A very simple system for heating water using solar energy. This system works, without a pump, using only the thermosiphon effect.
Domestic hot water, which is used for household and toilet needs, represents a significant consumption.
Turning solar energy into heat is simple and efficient. A thermal solar panel has an efficiency 3 to 4 times higher than a photovoltaic panel. However, electricity and fossil fuels are mostly used to heat water.
Solar water heating systems use solar panels, called collectors. This allows the heat from the sun to be collected and used to heat the water that is stored in a hot water tank.
There are two types of solar panels for water heating:
Vacuum collectors are known to be more efficient because they suffer less leakage (thanks to the air vacuum in the tubes) than flat collectors. They are nevertheless more complicated to realize in low-tech.We decided to test a plane-type sensor operating as a thermosiphon, i.e. without pumping system. n addition, we chose to heat the water directly, without using a heat transfer fluid that would transfer its calories to the water in the tank.
Our system has no pumping system. The water circulation is only done thanks to a thermodynamic phenomenon called thermosiphon.
The principle of the thermosiphon system is that cold water has a higher density than hot water because it is more compact. It is therefore heavier and sinking. However, all systems tend towards a state of thermodynamic equilibrium. There is a movement called thermal convection to mix hot and cold water.
For this reason, the solar collector is always mounted underneath the water storage tank, so that the cold water from the tank reaches the collector via a downhill water pipe. When the water in the collector heats up, the hot water rises naturally, pushed up by the cold water and returns to the tank. The cycle tank -> water pipe -> collector heats the water until it reaches an equilibrium temperature. The consumer can then use the hot water from the top of the tank.
The measurements are given for information only. They have to be adapted according to the size of your window.
In order to retain maximum heat inside the water heater, it is important that the frame is insulated as much as possible. This is not the case for this prototype.
Air leakage and thermal bridges must be avoided. We have therefore insulated the bottom of the frame.
- Cut cardboard (or other insulation) to fit the bottom of the frame perfectly.
- Cover the cardboard with 2 layers of aluminium foil. The purpose of this is to distribute the heat evenly over the surface in contact with the copper tube.
In this system, there is no heat exchanger as in a conventional hot water tank. The water in the tank passes directly through the copper pipe and heats up on contact with it. We will therefore form a circuit in order to maximize the exchange surface between the pipe and the water.
Note: It is important to use a suitable tool to make a nice bend and not to make a bend in the pipe. At this diameter, the pipe tends to bend quickly and will eventually break.
For the water tank, we have chosen a 30L waste bin with a lid. Ideally, the tank should be insulated to conserve heat.
Note: Be careful not to over-tighten the hose clamps which will eventually tear the silicone/latex hoses.