Thermosiphon (or thermosyphon) is a method of passive heat exchange, based on natural convection, which circulates a fluid without the necessity of a mechanical pump. This circulation can either be open-loop, as when the substance in a holding tank is passed in one direction via a heated transfer tube mounted at the bottom of the tank to a distribution point—even one mounted above the originating tank—or it can be a vertical closed-loop circuit with return to the original container. Its purpose is to simplify the transfer of liquid or gas while avoiding the cost and complexity of a conventional pump.

Apricus branded WOMBAT thermosiphon systems are the low cost type solar water heaters which supply solar hot water for domestic hot water applications. Apricus provides two choices based on water supply situation, with available capacity of 150L, 200L, 240L and 300L.
If you have a problem with a steady pressure water supply, you can choose the below Option 1 system.
If you have a constant pressurized municipal water supply, you can choose the below Option 2 system.

Option 1: Vented Thermosiphon System – Non-pressurized

Wombat vented thermosiphon solar water heaters are a great choice for consumers who want a cost effective hot water solution.
When mounted on the roof the house is provided with gravity fed hot water.
In high solar radiation areas, Wombat solar water heaters can be the sole energy source for hot water supply. In cooler climates Wombat systems can provide pre-heated hot water which saves on traditional energy costs such as electricity or gas. The tank has an optional electrical heating element for boosting for when the water is not hot enough.

Basic Operation
Evacuated tubes absorb sunlight and heat up the water inside. The warmer water rises into the storage tank while cooler water in the bottom of the tank flows down to the bottom of the tubes to repeat the cycle. This thermosiphon process occurs throughout the day, gradually heating up the water in the tank.
When hot water is used it drains from the bottom of the tank. The tank is slowly refilled with cold water, either manual via opening a cold water filling tap, or automatically if a optional small header tank is fitted to the top of the tank.

Option 2: ET&HP All-in-One System — Pressurized

Wombat heat pipe solar water heaters are an all-in-one solar water heating system. They are ideal for supplying pressurized hot water to residential customers who require a sustainable, easy to install, high efficiency and reliable solar hot water solution.
In high solar radiation areas, Wombat solar water heaters can be the sole energy source for hot water supply. In cooler climates Wombat systems can provide pre-heated hot water which saves traditional electric or gas energy costs. The tank has an optional electrical heating element for boosting.

Basic Operation
Step 1: Evacuated tubes absorb sunlight and convert it to usable heat.
Step 2: A vacuum between the two glass layers insulates against heat loss improvement efficiency. The heat transfer fin helps to transfer heat from the evacuated tube to the to the copper heat pipe.
Step 3: The heat pipe contains a small amount liquid which forms steam when heated, rapidly transferring the heat up to the water in the storage tank.