The efficient storage of the solar energy gained from the collectors is crucial to the successful operation of the whole system. The storage volume must at a minimum provide for the normal daily consumption of the household, but ideally, given the variability of our weather should also provide for the next day as well. This raises issues with the level of heat loss from the cylinder, the integration of the auxiliary heating system, the size of the area available for the hot water cylinder (the strength of the supporting floor and the size of doorways for installation access) and the prevention of overheating of the solar collectors in spells of prolonged hot weather. The type of hot water cylinder chose will depend on the type of system design that has been adopted. The range of cylinders employed varies from the modified use of the existing cylinder if it is still compliant with insulation regulations (BS ***) to the use of system specific polymer stores.

While much attention is provided to the main cylinder insulation, the heat loss through the connections is often neglected. These can be substantial particularly for connection near the top of the cylinder, where it is warmer. Check valves, s-bending (180 o loops) or specilaist connections such as Convectrol can be used to minimise these losses.

Desirable Solar Cylinder Properties

• High level of insulation of the cylinder.
• Good stratification of heated water in the cylinder.
• Prevention of heatlosses from cylinder connections.
• Sufficient storage volume for the daily demands of the household.
• Ability to control the auxiliary heating system.
• Provision of a reserved solar space that may be defined as a permanent physical volume or a volume reserved in time by interlock of the auxiliary heating
• Means of minimising legionella risk