those "100% solar" months. Re- setting the bypass valves twice yearly, and shutting down or restarting the auxiliary water heater are the only items requiring regular attention on most solar water heaters.