How are vacuum tubes used

How effectively does the solar system work with evacuated tube collectors?

"Solar energy with great potential"

A solar system with an evacuated tube collector is ideally suited for the preparation of hot water. In this way, you can efficiently use solar energy for your heating system or the hot water supply for washing machines and bathrooms. This results in great potential for simply saving energy and reducing costs.

A thermal solar system is ideal for saving energy costs!

When investing in a new heating system these days, it makes sense to think of a solar system with a vacuum tube collector. Solar collectors or the evacuated tube collector are not only an essential contribution to the protection and preservation of environmental resources, but they also save you money through lower costs for heating and hot water heating. The carbon dioxide emissions are sustainably reduced with such a system.

Modern heating systems enable the optimal interaction of all necessary components. Solar collectors for DHW heating and heating backup use the free solar energy from photovoltaics with a high degree of efficiency.

Design and function of a vacuum tube collector!

The vacuum tube collector for a photovoltaic solar system is available in different designs. Each solar thermal system has specific advantages. Inside the vacuum tube collector there is an absorber for the solar energy. This is insulated to prevent heat loss. A vacuum is used as insulation because of its optimal properties. Technologically speaking, the manufacture of a vacuum tube is simple. After the vacuum tube has been completely emptied, it is sealed airtight on both sides with a metal lid.

There is an absorber plate in the vacuum. Such photovoltaic systems are as efficient as possible. It is important that the transition from the vacuum tube to the metal is carried out very carefully. Otherwise hairline cracks may appear and air will penetrate. Constant changes in temperature favor this source of error. Thus, the tubes of the solar collectors were developed from two concentric fused glass tubes according to the principle of a thermos flask.

These tubes are called Sydney tubes. They consist entirely of glass and thus ensure the required vacuum over the long term.

Details about the Sydney vacuum tube for the use of solar energy by means of solar thermal energy!

The outer surface of the inner glass tube is coated with several layers of aluminum nitrite. This is why these tubes look slightly bluish from the outside with solar thermal energy. With this layer of aluminum nitrite, the short-wave solar radiation is converted into long-wave thermal radiation. In order to avoid heat loss through radiation, the tube is additionally vaporized with copper. Heat conducting sheets made of closely spaced aluminum conduct the heat to a copper pipe. This is integrated into the water cycle and transports the heat from the photovoltaics into the heating and hot water system of your house. Different designs are used. In addition to the copper pipes, there is also the variant with so-called heatpipe copper pipes.

The heat pipe vacuum tube in detail!

A heat pipe basically also consists of a copper pipe. This is filled with a liquid protected from frost. Only the phase transition from the liquid to the gaseous state is used here. The alkanes evaporate at lower temperatures in the heat pipe and then rise into the condenser part of the vacuum tube. This is where the steam condenses. The heat is transferred to the heat transfer fluid. When the condensate then flows back down, this process is repeated continuously. A suitable heat accumulator then transfers the heat to the system via a heat exchanger. A storage volume of at least 50 liters per square meter of collector surface is required. A big advantage of the heat pipes is the very simple assembly. Thanks to the dry connection, the tubes in a solar system with a vacuum tube collector can be replaced while the system is running.

Tube collectors from Viessmann and SUNEX presented as an example!

The tube collectors from Viessmann and SUNEX mentioned are highly efficient. Highly selectively coated absorbers capture a particularly large amount of sunlight. Additional thermal insulation ensures that the energy is not radiated again. This means that even a small amount of solar radiation is converted into heat. This is particularly important for you in the transitional periods and in winter in order to ensure the efficiency of your system. The heat pipe system is used in the Viessmann models. An automatic temperature switch-off ensures a high level of operational safety for the entire system. There are variants especially for large-area systems on flat roofs and those that can be used excellently on single and multi-family houses.

The SUNEX vacuum tube collectors consist of 12 tubes with special anti-reflective solar glass. This is 1.8 mm thick. The collecting pipes are made of copper with mineral wool insulation and are housed in a stainless steel housing with a highly selective absorber. Up to seven such collectors can be connected in series. The special solar glass even converts UV radiation into thermal energy. The nano-based anti-reflective coating ensures a long service life and transparency. The transmission therefore averages 96%. In addition, the tubes are very strong and therefore resistant to destruction even in the event of hailstorms. The absorber and absorber pipes are connected to one another using ultrasonic welding technology. This means that the thermal conductivity at the connection point is up to six times higher than with conventional soldered connections.

The possible operating pressure is given as 10 bar. The system temperature can be up to a maximum of 300 ° C. The flow rate is 58 l / h.

What are the advantages of the solar thermal system and for whom is it particularly suitable?

A big advantage is the savings in heating costs. So it is possible to save up to a third of heating oil annually with a solar system made up of tube collectors with oil heating. Given the current prices, this is not an insignificant amount. Tube collectors are used when the energy yield per square meter is to be high. They work about 30% more effectively than flat-plate collectors. Smaller roof areas can be efficiently equipped with tube collectors. Another advantage is the high temperatures that can be achieved with vacuum tube collectors.

When it comes to small private systems, a cost comparison with flat plate collectors based on the service life of the system and the energy savings must be made. Systems with flat-plate collectors are cheaper, but require a much larger roof area.

What does such a thermal solar system with evacuated tube collectors cost?

The construction and the structure of the evacuated tube collectors are relatively simple. What makes things more expensive is the special glass that is used. This must withstand heat, rain and other weather conditions without becoming cloudy. Everyone knows the so-called dishwasher effect on drinking glasses. This must not occur with glass for the solar system, because it would significantly reduce the solar energy. The efficiency of glass tubes made of window glass is very good thanks to modern manufacturing processes and is 96% light transmission. Thus only 4% of the solar energy is lost.

These glass tubes are so efficient because they are refined with nanotechnology. An anti-reflective layer effectively prevents the glass from weathering. Nowadays it is assumed that the vacuum in the tube will last for 20 years. This is only possible because the metal closures are connected to the glass tubes at high temperatures. The process is now fully operational and effectively prevents the hairline cracks that occurred in the past at the connection points.

Conclusion on a thermal solar system made from evacuated tube collectors!

These effective thermal solar systems have a clear advantage over systems with classic flat-plate collectors. If you look at it with a thermal imaging camera, you can see that the flat-plate collector radiates solar heat, which is therefore not used. Evacuated tube collectors do not show this effect and thus use the solar heat much better and more economically.

Heat pipe