Active Closed Loop Solar Water Heating Systems
with Preheat Tank


There are a variety of situations when a two tank system may be preferred, particularly when integrating with an existing system. Although less efficient, this system easily retrofits to existing systems with a minimum disturbance of the pipework.


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There are several ways to connect a two tank system. The traditional method is to have a solar preheat tank, in which the tanks are plumbed in series. Unless there is constant daytime use the pre-heat tank has to be quite large, and standby heat losses in the existing tank are not taken care of by the solar system



  • Easy to retrofit to existing tank with minimum disturbance of existing pipework
  • Versatile system - the preheat tank can be located away from the conventional tank
  • Useful if the conventional tank is gas or oil fired. Many gas fired DHW tanks have high standby heat losses and will waste solar energy.
  • The tank is usually cold in the morning and ready to receive solar energy.
  • Good control over the system and easily monitored performance.
  • Efficient if the house is occupied through the day. Solar heated water will frequently be drawn into the conventional tank, helping offset standby losses.
  • This solar system can be disassembled easily, leaving the existing system intact, and moved to another location.
  • Solar energy is only heating half of the available storage. If no-one is home through the day the solar heat remains in the preheat tank.
  • A larger pre-heat tank will be necessary than if a tank was added in parallel.
  • Stand-by losses are more than twice those of a single tank system.

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