STORAGE WATER TANKS and HEAT EXCHANGERS
All hot water systems need a well insulated storage tank. The closed loop system uses a twin coil solar storage tank in series with a conventional water heater. A heat exchanger transfers heated fluid from the solar panel collector to the storage tank and heats the household water supply. The heat exchanger itself is a series of copper coils submerged in the water storage tank or a compartment outside of the storage tank.

HEAT TRANSFER
In most designs of solar water heating system, heat is stored remotely from the solar collector. Mass flow of water is generally used to transfer heat from the collector to the store. While it is possible to use convection

Example of convection
During convection, heated portions of fluid rise from the source of heat, while colder portions sink.
to move water between the collector and the heat store, this requires wide bore pipe raising the thermal capacity of the primary circuit which reduces the speed of its response to sunlight. It also imposes the requirement that the heat store be higher than the solar collector, and is relatively inefficient because the flow of convecting water is not adequate to transfer heat from the panel at full efficiency.
Some estimates suggest that only 60% of available heat is delivered to the heat store by convection driven systems, and it is now normal practice to pump water through the solar collector and heat store, though this requires a control system to work efficiently.

SOLAR HEAT STORES
Solar water heaters / storage tanks require a well insulated heat store. This is integrated with the solar panel collector by means of copper pipes/tubes which are controlled by valves and a control sensor. These copper pipes/tubes feed into coils located inside the storage tank. Solar Free Power use a system called; INDIRECT FEED because it uses two coils contained inside the storage tank and the fluid inside these coils never comes into contact with the domestic hot water used when the hot water tap is turned on.
Solar thermal technologies can be used for water heating, space heating, space cooling and process heat generation.

TWIN COIL WATER STORAGE TANK ARE INDIRECT FEED
ie; the fluid inside coils never mixes with the water in the storage tank. Available are hot water storage tanks made of; copper or stainless steel. Given the cost, each type comes with benefits.
Long term, the better the system the better saving on energy and costs.

OPTIONAL HOT WATER STORAGE TANK
Tank-in-Tank technology represents a significant advance in the science of hot water production. A greater heat transfer surface means the Tank-in-Tank units recover much faster than any other type of hot water storage cylinder − keeping boiler cycling to a minimum, and ultimately giving improved fuel efficiency with outstanding hot water delivery.
The design of the inner cylinder not only ensures scale-free operation but also avoids the sediment problems that plague conventional cylinders. Even after years of use the inner stainless steel tank would be as clean as the day it was installed.