Solar water heating systems need a storage tank to keep water heated by the collector. Storage tanks are also used for liquid-based solar space heating systems.
Cold water from the bottom of the tank is pumped to the solar collector. After passing through the collector, the hot water returns to the tank. Because hot water rises, the water coming from the collector stays at the top of the tank. Hot water for the home is drawn from the top of the tank as needed.
Solar storage tanks should be well-insulated against heat loss, and may need a protective coating to prevent leaks or corrosion. Tank material will be dependent on your water quality and whether you are connected to the mains water supply. The following are the most common types of tanks:
- vitreous enamel or mild steel: most susceptible to corrosion, thus needing a sacrificial anode (a metal rod down the center of the tank) to avoid corrosion. This anode must be replaced periodically.
- stainless steel: less susceptible to corrosion and requires less maintenance, but are not recommended for areas with poor water quality
Solar water storage tanks are typically placed in one of two locations. Depending on available space, it may be more convenient to use several small storage tanks rather than one large one.
- roof mounted tanks are placed horizontally above collectors. This is called a thermosiphon system, which does not require pumps or controllers and leaves your ground level space free. The drawback is that such a system is a heavy load on the roof (650-1500lbs).
- a split system, with the tank on ground level, needs a pump to circulate the solar transfer fluid. A pump needs electricity to power it and requires maintenance. The tank should be placed close who where hot water is used the most, such as near a bathroom or kitchen, to minimize heat loss on the way.
Solar storage tanks should also meet all local regulations. The simplest option is to use a standard domestic water heater, because these are already made to comply with all building codes.