A check valve powered by the sun!
If you know anything about electronic components, a diode works like a check valve for electricity. It lets electricity flow in one direction but not back the other way. Since you know what a diode is, let’s dig a little deeper into what a thermic diode is. A thermic diode, or solar diode, is a check valve for water but it only lets the hot water flow rather than the cooler water flow. This will allow you to store the warm water where you want it without the warm water flowing back into the solar collector when the sun goes down and loosing the heat you gained during the day into the cool night air. The best part is: it does all of this without any moving parts or external power!
In this diagram, you can see where the warm water flows in at the top, left side. It flows up into the thermic diode where it meets a thick layer of oil. We are taught as small children that oil and water doesn’t mix and will always try to separate. This gives a barrier at the top of the container for the water. When the warm water flows in, the oil is displaced out of the way due to the pressure of the water being pumped by the thermosiphon effect. Luckily, since the pressure needed to move the oil out of the way is minuscule, the temperature difference it takes to get the thermosiphon pumping action started is lower. This is the reason that this type of valve works so well for this application. The warm water flows out of the exit holes into the insulated container. The cooler water at the bottom of the insulated container is then pulled out to the solar collector and heated to continue the cycle.
At night, when the sun has gone down and isn’t heating the solar collector anymore, the water will try to flow backwards from the hot side down into the cold side but the oil acts as a valve. Since there isn’t any pressure from the warm water side pushing the oil out of the way, the oil gets sucked down a little into the inlet pipe, stopping the flow of water. The water in the collector is trapped and can’t flow either direction. This keeps the water from cycling the opposite direction and causing all the hard earned heat to escape out into the night air from the collector.
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