Conventional heating systems can be adapted by placing a separate pre-heat cylinder between the existing cold water feed and the normal hot water storage. The other option is to replace an existing hot water storage cylinder with a larger double heat exchange cylinder. In a passive solar hot water system, the hot water storage tank must be located above the collector level.
Selecting The Type of A Hot Water Storage Tank
In a two-tank system, water is heated with solar collectors and then stored in the first tank (a pre-heat tank) before it enters the conventional water heater. A one-tank system is made up of a single cylinder with twin coils-- a combination of a solar storage tank and a back-up heater.
The three types of hot water storage tanks are: vented, mains pressure, and thermal store. Mains pressure cylinders and thermal store cylinders enable hot water to be maintained at the same pressure as the mains supply. However, these two types tend to be more expensive.
Conventional Boilers Are Not Always Suited For Solar Hot Water Storage
Conventional boilers, such as efficient condensing boilers, are often unsuitable for solar water storage. These boilers are designed to take in cold mains-pressure water, and then solar systems supply hot or warm water at a lower pressure. For solar hot water storage, an additional tank or boiler replacement may be required. Furthermore, most solar water heaters require a well-insulated storage tank where an additional outlet and inlet are connected to and from the collector.
Recent developments offer the possibility to connect a solar hot water system directly with a boiler without replacement. Contact a solar professional in your area to check if your boiler or tank is suitable.
Hot Water Storage Cylinder. Source: National Renewable Energy Laboratory
Size of A Hot Water Storage
Your hot water storage tank should be big enough to store 40 - 60 liters per day per person. Calculate with 200-300 liters per day for a family of four. Solar Collectors can typically produce a minimum of 80 -100 liters per m² of collector that flows in the water storage tank.