Although the installation of a solar water heater is considered a simple task for the plumber, in practice it has been proven that it is not always done properly.
In this short guide, we will not exhaust the topic of installation (base assembly, position selection, etc.) that you will find in all technical installation leaflets of solar, but we will emphasize the points due to which the most frequent failures are due to which You will not find information elsewhere on or off the internet.
Important points that we must pay attention to when installing our solar water heater are:
Installation of pressure reducer in the water supply network
Solar water heaters, like all water heating appliances, are designed and manufactured to operate at maximum operating pressure. (design pressure, rated pressure) If the mains pressure exceeds the rate for a long time, it is very likely that your solar panel will fail. Solar models made in Greece are usually designed for 10bar pressures, while cheap Greek and Chinese solar water heaters are designed for 6bar pressures or in some cases for lower pressures.
The pressure of the water supply network in most areas of our country is 3.5 ~ 4.5 bar, but there are many areas where much higher pressures are observed, especially in areas close to the source of the distribution network. In many areas also, although the pressure most hours of the day is “normal”, there are hours (usually at night) where very high pressures are observed, reaching up to 8bar.
So if our solar panel is designed to operate at 6bar pressures and we install it in an area where higher pressures occur, its lifespan will be significantly reduced.
In such areas, it is important to install a pressure reducer, a device that does not allow the pressure of the water supply network to pass in our house above a limit. It is correct to install the reducer at the entrance of the house and not in the hot water network only, on the one hand, to protect the other elements of the plumbing installation of the house (pipes, valves, coils, etc.) and on the other hand to avoid large pressure differences between cold and hot network.
The setting of the reducer in e.g. 4bar ensures that the pressure at home will never exceed 4bar, no matter what the network pressure.
Install a change filter
In areas with very hard water, it is useful to install a filter at the inlet of the solar to reduce the deposition of waste inside the boiler. The installation of this filter is not always necessary, but in combination with regular maintenance, it will maximize the lifetime of your solar water heater.
Installation of the expansion tank in the closed circuit of the solar.
It is known that when a solid or liquid body heats up, it expands, ie increases the volume it occupies.
It is also known that when we heat a liquid in a container of a certain volume that prevents the liquid from expanding, instead of increasing the volume, the pressure in the container increases.
The closed circuit of the solar (the circuit that includes the solar collector, the connection pipes with the boiler and the boiler exchanger and contains water and anti-coolant), is a closed “container”, with a specific volume, which does not allow the water of the closed-circuit to expand increasing its volume. The increase of the water temperature, therefore, implies the increase of the pressure in the closed circuit.
The reason why a locking valve is placed in the closed circuit is to relieve the pressure when it rises above a limit. But in addition to safety, a small expansion tank (1 liter is enough for solar compacts) should be placed in the closed-circuit at the highest point of the solar panel. The expansion vessel will give the closed-circuit water the required space so that it can expand without increasing the pressure in the closed circuit.
If the solar panel is installed without an expansion tank in the closed circuit, the water will not find space to expand, thus increasing the pressure in the closed circuit. The increase in pressure will cause the safety valve to open to relieve the pressure. When the valve is opened, water will come out of the closed circuit, which means that the closed-circuit will not close, and your solar panel will not work.
If you have a solar panel that frequently forces you to fill the closed circuit with water and antifreeze, check that your solar panel has an expansion tank in the closed circuit and if it does not, add an expansion tank.
Installation of an expansion tank in the open circuit of the solar panel.
Everything we said about the closed circuit, also applies to the open one (the circuit that contains the water of use, the water that ends up in our bathroom). In the open circuit, of course, the taps open, and the pressure is relieved, so one could assume that it is not necessary to install an expansion tank in the open circuit as well.
This thought turns out to be wrong when the water we heat in the solar is not used. If the user of the installation leaves the house for a few days in the summer, the pressure in the open circuit increases (since the taps do not open to relieve the pressure) and this results in our solar (but also the entire hot water network – pipes, valves, connection coils) to be stressed by high pressures and the safety of the solar to be constantly opened.
The same goes for high-performance vacuum heaters with vacuum tubes, which on summer days with maximum sunlight are subjected to very high pressures if the user does not use hot water.
Solar water heater open circuit expansion tank
Therefore, the installation of an open circuit expansion tank is considered necessary to protect our solar water heater and to enjoy hot water without any problems.
When installing any solar water heater, the solar panels should remain well covered until the closed and open circuit is filled with water.
If the installer exposes the collectors before filling the circuits, the temperature inside the collectors will rise to very high levels (> 100oC), which will make it very difficult to fill the closed circuit, since the water we will try to put in the closed-circuit will evaporate as soon as it comes in contact with the hot surfaces of the collector. Apart from the fact that it is impossible to calculate the coolant ratio, the filling of the closed-circuit will not be done correctly, due to the evaporation of water.
The filling of the closed-circuit is done with a solution of antifreeze and water in such a ratio, in order to protect our solar from the low temperatures of winter.
The ratio depends on the properties of the antifreeze and is always indicated on the antifreeze bottle. For the solution, it is good to prefer propylene glycol, which is safer for the health of the installer. The filling should be done carefully so that the installer does not breathe vapors of the solution containing antifreeze.
If the antifreeze does not contain dissolution instructions, we can say that for standard antifreeze, a solution of 25% ~ 30% in antifreeze protects our solar at temperatures up to -10oC, a solution of 50% up to -20oC, while for lower temperatures more antifreeze should be used.
The above are general instructions and as we said the proportions in the antifreeze bottle should be observed.
The filling of the closed-circuit must always be done carefully so that no air is trapped in the upper part of the collector or in the boiler-collector connection pipes.
Closed and open circuit piping insulation
The pipes of the open and closed circuit of our solar should be well insulated with armaflex type insulator of the thickness of 9mm and above (we prefer 13mm due to the high temperatures that develop).
All black foam insulators are not resistant to UV sunlight and for this reason, it is very important that the insulation material is protected against sunlight with white or black PVC film, or with a protective paint special to protect the insulation.
Solar water heaters reach their maximum efficiency 2 days after the completion of the installation. On high-quality models with top solar panels, you can use hot water from day one. In any case, do not rush to judge the performance of your solar panel before 2 days have elapsed.
Common causes for your solar panel not working properly
If the period of 2 days has passed and your solar panel does not heat water properly, then the installer should check that there is not one or more of the following causes for which a solar panel does not work properly.
- Poor choice of orientation
- The poor slope of the solar panel
- Shading of collectors from trees or other tall objects
- Poor filling of the closed-circuit
- Leakage in the closed-circuit piping.
- Incorrect connection of cold / hot piping after solar.
By following the above guidelines and provided you have purchased a high-quality solar water heater, you can be sure that you will enjoy plenty of free hot water for many years and you will definitely recoup the money of your investment.